Tensile Strength of Plant Fibre

BIOLOGY LAB REPORT TITLE

: THE STRENGTH OF PLANT FIBRES

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 Abstract  Plant has the ability to withstand all exerted force due to its high h igh tensile strength , resulted from the cell wall and sclerenchyma cell. In this experiment, experiment, we are to demonstrate the tensile strength of plant fibre than was extracted from pumpkin stem after soaking, retting and drying process carried out. The tensile strength of plant fibre of different diameter was calculated by exerting force (load) on the fibre until it is snapped and calculations (refer to results) were carried out to obtain average tensile strength of plant fibre. Introduction

(1)

Since mankind mankind exist on the earth’s surface, they has been strongly dependent on plant fibres for all kinds of purposes .Fibrous materials such as wood and bamboo have found particular application in construction. Other important uses have included tools, weapons and energy generation. A wide variety of fibres have also been used for production of textiles, pulp and paper and fibre boards. Not to be surprise, the strongest engineering materials are generally made as fibers (eg:carbon (eg:carbon fiber and Ultra-high-molecular-weight polyethylene). polyethylene). With the appearance of synthetic materials (eg: plastics) at the beginning of this century, which is very cheap and can be produce in large amount amou nt compared to natural fibres, synthetic-based materials have steadily replaced bio-based products.

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Scelerenchyma fibre/ Sclerenchymatous fibre(2)

Sclerenchyma consists of very long, narrow, thick and lignified cells, usually pointed at the both of the end. Sclerenchyma cell is made up of fibre (elongated cells) and sclereids/stone cells (roughly spherical). Mature sclerenchyma is composed of dead cell s and incapable of elongation thus do not mature until living cells around them reach maturity. Being hard, elastic and having thick walls with lignifies walls make m ake sclerenchyma cells important in strengthening and supporting plant parts that have ceased elongation.

Diagram 1 : The sclerenchyma cross-sectional and components(3) i.

Fibre

Fibres are generally long, slender, in needle-shaped with pointed tips, thick walls ,have rather small lumen and usually occur in strands or bundles. Their principal cell wall material is cellulose. Typical fibres contain high proportion of lignin and cellulose cell wall. In the middle of  fibre are the thickening layers of secondary wall that deposited one after another. Growth at  both tips of the cells lead to simultaneous elongation. During development, the layers of  secondary material seem like tubes( the outer one is always longer and older than the next). After completion of growth the missing parts are supplemented, the wall is evenly thickened up to the tips of the fibres. Fibres are grouped into xylary fibres(wood fibres) and extraxylery fibres. Extraxylery fibres are classified as phloem fibres, cortical fibres and perivascular fibres and lignifications for these fibres are not compulsory.

Fibres usually originate from meristematic tissue; main center of their production are cambium and procambium which both of them usually associated with the vascular bundles. The xylem fibres are always lignified while phloem fibres are cellulosic. Fibres are said to b e originate from tracheids , losing its water conductivity ability and reduce in pit’s size. Contrasting hard fibres are mostly found in monocots. Elasticity in fibres enables the plant body to withstand various strains. ii.

Sclereids

Sclereids are reduced form of sclerenchyma cells with highly thickened and lignified walls (thus making the lumen very small) and can be found in small bundles or groups in plants that form durable layers. The cells are variable in shape (can be isodiametri, prosenchymatic, for ked or more) and much elongated and flexible with tapered ends . Sclereids are relatively sho rt  compared to fibres and existence of branched pits (ramiform pits) are clearly visible on cell wall . Sclereids are commonly found in fruit wall, seed coat, epidermal scales, and occasionally found in cortex, pith, mesophyll and petiole of submerged aquatics.

Diagram 2 : Fibre cells(left) and Sclereids(right)(3)

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Strength of plant (4)

A plant stems must not only be strong, but they also must be able to bend according to the wind direction and recoil back to their original shape without any permanent distortion or damage. Tensile strength is the maximum stress caused by a pulling forces that a material can withstand without failing as the result of the molecules or atoms hold together or being elastic when being pulled apart while strength of plant fibre is the maximum stress a material can withstand without failing. Compression strength is the maximum stress caused by a pushing forces that a material can withstand without crushing as the result of the molecules or atoms do not slip pass each other . As long as the molecules or atoms remain in place, then the material can resist compression without necessarily having tensile strength.

