Nanocomposites from Latex Blends

Polyurethane (PUR), being polar and having a lower molecular mass compared to natural rubber, was supposed to intercalate better with LS. Moreover, the addition of PUR latex to NR latex can make the former cheaper without affecting the mechanical properties. Latex blends with various PUR/NR ratios 

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This is truly reflected in the morphology of the uncured clay preexfoliated rubber nanocomposite films (NLu NA) prepared by the latex blending method (Fig. 7a). Curing the NR/NA nanocomposites in situ prevulcanization (No>NA) does not alter the arrangements of dispersed clay layers greatly, as seen from the... 

Molesa et al. [61] compared compounded styrene-butadiene nanocomposites with polymer nanocomposites that were prepared by blending the latex with an aqueous dispersion of the montmoriUonite. The loading of the dispersed phase was at 10 phr. The initial results are consistent with the information found above. The flocculated rubber nanocomposite from the aqueous blend has superior strength properties when vulcanized and compared with the rubber nanocomposite prepared by compounding. MontmoriUonite that was organically treated demonstrated superior tensile strength when compared with rubber compounded with sUica. 

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. 

Styrene-butadiene copolymers are extremely important to the rubber industry. They are particularly important in tire manufacture. Styrene-butadiene polymer is produced by emulsion polymerization and solution polymerization. Most of the volume is by emulsion polymerization. This affords the opportunity to prepare polymer nanocomposites by several avenues. One can blend an aqueous dispersion of the nanoparticles with the styrene-butadiene latex before flocculation to produce the rubber crumb, disperse an organically treated nanoparticle in the styrene-butadiene solution polymer before the solvent is stripped from the polymer, disperse the organically treated nanoparticles into the monomers, or prepare the rubber nanocomposite in the traditional compounding approach. One finds all of these approaches in the literature. One also finds functional modifications of the styrene-butadiene polymer in the literature designed to improve the efficiency of the dispersion and interaction of the nanoparticles with the polymer. 

Boonmahitthisud et al., prepared natural rubber/carboxylated styrene butadiene rubber (NR/XSBR) (80/20) nanocomposites containing different loadings of carbon nanotube (CNT) (0.1-0.4 phr) by a latex stage compounding method. The dynamic mechanical properties, in terms of tan 8 and E, of the neat 80/20 NR/XSBR blend and its nanocomposites were evaluated from —80 to 100 °C. Figure 21 shows the influence CNT loadings, on the tan 8 and E as a function of temperature for the nanocomposites [100]. 

The results on MWCNT-polymer nanocomposites reported in this chapter demonstrate the versatility of the latex concept to prepare nanocomposites with a broad range of "home-made" or industrially manufactured polymers, namely, amorphous, semi-crystalline, and blended polymer matrixes. Note that blending can further be done in very different fashions, i.e., in situ, while the emulsion polymerization proceeds, by mixing of two different polymer latexes synthesized independently from each other, or by a "masterbatch approach." This study confirms that the CNT-polymer interactions are of major importance to influence the percolation behavior of the nanocomposites, as well as the viscosity, morphology, and the intrinsic conductivity of the polymer matrix. 

Thermal analysis using heated tip technology [115] has been reviewed by Price et al. [116], Wunderlich [117], Pollock and Hammiche [118], and Abad et al. [119]. Reviews on mechanical deformation of polymer films by nanoindentation [120] and AFM indentation [121] as well as in situ tensile deformation [122] have been published. A related area of force spectroscopy to extract intermolecular and intramolecular forces between polymer chains was reviewed by Hugel and Seitz in 2001 [123]. Bushan has written extensively on the use of SPM to study tribology [124], and frictional contrast has been discussed in reviews by Mate [125], Zasadzinski [126], and Feldman et al. [127]. Spatially localized adhesion studies using chemically modified AFM tips was reviewed in 2005 by Vezenov et al. [128] and Vancso et al. [129]. Characterization of polymer film surfaces [130,131], latexes [132,133], multiphase polymer blends [134, 135], and nanocomposites [136, 137] has also been reviewed. Authors from the laboratories of several manufacturers of industrial engineering polymers have published reviews on the application of SPM to characterization [138-140]. 

From the above, we can see that the mechanism of morphology formation is quite different from that of traditional polymer solution organic-inorganic nanocomposites. For traditional polymer solution systems, the phase separation mechanism is similar to that of polymer blends, i.e., nucleation and growth mechanism and spinodal decomposition mechanism.Generally, the component with higher content is apt to form the continuous phase and the other the dispersed phase. However, for the PEA/bentonite emulsion system, whether PEA can be continuous or not depends mainly on whether the PEA latex particles are in close contact before the complete volatilization of water. Instead, it depends on whether the content of PEA is larger than that of bentonite. 

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