Process‐resolved morphology of bismaleimide matrix composites

Abstract

AbstractA series of silicone‐modified bismaleimide resins have been examined as matrices for high performance continuous fiber‐reinforced composite materials. Detailed studies of the interrelation between processing, structure, and properties of both the neat resin and corresponding carbon‐fiber‐reinforced composite have identified that the silicone additive provides important morphological modification to the bismaleimide matrix for toughness improvements while, at the same time, retaining the elevated temperature performance. Micrographs of fracture surfaces of cured samples demonstrate remarkable similarities to fracture surfaces of rubber‐modified epoxy matrices. Specifically, a fracture surface covered with noncommunicating microcavities of 1.5 μm in diameter was observed. However, unlike rubber‐modified epoxies where the observed features are assumed to be created during fracture of the specimen, this study demonstrates that the microcavities are created during the cure process and, thus, exist in the bulk of the material before fracture. In simulated cures of the material either while obsered directly in a polarizing microscope or indirectly inside thermal analysis cells (DSC, TGA) and with examination of fractured surfaces of samples cured according to different temperature profiles, it is established that the silicone modifier, in conjunction with the processing conditions, is responsible for the morphological developments. Accordingly, a mechanism describing the observed morphology was proposed based on physical changes that the silicone additive experiences in relation to specific volatile products emitted during the cure process.