Semi-crystalline thermoplastic polymers are being used increasingly as matrices in high performance fiber reinforced composites. The crystallization kinetics and morphology of these polymers have been studied extensively, but relatively little attention has been given to the effects of the reinforcing fibers on the crystallization process.
We have studied the effects of glass, carbon and aramid fibers on the rates of crystallization, the degree of crystallinity, and the glass transition temperature of such typical thermoplastics as poly(phenylene sulfide) and poly(ethylene terephthalate). Based on the isothermal crystallization studies using DSC, we find that, in general, reinforcing fibers increase the rates of crystallization and decrease the degree of crystallinity, the extent of these effects being dependent on the weight fraction of fiber in the composite, the specific type of fiber, and the nature of surface finishes (sizes) that may have been applied.
The spherulitic morphology that develops in these polymers during the crystallization process, as characterized by polarized light microscopy, is also affected by the reinforcing fibers. In many cases, transcrystalline regions develop near the fiber surface due to nucleation effects.