Reduced fibre breakage in a glass-fibre reinforced thermoplastic through foaming

The processing of a glass fibre-reinforced polypropylene in the presence of a chemical blowing agent was found to dramatically reduce the occurrence of fibre breakage during processing within an injection molding machine. As the concentration of chemical blowing agent was increased from 0 to 5wt%, the fibre length distribution of the reinforcing agent more closely resembled the original distribution found in the virgin resin. An in-line rheometer was used on the injection molding machine to characterize the melt rheology of the polypropylene composite with and without the blowing agent. The results showed that the plasticizing effect of the dissolved gas affected both the magnitude of the shear viscosity as well as the pseudoplasticity of the material. It was revealed that the greater non-Newtonian flow behaviour of the polymer as the blowing agent concentration was increased, reduced the quantity of glass fibres exposed to shear flow. The reduction in fibre rotation as a result of the decreased shear region present within the flow field, decreased the occurrence of fibre breakage due to buckling and tensile fracture.