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Carbon black and high performance silica have been widely employed as binary system filler in tire tread formulations. This study evaluated the total and partial substitution of silica by metakaolin (MK) on the properties of tread rubber composites. Dynamic mechanical thermal analysis and abrasion tests were conducted as typical assessments of tire tread performance: rolling resistance (fuel consumption), wet traction (safety), and abrasion (durability). Further the energy spent by the equipment during the processing of formulations was also analyzed, as well as rheological and mechanical properties. A significant reduction of rolling resistance was obtained with 75% and 100% of silica substitution by MK, which could lead to lower heat buildup in tire tread applications, without showing negative effects on wet traction, although abrasion showed undesired results. The substitution of silica by MK also lowered energy demanded for processing. No major changes were observed in vulcanization parameters and mechanical properties, which is interesting considering the fact that MK is nonreinforce filler.

Biodiesel has been considered a suitable substitute for petroleum diesel, but their chemical composition differs greatly. For this reason, biodiesel interacts differently than petroleum diesel with various materials, including rubbers. Therefore, the resistance of some elastomers should be thoroughly evaluated, specifically those which are commonly used in automotive industry. Nitrile rubber (NBR) is widely used to produce vehicular parts that are constantly in contact with fuels. This paper aimed to assess the resistance of carboxylated nitrile rubber (XNBR) with 28% of acrylonitrile content to soybean biodiesel in comparison with non-carboxylated nitrile rubber samples, with high and medium acrylonitrile content (33 and 45%). NBR with medium acrylonitrile content showed little resistance to biodiesel. However, carboxylated nitrile rubber even with low acrylonitrile content had similar performance to NBR with high acrylonitrile content.

Summary:The vulcanization process of rubber compounds comprises multiple chemical reactions and the investigation of this process can be carried out using several techniques. This paper aims at investigating the influence of acrylonitrile content (28, 33 and 45%) and the presence of a carboxyl group in the vulcanization process of nitrile rubber. A methodology that uses rheometric parameters to determinate the cure rate constant (k) and activation energy (E) was conducted. The results showed that there was a decrease in cure rate constant with increasing of acrylonitrile content in the rubber, for a given vulcanization temperature. Furthermore, a higher value of activation energy was obtained for the 33% of acrylonitrile compound.

Derterminação das propriedades reométricas, mecânicas, densidade de ligações cruzadas e parâmetros termodinâmicos de nanocompósito de látex de sbr com mica sintéticaDertermination of the rheometric, mechanical, crosslinking density and thermodynamic parameters of sbr latex nanocomposite with synthetic mica

O objetivo deste trabalho foi produzir e analisar nanocompósitos de copolímero de butadieno-estireno (SBR), partindo da coagulação do látex SBR com mica sintética Somasif ME-100 em diferentes proporções, 0, 2, 4, 6, 8 e 10 phr. As propriedades reométricas e mecânicas destas composições foram determinadas, e verificou-se que a mica sintética age como uma carga semirreforçadora. A densidade de ligações cruzadas e os aspectos termodinâmicos sugerem alguma interação SBR-mica sintética, corroborada pelos resultados reométricos e mecânicos.

Nitrile rubber (NBR) nanocomposites with different contents of synthetic Somasif ME-100 mica (sodium-fluorohectorite) were obtained by melt compounding using a Semi Efficient curing system. The effect of curing on the nanocomposties was evaluated through rheometric properties, crosslink density (CLD) and mechanical properties. The ME-100 mica dispersion in NBR was assessed by transmission electron microscopy (TEM), the Payne effect and thermodynamic properties (ΔS and ΔG). Both the curing parameters and CLD pointd out that the addition of ME-100 directly affects crosslinks formation. It could also be observed that the nanofiller dispersion state is complex, exhibiting exfoliated and agglomerated structures (TEM); besides, agglomerations rose linearly as the nanofiller was added (the Payne effect). Notwithstanding these findings, and on the basis of unfilled formulations, NBR20 nanocomposite showed improvement in mechanical properties (tensile and tear strengths) which suggests that ME-100 might be considered a semi-reinforcing filler.