Molding behaviour and microstructure of injection molded short glass fiber reinforced polypropylene composites

Injection molded Short Glass Fiber Reinforced Thermoplastics (SFRTP) are widely used in industry because of advantages in material properties, availability, economics and ease of processing. The thermo-mechanical history experienced by the material during processing produces significantly anisotropic microstructural and consequently mechanical properties, varying not only spatially, but directionally.This work attempts to examine quantitatively various aspects of microstructure and the effect of processing conditions in SFRTP. The matrix phase properties, such as crystallinity, morphology and molecular orientation distribution, as well as the fiber phase microstructure such as concentration, length and orientation distributions have been analyzed quantitatively, and explained. Experimental techniques, including optical and electron microscopy, differential scanning calorimetry, Fourier transform infrared spectroscopy, thermo-gravimetric analysis, etc. have been used. The results indicate complex changes in microstructure from skin to core in the injection molded samples. Both matrix and fiber phase microstructures are affected by the basic thermal and flow processes that occur during the injection molding process. A first order model has been developed to predict fiber orientation distributions, which agree well with the experimental results