Synthetic Polymers ISC Project 2014

Polymer From Wikipedia, the free encyclopedia

IUPAC definition Substance composed of macromolecules. Note: Applicable to substance macromolecular in nature like cross-linked systems that can be considered as one macromolecule.

A polymer /ˈpɒlɨmər/[2][3] is a large molecule composed of many repeated subunits, known as monomers. Because of their broad range of properties,[4] both synthetic and natural polymers play an essential and ubiquitous role in everyday life.[5] Polymers range from familiar synthetic plastics such as polystyrene (orstyrofoam) to natural biopolymers such as DNA and proteins that are fundamental to biological structure and function. Polymers, both natural and synthetic, are created via polymerization of many monomers. Their consequently large molecular mass relative to small molecule compounds produces unique physical properties, including toughness, viscoelasticity, and a tendency to form glasses and semicrystalline structures rather than crystals. The term "polymer" derives from the ancient Greek word πολύς (polus, meaning "many, much") and μέρος (meros, meaning "parts"), and refers to a moleculewhose structure is composed of multiple repeating units, from which originates a characteristic of high relative molecular mass and attendant properties.[6] The units composing polymers derive, actually or conceptually, from molecules of low relative molecular mass. [7] The term was coined in 1833 by Jöns Jacob Berzelius, though with a definition distinct from the modern IUPAC definition.[8][9] Polymers are studied in the fields of biophysics and macromolecular science, and polymer science (which includes polymer chemistry and polymer physics). Historically, products arising from the linkage of repeating units by covalent chemical bonds have been the primary focus of polymer science; emerging important areas of the science now focus on non-covalent links. Polyisoprene of latex rubber and the polystyrene of styrofoam are examples of polymeric natural/biological and synthetic polymers, respectively. In biological contexts, essentially all biological macromolecules—i.e., proteins (polyamides), nucleic acids (polynucleotides), and polysaccharides—are purely polymeric, or are composed in large part of polymeric components—e.g., isoprenylated/lipid-modified glycoproteins, where small lipidic molecule and oligosaccharide modifications occur on the polyamide backbone of the protein.[10] Contents [hide]

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1 Common examples

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2 Polymer synthesis

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2.1 Biological synthesis

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2.2 Modification of natural polymers

3 Polymer properties

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3.1 Monomers and repeat units

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3.2 Microstructure

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3.2.1 Polymer architecture

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3.2.2 Chain length

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3.2.3 Monomer arrangement in copolymers

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3.2.4 Tacticity

3.3 Polymer morphology

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3.3.1 Crystallinity

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3.3.2 Chain conformation

3.4 Mechanical properties

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3.4.1 Tensile strength

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3.4.2 Young's modulus of elasticity

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3.5 Transport properties

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3.6 Phase behavior

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3.6.1 Melting point

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3.6.2 Glass transition temperature

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3.6.3 Mixing behavior

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3.6.4 Inclusion of plasticizers

3.7 Chemical properties

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4 Standardized polymer nomenclature

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5 Polymer characterization

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6 Polymer degradation

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6.1 Product failure

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7 See also

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8 References

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9 Bibliography

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10 External links

Common examples[edit]

Natural polymeric materials such as shellac, amber, wool, silk and natural rubber have been used for centuries. A variety of other natural polymers exist, such as cellulose, which is the main constituent of wood and paper. The list of synthetic polymers includes synthetic rubber, phenol formaldehyde resin (or Bakelite), neoprene, nylon, polyvinyl chloride (PVC or vinyl), polystyrene,polyethylene, polypropylene, polyacrylonitrile, PVB, silicone, and many more. Most commonly, the continuously linked backbone of a polymer used for the preparation of plastics consists mainly of carbon atoms. A simple example is polyethylene ('polythene' in British English), whose repeating unit is based on ethylene monomer. However, other structures do exist; for example, elements such as silicon form familiar materials such as silicones, examples beingSilly Putty and waterproof plumbing sealant. Oxygen is also commonly present in polymer backbones, such as those of polyethylene glycol, polysaccharides (in glycosidic bonds), and DNA (inphosphodiester bonds).

Polymer synthesis[edit] Main article: Polymerization

The repeating unit of the polymer polypropylene

Polymerization is the process of combining many small molecules known as monomers into a covalently bonded chain or network. During the polymerization process, some chemical groups may be lost from each monomer. This is the case, for example, in the polymerization of PET polyester. The monomers are terephthalic acid (HOOC-C6H4-COOH) and ethylene glycol (HO-CH2-CH2-OH) but the repeating unit is -OCC6H4-COO-CH2-CH2-O-, which corresponds to the combination of the two monomers with the loss of two water molecules. The distinct piece of each monomer that is incorporated into the polymer is known as a repeat unit or monomer residue. Laboratory synthetic methods are generally divided into two categories, step-growth polymerization and chaingrowth polymerization.[11] The essential difference between the two is that in chain growth polymerization, monomers are added to the chain one at a time only,[12] such as in polyethylene, whereas in step-growth polymerization chains of monomers may combine with one another directly,[13] such as in polyester. However, some newer methods such as plasma polymerization do not fit neatly into either category. Synthetic

polymerization reactions may be carried out with or without acatalyst. Laboratory synthesis of biopolymers, especially of proteins, is an area of intensive research.

Biological synthesis[edit]

Microstructure of part of a DNAdouble helix biopolymer

Main article: Biopolymer There are three main classes of biopolymers: polysaccharides, polypeptides, and polynucleotides. In living cells, they may be synthesized by enzyme-mediated processes, such as the formation of DNA catalyzed by DNA polymerase. The synthesis of proteins involves multiple enzyme-mediated processes totranscribe genetic information from the DNA to RNA and subsequently translate that information to synthesize the specified protein from amino acids. The protein may be modified further following translation in order to provide appropriate structure and functioning.

Modification of natural polymers[edit] Naturally occurring polymers such as cotton, starch and rubber were familiar materials for years before synthetic polymers such as polyethene and perspexappeared on the market. Many commercially important polymers are synthesized by chemical modification of naturally occurring polymers. Prominent examples include the reaction of nitric acid and cellulose to form nitrocellulose and the formation of vulcanized rubber by heating natural rubber in the presence of sulfur. Ways in which polymers can be modified include oxidation, cross-linking and end-capping.

Especially in the production of polymers, the gas separation by membranes has acquired increasing importance in the petrochemical industry and is now a relatively well-established unit operation. The process of polymer degassing is necessary to suit polymer for extrusion and pelletizing, increasing safety, environmental, and product quality aspects. Nitrogen is generally used for this purpose, resulting in a vent gas primarily composed of monomers and nitrogen.[14]

Polymer properties[edit] Polymer properties are broadly divided into several classes based on the scale at which the property is defined as well as upon its physical basis.[15] The most basic property of a polymer is the identity of its constituent monomers. A second set of properties, known as microstructure, essentially describe the arrangement of these monomers within the polymer at the scale of a single chain. These basic structural properties play a major role in determining bulk physical properties of the polymer, which describe how the polymer behaves as a continuous macroscopic material. Chemical properties, at the nano-scale, describe how the chains interact through various physical forces. At the macro-scale, they describe how the bulk polymer interacts with other chemicals and solvents.

Monomers and repeat units[edit] The identity of the monomer residues (repeat units) comprising a polymer is its first and most important attribute. Polymer nomenclature is generally based upon the type of monomer residues comprising the polymer. Polymers that contain only a single type of repeat unit are known as homopolymers, while polymers containing a mixture of repeat units are known as copolymers. Poly(styrene), for example, is composed only of styrene monomer residues, and is therefore classified as a homopolymer. Ethylene-vinyl acetate, on the other hand, contains more than one variety of repeat unit and is thus a copolymer. Some biological polymers are composed of a variety of different but structurally related monomer residues; for example, polynucleotides such as DNA are composed of a variety of nucleotide subunits. A polymer molecule containing ionizable subunits is known as a polyelectrolyte or ionomer.

Microstructure[edit] Main article: microstructure The microstructure of a polymer (sometimes called configuration) relates to the physical arrangement of monomer residues along the backbone of the chain.[16] These are the elements of polymer structure that require the breaking of a covalent bond in order to change. Structure has a strong influence on the other properties of a polymer. For example, two samples of natural rubber may exhibit different durability, even though their molecules comprise the same monomers.

Polymer architecture[edit]

Main article: Polymer architecture

Branch point in a polymer

An important microstructural feature of a polymer is its architecture and shape, which relates to the way branch points lead to a deviation from a simple linear chain.[17] A branched polymer molecule is composed of a main chain with one or more substituent side chains or branches. Types of branched polymers include star polymers, comb polymers, brush polymers, dendronized polymers, ladders, and dendrimers.[17] There exist also two-dimensional polymers which are composed of topologically planar repeat units. A polymer's architecture affects many of its physical properties including, but not limited to, solution viscosity, melt viscosity, solubility in various solvents, glass transition temperature and the size of individual polymer coils in solution. A variety of techniques may be employed for the synthesis of a polymeric material with a range of architectures, for example Living polymerization.

Various polymer architectures.

Chain length[edit] The physical properties[18] of a polymer are strongly dependent on the size or length of the polymer chain.[19] For example, as chain length is increased, melting and boiling temperatures increase quickly.[19] Impact resistance also tends to increase with chain length, as does the viscosity, or resistance to flow, of the polymer in its melt state.[20] Melt viscosity

is related to polymer chain length Z roughly as

~ Z3.2,

so that a tenfold increase in polymer chain length results in a viscosity increase of over 1000 times.[21] Increasing chain length furthermore tends to decrease chain mobility, increase strength and toughness, and increase the glass transition temperature (Tg)[citation needed]. This is a result of the increase in chain interactions such as Van der Waals attractions and entanglements that come with increased chain length[citation needed]. These interactions tend to fix the individual chains more strongly in position and resist deformations and matrix breakup, both at higher stresses and higher temperatures[citation needed]. A common means of expressing the length of a chain is the degree of polymerization, which quantifies the number of monomers incorporated into the chain.[22][23] As with other molecules, a polymer's size may also be expressed in terms of molecular weight. Since synthetic polymerization techniques typically yield a polymer product including a range of molecular weights, the weight is often expressed statistically to describe the distribution of chain lengths present in the same. Common examples are the number average molecular weight and weight average molecular weight.[24][25] The ratio of these two values is the polydispersity index, commonly used to express the "width" of the molecular weight distribution.[26] A final measurement is contour length, which can be understood as the length of the chain backbone in its fully extended state. [27] The flexibility of an unbranched chain polymer is characterized by its persistence length.

Monomer arrangement in copolymers[edit] Main article: copolymer

Monomers within a copolymer may be organized along the backbone in a variety of ways.

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Alternating copolymers possess regularly alternating monomer residues:[28] [AB...]n (2).

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Periodic copolymers have monomer residue types arranged in a repeating sequence: [AnBm...] m being different from n .

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Statistical copolymers have monomer residues arranged according to a known statistical rule. A statistical copolymer in which the probability of finding a particular type of monomer residue at a particular

point in the chain is independent of the types of surrounding monomer residue may be referred to as a truly random copolymer[29][30] (3).

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Block copolymers have two or more homopolymer subunits linked by covalent bonds[28] (4). Polymers with two or three blocks of two distinct chemical species (e.g., A and B) are called diblock copolymers and triblock copolymers, respectively. Polymers with three blocks, each of a different chemical species (e.g., A, B, and C) are termed triblock terpolymers.

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Graft or grafted copolymers contain side chains that have a different composition or configuration than the main chain.(5)

Tacticity[edit] Main article: Tacticity Tacticity describes the relative stereochemistry of chiral centers in neighboring structural units within a macromolecule. There are three types: isotactic (all substituents on the same side), atactic(random placement of substituents), and syndiotactic (alternating placement of substituents).

Polymer morphology[edit] Polymer morphology generally describes the arrangement and microscale ordering of polymer chains in space.

Crystallinity[edit] When applied to polymers, the term crystalline has a somewhat ambiguous usage. In some cases, the term crystalline finds identical usage to that used in conventional crystallography. For example, the structure of a crystalline protein or polynucleotide, such as a sample prepared for x-ray crystallography, may be defined in terms of a conventional unit cell composed of one or more polymer molecules with cell dimensions of hundreds of angstroms or more. A synthetic polymer may be loosely described as crystalline if it contains regions of three-dimensional ordering on atomic (rather than macromolecular) length scales, usually arising from intramolecular folding and/or stacking of adjacent chains. Synthetic polymers may consist of both crystalline and amorphous regions; the degree of crystallinity may be expressed in terms of a weight fraction or volume fraction of crystalline material. Few synthetic polymers are entirely crystalline.[31] The crystallinity of polymers is characterized by their degree of crystallinity, ranging from zero for a completely non-crystalline polymer to one for a theoretical completely crystalline polymer. Polymers with microcrystalline regions are generally tougher (can be bent more without breaking) and more impact-resistant than totally amorphous polymers.[32] Polymers with a degree of crystallinity approaching zero or one will tend to be transparent, while polymers with intermediate degrees of crystallinity will tend to be opaque due to light scattering by crystalline or glassy regions. Thus for many polymers, reduced crystallinity may also be associated with increased transparency.

Chain conformation[edit] The space occupied by a polymer molecule is generally expressed in terms of radius of gyration, which is an average distance from the center of mass of the chain to the chain itself. Alternatively, it may be expressed in terms of pervaded volume, which is the volume of solution spanned by the polymer chain and scales with the cube of the radius of gyration.[33]

Mechanical properties[edit]

A polyethylene sample neckingunder tension.

The bulk properties of a polymer are those most often of end-use interest. These are the properties that dictate how the polymer actually behaves on a macroscopic scale.

Tensile strength[edit] The tensile strength of a material quantifies how much stress the material will endure before suffering permanent deformation.[34][35] This is very important in applications that rely upon a polymer's physical strength or durability. For example, a rubber band with a higher tensile strength will hold a greater weight before snapping. In general, tensile strength increases with polymer chain length and crosslinking of polymer chains.

Young's modulus of elasticity[edit] Young's Modulus quantifies the elasticity of the polymer. It is defined, for small strains, as the ratio of rate of change of stress to strain. Like tensile strength, this is highly relevant in polymer applications involving the physical properties of polymers, such as rubber bands. The modulus is strongly dependent on temperature. Viscoelasticitydescribes a complex time-dependent elastic response, which will exhibit hysteresis in the stress-strain curve when the load is removed. Dynamic mechanical analysis or DMA measures this complex modulus by oscillating the load and measuring the resulting strain as a function of time.

Transport properties[edit]

Transport properties such as diffusivity relate to how rapidly molecules move through the polymer matrix. These are very important in many applications of polymers for films and membranes.

Phase behavior[edit] Melting point[edit] The term melting point, when applied to polymers, suggests not a solid-liquid phase transition but a transition from a crystalline or semi-crystalline phase to a solid amorphous phase. Though abbreviated as simply Tm, the property in question is more properly called the crystalline melting temperature. Among synthetic polymers, crystalline melting is only discussed with regards tothermoplastics, as thermosetting polymers will decompose at high temperatures rather than melt.

Glass transition temperature[edit] A parameter of particular interest in synthetic polymer manufacturing is the glass transition temperature (Tg), at which amorphous polymers undergo a transition from a rubbery, viscous liquid, to a brittle, glassy amorphous solid on cooling. The glass transition temperature may be engineered by altering the degree of branching or crosslinking in the polymer or by the addition ofplasticizer.[36]

Mixing behavior[edit]

Phase diagram of the typical mixing behavior of weakly interacting polymer solutions.

In general, polymeric mixtures are far less miscible than mixtures of small molecule materials. This effect results from the fact that the driving force for mixing is usually entropy, not interaction energy. In other words,

miscible materials usually form a solution not because their interaction with each other is more favorable than their self-interaction, but because of an increase in entropy and hence free energy associated with increasing the amount of volume available to each component. This increase in entropy scales with the number of particles (or moles) being mixed. Since polymeric molecules are much larger and hence generally have much higher specific volumes than small molecules, the number of molecules involved in a polymeric mixture is far smaller than the number in a small molecule mixture of equal volume. The energetics of mixing, on the other hand, is comparable on a per volume basis for polymeric and small molecule mixtures. This tends to increase the free energy of mixing for polymer solutions and thus make solvation less favorable. Thus, concentrated solutions of polymers are far rarer than those of small molecules. Furthermore, the phase behavior of polymer solutions and mixtures is more complex than that of small molecule mixtures. Whereas most small molecule solutions exhibit only an upper critical solution temperature phase transition, at which phase separation occurs with cooling, polymer mixtures commonly exhibit a lower critical solution temperature phase transition, at which phase separation occurs with heating. In dilute solution, the properties of the polymer are characterized by the interaction between the solvent and the polymer. In a good solvent, the polymer appears swollen and occupies a large volume. In this scenario, intermolecular forces between the solvent and monomer subunits dominate over intramolecular interactions. In a bad solvent or poor solvent, intramolecular forces dominate and the chain contracts. In the theta solvent, or the state of the polymer solution where the value of the second virial coefficient becomes 0, the intermolecular polymer-solvent repulsion balances exactly the intramolecular monomer-monomer attraction. Under the theta condition (also called the Flory condition), the polymer behaves like an ideal random coil. The transition between the states is known as a coil-globule transition.

