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Titanium dioxide (TiO2) possesses excellent photocatalytic activity and provides UV protection for polymeric materials. The nanosized TiO2 particles with larger surface area to volume ratio and an increased surface reactivity shall impart better photocatalysis and UV protection efficiency to the rubber compounds, compared to the use of conventional micron-sized particles. Direct incorporation of TiO2 nanoparticles (n-TiO2) into non-polar rubbers faces incompatibility problem between the two phases. One of the solutions to overcome this problem is to treat the nanoparticle surface by using silane coupling agent such as bis-(3-triethoxysilylpropyl) tetrasulfide (TESPT). This work prepared n-TiO2 from commercial micron sized-TiO2 by ultrasonication technique. Particle size of TiO2 was measured by laser light scattering particle size analyzer. The morphology of TiO2 nanoparticles was characterized by field emission scanning electron microscope (FESEM). The grafting reaction of silane on TiO2 nanoparticles surface was studied at varying reaction temperatures and times. The purified grafted materials were characterized by energy dispersive X-ray analysis (EDX), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR). The characterization data confirm a presence of grafted silane on the TiO2 nanoparticles surface. The result shows that ultrasonication technique can effectively decrease particle size and the grafting reaction of silane coupling agent onto TiO2 nanoparticles can be successfully carried out at 140°C for 8 h.

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Silanol groups on a silica surface lead to strong hydrogen bonding between the silica particles and aggregates, resulting in a poor dispersion of silica in rubber compounds. This study improved the compatibility between silica and rubber by coating the silica surface with a polyisoprene film using an admicellar polymerization technique. The modified silica was characterized by Fourier-transform infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy. A comparison of the properties of natural rubber compounds filled with modified silica, silica with silane, carbon black and a mixed filler of silica and carbon black showed that the silicasilane filled compound exhibited the highest mixing torque and Mooney viscosity, whereas the modified silica-filled compound exhibited the lowest values. The silica-silane filled vulcanizates showed a higher modulus, reinforcing index, hardness and abrasion resistance than the vulcanizates containing modified silica. On the other hand, the modified silica-filled vulcanizates exhibited excellent ultimate tensile properties. The loss tangent at 0 ºC and 60 ºC of the vulcanizates filled with different types of fillers as well as filler dispersion are also discussed.

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