Moisture absorption by cyanate ester modified epoxy resin matrices. Part III. Effect of blend composition

The moisture absorption of thermally cured cyanate ester modified epoxy resin matrices has been studied under constant hygrothermal conditions and with a series of thermal spikes. Various resin blends of differing composition were studied, so that the effect of resin structure on moisture absorption could be assessed. It was found that intermittently applied thermal spikes can enhance the moisture absorption by cyanate esters and their blends with epoxy resin. The equilibrium moisture concentration was found to increase with the fraction of cyanate ester in the blend. The results of the desorption study on both control and spiked specimens showed that some of the water molecules remain entrained in the resin, probably as a result of hydrolysis of the polymer matrix. Up to a thermal spiking temperature of 160 degreesC, the crosslink density remained constant but at higher temperatures tended to decrease, as observed by examination of the modulus above the glass transition temperature. (C) 2002 Elsevier Science Ltd. All rights reserved.