Inclusion of plasticizers[edit] Inclusion of plasticizers tends to lower Tg and increase polymer flexibility. Plasticizers are generally small molecules that are chemically similar to the polymer and create gaps between polymer chains for greater mobility and reduced interchain interactions. A good example of the action of plasticizers is related to polyvinylchlorides or PVCs. An uPVC, or unplasticized polyvinylchloride, is used for things such as pipes. A pipe has no plasticizers in it, because it needs to remain strong and heat-resistant. Plasticized PVC is used in clothing for a flexible quality. Plasticizers are also put in some types of cling film to make the polymer more flexible.

Chemical properties[edit] The attractive forces between polymer chains play a large part in determining a polymer's properties. Because polymer chains are so long, these interchain forces are amplified far beyond the attractions between conventional molecules. Different side groups on the polymer can lend the polymer to ionic

bonding or hydrogen bonding between its own chains. These stronger forces typically result in higher tensile strength and higher crystalline melting points. The intermolecular forces in polymers can be affected by dipoles in the monomer units. Polymers containing amide or carbonyl groups can form hydrogen bonds between adjacent chains; the partially positively charged hydrogen atoms in N-H groups of one chain are strongly attracted to the partially negatively charged oxygen atoms in C=O groups on another. These strong hydrogen bonds, for example, result in the high tensile strength and melting point of polymers containing urethane or urea linkages. Polyesters have dipole-dipole bonding between the oxygen atoms in C=O groups and the hydrogen atoms in H-C groups. Dipole bonding is not as strong as hydrogen bonding, so a polyester's melting point and strength are lower than Kevlar's (Twaron), but polyesters have greater flexibility. Ethene, however, has no permanent dipole. The attractive forces between polyethylene chains arise from weak van der Waals forces. Molecules can be thought of as being surrounded by a cloud of negative electrons. As two polymer chains approach, their electron clouds repel one another. This has the effect of lowering the electron density on one side of a polymer chain, creating a slight positive dipole on this side. This charge is enough to attract the second polymer chain. Van der Waals forces are quite weak, however, so polyethylene can have a lower melting temperature compared to other polymers.

Standardized polymer nomenclature[edit] There are multiple conventions for naming polymer substances. Many commonly used polymers, such as those found in consumer products, are referred to by a common or trivial name. The trivial name is assigned based on historical precedent or popular usage rather than a standardized naming convention. Both the American Chemical Society (ACS)[37] and IUPAC[38] have proposed standardized naming conventions; the ACS and IUPAC conventions are similar but not identical.[39] Examples of the differences between the various naming conventions are given in the table below:

Common name

ACS name

IUPAC name

Poly(ethylene oxide) or PEO Poly(oxyethylene)

Poly(oxyethene)

Poly(ethylene terephthalate) or PET

Poly(oxy-1,2-ethanediyloxycarbonyl-1,4phenylenecarbonyl)

Poly(oxyetheneoxyterephthaloyl)

Nylon 6

Poly[amino(1-oxo-1,6-hexanediyl)]

Poly[amino(1-oxohexan-1,6diyl)]

In both standardized conventions, the polymers' names are intended to reflect the monomer(s) from which they are synthesized rather than the precise nature of the repeating subunit. For example, the polymer synthesized from the simple alkene ethene is called polyethylene, retaining the -ene suffix even though the double bond is removed during the polymerization process:

Polymer characterization[edit] Main article: Polymer characterization The characterization of a polymer requires several parameters which need to be specified. This is because a polymer actually consists of a statistical distribution of chains of varying lengths, and each chain consists of monomer residues which affect its properties. A variety of lab techniques are used to determine the properties of polymers. Techniques such as wide angle X-ray scattering, small angle X-ray scattering, and small angle neutron scattering are used to determine the crystalline structure of polymers. Gel permeation chromatography is used to determine the number average molecular weight, weight average molecular weight, andpolydispersity. FTIR, Raman and NMR can be used to determine composition. Thermal properties such as the glass transition temperature and melting point can be determined by differential scanning calorimetry and dynamic mechanical analysis. Pyrolysis followed by analysis of the fragments is one more technique for determining the possible structure of the polymer.Thermogravimetry is a useful technique to evaluate the thermal stability of the polymer. Detailed analysis of TG curves also allow us to know a bit of the phase segregation in polymers.Rheological properties are also commonly used to help determine molecular architecture (molecular weight, molecular weight distribution and branching) as well as to understand how the polymer will process, through measurements of the polymer in the melt phase. Another polymer characterization technique is Automatic Continuous Online Monitoring of Polymerization Reactions (ACOMP) which provides real-time characterization of polymerization reactions. It can be used as an analytical method in R&D, as a tool for reaction optimization at the bench and pilot plant level and, eventually, for feedback control of full-scale reactors. ACOMP measures in a modelindependent fashion the evolution of average molar mass and intrinsic viscosity, monomer conversion kinetics

and, in the case of copolymers, also the average composition drift and distribution. It is applicable in the areas of free radical and controlled radical homo- and copolymerization, polyelectrolyte synthesis, heterogeneous phase reactions, including emulsion polymerization, adaptation to batch and continuous reactors, and modifications of polymers.[40][41][42]

Polymer degradation[edit] Main article: Polymer degradation

A plastic item with thirty years of exposure to heat and cold, brake fluid, and sunlight. Notice the discoloration, swelling, and crazing of the material

Polymer degradation is a change in the properties—tensile strength, color, shape, or molecular weight—of a polymer or polymer-based product under the influence of one or more environmental factors, such as heat, light, chemicals and, in some cases, galvanic action. It is often due to the scission of polymer chain bonds via hydrolysis, leading to a decrease in the molecular mass of the polymer. Although such changes are frequently undesirable, in some cases, such as biodegradation and recycling, they may be intended to prevent environmental pollution. Degradation can also be useful in biomedical settings. For example, a copolymer of polylactic acid and polyglycolic acid is employed in hydrolysable stitches that slowly degrade after they are applied to a wound. The susceptibility of a polymer to degradation depends on its structure. Epoxies and chains containing aromatic functionalities are especially susceptible to UV degradation while polyesters are susceptible to degradation by hydrolysis, while polymers containing an unsaturated backbone are especially susceptible to ozone cracking. Carbon based polymers are more susceptible to thermal degradation than inorganic polymers such as polydimethylsiloxane and are therefore not ideal for most high-temperature applications. High-temperature matrices such as bismaleimides(BMI), condensation polyimides (with an O-C-N bond), triazines (with a nitrogen (N) containing ring), and blends thereof are susceptible to polymer degradation in the form of galvanic

corrosion when bare carbon fiber reinforced polymer CFRP is in contact with an active metal such as aluminium in salt water environments. The degradation of polymers to form smaller molecules may proceed by random scission or specific scission. The degradation of polyethylene occurs by random scission—a random breakage of the bonds that hold the atoms of the polymer together. When heated above 450 °C, polyethylene degrades to form a mixture of hydrocarbons. Other polymers, such as poly(alpha-methylstyrene), undergo specific chain scission with breakage occurring only at the ends. They literally unzip or depolymerize back to the constituent monomer. The sorting of polymer waste for recycling purposes may be facilitated by the use of the Resin identification codes developed by the Society of the Plastics Industry to identify the type of plastic.

Product failure[edit]

Chlorine attack of acetal resin plumbing joint

In a finished product, such a change is to be prevented or delayed. Failure of safety-critical polymer components can cause serious accidents, such as fire in the case of cracked and degraded polymer fuel lines. Chlorine-induced cracking of acetal resin plumbing joints and polybutylene pipes has caused many serious floods in domestic properties, especially in the USA in the 1990s. Traces of chlorine in the water supply attacked vulnerable polymers in the plastic plumbing, a problem which occurs faster if any of the parts have been poorly extruded or injection molded. Attack of the acetal joint occurred because of faulty molding, leading to cracking along the threads of the fitting which is a serious stress concentration.

Ozone-induced cracking in natural rubber tubing

Polymer oxidation has caused accidents involving medical devices. One of the oldest known failure modes is ozone cracking caused by chain scission when ozone gas attacks susceptible elastomers, such as natural

rubber andnitrile rubber. They possess double bonds in their repeat units which are cleaved during ozonolysis. Cracks in fuel lines can penetrate the bore of the tube and cause fuel leakage. If cracking occurs in the engine compartment, electric sparks can ignite the gasoline and can cause a serious fire. Fuel lines can also be attacked by another form of degradation: hydrolysis. Nylon 6,6 is susceptible to acid hydrolysis, and in one accident, a fractured fuel line led to a spillage of diesel into the road. If diesel fuel leaks onto the road, accidents to following cars can be caused by the slippery nature of the deposit, which is like black ice.

List of synthetic polymers From Wikipedia, the free encyclopedia

Synthetic polymers are human-made polymers. From the utility point of view they can be classified into four main categories: thermoplastics, thermosets, elastomers and synthetic fibers. They are found commonly in a variety of consumer products such as money, super glue, etc. A wide variety of synthetic polymers are available with variations in main chain as well as side chains. The back bones of common synthetic polymers such as polythene and polystyrene, poly acrylates are made up of carbon-carbon bonds, whereas hetero chain polymers such as polyamides, polyesters, polyurethanes polysulfides and polycarbonates have other elements (e.g. oxygen, sulfur, nitrogen) inserted along the backbone. Also silicon form familiar materials such as silicones through siloxane linkages, which does not have any carbon atoms and is said to be aninorganic polymer. Coordination polymers may contain a range of metals in the backbone, with non-covalent bonding present. Some familiar house-hold synthetic polymers include Nylons in textiles and fabrics, Teflon in non-stick pans, Bakelite for electrical switches, polyvinyl chloride in pipes, etc. The common PET bottles are made of a synthetic polymer, polyethylene terephthalate. The plastic kits and covers are mostly made of synthetic polymers like polythene and tires are manufactured from Buna rubbers.[1] However, due to the environmental issues created by these synthetic polymers which are mostly non-biodegradable and often synthesized from petroleum, alternatives like bioplasticsare also being considered. But they are expensive when compared to the synthetic polymers.[2]

IUPAC definition Artificial polymer: Man-made polymer that is not a biopolymer. Note 1: Artificial polymer should also be used in the case of chemically modified biopolymers. Note 2: Biochemists are now capable of synthesizing copies of biopolymers that should be named synthetic biopolymers to make a distinction with true biopolymers. Note 3: Genetic engineering is now capable of generating non-natural analogues of biopolymers that should be referred to as artificial biopolymers, e.g., artificial protein, artificial polynucleotide, etc.[3]

Contents

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1 Inorganic polymers

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2 Organic polymers

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3 Brand names

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4 See also

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5 References

Inorganic polymers[edit source] Main article: Inorganic polymer

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Polysiloxane

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Polyphosphazene

Organic polymers[edit source] The seven most common types of synthetic organic polymers, which are commonly found in households are:

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Low Density Polyethylene (LDPE),

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High Density Polyethylene (HDPE),

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Polypropylene (PP)

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Polyvinyl Chloride (PVC)

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Polystyrene (PS)

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Nylon, nylon 6, nylon 6,6

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Teflon (Polytetrafluoroethylene)

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Thermoplastic polyurethanes (TPU)

List of some addition polymers and their uses

Polymer

Abbreviation

Properties

Uses

Low Density Polyethylene LDPE

Chemically inert, flexible, insulator

Squeeze bottles, toys, flexible pipes, insulation cover (electric wires), six pack rings, etc.

High Density Polyethylene HDPE

Inert, thermally stable, tough and high tensile strength

Bottles, pipes, inner insulation of coax cable, plastic bags, etc.

Polypropylene

PP

Auto parts, industrial fibers, food Resistant to acids and alkalies, High containers, liner in bags, dishware tensile strength and as a wrapping material for textiles and food

Polystyrene (thermocole)

PS

Thermal insulator. Properties Petri dishes, CD case, plastic depends on the form, expanded form cutlery is tough and rigid

Polytetrafluoroethylene

PTFE

Very low coefficient of friction, excellent dielectric properties, chemically inert

Low friction bearings, non-stick pans, coating against chemical attack etc.

Insulator

Pipe, fencing, lawn chairs, handbags, curtain clothes, non-food bottles, raincoats, toys, vinyl flooring etc.

Polyvinylchloride

PVC

Polychlorotrifluoroethylene PCTFE

Stable to heat and thermal attacks, valves, seals, gaskets etc. high tensile strength and non wetting

Brand names[edit source] These polymers are often better known through their brand names, for instance:

Brand Name

Polymer

Characteristic properties

Uses

Bakelite

Phenol-formaldehyde resin

High electric, heat and chemical resistance

Insulation of wires, manufacturing sockets, electrical devices, breakpads, etc.

Kevlar

Para-aramid fibre

High tensile strength

Manufacturing armour, sports and musical equipment. Used in the field of cryogenics

Twaron

Para-aramid

Bullet-proof body armor, helmets, brake Heat resistant and strong fibre pads, ropes, cables and optical fibre cables, etc. and as anasbestos substitute

High strength and stiffness, less permeable to gases, almost reflects light completely

Food packaging, transparent covering over paper, reflector for rollsigns and solar cooking stoves

Neoprene Polychloroprene

Chemically inert

Manufacturing gaskets, corrosion resistant coatings, waterproof seat covers, substitute for corks and latex

Nylon

Polyamide

Silky, thermoplastic and resistant to biological and chemical agents

Stockings, fabrics, toothbrushes. Molded nylon is used in making machine screws, gears etc.

Nomex

Meta-aramid polymer

Hood of firefighter's mask, electrical Excellent thermal, chemical, lamination of circuit and radiation resistance, rigid, boards and transformer cores and durable and fireproof. in Thermal Micrometeoroid Garment

Orlon

Polyacrylonitrile (PAN)

Wool-like, resistant to chemicals, oils, moths and sunlight

Used for making clothes and fabrics like sweaters, hats, yarns, rugs, etc., and as a precursor of carbon fibres

Bioplastic

Used in high-performance applications such as sports shoes, electronic device components, automotive fuel lines, pneumatic airbrake tubing, oil and gas flexible pipes and control fluid umbilicals, and catheters.

High tensile strength, resistance to corrosion, heat, chemicals and saltwater

Used for manufacturing optical fiber cables, umbilical cables, drumheads, automotive industry, ropes, wire ropes and cables

Mylar

Rilsan

Polyethylene terephthalate film

Polyamide 11 & 12

Technora Copolyamid

Teflon

Very low coefficient of Plain bearings, gears, non-stick pans, etc. friction, Polytetrafluoroethylene(PTFE) due to its low friction. Used as a tubing excellent dielectricproperties, for highly corrosivechemicals. high melting, chemically inert

Ultem

Polyimide

Heat,flame and solvent resistant. Has high dielectric

Used in medical and chemical instrumentation, also in guitar picks

strength

High thermal and chemical stability. Golden color. Has high strength, low creep, and is moisture resistant

Vectran

aromatic polyester

Viton

Polytetrafluoroethylene(PTFE) Elastomer

Zylon

poly-p-phenylene-2,6benzobisoxazole(PBO)

Used as reinforcing fibres for ropes, cables, sailcloth. Also used in manufacturing badminton strings, bike tires and in electronics applications. Is the key component of a line of inflatable spacecraft developed byBigelow Aerospace

Depends on the grade of the polymer. Viton B is used in chemical process plants and gaskets.

Very high tensile strength and Used in tennis racquets, table tennis thermal stability blades, body armor, etc.

Thermoplastic From Wikipedia, the free encyclopedia

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (October 2009) A thermoplastic, or thermosoftening plastic, is a polymer that becomes pliable or moldable above a specific temperature, and returns to a solid state upon cooling.[1][2] Most thermoplastics have a high molecular weight. The polymer chains associate through intermolecular forces, which permits thermoplastics to be remolded because the intermolecular interactions increase upon cooling and restore the bulk properties. In this way, thermoplastics differ from thermosetting polymers, which form irreversible chemical bonds during the curing process. Thermosets often do not melt, but break down and do not reform upon cooling.

Stress strain graph of thermoplastic material.

Above its glass transition temperature, Tg, and below its melting point, Tm, the physical properties of a thermoplastic change drastically without an associated phase change. Within this temperature range, most thermoplastics are rubbery due to alternating rigid crystalline and elastic amorphousregions, approximating random coils.[citation needed] Some thermoplastics do not fully crystallize above glass transition temperature Tg, retaining some, or all of their amorphous characteristics. Amorphous and semi-amorphous plastics are used when high optical clarity is necessary, as a light wave cannot pass through smaller crystallites than its wavelength. Amorphous and semiamorphous plastics are less resistant to chemical attack and environmental stress cracking because they lack a crystalline structure. Brittleness can be lowered with the addition of plasticizers, which interfere with crystallization to effectively lower Tg. Modification of the polymer throughcopolymerization or through the addition of non-reactive side chains to monomers before polymerization can also lower Tg. Before these techniques were employed, plastic automobile parts would often crack when exposed to cold temperatures. Recently, thermoplastic elastomers have become available.[citation needed] Contents

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1 Acrylic

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2 Nylon

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3 Polyethylene

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4 Polypropylene

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5 Polystyrene

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6 Polyvinyl chloride

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7 Teflon

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8 References

Acrylic[edit] Acrylic, a polymer called poly(methyl methacrylate) (PMMA), is also known by trade names such as Lucite, Perspex and Plexiglas. It serves as a sturdy substitute for glass for such items as aquariums, motorcycle helmet visors, aircraft windows, viewing ports of submersibles, and lenses of exterior lights of automobiles. It is extensively used to make signs, including lettering and logos. In medicine, it is used in bone cement and to replace eye lenses. Acrylic paint consists of PMMA particles suspended in water.

