Properties Enhancement of Short-Glass-Fiber Reinforced Thermoplastics by Sandwich Injection Molding Technique

Abstract

This article demonstrates the possibility of using sandwich injection molding in order to improve the mechanical properties of short-glass-fiber-reinforced thermoplastic by investigating the effect of fiber orientation, compared with conventional injection molding. The effects of short-glass-fiber content within skin and core materials, in the present case PP, varying from 0 to 40 wt % were studied. The results showed an increase in the maximum tensile stress and impact strength as the concentration of the shortglass-fiber was increased. The mechanical properties of sandwich moldings were observed to be slightly higher than conventional injection moldings, which is attributed to the higher fiber orientation and lesser voids within the core layer. The effect of different processing types on the phase distribution of shortglass-fibers showed no significant phase separation effects between sandwich and conventional injection molding processes, except when using of sandwich injection process with different materials. The results obtained by analyzing the fiber attrition inside the skin and core regions in the longitude direction of tensile specimens showed that the degree of fiber degradation inside the skin layers were higher than the core layers and there are only minor differences in fiber length inside skin regions observed between sandwich and conventional injection molding processes, whilst this effect being more pronounced in the core regions and for the higher fiber volume fraction. The theoretically calculated values of the ultimate tensile stress (UTS) were found to be considerably higher than the experimental values. However, a more realistic estimation of UTS can be achieved by using measured values for fiber length within skin and core layers.