Effects of electron-beam (EB)-irradiation on 60/40 natural rubber/polystyrene blends in the presence of m-phenylene bismaleimide (HVAC-2)

Poor compatibility of natural rubber (NR/polystyrene (PS) blend can be improved by addition of HVA-2 and/or radiation. Effects of HVA-2 on radiation-induced crosslinking in 60/40 NR/PS blends were investigated. The blends were irradiated using a 2.0 MeV electron beam machine with doses ranging from 0 to 250 kGy. Results indicate that under the irradiation employed, the NR/PS blends were crosslinked. The presence of HVA-2 in the blends reduced the optimum dose and the blends exhibit better tensile properties. Within the dose range studied, the degradation caused by electron beam irradiation was found to be minimal. The gel content and tensile strength measurements were used to monitor the degree of radiation-induced crosslinking in the blends. For the blends containing 2.0 phr HVA-2, the optimum tensile strength and the dose were 10.4 Mpa and 50 kGy, respectively. For the blends without HVA-2, the optimum tensile strength and the dose, were 7.9 Mpa and 200 kGy, respectively. The dynamic mechanical analysis studies further confirmed these observations. The shift in Tg with irradiation dose indicates the formation of irradiation-induced interactions i.e. cross-links. This was further supported by a decrease in tan δmax peaks. Morphological studies by SEM indicate that, the irradiated blends with HVA-2 show the finest phase. (Author)