Silica-organoclay nanocomposites

The intermediate silica-organoclay nanocomposites clearly show the delamination of the layered silicates evidenced from the XRD patterns, showing the absence of the 001 rational order characteristics of the starting silicates. Figure 14.6 shows the loss of crystallinity of the layered silicates after reaction with TMOS in -butanol at 50°C in 1 1 clay/TMOS w/w ratio, with the gelation time ranging from 0.5 to 2 h. 

Moreover Ponomarenko et al. reported the melt-compounded composites of synthetic styrene-co-butadiene mbber (BUNA SL18) and silica particles (Silica VN3, Degussa). They showed that at low elongations, silica particles provided a considerably weaker reinforcement effect of the mbber matrix when compared to organoclay nanoparticles. The overall tiiermoelastic behavior of both the mbber/ silica composites and the mbber/organoclay nanocomposites could be quantitatively... 

Fig. 13.12 Polymer nanocomposites containing spherical silica nanoparticles in vinyl ester (left) and exfoliated organoclay...

In ternary nanocomposites, compatibilizers have been mostly used to improve the adhesion at the polymer/filler interface rather than to modify the polymer/elastomer interface. Mishra et al. [80] compounded PP/EPDM/organoclay (75/25/5 wt%) and added PP-g-MA (1 wt% MA) as a compatibilizer with a clay/PP- -MA ratio of 1/3. They characterized the interlayer spacing of the clay platelets by XRD and observed that it increased from 3.4 to 4.3 nm for systems without and with compatibilizer. This was attributed to a better diffusion of the PP-g-MA chains inside the interlayer spacing thanks to their functional groups. Numerous other authors prepared and characterized ternary composites with a compatibilizer. Examples include Lim et al. [81] and Lee et al. [5] on PP/PP- -MA/POE/ organoclay systems, Mehta et al. [23] on PP/PP-g-MA/EPR/organoclay systems, and Liu and Kontopoulou [24,45] on PP/PP-g-MA/ethylene-octene copolymer/silica composites. It should be noted that the compatibilizer itself may affect the properties of the matrix... 

The effectiveness of organoclay in NR was observed and reported by Carli et They evaluated the technical feasibility of NR nanocomposites with Cloisite 15A, a commercial organoclay to substitute conventional silica (Si02) filler. TEM analysis indicated that the OMt was homogeneously dispersed in the rubber matrix. A shift of the characteristic peaks to lower angles was observed in XRD, attributed to the intercalation of the OMt by macromolecular rubber chains. Based on the mechanical properties of the compounds they concluded that 50 phr of silica can be replaced by 4 phr of OMt with a reduction in the filler content by 12.5 times, without adversely affecting the tensile properties of the final material even after ageing. 

Cassagnau P (2008) Melt rheology of organoclay and fumed silica nanocomposites. Polymer 49 2183-2196... 

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