TEXTILE FINISHING Any operation (other than preparation and coloring) that improves the appearance and/or usefulness of fabric after it leaves the loom or knitting machine. TERMS USED TO CATEGORIZE FINISHES • • • • • •
Chemical Mechanical Wet Dry Durable Non-durable Chemical Finishes
Resin Finishes (’Permanent Press’? • • • • • •
Used on cotton or rayon Keeps fabric smooth after washing and drying with little or no ironing needed Improves shrinkage control Reduces fabric strength May have odor problem All resins contain formaldehyde
SOFTENERS • Generally used with resins t o improve the way the fabric feels • May cause fastness problems • May cause yellowing or odor problems • Soil Release Finishes • Used extensively on carpets and upholstery fabrics • Also used on apparel fabrics, especially those containing polyester • Very durable if applied at the finishing plant; little durability if applied by the consumer Three main types 1. Wax finish 2. Silicone finish 3. Fluorhefinish 4.Flame Retardant Very important finish, especially for children’s sleepwear Can be accomplished by using special fiber types or by applying special chemical finishes.
FUNCTIONAL FINISHES The properties of synthetic fibers, most important among them being polyamide, polyester and polyacrilonitrile, are essentially different from those of natural cellulosic and wool fibers. Hence the sequence of finishing operations is likely to be different. While cellulosic's require a resin finishing treatment to impart easy-care properties, synthetic fibers already have these easy-care criteria and require only a heat setting operation. The use of 100% synthetic textiles has increased considerably since the arrival texurised yarns consisting of filaments and the growing production of knit goods. The use of open weave has enabled production of lighter, air permeable, fabrics to ensure better wearing comfort.
HEAT SETTING Heat setting of synthetic fabrics eliminates the internal tensions within the fiber generated during manufacture and the new state can be fixed by rapid cooling. This heat setting fixes the fabrics in the relaxed state and thus avoids subsequent shrinkage or creasing of fabric. Presetting of goods make it possible to use higher temperature for setting without considering the sublimation properties of dyes and also has a favorable effect on dyeing behavior and running properties of goods. On the other hand, post setting can be combined with some other operations such as thermosol dyeing or optical brightening of polyester, post setting as a final finish is useful to get a high dimensional stability along with desired handle. The application of heat in heat setting can be done by hot air, on a pin stenter at 220c for 20-30 seconds for polyester goods and at a lower temperature range of 190-225C for 15 -20 seconds for polyamides . Acrylics may be heat set partially at 170-190 c for 15-60 seconds to reduce formation of running creases. But higher temperature should be avoided to prevent yellowing. Hydro setting is so rarely used particularly to get fuller and softer handle on polyamides at 125135c in autoclaves for 20-30 minutes. It can be combined with dyeing or optical brightening. Steam setting can be done by saturated or super heated steam. During steaming, uniform treatment can be ensured by initial sequence of alternate short steaming and vacuum application for 20-30 min at 130C under pressure. Super heated steam can be used in stenters and setting time is 25% shorter than for hot air on account of quicker heating up rate. Acrylic fibers have to be protested as some may under go excessive shrinkage or loss of handle. Before the material is heat set, it should be thoroughly washed to remove spin preparations, lubricants, sizing agents and impurities as these are likely to be burned in drying heat setting making their removal difficult.
FILLING AND STIFFENING FINISHES
A stiffening effect is desirable in certain polyamides and polyester materials for petticoats, collar interlinings, etc., which can be done by reducing the mutual independence of structural element of fabric by polymer deposition on coating as a fine film. Some special Urea-formaldehyde precondensates have been found to be useful. Application of film-forming acrylates dispersions as well as latex rubber emulsions gives a fuller effect with sufficient stiffness. When softening is desired it can be achieved by reducing the frictional coefficient between structural elements of fabrics, cationic long chain fatty derivatives and silicones may be used in conjunction with polymer forming agents. Recently some cationic softeners having reactive functional groups have been developed to get better fastness of finish.
HYDROPHILIC FINISHES On account of lower moisture and water absorption capacity synthetic fiber materials become uncomfortable in contact with skin. Certain products based on modified (oxy-ethylated) polyamides makes the wearing more pleasant by reducing the cohesion of water so that it spreads over a larger area and thus evaporates more rapidly.
ANTI-PILLING FINISHES Pilling is an unpleasant phenomenon associated with spun yarn fabrics especially when they contain synthetics. Synthetic fibers are more readily brought to the surface of fabric due to their smooth surface and circular cross section and due to their higher tensile strength and abrasion resistance; the pills formed take a long time to be abraded by wear. With knit fabric, two more problems occur, viz., "picking" where the abrasion individual fibers work themselves out of yarn loops onto the surface when garment catches a pointed or rough object. These two effects are more predominant in the weave, is more open and yarn is bulkier. The finish has to cement the fibers within the yearn so that their dragging becomes more difficult, without affecting the handle adversely. Special polymer formers of acrylate type or latex type are useful but should form a film of good cohesion, should hydrophilic and should not form a tacky surface. Padding in polymer dispersion or emulsion followed by drying at moderate temperature gives the desired effect.
