Recycling of poly(propylene)-based car bumpers as carrier resin for short glass fiber composites

Abstract

The production of composite materials from post-consumer polypropylene car bumper waste (PP-CBW) and short glass fibers (SGF) by melt processing was investigated during this study. To improve the interfacial adhesion between the fibers and the matrix, two coupling agents maleic anhydride-grafted linear low-density polyethylene (LLDPE-g-MA) and Retain were introduced during the compounding process. The effect of various SGF loadings, types of coupling agents, SGF to coupling agent ratio and short glass fiber length on thermal, physical and mechanical properties were thoroughly investigated during this study. Differential scanning calorimetry (DSC) analysis indicated significant changes in the crystallization temperature (Tc) and percentage crystallinity (Xc) when the SGF content and length were modified. It was deduced also from thermal analysis that using LLDPE-g-MA as a coupling agent increases the nucleating role of the SGF by effectively distributing the fibers inside the matrix. The average length (Lave) was found to decrease with increasing the SGF loading. On the other hand, Lave values increased with the original glass fiber length and when a SGF/LLDPE-g-Ma ratio of 5:1 was used compared to the ratio 3:1. The incorporation of SGF improved drastically the flexural and the tensile properties but decreased the impact properties. The impact properties improved when a ratio of SGF/LLDPE-g-MA of 3:1 was used. However, the flexural modulus was reduced and no significant effect was observed on the tensile and flexural strength. Mechanical results showed also that the LLDPE-g-MA is a better compatibilizer than Retain for stiffness and strength, whereas Retain composites resulted in higher impact properties than LLDPE-g-MA composites. Stiffness decreased when fiber length increased from 6 to 12 mm and the same tendency was observed for tensile and flexural strength denoting that poor fiber dispersion and distribution was achieved for high fiber length. The scanning electron microscopy (SEM) results revealed that SGFs are evenly distributed in PP-CBW matrices, and no distinct voids appear between these two materials, indicating a good interfacial adhesion.