Effect of extrusion compounding on the mechanical properties of rubber-toughened polymers containing short glass fibers

The composites fabricated are rubber-toughened nylon 6,6 containing short glass fibers at 0, 10, 20, 30 and 40 wt.%. The materials were dry mixed prior to injection molding and extrusion compounding. Results showed that the composites under one-step injection molding sufficed to provide superior strengthening and toughening for the toughened matrix. Fracture toughness of the composites was rigorously determined using the concept of essential work of fracture (EWF). It was shown that the specific essential fracture work of the composites containing 10 wt.% fibers increased 2-fold in comparison to that of the rubber-toughened matrix without fiber reinforcements. The tensile strength and modulus increased following a linear additive behavior. The predominant failure mechanisms appeared to be fiber bridging followed by fiber pull-out in the composites, whereas extensive geometry-dependent plastic deformation prevailed in the unreinforced rubber-toughened nylon. The enhancement in fracture toughness arising from fiber bridging was best served by processing in one-step injection molding because the original fiber lengths could be best preserved in a one-step process versus severe thermomechanical degradation in extrusion compounding. The important findings in this study appeared contrary to the notion that when both rubber and short glass fibers are added, the fracture toughness of nylon 6,6 is decreased.