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Xylem vessel(5)

Xylem tissues are produced by meristematic cambium cells that located in a layer just inside the tree bark. In dicotyledonous stems, the xylem cells can be noted inside the cambium layer while in monocotyledonous stem, it can be seen to be scattered all over. Xylem tissue conducts water and mineral ions from root to other parts of plant , against the gravitational force with help of  adhesion and cohesion of water molecule. The xylem tissue is co mposed of tracheids (elongate cells with pointed ends) and vessel elements (shorter and wider cells).

Diagram 3 : Xylem tracheids and vessel elements(3)

The xylem walls are heavily lignified with pits(composed of cellulose and pectins) . After the cel l death, tracheids and vessels become hollow, water -conducting pipeline and its protoplasm disintegerates. In flowering plants, xylem contains numerous fibres (resulting in having harder and heavier wood than gymnosperms), elongate cells with tapering ends and very thick walls. To be frank, xylem tissues are actually composed of dead cells that have dried out over the years and with the presence of lignin in the thickened secondary cell wall, it make the whole structure hard and dense, providing support for the plant.

Objective To investigate the tensile strength of plant fibre (pumpkin stem fibre) and compares it to tensile strength of concrete. Problem Statement  Are plant fibre’s tensile strength is stronger than the tensile strength of co ncrete? Hypothesis Plant fibre has a higher tensile strength than concrete’s.

 Apparatus Retort stand with clamps, different masses of load (2g and 10g), hook, Rubber gloves, Paper towels, Measuring cylinder, 100ml beaker, a pair of scissors , tray ,Force Meter

Materials Stems of mature pumpkin stems, distilled water

Procedure

a) Extracting fibres from mature pumpkin stem

1. The pumpkin stems were prepared by laboratory assistant by remo ving any leaves or flowers from the stems of pumpkin using scissors. 2. The stems are then let to dry on a tray covered by tissue papers for three days. 3. The dried pumpkin stems were placed in a measuring cylinder and were fully immersed in water. 4. The stems were then left soaked (retting process) for 8 days. 5. Pumpkin stems were removed from water and washed gently to remove the softened tissue and fungus. The stems were rubbed by using gloved hands under running tap water to remove the softened stem tissue to obtain/extract the fibres needed. 6. The pumpkin stem fibres were separated using gloved hands slowly with care. 7. The fibres were then placed on a tray that was covered by tissue papers to dry and were left in care of laboratory assistant.

b) Testing Fibre Strength

1. A strand of pumpkin stem fibre was chosen. 2. Loops were made at both ends of the fibre to attach one side to the spring balance and the other one to the loads hook. 3. The spring balance was hooked onto the clamp of the retort stand (attached to the table) .the fibre stand was the attached to the spring balance and slowly attached to load’s hook  on the other end (make sure that the fibre can withstand the load’s hook). 4. The spring balance reading was then adjusted until it returns to its zero value. 5. A piece of load with mass 2g was put to the hook. 6. The reading of spring balance was recorded. 7. Loads were continued to put until the fibre strand snap and every load that was slipped into hook(total load) and the reading of the spring balance was recorded. 8. Light micrometer was set up and stage micrometer was placed on the micrometer stage. 9. The eyepiece graticule and stage micrometer were positioned to be parallel with each other and scale of eyepiece was calibrated (shown below) and recorded. 10. The fibre strand that was used in experiment was cut horizontally and placed on a slide. It  was then placed in micrometer stage and the diameter of the stem was measured using the scale on eyepiece graticule. 11. The tensile strength of fibre strand was calculated using formula (shown below) and was recorded in a table. 12. The experiment was repeated for twice using different diameter of fibre strand and data obtained were recorded in a table.

