The influence of the rubber carboxyl functionality on the processability and properties of solid rubber modified epoxy mixtures

Abstract

A high molecular weight, carboxyl functionalised solid rubber was added to an epoxy resin-aromatic amino system developed for autoclave curing of honeycomb core composite structures. The achievement of an optimal balance of viscous flow and viscoelasticity of the resin, by controlling the nature and extent of cross-linking of the functionalised rubber, was proposed as a route to void-free honeycomb skins. The aim of the present investigation is to understand howthe concentration of carboxylic groups of the rubber, prereacted with one of the epoxy monomers, affects the matrix resin flow properties. The concentration of carboxyl groups was changed by reacting them with a monofunctional epoxy resin. Dynamic shear viscosity profiles varying frequency, temperature and as function of time during isothermal cure have been determined for blends with differently functionalised rubbers. Carbon fibre wettability and laminate consolidation quality have been evaluated, making composite samples according to conventional prepregging and autoclave curing processes, through electron microscopy of fracture surfaces from transverse flexural strength tests.