Mechanical properties prediction of polypropylene/short coir fibers composites using a self‐consistent approach

Abstract

Short coir fibers composite of thermoplastic polypropylene (PP) matrix was successfully prepared by using a twin‐screw extruder and an injection molding machine. In order to provide a better understanding of the effect of fiber orientation and concentration (2.5, 5, and 10 wt%) on the mechanical properties of short coir fibers reinforced PP, a self‐consistent approach was developed based on a modified Hirsch model by taking the empirical parameter (x) proportionally to the fiber orientation factor (α). Finally, the results are compared with other models (Hirsch and Tsai‐Pagano) and validated with experimental data. Overall, our approach was found to better predict the mechanical results in terms of Young's modulus, tensile strength and torsion modulus. POLYM. COMPOS., 40:1919–1929, 2019. © 2018 Society of Plastics Engineers

Injection molding of short fiber thermoplastic bio-composites: Prediction of the fiber orientation

“…22 For a rectangular mold (Figure 3(a)), once the melt comes in contact with the cold mold surfaces, a frozen layer is immediately formed along the mold walls leading the converging flow to flow-align fibers, while the diverging flow in the central zone tend to align the fibers perpendicularly. 6,22 On the other hand, the stretching (diverging) flow is highly significant near the gate in a circular mold (Figure 3(b)). Consequently, this shearing/stretching nature of the flow tend to align the fibers transversely near the mid-plane and along the circumferential direction close to the mold surfaces.…”

“…Since extrusion and injection process are known to mechanically degrade the fibers length, the obtained average lengths are 2.25 mm and 2.00 mm for the coir and cactus fibers, respectively (Figure 2(a’) and (b’)). Effectively, in our previous work 6 to evaluate the extrusion process effect on coir fiber length, some parts (100 mm) of the compounds coming out of the extruder were laid side by side, then pressed together using an automatic hot press (Carver Inc., USA). After that the fiber length was measured to conclude that an average length of 4.55mm after grinding/sieving, the extrusion reduced the fibers length by half to get an average of 2.50 mm.…”

“…The short fibers are then frozen into the matrix, and this anisotropic flow-induced fiber orientation becomes a key feature of the finished product anisotropic performance. 6–9 However, it is very difficult to predict the fiber orientation state during the molding process because the physical mechanisms that orient the fibers are not yet fully understood. 10,11 For example, the flow of fiber filled thermoplastics in the molten state is modified by the presence of fibers while the fiber motion and rotation is affected by the flow.…”

“…19 However according to Pontes et al., 20 no complete theory is available to predict the fiber orientation distribution resulting from the injection molding process. 6,20…”

Injection molding of short coir fiber polypropylene biocomposites: Prediction of the mold filling phase

“…Injection molding represents one of the most important process to manufacture plastic parts, especially for complex geometries because of its high productivity, high precision and low cost . For a specific injection molding machine, thermoplastic resin and mold, the process can be decomposed into three distinct stages: filling, postfilling, and cooling .…”