Study of Rubber Toughening Through Alloy Formation Combined with Sol-gel Method

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Stereorubbers were toughened by silica in-situ formed with a sol-gel method. The introduction of water into hydrophobic rubber was carried out by alloy formation of rubber with poly(ethylene-co-vinylalcohol)(EVAL) in the presence of compatibilizer. Tetraethylorthosilicate(TEOS) dissolved in rubber reacted with water during blending and curing to form silica particles in rubber matrix, which were identified by FTIR, EDX and EPMA.Mechanical properties of alloy rubber vulcanizate were superior to those of the corresponding pure rubber vulcanizate. Silica particles formed by sol-gel reaction further reinforced alloy rubber.It was found in a preliminary work that an immiscible system of TEOS and water could be smoothly reacted in the presence of ethanol which playd a role of compatibilizer. Vinylalcohol unit in EVAL resembled molecular structure of ethanol and presented a suitable reaction site for sol-gel reaction. Ethylene unit of EVAL was nonpolar with some affinity to rubber matrix. EVA … More L with lowest melting tempeature was selected from market brands and to thisperse EVAL in rubber matrix, a compatibilizer of PIR-AM was employed which included a functional imidatonium ion group. This group formed a strong ion-dipole bond with hydroxyl group in EVAL, resulting in formation of morphology of alloy rubber dispersed by EVAL fine particles. The silica particles with diameter of 3 mu m or less could be clearly detected by their clear-cut interface in BDR matrix or at the side of EVAL particles.Tensile properties were evaluated for both series of BDR and PIR.The samples were pure rubber vulcanizates, the ones modified by alloy formation with various compositions of EVAL and PIR-AM, and the ones reinforced by the silica in-situ formed in alloy rubber matrix. The hydrogen bonds in EVAL particles dispersed in alloy were considered to be effectively deformation-resistant and provide toughness. Precipitated silica by the reaction of TEOS and water increased elongation-at-break. When compared with the data for BDR, the effectiveness of EVAL and PIR-AM on rubber properties of PIR was more distinctive. Use of PIR/EVAL/PIR-AM=100/20/20 resulted in 12 MPa of tensile strength and 900 % of elongation-at-break. The in-situ formation of silica in rubber matrix was clearly effective in reinforcement. Less