Bharat P. Kapgate

Reinforcing efficiency and compatibilizing effect of sol–gel derived in situ silica for natural rubber/chloroprene rubber blends

Nano silica is grown, in situ, in natural rubber (NR)/chloroprene rubber (CR) blends, by the soaking sol–gel method. Much better silica dispersion in the rubber blends is achieved following this technique in comparison to the rubber blends with externally filled silica at the same filler loading and same blend composition. This leads to a significant improvement in modulus, tensile strength and dynamic mechanical properties of all the in situ silica filled composites relative to externally filled composites. Additionally, analysis of glass transition temperature (Tg) values reveals that compatibility of NR and CR in the blend is enhanced when silica is incorporated in situ which in turn contributes to improving the physical properties of the composites. This enhancement in the compatibility of rubber blends is attributed to the preferential accumulation of in situ silica at the interphase of the two constituent rubbers. The best mechanical properties are shown by the in situ filled composite with NR/CR at a 40/60 blend ratio. This result is in agreement with the rheological properties, thermal properties and viscoelastic behaviors of this particular composite. The ultimate properties of the composites are found to be governed by the blend composition, blend compatibility and state of filler dispersion, in addition to the filler content.

Effect of sol–gel derived in situ silica on the morphology and mechanical behavior of natural rubber and acrylonitrile butadiene rubber blends

Silica particles were generated and grown in situ by sol–gel method into rubber blends comprised of natural rubber (NR) and acrylonitrile butadiene rubber (NBR) at various blend ratios. Silica formed into rubber matrix was amorphous in nature. Amount of in situ silica increased with increase in natural rubber proportion in the blends during the sol–gel process. Morphology studies showed that the generated in situ silica were nanoparticles of different shapes and sizes mostly grown into the NR phase of the blends. In situ silica filled NR/NBR blend composites showed improvement in the mechanical and dynamic mechanical behaviors in comparison to those of the unfilled and externally filled NR/NBR blend composites. For the NR/NBR blend at 40/60 composition, in particular, the improvement was appreciable where size and dispersion of the silica particles into the rubber matrix were found to be more uniform. Dynamic mechanical analysis revealed a strong rubber–in situ silica interaction as indicated by a positive shift of the glass transition temperature of both the rubber phases in the blends.

Rubber composites based on silane-treated stöber silica and nitrile rubber Interaction of treated silica with rubber matrix

Role of silane-treated stöber silica as reinforcing filler for nitrile rubber (NBR) has been studied. Stöber silica is synthesized by sol–gel method, and the surface of silica is modified with the treatment of silane-coupling agent viz. γ-mercaptopropyltrimethoxysilane (γ-MPS) in varying proportions. Average particle size of stöber silica of spherical shape in the range of 200 to 400 nm is evident from scanning electron microscopy (SEM). Surface modification of silica particle with silane-coupling agents decreases surface energy and reduces agglomeration of silica particles in rubber matrix. Stress–strain study and dynamic mechanical analysis of silica-filled composites are compared with the unfilled ones. Analysis of cross-linking density, mechanical properties, and storage moduli indicates a strong rubber–filler interaction in the silane-treated, silica-filled NBR composites. Silane treatment is found to be effective in uniform dispersion of silica in rubber matrix and in improving the mechanical properties of rubber composite. Different functionalities of organosilane at its both end improve the compatibility of silica with rubber matrix and offer better rubber–filler interaction.

Controlled growth of in situ silica in a NR/CR blend by a solution sol–gel method and the studies of its composite properties

Silica is grown in situ into a natural rubber (NR)/chloroprene rubber (CR) blend (at 40/60 ratio), by a solution sol–gel method, where the silica content in rubber blend is increased in a controlled manner exceeding the limit found for the same blend ratio in the soaking sol–gel method. Reaction conditions have been optimized to get adequate conversion of tetraethoxysilane (TEOS, a silica precursor) to silica. Rheological, thermal, mechanical and viscoelastic properties of all the composites are compared with those of the unfilled rubber blend at similar conditions. Thermal and mechanical properties of the composites are found to improve consistently as silica content in the composite increases owing to increased rubber–filler interaction as revealed in dynamical mechanical analysis (DMA). Further improvement in the properties is observed for a particular composite where a silane coupling agent ((γ-aminopropyl)trimethoxysilane, γ-APS) is used in the reactive sol–gel system during in situ generation of silica. This is attributed to the uniform distribution of silica in the rubber matrix and strong rubber–filler interaction, caused by bifunctionality of silane, as revealed by morphology and DMA studies respectively. The reinforcement effect of silica is evaluated by comparing the experimental results with theoretical values obtained from the Guth–Gold model and the modified Guth model. The present study supplements the in situ silica generation in NR/CR blend of 40/60 ratio, following the solution sol–gel method, to the earlier study involving the soaking sol–gel method where the maximum reinforcement was found for this composition.

Electronic Applications of Chloroprene Rubber and Its Composites

This chapter is intended to give an overview of electrical conductivity and dielectric properties of chloroprene rubber (CR) composites with reference to their application in the field of electronics. Influence of different types of filler on the dielectric properties of the CR composites, in a wide frequency range and varying temperature condition, is thoroughly discussed. Type, concentration, and state of dispersion of fillers as well as the polar nature of CR are noticed to play a significant role in governing the electrical conductivity of CR composites. Electrical conductivity studies of carbon black (CB) and carbon fiber-based CR composites are discussed in terms of filler concentration, filler dispersion, and processing techniques. The role of ionic liquid-modified multi-walled carbon nanotube (MWCNT) in improving the electrical conductivity of CR composites is emphatically reviewed. The effects of different types of aging on the electrical properties of CR composites are also focused in this chapter. The CR composites discussed herewith could potentially be used in the field of electromagnetic interference (EMI) shielding, microwave absorbance, and conductive adhesive.