OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 3 2024 2 3 , 2 FL wd σ = u (2) where F is the maximum force applied; L is the length of the sample; w is the width of the sample; d is the depth of the sample. Table 6 shows the average flexural strength of four composite specimens made Sida cordifolia reinforced with jute fiber with biodegradable PLA polymer as the matrix. To optimize the performance of a hybrid composite made from jute, PLA and Sida cordifolia fibers, several parameters need to be carefully considered. – Uniform temperature distribution within composite materials to reduce internal stresses and prevent thermal cracking during moulding. Analysis of the effects of different preheating temperatures and durations on PLA viscosity and natural fiber integrity can provide insight into the optimal processing conditions that minimize fiber damage and improve the mechanical properties of the composite. To ensure good wetting and bonding, complete melting of PLA and proper flow around jute and Sida cordifolia fibers should be achieved. It is very important to adjust the mold temperature to ensure uniform flow of PLA without destroying the natural fibers. A balance should be found where the temperature is high enough to ensure PLA flow, but low enough to prevent thermal degradation of jute and Sida cordifolia fibers. – Proper compression of composites to reduce voids and improve fiber-matrix adhesion. The applied load (as listed in Table 4) should be optimized depending on the composite thickness and fiber arrangement. Increasing the load can help achieve better compaction and homogeneity. The time under load, especially at high temperatures, should be minimized to prevent thermal degradation. This will allow the PLA matrix to solidify under pressure, ensuring good mechanical bonding and adhesion between the matrix and fibers. Cooling rate and curing pressure are critical; too rapid cooling can cause residual stresses, while insufficient pressure can lead to delamination or void formation. Optimizing these parameters can improve the dimensional stability and mechanical properties of the composite. – Uniform distribution of fibers within the matrix and between the layers of the composite to ensure isotropic properties. It is important to control the weight and distribution of each layer (as shown in Table 5) to optimize the mechanical properties. The increase in the amount of treated Sida cordifolia fibers in subsequent specimens suggests that a strategy was developed to improve certain mechanical properties such as tensile strength and flexural strength. Adhesion between the fibers and the PLA matrix is improved for effective stress transfer. For a visual presentation of the results obtained, the data from the table are graphically presented in Figures 4 and 5. Figure 4 shows the peak loads obtained for different samples of 4 specimens: – the first specimen with four layers of jute (94 g) and PLA matrix (160 g) used to make the composite achieved a tensile strength of 27.029 MPa; – the second specimen with four layers of jute (92.5 g), untreated Sida cordifolia fibers (12 g) and PLA matrix (160 g) achieved a tensile strength of 25.0844 MPa; – the third specimen with four layers of jute (92.5 g), treated Sida cordifolia fibers (12 g) and PLA matrix (160 g) achieved a tensile strength of 32.297 MPa; – the fourth specimen with four layers of jute (89.5 g) treated Sida cordifolia fibres (15 g) and PLA matrix (160 g) achieved a tensile strength of 43.658 MPa. According to the obtained results, the weight of Sida cordifolia fibers increased with a decrease in the weight of jute fiber; keeping weight fraction constant the tensile strength of the composite increased to an optimal value. The use of untreated Sida cordifolia fibers shows low tensile strength compared to treated Sida cordifolia stem fibers. Figure 5 shows the peak loads obtained for different samples from 4 specimens: – the first specimen with four layers of jute (94 g) and PLA matrix (160 g) used to make the composite achieved a flexural strength of 3.326 MPa; – the second specimen with four layers of jute (92.5 g), untreated Sida cordifolia fibers (12 g) and PLA matrix (160 g) achieved a flexural strength of 3.290 MPa;
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