Effect of the Varying Percentage Diss Fiber on Mechanical Behaviour of the Based Polyester Bio-Composite

Currently the preservation of the environment and the use of renewable resources are the objectives to be achieved by all. The development of materials with renewable resources as reinforcement of composite materials are more and more used in several fields, in particular in industrial activities such as the automobile sector, textile, and furniture etc.

The mechanical properties of composite materials reinforced with vegetable fibers depend on several factors of which we quote: the fiber dosage i.e., the rate of fiber in the material, the length and orientation of these fibers. Several works have supported the use of plant fibers in organic matrices (thermoplastic, thermosetting) or in cement matrices, citing us: Diss [1, 2], Alfa [3], Kenaf [4-6], Lin [7, 8], Jute [9], Date palm [10, 11], Agave [12, 13], Pineapple Leaf [14, 15] Sisal [16].

Nouri et al. [17] in their work show that the Diss fiber bundles with slight diameter and rough surface with the presence of thorns and with low density shows a tensile strength that can reach 270 MPa. They also demonstrate that all the treatments adopted has demonstrated improvements regarding the fibrillation of fiber bundles, their surface state, their thermal stability and practically their mechanical behavior (could reach +60% for Young’s modulus and +15% for tensile stress).

Sarasini et al. [18] In their work investigating about the morphology, the thermal, and mechanical properties of the Diss fibers by using an experimental process covering mechanical aspects, mild chemical, and enzymatic steps. They confirm that the structure of Diss fibres make them suitable as a reinforcing filler in polymer composites, which was assessed by manufacturing bio composites with improved stiffness and a tensile strength.

Ashok et al. [19] in their investigation have showed that the addition of nanofiller of Luffa could enhance the mechanical strength of the natural fiber composite.

Salem et al. [20], had studied the mechanical behaviour of Reinforced Alfa fibber with high density polyethylene composites strength by the tensile they showed that the tensile strength of the composites increased with the quantity of fiber in the composite.

Djoudi et al. [21] in their study related to the physical and mechanical characterizations of bio composite materials based on palm fibers, they have found that tensile strength tests of the bio composite material with different fiber percentages (04, 07, 10 and 15%) shows an improvement in the mechanical properties of the virgin resin proportional to the fiber mass ratio up to 10% while a degradation of these properties is detected for a fiber mass ratio of 15%.

Nciri et al. [22] shows that when the polypropylene matrix is reinforced by the addition of short alfa fibers in the range of 05 and 15% by injection process, they found that composite behavior is sensitive to the strain rate, they also found that anisotropy increase when increasing fiber.

The problems related to the fiber / polyester interface because of the amorphous materials that the surface of the fiber contains are reduced by the different treatments, in our case study we used the alkaline treatment (with NaOH) and consequently an improvement in the mechanical characteristics of the composite material is manifested.

3.1 Observations to the scanning electronic microscope

The samples of the different fibers are observed with the ESM (Figure 2) after metallization to make their surfaces conductive (Figure 1), the use of this distinction leads to deducing the morphology and the measurements of the fibers.

5a.png

(a)

5b.png

(a')

Figure 5. (a, a’) SEM micrograph in longitudinal view of Diss fiber in its raw state

6a.png

(b)

6b.png

(b')

Figure 6. (b b’) SEM micrograph in longitudinal view of Diss fiber after treatment with NaOH

7.png

Figure 7. SEM micrograph transverse view of Diss fiber in its raw state

8.png

Figure 8. SEM micrograph transverse view of Diss fiber after treatment with NaOH

Figures 5 to 8 Illustrate the difference between Diss fibers in their raw and processed states. The surfaces of the raw fibers are smooth because of the wax and cellulosic component, on the other hand the treated fibers have rough surfaces of snakeskin.

The figure a 'and b' are exposed to justify the measurements of the diameters of the fibers.

3.2 Traction test

The traction test is the most used for the characterization of materials to deduce their mechanical parameters, this test consists in subjecting a specimen to a unidirectional traction force until failure.

