Thermal properties and morphologies of poly(ethylene terephthalate) in blends with epoxidised natural rubber of 25 and 50 mol.-% of epoxy content

Abstract

Thermal properties and morphologies for polymer blends of poly(ethylene terephthalate) (PET) and epoxidised natural rubber with 25 mol.-% (ENR-25) and 50 mol.-% (ENR-50) epoxy contents were studied using differential scanning calorimeter (DSC) and polarising optical microscope (POM) respectively. The blends were prepared by precipitation method. Immiscibility of the components is revealed by observation of two glass transition temperatures Tg that correspond to that of the neat constituents. Equilibrium melting points Tom of PET in blends was determined by applying Hoffman–Weeks stepwise annealing procedure. The degree of crystallinity of PET in blends with ENR-25 remains constant, whereas the authors observe an increase in the degree in blends with ENR-50. The rate of crystallisation of PET in blends is characterised by the reciprocal halftime t–10·5. It displays an Arrhenius-like behaviour with respect to temperature and it stays constant at isothermal crystallisation temperature (Tc=constant) as long as PET is in excess. Rate of crystallisation of PET in the blends decreases exponentially as the Tc increases. Dispersed phases of ENR-25 and ENR-50 in the matrix of PET can be observed when the content of PET is in excess.