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Itaconic acid has been employed as a special facilitator to construct divalent metal ion based ionic crosslinking framework in the acrylonitrile butadiene rubber matrix. Readily accessible double bonds in itaconic acid could directly react with the elastomer to form effective covalent bonds. On the other hand, presence of easily dissociable protons in itaconic acid enables them to form ionic bonds that leads to an increase in crosslinking density of the vulcanizates. The synergistic effect of covalent crosslinking induced by peroxide and ionic crosslinking induced by metal carboxylate could effectively enhance the overall mechanical and dynamic mechanical properties of the rubber composites. In this study, three metal oxides, that is, zinc oxide, magnesium oxide, and calcium oxide, have been selected for this purpose. Tensile strength of nitrile rubber composites depends on the strength of ionic crosslinks, which in turn is influenced by the size of the alkaline earth metals, such as Mg, Ca, etc., and stoichiometric quantity of itaconic acid, which is at par in the formulation of this study. The novelty of this study is that the introduction of a dicarboxylic acid in combination with metal oxides enhances the crosslink density and tensile strength of nitrile rubber composites which could result from the metal organic framework.

Ultra-thin graphene has been receiving significance in the diverse sections of material science, owing to its exceptional physicochemical and thermo-mechanical characteristics. Currently, the fabrication of high-grade graphene in an economical target and green procedures area is a massive concern. Among the diverse techniques, chemical-mediated fabrication is believed to be the finest process since it is simple, scalable, and of low-cost; however, it involves noxious or hazardous chemical reducers for producing functional graphene-based Nanocomposites (NCs). Therefore, around the globe, scientists are endeavoring to adopt the bioinspired techniques to manufacture the functional reduced Graphene Oxide (rGO) and reduced Graphene Oxide-Metal/Metal Oxide (rGO-M/MO) NCs. Hence, keeping this issue in mind, the present review article summarize and integrates the current state of knowledge about the diverse bioinspired strategies developed to obtain rGO and rGO-M/MO NCs and their photocatalytic, antibacterial, and cytotoxic assessments.

Titania nanoparticles are introduced in situ into SSBR matrix (solution of styrene butadiene rubber) by solution sol-gel method under controlled reaction condition that shows outstanding reinforcing efficiency because of its favourable morphological features and enhanced polymer-filler interaction. Surface treatment of titania particles in reactive sol-gel system using an organosilane, TESPT (bis-(3-triethoxysilylpropyl)-tetrasulfide) further strengthens the reinforcement effect. Notably, more than 85% conversion of titania from it's precursor (titanium n-butoxide, TNB) is achieved within 1 h reaction time without employing any catalyst. Additionally, controlled growth of titania particles inside rubber matrix imparts particular characteristics of the titania particles that enables them to deliver rich dielectric and antifungal properties to the composites. In-depth investigation of the composites including rheological, thermal, morphological, mechanical, dynamic mechanical, dielectric and antifungal studies have been carried out and structure-property relationship is established in respect to SSBR gum and externally titania filled composites prepared at similar condition.

Functionalization of non-polar ethylene propylene diene monomer (EPDM) rubber by melt grafting of maleic anhydride (MA) and in situ incorporation of sol–gel derived silica in the MA grafted EPDM has been done to prepare EPDM/silica composites to use dual benefits of both the approaches, which results in adequate rubber–filler compatibility, good filler dispersion, and enhanced composite properties. Controlled growth of silica up to 25 parts per hundred rubber (phr) is carried out with the solution sol–gel process using tetraethoxysilane (TEOS) as a silica precursor. Mechanical and dynamical properties of the composites are found to improve consistently as silica content increases. Furthermore, treatment of maleic anhydride grafted EPDM by γ-aminopropyltrimethoxysilane (γ-APS) results in remarkable improvement in composite properties even at the same silica content. This is attributed to the generation of uniformly dispersed spherically shaped nanosilica throughout the rubber matrix as observed in a transmission electron microscopic (TEM) study. This contributes to enhanced crosslinking density and improved rubber–filler interaction. In fact, the reinforcement effect brought by in situ silica relative to unmodified in situ silica/EPDM composites is found to be much higher than that reported in recent work on EPDM/in situ silica composites even with higher silica loading. The mechanical, rheological, and dynamic mechanical behaviors of all the composites are evaluated and compared in detail.

Remarkable improvement in mechanical properties of acrylonitrile butadiene rubber (NBR) composites is achieved by incorporating nano-titania that is synthesised in solution of the raw rubber using titanium n -butoxide (TNB) as the titania precursor. This is achieved by designed and controlled incorporation of titania that resulted in very good dispersion of titania of nanometric dimension in rubber matrix and enhanced rubber-filler interaction. This sol-gel transformation is carried out under optimised reaction condition. Surface modification of titania by a silane coupling agent (bis-(3-triethoxysilylpropyl)-tetrasulfide, TESPT) causes further improvement in filler dispersion and composite properties when added in the reactive sol-gel system during in situ titania generation rather than it's external addition in the titania filled NBR during mixing and compounding. Thorough characterisation of the composites are done that encompasses a wide range of studies on thermal, morphological, mechanical, dielectric, dynamic mechanical, rheological and antifungal properties. The results are analysed on a comparative basis to investigate the effect of in situ incorporation and in situ surface modification of titania on the composite properties.

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.

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.

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.

Nano silica is generated in situ inside the uncrosslinked chloroprene rubber (CR) by the sol-gel reaction of tetraethoxysilane (TEOS). This results in appreciable improvement in mechanical properties of the CR composites at relatively low filler content. Furthermore, exploitation of reactive organosilanes, γ-aminopropyltrimethoxysilane (γ-APS) in particular, in the silica synthesis process facilitates growing of spherical silica particles with a size distribution in the range of 20-50 nm. The silica particles are found to be uniformly dispersed and they do not suffer from filler-filler interaction. Additionally, it is observed that the silica particles are coated by silane and rubber chains together which are popularly known as bound rubber. The existence of the bound rubber on silica surface has been supported by the detailed investigations with transmission electron microscopy (TEM), energy filtered transmission electron microscopy (EFTEM) and energy dispersive X-ray spectroscopy (EDAX). The interaction between rubber and silica, via bi-functionality of the γ-APS, has been explored by detailed FTIR studies. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43717.

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.

Nitrile rubber/silica composites are prepared by a sol–gel process using tetraethoxysilane as precursor in the presence of γ-mercaptopropyltrimethoxysilane 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. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40054.