Rubber blends vulcanization/grafting

Improvement in the solvent and oil resistance of rubbers can be achieved via grafting of acrylonitrile onto rubber [140-142] and rubber blends [143]. The careful control of the degree of grafting allows vulcanized rubber with high-mechanical properties compared with ungrafted vulcanized rubber to be obtained. Also, acid resistance [144] and resistance to microbiological attack [145,146] was improved for cellulose grafted with acrylonitrile, and increases in base resistance were also noted for MMA and a mixture of MMA and ethyl acrylate [13],... 

Similar results were obtained by shear blending of two synthetic elastomers (45). The formation of a block or graft copolymer during the process of mixing butadiene rubber (SKB) and styrene-containing rubber (SKS-30A) was postulated by Slonimskii and Reztsova (49). They claimed that the anomalies observed in the dependences on composition of the mechanical properties of a mixture of two mutually insoluble rubbers after vulcanization may be reduced by increasing the part played by the mechanical mixing (inert atmosphere, reduction of radical acceptors, intensity of mechanical action). 

Compatibilization along with dynamic vulcanization techniques have been used in thermoplastic elastomer blends of poly(butylene terephthalate) and ethylene propylene diene rubber by Moffett and Dekkers [28]. In situ formation of graft copolymer can be obtained by the use of suitably functionalized rubbers. By the usage of conventional vulcanizing agents for EPDM, the dynamic vulcanization of the blend can be achieved. The optimum effect of compatibilization along with dynamic vulcanization can be obtained only when the compatibilization is done before the rubber phase is dispersed. 

TPV nanocomposites of LLDPE/reclaimed rubber with nanoclay and 1 wt.% MA-grafted PE and curative were prepared using a Brabender internal mixer at 170°C (Razmjooei et al., 2012). Contents of the reclaimed rubber, nanoclay, and compatibilizer were varied up to 30, 7, and 21 wt.%, respectively. The blends without the compatibilizer were also prepared. Morphological, thermal, and mechanical properties of the nanoclay-reinforced TPV nanocomposites indicated intercalation and partial exfoliation by the high-shear stress during mixing with the reclaimed rubber. Vulcanization of rubber phase led to an increase of viscosity. The size of rubber particles in TPV was reduced with the addition of nanoclay and compatibilizer. 

The poly(methyl methacrylate) molecules were dispersed in the natural rubber matrix, or vice versa, to form spherical droplets, as observed by optical photographs or scanning electron microscopy. The compatible natural rubber/poly(methyl methacrylate) blends had been made by the addition of the graft copolymer of natural rubber-gr t-poly(methyl methacrylate) as the compatibilizing agent due to its ability to enhance the interfacial adhesion between the two homopolymers. Moreover, Nakasorn and coworkers reported that natural rubber-gr i -poly(methyl methacrylate) could be blended with poly(methyl methacrylate) via a dynamic vulcanization technique with a conventional sulfur vulcanization system. The natural rubber-gra/t-poly(methyl methacrylate) was synthesized by a semi-batch emulsion polymerization technique via different bipolar redox initiation systems, i.e. cumene hydroperoxide and tetraethylene pentamine. ... 

Oommen et al. had studied melt rheological behaviour of the blends between NR and poly(methyl methacrylate) based on the effect of blend ratio, processing conditions and graft copolymer concentration as a function of shear stress and temperature. It was clarified that the viscosity of the blends increased with the increase of the amount of NR. On the other hand, the flow behaviour of the blends was found to be influenced by dynamic vulcanization of the rubber phase. 

In recent years, some works have focused on the possibility of using silica nanoparticles as a com-patibilizer for polymer blends. Blends of PP and dynamically vulcanized EPDM rubber are called TPVs. Wu et al. [114] prepared nanocomposites of TPV/SiOj. The CTAB-treated SiO was melt-blended with TPV in the presence of MA grafted PP (mPP), which acted as a function ized com-patibilizer. During melt blending, CTAB and mPP tethered themselves onto the TPV backbone by a grafting reaction. The strong interaction caused by the grafting reaction improved the dispersion of silica in the TPV matrix. 

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