Mechanical Properties Of Biopolymer Biology Essay

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Polymers are combination of repeating units or mers, normally under condensation process. Biopolymers are biodegradable polymers which are nontoxic and can be decomposed by natural process. The origin of biopolymers is either from synthetic or renewable natural source.

The main advantage of biopolymers is their biodegradability property which allows the polymers decomposed in living cells without causing inflammation and does not release harmful toxin. Thus, biopolymers are widely use in biomedical field. Moreover, it is also environmental friendly.

There are many usages of biopolymers in different fields. For instance in medical field, polyalctides is used in surgical implants which do not require operative removal because it decomposes harmlessly in human body. Besides, natural biopolymer such as cellulose is used as packing material for its transparency and good folding properties. Polylactic acid is widely used in biomedical application for sutures, tissue engineering and absorbable wound closure products due to its good tensile strength, flexibility and durability.

The polymer used in this experiment is agar which is composed of repeating units of galactose. Agar is eatable and often used in making desserts for example, pudding and jelly. In gel electrophoresis, agar is used as matrix in separation of nucleic acids molecule compositions. Agar contributes to plant culture tissues in biotechnology field. Other than that, in microbiology, agar acts as a substratum for preparing bacteria cultures. Therapeutic agent is another role of agar in digestive tract malfunctions treatment.

Procedure (preparing agar film)

64ml of 2% (v/v) aqueous glycerol solution was placed in a 200ml beaker. 56ml distilled water was added and the beaker content was then heated.

1g starch and 5g agar were measured and poured into the solution.

The mixture is heated with stirring until the polymer forms solution.

The solution was poured into five petri dish separately on a flat level surface. The present of imperfections or bubbles on the surface was avoided.

The petri dish content was allowed to cool. Then, it was cut into films in rectangular shape. The F1 agar films were done prepared.

Steps 1 until 5 were repeated to prepare F2 agar film with different composition of 64ml glycerol solution, 56ml distilled water, 3g starch and absence of starch.

The table below shows the composition of each specimen.

Sample

Water(mL)

Glycerol(mL)

Starch(g)

Agar(g)

F1

56

64

1.0

5.0

F2

56

64

0

3.0

Sample A1, A2, E1 and E2 were used for Instron test.

Sample

Water(mL)

Glycerol(mL)

Starch(g)

Agar(g)

A1

88

32

4.8

4.8

A2

88

32

0.0

4.8

E1

56

64

4.8

4.8

E2

56

64

0.0

4.8

Calculation for weight percent of samples:

For specimen A1:

Given the glycerol density = 1.26gml-1

Density, ρ =

1.26 g/mol =

Mass of glycerol, mglycerol = 40.32 g

Total weight of solution = massglycerol + massstarch + massagar

= 40.32 g + 4.8 g + 4.8 g

= 49.92 g

Weight percent of sample = x 100%

Weight percent of glycerol = x 100%

= 81%

Weight percent of starch = x 100%

= 9.5%

Weight percent of agar = x 100%

= 9.5 %

The calculation steps were repeated for samples A2, E1 and E2. The calculation result was recorded in Table 1.

Table 1: The weight percentage of samples composition

Sample

Distilled Water (mL)

Glycerol

Starch

Agar

Volume (mL)

Weight percent, %

Mass (g)

Weight percent, %

Mass (g)

Weight percent, %

A1

88

32

81

4.8

9.5

4.8

9.5

A2

88

32

89

0.0

0.0

4.8

11

E1

56

64

89

4.8

5.5

4.8

5.5

E2

56

64

94

0.0

0.0

4.8

6.0

Calculation for mechanical properties of samples:

For specimen A1:

Tensile strength

By referring at the result table,

Mean value =

= 0.477146

= 0.477 (3 significant figures)

Standard deviation =

=

= 0.7165

Standard deviation =

= 0.69926

= 0.699 (3 significant figures)

Elongation

By referring at result table,

Elongation percentage =

= tensile strain x 100%

Tensile strain

% Elongation

0.08094

8.094

0.07915

7.915

0.07330

7.330

0.09376

9.376

0.10052

10.052

Mean

= 8.5534

= 8.5 (2 significant figures)

Standard deviation =

=

= 74.168

Standard deviation =

= 1.00377

= 1.0 (2 significant figures)

Elastic modulus

By referring at the result table,

Elastic modulus = tensile stress/ tensile strain

Tensile stress

Tensile strain

Elastic modulus

0.11554

0.08094

1.4275

0.01769

0.07915

0.2235

1.86417

0.07330

25.432

0.09830

0.09376

1.0484

0.29003

0.10052

2.8853

Mean

= 6.20334

= 6.20 (3 significant figures)

Standard deviation =

=

= 131.6597

Standard deviation =

= 9.65289

= 9.65 (3 significant figures)

The calculation steps were repeated for samples A2, E1 and E2. The calculation result was recorded in Table 2.

Table 2: Mechanical properties testing samples

Samples

Tensile Strength(MPa)

Elongation (%)

Elastic Modulus(MPa)

Mean value

Standard Deviation

Mean value

Standard Deviation

Mean value

Standard Deviation

A1

0.477

0.699

8.5

1.0

6.20

9.65

A2

0.021

0.005

10

1.9

0.226

0.082

E1

0.361

0.321

6.4

2.3

6.71

5.39

E2

0.021

0.003

10

1.6

0.213

0.019

Discussion

From the table, the sample A1 and E1 show the higher tensile strength and elastic modulus. This is because sample A1 and E1 have large amount of starch in its composition. The starch is absent in sample A2 and E2 and thus result low tensile strength and elastic modulus in these two samples. The high bonding strength in the starch molecules enable the sample to sustain more tensile stress and thus result higher tensile strength. The increased tensile stress increases the elastic modulus (tensile stress/ tensile strain) and so for its stiffness.

Glycerol weakens the intermolecular forces within the sample and yields low tensile strength and also elastic modulus. Besides, glycerol enhances the elasticity of film and enables the film undergoes deformation easily. Thus, sample A2 and E2 elongate more among the samples due to the higher glycerol composition.

The agar functions in improving the film microstructure. The tensile strength was increased with the present of agar under high moisture environment. In comparison, the sample which contains agar in its constituent, results higher yield strength and thus for its elastic modulus. However, for the sample which agar is absent, the elasticity is greater and produces greater elongation. If agar was replaced by starch, the tensile strength will be decreased as agar has results greater tensile strength in samples rather than starch.

In this experiment, there are some problems has occurred. Most of the samples which used for mechanical properties testing are irregular in shape. This affects the initial measurement of sample’s thickness, length and width. Other than that, the presence of cracks in sample cause the sample breaks before reaching the limits. This leads to inaccurate tensile strength obtained.

Conclusion

The different composition in a sample affects its mechanical properties in different way.

The biopolymers application in biomedical field was developed in knowledge.

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