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Abstract. Natural Rubber (NR) grafted with 3-octanoylthio-1-propyltriethoxysilane (NXT) was prepared by melt mixing using 1,1′-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane as initiator at 140°C with NXT contents of 10 and 10 parts per hundred rubber [phr] and initiator 0.1 phr. The silane grafted on NR molecules was confirmed by Fourier transform infrared (FTIR), proton nuclear magnetic resonance (1H-NMR) and scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM-EDX). Based on1H-NMR, the use of 10 and 10 phr (parts per hundred resin) of silane resulted in grafted NXT onto NR of 0.66 and 1.31 mol%, respectively, or a grafting efficiency of approx.38%. The use of NXT-grafted NR as compatibilizer in silica-filled NR compounds, to give a total amount of NXT in both grafted and non-grafted forms in the range of 0.8-6.1 wt% relative to the silica, decreases the Mooney viscosity and Payne effect of the compounds, improves filler-rubber interaction, and significantly increases the tensile properties of the silica-filled NR-compounds compared to the non-compatibilized one. At the same silane-content, the use of silane-grafted NR gives slightly better properties than the straight use of the same silane. With sulfur compensation, the use of NXT-grafted-NR with about 6 wt% NXT relative to the silica gives technical properties that reach the levels obtained for straight use of bis-(3-triethoxysilyl-propyl)tetrasulfide (TESPT) at 8.6 wt% relative to the silica.
Keywords: rubber, reinforcement, natural rubber, silica, silane grafted NR
(ProQuest: ... denotes formulae omitted.)
1.Introduction
Silica has a hydrophilic surface by its specific character of a large number of surface silanol groups, i.e. 4.9 OHmm-1 [1], leading to strong hydrogen bonding between silica particles and poor filler-rubber interactions in non-polar elastomers. In general, a silane coupling agent is added together with silica into a rubber during the mixing process to enhance the silica-rubber compatibility. Under suitable mixing conditions, the silane coupling agent undergoes a silanization reaction with silanol groups on the silica involving primary and secondary reactions [1]. To complete the reaction between silica and, for example, bis-(3-triethoxysilylpropyl)tetrasulfide (TESPT) silane during mixing, the discharge temperature of a silicafilled Styrene-Butadiene Rubber (SBR) compound should be above 130°C. But at a temperature above 160°C the silane starts to react with the elastomer to form premature crosslinks [3]. For silica-filled NR compounds with TESPT as coupling agent,...