Property Evaluation of Hybrid OPEBF/Banana/Glass Fiber Reinforced Unsaturated Polyester Composites

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Figure 2. Palm oil empty fruit fiber grinded to fine powder

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Extraction and chemical treatment of the empty bunch banana fiber

The fiber from the banana bunch (Figure 3) was extracted manually. The banana fibers (Figure 4) were washed using a clean tap water and sundried subsequently. Distilled water containing 6% NaOH was prepared. The sundried fibers were soaked in the NaOH solution for 4 hours 30 minutes. Thereafter, the fibers were removed and washed in running water and dried for 7 hours before it was used in the fabrication of the composite.

Figure 3. Banana empty fruit bunch

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Figure 4. Banana empty fruit bunch fiber

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Table 1. Sample Designation for the OPEFB -Banana-Glass Fiber Reinforced Polyester Based Composite

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Tables index

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Table 1 shows the composition used in the manufacture of the composite.

The composite with fiber loadings of 5%, 10%, 15% and 20% volume fraction were fabricated using hand layup technique with a mould size of 120mm (length), 15mm (width) and 5mm (thickness). Releasing agent (Vaseline) was smeared at the bottom and walls of the mould to allow easy removal of the composite. Thereafter, the calculated quantity of polyester resin, methyl ethyl ketone (catalyst) and cobalt naphthalene (accelerator) were added and the mixture was stirred manually for about 5minutes to create a homogeneous mixture. The chopped strand fibers were then impregnated with the matrix in a randomly distributed manner. The mixture was poured into the mould and rammed mildly for uniform settlement. Other samples were moulded using the composition presented in Table 1. A dead weight weighing about 20kg was placed on the mould to increase the compactness of the samples. The samples was removed from the mould after three hours and allowed to cure.

2.4. Physical Properties Test

The physical properties tested on the samples were as follows:

Density

The density of the composite was determined using the relationship below:

Where,

m= mass the fiber specimen (g)

v= volume of the fiber specimen (cm³)

The masses, m, of the fibers were determined to the nearest 0.001g by using the Mettler Electronic top pan balance. The volume, of each fiber specimen was calculated by percentage mass of the total specimen mass.

Water Absorption test

The water absorption of the composite was determined using the relationship below:

Where:

w₀= the weight of the specimen before immersion,

w₁ = the weight of the specimen 8hrs after immersion in water.

2.5. Mechanical Properties
Hardness test

The hardness test was carried out to measure the degree to which the material resists scratch, cutting, or indentation.

Figure 5. Hardness Test specimens

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Figure 6. Micro Vickers Hardness Tester

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The samples used for the hardness test is shown in Figure 5 A piece was cut from each sample and was placed on the machine; the hardness test was carried out at three different spots on each sample. The test was taken on two different points on each sample and the average hardness of the points was recorded using the micro Vickers hardness tester presented in Figure 6.

Tensile Test

The tensile test was performed on flat specimens. The dimension of the specimen was 120mm × 15mm × 5mm and a uniaxial load was applied on both ends. The ASTM standard test method for tensile properties of fiber resin composites has the designation D 3039-76. In the present work, this test was performed using the Hounsfield Tensometer (Figure 7) at a crosshead speed of 5 mm/min and the results were used to calculate the tensile strength of composite samples presented in Figure 8. The loading arrangement is shown in Figure. Here, the test was repeated three times on each composite type and the mean value was reported as the tensile strength of that composite.

Figure 7. Hounsfield Tensometer

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Figure 8. Tensile Test specimens

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The tensile strength and tensile modulus were expressed as:

(1)

(2)

where,

P = pulling force (N)

b=specimen width(mm)

h= specimen thickness (mm)

=stress (N/mm²), = strain

Flexural Test

The flexural strength of a composite is the maximum tensile stress that it can withstand during bending (Figure 9) before reaching the breaking point. The three point bend test was conducted on all the composite samples according to ASTM D790 in the universal testing machine at a constant rate of 2mm/min. The dimension of each specimen was 120mm × 15mm × 5mm. Span length of 100mm are maintained. For both flexural strength and flexural modulus, the test was repeated three times for each composite type and the mean value was reported.

The flexural strength and flexural modulus were calculated using the following equations.

(3)

(4)

Where,

P = maximum load applied on test specimen (N)

L = sport span (mm)

B = width of specimen tested (mm)

H = thickness of specimen tested (mm)

m = slope of tangent to the initial straight line portion of load deflection curve (N/mm)

Figure 9. Flexural testing machine

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Impact Test

The test was conducted in accordance with ASTM D 256 using Avery Denison test machine (Figure 10). Charpy impact tests were conducted on notched samples. Low velocity instrumented impact tests were carried out on the composite specimens. Standard un-notched rectangular impact test sample of measuring 120mm × 15mm × 5mm were used. Before the test samples were tested, the machine was calibrated. The test samples were then gripped horizontally in a vice and the force required to break the bar was released from the freely swinging pendulum. The value of the angle through which the pendulum has swung before the test sample was broken corresponded with the value of the energy absorbed in breaking the sample (Figure 11) and this was read from the calibrated scale on the machine.

