Modification of styrene-butadiene rubber with polymethylsiloxanes.
Part II. Systems filled with silica
Polimery 2007, No 4, 268
The effects of several modifiers, from the group of polymethylhydrosiloxanes (PMHS, Table 1), on the morphology and selected properties of styrene-butadiene rubber (SBR) vulcanizates filled with silica (Table 2) were studied. The kinetics of rubber crosslinking changes as a result of blocking of active centers on the silica surface by the particles of reactive modifier (Table 3). Crosslinking density of vulcanizate increases with an increase in reactivity of modifier used, expressed as a ratio of the amounts of methylhydrosiloxane mers (DH) and dimethylsiloxane ones (D) in its particle (Table 4). The results of investigations of degree of filler dispersion in the rubber matrix (Fig. 1 a-e) correspond with the results of an estimation of vulcanizates' mechanical characteristics (Table 5). Namely, better silica dispersion causes clear increase in rubber tensile strength with just slight decrease in relative elongation at break. So PMHS investigated play a double role in the filled SBR as dispersants and crosslinking co-agents. Migration of modifiers to the rubber surface, causing decrease in friction factor (Fig. 2), was also found. This effect is the greater the lower reactivity of modifier used. An interpretation of this phenomenon is presented.
Key words: styrene-butadiene rubber, silica, polymethylhydrosiloxanes, modification, morphology, crosslinking density, mechanical properties, friction factor
D. Bieliński, P. Głąb, J. Chruściel
Modification of styrene-butadiene rubber with polymethylsiloxanes. Part II. Systems filled with silica