The mechanical properties of styrene-butadiene rubber (SBR) vulcanizates prepared using various plasticizers including liquid polybutadiene and styrene-butadiene copolymers were investigated. The effect of the liquid polymers as the plasticizers on the mechanical properties of the polymers, such as the hardness, tensile storage modulus, tand, and the modulus at 100% elongation values, were determined before and after the thermal aging. As a result, it was revealed that the use of these liquid polymers gave less amount of change in the measurement values for the mechanical properties during the aging. The crosslinking density and the amount of free polymers were also determined on the basis of the swelling and extraction data, respectively, using several organic solvents. These results support the fact that the added liquid polymers are fixed to the SBR networks. We revealed the superiority of the liquid styrene-butadiene copolymers as the plasticizer, which provides sufficient mechanical properties after vulcanization and the excellent maintenance of the properties during the thermal aging process.

Thermus thermophilus cells formed siliceous deposits in the presence of supersaturated silicic acid (600 p.p.m SiO 2 ). The supersaturated silicic acid promoted interaction between cells and the inside walls of glass culture bottles, leading to the development of cell aggregates or biofilms. Electron probe microanalysis showed that within the aggregates most of the cell surfaces were covered with silica. Under these conditions, there was remarkable production of silica-induced protein (Sip), a solute-binding component of the Fe 3 þ -binding ABC transporter. Furthermore, supersaturated silica enhanced resistance to the peptide antibiotics bacitracin, colistin and polymyxin B, which all act on the cell envelope. By contrast, supersaturated silica did not induce resistance to ampicillin, chloramphenicol, kanamycin and tetracycline, which inhibit peptide synthesis. Although strong expression of Sip was detected in liquid cultures of T. thermophilus in the presence of supersaturated silica and colistin, upregulated transcription of putative efflux pump and multidrug resistance ABC transporter genes were not detected by quantitative real-time PCR analysis. These findings suggest Sip promotes silica deposition on the surfaces of cells, after which the silicified outer membrane may serve as a 'suit-of-armor,' conferring resistance to peptide antibiotics.

Styrene-butadiene rubber (SBR) vulcanizates were prepared using plasticizers including the four liquid types of styrene-butadiene copolymers (LPSB), polybutadiene (LPB), polyisoprene (LPI), and the hydrogenated polyisoprene (LHPI) as well as the conventional process oil, and their phase-separated structures and mechanical properties were investigated by differential scanning calorimetry and dynamic mechanical spectroscopy. The phase separation was observed for the SBR vulcanizates when LPI and LHPI were used as the plasticizers, while the LPSB and LPB gave homogeneous structures because of the good miscibility with the SBR. The phase-separated structure of the SBR vulcanizate prepared using LPI changed to the homogeneous during the thermal aging. We revealed the role of the liquid polymers as the plasticizers in maintaining the physical and mechanical properties of the SBR vulcanizates during the thermal aging process when the plasticizers were miscible to the SBR. V C 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: [434][435][436][437][438][439][440] 2011

The ring-shaped styrene-butadiene rubbers (SBRs) test pieces ran on a rotating stainless-steel ring using an abrasion tester to evaluate the changes in the mechanical properties, such as the tensile storage modulus and tan d values, the modulus at 300% elongation, and the strength and extension ratio at the breaking point, after a mechanical aging process. The surface of the SBR test pieces and the formed rubber debris after the running experiment was investigated using scanning electron microscopy. A change in the crosslinking density of the SBRs and the analysis of the isolated free polymers showed the occurrence of bond scission of the copolymer chains. On the other hand, the mechanical properties of whole SBR samples showed only a small change during the mechanical aging test.