Formula’s used :

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Calibration

Under x4 Magnification

100 division of stage micrometer = 40 division of eyepiece graticule 100 division of stage micrometer = 1 millimeter 1mm of division of stage micrometer = 40 division of eyepiece graticule 1 division of eyepiece graticule = 1mm/40 = 0.025 mm or 2.5 x10-5m

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Tensile strength

=

Safety precaution In order to avoid any accident or injury during the experiment in laboratory, the precautionary steps should be taken and applied.

Wearing lab coat and a pair of suitable shoes are

compulsory when conducting an experiment in the lab at all times to protect the skin and clothing from spillage of any chemical substance. Washing hands thoroughly with soap and water before and after conducting experiment is vital to avoid contamination. Cover hands with rubber gloves during washing process of the stem is important to avoid getting contact  with microorganism or prevent smelly hand which will be unpleasant as the smell will stay on hand for quite a while. Furthermore, the glassware such as measuring cylinder should be handled with full care because they are fragile. The apparatus such as forceps and scissors are also sterilized to prevent infection of microorganism. After using all samples and apparatus at  the end of experiment, they should be discarded properly and returned back to their places to avoid injuries and unnecessary accidents that may result fatal results.

Risk Assessment  The pumpkin plant should have to be fully immersed in a big measuring cylinder of water for at  least one week, or in this case for 8 days. This is to soften the tissues of pumpkin stem and it will be easier to extract fibres out from the stem later. The extracted fibres need to be thinner as much as possible to make sure only one strand fibre will be used in this experiment. The plant  fibre is handled with care while transferring onto tissue paper to let them dry as they are very fragile. Once apparatus (measuring cylinder) was used, they were washed and placed in their place. Other than that, when the horizontal sectional of fibre is transferred to a coverslip and is being covered, the coverslip must not be pressed too firmly that may cause breakage of the cover slip or alter the radius of the stem. Tying the fibre using thread also should be given care so that  the knot done is able to prevent the fibre from sliding off. It is also to prevent the fibre from detached when load is added to the hook. But, the knot made shouldn’t be too tight as it will break the fibre. During placing the load into the hook, extra care was taken to prevent any exertion of sudden force onto the fibre which will lead to breakage of plant fibre.

Results Fibre

Radius

Mean Radius

1

2

3

1

6.5

12.5

11.0

10.0

2

20.0

19.0

20.0

19.67

3

21.0

22.5

22.5

22.0

Table 1 : Mean Radius of each Fibre Fibre 1

Fibre 2

Fibre 3

Force

Force

Force

= 0.006kg x 9.8ms-2

= 0.036kg x 9.8ms-2

= 0.086kg x 9.8ms-2

= 0.069 N

= 0.353 N

= 0.843 N

Radius

Radius

Radius

= 10 x 2.5 x10-5m

= 19.67 x 2.5 x10-5m

= 22.0 x 2.5 x10-5m

= 2.5 x 10-4m

= 4.92 x 10-4m

= 5.50 x 10-4m

Cross-sectional Area

Cross-sectional Area

Cross-sectional Area

= 3.142 x (2.5 x 10-4m)2

= 3.142 x (4.92 x 10-4m)2

= 3.142 x (5.50 x 10-4m)2

= 1.96375 x 10-7m2

= 7.60565 x 10-7m2

= 9.50455 x 10-7m2

Tensile Strength

Tensile Strength

Tensile Strength

= 0.069 N / 1.96375 x 10-7m2

= 0.353 N / 7.60565 x 10-9m2

= 0.843 N / 9.50455 x 10-9m2

= 3.51 x 105Nm-2

= 4.64 x 105Nm-2

= 8.87 x 105Nm-2

Table 2 : Calculations for the fibres

Fibre

Mass of loads

Force (mg)/N

Cross-sectional Area (

(m)/kg

Tensile

)/m2 Strength (Nm-2)

