Nanoclays exfoliation/intercalation

Yeh et al. (2009) investigated the effect of nanoclay on the dielectric and thermal transport properties of PMMA nanocomposite foams. As shown in Figure 1.18, the nanocomposite foams showed lower dielectric constants than the neat PMMA foam. And the effect is more prominent when the clay nanoparticles were better dispersed (CCLMA clay) and when the clay concentration was increased. The effect on thermal conductivity (Figure 1.19) was slightly more complicated. While the nanocomposite foams with better dispersion, that is, CCLMA nanocomposites with an exfoliated-intercalated mixed morphology, showed a deaease in thermal conductivity, the thermal conductivity of the intercalated ACLMA nanocomposite foam was higher than that of neat PMMA foam. They have also prepared PMMA M WCNT nanocomposite foams and measured their insulation property. Interestingly, they noticed a decrease in both dielectric constant (22.6%) and thermal conductivity (19.7%) in the nanocomposite foams with 0.3 wt% carboxyl-multi-walled carbon nanotubes (c-MWNTs). 

The results suggest that the thermal stability improves with higher loading till 6 phr of nanoclay and this improvement is attributed to the barrier effect of the exfoliated and the intercalated nanoclay particles. 

This is a highly polar polymer and crystalline due to the presence of amide linkages. To achieve effective intercalation and exfoliation, the nanoclay has to be modified with some functional polar group. Most commonly, amino acid treatment is done for the nanoclays. Nanocomposites have been prepared using in situ polymerization [85] and melt-intercalation methods [113-117]. Crystallization behavior [118-122], mechanical [123,124], thermal, and barrier properties, and kinetic study [125,126] have been carried out. Nylon-based nanocomposites are now being produced commercially. 

In subsequent discussion, we will demonstrate the use and interpretation of some of these techniques. Figure 2a shows typical XRD traces of nanocomposite systems of styrene butadiene rubber (SBR) containing unmodified and modified nanoclay, describing an exfoliated and intercalated nanocomposite [5]. photographs of these systems are also given in the same figure (Fig. 2b, c). In the present case, the information obtained from both the techniques is complimentary. 

It is a common phenomenon that the intercalated-exfoliated clay coexists in the bulk and in the interface of a blend. Previous studies of polymer blend-clay systems usually show that the clay resides either at the interface [81] or in the bulk [82]. The simultaneous existence of clay layers in the interface and bulk allows two functions to be attributed to the nanoclay particles one as a compatibilizer because the clays are being accumulated at the interface, and the other as a nanofiller that can reinforce the rubber polymer and subsequently improve the mechanical properties of the compound. The firm existence of the exfoliated clay layers and an interconnected chain-like structure at the interface of CR and EPDM (as evident from Fig. 42a, b) surely affects the interfacial energy between CR and EPDM, and these arrangements seem to enhance the compatibility between the two rubbers. 

Nano-clay particles, 476 Exfoliated, 476 Intercalated, 476 Nanoclay, 190... 

TPV nanocomposites of LLDPE/reclaimed rubber with nanoclay and 1 wt.% MA-grafted PE and curative were prepared using a Brabender internal mixer at 170°C (Razmjooei et al., 2012). Contents of the reclaimed rubber, nanoclay, and compatibilizer were varied up to 30, 7, and 21 wt.%, respectively. The blends without the compatibilizer were also prepared. Morphological, thermal, and mechanical properties of the nanoclay-reinforced TPV nanocomposites indicated intercalation and partial exfoliation by the high-shear stress during mixing with the reclaimed rubber. Vulcanization of rubber phase led to an increase of viscosity. The size of rubber particles in TPV was reduced with the addition of nanoclay and compatibilizer. 

This work thus deals with the addition of different types of montmorillonite nanoclays, especially NaMMT, to thermosetting PF and PUF resins to study (1) the effect of the PF and PUF resins on the level of intercalation or exfoliation of the montmorillonite nanoclays (2) the influence of resin structure on intercalation and (3) the improvement in performance of the resin by analysing the performance of wood panels/composites bonded with PF/montmorillonite nanoclays. 

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