Silica-reinforced natural rubber: use of natural rubber grafted with chemical functionalities as compatibilizer

Epoxidized natural rubber (ENR) is a modified form of NR bearing polar epoxy groups. This work investigates a silica-reinforced NR tire tread compounds with ENR as a compatibilizer. The ENRs consisting of 10, 38 and 51 mol% epoxide are used in a range of 2.5 to 15.0 parts per hundred parts of rubber (phr). The use of ENR as compatibilizer improves the filler-rubber interaction, silica dispersion and tensile strength. Increase of the ENR content and mole% of epoxide groups decreases the filler-filler interaction and improves silica dispersion, as reflected in a lower Mooney viscosity, Payne effect, flocculation rate constant and filler networking factor. With respect to tire performance, the presence of ENR-38 and ENR-51 as compatibilizer improves wet grip but negatively affects rolling resistance due to an increased glass transition temperature of the epoxidized NR. The addition of ENR-51 at 7.5 phr shows the best overall properties, however still somewhat lower when compared to a compound with the commonly employed bis-(triethoxysilylpropyl)tetrasulfide (TESPT) silane as coupling agent. The use of ENR-51 at 7.5 phr with TESPT at 4 wt% relative to silica and sulfur compensation gives vulcanizates with the same levels of tensile strength compared to vulcanizates with TESPT at 8.6 wt% relative to silica. The presence of ENR in the silica-filled NR affects the dynamic mechanical properties. The addition of TESPT to the ENR-compatibilized compounds causes only a small change in glass transition temperature (Tg) and tan δ at 5oC, but lowers tan δ at 60oC. Furthermore, the addition of extra sulfur leads to an increase of Tg and lower tan δ at both 5oC and 60oC as a result of increased crosslink density. SEM micrographs clearly show good silica dispersion in all compatiblized vulcanizates, and the tensile fracture surfaces of the materials show different tear line patterns dependent on their tensile strengths

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

Effect of acrylonitrile butadiene rubber on the properties of silica-reinforced natural rubber

Abstract The effect of acrylonitrile butadiene rubber (NBR) as a compatibilizer in silica-reinforced natural rubber (NR) is studied. NBR, Emulcril 3380 with 32-34%, was various at 5, 10, 15, 20 and 25 part per hundred parts of rubber (phr) to be used as a compatibilizer for silica-filled NR. The use of NBR as a compatiblizer can improve cure time (T90), cure rate index (CRI), and Mooney viscosity of silica-filled NR compounds, but the re-agglomeration of filler still observes. The use of NBR does not show significantly effect on bound rubber contents. However, tensile strength, reinforcement index and tear strength are increased with increasing amount of NBR contents due to a presence of some rubber-filler interaction through acrylonitrile groups of NBR and silanol groups on the silica surface. It leads to observe more surface roughness on tensile fractured surfaces.</jats:p