Thermal conductivities of silicone rubber filled with ZnO in a wide volume range were measured in order to study the effect of formed conductive particle chains on thermal conductivities. With the increasing of content of ZnO particles in silicone rubber, the amount of formed conductive chains increases and the conductive chains tend linearly to increase the thermal conductivity of the composite. The experimental results obtained were also analyzed using the Nielsen and Agari models to explain the effect of ZnO filler on the formation of thermal conductive networks. Thermal conductivities of a polymer filled with high volume content of particles evidently increased with the adding of small size fillers. The scanning electron microscopy (SEM) showed that percolation threshold has been reached at 31.4 vol% ZnO filler loading, and the hybrid fillers are more densely packed than single fillers in the silicone rubber matrix. There occurs a positive temperature coefficient (PTC) phenomenon in thermal resistance in composites of silicone rubber filled with ZnO. POLYM. COMPOS., 28:125-130, 2007.

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Phenol formaldehyde resin (PF) reinforced with short sisal fibers (SF) were obtained by two methods, directmixing and polymerization filling. Impact and bending properties of resulting composites were compared. Under the same compression molding conditions, polymerization filled composites showed better mechanical properties than those of direct-mixed composites. The influences of fiber modifications on the mechanical properties of SF/PF in-situ (polymerization filled) composites have been investigated. Treated-SF-reinforced composites have better mechanical properties than those of untreated-SF-reinforced composites. The effects of SF on water absorption tendencies of SF/PF composites have also been studied. In addition, sisal/ glass (SF/GF) hybrid PF composites of alkali-treated SF were prepared. Scanning electron microscopic studies were carried out to study the fiber-matrix adhesion.

A novel methylphenyl silicone resin, with M, D, and T units, was synthesized by cohydrolysis and cocondensation method from dimethyldimethoxysilane (Me 2 Si(OMe) 2 ), phenyltrimethoxysilane (PhSi(OMe) 3 ), hexamethyldisiloxane, and 1,3-divinyl-1,1,3,3tetramethyldisiloxane in toluene/water mixture catalyzed by hydrochloric acid and trifluoromethanesulfonic acid. The vinyl endcapped MDT silicone resins were chosen for reinforcement filler to enhance the mechanical properties of silicone-based ablative composites. The effects of resins with various R/Si ratios, vinyl content, and loadings on mechanical properties of PMPS rubbers were investigated. It was revealed that on the premise of good fluidity and processing performance, MDT resin showed excellent reinforcing effect and thermal stability compared with silica. MDT reinforced ablative composite showed satisfactory mechanical and antiablative properties. The linear ablation rate was 0.01 mm/s, which maybe associated with high yield of charred residue in thermogravimetric analysis results.