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. g-mercaptopropyltrimethoxysilane (g-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.

The strong CR/in situ silica interaction causes filler accumulation at the interphase and enhances the compatibility and reinforcement in the NR/CR blend.

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Chemical cross-linking of rubber is a process to significantly modify the physical properties of the polymer. By this transformation, a highly viscous rubber compound is converted into an elastomer suitable for high-performance products like tires. Conventionally, sulfur or peroxide cross-linking is the preferred mode of vulcanization of the polymer practiced by different rubber industries. To fulfill the growing demand for more durable, high-performance rubber products, the development of self-healing rubber is considered one of the most promising approaches. The present study is an endeavor to mimic self-healing property in commercial epoxidized natural rubber (ENR) utilizing a mechanism that ensures the continuous supply of the healing agent to the affected area. With the advancement of metal coordination as a means of network structure, here, we report for the first time a different method for the preparation of self-healable ENR using mixed metals ions and diamine as cross-linking agents. The availability of a nitrogen coordination site of the diamine along with the reactivity of the oxirane group of epoxidized natural rubber toward metal ions enables the re-establishment of cross-linking sites in a damaged polymer network. A slow release of the metal ions from the metal amine complex to the ultra-active oxirane groups assists this reformation of the network. Additionally, some of the physical properties of the metal ion cross-linked samples are found to be comparable with those of conventional sulfur cross-linked samples.

Nitrile rubber/silica composites are prepared by a sol-gel process using tetraethoxysilane as precursor in the presence of cmercaptopropyltrimethoxysilane as a silane coupling agent. Here, we follow a novel processing route where the silica particles are generated inside the rubber matrix before compounding with vulcanizing ingredients. The effect of in situ generated silanized silica on the properties of the rubber composite has been evaluated by studying curing characteristics, morphology, mechanical and dynamic mechanical properties. Enhanced rubber-filler interaction of these composites is revealed from stress-strain studies and dynamic mechanical analysis. Excessive use of silane shows an adverse effect on mechanical properties of the composites. Due to finer dispersed state of the in situ silica and enhanced rubber-filler interaction, the mechanical properties and thermal stability of the composites are improved compared to corresponding ex situ processed composite.

Potential of crystalline nanocellulose (CNC), as green reinforcing filler, has been evaluated for the preparation of natural rubber (NR) composites. CNC is derived from a natural source (ramie fiber) and its surface is modified with different organosilanes to strengthen the rubber‐filler interaction at the interface. It is found that, although at 2.5 phr (parts per hundred parts of rubber) loading of CNC the mechanical property of the NR composites is improved, it deteriorates at 5 phr loading. Surface modification of CNC by organosilanes is found very useful to overcome this issue. The modulus values at low strain become almost 1.5 to 2 times higher while tensile strength becomes 2.5 times higher for the modified CNC filled composites relative to those of CNC filled composites at 5 phr loading. These results are corroborated with a morphological study, where a very good state of dispersion of CNC particles is found in the surface‐modified CNC filled composites. Moreover, the particle size of CNC becomes almost half, in respect to that of unmodified CNC particles, upon surface modification by organosilane. The reinforcement effect delivered by CNC and surface‐modified CNC is also reflected by a small positive shift in Glass Transition Temperature (Tg) in differential scanning calorimetry study.

Controlled growth of in situ silica, into natural rubber (NR)/nitrile rubber (NBR) blend (40/60 composition by weight) following solution sol-gel method, results in a coherent blend morphology with enhanced composite properties. Similar composites, i.e., in situ silica-filled NR/ NBR blend (40/60 by weight), showed better mechanical properties than any other composition that were prepared by soaking sol-gel method in earlier study. However, silica content in the rubber blend was limited to 20 phr (parts per hundred parts of rubber) and could not be increased under experimental condition following soaking sol-gel method. In the present work, silica content is increased (up to 30 phr) beyond that limit for the same blend composition. Accordingly, mechanical properties of the NR/NBR composites are improved. Use of a silane coupling agent, viz., bis-(3-triethoxysilylpropyl)-tetra sulfide, in the reactive sol-gel system during in situ silica generation brings in remarkable effect in silica distribution, rubber-filler interaction and mechanical properties of the composites. TEM micrographs of the selected composites reveal that silica is mostly grown at the interfacial region, when silane is used in particular. This results in further enhancement in mechanical properties and compatibility of the blend at the same silica content as evident from stress-strain and dynamic mechanical analysis studies. The reinforcement of effect in situ silica is assessed by Guth-Gold equation and modified form of Guth equation (with shape factor f = 2.53). The results are supported by the detailed studies on rheological, morphological, mechanical and viscoelastic properties of the composites. Graphical AbstractKeywords Rubber blend Á Sol-gel method Á In situ silica Á Rubber-filler interaction Á Silane treatment Á Reinforcement

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