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.

Natural silica in fly ash (FA) particles of 30 and 60 phr were incorporated as reinforcing filler in natural rubber (NR) compounds. Improvements of cure characteristics and mechanical properties of the FA/NR composites were expected by surface treatment of the FA particles, this being carried out using various contents of bis-(3triethoxysilylpropyl) tetrasulfane (Si69), as a chemical silane coupling agent, and sodium hydroxide (NaOH) solution. The results suggested that the Si69 coupling agent was a satisfactory property promoter in the FA/NR composites through COS bonding with rubber molecules and siloxane linkages with FA particles. Using NaOH solution did not improve the mechanical properties of the composites. The mechanical properties of the FA/NR composites appeared to increase at low Si69 concentrations of 2.0 -4.0 wt%, but decreased at high Si69 loadings of 6.0 -8.0 wt%. The decrease in mechanical properties resulted from a reduction of crosslink density and a formation of flexible polysiloxane from the self-condensation reaction of the Si69. The presence of Si69 was observed to interfere with the sulphur crosslink formation. No synergetic effect on the properties of the rubber composites was observed when using a mixture of NaOH and Si69. This article recommends concentrations of 2.0 -4.0 wt% Si69 to be introduced into the FA/NR composites to achieve the optimum properties.

The use of untreated sawdust as a filler in poly(vinyl chloride) (PVC) was examined—the effects of sawdust content on structural and thermal changes, and rheological and mechanical properties being of main interest. The results revealed that the torque and die entrance pressure drop values during mixing were independent of sawdust particles up to 23.1 wt%. The extrudate swell monotonically decreased up to 33.3 wt% sawdust content. Smooth wood‐like texture with controllable size of the extrudate could be obtained at a sawdust content greater than 33.3 wt%. Tensile, impact, flexural and hardness properties of the PVC/sawdust composites considerably decreased with up to 16.7 wt% sawdust content before leveling off for higher sawdust loadings. The composites having sawdust higher than 16.7 wt% showed a benefit of cost savings. The decreases in the mechanical properties of PVC with sawdust are explained in association with the presence of moisture, interfacial defects between fibre and polymer, and fibre dispersions in the PVC matrix. Thermal degradations of PVC in PVC/sawdust composites were evidenced by a decrease in decomposition temperature and an increase in polyene sequences, which were caused by Cl cleavage due to strong hydrogen bonds of fibre–PVC molecules. The maximum of tanδ transition and the glass transition temperature were found to improve with sawdust content as a result of re‐formation of hydrogen bonds between the macromolecules of the fibre and the polymer. The overall results in this work suggest that the properties of PVC/sawdust composites were strongly influenced by sawdust content up to 16.7 wt%. Beyond this value the effect of sawdust content on the properties was comparatively small. Copyright © 2003 Society of Chemical Industry

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