Reinforcement of Natural Rubber by Precipitated Silica: The Influence of Processing Temperature

Abstract

The thermal history, and in particular the mixing dump temperature, is a parameter of paramount importance in mixing rubber and silica with a silane coupling agent in order to achieve proper silanization of silica and to avoid premature scorch reactions. The influence of the mixing dump temperature on the performance of silica-reinforced natural rubber (NR) is investigated. The investigation also includes the effect of nonrubber constituents, primarily proteins in NR, by using deproteinized natural rubber (DPNR) and synthetic polyisoprene (IR). The vulcanization properties and rubber-to-filler interactions of silica-reinforced NR in the presence and absence of a silane coupling agent are highlighted. With increasing mixing dump temperature, the silanization reaction between silica and silane coupling agent proceeds further. At a sufficiently high dump temperature, filler–filler interactions in the NR–silica compounds are reduced and the silica–rubber interaction improved, as evidenced by a drop in the Payne effect and increment in chemically bound rubber. It is demonstrated that NR and IR compounds mixed until they are above the optimum dump temperature exhibit cure reversion and reduction in tensile properties. On the other hand, DPNR–silica vulcanizates show slightly more constant physical properties.

Structure–property relationships of silica/silane formulations in natural rubber, isoprene rubber and styrene–butadiene rubber composites

“…In particular, they used a special preparation technique (swelling in polystyrene followed by polymerization), allowing for TEM investigations at swollen samples. From the TEM micrographs, it could be realized that the swelling pressure led to the formation of vacuoles around the silica particles for the samples without silane, whereas no vacuoles were found for the samples with coupling silane . Another reason might be a partial supression of SIC in the presence of silica.…”

“…This has been studied by Sarkawi et al . who found a reasonable silane coupling independent of the amount of proteins . In particular, they used a special preparation technique (swelling in polystyrene followed by polymerization), allowing for TEM investigations at swollen samples.…”

The effects of natural astaxanthin‐modified silica on properties of natural rubber

“…Silica is well‐known as being a type of reinforcing agent to enhance the properties of rubber matrix and its consumption is next only to the carbon black in the field of rubber processing . Compared with carbon black, the tread rubber filled with silica has the advantages of low hysteresis loss, small rolling resistance and strong wet grasping force . Replacement of carbon black by silica has been growing steadily, especially in the tire industry, as the introduction of the “Green Tire Technology” by Michelin in 1992 .…”

Cardanol grafted natural rubber: A green substitute to natural rubber for enhancing silica filler dispersion

“…Although silane coupling agents can enhance interaction between silica and the rubber, they only serve a minor effect on improving the dispersion of fillers in rubber . Moreover, the highly dispersible silica technology, as it is used now‐a‐days, employs mainly solution‐polymerized synthetic rubbers and is still not fully commercially feasible with natural rubber …”

“…6 Moreover, the highly dispersible silica technology, as it is used nowa-days, employs mainly solution-polymerized synthetic rubbers and is still not fully commercially feasible with natural rubber. 8 In the recent years, as silica filler has become an active, highperformance additive for rubber, dispersion of silica particles is of utmost importance to improve reinforcement in the rubber matrices. 9 Therefore, improving the dispersion of silica in rubber and enhancing interaction between silica surface and rubber matrix have thrown open challenges in the arena of rubber research.…”