RUBBER-MODIFIED THERMOSETS CURED IN HEATED MOLDS - EXPERIMENTAL-STUDYOF PHASE-SEPARATION PROFILES

An epoxy-amine thermosetting polymer, modified by 15 wt% castor oil (C O) or by a commercial rubber (epoxy-terminated butadiene-acrylonitrile copolymer, ETBN), was cured in a mold at different heating rates. CO- modified materials cured at high heating rates exhibited a nonuniform phase separation profile, i.e. a single-phase transparent core surroun ded by opaque layers containing dispersed domains, The resulting struc ture was explained by simulating conversion vs. temperature trajectori es taking place during the cure. Thermal and mechanical properties of uniform and nonuniform materials were compared. These include glass tr ansition temperature, microhardness, yield stress and yield strain in uniaxial compression, and fracture toughness. Some possibilities for f urther research in this area are discussed.