Thermal and Dimensional Stability of Injection-Molded Sisal-Glass Fiber Hybrid PP Biocomposites

This article reports on the thermal and dimensional stability of sisal-glass fiber hybrid biocomposites with 30% fiber (wt%) reinforcement in polypropylene (PP) matrix. Hybrid-fiber effect on thermal properties such as specific heat (Cp), melting and crystallization behavior, thermal degradation and dimensional properties such as water absorption and volumetric coefficient of thermal expansion (CTE) was studied. Hybrid biocomposites showed a decrease in specific heat capacity, % crystallinity and thermal degradation at 210 °C (<0.4 wt%). The analysis of heating and cooling rates (5, 10, 15 °C/min) on crystallization kinetics of hybrid biocomposites showed no significant influence of on melting and crystallization enthalpies. Comparison of injection and extrusion process exhibited increased % crystallinity and fiber attrition in hybrid biocomposites after injection molding. Compared to sisal fibers, degradation in glass fiber length was 18.5 and 15% higher after extrusion and injection molding respectively. Difference in derivative thermograms (DTG) peaks after injection and extrusion process were within 2–3% suggesting the uniform distribution of fibers in PP. On the dimensional stability, hybrid biocomposites showed significant improvement (<0.3 wt%) in water absorption and CTE properties at sub-zero (30 to −30 °C) temperature.