Nylon[edit] Nylon, belonging to a class of polymers called polyamides, has served as a substitute for silk in products such as parachutes, flak vests and women's stockings. Nylon fibers are useful in making fabrics, rope, carpets and strings for musical instruments. In bulk form, nylon is used for mechanical parts, including machine screws, gear wheels and power tool casings. In addition, nylon is used in the manufacture of heat-resistant composite materials.

Polyethylene[edit] Polyethylene (or polyethene, polythene, PE) is a family of similar materials categorized according to their density and molecular structure. For example, ultra-high molecular weight polyethylene (UHMWPE) is tough and resistant to chemicals, and it is used to manufacture moving machine parts, bearings, gears, artificial joints and some bulletproof vests. High-density polyethylene (HDPE), recyclable plastic no. 2, is commonly used as milk jugs, liquid laundry detergent bottles, outdoor furniture, margarine tubs, portable gasoline cans, water drainage pipes, and grocery bags. Medium-density polyethylene (MDPE) is used for packaging film, sacks and gas pipes and fittings. Low-density polyethylene (LDPE) is softer and flexible and is used in the manufacture of squeeze bottles, milk jug caps, retail store bags. and (LLDPE) as stretch wrap in transporting and handling boxes of durable goods, and as the common household food covering. XLPE or "PEX" (cross-linked polyethylene) is a semi-rigid/flexible material which has gained wide use in cold or hot water building

heating/cooling applications (hydronic heating and cooling) due to its exceptional resistance to breakdown from wide temperature variations.

Polypropylene[edit] Polypropylene (PP) is useful for such diverse products as reusable plastic food containers i.e.) "microwave and dishwasher safe" plastic containers, diaper lining, sanitary pad lining and casing, ropes, carpets, plastic moldings, piping systems, car batteries, insulation for electrical cables and filters for gases and liquids. In medicine, it is used in hernia treatment and to make heat-resistant medical equipment. Polypropylene sheets are used for stationery folders and packaging and clear storage bins. Polypropylene is defined by the recyclable plastic number 5. Although relatively inert, it is vulnerable to ultraviolet radiation and can degrade considerably in direct sunlight. It may be worthy to note that (PP) is not as impact-resistant as the polyethlenes (HDPE, LDPE). PP is also somewhat permeable to highly volatile gases and liquids.

Polystyrene[edit] Polystyrene is manufactured in various forms that have differing applications. Extruded polystyrene (PS) is used in the manufacture of disposable cutlery, CD and DVD cases, plastic models of cars and boats, and smoke detector housings. Expanded polystyrene foam (EPS) is used in making insulation and packaging materials, such as the "peanuts" and molded foam used to cushion fragile products. Extruded polystyrene foam (XPS), known by the trade name Styrofoam, is used to make architectural models and drinking cups for heated beverages. Polystyrene copolymers are used in the manufacture of toys and product casings.

Polyvinyl chloride[edit] Polyvinyl chloride (PVC) is a tough, lightweight material that is resistant to acids and bases. Much of it is used by the construction industry, such as for vinyl siding, drainpipes, gutters and roofing sheets. It is also converted to flexible forms with the addition of plasticizers, thereby making it useful for items such as hoses, tubing, electrical insulation, coats, jackets and upholstery. Flexible PVC is also used in inflatable products, such as water beds and pool toys.

Teflon[edit] Teflon is the brand name given by DuPont Corp. for a polymer called polytetrafluoroethylene (PTFE), which belongs to a class of thermoplastics known as fluoropolymers. It is famous as a coating for non-stick cookware. Being chemically inert, it is used in making containers and pipes that come in contact with reactive chemicals. It is also used as a lubricant to reduce wear from friction between sliding parts, such as gears, bearings and bushings.

Thermosetting polymer From Wikipedia, the free encyclopedia (Redirected from Thermoset)

A thermosetting plastic, also known as a thermoset, is polymer material that irreversibly cures. The cure may be induced by heat, generally above 200 °C (392 °F), through a chemical reaction, or suitable irradiation. Thermoset materials are usually liquid or malleable prior to curing and designed to be molded into their final form, or used as adhesives. Others are solids like that of the molding compound used in semiconductors and integrated circuits (IC). Once hardened a thermoset resin cannot be reheated and melted to be shaped differently. Thermosetting polymers may be contrasted with thermoplastic polymers which are commonly produced in pellets and shaped into their final product form by melting and pressing or injection molding. Contents [hide]

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1 Definition

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2 Process

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3 Properties

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4 Examples

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5 See also

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6 References

Definition[edit] IUPAC defines a thermosetting polymer as a prepolymer in a soft solid or viscous state that changes irreversibly into an infusible, insoluble polymer network by curing. Curing can be induced by the action of [1] heat or suitable radiation, or both. A cured thermosetting polymer is called a thermoset.

Process[edit] The curing process transforms the resin into a plastic or rubber by a cross-linking process. Energy and/or catalysts are added that cause the molecular chains to react at chemically active sites (unsaturated or epoxy sites, for example), linking into a rigid, 3-D structure. The cross-linking process forms a molecule with a larger molecular weight, resulting in a material with a higher meltingpoint. During the reaction, the molecular weight has increased to a point so that the melting point is higher than the surrounding ambient temperature, the material forms into a solid material. Uncontrolled reheating of the material results in reaching the decomposition temperature before the melting point is obtained. Therefore, a thermoset material cannot be melted and re-shaped after it is [2] cured. This implies that thermosets cannot be recycled, except as filler material.

Properties[edit]

Thermoset materials are generally stronger than thermoplastic materials due to this three dimensional network of bonds (cross-linking), and are also better suited to high-temperature applications up to the decomposition temperature. However, they are more brittle. Since their shape is permanent, they tend not to be recyclable as a source for newly made plastic.

Examples[edit] 

Polyester fibreglass systems: sheet molding compounds and bulk molding compounds)

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Polyurethanes: insulating foams, mattresses, coatings, adhesives, car parts, print rollers, shoe soles, flooring, synthetic fibers, etc. Polyurethane polymers are formed by combining two bi- or higher functional monomers/oligomers.

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Vulcanized rubber

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Bakelite, a phenol-formaldehyde resin used in electrical insulators and plasticware

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Duroplast, light but strong material, similar to bakelite used for making car parts

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Urea-formaldehyde foam used in plywood, particleboard and medium-density fiberboard

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Melamine resin used on worktop surfaces

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Epoxy resin used as the matrix component in many fiber reinforced plastics such as glass-reinforced plastic and graphite-reinforced plastic)

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Polyimides used in printed circuit boards and in body parts of modern aircraft

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Cyanate esters or polycyanurates for electronics applications with need for dielectric properties and high glass temperature requirements in composites

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Mold or mold runners (the black plastic part in integrated circuits or semiconductors)

[3]

Some methods of molding thermosets are: 

Reactive injection molding (used for objects such as milk bottle crates)

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Extrusion molding (used for making pipes, threads of fabric and insulation for electrical cables)

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Compression molding (used to shape most thermosetting plastics)

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Spin casting (used for producing fishing lures and jigs, gaming miniatures, figurines, emblems as well as production and replacement parts)

Elastomer From Wikipedia, the free encyclopedia

An elastomer is a polymer with viscoelasticity (colloquially "elasticity"), generally having low Young's modulus and high failure strain compared with other materials. The term, which is derived from elastic polymer, is often used interchangeably with the term rubber, although the latter is preferred when referring to vulcanisates. Each of the monomers which link to form the polymer is usually made of carbon, hydrogen, oxygen and/or silicon. Elastomers are amorphous polymers existing above their glass transition temperature, so that considerable segmental motion is possible. At ambient temperatures, rubbers are thus relatively soft (E~3MPa) and deformable. Their primary uses are for seals, adhesives and molded flexible parts. Application areas for different types of rubber are manifold and cover segments as diverse as tires, shoe soles as well as dampening and insulating elements. The importance rubbers have can be judged from the fact that global revenues are forecast to rise to US$56 billion in 2020. [1]

IUPAC definition Polymer that displays rubber-like elasticity.[2]

Contents [hide]

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1 Background

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2 Examples of elastomers

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3 References

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4 External links

Background[edit]

(A) is an unstressed polymer; (B) is the same polymer under stress. When the stress is removed, it will return to the A configuration. (The dots represent cross-links)

Elastomers are usually thermosets (requiring vulcanization) but may also be thermoplastic (see thermoplastic elastomer). The long polymer chains cross-linkduring curing, i.e., vulcanizing. The molecular structure of elastomers can be imagined as a 'spaghetti and meatball' structure, with the meatballs signifying cross-links. The elasticity is derived from the ability of the long chains to reconfigure themselves to distribute an applied stress. The covalent cross-linkages ensure that the elastomer will return to its original configuration when the stress is removed. As a result of this extreme flexibility, elastomers can reversibly extend from 5-700%, depending on the specific material. Without the cross-linkages or with short, uneasily reconfigured chains, the applied stress would result in a permanent deformation. Temperature effects are also present in the demonstrated elasticity of a polymer. Elastomers that have cooled to a glassy or crystalline phase will have less mobile chains, and consequentially less elasticity, than those manipulated at temperatures higher than the glass transition temperature of the polymer. It is also possible for a polymer to exhibit elasticity that is not due to covalent cross-links, but instead for thermodynamic reasons.

Examples of elastomers[edit] Unsaturated rubbers that can be cured by sulfur vulcanization:



Natural polyisoprene: cis-1,4-polyisoprene natural rubber (NR) and trans-1,4-polyisoprene gutta-percha

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Synthetic polyisoprene (IR for Isoprene Rubber)

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Polybutadiene (BR for Butadiene Rubber)

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Chloroprene rubber (CR), polychloroprene, Neoprene, Baypren etc.

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Butyl rubber (copolymer of isobutylene and isoprene, IIR)

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Halogenated butyl rubbers (chloro butyl rubber: CIIR; bromo butyl rubber: BIIR)

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Styrene-butadiene Rubber (copolymer of styrene and butadiene, SBR)

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Nitrile rubber (copolymer of butadiene and acrylonitrile, NBR), also called Buna N rubbers

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Hydrogenated Nitrile Rubbers (HNBR) Therban and Zetpol

(Unsaturated rubbers can also be cured by non-sulfur vulcanization if desired). Saturated rubbers that cannot be cured by sulfur vulcanization:

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EPM (ethylene propylene rubber, a copolymer of ethylene and propylene) and EPDM rubber (ethylene propylene diene rubber, a terpolymer of ethylene, propylene and a diene-component)

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Epichlorohydrin rubber (ECO)

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Polyacrylic rubber (ACM, ABR)

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Silicone rubber (SI, Q, VMQ)

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Fluorosilicone Rubber (FVMQ)

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Fluoroelastomers (FKM, and FEPM) Viton, Tecnoflon, Fluorel, Aflas and Dai-El

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Perfluoroelastomers (FFKM) Tecnoflon PFR, Kalrez, Chemraz, Perlast

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Polyether block amides (PEBA)

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Chlorosulfonated polyethylene (CSM), (Hypalon)

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Ethylene-vinyl acetate (EVA)

"The definitions are not authentic as the Rubber which is classified in World Customs Organisation Books in Chapter 40, where as the above definitions stating all rubber and different polymers in same chapter which is classified in Chapter 39 of the World Custom Organisation's Harmonised Commodity for Description and coding system. One should go through all differentiation while editing between Plastics and articles thereof and Rubber and articles thereof." Various other types of elastomers:



Thermoplastic elastomers (TPE)



The proteins resilin and elastin

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Polysulfide rubber

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Elastolefin, elastic fiber used in fabric production

Synthetic fiber From Wikipedia, the free encyclopedia Part of a series on

Fiber

Natural fibers

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Synthetic fibers

Cellulose[show]

Mineral[show]

Polymer[show]

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Agriculture and Agronomy portal

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Engineering portal

Category: Fibers

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V

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T

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Synthetic fibers are the result of extensive research by scientists to improve on naturally occurring animal and plant fibers. In general, syntheticfibers are created by forcing, usually through extrusion, fiber forming materials through holes (called spinnerets) into the air, forming a thread. Before synthetic fibers were developed, artificially manufactured fibers were made from cellulose, which comes from plants. These fibers are called cellulose fibers. Contents [hide]

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1 Description

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2 Advantages

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3 Disadvantages

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4 History

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5 Industry structure

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6 See also

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7 References

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8 External links

Description[edit] Synthetic fibers are made from synthesized polymers or small molecules. The compounds that are used to make these fibers come from raw materials such as petroleum based chemicals or petrochemicals. These materials are polymerized into a long, linear chemical that bond two adjacent carbon atoms. Differing chemical compounds will be used to produce different types of fibers. Although there are several different synthetic fibers, they generally have the same common properties. Generally, they are known for being:

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Heat-sensitive

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Resistant to most chemicals

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Resistant to insects, fungi and rot.

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Low moisture absorbency

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Electrostatic

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Flame resistant

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Density or specific gravity

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May pill easily

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Low melting temperature

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Often less expensive than natural fibers.

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Easy to wash and maintain.

Advantages[edit] 

Synthetic fibers do not depend either on an agricultural crop or on animal farming.

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They are generally cheaper than natural fiber.

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Synthetic fibers possess unique characteristics which make them popular dress material.

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They dry up quickly, are durable, readily available and easy to maintain.

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More stain resistant than natural fibres

Disadvantages[edit] 

Synthetic fibers burn more readily than natural

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Prone to heat damage, they melt relatively easily

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Prone to damage by hot washing

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More electrostatic charge is generated by rubbing than with natural fibres

There are several methods of manufacturing synthetic fibers but the most common is the Melt-Spinning Process. It involves heating the fiber until it begins to melt, then you must draw out the melt with tweezers as quickly as possible. The next step would be to draw the molecules by aligning them in a parallel arrangement. This brings the fibers closer together and allows them to crystallize and orient. Lastly, is Heat-Setting. This utilizes heat to permeate the shape/dimensions of the fabrics made from heat-sensitive fibers. Synthetic fibers account for about half of all fiber usage, with applications in every field of fiber and textile technology. Although many classes of fiber based on synthetic polymers have been evaluated as potentially valuable commercial products, four of them - nylon, polyester, acrylic and polyolefin - dominate the market. These four account for approximately 98 percent by volume of synthetic fiber production, with polyester alone accounting for around 60 per cent.[1]

History[edit] The first artificial fiber, known as artificial silk, became known as viscose around 1894, and finally rayon in 1924. A similar product known as cellulose acetate was discovered in 1865. Rayon and acetate are both

artificial fibers, but not truly synthetic, being made from wood. Although these artificial fibers were discovered in the mid-nineteenth century, successful modern manufacture began much later (see the dates below). Nylon, the first synthetic fiber, made its debut in the United States as a replacement for silk, just in time for World War II rationing. Its novel use as a material for women's stockings overshadowed more practical uses, such as a replacement for the silk in parachutes and other military uses. Common synthetic fibers include:

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Nylon (1931)

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Modacrylic (1949)

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Olefin (1949)

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Acrylic (1950)

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Polyester (1953)

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Carbon fiber (1958)

Specialty synthetic fibers include:

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Vinyon (1939)

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Sulfar (1983)

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Saran (1941)

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Lyocell (1992) (artificial, not synthetic)

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Spandex (1959)

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PLA (2002)

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Vinalon (1939)

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M-5 (PIPD fiber)

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Aramids (1961) - known

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Orlon

as Nomex, Kevlar and Twaron

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Zylon (PBO fiber)

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Modal (1960's)

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Vectran (TLCP fiber) made from Vectra LCP

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Dyneema/Spectra (1979)

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PBI (Polybenzimidazole fiber) (1983)

polymer 

Derclon used in manufacture of rugs

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Rayon artificial silk

Other synthetic materials used in fibers include:

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Acrylonitrile rubber (1930)

Modern fibers that are made from older artificial materials include:

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Glass fiber (1938) is used for:

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industrial, automotive, and home insulation (glass wool)

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reinforcement of composite materials (glass-reinforced plastic, glass fiber reinforced concrete)

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specialty papers in battery separators and filtration

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Metallic fiber (1946) is used for:

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adding metallic properties to clothing for the purpose of fashion (usually made with composite plastic and metal foils)

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elimination and prevention of static charge build-up

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conducting electricity to transmit information

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conduction of heat

In the horticulture industry synthetics are often used in soils to help the plants grow better. Examples are:

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expanded polystyrene flakes

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urea-formaldehyde foam resin

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polyurethane foam

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phenolic resin foam

Industry structure[edit] During the last quarter of the 20th century, the Asian share of global output of synthetic fibers doubled to 65 per cent.[2]

See also

Siloxane From Wikipedia, the free encyclopedia (Redirected from Polysiloxane)

Not to be confused with Silicone.

A siloxane is a functional group in organosilicon chemistry with the Si–O–Si linkage. The parent siloxanes include the oligomeric andpolymeric hydrides with the formulae H(OSiH2)nOH and (OSiH2)n.[1] Siloxanes also include branched compounds, the defining feature being that each pair of silicon centres is separated by one oxygen atom. The siloxane functional group forms the backbone of silicones, the premier example of which is polydimethylsiloxane.[2] Contents [hide]

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1 Structure

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2 Synthesis of siloxanes

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3 Reactions

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4 Nomenclature

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5 References

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6 External links

Structure[edit] Siloxanes generally adopt structures expected for linked tetrahedral ("sp3-like") centers. The Si–O bond is 1.64 Å (vs Si–C distance of 1.92 Å) and the Si–O–Si angle is rather open at 142.5°.[3]By way of contrast, the C– O distance in a typical dialkyl ether is much shorter at 1.414(2) Å with a more acute C–O–C angle of 111°.[4] It can be appreciated that the siloxanes would have low barriers for rotation about the Si–O bonds as a consequence of low steric hindrance. This geometric consideration is the basis of the useful properties of some siloxane-containing materials, such as their low glass transition temperatures.