1

0.006

0.069

1.96375 x 10-7

3.51 x 105

2

0.036

0.353

7.60565 x 10-7

4.64 x 105

3

0.086

0.843

9.50455 x 10-7

8.87 x 105

Table 3 : Tensile Strength of Different Fibres

Average tensile Strength of Different Fibres

= ( 3.51 x 10 5Nm-2 + 4.64 x 105Nm-2 + 8.87 x 105Nm-2) 3 = 5.67 x 105Nm-2

Data Interpretation

Table 1 shows the mean radius of all three fibres that were used in the experiment. The radius for each fibre was taken for three times to obtain the mean .The mean radius for each fibre (in metre) was calculated . Mean radius for one fibre is obtained by adding all three readings and divided it with three (number of readings taken). Then, it was multipled with the calibration, which is 2.5 x10-5m to obtain radius of the fibre in metre. This is clearly shown in table 2 (calculations). From there it can be concluded that the third fibre has the biggest radius (5.50 x 10-4m) while the first fibre has the smallest radius (2.5 x10-4m) among the three. In Table 2, all the calculations were made clearly to obtain the force exerted on the fibre (N), radius of the fibre (as discussed earlier), cross-sectional area of the fibre and the tensile strength of the pumpkin fibre. According to the Table 3, third fibre withstands the maximum load (0.086kg) , followed by the second fibre (0.036kg) and the least maximum load withstand by the first fibre (0.006kg). This results was obtained by adding loads (in g ram) into the hook that was attached to the fibre , (starting from 2g) until the fibre is snapped. By multiplying the mass (final mass before the fibre snap) with gravitational force (approximately 9.81ms -2 ), the maximum force (N) withstand by the all three fibres were calculated and recorded. From both (table 2 and 3), it can be seen that the first fibre had withstand the least load (0.069N), followed by the second fibre (0.353N) and the third fibre had withstand the most highest load (0.843N) . For the calculations of cross-sectional area of each fibre, it is shown on Table 2. Basically, radius that  obtained earlier were squared and multiplied with pi (3.142). Using formula, it can be seen that  cross-sectional area of the third fibre is the highest (9.50455 x 10-7 m2), which results in the highest tensile strength among all three fibres (8.87 x 10 5 Nm-2).

This is followed by the second fibre which has cross-sectional area of 7.60565 x 10-7 m2, resulting in 4.64 x 105 Nm-2 tensile strength. The lowest one in cross-sectional area among all three fibres (first fibre), which is 1.96375 x 10 -7 m2 resulting in the lowest tensile strength among the three fibres (3.51 x 105 Nm-2). The results shows the tensile strength of fibre with the highest radius (the third fibre) has the highest cross-sectional area, giving rise to highest tensile strength. The vice versa happened to the first fibre(lowest radius results in lowest tensile strength). Average tensile strength of fibres that were used in this experiment is 5.67 x 105Nm-2.

DISCUSSION From the experiment that carried out, we know that the average strength of the plant fibre or more precisely, pumpkin fibre is 5.67 x 10 5Nm-2. This plant fibre is concluded to be strong because of some reason. The strength and rigidity from these fibres are provided by cellulose cell wall that contains interlocking fibre arrangements .These cell walls are heavily thickened with sclerenchyma cells that are designed to support the plant body. As the plant grow in size and height, more support is required to ensure the survival of the pl ant and various types of  sclerenchyma tissues (most entirely of fibres) are formed to meet the need. As discussed earlier in the introduction, fibre plays important role in determining the tensile strength of plant  because of their interlace arrangement and their capability in stretching and contracting. Presence of lignin further increases the strength of the cell wall without affecting its water conducting ability. It’s a well known fact that concrete is stronger than a mere plant fiber. But in reality, concrete has lower tensile strength but higher compressive strength. Instead of one plant fibre, a bundle of fibres will result in stronger tensile strength than concrete. Assumption were made that a concrete sample's tensile strength is about 10 percent to 15 percent of its compressive strength. As a result, without compensating, concrete would almost always fail from tensile stresses even when loaded in compression. The practical implication of this is that concrete elements subjected to tensile stresses must be reinforced with mater ials that are strong in tension and this is influenced by the water-cementitious ratio (w/cm), the design constituents, and the mixing, placement and curing methods employed. All things being equal, concrete with a lower water-cement ratio makes a stronger concrete than that with a higher ratio.

