Strength of plant fibre

AIM To investigate the tensile strength of plant fibre by using pumpkin stems and compares it to tensile strength of concrete.

INTRODUCTION This experiment is carried out to measure the tensile strength of plant fibre and compare ot with the strength of concrete. Tensile strength is the stress at which a material breaks or permanently deforms. Tensile strength is an intensive property and, consequently, does not depend on the size of the test specimen. However, it is dependent on the preparation of the specimen and the temperature of the test environment and material. Tensile strength is measured in units of force per unit area. In the SI system, the units are Newton per square metre (N/m²) or Pascal (Pa), with prefixes as appropriate. Tensile stress is the stress experienced by the object produced.

PROBLEM STATEMENT Are tensile strength of plant fibre stronger or weaker than the tensile strength of concrete which is 2.0 x 6

-2

10 Nm ?

HYPOTHESIS Plant fibre has a higher hig her tensile strength than concrete.

APPARATUS Rubber gloves, beaker, a pair of scissors, retort stand with w ith clamps, loads with different masses, hook.

MATERIAL Stems of mature pumpkin plant, distilled water.

PROCEDURE

A. Extracting fibres from plant stem 1. Leaves and any flowers from stems of plants are removed using a scissor. 2. The stems are then place in a beaker and let them fully immerse in water. 3. The stems are then left soaked for a week. 4. Stems are removed from water after a week and washed to remove to remove softened tissue and fungus. 5. The stem is rubbed by hand gently under running tap water to remove stem tissues around bundle to extract the fibres. 6. The fibres are separated using hands into single fibres. 7. The fibres are then dried. The outside cuticle and epidermal layer w ill rub away and the central pith will be left when the fibres are peeled away.

B. Testing fibre strength 1. A strand of dried fibre is cut into 3 cm long. 2. Loops are made at both ends of the fibre to attached the fibre to the spring balance and hook of loads. 3. The fibre strand is then attached to spring balance which is hanged to re tort stand. 4. The hook is attached at the other end and observation is made whether the fibre cam withstand the load. 5. A piece of load with mass 2g is slipped to the hook. 6. Another load of mass 2g is added if the fibre does not snap and the loads are continue to be added until the fibre snap. 7. The total mass of loads added before the fibre snapped is recorded. 8. Light microscope is set up and stage micrometer is placed on the stage of micrometer. 9. The eyepiece graticule and stage micrometer are postioned to be parallel with each other and the scale of eyepiece is calibrated. 10. The fibre strand being used in experiment is placed under on a slide and the diameter is measured using the scale on eyepiece graticule. 11. The tensile strength of fibre strand is calculated using this formula.

      12. This experiment is repeated for another 2 times. 13. The data obtained are recorded in a table.

RESULT Calculations:

Fibre 1 Force = 0.022 kg x 9.81 ms

-2

= 0.22 N -5

Radius = 7.5 x 10 m Cross-sectional

-5

area = 3.14 x (7.5 x 10 )² -8

= 1.76625 x 10 Tensile strength =

  7

-2

= 1.25 x 10 Nm

Fibre 2 Force = 0.022 kg x 9.81 ms

-2

= 0.22 N -5

Radius = 8.5 x 10 m Cross-sectional

-5

area = 3.14 x (8.5 x 10 )² -8

= 2.26865 x 10 Tensile strength =

  6

= 9.7 x 10 Nm

-2

Fibre 3 Force = 0.026 kg x 9.81 ms

-2

= 0.26 N -5

Radius =6.0 x 10 m Cross-sectional

-5

area = 3.14 x (6.0 x 10 )² -8

= 1.1304 x 10 Tensile strength =

  7

-2

= 2.3 x 10 Nm

Trials

Diameter (mm)

Radius (mm)

Radius (m)

1

0.15

0.075

7.5 x 10

2

0.17

0.085

8.5 x 10

3

0.12

0.060

6.0 x 10

-5 -5

-5

Table 1 Diameter and radius of each fibre

Fibre

Mass of loads (kg)

