Reaction mechanisms in γ irradiated high surface silica-elastomer systems

Complete text of publication follows. In this work the mechanism of the γ-ray induced vulcanization of the binary systems consisting of styrene butadiene rubber (SBR; 30% stryrene, 25% vinyl units) and high surface silica (160-1000 m2/g) are investigated by matrix EPR spectroscopy, ATR-FTIR and by measuring the crosslinking kinetics. The experiments have dealt with pristine silica, silica modified by radiation grafting of polybutadiene olygomers (SiO2/PB) and the SBR compounds containing 30-40% of pristine or modified silica. The irradiation under vacuum of the pristine silica gives rise to thermally unstable species which decay at very low temperature, below 180 K. When the SBR/silica compounds are irradiated, in addition to the SBR radicals, also SBR chain radicals is greatly enhanced when using silica coated with polybutadiene olygomers bearing high (25-45%) vinyl double bond content. The rationale of such observation is that the species generated within the bulk of the silica particles migrate to the surface where are scavenged by the vinyl double bonds of the absorbed chains. It is thus assessed that the direct radiolysis of silica plays an active role in the radiation vulcanization process by promoting the formation of silica-rubber chemical links which are of key importance in the reinforcement mechanism. The crosslinking kinetics were found to be coherent with the above observation showing that the crosslinks yield vs dose ratios increase in the order: pure SBR < SBR/pristine SiO2 < SBR/SiO2(PB).