The total quantity of cementitious materials can affect strength, water demand, shrinkage, abrasion resistance and density. In conclusion, tensile strength of plant fibre is stronger than concrete and all the credits goes to the plant fibres. This high tensile strength enables the plant to keep in structure and face all natural forces without getting damage.

Limitations

There are several limitations that have been identified throughout this experiment.

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Fibre strands that were extracted from pumpkin stem have different level of maturity. Although the stem is taken from pumpkin of same species, but the stem may extracted from different part of plant and this give rise to variation which may lead to inaccurate result.

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Besides that, the radius of the stem may differ along the strand and this will influence the reading of radius depending on the part of stem that they were taken, making the calculations inaccurate.

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Other than that, drying process of the fibres also may not fulfill. The fibres were too overdried during the experiment which results in oversensitivity and more brittleness in the fibre. This will cause the fibre to snap even for the lowest load thus giving wrong information on their real tensile strength.

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Assumptions were made that the cross-sectional of the strand is perfectly round when in reality it’s the vice versa. Thus taking radius reading using this might not be perfectly accurate.

Sources of errors Several sources of error in this experiment were identified and steps were taken to minimize these errors to make the result more accurate.

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Stem was soaked in water for more than one week and this might led to unwanted moisture absorption and production off bacteria of breakdown of cellulose cell wall may cause the fibre to lose its strength. This was overcome by carrying retting process right in the early morning on the eight day.

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Since the stem provided is long, thus it was bended when soaking process carried out. This bending damages the fibre of the pumpkin stem and weakens its strength ability, leading to the same inaccurate tensile strength. Thus, to avoid this, the stems were placed were slowly and exert slight pressure to bend it when soaking process was carried o ut.

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During extraction of fibre from the stem, the fibres may accidently experience some damage at some part which results in less strength, thus causes less accurate in tensile strength calculation. Thus, hands were covered by gloves to reduce friction formation between the stem and fingertips. Care was taken by applying less pressure on the fibre during peeling process to avoid the fibre from tear.

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During measurement of plant stem fibre radius when viewing under light microscope, the sales on eyepiece graticule might interpret wrongly due to parallax error. This was avoided by using different people positioning their eyes perpendicularly to the scales to read the scales and take three readings for each fibre.

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Putting loads without care onto the hook may cause the fibre to break. Thus,extra care were taken during adding load on the hook that was tied to the fibre. The loads should be place one by one, from the smallest weight, gently and softly to avoid exert unintentional forces that may affect the stress tension of the fibre and lead to unreliable and invalid data.

Conclusion Theoretically, plant fibre are stronger than concrete (2x106Nm-2). But, in this experiment , due to some limitations and error, the tensile strength of plant fibre is lower (5.67 x 105Nm-2) than the concrete’s tensile strength. The sole purpose of have high tensile strength in pl ant is to ensure its survival by overcoming the external force while tensile strength of concrete is more used in construction. Thus, the hypothesis is accepted.

Further Investigation Another experiment can be carried out using hair as substitution for the plant fibre to find out  whether hair is stronger than the plant fibre or not. This is because hair is also made up of strong fibre structure and keratin.

References 1. http://www.ienica.net/fibresseminar/olesen.pdf . Accessed on 17th February 2012 2. Wikipedia Foundation. Last modified on 2012. Ground Tissue. Available from http://en.wikipedia.org/wiki/Ground_tissue. Accessed on 17th February 2012. 3. http://preuniversity.grkraj.org/html/3_PLANT_ANATOMY.htm.Accessed on 17th February 2012. 4. Gan W.Y . 2007. Biology SPM Success. Edition 4. 135.p.Shah Alam : Oxford Fajar Sdn.Bhd. 5. Wikipedia Foundation. Last modified on 2012. Xylem. Available from http://en.wikipedia.org/wiki/Xylem. Accessed on 17th February 2012.