ABSTRACT:In this study, we investigated the effects of untreated precipitated silica (PSi) and fly ash silica (FASi) as fillers on the properties of natural rubber (NR) and styrenebutadiene rubber (SBR) compounds. The cure characteristics and the final properties of the NR and SBR compounds were considered separately and comparatively with regard to the effect of the loading of the fillers, which ranged from 0 to 80 phr. In the NR system, the cure time and minimum and maximum torques of the NR compounds progressively increased at PSi loadings of 30 -75 phr. A relatively low cure time and low viscosity of the NR compounds were achieved throughout the FASi loadings used. The vulcanizate properties of the FASi-filled vulcanizates appeared to be very similar to those of the PSi-filled vulcanizates at silica contents of 0 -30 phr. Above these concentrations, the properties of the PSi-filled vulcanizates improved, whereas those of the FASi-filled compounds remained the same. In the SBR system, the changing trends of all of the properties of the filled SBR vulcanizates were very similar to those of the filled NR vulcanizates, except for the tensile and tear strengths. For a given rubber matrix and silica content, the discrepancies in the results between PSi and FASi were associated with fillerfiller interactions, filler particle size, and the amount of nonrubber in the vulcanizates. With the effect of the FASi particles on the mechanical properties of the NR and SBR vulcanizates considered, we recommend fly ash particles as a filler in NR at silica concentrations of 0 -30 phr but not in SBR systems, except when improvement in the tensile and tear properties is required.
This article explored the possibility of using silica from fly-ash particles as reinforcement in natural rubber/styrene-butadiene rubber (NR/SBR) vulcanizates. For a given silica content, the NR : SBR blend ratio of 1 : 1 (or 50 : 50 phr) exhibited the optimum mechanical properties for flyash filled NR/SBR blend system. When using untreated silica from fly-ash, the cure time and mechanical properties of the NR/SBR vulcanizates decreased with increasing silica content. The improvement of the mechanical properties was achieved by addition of Si69, the recommended dosage being 2.0 wt % of silica content. The optimum tensile strength of the silica filled NR/SBR vulcanizates was peaked at 10-20 phr silica contents. Most mechanical properties increased with thermal ageing. The addition of silica from fly-ash in the NR/SBR vulcanizates was found to improve the elastic behavior, including compression set and resilience, as compared with that of commercial precipitated silica. Taking mechanical properties into account, the recommended dosage for the silica (FASi) content was 20 phr. For more effective reinforcement, the silica from fly-ash particles had to be chemically treated with 2.0 wt % Si69. It was convincing that silica from fly-ash particles could be used to replace commercial silica as reinforcement in NR/SBR vulcanizates for cost-saving and environment benefits.
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