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Rice husk ash (RHA) and siliceous earth (SE) were compared as alternative reinforcing fillers in epoxidized natural rubber (ENR) vulcanizates. The effects of RHA and SE on processability, curing characteristics, mechanical, thermal and morphological properties, and thermoelastic behavior of vulcanizates were studied, in the presence and absence of bis(triethoxysilylpropyl) tetrasulfide (TESPT) silane coupling agent. The results indicated that the RHA offers processing advantages over the commercial SE. The filled ENR vulcanizates without TESPT provided higher tensile strengths than the unfilled ENR vulcanizates, but had lower elongations at break. This is attributed to physical interactions between filler particles and rubber matrix, which affects the reinforcement by the filler. The modification of filler surfaces with TESPT resulted in further improved properties of the rubber vulcanizates. This is attributed to the coupling of polymer matrix and filler particles via TESPT linkages that increased the polymer–filler interactions. It was also found that the RHA filler, a renewable resource, exhibited similar reinforcement to the conventional SE. This indicates that the RHA has great potential as a reinforcing filler that can substitute for conventional SE in polymer composites. POLYM. COMPOS., 39:414–426, 2018. © 2016 Society of Plastics Engineers

In polymeric materials combining desirable properties, compatibility between constituent components of incompatible blends is necessary. The influence of two types of blend compatibilizers, a graft copolymer of maleic anhydride and polypropylene (PP) and phenolic-modified PP, on the rheological, mechanical, and morphological properties of epoxidized natural rubber/PP thermoplastic vulcanizates was investigated at varied concentrations. All properties improved in a range of loading levels of compatibilizers at 0-7.5 wt % of PP. This was attributed to a chemical interaction between the different phases caused by the functionalized compatibilizers.Increasing chemical interaction between interfaces improved the interfacial tension and led to a microscale size of the dispersion. A decreasing trend in the properties was observed at compatibilizer levels higher than 7.5 wt % of PP because of segregation, which led to a third blend component dispersed in the PP matrix. The compatibilizers behaved as lubricants in the polymer melt flow.

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Thermoplastic vulcanizates (TPVs) from natural rubber (NR) and polypropylene (PP) were studied, prepared by dynamic vulcanization during melt mixing, using various peroxides to crosslink the rubber phase. The objective was to find a proper balance between degree of crosslinking of the rubber and degradation of the PP-phase, and the tendency of the peroxide to form smelly by-products, in particular acetophenone. Four types of peroxides were investigated: 2,5-dimethyl-2,5-di(tert-butylperoxy) hexyne-3 (DTBPHY), 2,5-dimethyl-2,5-di(tert-butylperoxy) hexane (DTBPH), di(tert-butylperoxyisopropyl) benzene (DTBPIB), and dicumyl peroxide (DCP), at two mixing temperatures: 160 and 1808C for a 60/40 NR/PP TPV. The maximum and final mixing torques are clearly related to the intrinsic decomposition temperature of the particular peroxide used, where DCP and DTBPIB turn out to be effective at 1608C, whereas the other two require a higher temperature of 1808C. The best mechanical properties, tensile strength, elongation at break and compression set are obtained at lower mixing temperature with DCP and DTBPIB, presumably due to less degradation of the NR and PP. Unfortunately, these two peroxides form more smelly by-products than DTBPHY and DTBPH. Dependent on the requirements of the pertinent application, a balanced selection needs to be made between the various factors involved to obtain an optimal product performance of these NR/PP TPVs.

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