Surface treatments of natural fibers in polymer-wood composites (PWC) are still one of the most interesting subjects for research among technologists, especially with inclusion of other property modifiers in the composites. This work investigated the effects of incorporating different types and contents of maleic anhydride grafted polypropylene (MAPP) and impact modifiers, as property promoters, on the mechanical properties of PP/wood sawdust composites. The concentration of wood sawdust was also varied. The experimental results revealed that increasing the wood fiber into the PP matrix reduced the overall strength and toughness of the composites. It was observed that the higher the impact modifier concentration, the greater the improvement in toughness of the PP/wood composites, and therefore an impact modifier with high comonomer content and high melt flow rate is recommended. This work recommends a MAPP concentration of 2.0 wt % (of sawdust) to be introduced into the PP/wood composites containing 11.1 wt % selected impact modifier, for optimization of the overall composite mechanical strength. The recommended MAPP coupling agent should possess a high wt % MAH-grafting level and high molecular weight of PP copolymer. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: [475][476][477][478][479][480][481][482][483][484] 2005

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.

Mechanical properties and thermal and structural changes of poly(vinyl chloride) (PVC)/wood sawdust composites were assessed with respect to the effect of moisture content, varying from 0.33 to 3.00 % by weight in the composite, for three different wood sawdust contents. The swell ratio and texture characteristics of the composite extrudates were also evaluated. Unique explanations were given to describe changes in the composite properties in terms of molecular interactions between PVC, cellulosic sawdust and moisture, such as dipole–dipole interactions, interfacial defects and bonding, fibre swelling, and moisture evaporation. The results suggest that at low moisture content the tensile modulus decreased and elongation at break of the composites increased with moisture content, the effect being reversed for high moisture content. Tensile strength decreased with increasing moisture content up to 1–2 %, and then unexpectedly increased at higher moisture contents. The effect of moisture content on flexural properties of the composite was similar to that on tensile properties. Impact strength of the composites was considerably improved with moisture content at low sawdust contents (16.7 wt%), and was independent of the moisture content at higher sawdust contents (28.6 and 37.5 wt%). A decrease in decomposition temperature with an increase in polyene content was evidenced with increasing moisture content, while the glass transition temperature did not change with varying moisture content. The extrudate swell ratio increased with the shear rate but remained unaffected by moisture content. The bubbling and peeling‐off in the composite extrudate occurred as a result of the evaporation of water molecules and the application of a high shear rate. Copyright © 2004 Society of Chemical Industry

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