Crystallinity morphology and dynamic mechanical characteristics of PBT polymer and glass fiber-reinforced composites

The crystalline morphologies of PBT (polybutylene terephthalate) and its glass fiber reinforced composite systems were investigated in a thin-film form by polarized optical microscopy and wide-angle X-ray diffraction. Three different types of PBT morphology were identified in the Maltese cross pattern: 45° cross pattern (usual type) by solvent crystallization, 90° cross pattern (unusual type) by melt crystallization at low crystallization temperature, and mixed type by melt crystallization at crystallization temperatures higher than 160°C. The glass fibers increased the number density of spherulites and decreased the size of crystallites acting as crystallization nucleation sites without exhibiting trans-crystallinity at the vicinity of the glass fiber surfaces. Finally, the storage modulus was analyzed by using a dual-phase continuity model describing the modulus by the power-law sum of the amorphous- and crystalline-phase moduli. The crystalline-phase modulus was extracted out from the PBT polymer and composite systems containing different amount of crystallinity.