Improvement of the properties of styrene-butadiene rubber with different nanofillers

In this study, the addition of methacrylate-functional polyhedral oligomeric silsesquioxane (MA-POSS) and octaisobutyl POSS (OIB-POSS) nanoparticles to styrene-butadiene rubber (SBR) composites was evaluated in terms of rheological, mechanical, and morphological properties. The aging process and crosslink density of rubber nanocomposites were also examined in the presence of nanofillers. The sulfur vulcanization characteristics of SBR nanocomposites were determined by moving die rheometer. It was indicated that the addition of MA-POSS and OIB-POSS to SBR composites retarded the curing time and decreased the crosslink density. Due to the good interaction between MA-POSS/OIB-POSS nanoparticles and SBR matrix and excellent dispersion of POSS, the mechanical properties of nanocomposites were higher than those of the reference compound without nanofiller. The presence as well as a random distribution of MA-POSS/OIB-POSS in the SBR matrix was confirmed by TEM analysis. The crosslink densities of composites, which were calculated using Flory-Rehner equation, decreased with increasing amount of POSS nanofiller. Also, it was revealed that the thermal aging dramatically reduced the mechanical properties and crosslink density POSS/SBR nanocomposites. The inclusion of halloysite nanotubes (HNT) and montmorillonite nanoclays (MMT) modified with thiol or vinyl groups to SBR matrix was also assessed in terms of the same properties. It was determined that SBR/HNT-Thiol nanocomposite had higher crosslink density than the other SBR nanocomposites prepared with pure HNT or HNT-Vinyl due to sulfur in the thiol groups contributing to more crosslink formation. Also, the nanocomposites containing either pure or modified HNT nanofillers provided enhanced mechanical properties than those of the reference compound. Interestingly, it was found that SBR/MMT-Thiol has lower crosslink density and reduced mechanical properties than SBR/MMT and SBR/MMT-Vinyl. Therefore, it was revealed that the shape of nanofiller had also great importance in the reaction mechanism and crosslink formation of the compound. Increases in the mechanical properties appeared to be more related to the reinforcing effect of the HNT and MMT rather than the crosslinking effect. In addition, the crosslink densities and mechanical strengths of SBR/HNT and SBR/MMT nanocomposites increased with termal aging. This result confirmed the post-curing effect. Keywords: Halloysite, montmorillonite, nanocomposites, polyhedral oligomeric silsesquioxane, rubber, styrene-butadiene copolymer