Influence of a two-step process and of different cure schedules on the generated morphology of a rubber-modified epoxy system based on aromatic diamines

Abstract

Toughened epoxy networks based on diglycidyl ether of bisphenol A (DGEBA) prepolymer, 4,4′-diamino diphenyl sulphone (DDS) curing agent and epoxy-terminated butadiene-acrylonitrile copolymer-2,2′-bis(4-aminophenoxy)phenyl propane (ETBN-BAPP) adduct were prepared using a two-step process and compared to DGEBA-DDS-ETBN networks prepared using a one-step process. The kinetics of the reaction was followed by size exclusion chromatography and differential scanning calorimetry: the extent of reaction was found to be higher at the cloud point and lower at gelation in the two-step process. The morphology was studied by transmission and scanning electron microscopy. For the same initial rubber content, large differences were observed: when a two-step process was used, the dispersed particles showed irregular contours with a broad diameter distribution, but the volume fraction of dissolved rubber in the rigid matrix was independent of the process. The effect of the cure cycle on the morphology, mechanical and viscoelastic properties was examined. All of the samples had the same impact strength ( ⋍30 kJ m −2 ) with an identical modulus and glass transition temperature. These results confirm that the most important parameter is the volume fraction rather than the diameter of the dispersed-phase particles.