The fibers of the papaya tree trunks are obtained in a long process as shown in Figure 1.

We used the male papaya trees after the second flowering. The papaya tree trunks were cut into 40 cm long pieces, then cut longitudinally. The elements thus acquired were soaked in water without additive for a period of one month as shown in Figure 2. The extraction of our papaya trunk fibers is done by retting as shown in Figures 2(c) and Figure 3 [10].

The folds thus obtained were immersed in hot water (70˚C) mixed with a molar concentration sodium hydroxide for two days then we extract the fibers. Figure 3 shows the process for obtaining papaya fibers.

The cores obtained are illustrated by Figure 4.

The kernels of the pili fruit are crushed in order to extract the fines. The empty cores are grounded and sieved with 800 μm and 1.60 mm sieves (Figure 5) to obtain the corresponding particles (Figure 6) [10] [11].

The particle sizes obtained are as follows ≤ 800 µm (fine particles) and ≤1.60 mm (large particles) as shown in Figure 6.

The samples with reinforced rate of 30% are used because it the composite exhibits poor characteristics [12]. Table 1 gives the dimensions and the proportions of the elements used the polyester resin is mixed with 1% hardener [11].

The test pieces shaped according to standard BSI 2782 are parallelepipedic block of 150 × 10 × 10 (mm). The main steps in shaping our test pieces are given in Figure 7.

The samples obtained and classified by type of reinforcement are shown in Figure 8.

To determine the density of our composite material, we calculate the apparent density for each of the samples using Equation (1).

ρ a = P r v r (1)

with: ρ a : apparent density; P r : mass of reinforcement; v r : the reinforcement volume.

For each formulation, the experimental density of the composite is obtained by averaging Equation (2) for each test piece [13].

ρ exp = P e Δ v − m p ρ p (2)

with: ρ exp : experimental density; P e : mass of test piece; m p : paraffin mass; ρ p : paraffin density; Δ v variation of water volume.

Finally, the analytical density of the composite material ρ a n (in Kg/m³) of each sample for each formulation was determined using Equation (3)

ρ a n = ρ r V r + ρ m V m (3)

The densities of the reinforcements are ρ r = 1125 Kg/m³, the density of the matrix is ρ m = 1140 Kg/m³; V r : volume fraction of reinforcements; V m : volume fraction of matrix; ρ m : analytical density (Table 2, Figures 9-11).

From these histograms, it appears that the density of the papaya fiber-reinforced composites is comprised/varies between [1047.5; 1062 Kg/m³] the addition of papaya trunk fiber to the polyester reduces the density of the latter and for composites with particle reinforcement of the kernels of fruit of the wing is between [1240.5; 1346 Kg/m³] the addition of black fruit kernel particles in the polyester increases the density value of the latter. In addition, the length of the fibers (long or short) and the particle size of the kernels of fruit of the pili have a negligible influence of the order of on the density (of the order of 0.02% to 0.05% for the composites with reinforcement of fibers of trunk of papaya and of the order of 0.08% to 0.09%).

The amounts of water absorbed by our composite materials reinforced with papaya trunk fibers and particles of the seeds of the garlic shown by Figure 12 are determined by Equation (4).

% H = M o − M f M o × 100 (4)

The water absorption curves of the various composites reinforced with papaya trunk fibers (long and short) and particles of the seeds of the winged fruit (large and fine) are similar to room temperature, the one given by Fick’s law of diffusion in a binary medium [14]. The following observations are made:

• For composites with particle reinforcement of the kernels of garlic, the particle size does not influence the rate of water infiltration.

• In the case of composites with a reinforcement of trunk fibers from papaya trees, the longer the fibers, the less water the material takes up.

• Composites with short fiber reinforcement take more water than composites with particles of garlic kernels which absorb more than those with long fiber reinforcement.

The samples for each formulation are submitted to compression test carried out with a PERRIER 14570 200 KN. Equation (5) is used to determine the Young Modulus/the elasticity modulus [7] [11] [15] [16].

E = F L 0 S 0 Δ L (5)

The comparative study of the average values of the Young’s moduli obtained during the compression test helped us to plot the histogram of Figure 13.

From Figure 13 we see that:

• The Young’s modulus of long fiber reinforced composites is greater than that of short fibers.

• The length of the fibers influences the mechanical behavior of the composites, composites with long fiber reinforcements have better behavior in the elastic range compared to those with short fiber reinforcement.

• The Young’s modulus of fine particle reinforcement composites is greater than that of medium black fruit core particles. The mechanical characteristics of composites with reinforcement of black fruit kernel particles fluctuate with the particle size distribution (of the interstices in the material).

• Reducing the particle size of the particles improves their behavior in the elastic range.

The three points bending test is carried out using a CBR press (CONTROLS T1004) and Equation (6) and Equation (7) enable us to determine the modulus

of elasticity in bending (MEF) and modulus of resistance to bending (MRF) respectively [8] [11] [17] [18].

MEF = α L 3 4 b e 3 (MPa) (6)

MRF = 3 L F R u p 2 b e 2 (MPa) (7)

with: L: distance between supports; b: width of the test piece; e: thickness of the test piece; α: slope of the straight line determined by the plot of the force-deformation curve in the elastic domain; F R u p : force measured at break.

The results are presented in Table 3.

The comparative study of flexural elasticity modules (FEM) and flexural resistance modules (FRM) of fiber and particle reinforced composites is given in Figure 14 and Figure 15 respectively [11] [19] [20].

These histograms reveal that:

· The elastic modulus of flexion does not vary with the size or the type of reinforcement because the difference between the different values of modules is minimal;

· The multidirectional nature of composites with short fiber reinforcement gives it a modulus of flexural strength significantly higher than the composites one with long fiber reinforcement (report 1.27);

· The resistance modulus of composites with fine particle reinforcement (≤800 µm) is 2.27 times higher than the composites with medium particle reinforcement (≥1.6 mm). This difference may be caused by the particle size and the presence of a gap in large-particle composites which is not completely homogenized with the resin.