Microwave curing of epoxy-amine system - effect of curing agent on the rate enhancement

Abstract

Increasing application in the aerospace and microelectronics industries have led to the demand for accelerated curing of high performance structural adhesive systems like epoxy. Particularly for the microelectronics industry, the curing of such thermoset systems have become the bottleneck of the whole production process. Alternative accelerated curing systems like Ultra Violet light, Gamma rays and Electron Beams have been limited by their respective disadvantages. More recently microwave curing has been shown to be a viable alternative as an accelerated curing system. This paper investigates the effect of different curing agents in microwave curing for an epoxy system. Microwave radiation and thermal heating were performed on the epoxy Araldite GY6010, which is a resin of di-glycidyl ether of bisphenol-A (DGEBA). The three types of curing agents used were 4,4′-Diamino-di-phenyl-sulfone (DDS), 4,4′-Diamino-diphenyl-methane (DDM) and meta-Phenylene-diamine (mPDA). Thermal cure temperatures were determined between the onset and midway to the peak temperature of the freshly prepared epoxy/amine systems of the DSC exotherm curves. Microwave curing of the epoxy/amine systems was carried out with a 1.1 kW variable power generator with a 2.45 GHz magnetron coupled to a multimodal cavity through a wave guide. Curing was done between 200 W and 600 W microwave power. The curing was strongly dependent on the curing agent used. A low degree of cure at a relatively low microwave power was observed in DGEBA/DDS system, and has been attributed to the sluggish reaction of DDS with epoxy, resulting in the entrapment of the functional group in the cross-link network. DDM and mPDA were more reactive than DDS and gave relatively faster full curing times than DDS.