Studies on bismaleimide co-cured Novolac epoxy–diallyl bisphenol-A system

Abstract

The novolac epoxy (EPN)–2-2′-diallyl bisphenol-A (DABA) system was modified by reactive blending with bisphenol-A bismaleimide (BMI) to improve its high temperature properties. Molar concentration of BMI in the stochiometric (1:1) blend of EPN and DABA was varied and the cure conditions were optimized for these systems by DSC, DMA and rheological studies. The glass composites processed using these ternary blends were characterized for their thermal, mechanical and dynamic mechanical properties. The incorporation of BMI into the epoxy–phenol system yielded a matrix system with improved glass transition temperature and comparable mechanical properties. The increase in BMI molar concentration beyond 1.0 resulted in deterioration in the mechanical properties and fracture toughness. But the high temperature performance of the composites, determined from their inter-laminar shear strength retention, showed systematic improvement with concentration of BMI in the system. The toughening of the system using polyether sulphone improved its mechanical properties with a marginal penalty on its glass transition temperature. The dependence of properties of composites on the type, orientation and stacking sequence of the laminates was investigated. The influence of the nature of the bismaleimide on the properties of the ternary reactive blend and its glass laminates was also examined. On changing the BMI, it was seen that the rigidity of the molecular backbone of the bismaleimide contributed to the high temperature properties of the ternary blend, while BMI with better flexibility has improved the mechanical properties of the resultant composite systems.