Synthesis of siloxanes[edit]

The main route to siloxane functional group is by condensation of two silanols: 2 R3Si–OH → R3Si–O–SiR3 + H2O Usually the silanols are generated in situ by hydrolysis of silyl chlorides. With a disilanol, R2Si(OH)2 (derived from double hydrolysis of a silyldichloride), the condensation can afford linear products terminated with silanol groups: n R2Si(OH)2 → H(R2SiO)nOH + n−1 H2O Alternatively the disilanol can afford cyclic products n R2Si(OH)2 → (R2SiO)n + n H2O Starting from trisilanols, cages are possible, such as the species with the formula (RSi) nO3n/2 with cubic (n = 8) and hexagonal prismatic (n = 12). (RSi)8O12 structures. The cubic cages is an expanded analogues of the hydrocarbon cubane, with silicon centers at the corners of a cube oxygen centres spanning each of the twelve edges.[5]

Reactions[edit] Oxidation of organosilicon compounds, including siloxanes, gives silicon dioxide. This conversion is illustrated by the combustion of hexamethylcyclotrisiloxane: ((CH3)2SiO)3 + 12 O2 → 3 SiO2 + 6 CO2 + 9 H2O Strong base degrades siloxane group, often affording siloxide salts: ((CH3)3Si)2O + 2 NaOH → 2 (CH3)3SiONa + H2O This reaction proceeds by production of silanols. Similar reactions are used industrially to convert cyclic siloxanes to linear polymers.[2]

Nomenclature[edit]

Decamethylcyclopentasiloxane, or D5, a cyclic siloxane.

The word siloxane is derived from the words silicon, oxygen, and alkane. In some cases, siloxane materials are composed of several different types of siloxide groups; these are labeled according the number of Si-O bonds. M-units: (CH3)3SiO0.5, D-units: (CH3)2SiO, T-units: (CH3)SiO1.5

Cyclic siloxanes

Linear siloxanes

D3: hexamethylcyclotrisiloxane

MM: hexamethyldisiloxane

D4: octamethylcyclotetrasiloxane

MDM: octamethyltrisiloxane

D5: decamethylcyclopentasiloxane

MD2M: decamethyltetrasiloxane

D6: dodecamethylcyclohexasiloxane MDnM: polydimethylsiloxane

Polyphosphazene From Wikipedia, the free encyclopedia

General structure of polyphosphazenes. Gray spheres represent any organic or inorganic group.

Polyphosphazenes include a wide range of hybrid inorganic-organic polymers with a number of different skeletal architectures that contain alternatingphosphorus and nitrogen atoms.[1] Nearly all of these molecules contain two organic or organometallic side groups attached to each phosphorus atom. These include linear polymers with the formula (N=PR1R2)n, where R1 and R2 are organic or organometallic side groups. The linear polymers are the largest group, with the general structure shown schematically in the picture. Other known architectures are cyclolinear and cyclomatrix polymers in which small phosphazene rings are connected together by organic chain units. Other architectures are available, such as block copolymer, star,dendritic, or comb-type structures. More than 700 different polyphosphazenes are known, with different side groups (R) and different molecular architectures. Many of these polymers were first synthesized and studied in the research group of Harry R. Allcock at The Pennsylvania State University.[1][2][3][4][5] Contents [hide]

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1 Synthesis

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2 Properties and uses

o

2.1 Thermoplastics

o

2.2 Phosphazene elastomers

o

2.3 Polymer electrolytes

o

2.4 Hydrogels

o

2.5 Bioerodible polyphosphazenes

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3 Commercial aspects

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4 References

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5 Further information

Synthesis[edit] The method of synthesis depends on the type of polyphosphazene. The most widely used method for linear polymers is based on a two-step process.[1][2][3][4] In the first step a cyclic small molecule phosphazene, known as hexachlorocyclotriphosphazene, with the formula (NPCl2)3, is heated in a sealed system at 250 °C to convert it to a long chain linear polymer with typically 15,000 or more repeating units. In the second step the chlorine atoms linked to phosphorus in the polymer are replaced by organic groups through reactions with alkoxides, aryloxides, amines ororganometallic reagents. Because many different reagents can participate in this macromolecular substitution reaction, and because two or more different reagents may be used, a large number of different polymers can be produced, each with a different combination of properties. Variations to this process are possible using poly(dichlorophosphazene) made by condensation reactions.[6]

Another synthetic process uses a living cationic polymerization that allows the formation of block copolymers or comb, star, or dendritic architectures.[7][8] Other synthetic methods include the condensation reactions of organic-substituted phosphoranimines.[9][10][11][12] Cyclomatrix type polymers made by linking small molecule phosphazene rings together employ difunctional organic reagents to replace the chlorine atoms in (NPCl2)3, or the introduction of allylor vinyl substituents, which are then polymerized by free-radical methods.[13] Such polymers may be useful as coatings or thermosetting resins, often prized for their thermal stability.

Properties and uses[edit] The linear high polymers have the geometry shown in the picture. More than 700 different macromolecules that correspond to this structure are known with different side groups or combinations of different side groups. In these polymers the properties are controlled partly by the high flexibility of the backbone, its radiation resistance, high refractive index, ultraviolet and visible transparency, and its fire resistance. However, the side groups exert an equal or even greater influence on the properties since they impart properties such as hydrophobicity, hydrophilicity, color, useful biological properties such as bioerodibility, or ion

transport properties to the polymers. Representative examples of these polymers are shown below.

Thermoplastics[edit] The first stable thermoplastic poly(organophosphazenes), isolated in the mid 1960’s by Allcock, Kugel, and Valan, were macromolecules with trifluoroethoxy, phenoxy, methoxy, ethoxy, or various amino side groups.[2][3][4] Of these early species, poly[bis(trifluoroethoxyphosphazene], [NP(OCH2CF3)2]n, has proved to be the subject of intense research due to its crystallinity, high hydrophobicity, biological compatibility, fire resistance, general radiation stability, and ease of fabrication into films, microfibers and nanofibers. It has also been a substrate for various surface reactions to immobilize biological agents. The polymers with phenoxy or amino side groups have also been studied in detail.

Phosphazene elastomers[edit] The first large-scale commercial uses for linear polyphosphazenes were in the field of high technology elastomers, with a typical example containing a combination of trifluoroethoxy and longer chain fluoroalkoxy groups.[14][15][16][17] The mixture of two different side groups eliminates the crystallinity found in single-substituent polymers and allows the inherent flexibility and elasticity to become manifest. Glass transition temperatures as low as -60 °C are attainable, and properties such as oil-resistance and hydrophobicity are responsible for their utility in land vehicles andaerospace components. They have also been used in biostable biomedical devices.[18] Other side groups, such as non-fluorinated alkoxy or oligo-alkyl ether units, yield hydrophilic or hydrophobic elastomers with glass transitions over a broad range from -100 °C to + 100 °C.[19]Polymers with two different aryloxy side groups have also been developed as elastomers for fire-resistance as well as thermal and sound insulation applications.

Polymer electrolytes[edit]

Linear polyphosphazenes with oligo-ethyleneoxy side chains are gums that are good solvents for salts such as lithium triflate. These solutions function as electrolytes for lithium ion transport, and they have been the focus of much research designed to incorporate them into fire-resistant rechargeable lithium-ion polymer battery.[20][21][22] The same polymers are also of interest as the electrolyte in experimental dye-sensitized solar cells.[23] Other polyphosphazenes with sulfonated aryloxy side groups are proton conductors of interest for use in the membranes of proton exchange membrane fuel cells.[24]

Hydrogels[edit] Water-soluble poly(organophosphazenes) with oligo-ethyleneoxy side chains can be cross-linked by gammaradiation techniques. The cross-linked polymers absorb water to form hydrogels which are responsive to temperature changes, expanding to a limit defined by the cross-link density below a critical solution temperature, but contracting above that temperature. This is the basis of controlled permeability membranes. Other polymers with both oligo-ethyleneoxy and carboxyphenoxy side groups expand in the presence of monovalent cations but contract in the presence of di- or tri-valent cations, which form ionic crosslinks.[25][26][27][28][29] Phosphazene hydrogels have been utilized for controlled drug release and other medical applications.[26]

Bioerodible polyphosphazenes[edit] The ease with which properties can be controlled and fine-tuned by the linkage of different side groups to polyphosphazene chains has prompted major efforts to address biomedical materials challenges using these polymers. Different polymers have been studied as macromolecular drug carriers, as membranes for the controlled delivery of drugs, as biostable elastomers, and especially as tailored bioerodible materials for the regeneration of living bone.[30][31][32][33] An advantage for this last application is that poly(dichlorophosphazene) reacts with amino acid ethylesters (such as ethyl glycinate or the corresponding ethyl esters of numerous other amino acids) through the amino terminus to form polyphosphazenes with amino acid ester side groups. These polymers hydrolyze slowly to a near-neutral, pH-buffered solution of the amino acid, ethanol, phosphate, and ammonium ion. The speed of hydrolysis depends on the amino acid ester, with half-lives that vary from weeks to months depending on the structure of the amino acid ester. Nanofibers and porous constructs of these polymers assist osteoblast replication and accelerate the repair of bone in animal model studies.

Commercial aspects[edit] The cyclic trimer, (NPCl2)3, is commercially available and has formed the starting point for most commercial developments. Prominent among these developments has been the high performanceelastomers known as PN-F or Eypel-F, which have been manufactured for seals, O-rings, and dental devices. An aryloxy-substituted polymer has also been developed as a fire resistant expanded foam for thermal and sound insulation. The

patent literature contains many references to cyclomatrix polymers derived from cyclic trimeric phosphazenes incorporated into cross-linked resins for fire resistant circuit boards and related applications.

Low-density polyethylene From Wikipedia, the free encyclopedia (Redirected from Low Density Polyethylene)

LDPE has SPIresin ID code 4

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (April 2009) Low-density polyethylene (LDPE) is a thermoplastic made from the monomer ethylene. It was the first grade of polyethylene, produced in 1933 by Imperial Chemical Industries (ICI) using a high pressure process via free radical polymerization.[1] Its manufacture employs the same method today. The EPA estimates 5.7% of LDPE (recycling number 4) is recycled.[2] Despite competition from more modern polymers, LDPE continues to be an important plastic grade. In 2009 the worldwide LDPE market reached a volume of US$22.2 billion (€15.9 billion).[3] Contents [hide]



1 Properties

o

1.1 Chemical resistance



2 Applications



3 See also



4 References



5 External links

Properties[edit] LDPE is defined by a density range of 0.910–0.940 g/cm3. It is not reactive at room temperatures, except by strong oxidizing agents, and some solvents cause swelling. It can withstand temperatures of 80 °C continuously and 95 °C for a short time. Made in translucent or opaque variations, it is quite flexible, and tough but breakable.[citation needed]

LDPE has more branching (on about 2% of the carbon atoms) than HDPE, so its intermolecular forces (instantaneous-dipole induced-dipole attraction) are weaker, its tensile strength is lower, and its resilience is higher. Also, since its molecules are less tightly packed and less crystalline because of the side branches, its density is lower. LDPE contains the chemical elements carbon andhydrogen.

Chemical resistance[edit] 

Excellent resistance (no attack) to dilute and concentrated acids, alcohols, bases and esters



Good resistance (minor attack) to aldehydes, ketones and vegetable oils



Limited resistance (moderate attack suitable for short-term use only) to aliphatic and aromatic hydrocarbons, mineral oils, and oxidizing agents



Poor resistance, and not recommended for use with halogenated hydrocarbons.[4]

Applications[edit] LDPE is widely used for manufacturing various containers, dispensing bottles, wash bottles, tubing, plastic bags for computer components, and various molded laboratory equipment. Its most common use is in plastic bags. Other products made from it include:



Trays and general purpose containers



Corrosion-resistant work surfaces



Parts that need to be weldable and machinable



Parts that require flexibility, for which it serves very well



Very soft and pliable parts such as snap-on lids



Six pack rings



Juice and milk cartons are made of liquid packaging board, a laminate of paperboard and LDPE (as the water-proof inner and outer layer), and often with of a layer of aluminum foil (thus becoming aseptic packaging).[5][6]



Parts of computer hardware, such as hard disk drives, screen cards, and optical disc drives



Playground slides



Plastic wraps

High-density polyethylene

From Wikipedia, the free encyclopedia (Redirected from High Density Polyethylene)

HDPE has SPI resin ID code 2

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (May 2010) High-density polyethylene (HDPE) or polyethylene high-density (PEHD) is a polyethylene thermoplastic made from petroleum. Known for its large strength to density ratio, HDPE is commonly used in the production of plastic bottles, corrosion-resistant piping, geomembranes, and plastic lumber. HDPE is commonly recycled, and has the number "2" as its recycling symbol. In 2007, the global HDPE market reached a volume of more than 30 million tons.

[1]

Contents [hide]



1 Properties



2 Applications



3 See also



4 References



5 External links

Properties[edit] [2]

HDPE is known for its large strength to density ratio. The mass density of high-density polyethylene can 3 [3] range from 0.93 to 0.97 g/cm . Although the density of HDPE is only marginally higher than that of lowdensity polyethylene, HDPE has little branching, giving it stronger intermolecular forces and tensile strength than LDPE. The difference in strength exceeds the difference in density, giving HDPE a [4] higher specific strength. It is also harder and more opaque and can withstand somewhat higher temperatures (120 °C/ 248 °F for short periods, 110 °C /230 °F continuously). High-density polyethylene, unlike polypropylene, cannot withstand normally required autoclaving conditions. The lack of branching is ensured by an appropriate choice of catalyst(e.g., Ziegler-Natta catalysts) and reaction conditions.

Applications[edit]

HDPE pipe installation in storm drain project in Mexico.

HDPE is resistant to many different solvents and has a wide variety of applications, including: 

3-D printer filament



Arena Board (puck board)



Backpacking frames



Ballistic plates

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Banners



Bottle caps

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Chemical resistant piping systems



Coax cable inner insulator

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Food storage containers

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Fuel tanks for vehicles

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Corrosion protection for steel pipelines

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Electrical and plumbing boxes

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Far-IR lenses

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Folding chairs and tables

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Geomembrane for hydraulic applications (such as canals and bank reinforcements) and chemical containment



Geothermal heat transfer piping systems

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Heat-resistant fireworks mortars



Hard hats



Hula hoops



Natural gas distribution pipe systems



Fireworks



Plastic bags



Plastic bottles suitable both for recycling (such as milk jugs) or re-use



Plastic lumber



Plastic surgery (skeletal and facial reconstruction)



Root barrier



Snowboard rails and boxes



Stone paper

[5]



Storage sheds



Telecom ducts



Tyvek



Water pipes for domestic water supply and agricultural processes



Wood plastic composites (utilizing recycled polymers)

HDPE is also used for cell liners in subtitle D sanitary landfills, wherein large sheets of HDPE are either extrusion or wedge welded to form a homogeneous chemical-resistant barrier, with the intention of preventing the pollution of soil and groundwater by the liquid constituents of solid waste. HDPE is preferred by the pyrotechnics trade for mortars over steel or PVC tubes, being more durable and safer. HDPE tends to rip or tear in a malfunction instead of shattering and becoming shrapnel like the other materials. Milk jugs and other hollow goods manufactured through blow molding are the most important application area for HDPE – More than 8 million tons, or nearly one third of worldwide production, was applied here. In addition to being recycled using conventional processes, HDPE can also be processed [6] by recyclebots into filament for 3-D printers via distributed recycling. Above all, China, where beverage bottles made from HDPE were first imported in 2005, is a growing market for rigid HDPE packaging, as a result of its improving standard of living. In India and other highly populated, emerging nations, infrastructure expansion includes the deployment of pipes and cable [1] insulation made from HDPE. The material has benefited from discussions about possible health and environmental problems caused by PVC and Polycarbonate associated Bisphenol A, as well as its advantages over glass, metal and cardboard.

Polypropylene

From Wikipedia, the free encyclopedia

Polypropylene

IUPAC name[hide] poly(propene)

Other names[hide] Polypropylene; Polypropene; Polipropene 25 [USAN];Propene polymers; Propylene polymers; 1-Propene

Identifiers CAS number

9003-07-0 Properties

Molecular formula

(C3H6)n

Density

0.855 g/cm3, amorphous 0.946 g/cm3, crystalline

Melting point

130–171 °C (266–340 °F)

(verify) (what is:

/ ?)

Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox references

Polypropylene (PP), also known as polypropene, is a thermoplastic polymer used in a wide variety of applications including packaging and labeling, textiles (e.g., ropes, thermal underwear and carpets), stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes. An addition polymer made from the monomer propylene, it is rugged and unusually resistant to many chemical solvents, bases and acids.