Force,F =mg (N)

Cross-sectional

Tensile strength

area, A = r² (m²)

(Nm ) 1.25 x 10

-8

9.7 x 10

6

2.3 x 10

7

0.022

0.22

1.76625 x 10

2

0.022

0.22

2.26865 x 10

3

0.026

0.26

1.1304 x 10

Average tensile strength of plant fibre =

-8

1

Table 2 Tensile strength of different fibres

      7

= 1.51 × 10 Nm

-2

2

-8

7

DISCUSSION

Data interpretation

Table 1 shows the diameter of all three fibres used in three experiments. Radius for each fibre in -5

metre is then calculated. For the first fibre, its radius is 7.5 x 10 m. Second fibre has the largest radius -5

-5

which is 8.5 x 10 m. Meanwhile, the last fibre used has the smallest radius which is 6.0 x 10 m. Based on Table 2, third fibre withstands the maximum of loads of 0.026 kg. Both first and second fibres snapped after mass of loads of 0.022 kg is added to the hook attached to the fibre. -2

Multiplying the mass with gravitational force which is 9.81 ms , the maximum force (N) withstand by the first fibre and second fibre is 0.22 N. Third fibre can withstand force of 0.26 N. From radius calculated in Table 1, cross-sectional area of each fibre can be calculated. Cross-8

7

-2

sectional area for the first fibre is 1.76625 x 10 m² and this fibre has tensile strength 1.25 x 10 Nm . -8

The second fibre used has the 2.26865 x 10 m ² of cross-sectional area and the tensile strength 6

-2

calculated is 9.7 x 10 Nm . From calculation, third fibre used has the highest tensile strength of 2.3 x 7

-2

-8

10 Nm with 1.1304 x 10 m² cross-sectional area. The result shows the tensile strength of fibre with smallest diameter which is the third fibre has the highest tensile strength. This proved the relationship between cross-sectional area and tensile 7

-2

strength. Average tensile strength of fibre used i n this experiment is 1.51 × 10 Nm .

Limitations As this experiment is carried out to investigate whether plant fibre under tension are stronger or weaker than concrete, tensile strength has to be calculated. Theoretically, tensile strength of plant fibre 6

-2

should be more than 2.0 x 10 Nm which is the tensile strength of concrete. However, there are a few limitations in this experiment. First, the fibre strands taken from the stem have different maturity. If extracted from different part or different plant but of the same species, the strengths may have big variations. Other than that, in a fibre, the diameter may be different at different part along the strand. For example, the end of fibre may have thicker diameter but thinner in the middle. Besides, when drying the fibre, the fibre may become over-dried. This will result in more brittleness in the fibre. Thus the fibre may snap easily even with the smallest mass of loads and give a wrong implication on their real tensile strength.

Sources of error Careless in handling is the main source of error

in this experiment. As the fibre is very thin and

easily snapped with a smallest external force, it should be handled gently and extra careful.

During

experiment the mass should be supported with palm and released slowly so that sudden snap can be avoided. Tie both ends carefully and attached the loops carefully at the force meter and hook of loads to minimize pulling force towards the fibre. If the hook of loads swings too much, the force on the fibre also will be added unnecessarily.

SAFETY PRECAUTIONS 1.

When

extracting the fibre, wear cloves to prevent from being stung.

2. Tie the strand well so it will no snap suddenly and preventing the loads from falling down. 3. Add loads with small and constant mass in each trial so that the maximum mass withstand by the fibre can be observed more precisely.

CONCLUSION Plant fibre extracted from pumpkin plant is stronger than concrete. The tensile strength 7

-2

calculated in this experiment is 1.51 × 10 Nm .

REFERENCES 1.

C

J Clegg, Edexcel Biology for AS, Hodder Education, 2008

2.

Wikipedia :

http://en.wikipedia.org/wiki/ Cucurbita_maxima

3. Plants for a Future : http://www.pfaf.org/leaflets/fibplant.php 4. Plant Fibres : http://waynesword.palomar.edu/traug99.htm