PERMANENT ANTI-STATIC EFFECTS Anti-static effective chemicals are largely chemically inert and require Thermosol or heat treatment for fixing on polyester goods. Agents of polyether type are found to be useful but should not affect the dye-equilibrium on fiber otherwise the rubbing fastness is impaired. In general Thermsolable anti-static agents also have a good soil release action which is as
permanent as the anti-static effect. Anti-static finishes may also be of polyamide type being curable at moderate temperatures.
NON-SLIP FINISHES Synthetic warp and weft threads in loosely woven fabrics are particularly prone to slip because of their surface smoothness when the structure of fabric is disturbed and appearance is no loner attractive. To avoid this attempts are made to give the filaments a rougher surface. Silica-gel dispersions or silicic acid colloidal solutions are quite useful and they are used with advantage in combination with latex polymer or acrylates dispersions to get more permanent effect along with simultaneous improvement in resistance to pilling or snagging. These polymer finishes are also capable of imparting a soft and smooth handle to synthetic fabric without imparting water repellency.
FIRE RESISTANT FINISHES With synthetic fiber which melts on igniting by a flame, the molten moss is itself quite dangerous and a fire resistant treatment is desirable for certain end uses. Polyester fabrics can be made flame resistant by treatment with an aqueous emulsion of xylene soluble 2, 3dibromopropyl phosphate in a pad-cure sequence. A semi-permanent effect can be produced by treating with a mixture of ammonium bromide and brominated phosphoric acid esters. Polyamides can be made flame resistant by applying phosphorous tri-chloride ammonia reaction products or ammonium bromide with amino-triazine condensation products. For acrylics trisdibromopropyl-phosphate as well as 2-cyanoethyl-tetramethyl-di-amino-phosphate is quite effective.
ANTI-MICROBIAL FINISHES With the increasing use synthetic fibers for carpets and other materials in public places, antimicrobial finishes have assumed importance. A reduction in soiling tendency will along way in keeping textiles free from germs and usual soil repellant as well as soil release finishes are effective in some way. Products which are commonly applied are brominated phenols, quaternary ammonium compounds, organo-silver and tin compounds which can be applied as solutions or dispersions. They can also be incorporated in a polymeric film deposited on the surface to get controlled release. Some reactive systems similar to those for reactive dyes have been recently tried to incorporate anti-microbial structural features.
WRINKLE FREE FINISHES
The wrinkle free finish (also known as "Easy Care", Durable Press", "and Wrinkle-Resistant “,” Wash and Wear, No-Iron" etc.) is obtained by cross-linking cotton. Permanent press finishes function by forming cross-links between adjacent cellulose polymer chains; these give cotton some elastic and resiliency properties. Such cross-linked cotton can recover from deformation stresses and thus wrinkles will not form. Even today, DMDHEU is the main cross-linking agent. With magnesium chloride as the acid catalyst to initiate a reaction, it forms cross links in the amorphous regions of the fibre. The structure and reaction of DMDHEU is shown in the figure 1. Through the reaction (>NCH2=>NH+HCHO) free formaldehyde is released. Inadequate curing also leads to the liberation of formaldehyde at high temperature. A number of approaches have been developed to limit the amount of formaldehyde released, such as after washing of cured fabrics; the addition of formaldehyde scavengers like carbohydrazide to the bath; use of urea in the pad-bath or application through a spray; modification of DMDHEU to etherized, glycolated or methylated DMDHEU Alternatives to DMDHEU are also being researched. Main alternatives are polycarboxlicacids, typically BTCA (1, 2, 3, 4 butane tetra carboxylic acid) or citric acid. However, BTCA is expensive to use and citric acid causes yellowing. Another approach has been to use polymers of maleic acid to form ester cross-links, and yet another to fix a quaternary group through an epoxidation reaction to the cellulose chain to form cross-links. Research on all these alternatives continues. Commercially, it is the modified DMDHEU (glycolated or methylated) that is most used today. The product is pre-buffered to prevent premature curing and also pre-blended with a catalyst. Magnesium based catalysts are the most popular in use today. Citric acid or aluminum chloride can also be blended to increase catalysis when curing times are short. A typical formula for a pre-cure or post-cure finish is as follows: DMDHEU (45%), 2-20% of weight of DMDHEU but not less than 1% owb; wetting agent. 0.1% owb; and softeners, 2-8% owb. The wetting agent allows the fibre to be internally penetrated, so cross linking can take place throughout the fibre cross-section. A high density polyethylene restores some of the lost tear strength and abrasion resistance by providing lubrication. It also has a synergetic effect with silicone or fatty-based softeners to produce a very pleasing hand. Among the silicone softeners, reactive polysiloxanies with silanol functional end-groups ( Fig 2 ) act as elastomeric finishes imparting higher crease resistance, good dimensional stability (smooth drying properties) and excellent soft handle with good sewability. They can also reduce free formaldehyde release by replacing part of the resin. Several types are available today: Pretavyl VP 1601A by Boehme Filatex Inc., and siltouch RS by Yorkshire Chemicals.