In 2008, the global market for polypropylene had a volume of 45.1 million metric tons, which led to a turnover of about $65 billion (~ €47.4 billion).[1] Contents [hide]



1 Chemical and physical properties

o

1.1 Degradation



2 History



3 Synthesis



4 Industrial processes



5 Manufacturing



6 Biaxially oriented polypropylene (BOPP)



7 Development trends



8 Applications

o

8.1 Clothing

o

8.2 Medical

o

8.3 EPP toy aircraft



9 Recycling



10 Repairing



11 Health concerns



12 References



13 External links

Chemical and physical properties[edit]

Micrograph of polypropylene

Most commercial polypropylene is isotactic and has an intermediate level of crystallinity between that of lowdensity polyethylene (LDPE) and high-density polyethylene (HDPE). Polypropylene is normally tough and flexible, especially when copolymerized with ethylene. This allows polypropylene to be used as an engineering plastic, competing with materials such as ABS. Polypropylene is reasonably economical, and can be made translucentwhen uncolored but is not as readily made transparent as polystyrene, acrylic, or certain other plastics. It is often opaque or colored using pigments. Polypropylene has good resistance to fatigue. The melting point of polypropylene occurs at a range, so a melting point is determined by finding the highest temperature of a differential scanning calorimetry chart. Perfectly isotactic PP has a melting point of 171 °C (340 °F). Commercial isotactic PP has a melting point that ranges from 160 to 166 °C (320 to 331 °F), depending on atactic material and crystallinity. Syndiotactic PP with a crystallinity of 30% has a melting point of 130 °C(266 °F).[2] The melt flow rate (MFR) or melt flow index (MFI) is a measure of molecular weight of polypropylene. The measure helps to determine how easily the molten raw material will flow during processing. Polypropylene with higher MFR will fill the plastic mold more easily during the injection or blow-molding production process. As the melt flow increases, however, some physical properties, like impact strength, will decrease. There are three general types of polypropylene: homopolymer, random copolymer, and block copolymer. The comonomer is typically used with ethylene. Ethylene-propylene rubber or EPDMadded to polypropylene homopolymer increases its low temperature impact strength. Randomly polymerized ethylene monomer added to polypropylene homopolymer decreases the polymer crystallinity and makes the polymer more transparent.

Degradation[edit] Polypropylene is liable to chain degradation from exposure to heat and UV radiation such as that present in sunlight. Oxidation usually occurs at the tertiary carbon atom present in every repeat unit. A free radical is formed here, and then reacts further with oxygen, followed by chain scission to yield aldehydes and carboxylic acids. In external applications, it shows up as a network of fine cracks and crazes that become deeper and more severe with time of exposure. For external applications, UV-absorbing additives must be used. Carbon black also provides some protection from UV attack. The polymer can also be oxidized at high temperatures, a common problem during molding operations. Anti-oxidants are normally added to prevent polymer degradation.

History[edit] Propylene was first polymerized to a crystalline isotactic polymer by Giulio Natta as well as by the German chemist Karl Rehn in March 1954.[3] This pioneering discovery led to large-scale commercial production of isotactic polypropylene by the Italian firm Montecatini from 1957 onwards.[4] Syndiotactic polypropylene was also first synthesized by Natta and his coworkers.

Polypropylene is the second most important plastic with revenues expected to exceed US$145 billion by 2019. The demand for this material was growing at a rate of 4.4% per year between 2004 and 2012.[5]

Synthesis[edit] This section provides insufficient context for those unfamiliar with the subject. Please help improve the article with a good introductory style. (June 2012)

Short segments of polypropylene, showing examples of isotactic (above) and syndiotactic (below) tacticity.

An important concept in understanding the link between the structure of polypropylene and its properties istacticity. The relative orientation of each methyl group (CH 3

in the figure) relative to the methyl groups in neighboring monomer units has a strong effect on the polymer's

ability to form crystals. A Ziegler-Natta catalyst is able to restrict linking of monomer molecules to a specific regular orientation, either isotactic, when all methyl groups are positioned at the same side with respect to the backbone of the polymer chain, or syndiotactic, when the positions of the methyl groups alternate. Commercially available isotactic polypropylene is made with two types of Ziegler-Natta catalysts. The first group of the catalysts encompases solid (mostly supported) catalysts and certain types of soluble metallocene catalysts. Such isotactic macromolecules coil into a helical shape; these helices then line up next to one another to form the crystals that give commercial isotactic polypropylene many of its desirable properties.

A ball-and-stick model of syndiotactic polypropylene.

Another type of metallocene catalysts produce syndiotactic polypropylene. These macromolecules also coil into helices (of a different type) and form crystalline materials. When the methyl groups in a polypropylene chain exhibit no preferred orientation, the polymers are called atactic. Atactic polypropylene is an amorphous rubbery material. It can be produced commercially either with a special type of supported Ziegler-Natta catalyst or with some metallocene catalysts. Modern supported Ziegler-Natta catalysts developed for the polymerization of propylene and other 1-alkenes to isotactic polymers usually use TiCl 4

as an active ingredient and MgCl

2

as a support.[6][7][8] The catalysts also contain organic modifiers, either aromatic acid esters and diesters or

ethers. These catalysts are activated with special cocatalysts containing an organoaluminum compound such as Al(C2H5)3 and the second type of a modifier. The catalysts are differentiated depending on the procedure used for fashioning catalyst particles from MgCl2 and depending on the type of organic modifiers employed during catalyst preparation and use in polymerization reactions. Two most important technological characteristics of all the supported catalysts are high productivity and a high fraction of the crystalline isotactic polymer they produce at 70–80 °C under standard polymerization conditions. Commercial synthesis of isotactic polypropylene is usually carried out either in the medium of liquid propylene or in gas-phase reactors. Commercial synthesis of syndiotactic polypropylene is carried out with the use of a special class of metallocene catalysts. They employ bridged bis-metallocene complexes of the type bridge-(Cp1)(Cp2)ZrCl2 where the first Cp ligand is the cyclopentadienyl group, the second Cp ligand is the fluorenyl group, and the bridge between the two Cp ligands is -CH2-CH2-, >SiMe2, or >SiPh2.[9] These complexes are converted to polymerization catalysts by activating them with a special organoaluminum cocatalyst, methylaluminoxane (MAO).[10]

Industrial processes[edit] Traditionally, three manufacturing process are the most representative ways to produce polypropylene.[11] Hydrocarbon slurry or suspension: Uses a liquid inert hydrocarbon diluent in the reactor to facilitate transfer of propylene to the catalyst, the removal of heat from the system, the deactivation/removal of the catalyst as well as dissolving the atactic polymer. The range of grades that could be produced was very limited. (The technology has fallen into disuse). Bulk (or bulk slurry): Uses liquid propylene instead of liquid inert hydrocarbon diluent. The polymer does not dissolve into a diluent, but rather rides on the liquid propylene. The formed polymer is withdrawn and any unreacted monomer is flashed off. Gas phase: Uses gaseous propylene in contact with the solid catalyst, resulting in a fluidized-bed medium.

Manufacturing[edit] Melt processing of polypropylene can be achieved via extrusion and molding. Common extrusion methods include production of melt-blown and spun-bond fibers to form long rolls for future conversion into a wide range of useful products, such as face masks, filters, diapers and wipes. The most common shaping technique is injection molding, which is used for parts such as cups, cutlery, vials, caps, containers, housewares, and automotive parts such as batteries. The related techniques of blow molding and injection-stretch blow molding are also used, which involve both extrusion and molding. The large number of end-use applications for polypropylene are often possible because of the ability to tailor grades with specific molecular properties and additives during its manufacture. For example, antistatic additives can be added to help polypropylene surfaces resist dust and dirt. Many physical finishing techniques can also be used on polypropylene, such as machining. Surface treatments can be applied to polypropylene parts in order to promote adhesion of printing ink and paints.

Biaxially oriented polypropylene (BOPP)[edit] When polypropylene film is extruded and stretched in both the machine direction and across machine direction it is called biaxially oriented polypropylene. Biaxial orientation increases strength and clarity.[12] BOPP is widely used as a packaging material for packaging products such as snack foods, fresh produce and confectionery. It is easy to coat, print and laminate to give the required appearance and properties for use as a packaging material. This process is normally called converting. It is normally produced in large rolls which are slit on slitting machines into smaller rolls for use on packaging machines.

Development trends[edit] With the increase in the level of performance required for polypropylene quality in recent years, a variety of ideas and contrivances have been integrated into the production process for polypropylene.[13] There are roughly two directions for the specific methods. One is improvement of uniformity of the polymer particles produced using a circulation type reactor, and the other is improvement in the uniformity among polymer particles produced by using a reactor with a narrow retention time distribution.

Applications[edit]

Polypropylene lid of a Tic Tacs box, with a living hinge and the resin identification code under its flap

As polypropylene is resistant to fatigue, most plastic living hinges, such as those on flip-top bottles, are made from this material. However, it is important to ensure that chain molecules are oriented across the hinge to maximise strength. Very thin sheets of polypropylene are used as a dielectric within certain high-performance pulse and lowloss RF capacitors. Polypropylene is used in the manufacturing piping systems; both ones concerned with high-purity and ones designed for strength and rigidity (e.g. those intended for use in potable plumbing, hydronic heating and cooling, and reclaimed water).[14] This material is often chosen for its resistance to corrosion and chemical leaching, its resilience against most forms of physical damage, including impact and freezing, its environmental benefits, and its ability to be joined by heat fusion rather than gluing.[15][16][17]

A polypropylene chair

Many plastic items for medical or laboratory use can be made from polypropylene because it can withstand the heat in an autoclave. Its heat resistance also enables it to be used as the manufacturing material of consumergradekettles[citation needed]. Food containers made from it will not melt in the dishwasher, and do not melt during industrial hot filling processes. For this reason, most plastic tubs for dairy products are polypropylene sealed with aluminum foil (both heat-resistant materials). After the product has cooled, the tubs are often given lids made of a less heat-resistant material, such as LDPE or polystyrene. Such containers provide a good hands-on example of the difference in modulus, since the rubbery (softer, more flexible) feeling of LDPE with respect to polypropylene of the same thickness is readily apparent. Rugged, translucent, reusable plastic containers made in a wide variety of shapes and sizes for consumers from various companies such as Rubbermaid and Sterilite are commonly made of polypropylene, although the lids are often made of somewhat more flexible LDPE so they can snap on to the container to close it. Polypropylene can also be made into disposable bottles to contain liquid, powdered, or similar consumer products, although HDPE and polyethylene terephthalate are commonly also used to make bottles. Plastic pails, car batteries, wastebaskets, pharmacy prescription bottles, cooler containers, dishes and pitchers are often made of polypropylene or HDPE, both of which commonly have rather similar appearance, feel, and properties at ambient temperature. A common application for polypropylene is as biaxially oriented polypropylene (BOPP). These BOPP sheets are used to make a wide variety of materials including clear bags. When polypropylene is biaxially oriented, it becomes crystal clear and serves as an excellent packaging material for artistic and retail products. Polypropylene, highly colorfast, is widely used in manufacturing carpets, rugs and mats to be used at home. [18]

Polypropylene is widely used in ropes, distinctive because they are light enough to float in water. [19] For equal mass and construction, polypropylene rope is similar in strength to polyester rope. Polypropylene costs less than most other synthetic fibers. Polypropylene is also used as an alternative to polyvinyl chloride (PVC) as insulation for electrical cables for LSZH cable in low-ventilation environments, primarily tunnels. This is because it emits less smoke and no toxic halogens, which may lead to production of acid in high-temperature conditions. Polypropylene is also used in particular roofing membranes as the waterproofing top layer of single-ply systems as opposed to modified-bit systems. Polypropylene is most commonly used for plastic moldings, wherein it is injected into a mold while molten, forming complex shapes at relatively low cost and high volume; examples include bottle tops, bottles, and fittings. It can also be produced in sheet form, widely used for the production of stationery folders, packaging, and storage boxes. The wide color range, durability, low cost, and resistance to dirt make it ideal as a protective cover for papers and other materials. It is used in Rubik's Cube stickers because of these characteristics. The availability of sheet polypropylene has provided an opportunity for the use of the material by designers. The light-weight, durable, and colorful plastic makes an ideal medium for the creation of light shades, and a number of designs have been developed using interlocking sections to create elaborate designs. Polypropylene sheets are a popular choice for trading card collectors; these come with pockets (nine for standard-size cards) for the cards to be inserted and are used to protect their condition and are meant to be stored in a binder. Expanded polypropylene (EPP) is a foam form of polypropylene. EPP has very good impact characteristics due to its low stiffness; this allows EPP to resume its shape after impacts. EPP is extensively used in model aircraft and other radio controlled vehicles by hobbyists. This is mainly due to its ability to absorb impacts, making this an ideal material for RC aircraft for beginners and amateurs. Polypropylene is used in the manufacture of loudspeaker drive units. Its use was pioneered by engineers at the BBC and the patent rights subsequently purchased by Mission Electronics for use in their Mission Freedom Loudspeaker and Mission 737 Renaissance loudspeaker. Polypropylene fibres are used as a concrete additive to increase strength and reduce cracking and spalling.[20][21] Polypropylene is used in polypropylene drums.

Clothing[edit]

Polypropylene is a major polymer used in nonwovens, with over 50% used[citation needed] for diapers or sanitary products where it is treated to absorb water (hydrophilic) rather than naturally repelling water (hydrophobic). Other interesting non-woven uses include filters for air, gas, and liquids in which the fibers can be formed into sheets or webs that can be pleated to form cartridges or layers that filter in various efficiencies in the 0.5 to 30 micrometre range. Such applications could be seen in the house as water filters or air-conditioning-type filters. The high surface area and naturally oleophilic polypropylene nonwovens are ideal absorbers of oil spills with the familiar floating barriers near oil spills on rivers. In New Zealand, in the US military, and elsewhere, polypropylene, or 'polypro' (New Zealand 'polyprops'), has been used for the fabrication of cold-weather base layers, such as long-sleeve shirts or long underwear (More recently, polyester has replaced polypropylene in these applications in the U.S. military, such as in the ECWCS [22]). Polypropylene is also used in warm-weather gear such as some Under Armour clothing, which can easily transport sweat away from the skin. Although polypropylene clothes are not easily flammable, they can melt, which may result in severe burns if the service member is involved in an explosion or fire of any kind.[23] Polypropylene undergarments are known for retaining body odors which are then difficult to remove. The current generation of polyester does not have this disadvantage.[24] Thanks to its specific weight, polypropylene yarn is the lightest fibre of all synthetic and natural fibers. Producers gain economic and ecological advantages when producing fabrics and clothes out of polypropylene yarn. Final users gain more comfort because the garments are lighter. This enables them to give better performance during their activities and gives them the freedom of movement. For example, If they hike, they have less weight to carry. Polypropylene yarn has very good insulation properties. Its water absorption is almost nil. Fabric made of polypropylene yarn transports humidity to the outside or to another absorbent layer from where it gradually evaporates. The material has recently been introduced into the fashion industry through the work of designers such as Anoush Waddington, who have developed specialized techniques to create jewelry and wearable items from polypropylene.

Medical[edit] Its most common medical use is in the synthetic, nonabsorbable suture Prolene, manufactured by Ethicon Inc. Polypropylene has been used in hernia and pelvic organ prolapse repair operations to protect the body from new hernias in the same location. A small patch of the material is placed over the spot of the hernia, below the skin, and is painless and rarely, if ever, rejected by the body. However, a polypropylene mesh will erode over the uncertain period from days to years. Therefore, the FDA has issued several warnings on the use of polypropylene mesh medical kits for certain applications in pelvic organ prolapse, specifically when introduced in close proximity to the vaginal wall due to a continued increase in number of mesh erosions reported by

patients over the past few years.[25] Most recently, on 3 January 2012, the FDA ordered 35 manufacturers of these mesh products to study the side effects of these devices.

EPP toy aircraft[edit] Since 2001, expanded polypropylene (EPP) foams have been gaining in popularity and in application as a structural material in hobbyist radio control model aircraft. Unlike expanded polystyrene foam (EPS) which is friable and breaks easily on impact, EPP foam is able to absorb kinetic impacts very well without breaking, retains its original shape, and exhibits memory form characteristics which allow it to return to its original shape in a short amount of time.[26] In consequence, a radio-control model whose wings and fuselage are constructed from EPP foam is extremely resilient, and able to absorb impacts that would result in complete destruction of models made from lighter traditional materials, such as balsa or even EPS foams. EPP models, when covered with inexpensive fibreglass impregnated self-adhesive tapes, often exhibit much increased mechanical strength, in conjunction with a lightness and surface finish that rival those of models of the aforementioned types. EPP is also chemically highly inert, permitting the use of a wide variety of different adhesives. EPP can be heat molded, and surfaces can be easily finished with the use of cutting tools and abrasive papers. The principal areas of model making in which EPP has found great acceptance are the fields of:



Wind-driven slope soarers



Indoor electric powered profile electric models



Hand launched gliders for small children

In the field of slope soaring, EPP has found greatest favour and use, as it permits the construction of radiocontrolled model gliders of great strength and maneuverability. In consequence, the disciplines of slope combat (the active process of friendly competitors attempting to knock each other's planes out of the air by direct contact) and slope pylon racing have become commonplace, in direct consequence of the strength characteristics of the material EPP.

