Nanostructured clay intercalation

Clays are a very important group of inorganic compounds due to their many possible practical applications, such as supports for catalysts, as lubricants, and for thermal insulation. Many clays such as vermicuHte, montmorUlonite, and steatite exhibit a lamellar nanostructure, which make them suitable hosts for the preparation of intercalation compoimds. As recently [1] demonstrated for soapstone, a compact form of steatite (talcum powder), even very small variations in chemical composition can exert significant effects on physical and chemical properties. 

Rocha e Silva et al. [52] have prepared layered PHB nanostructured materials by adding different amounts of commercial clays on PHB matrix. They have demonstrated that the obtained nanostructured materials exhibited an excellent degree of dispersion (intercalation/exfoliation) and that the clay was able to promote changes in the structure of neat polymer by reducing its crystallinity degree. 

Natural montroriUonite and organically modified MMT with methyl tallow bis-2-hydroxyethyl ammonium cations located in the silicate gallery (Cloisite 30B) were evaluted in starch-based nanocomposite [232]. It was observed that the TPS/ Cloisite Na-t nanocomposites showed higher tensile strength and thermal stability, better barrier properties to water vapor than the TPS/Cloisite 30B nanocomposites, as well as the pristine TPS, due to the formation of the intercalated nanostructure. Perez et al. [233] compared three different clays (Cloisite Na+, Cloisite 30B and Cloisite 10A) and found the best properties were achieved with Cloisite lOA due to their greatest compatibility with the matrix. 

Choi and Chung [16] were the first to prepare phenolic resin/layered sihcate nanocomposites with intercalated or exfoliated nanostructures by melt interaction using linear novolac and examined their mechanical properties and thermal stability. Lee and Giannelis [10] reported a melt interaction method for phenolic resin/clay nanocomposites, too. Although PF resin is a widely used polymer, there are not many research reports on PF resin/montmorillonite nanocomposites, and most of the research investigations have concentrated on linear novolac resins. Up to now, only limited research studies on resole-type phenolic resin/layered silicate nanocomposites have been published [17-19] and there is still no report on the influence of nano-montmorillonite on phenolic resin as wood adhesive. Normally H-montmorillonite (HMMT) has been used as an acid catalyst for the preparation of novolac/layered silicate nanocomposites. Resole resins can be prepared by condensation reaction catalyzed by alkaline NaMMT, just as what HMMT has done for novolac resins. 

Nanoparticles exist in spherical, mbe and whisker, and plate-like shapes and at least one of the three dimensions is required to be on a nanometric scale. Nanostructures of layered clays are further categorized as intercalated, in which the polymer chains have penetrated between the clay layers in a well-ordered multilayer morphology, and exfoliated, in which the clay layers have dispersed along the matrix and have no organized slnictme [7]. Carbon nanombes also exhibit two nanostructmes single-walled nanotube and mnltiwalled nanotube, which is composed of several tubes within each other. 

Maiti et al. [32] prepared a series of PLA-based nanostructured materials with three different types of pristine clays, saponite, MMT, and synthetic mica (SM), and each was modified with alkylphosphonium salts having different chain lengths. In their work, they first tried to determine the effect of varying the chain length of the alkylphosphonium modifier on the properties of the organoclay, and how the various clays behaved differently with the same organic modifier. They also studied the effects of dispersion, intercalation, and the aspect ratio of the clay on the properties of PLA. 

Mitsunaga, M., Ito, Y., Ray, S. S., Okamoto, M., and Hironako, K. 2003. Intercalated polycarbonate/clay nanocomposites Nanostructure control and foam processing. Macromol Mater Eng 288 543. 

---