Organoclays Volume

Utracki, L. A., and Simha, R., Pressure-volume-temperature dependence of polypropy-lene/organoclay nanocomposites. Macromolecules, 37, 10123-10133 (2004). 

FIGURE 6.5 Loss of free volume caused by addition of 2 wt% organoclay versus interlayer spacing. (From Tanoue et al. [2004].)... 

Polypropylene (PP) is one of the most widely used plastics in large volume. To overcome the disadvantages of PP, such as low toughness and low service temperature, researchers have tried to improve the properties with the addition of nanoparticles that contains p>olar functional groups. An alkylammonium surfactant has been adequate to modify the clay surfaces and promote the formation of nanocomposite structure. Until now, two major methods, i.e., in-situ polymerization( Ma et al., 2001 Pirmavaia, 2000) and melt intercalation ( Manias et al.,2001) have been the techniques to prepare clay/PP nanocomposites. In the former method, the clay is used as a catalyst carrier, propylene monomer intercalates into the interlayer space of the clay and then polymerizes there. The macromolecule chains exfoliate the silicate layers and make them disperse in the polymer matrix evenly. In melt intercalation, PP and organoclay are compounded in the molten state to form nanocomposites. 

Research on the crosslinking of UP resins in the presence of organically modified clays was conducted by Xu and Lee. They have found that by adding 1-3 wt% organoclay to UP-styrene-poly(vinyl acetate) system cured at room temperature, the volume shrinkage of the crosslinked polymer could be eliminated [16]. In another study Xu and Lee investigated the effect of nanoclay on the cure kinetics of UP resin and the mechanical properties of the resulting UP nanocomposites [17]. 

The improvement in thermal stability of the nanocomposites compared to the neat EVA/natural rubber is due to the barrier effect and insulating properties of organoclay. The well dispersed plate-like silicate layers form a tortuous path in the polymer matrix which gives a barrier effect and inhibits the diffusion of volatile degradation product from the inside of the polymer matrix. Moreover the well-dispersed silicate layers restrict the movement of polymeric chains, hence reducing the free volume for diffusion of volatile degradation products. Other researchers also confirm that organoclay tends to form a compact char-like residue on the surface of the nanocomposites when it is burnt. This char-like structure is incombustible and acts as an insulator which inhibits heat transfer to the inside of the nanocomposites. At 8 phr... 

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