Rubber blend composites reinforcing fillers

Figure 12.5. Volume resistivity against filler loading for SBR composites filled with carbon black (CB Ensaco 250G from Timcal) and MWNTs. [Figure 5A is reprinted from L. Bokobza, M. Rahmani, C. Belin, J.-L. Bruneel, N.-E. El Bounia "Blends of carbon blacks and multwall carbon nanotubes as reinforcing fillers for hydrocarbon rubbers", Journal of Polymer Science Part B Polymer Physics, 46,1939, 2008, permission from John Wiley and Sons].

Jong et prepared NR composites reinforced with hybrid filler consisting of defatted soy flour (DSF) and CB. Aqueous dispersions of DSF and CB were first mixed, and then blended with NR latex and sulfur dispersion, respectively. The homogenous composite mixtures were quickly freeze-dried and compression moulded to offer the NR composites. They found that the NR composites reinforced with 40% of hybrid filler (the ratio of DSF to CB was 1 1) exhibited a 90-fold improvement in the rubber plateau modulus compared with unfilled NR, showing a significant reinforcement effect by the hybrid filler. 

Machalkova [643] has described analysis of polymer composites and rubber blends with emphasis on separation of low-MW additives by instrumental methods. Examples refer to analysis of inorganic filler- or synthetic fibre-reinforced plastics and laminated plastic Aims using PyGC and IR. The versatility of PyGC has further been exemplified by Jones [633] as a thermovolatilisation technique for direct determination of occluded volatiles and low-MW additives in lube oil, novolac resins and HDPE, of plasticisers and vinylchloride in PVC, and of solvent residues in paints and bitumens, etc. Dicumylperoxide (DCP) in LDPE was identified through detection of three main by-products of reaction, acetophenone, a-methylstyrene and 2-phenylpropan-2-ol [633]. 

The tire is a complicated composite product consisting of tread, undertread, carcass, innerliner, bead, and sidewall. Many different types of rubber and carbon black reinforcement are used in manufacturing tires. Therefore, GRT is a blend of various rubbers and carbon blacks. Accordingly, in using GRT powder and devulcanized GRT in new tire manufacturing, many factors should be considered. Evidently, scrap tire powder can be used as a filler for virgin rubbers and devulcanized GRT can be used in blends with virgin rubbers. This market consumed approximately 1.354 x 10 tons of scrap tire rabber in 2009 (US Scrap Tire Markets, 2009). 

NR composites and nanocomposites can be fabricated by three main techniques, namely latex compounding, solution mixing and melt blending. A variety of nanofillers, such as carbon black, silica, carbon nanotubes, graphene, calcium carbonate, organomodified clay, reclaimed rubber powder, recycled poly(ethylene terephthalate) powder, cellulose whiskers, starch nanocrystals, etc. have been used to reinforce NR composites and nanocomposites over the past two decades. In this chapter, we discuss the preparation and properties of NR composites and nanocomposites from the viewpoint of nanofillers. We divide nanofillers into four different types conventional fillers, natural fillers, metal or compound fillers and hybrid fillers, and the following discussion is based on this classification. 

Mohamed et al. [149] evaluated the use of several types of sulfosuccinate anionic surfactants in the dispersion of MWCNTs in NR latex matrices. Sodium l,5-dioxo-l,5-bis(3-phenylpropoxy)-3-((3-phenylpropoxy)carbonyl) pentane-2-sul-fonate showed the best dispersion capabihty and improved the electrical conductivity of the resulted composites. These results have significant implications in the development of new materials for aerospace applications because the filler s dispersiou directly influences the properties of the final material. Jo et al. [150] obtained pristine MWCNt-Ti02 nanoparticles filled with NR-CllR and epoxidized NR-CUR, concluding that the second blend proved higher thermal conductivity because the epoxy branches in ENR and the functionalized MWCNT form a stronger network. Conductivity in CNTs reinforced with rubber-based blends can be improved when reaching a critical concentration of the filler known as the percolation threshold, when a continuous network structure is formed. Thankappan Nair et al. [151] discussed the percolation mechanism in MWCNT-polypropylene-NR blends. 

These studies have shown that POSS can reinforce PDMS especially when it is partially bonded to the polymer network. What s more, when POSS fillers blended with a PDMS silanol-terminated matrix (without bonding), the mechanical properties remained on the same level. Chemical bonds between the filler and the matrix are not directly correlated with the reinforcement of the system, but improve the dispersion of the filler in the polymer network. Bonded composites possess a dynamic mechanical response very similar to rubbers filled with colloidal silica. 

The barrier properties of 70/30 acrylonitrile-butadiene mbber/ethylene propylene diene monomer rubber (NBR/EPDM) vulcanizates, when loaded with carbon black fillers [e.g., I SAP (intermediate super-abrasion furnace), HAF (high-abrasion furnace) and SRF (semi-reinforcing furnace)] and using benzene, toluene and xylene as penetrants, have been examined with reference to the type of filler employed [66]. The filled samples were found to exhibit a better resistance to uptake of the three organic solvents when compared to the respective unfilled blends for any given blend ratio. With regards to the three types of carbon black used, solvent uptake was in the order SRF-> HAF-> ISAF-filled samples. The reason for this order was attributed to the better filler reinforcements and enhanced crosslink densities of the matrix as the size of the carbon black particles used was decreased. A similar behavior was also identified for NR/EVA composites [52]. 

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