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D. Bieliński, P. Głąb, J. Chruściel

Modification of styrene-butadiene rubber with polymethylsiloxanes

Polimery 2007, No 3, 195


Summary

The results of investigations on structural aspects of styrene-butadiene rubber (SBR) modification with polymethylhydrosiloxanes (PMHS) or polydimethylsiloxanes (PDMS) were presented. The modifiers varied in reactivity, measured as a ratio of methylhydrosiloxane and dimethylsiloxane units (Table 1). The effects of modifier reactivity on the kinetics of radical reaction of rubber curing in the presence of dicumyl peroxide (DCP) as well as on the sulfur-induced vulcanization were determined (Table 2-5, Fig. 2 and 3). In case of DCP use the curing rate and efficiency increase with increasing reactivity of modifier used. However, in case of sulfur-induced vulcanization the systems containing less active PMHS showed the highest reaction rate. No modifier effect on the efficiency of sulfur-induced vulcanization was observed. It can be the result of active complex blocking by polysiloxanes, wetting the surface of ZnO being an activator of sulfur curing system. The curing in the presence of DCP is accompanied with the reactions of PMHS grafting onto elastomer and its polymerization in the rubber matrix. Organosilicon modifiers show the tendency to surface migration and segregation in the rubber. Together with the change in system morphology (Fig. 1) it influences mechanical (Table 6) and tribological properties (Table 8) of cured SBR. Namely, the introduction of a modifier into the rubber caused decrease in tensile strength, especially in case of the rubber cured in the presence of DCP. Macroscopic coefficient of friction for modified sulfur vulcanizates increases. However, in the case of SBR cured in the presence of DCP this coefficient can be lowered when low reactive PDMS or PMHS are used for modification.


Key words: styrene-butadiene rubber, polymethylhydrosiloxanes, polydimethylsiloxanes, modification, curing, morphology, mechanical strength, surface energy, friction


e-mail: dbielin@mail.p.lodz.pl


D. Bieliński, P. Głąb, J. Chruściel

Modification of styrene-butadiene rubber with polymethylsiloxanes