Figure 10. Impact testing machine

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Figure 11. Impact Test Specimens

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(5)

Where,

J = Energy absorbed (J)

A= Area of cross section of the specimen (m²)

(b) Loading arrangement for tensile test

(a) Avery Denison test machine.

3. Results and Discussion

3.1. Density

Figure 12 shows the densities of the samples. It was found that Banana fiber 15%/Glass fiber 5% and Banana Fiber 20% had densities of 1.5123g/cm³ and 1.5333g/cm³, respectively. The density of glass fiber is more than the density of banana fiber. However, the banana fiber has more affinity to water molecules than glass fiber hence, the possible reason for the variation in densities. Their increase in densities is as a result of increase in water absorption and the inherent properties of the composite ingredients. The result also shows that the density of the samples increased significantly with increase in banana fiber.

3.2. Water Absorption

Figure 13 shows the percentage water absorption of the samples. It was found that Banana fiber15%/Glass fiber 5% had 4.19% water absorption and this was closely followed by banana fiber 20% with water absorption on 4.12%. As earlier asserted the figure shows that there was an increase in water absorption rate with increase in banana fiber. Hence, when the composite is exposed to moisture, the banana fiber composite might swell up a bit. The swelling could lead to the formation of micro cracking in the composite. As the absorption increases, the crack increases, eventually, capillarity and transport via micro cracks becomes active and water molecule flow along the fiber matric interfaces. This could eventually result in weakening the strength of the fiber and matrix.

Figure 12. Density Test Values for banana and glass fiber polyester composite

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Figure 13. Water absorption Test Values for banana and glass fiber polyester composite

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Figure 14. Hardness Test Values for banana and glass fiber polyester composite

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3.3. Hardness

Figure 14 shows the mean hardness values of the specimens. The hardness of the samples was influenced by a considerable increase in banana fiber content in the composite. For instance, it was found that banana fiber15%/glass fiber 5% hybrid composite has the highest hardness (3.55HV representing 136.67% improvement on the hardness of the polyester (1.5HV). The improvement in the hardness of the composite material could lead to reduction in wear rate when in service. A careful examination of the results shows that banana-glass hybrid composite showed better hardness than composite that consisted individually of banana fiber and glass fiber with a constant percentage of OPEFB.

3.4. Impact Strength

The impact strength of a material is the measure of the amount of energy which the material can absorb before its failure. The impact test was therefore carried out in order to analyse the impact strength of the specimens. From Figure 15, the relationship between the average energy and impact strength of the composites is clearly shown. Banana10%Glass10% hybrid composite has the highest impact strength (55.556 J/m²), which was followed by Glass15%Banana5% with impact strength of 24.556 J/m². This value was greatly influenced by the percentage of glass fiber in the composite because of its toughness; glass fiber has a higher resistance to impact force. In parts where high impact strength is required the exploitation of 50:50 mixtures of hybrid banana fiber and glass fiber could be considered. This will lead to the utilization of more environmentally friendly and sustainable materials such as banana fiber.

Figure 15. Impact Test Values for banana and glass fiber polyester composite

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3.5. Flexural Strength

Figure 16 shows the mean loading and flexural strength values for the various composites. It could be seen that the Banana fiber 20% with 5% OPEFB composites presented the lowest flexural strength of 18.51Mpa before failure, while banana fiber5%/Glass fiber15% had 44.84Mpa before failure composites showed the highest results and, is closely followed by Glassfiber20% with 36.72Mpa. It was observed that as the banana fiber content increased there was a decline in the flexural strength. However, increasing the glass fiber content resulted in corresponding increase in flexural strength. Under flexural loading, the upper and lower surfaces of the specimen are subjected to higher deformation than the mid-plane. Therefore, flexural strength and stiffness depends on the properties of the surface layers. Therefore, glass fiber has greater flexural strength than banana fiber.

Figure 16. Flexural Test Values for banana and glass fiber polyester composite

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3.6. Tensile Strength

The tensile property of the unreinforced specimen sample was 15.05 MPa. Figure 17 shows the extension, strain and tensile strength of the specimens. Glass fiber had the highest extension, strain and tensile strength of 6.72mm, 0.056J and 24.66MN/mm²(77.14% improvement over the virgin polyester tensile strength), respectively. This was closely followed by Banana fiber 5%/Glass fiber15% hybrid composite with extension, strain and tensile strength of 6.5mm, 0.055J and 24.35MN/mm² (61.79% improvement over the virgin polyester tensile strength), respectively. The tensile strength of the composite depends to a large extent on the interfacial bonding strength between the matrix, reinforcement and fillers and also on the inherent properties of the composite ingredients. Improvement in tensile strength of composite helps the composite to withstand more tensile forces when they are in service. Also, materials with more strain are likely to fail safe in service.

Figure 17. Tensile Test Values for banana and glass fiber polyester composite

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