Physical ageing of epoxy resin - polyethersulphone blends

Abstract

In view of an increasing number of reports describing epoxy resinthermoplastic blends, it is clearly important to identify the effects of the thermoplastic on the blend properties. In this work difunctional epoxy resin monomer (Epikote 828) cured with diaminodiphenylsulphone (DDS) or dicyandiamide (DICY) are the model systems used. The thermoplastic is a polyethersulphone (PES) with either hydroxyl terminations (Victrex 5003P, ICI) capable of reaction with epoxy monomer or chlorine terminated (Ultrason E2010, BASF) which is incapable of reaction. The glass transition characteristics of the PES materials are very similar but the Ultrason E2010 is of lower average molecular weight and can be expected to contain more chain ends. Epoxy-DDS-PES systems were prepared with 20phr and 30phr of PES. The effects of the PES on crosslinking and isothermal physical ageing behaviour were examined. Enthalpy relaxation data were curve fitted using a Kohlrausch function. Mechanical and dielectric spectroscopy data were analysed using W-L-F and power law methods. Despite a tendency for the PES to reduce the crosslink density of the network, the blends had glass transition temperatures almost identical to the unmodified resin. The reduction in crosslink density improved Glc compared to the unmodified resin but promoted faster physical ageing and more rapid embrittlement when the blends were aged at the same temperature as the neat resin. The epoxy-DICY-PES system was studied at one composition of 30phr PES. The system was two phase but fast curing led to premature arrest of the phase separation process. Annealing at various temperatures from below the glass transition of the low temperature phase to just below the glass transition of the high temperature phase resulted in what is believed to be microscopic morphological changes detectable only barely by DSC and quite clearly from dynamic mechanical analysis. These changes were not manifest in the morphology of fracture surfaces. Annealing was found to decrease G1c.