Crystallization and Equilibrium Melting Behavior of Poly(Butylene Terephthalate)/Epoxy Blends

Abstract

Blends of poly(butylene terephthalate) (PBT) with epoxy resin (diglycidyl ether of bisphenol-A) have been prepared by blending in a mini-mixer and then cured using a 4-functional amine curing agent at 175°C for 4 hr. Melting and crystallization behavior of the uncured and cured blends has been studied using differential scanning calorimetry. Isothermal crystallization studies of the uncured, as well as cured, blends have been carried out to determine the induction time for the onset of the nucleation process. The equilibrium melting behavior of cured and uncured blends has been studied using Hoffman‐Week's linear extrapolation method. From the equilibrium melting temperature γ, the proportionality factor between initial thickness of chain-folded lamella and final thickness was calculated. The Flory interaction parameter, χ, between PBT and epoxy resin has been calculated using the Nishi–Wang equation. The interaction parameter is found to be negative, indicating that PBT forms a thermodynamic stable mixture with the epoxy monomer. It has been shown that PBT forms miscible blend with uncured epoxy, which affects the crystallization and equilibrium melting behavior of PBT. After curing, due to the phase separation of PBT and epoxy, the melting and crystallization behavior of cured blends is closer to that of pure PBT.