CONTROLLED COMPRESSIVE SHRINKAGE The internationally well-known and most important shrinking process today dates back more than 70 years. Though the correct expression for this process is Controlled Compressive Shrinkage, the average person knows it as SANFORIZED. The process is a purely mechanical treatment without any addition of chemicals. The word SANFORIZED is derived from the first name of the inventor of the compressive shrinkage process, Mr. Sanford L. Cluett. The Sanforized Company, a division of Cluett Peabody & Co., Inc., New York, USA, is sole owner of the registered trademarks Sanforized, Sanfor and Sanforizado. The Sanforized label means dimensional stability for garments made up of Sanforized labeled fabrics. The purpose of the process is to shrink fabrics in such a way that textiles made up of these fabrics do not shrink during washing. The amount of potential wash shrinkage must be determined prior to shrinking. A full width sample is wash-tested according to the test method. After the lengthwise and widthwise shrinkage has been determined, the compressive shrinkage machine can be adjusted accordingly.
SUEDING MACHINES From a light sueding effect up to the classical peach-skin effect
USE For wovens and knitteds of natural and synthetic fibres and all kinds of blends. The fabric is guided horizontally over 5 sueding rollers and delivered by a plaiter or rolled on big batch. The range of effects is versatile, from a slight sueding effect up to the so-called peach-skin effect. Improvement of touch, i.e. fabric surface becomes softer and more voluminous, so touch will be more textile-like, especially important in case of synthetic fibres. Creation of a pile, depending on kind of fabric a flannel or peach-skin effect Pleasant to the skin and comfortable wearing
Additionally to the softer touch, also a wanted „softer“ appearance with regard to colours and contours depending on kind of fabric. Used character „Cleaning“of fabric surface For effect formation a variety of parameters, all reproducible, can be used: Fabric tension, emery coverings, sense of rotation of sueding rollers, fabric speed, variable angle of contact of each sueding roller and sueding roller rotating speed (option). A heating plate and a steamer in the machine entry serve to improve effects and to eliminate creases resulting from storage.
SOIL RELEASE FINISH Durable press fabrics containing polyester fibres are known to show tendency to retain stains and also attract soil from the wash liquor during washing. This is due to hydrophobic nature of these fabrics. Various soil-release agents have been developed. These are described as durable film forming polymers containing polymer groups which are capable of hydrogen bonding with water. These finishes are applied by a pad-cure process along with the resin. Treatment of synthetic fibers with hydrophilic polymers is in general called soil release finishing, which makes the soil adhereing the hydrophobic fibers more accessible to water and easily removable. The fluorocarbons use for this purpose is dual action fluro polymers containing hydrophilic hydrocarbons as well as perfluroalkyl groups. These finishes are generally applied to synthetic fibers which are generally prone to soiling. When a finished fabric is immersed in a liquid, hydrophilic hydrocarbon groups orient towards polar aqueous environement and flurocarbon groups collapse below the surface promoting the release of stains. Thus easy removal of stains takes place when the fabric is subjected to laundering. This finish can be applied by pad-dry-cure method along with durable press finish. Although these finishes are the most expensive ones, they are the most widely used because of their performance, comfort ability with durable press finish and not side effects.
ANTISTATIC FINISHING During spinning, weaving and finishing, textile fibres, yarns and fabrics are subjected to friction. Static electricity is thus generated on the fibre. Polyester fibre has low conduction hence it accumulates static electricity. Static electricity gives rise to a number of problems. For instance, the operator at the delivery end of a stenter may get electric shocks because of static electricity. Garments made of
polyester fibres attract soil during normal wear and also have a tendency to cling to the body of the wearer. Non-durable antistatic agents are usually hygroscopic surface-active materials, closely allied in composi6on to softeners and wetting agents. A permanent antistatic finish can be given by using a combination of a cationic and an anionic compound. Cationic quaternary ammonium compound - 3-4% Acetic acid (30%) - 0.5-1 cc/l Treat the fabric with the above composition for 10-20 min at 70'C (in a jigger). Then add (anionic alkyl sulphate) - 1.6-2.2% Continue treatment for another 10-20 min. Dry and cure if required.
WATER REPELLENT FINISH Water repellency or durable shower proofing is an important finishing process. It is usually applied to fabrics for outerwear where an excellent wash fastness is expected. Also, often internal resin treatment is required to be given to the same fabric. Both finishes can be combined. Recipe Dimethyl Dihydroxy Ethylene Urea - 40-60 g/l Ziroconium salt-containing wax emulsion - 60 g/l Reactive Softener - 60 g/l Magnesium chloride. - l0 g/l Pad, dry and cure at 150oC for 5 min. For further reading on water repellent finish: