ROLE OF POLYESTER RESIN ON THE EPOXY MATRIX SYSTEM

Interpenetrating polymer network (IPN) as a polymer blend matrix was p repared using different ratios of polyester (PE) to epoxy (E) resins. It was observed that 11.33 wt % PE in the blend provides maximum mecha nical properties, particularly the modulus for the casting, and such a blend is referred to as ''optimum casting'' (OC). The density of the blends containing up to 11.33% PE, especially of OC, was found to have increased by the presence of PE in the E network significantly more t han would have been estimated from the calculation based on the rule o f additivity. The thermal expansion coefficient parameter (Delta alpha (i)) of the OC was found to be 2.68 X 10(-4) K-1. The scanning electro n micrograph (SEM) of the fracture surface of OC only showed a glass-l ike smooth surface. The change in the mechanical properties due to the varying proportions of PE in the blend was studied critically on the basis of failure mechanisms and morphological features. The differenti al thermogravimetric analysis (DTGA) of OC indicated only one peak in spite of the presence of two resin constituents, whereas castings with an excess of PE in the blend showed multiple peaks. Interestingly, as far as the DTGA is concerned, a domain of seemingly OC origin was fou nd to remain, even in the blends containing PE resin above its optimum level (> 11.33 wt %). (C) 1995 John Wiley and Sons, Inc.