Recycling[edit] Polypropylene is recyclable and has the number "5" as its resin identification code:

.[27]

Repairing[edit] Many objects are made with polypropylene precisely because it is resilient and resistant to most solvents and glues. Also, there are very few glues available specifically for gluing PP. However, solid PP objects not subject to undue flexing can be satisfactorily joined with a two part epoxy glue or using hot-glue guns. Preparation is important and it is often helpful to roughen the surface with a file, emery paper or other abrasive material to provide better anchorage for the glue. Also it is recommended to clean with mineral spirits or similar alcohol

prior to gluing to remove any oils or other contamination. Some experimentation may be required. There are also some industrial glues available for PP, but these can be difficult to find, especially in a retail store. [citation needed]

PP can be melted using a speed welding technique. With speed welding, the plastic welder, similar to a soldering iron in appearance and wattage, is fitted with a feed tube for the plastic weld rod. The speed tip heats the rod and the substrate, while at the same time it presses the molten weld rod into position. A bead of softened plastic is laid into the joint, and the parts and weld rod fuse. With polypropylene, the melted welding rod must be "mixed" with the semi-melted base material being fabricated or repaired. A speed tip "gun" is essentially a soldering iron with a broad, flat tip that can be used to melt the weld joint and filler material to create a bond.

Health concerns[edit] In 2008, researchers in Canada asserted that quaternary ammonium biocides and oleamide were leaking out of certain polypropylene labware, affecting experimental results.[28] As polypropylene is used in a wide number of food containers such as those for yogurt, Health Canada media spokesman Paul Duchesne, said the department will be reviewing the findings to determine whether steps are needed to protect consumers. [29] The Environmental Working Group classifies PP as of low to moderate hazard.[30] PP is dope-dyed, no water is used of its dyeing in comparison for example with cotton.[31]

Polyvinyl chloride From Wikipedia, the free encyclopedia (Redirected from Polyvinyl Chloride)

"PVC" redirects here. For other uses, see PVC (disambiguation).

Polyvinyl chloride

IUPAC name[hide] poly(1-chloroethylene)[1]

Other names[hide] Polychloroethylene

Identifiers Abbreviations

PVC

CAS number

9002-86-2

KEGG

C19508

MeSH

Polyvinyl+Chloride

ChEBI

CHEBI:53243 Properties (C2H3Cl)n[2]

Molecular formula

Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox references

Mechanical properties

Elongation at break

Notch test

Glass temperature

20–40%

2–5 kJ/m2

82 °C[3]

Melting point

100–260 °C[3]

Effective heat of combustion

17.95 MJ/kg

Specific heat (c)

0.9 kJ/(kg·K)

Water absorption (ASTM)

0.04–0.4

Dielectric Breakdown Voltage

40 MV/m

PVC is used extensively in sewage pipe due to its low cost, chemical resistance and ease of jointing

Poly(vinyl chloride), commonly abbreviated PVC, is the third-most widely produced plastic, after polyethylene and polypropylene.[4] PVC is used inconstruction because it is more effective than traditional materials such as copper, iron or wood in pipe and profile applications. It can be made softer and more flexible by the addition of plasticizers, the most widely used being phthalates. In this form, it is also used in clothing and upholstery, electrical cable insulation, inflatable products and many applications in which it replaces rubber.[5] Pure poly(vinyl chloride) is a white, brittle solid. It is insoluble in alcohol, but slightly soluble in tetrahydrofuran. Contents [hide]



1 Discovery and production

o 

1.1 Microstructure

2 Additives to finished polymer

o

2.1 Phthalate plasticizers

 o



2.1.1 High and low molecular weight phthalates

2.2 Heat stabilizers



2.2.1 Rigid PVC Applications



2.2.2 Flexible PVC Applications

3 Physical properties



o

3.1 Mechanical properties

o

3.2 Thermal properties

o

3.3 Electrical properties

4 Applications

o

4.1 Pipes

o

4.2 Electric cables

o

4.3 Unplasticized poly(vinyl chloride) (uPVC) for construction

o

4.4 Signs

o

4.5 Clothing and furniture

o

4.6 Healthcare



4.6.1 Plasticisers

o

4.7 Flooring

o

4.8 Other applications



5 Chlorinated PVC



6 Health and safety

o

6.1 Degradation

o

6.2 Plasticizers



6.2.1 EU decisions on phthalates

o

6.3 Vinyl chloride monomer

o

6.4 Dioxins

o

6.5 End-of-life



6.5.1 Industry initiatives



6.5.2 Restrictions



7 Sustainability



8 See also



9 References

o 

9.1 Bibliography

10 External links

Discovery and production[edit] PVC was accidentally discovered at least twice in the 19th century, first in 1835 by French chemist Henri Victor Regnault and then in 1872 by German chemist Eugen Baumann. On both occasions the polymer appeared as a white solid inside flasks of vinyl chloride that had been left exposed to sunlight. In the early 20th century the Russian chemist Ivan Ostromislensky and Fritz Klatte of the German chemical company Griesheim-Elektron

both attempted to use PVC in commercial products, but difficulties in processing the rigid, sometimes brittle polymer blocked their efforts. Waldo Semon and the B.F. Goodrich Company developed a method in 1926 to plasticize PVC by blending it with various additives. The result was a more flexible and more easily processed material that soon achieved widespread commercial use. Polyvinyl chloride is produced by polymerization of the monomer vinyl chloride (VCM), as shown.[6]

About 80% of production involves suspension polymerization. Emulsion polymerization accounts for about 12% and bulk polymerization accounts for 8%. Suspension polymerizations affords particles with average diameters of 100 – 180 μm, whereas emulsion polymerization gives much smaller particles of average size around 0.2 μm. VCM and water are introduced into the reactor and a polymerization initiator, along with other additives. The reaction vessel is pressure tight to contain the VCM. The contents of the reaction vessel are continually mixed to maintain the suspension and ensure a uniform particle size of the PVC resin. The reaction is exothermic, and thus requires cooling. As the volume is reduced during the reaction (PVC is denser than VCM), water is continually added to the mixture to maintain the suspension.[4] The polymerization of VCM is started by compounds called initiators that are mixed into the droplets. These compounds break down to start the radical chain reaction. Typical initiators include dioctanoyl peroxide and dicetyl peroxydicarbonate, both of which have fragile O-O bonds. Some initiators start the reaction rapidly but decay quickly and other initiators have the opposite effect. A combination of two different initiators is often used to give a uniform rate of polymerization. After the polymer has grown by about 10x, the short polymer precipitates inside the droplet of VCM, and polymerization continues with the precipitated, solvent-swollen particles. The weight average molecular weights of commercial polymers range from 100,000 to 200,000 and the number average molecular weights range from 45,000 to 64,000. Once the reaction has run its course, the resulting PVC slurry is degassed and stripped to remove excess VCM, which is recycled. The polymer is then passed though a centrifuge to remove water. The slurry is further dried in a hot air bed, and the resulting powder sieved before storage or pelletization. Normally, the resulting PVC has a VCM content of less than 1 part per million. Other production processes, such as micro-suspension polymerization and emulsion polymerization, produce PVC with smaller particle sizes (10 μm vs. 120–150 μm for suspension PVC) with slightly different properties and with somewhat different sets of applications.

Microstructure[edit]

The polymers are linear and are strong. The monomers are mainly arranged head-to-tail, meaning that there are chlorides on alternating carbon centres. PVC has mainly an atactic stereochemistry, which means that the relative stereochemistry of the chloride centres are random. Some degree of syndiotacticity of the chain gives a few percent crystallinity that is influential on the properties of the material. About 57% of the mass of PVC is chlorine. The presence of chloride groups gives the polymer very different properties from the structurally related materialpolyethylene.[7]

Additives to finished polymer[edit] The product of the polymerization process is unmodified PVC. Before PVC can be made into finished products, it always requires conversion into a compound by the incorporation of additives such as heat stabilizers, UV stabilizers, lubricants, plasticizers, processing aids, impact modifiers, thermal modifiers, fillers, flame retardants, biocides, blowing agents and smoke suppressors, and, optionally pigments.[8] The choice of additives used for the PVC finished product is controlled by the cost performance requirements of the end use specification e.g. underground pipe, window frames, intravenous tubing and flooring all have very different ingredients to suit their performance requirements.

Phthalate plasticizers[edit] Most vinyl products contain plasticizers which dramatically improve their performance characteristic. The most common plasticizers are derivatives of phthalic acid. The materials are selected on their compatibility with the polymer, low volatility levels, and cost. These materials are usually oily colourless substances that mix well with the PVC particles. 90% of the plasticizer market, estimated to be millions of tons per year worldwide, is dedicated to PVC.[8]

Bis (2-ethylhexyl) phthalate is a common plasticizer for PVC.

High and low molecular weight phthalates[edit] Phthalates can be divided into two groups: high and low molecular weight, with high molecular weight phthalates now representing over 80 percent of European market for plasticisers. Low molecular weight phthalates include those with 3-6 carbon atoms in their chemical backbone; the most common types being Di(2-ethylhexyl) phthalate (DEHP), Di-butyl phthalate (DBP), Di- isobutyl phthalate (DIBP) and Butyl

benzyl phthalate (BBP). Because of possible health effects of low phthalates in the environment, including Di(2ethylhexyl) phthalate, there is movement to replace them with safer alternatives in Canada, the European Union, and the United States. They represent about 15% of the European market. High molecular weight phthalates include those with 7-13 Carbon atoms in their chemical backbone, which gives them increased permanency and durability. The most common types of high phthalates include di-isononyl phthalate (DINP) and di-isodecyl phthalate (DIDP). The European market has been shifting in the last decade from low to high phthalates, which today represent over 80% of all the phthalates currently being produced in Europe.

Heat stabilizers[edit] One of the most crucial additives are heat stabilizers. These agents minimize loss of HCl, a degradation process that starts above 70 °C. Once dehydrochlorination starts, it is autocatalytic. Many diverse agents have been used including, traditionally, derivatives of heavy metals (lead, cadmium). Increasingly, metallic soaps (metal "salts" of fatty acids) are favored, species such as calcium stearate.[4] Addition levels vary typically from 2% to 4%. The choice of the best heat stabilizer depends on its cost effectiveness in the end use application, performance specification requirements, processing technology and regulatory approvals.

Rigid PVC Applications[edit] In Europe there has been a commitment to eliminate the use of cadmium (previously used as a part component of heat stabilizers in window profiles) and phase out lead based heat stabilizers (as used in pipe and profile areas) by 2015. According to the final report of Vinyl 2010[9] cadmium was eliminated across Europe by 2007. The progressive substitution of lead-based stabilizers is also confirmed in the same document showing a reduction of 75% since 2000 and ongoing. This is confirmed by the corresponding growth in calcium-based stabilizers, used as an alternative to lead-based stabilizers, more and more, also outside Europe. Tin based stabilizers are mainly used in Europe for rigid, transparent applications due to the high temperature processing conditions used. The situation in North America is different where tin systems are used for almost all-rigid PVC applications. Tin stabilizers can be divided into two main groups, the first group containing those with tin-oxygen bonds and the second group with tin-sulphur bonds. According to the European Stabiliser producers[10] most organotin stabilisers have already been successfully REACH registered. More chemical and use information is also available on this site.

Flexible PVC Applications[edit] Flexible PVC coated wire and cable for electrical use has traditionally been stabilised with lead but these are being replaced, as in the rigid area, with calcium based systems. Liquid mixed metal stabilisers are used in several PVC flexible applications such as calendered films, extruded profiles, injection moulded soles and footwear, extruded hoses and plastisols where PVC paste is

spread on to a backing (flooring, wall covering, artificial leather). Liquid mixed metal stabiliser systems are primarily based on Barium, Zinc and Calcium carboxylates. In general liquid mixed metals like BaZn, CaZn require the addition of co-stabilisers, antioxidants and organo-phosphites to provide optimum performance. BaZn stabilisers have successfully replaced Cadmium-based stabilisers in Europe in many PVC semi-rigid and flexible applications according to the European producers.[11]

Physical properties[edit] PVC is a thermoplastic polymer. Its properties for PVC are usually categorized based on rigid and flexible PVCs.

Property

Rigid PVC

Flexible PVC

Density [g/cm3][12]

1.3–1.45

1.1–1.35

Thermal conductivity [W/(m·K)][13]

0.14–0.28

0.14–0.17

Yield strength [psi][12]

4500 - 8700 1450 - 3600

Young's modulus [psi]

490,000[14]

Flexural strength (yield) [psi]

10,500[14]

Compression strength [psi]

9500[14]

Coefficient of thermal expansion (linear) [mm/(mm °C)] 5×10−5[14]

Vicat B [°C][13]

65–100

Not recommended

Resistivity [Ω m][15][16]

1016

1012–1015

Surface resistivity [Ω][15][16]

1013–1014

1011–1012

Mechanical properties[edit]

PVC has high hardness and mechanical properties. The mechanical properties enhance with the molecular weight increasing, but decrease with the temperature increasing. The mechanical properties of rigid PVC (uPVC) is very good, the elastic modulus can reach to 1500-3,000 MPa. The soft PVC (Flexible PVC) elastic is 1.5-15 MPa. However, elongation at break is up to 200% -450%. PVC friction is ordinary, the static friction factor is 0.4-0.5, the dynamic friction factor is 0.23.[17]

Thermal properties[edit] The heat stability of PVC is very poor, when the temperature reaches 140 °C PVC starts to decompose. Its melting temperature is 160 °C. The linear expansion coefficient of the PVC is small and has flame retardancy, the oxidation index is up to 45 or more. Therefore, the addition of a heat stabilizer during the process is necessary in order to ensure the product's properties.

Electrical properties[edit] PVC is a polymer with good insulation properties but because of its higher polar nature the electrical insulating property is inferior to non polar polymers such as polyethylene and polypropylene. As the dielectric constant, dielectric loss tangent value and volume resistivity are high, the corona resistance is not very good, it is generally suitable for medium or low voltage and low frequency insulation materials.

Applications[edit] PVC's relatively low cost, biological and chemical resistance and workability have resulted in it being used for a wide variety of applications. It is used for sewerage pipes and other pipe applications where cost or vulnerability to corrosion limit the use of metal. With the addition of impact modifiers and stabilizers, it has become a popular material for window and door frames. By adding plasticizers, it can become flexible enough to be used in cabling applications as a wire insulator. It has been used in many other applications. PVC demand is likely to increase at an average annual rate of 3.9% over the next years.[18]

Pipes[edit] Roughly half of the world's polyvinyl chloride resin manufactured annually is used for producing pipes for municipal and industrial applications.[19] In the water distribution market it accounts for 66% of the market in the US, and in sanitary sewer pipe applications, it accounts for 75%.[20] Its light weight, low cost, and low maintenance make it attractive. However, it must be carefully installed and bedded to ensure longitudinal cracking and overbelling does not occur. Additionally, PVC pipes can be fused together using various solvent cements, or heat-fused (butt-fusion process, similar to joining HDPE pipe), creating permanent joints that are virtually impervious to leakage. In February, 2007 the California Building Standards Code was updated to approve the use of chlorinated polyvinyl chloride (CPVC) pipe for use in residential water supply piping systems. CPVC has been a nationally

accepted material in the US since 1982; California, however, has permitted only limited use since 2001. The Department of Housing and Community Development prepared and certified an environmental impact statement resulting in a recommendation that the Commission adopt and approve the use of CPVC. The Commission's vote was unanimous and CPVC has been placed in the 2007 California Plumbing Code. In the United States and Canada, PVC pipes account for the largest majority of pipe materials used in buried municipal applications for drinking water distribution and wastewater mains.[21] Buried PVC pipes in both water and sanitary sewer applications that are 4 inches (100 mm) in diameter and larger are typically joined by means of a gasket-sealed joint. The most common type of gasket utilized in North America is a metal reinforced elastomer, commonly referred to as a Rieber sealing system.[22]

Electric cables[edit] PVC is commonly used as the insulation on electrical cables; PVC used for this purpose needs to be plasticized. In a fire, PVC-coated wires can form hydrogen chloride fumes; the chlorine serves to scavenge free radicals and is the source of the material's fire retardance. While HCl fumes can also pose ahealth hazard in their own right, HCl dissolves in moisture and breaks down onto surfaces, particularly in areas where the air is cool enough to breathe, and is not available for inhalation.[23]Frequently in applications where smoke is a major hazard (notably in tunnels and communal areas) PVC-free cable insulation is preferred, such as low smoke zero halogen (LSZH) insulation. Any metal parts must not be mixed together during the raw material stage, as it may lead to EMI.

Unplasticized poly(vinyl chloride) (uPVC) for construction[edit]

"A modern Tudorbethan" house with uPVC gutters and downspouts, fascia, decorative imitation "half-timbering", windows, and doors

uPVC, also known as rigid PVC, is extensively used in the building industry as a low-maintenance material, particularly in Ireland, the United Kingdom, and in the United States. In the USA it is known as vinyl, or vinyl siding.[24] The material comes in a range of colors and finishes, including a photo-effect wood finish, and is used

as a substitute for painted wood, mostly for window frames and sills when installing double glazing in new buildings, or to replace older single-glazed windows. Other uses include fascia, and siding or weatherboarding. This material has almost entirely replaced the use ofcast iron for plumbing and drainage, being used for waste pipes, drainpipes, gutters and downspouts. uPVC does not contain phthalates, since those are only added to flexible PVC, nor does it contain BPA. uPVC is known as having strong resistance against chemicals, sunlight, and oxidation from water.[25]

Double glazed units

Signs[edit] Poly(vinyl chloride) is formed in flat sheets in a variety of thicknesses and colors. As flat sheets, PVC is often expanded to create voids in the interior of the material, providing additional thickness without additional weight and minimal extra cost (see Closed-cell PVC foamboard). Sheets are cut usingsaw and rotary cutting equipment. Plasticized PVC is also used to produce thin, colored, or clear, adhesive-backed films referred to simply as vinyl. These films are typically cut on a computer-controlled plotter or printed in a wide-format printer. These sheets and films are used to produce a wide variety of commercial signage products and markings on vehicles, e.g. car body stripes.

