Mechanical Properties and Morphology of Crystalline Polymers and Their Continuous Fiber Composites

Abstract

The morphology, microstructure and mechanical properties of a model crystalline thermoplastic (PP), its rubber toughened versions, and their corresponding continuous fiber composites were investigated. Adding a rubbery phase in a PP matrix results in a less regular spherulite texture with less sharp spherulite boundaries. The average spherulite dimensions have not been reduced appreciably. The rubber particles are found to be uni formly dispersed in the PP matrix and their sizes increase with an increased weight frac tion of rubber. "Transcrystalline" regions can be found with those thin PP specimens con taining a low fraction of glass fibers. Delamination is the dominant failure mode in PP-fiber composite subjected to low-velocity impact. The maximum load tolerated by the laminates just prior to delamination appears to be controlled by the resin yield strength and the fiber-matrix interfacial adhesion. The magnitudes of the residual thermal stresses have been estimated and are found to decrease with increasing end-use (or test) tempera ture. No evidence of crazing can be found in fiber-PP composites. A much lesser degree of stress whitening phenomenon was observed in glass fiber reinforced rubber-modified PP than in their unreinforced counterparts. A toughness increase of PP matrix using the technique of rubber modifications did not necessarily lead to an improvement in impact re sistance of fiber composite. In general, the matrix toughness and composite impact prop erties cannot be definitively correlated for this model group of continuous fiber reinforced thermoplastics.