Crystallization kinetics and morphological behavior of reactively processed PBT/epoxy blends

Polybutylene terephthalate (PBT), a versatile engineering thermoplastic, has been processed using epoxy resin as a reactive solvent. Following processing of this blend, the epoxy was cured using a bi-functional amine curing agent, resulting in phase separation and phase inversion thus producing a different morphology. Change in crystallization kinetics of PBT in the presence of the epoxy monomer and cured epoxy resin has been studied using differential scanning calorimetry. Half time of crystallization (t1/2) of PBT decreased in the presence of epoxy monomer while it remained constant in the presence of cured epoxy resin. The value of Avrami exponent varied between 1 and 2 in pure PBT as well as for uncured and cured blends, indicating mixed type of spherulitic growth. Morphology of the uncured and cured blends was studied using small angle light scattering (SALS) and polarizing microscopy for samples crystallized at different temperatures at all levels of the epoxy resin. Scattering pattern in Hv and Vv mode of SALS provided information about the type of spherulites as well as volume filling nature of the spherulites. In general, typical unusual type of spherulitic pattern for PBT, in which scattering lobes lie along the polar axis, changed to usual type of pattern for PBT/epoxy blends, in which scattering lobes lie at 45° to the polar axis.