Clothing and furniture[edit]

Black PVC pants

PVC has become widely used in clothing, to either create a leather-like material or at times simply for the effect of PVC. PVC clothing is common inGoth, Punk, clothing fetish and alternative fashions. PVC is cheaper than rubber, leather, and latex which it is therefore used to simulate. PVC fabric has a sheen to it and is waterproof so is used in coats, skiing equipment, shoes, jackets, aprons, and bags.

Healthcare[edit] The two main application areas for single use medically approved PVC compounds are flexible containers and tubing: containers used for blood and blood components for urine or for ostomy products and tubing used for blood taking and blood giving sets, catheters, heart-lung bypass sets, haemodialysis set etc. In Europe the consumption of PVC for medical devices is approximately 85.000 tons every year. Almost one third of plastic based medical devices are made from PVC.[26] The reasons for using flexible PVC in these applications for over 50 years are numerous and based on cost effectiveness linked to transparency, light weight, softness, tear strength, kink resistance, suitability for sterilization and biocompatibility.

Plasticisers[edit] DEHP (Di-2ethylhexylphthalate) has been medically approved for many years for use in such medical devices; the PVC-DEHP combination proving to be very suitable for making blood bags because DEHP stabilises red blood cells so minimising haemolysis (red blood cell rupture) However DEHP is coming under increasing pressure in Europe. The assessment of potential risks related to phthalates and in particular the use of DEHP in PVC medical devices has been subject to scientific and policy review by the European Union authorities. As

of 21 March 2010, a specific labelling requirement has subsequently been introduced across the EU for all devices containing phthalates that are classified as CMR (carcinogenic, mutagenic or toxic to reproduction).[27] The label aims to enable healthcare professionals to use this equipment safely and, where needed, take appropriate precautionary measures for patients at risk of over-exposure. DEHP alternatives, which are gradually replacing it, are Adipates, Butyryltrihexylcitrate (BTHC), Cyclohexane-1,2-dicarboxylic acid, diisononylester (DINCH), Di(2-ethylhexyl)terephthalate, polymerics and trimellitic acid, 2-ethylhexylester (TOTM).

Flooring[edit] Flexible PVC flooring is inexpensive and used in a variety of buildings covering the home, hospitals, offices, schools, etc. Complex and 3D designs are possible due to the prints that can be created which are then protected by a clear wear layer. A middle vinyl foam layer also gives a comfortable and safe feel. The smooth, tough surface of the upper wear layer prevents the build up of dirt which prevents microbes from breeding in areas that need to be kept sterile, such as hospitals and clinics. See also: Vinyl composition tile

Other applications[edit] PVC has been used for a host of consumer products of relatively smaller volume compared to the industrial and commercial applications described above. Another of its earliest mass-market consumer applications was to make vinyl records. More recent examples include wallcovering, greenhouses, home playgrounds, foam and other toys, custom truck toppers (tarpaulins), ceiling tiles and other kinds of interior cladding.

Chlorinated PVC[edit] PVC can be usefully modified by chlorination, which increases its chlorine content to 67%. The new material has a higher heat resistance so is primarily used for hot water pipe and fittings, but it is more expensive and it is found only in niche applications, such as certain water heaters and certain specialized clothing. An extensive market for chlorinated PVC is in pipe for use in office building, apartment and condominium fire protection. CPVC, as it is called, is produced by chlorination of aqueous solution of suspension PVC particles followed by exposure to UV light which initiates the free-radical chlorination.[4]

Health and safety[edit] Degradation[edit] Degradation is a chemical change that drastically reduces the average molecular weight of the polymer. Since the mechanical integrity of plastics invariably depends on their high average molecular-weight, any significant extent of degradation inevitably weakens the material. Weathering degradation of plastics results in their surface embrittlement and microcracking, yielding microparticles that continue on in the environment, known

as microplastics. Microplastics concentrate Persistent Organic Pollutants (POPs). The relevant distribution coefficients for common POPs are several orders of magnitude in favor of the plastic medium. Consequently, the microparticles laden with high levels of POPs can be ingested by organisms in the biosphere. Given the increased levels of plastic pollution of the environment, this is an important concept in understanding the food web.[28]

Plasticizers[edit] Phthalates, which are incorporated into plastics as plasticizers comprise ∼70% of the U.S. plasticizer market; phthalates are by design not covalently bound to the polymer matrix, which makes them highly susceptible to leaching. Phthalates are contained in plastics at high percentages. For example, they can contribute up to 40% by weight to intravenous medical bags and up to 80% by weight in medical tubing.[29] Vinyl products are pervasive—including toys,[30] car interiors, shower curtains, and flooring—and initially release chemical gases into the air. Some studies indicate that this outgassing of additives may contribute to health complications, and have resulted in a call for banning the use of DEHP on shower curtains, among other uses. [31] The Japanese car companies Toyota, Nissan, and Honda have eliminated PVC in their car interiors starting in 2007. In 2004 a joint Swedish-Danish research team found a statistical association between allergies in children and indoor air levels of DEHP and BBzP (butyl benzyl phthalate), which is used in vinyl flooring.[32] In December 2006, the European Chemicals Bureau of the European Commission released a final draft risk assessment of BBzP which found "no concern" for consumer exposure including exposure to children.[33]

EU decisions on phthalates[edit] Risk assessments have led to the classification of low molecular weight and labeling as Category 1B Reproductive agents. Three of these phthalates, DBP, BBP and DEHP were included on annex XIV of the REACH regulation in February 2011 and will be phased out by the EU by February 2015 unless an application for authorisation is made before July 2013 and an authorisation granted. DIBP is still on the REACH Candidate List for Authorisation. Environmental Science & Technology, a peer reviewed journal published by the American Chemical Society states DEHP poses a serious risk to human health. [34] In 2008 the European Union's Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR) reviewed the safety of DEHP in medical devices. The SCENIHR report states that certain medical procedures used in high risk patients result in a significant exposure to DEHP and concludes there is still a reason for having some concerns about the exposure of prematurely born male babies to medical devices containing DEHP.[35] The Committee said there are some alternative plasticizers available for which there is sufficient toxicological data to indicate a lower hazard compared to DEHP but added that the functionality of these plasticizers should be assessed before they can be used as an alternative for DEHP in PVC medical devices. Risk assessment results have shown positive results regarding the safe use of High Molecular Weight Phthalates. They have all been registered for REACH and do not require any classification for health and

environmental effects, nor are they on the Candidate List for Authorisation. High phthalates are not CMR (carcinogenic, mutagenic or toxic for reproduction), neither are they considered endocrine disruptors. In the EU Risk Assessment the European Commission has confirmed that Di-isononyl phthalate (DINP) and Diisodecyl phthalate (DIDP) pose no risk to either human health or the environment from any current use. The European Commission's findings (published in the EU Official Journal on April 13, 2006)[36] confirm the outcome of a risk assessment involving more than 10 years of extensive scientific evaluation by EU regulators. Following the recent adoption of EU legislation with the regard to the marketing and use of DINP in toys and childcare articles, the risk assessment conclusions clearly state that there is no need for any further measures to regulate the use of DINP. In Europe and in some other parts of the world, the use of DINP in toys and childcare items has been restricted as a precautionary measure. In Europe, for example, DINP can no longer be used in toys and childcare items that can be put in the mouth even though the EU scientific risk assessment concluded that its use in toys does not pose a risk to human health or the environment. The rigorous EU risk assessments, which include a high degree of conservatism and built-in safety factors, have been carried out under the strict supervision of the European Commission and provide a clear scientific evaluation on which to judge whether or not a particular substance can be safely used. The FDA Paper titled "Safety Assessment of Di(2-ethylhexyl)phthalate (DEHP)Released from PVC Medical Devices" states that [3.2.1.3] Critically ill or injured patients may be at increased risk of developing adverse health effects from DEHP, not only by virtue of increased exposure relative to the general population, but also because of the physiological and pharmacodynamic changes that occur in these patients compared to healthy individuals.[37]

Vinyl chloride monomer[edit] Main article: vinyl chloride In the early 1970s, the carcinogenicity of vinyl chloride (usually called vinyl chloride mononomer or VCM) was linked to cancers in workers in the polyvinyl chloride industry. Specifically workers in polymerization section of a B.F. Goodrich plant near Louisville, Kentucky (US) were diagnosed with liver angiosarcoma also known as hemangiosarcoma, a rare disease.[38] Since that time, studies of PVC workers in Australia, Italy, Germany, and the UK have all associated certain types of occupational cancers with exposure to vinyl chloride, and it has become accepted that VCM is a carcinogen.[4] Technology for removal of VCM from products have become stringent commensurate with the associated regulations.

Dioxins[edit] Main article: Polychlorinated dibenzodioxins PVC produces HCl upon combustion almost quantitatively related to its chlorine content. Extensive studies in Europe indicate that the chlorine found in emitted dioxins is not derived from HCl in the flue gases. Instead,

most dioxins arise in the condensed solid phase by the reaction of inorganic chlorides with graphitic structures in char-containing ash particles. Copper acts as a catalyst for these reactions.[39] Studies of household waste burning indicate consistent increases in dioxin generation with increasing PVC concentrations.[40] According to the EPA dioxin inventory, landfill fires are likely to represent an even larger source of dioxin to the environment. A survey of international studies consistently identifies high dioxin concentrations in areas affected by open waste burning and a study that looked at the homologue pattern found the sample with the highest dioxin concentration was "typical for the pyrolysis of PVC". Other EU studies indicate that PVC likely "accounts for the overwhelming majority of chlorine that is available for dioxin formation during landfill fires."[40] The next largest sources of dioxin in the EPA inventory are medical and municipal waste incinerators.[41] Various studies have been conducted that reach contradictory results. For instance a study of commercial-scale incinerators showed no relationship between the PVC content of the waste and dioxin emissions.[42][43] Other studies have shown a clear correlation between dioxin formation and chloride content and indicate that PVC is a significant contributor to the formation of both dioxin and PCB in incinerators.[44][45][46] In February 2007, the Technical and Scientific Advisory Committee of the US Green Building Council (USGBC) released its report on a PVC avoidance related materials credit for the LEED Green Building Rating system. The report concludes that "no single material shows up as the best across all the human health and environmental impact categories, nor as the worst" but that the "risk of dioxin emissions puts PVC consistently among the worst materials for human health impacts."[47] In Europe the overwhelming importance of combustion conditions on dioxin formation has been established by numerous researchers. The single most important factor in forming dioxin-like compounds is the temperature of the combustion gases. Oxygen concentration also plays a major role on dioxin formation, but not the chlorine content.[48] The design of modern incinerators minimises PCDD/F formation by optimising the stability of the thermal process. To comply with the EU emission limit of 0.1 ng I-TEQ/m3 modern incinerators operate in conditions minimising dioxin formation and are equipped with pollution control devices which catch the low amounts produced. Recent information is showing for example that dioxin levels in populations near incinerators in Lisbon and Madeira have not risen since the plants began operating in 1999 and 2002 respectively. Several studies have also shown that removing PVC from waste would not significantly reduce the quantity of dioxins emitted. The European Union Commission published in July 2000 a Green Paper on the Environmental Issues of PVC. "[49] The Commission states (page 27) that it has been suggested that the reduction of the chlorine content in the waste can contribute to the reduction of dioxin formation, even though the actual mechanism is not fully understood. The influence on the reduction is also expected to be a second or third order relationship. It is most likely that the main incineration parameters, such as the temperature and the

oxygen concentration, have a major influence on the dioxin formation". The Green Paper states further that at the current levels of chlorine in municipal waste, there does not seem to be a direct quantitative relationship between chlorine content and dioxin formation. A study commissioned by the European Commission on "Life Cycle Assessment of PVC and of principal competing materials" states that "Recent studies show that the presence of PVC has no significant effect on the amount of dioxins released through incineration of plastic waste."[50]

End-of-life[edit] The European waste hierarchy refers to the 5 steps included in the article 4 of the Waste Framework Directive:[51] 1. Prevention - preventing and reducing waste generation. 2. Reuse and preparation for reuse - giving the products a second life before they become waste. 3. Recycle - any recovery operation by which waste materials are reprocessed into products, materials or substances whether for the original or other purposes. It includes composting and it does not include incineration. 4. Recovery - some waste incineration based on a political non-scientific formula[citation needed] that upgrades the less inefficient incinerators. 5. Disposal - processes to dispose of waste be it landfilling, incineration, pyrolysis, gasification and other finalist solutions. Landfill is restricted in some EU-countries through Landfill Directives and there is a debate about Incineration E.g. original plastic which contains a lot of energy is just recovered in energy and not recycled. According to the Waste Framework Directive the European Waste Hierarchy is legally binding except in cases that may require specific waste streams to depart from the hierarchy. This should be justified on the basis of life-cycle thinking. The European Commission has set new rules to promote the recovery of PVC waste for use in a number of construction products. It says: "The use of recovered PVC should be encouraged in the manufacture of certain construction products because it allows the reuse of old PVC [..] This avoids PVC being discarded in landfills or incinerated causing release of carbon dioxide and cadmium in the environment".[52]

Industry initiatives[edit] In Europe, developments in PVC waste management have been monitored by Vinyl 2010,[53] established in 2000. Vinyl 2010's objective was to recycle 200,000 tonnes of post-consumer PVC waste per year in Europe by the end of 2010, excluding waste streams already subject to other or more specific legislation (such as the European Directives on End-of-Life Vehicles, Packaging and Waste Electric and Electronic Equipment).

Since June 2011, it is followed by Vinylplus, a new set of targets for sustainable development.[54] Its main target is to recycle 800,000 tonnes/year of PVC by 2020 including 100,000 tonnes ofdifficult to recycle waste. One technology for collection and recycling of PVC waste is Recovinyl[55] which reported the recycled tonnage as follows: pipe 25 kT, profile 107 kT, rigid film 6 kT, flexible cables 79 kt and mixed flexible 38 kT. One approach to address the problem of waste PVC is through the process called Vinyloop. It is a mechanical recycling process using a solvent to separate PVC from other materials. This solvent turns in a closed loop process in which the solvent is recycled. Recycled PVC is used in place of virgin PVC in various applications: coatings for swimming pools, shoe soles, hoses, diaphragms tunnel, coated fabrics, PVC sheets.[56] This recycled PVC's primary energy demand is 46 percent lower than conventional produced PVC. So the use of recycled material leads to a significant better ecological footprint. The global warming potential is 39 percent lower.[57]

Restrictions[edit] In November, 2005 one of the largest hospital networks in the U.S., Catholic Healthcare West, signed a contract with B. Braun Melsungen for vinyl-free intravenous bags and tubing.[58] In January, 2012 a major U.S. West Coast healthcare provider, Kaiser Permanente, announced that it will no longer buy intravenous (IV) medical equipment made with polyvinyl chloride (PVC) and DEHP (di-2-ethyl hexyl phthalate) type plasticizers.[59]

Sustainability[edit] The Olympic Delivery Authority (ODA) has chosen PVC as material for different temporary venues of the London Olympics 2012. The ODA want to ensure to meet the highest environmental and social standards for the PVC materials. E.g. temporary parts like Roofing covers of the Olympic Stadium, the Water Polo Arena and the Royal Artillery Barracks will be deconstructed and a part will be recycled in the Vinyloop process.[60] As we have done in the past with materials such as timber and concrete, we want to use the opportunity of hosting the London 2012 Games to work with industry to set new standards. In this case this may help move the industry towards more sustainable manufacture, use and disposal of PVC fabrics. Dan Epstein Head of Sustainable Development at Olympic Delivery Authority (ODA)[61] The ODA after initially rejecting PVC as material has reviewed its decision and develop a policy for the use of PVC.[62] The PVC policy has focused attention on the use of PVC across the project and highlighted that the functional properties of PVC make it the most appropriate material in certain circumstances. Environmental and social impacts across the whole life cycle played an important role, with e.g. the rate for recycling or re-use and the percentage of recycled content.[63]

Nylon From Wikipedia, the free encyclopedia

For other uses, see Nylon (disambiguation).

Nylon

6,6 Density Electrical conductivity (ζ) Thermal conductivity Melting point

1.15 g/cm3 10−12 S/m 0.25 W/(m·K) 463–624 K 190–350 °C 374–663 °F

Nylon is a generic designation for a family of synthetic polymers known generically as aliphatic polyamides, first produced on February 28, 1935, by Wallace Carothers at DuPont's research facility at the DuPont Experimental Station. Nylon is one of the most commonly used polymers.[1] Key representatives are nylon6,6, nylon-6, nylon-6,9, nylon-6,12, nylon-11, nylon-12 and nylon-4,6.[1] Contents [hide]



1 Overview



2 Chemistry



o

2.1 Concepts of nylon production

o

2.2 Characteristics

3 Bulk properties



4 Historical uses

o

4.1 Instrument strings



5 Use in composites



6 Hydrolysis and degradation



7 Incineration and recycling



8 Etymology



9 See also



10 References



11 Further reading



12 External links

Overview[edit]

Wallace Carothers

Nylon is a thermoplastic,[2] silky material, first used commercially in a nylon-bristled toothbrush (1938), followed more famously by women's stockings ("nylons"; 1940) after being introduced as a fabric at the 1939 New York World's Fair. Nylon is made of repeating unitslinked by amide bonds and is frequently referred to as polyamide (PA). Nylon was the first commercially successful synthetic thermoplastic polymer. There are two common ways of making nylon for fiber applications. In one approach, molecules with an acid (-COOH) group on each end are reacted with molecules containing amine (-NH2) groups on each end. The resulting nylon is named on the basis of the number of carbon atoms separating the two acid groups and the two amines. These are formed into monomers of intermediate molecular weight, which are then reacted to form long polymer chains. Nylon was intended to be a synthetic replacement for silk and substituted for it in many different products after silk became scarce during World War II. It replaced silk in military applications such as parachutes and flak vests, and was used in many types of vehicle tires.

