Relationships between structure and mechanical properties of rubber-modified epoxy networks cure with dicyanodiamide hardener

Epoxy network systems based on DGEBA and dicyanodiamide (DDA) and modified with a low molecular weight rubber (CTBN) were prepared and characterized. The kinetics of the adduct formation is followed using GPC analysis. The phase separation of the rubber phase is evidenced with DSC and SEM for all samples up to 20% CTBN. The GPC analysis of the soluble fraction demonstrates a chemical modification of the network. The mechanical properties and specially the impact strength behavior are enhanced with CTBN, but exhibit a maximum for 15% CTBN. In connection with SEM of fracture surfaces, these results are discussed and both modification of the rubber morphology and decrease in crosslinking density are taken into account.