Silica-reinforced natural rubber compounds compatibilized through the use of epoxide functional groups and TESPT combination

Epoxidized natural rubber (ENR) and bis-(3-triethoxysilylpropyl) tetrasulfide (TESPT) were used to improve the properties of silica-filled NR. The use of ENR containing 51 mol% epoxide groups (ENR-51) as a compatibilizer without TESPT was optimized at 7.5 phr, based on the results of Payne effect and tensile strength. By using 7.5 phr of ENR-51 with varying amounts of TESPT in a range of 2 to 5 wt% relative to the silica, the properties of compounds were compared to those of the ones with optimum TESPT content (i.e. 8.6 wt% relative to the silica) and without. The addition of TESPT to the ENR-51 compatibilized silica-filled NR compound had no effect on Mooney viscosity but lowered the Payne effect to the same level as that of the silica/TESPT compound, and significantly decreased both scorch and optimum cure times. The silica-filled NR with ENR and the small amount of TESPT combination showed a further increase in tensile strength to match that of the optimized silica/TESPT system, while maintained the elongation at break. This work demonstrates that the use of ENR as compatibilizer clearly enhances the properties of silica-filled NR compounds, and that such properties can be further improved by adding TESPT at a half or less amount of TESPT normally needed for silica-filled compounds

Use of epoxidized natural rubber as a compatibilizer in silica-filled natural rubber tire tread compounds ; Verwendung von epoxydiertem Naturkautschuk als Verträglichkeitsvermittler in Zusammensetzungen aus kieselsäuregefülltem Naturkautschuk für Reifenlaufflächen

Silica-reinforced natural rubber (NR) tire tread compounds with epoxidized natural rubber (ENR) as a compatibilizer are investigated. ENR contents of 2.5-15.0 phr, with epoxide levels of 10, 38 and 51 mol%, are used. The addition of ENRs, especially ENR-38 and ENR-51, as compatibilizers decreases the Mooney viscosity and Payne effect (i.e. filler-filler interaction), which implies an improvement of silica dispersion in the compounds. Chemically bound rubber contents of the compounds, indicative for interaction/reaction between the epoxidegroups of the ENR and silanol-groups on the silica surfaces, also increase with higher epoxide-contents of the ENR. Raising the ENR contents and mole% of epoxide prolongs cure and scorch times of the silica-filled compounds, when compared with a silica-filled NRcompound without ENR. Tensile strength of vulcanizates is improved with increasing mole% of epoxide, and an optimum value is observed when 7.5 phr of ENR-51 was used. The results show overall, that the properties of silica-reinforced NR can be substantially improved by adding ENR as a compatibilizer, when compared with a compound without

Silane grafted natural rubber and its compatibilization effect on silica-reinforced rubber tire compounds

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 20 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 on 1H-NMR, the use of 10 and 20 phr (parts per hundred resin) of silane resulted in grafted NXT onto NR of 0.66 and 1.32 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

Reduced ethanol emissions by a combination of epoxidized natural rubber and silane coupling agent for silica-reinforced natural rubber-based tire treads

In an attempt to reduce the high volatile organic compound (ethanol) emissions from silica-reinforced NR compounds, this work aimed to, at least partially, replace the use of large quantities of silane coupling agent bis-(3-triethoxysilylpropyl) tetrasulfide (TESPT). The use of 7.5 phr of epoxidized natural rubber (ENR-51) as compatibilizer between NR and silica enhances the properties, which can be further improved by half or even lower amounts than required with TESPT alone. The properties obtained with TESPT are nearly matched, except for steric limitations imposed upon the ENR molecules to cap the silanol groups on the silica surface to the same extent as TESPT can do. Furthermore, TESPT donates reactive elemental sulfur to the compound during vulcanization, which needs to be compensated for in use with ENR