Nylon fibers are used in many applications, including clothes fabrics, bridal veils, package paper, carpets, musical strings, pipes, and rope etc. Nylon is used for mechanical parts such as machine screws, gears and other low- to medium-stress components previously cast in metal. Engineering-grade nylon is processed by extrusion, casting, and injection molding. Solid nylon is used in hair combs. Type 6,6 Nylon 101 is the most common commercial grade of nylon, and Nylon 6 is the most common commercial grade of molded nylon. For use in tools such as the spudger, a nylon is available in glass-filled variants which increase structural and impact strength and rigidity, and molybdenum sulfide-filled variants which increase lubricity.

Chemistry[edit] Nylons are condensation copolymers formed by reacting equal parts of a diamine and a dicarboxylic acid, so that amides are formed at both ends of each monomer in a process analogous topolypeptide biopolymers. Chemical elements included are carbon, hydrogen, nitrogen, and oxygen. The numerical suffix specifies the numbers of carbons donated by the monomers; the diamine first and the diacid second. The most common variant is nylon 6-6 which refers to the fact that the diamine (hexamethylene diamine, IUPAC name: hexane-1,6-diamine) and the diacid (adipic acid,IUPAC name: hexanedioic acid) each donate 6 carbons to the polymer chain. As with other regular copolymers like polyesters and polyurethanes, the "repeating unit" consists of one of each monomer, so that they alternate in the chain. Since each monomer in this copolymer has the same reactive group on both ends, the direction of the amide bond reverses between each monomer, unlike natural polyamide proteins which have overall directionality: C terminal → N terminal. In the laboratory, nylon 6-6 can also be made using adipoyl chloride instead of adipic. It is difficult to get the proportions exactly correct, and deviations can lead to chain termination at molecular weights less than a desirable 10,000 daltons (u). To overcome this problem, acrystalline, solid "nylon salt" can be formed at room temperature, using an exact 1:1 ratio of the acid and the base to neutralize each other. Heated to 285 °C (545 °F), the salt reacts to form nylon polymer. Above 20,000 daltons, it is impossible to spin the chains into yarn, so to combat this, some acetic acid is added to react with a free amine end group during polymer elongation to limit the molecular weight. In practice, and especially for 6,6, the monomers are often combined in a water solution. The water used to make the solution is evaporated under controlled conditions, and the increasing concentration of "salt" is polymerized to the final molecular weight. DuPont patented[3] nylon 6,6, so in order to compete, other companies (particularly the German BASF) developed the homopolymer nylon 6, or polycaprolactam — not a condensation polymer, but formed by a ringopening polymerization (alternatively made by polymerizing aminocaproic acid). The peptide bond within the caprolactam is broken with the exposed active groups on each side being incorporated into two new bonds as the monomer becomes part of the polymer backbone. In this case, all amide bonds lie in the same direction,

but the properties of nylon 6 are sometimes indistinguishable from those of nylon 6,6 — except for melt temperature and some fiber properties in products like carpets and textiles. There is also nylon 9. The 428 °F (220 °C) melting point of nylon 6 is lower than the 509 °F (265 °C) melting point of nylon 6,6. [4] Nylon 5,10, made from pentamethylene diamine and sebacic acid, was studied by Carothers even before nylon 6,6 and has superior properties, but is more expensive to make. In keeping with this naming convention, "nylon 6,12" (N-6,12) or "PA-6,12" is a copolymer of a 6C diamine and a 12C diacid. Similarly for N-5,10 N6,11; N-10,12, etc. Other nylons include copolymerized dicarboxylic acid/diamine products that are not based upon the monomers listed above. For example, some aromatic nylons are polymerized with the addition of diacids like terephthalic acid (→ Kevlar,Twaron) or isophthalic acid (→ Nomex), more commonly associated with polyesters. There are copolymers of N-6,6/N6; copolymers of N-6,6/N-6/N-12; and others. Because of the way polyamides are formed, nylon would seem to be limited to unbranched, straight chains. But "star" branched nylon can be produced by the condensation of dicarboxylic acids with polyamineshaving three or more amino groups. The general reaction is:

Two molecules of water are given off and the nylon is formed. Its properties are determined by the R and R' groups in the monomers. In nylon 6,6, R = 4C and R' = 6C alkanes, but one also has to include the two carboxyl carbons in the diacid to get the number it donates to the chain. In Kevlar, both R and R' are benzene rings.

Concepts of nylon production[edit] The first approach: combining molecules with an acid (COOH) group on each end are reacted with two chemicals that contain amine (NH2) groups on each end. This process creates nylon 6,6, made of hexamethylene diamine with six carbon atoms and adipic acid. The second approach: a compound has an acid at one end and an amine at the other and is polymerized to form a chain with repeating units of (-NH-[CH2]n-CO-)x. In other words, nylon 6 is made from a single six-carbon substance called caprolactam. In this equation, if n = 5, then nylon 6 is the assigned name (may also be referred to as polymer). The characteristic features of nylon 6,6 include:



Pleats and creases can be heat-set at higher temperatures



More compact molecular structure



Better weathering properties; better sunlight resistance



Softer "Hand"



Higher melting point (256 °C/492.8 °F)



Superior colorfastness



Excellent abrasion resistance

On the other hand, nylon 6 is easy to dye, more readily fades; it has a higher impact resistance, a more rapid moisture absorption, greater elasticity and elastic recovery.

Characteristics[edit] 

Variation of luster: nylon has the ability to be very lustrous, semilustrous or dull.



Durability: its high tenacity fibers are used for seatbelts, tire cords, ballistic cloth and other uses.



High elongation



Excellent abrasion resistance



Highly resilient (nylon fabrics are heat-set)



Paved the way for easy-care garments



High resistance to insects, fungi, animals, as well as molds, mildew, rot and many chemicals



Used in carpets and nylon stockings



Melts instead of burning



Used in many military applications



Good specific strength



Transparent to infrared light (−12dB)[5]

Bulk properties[edit] Above their melting temperatures, Tm, thermoplastics like nylon are amorphous solids or viscous fluids in which the chains approximate random coils. Below Tm, amorphous regions alternate with regions which are lamellar crystals.[6] The amorphous regions contribute elasticity and the crystalline regions contribute strength and rigidity. The planar amide (-CO-NH-) groups are very polar, so nylon forms multiple hydrogen bonds among adjacent strands. Because the nylon backbone is so regular and symmetrical, especially if all the amide bonds are in the trans configuration, nylons often have high crystallinity and make excellent fibers. The amount of crystallinity depends on the details of formation, as well as on the kind of nylon. Apparently it can never be quenched from amelt as a completely amorphous solid.

Hydrogen bonding in Nylon 6,6 (in mauve).

Nylon 6,6 can have multiple parallel strands aligned with their neighboring peptide bonds at coordinated separations of exactly 6 and 4 carbons for considerable lengths, so the carbonyl oxygens and amide hydrogens can line up to form interchain hydrogen bondsrepeatedly, without interruption (see the figure opposite). Nylon 5,10 can have coordinated runs of 5 and 8 carbons. Thus parallel (but not antiparallel) strands can participate in extended, unbroken, multi-chain β-pleated sheets, a strong and tough supermolecular structure similar to that found in natural silk fibroin and the β-keratins in feathers. (Proteins have only an amino acid α-carbon separating sequential -CO-NH- groups.) Nylon 6 will form uninterrupted H-bonded sheets with mixed directionalities, but the β-sheet wrinkling is somewhat different. The three-dimensional disposition of each alkane hydrocarbon chain depends on rotations about the 109.47° tetrahedral bonds of singly bonded carbon atoms. When extruded into fibers through pores in an industrial spinneret, the individual polymer chains tend to align because of viscous flow. If subjected to cold drawing afterwards, the fibers align further, increasing their crystallinity, and the material acquires additional tensile strength.[7] In practice, nylon fibers are most often drawn using heated rolls at high speeds. Block nylon tends to be less crystalline, except near the surfaces due to shearing stresses during formation. Nylon is clear andcolorless, or milky, but is easily dyed. Multistranded nylon cord and rope is slippery and tends to unravel. The ends can be melted and fused with a heat source such as a flame or electrode to prevent this. When dry, polyamide is a good electrical insulator. However, polyamide is hygroscopic. The absorption of water will change some of the material's properties such as its electrical resistance. Nylon is less absorbent than wool or cotton.

Historical uses[edit]

The worn out nylon stockings will be reprocessed and made into parachutes for army fliers c. 1942

Blue Nylon fabric ball gown by Emma Domb, Chemical Heritage Foundation

Bill Pittendreigh, DuPont, and other individuals and corporations worked diligently during the first few months of World War II to find a way to replace Asian silkand hemp with nylon in parachutes. It was also used to make tires, tents, ropes, ponchos, and other military supplies. It was even used in the production of a highgrade paper for U.S. currency. At the outset of the war, cotton accounted for more than 80% of all fibers used and manufactured, and wool fibers accounted for nearly all of the rest. By August 1945, manufactured fibers had taken a market share of 25%, at the expense of cotton. After the war, because of shortages of both silk and nylon, nylon parachute material was sometimes repurposed to make dresses.[8] Some of the terpolymers based upon nylon are used every day in packaging. Nylon has been used for meat wrappings and sausage sheaths. Nylon was used to make the stock of the Remington Nylon 66 shotgun. The frame of the modern Glock pistol is made of a nylon composite.

Instrument strings[edit] In the mid-1940s, classical guitarist Andrés Segovia mentioned the shortage of good guitar strings in the United States, particularly his favorite Pirastro catgut strings, to a number of foreign diplomats at a party, including General Lindeman of the British Embassy. A month later, the General presented Segovia with some nylon strings which he had obtained via some members of the DuPont family. Segovia found that although the strings produced a clear sound, they had a faint metallic timbre which he hoped could be eliminated.[9]

Nylon strings were first tried on stage by Olga Coelho in New York in January, 1944.[10] In 1946, Segovia and string maker Albert Augustine were introduced by their mutual friend Vladimir Bobri, editor of Guitar Review. On the basis of Segovia's interest and Augustine's past experiments, they decided to pursue the development of nylon strings. DuPont, skeptical of the idea, agreed to supply the nylon if Augustine would endeavor to develop and produce the actual strings. After three years of development, Augustine demonstrated a nylon first string whose quality impressed guitarists, including Segovia, in addition to DuPont. [9] Wound strings, however, were more problematic. Eventually, however, after experimenting with various types of metal and smoothing and polishing techniques, Augustine was also able to produce high quality nylon wound strings.[9]

Use in composites[edit] Nylon can be used as the matrix material in composite materials, with reinforcing fibers like glass or carbon fiber; such a composite has a higher density than pure nylon. Such thermoplastic composites (25% to 30% glass fiber) are frequently used in car components next to the engine, such as intake manifolds, where the good heat resistance of such materials makes them feasible competitors to metals.

Hydrolysis and degradation[edit] All nylons are susceptible to hydrolysis, especially by strong acids, a reaction essentially the reverse of the synthetic reaction shown above. The molecular weightof nylon products so attacked drops fast, and cracks form quickly at the affected zones. Lower members of the nylons (such as nylon 6) are affected more than higher members such as nylon 12. This means that nylon parts cannot be used in contact with sulfuric acid for example, such as the electrolyte used in lead–acid batteries. When being molded, nylon must be dried to prevent hydrolysis in the molding machine barrel since water at high temperatures can also degrade the polymer. The reaction is of the type:

Incineration and recycling[edit] Various nylons break down in fire and form hazardous smoke, and toxic fumes or ash, typically containing hydrogen cyanide. Incinerating nylons to recover the high energy used to create them is usually expensive, so most nylons reach the garbage dumps, decaying very slowly.[11] Some recycling is done on nylon, usually creating pellets for reuse in the industry.[12]

Polytetrafluoroethylene From Wikipedia, the free encyclopedia (Redirected from Teflon)

"Teflon" redirects here. For other uses, see Teflon (disambiguation).

Polytetrafluoroethylene

IUPAC name[hide] poly(1,1,2,2-tetrafluoroethylene)[1]

Other names[hide] Syncolon, Fluon, Poly(tetrafluoroethene), Poly(difluoromethylene), Poly(tetrafluoroethylene)

Identifiers Abbreviations

PTFE

CAS number

9002-84-0

KEGG

D08974 =

ChEBI

CHEBI:53251 Properties

Molecular formula

(C2F4)n

Density

2200 kg/m3

Melting point

Thermal conductivity

600 K

0.25 W/(m·K) Hazards

MSDS

External MSDS

NFPA 704

0 1 0 Supplementary data page Structure and

n, εr, etc.

properties Thermodynamic

Phase behaviour

data

Solid, liquid, gas

Spectral data

UV, IR, NMR, MS (verify) (what is:

/ ?)

Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox references

Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. The best known brand name of PTFE is Teflon by DuPont Co. PTFE is a fluorocarbon solid, as it is a high-molecular-weight compound consisting wholly of carbon and fluorine. PTFE is hydrophobic: neither water nor water-containing substances wet PTFE, as fluorocarbons demonstrate mitigated London dispersion forces due to the high electronegativity of fluorine. PTFE has one of the lowest coefficients of friction against any solid. PTFE is used as a non-stick coating for pans and other cookware. It is very non-reactive, partly because of the strength of carbon–fluorine bonds, and so it is often used in containers and pipework for reactive and corrosive chemicals. Where used as a lubricant, PTFE reduces friction, wear, and energy consumption of machinery. It is also commonly used as a graft material in surgical interventions.

It is commonly believed that Teflon is a spin-off product from the NASA space projects. Though it has been used by NASA, the assumption is incorrect.[2] Contents [hide]



1 History



2 Formation



3 Properties



4 Applications and uses



5 Safety

o

5.1 PFOA



6 Similar polymers



7 See also



8 References



9 Further reading



10 External links

History[edit] PTFE was accidentally discovered in 1938 by Roy Plunkett, in New Jersey while he was working for Kinetic Chemicals. As Plunkett was attempting to make a new chlorofluorocarbon refrigerant, the tetrafluoroethylene gas in its pressure bottle stopped flowing before the bottle's weight had dropped to the point signaling "empty." Since Plunkett was measuring the amount of gas used by weighing the bottle, he became curious as to the source of the weight, and finally resorted to sawing the bottle apart. Inside, he found it coated with a waxy white material which was oddly slippery. Analysis of the material showed that it was polymerized perfluoroethylene, with the iron from the inside of the container having acted as a catalyst at high pressure. Kinetic Chemicals patented the new fluorinated plastic (analogous to known polyethylene) in 1941,[3] and registered the Teflon trademark in 1945.[4][5] DuPont, which founded Kinetic Chemicals in partnership with General Motors, was producing over two million pounds (900 tons) of Teflon brand PTFE per year in Parkersburg, West Virginia, by 1948.[6] An early advanced use was in the Manhattan Project as a material to coat valves and seals in the pipes holding highly reactive uranium hexafluoride at the vast K-25 uranium enrichment plant at Oak Ridge, Tennessee.[7] In 1954, French engineer Marc Grégoire created the first pan coated with Teflon non-stick resin under the brand name of Tefal after his wife Collete urged him to try the material he had been using on fishing tackle on her cooking pans.[8] In the United States, Kansas City, Missouri resident Marion A. Trozzolo, who had been

using the substance on scientific utensils, marketed the first US-made Teflon coated frying pan, "The Happy Pan", in 1961.[9] In the 1990s, it was found that PTFE can be radiation cross-linked above its melting point and in an oxygen free environment.[10] Electron beam processing is one example of radiation processing. Cross-linked PTFE has improved high temperature mechanical properties and radiation stability. This is significant because for many years irradiation at ambient conditions has been used to break down PTFE for recycling.

[11]

The radiation

induced chain scissioning allows it to be more easily reground and reused.

Formation[edit] It is formed by the polymerization of tetrafluoroethylene: nF2C=CF2 → —{ F2C—CF2}—

Properties[edit]

PTFE is often used to coat non-stickfrying pans as it is hydrophobic and possesses fairly high heat resistance.

PTFE is a thermoplastic polymer, which is a white solid at room temperature, with a density of about 2200 kg/m3. According to DuPont, its melting point is 600 K (327 °C; 620 °F).[12] Its mechanical properties degrade gradually at temperatures above 194 K (−79 °C; −110 °F).[13] PTFE gains its properties from the aggregate effect of carbon-fluorine bonds, as do all fluorocarbons. The only chemicals known to affect these carbon-fluorine bonds are certain alkali metals and most highly reactive fluorinating agents.[14]

Property

Value

Density

2200 kg/m3

Melting point

600 K

Thermal expansion

135 · 10−6 K−1 [15]

Thermal diffusivity

0.124 mm²/s [16]

Young's modulus

0.5 GPa

Yield strength

23 MPa

Bulk resistivity

1016 Ω·m [17]

Coefficient of friction

0.05–0.10

Dielectric constant

ε=2.1,tan(δ)