This test allows to study in detail the influence of the additions of fibers to the matrix and to observe the evolution of the mechanical characteristics of the bio-composite material.

3.2.1 Production of test Specimens

The traction specimens are cut according to the ISO 527-2 B1 standard (Figures 9, 10 and 11), these specimens have different volume fraction as a percentage of fibers. The specimens are on average six specimens for each type of test.

9.png

Figure 9. Tensile specimens in Polyester resin

10.png

Figure 10. Tensile specimens reinforced with 05% untreated Diss fiber

11.png

Figure 11. Tensile specimens reinforced with 05% treated Diss fiber

12.png

Figure 12. Stress-strain curve of the resin and at 20% of treated and untreated Diss fibers

13.png

Figure 13. Variation of the stress at break as a function of the fiber rate of Diss

The stress-strain curves of (Figure 12) represent an example of the results obtained from the tensile test on the reference specimen (Polyester resin) and two specimens with a volume content of 20% of fibers of Diss treated and untreated (Figures 13, 14).

14.png

Figure 14. Variation of the Young's modulus E as a function of the fiber rate of Diss (from 0% to 20%)

Note: Given the decrease in the value of Young's modulus for the range of (15% - 20%), which presents a degradation of the matrix’s material, we limit the study to the range of the volume fraction (from 0% to 15%) (Figure 15).

15.png

Figure 15. Variation of the Young's modulus E as a function of the fiber rate of Diss (0% -15%)

3.3 Hardness test

The hardness tests are made to know some properties of the material such as its ductility and resistance to penetration. They are carried out by an HBRV-187,5 Hardness Tester (Figure 4). These tests are carried out for test pieces with different percentage of Diss fiber content in their raw and processed states. Four specimens for each type of material are tested. Six measurements are taken for each specimen, therefore 26 readings for the same specimen. Brinell hardness value is given by predefined tables (Tables 1 and 2) after calculating the product of the difference in reading on the microscope multiplied by the amplification coefficient of the microscope.

$\mathrm{L}=\left(\mathrm{L}_{\mathrm{MAX}}-\mathrm{L}_{\mathrm{MIN}}\right) \mathrm{I} \rightarrow \mathrm{HB}$      (1)

I=0.004 when the objective is 2.5x.

I =0.002 when the objective is 5x.

We can also calculate the Brinell hardness by the following expression:

$\mathrm{HB}=\frac{2 \mathrm{f}}{\pi \mathrm{D}\left(\mathrm{D}-\sqrt{\mathrm{D}^{2}}-\mathrm{d}^{2}\right)} 0,102$     （2）

Table 1. Brinell hardness values for a specimen at a rate of 20% of Diss fibers

Table 2. Average values of hardness for each type of specimen

The two Figures 13 and 14 show that the density fractions increase of diss fibers in the polyester matrix improves the strength and modulus of elasticity.

Concerning the hardness testing, by analyzing the measurements of the various tests carried out, we can say that on average the hardness values increase as a function of the volume rates of the Diss fibers (Figure 16), this increase is linked to the hardness of the fibers. It is also noted that the values of the Brinell hardness are not stable for the simple reason that the indentor sinking depends on the contact zone. These values vary depending on whether the fiber is very near or far from the pressure zone. Because the fiber of Diss is considered more rigid and therefore opposes the indenter. The hardness is stable around 19 HB for the resin, on the other hand there is a high probability of having values greater than 25 HB and a low probability of having values below 25 HB for a volume fraction of fiber greater than 20%. On the contrary, there is a high probability of having values of about 20 HB and a low probability of having values greater than 25 HB for volume fractions of less than 10%.

The evolution of the Brinell hardness values as a function of the elastic limit and the evolution of these same values as a function of Young’s modulus are proportional and in agreement (Figure 17) and (Figure 18).

16.png

Figure 16. Change in Brinell hardness with volume fraction of Diss fibers

17.png

Figure 17. Evolution of Brinell hardness and elastic limit

18.png

Figure 18. Evolution of Brinell hardness and Young's Modulus