Polymer-silicate composite preparation

Alexandre, M. and Dubois, P. 2000. Polymer-layered silicate nano-composites preparation, properties and uses of a new class of materials. Materials Science and Engineering 28 1- 63. 

PP-g-MA) silicate nanocomposites and intercalated thermoset silicate nanocomposites for flame-retardant applications were characterised by XRD and TEM [333], XRD, TEM and FTIR were also used in the study of ID CdS nanoparticle-poly(vinyl acetate) nanorod composites prepared by hydrothermal polymerisation and simultaneous sulfidation [334], The CdS nanoparticles were well dispersed in the polymer nanorods. The intercalation of polyaniline (PANI)-DDBSA (dodecylbenzene-sulfonate) into the galleries of organo-montmorillonite (MMT) was confirmed by XRD, and significantly large 4-spacing expansions (13.3-29.6A) were observed for the nanocomposites [335],... 

The dispersion of clay platelets (exfoliation and intercalation level of the silicate layers) and surface area of silicate platelets have the potential to alter the rheological behavior of the nanocomposites. In-situ polymerized nano composites exhibit more exfoliated structure than the composites prepared by the melt blending technique. Irrespective of the processing parameter, the nanocomposites show shear thinning behavior at high shear rate (Figure 9.14), whereas the pristine polyamide exhibits Newtonian behavior (i.e., the viscosity remains almost the same). It has also been reported that the polymer nanocomposite possesses higher steady shear viscosity than pristine polyamide at low shear rates. 

In the last decade, considerable progress was observed in the field of PO/compatibil-izer (predominantly on the base of PO-g-MA)/organo-surface-modified clay nanocomposites. Polyethylene (PE), polypropylene (PP), and ethylene-propylene (EP) rubber are one of the most widely used POs as matrix polymers in the preparation of nanocomposites [3,4,6,30-52]. The PO silicate/silica (other clay minerals, metal oxides, carbon nanotubes, or other nanoparticles) nanocomposite and nanohybrid materials, prepared using intercalation/exfoliation of functionalized polymers in situ processing and reactive extrusion systems, have attracted the interest of many academic and industrial researchers because they frequently exhibit unexpected hybrid properties synergisti-cally derived from the two components [9,12,38-43]. One of most promising composite systems are nanocomposites based on organic polymers (thermoplastics and thermosets). 

PMMA migrate to the interfaces (i.e. act as a surfactant) and effectively compatibilise the polymer blend [234], TEM analysis of nanostructured cured elastomeric sealant compositions prepared by sonicating a mixture of silylated apophyUite filler in PDMS showed unambiguously that silicate layers are exfoliated [235]. Watkins et al. [174] have studied platinum/poly(4-methyl-l-pentene) (PMP) nanocomposites by means of TEM. For nanocomposite science and technology, cfr. also ref. [236]. 

Nanometer-scale composites prepared from layered inorganic materials, especially clay, and polymers have also attracted much attention because of their unique optical, thermal, mechanical, gas barrier, and electrical properties. There are many reports describing polymer-clay nanocomposites. " The clay can be, for example, a sihca or silicate. In such a hybrid composite, weak dipolar and van der Waals forces provide the driving force for interactions between the layers, and they result in galleries being formed. There are three types of clay-polymer composites conventional, intercalated, and exfohated. Three mediods are widely used for the preparation of polymer-clay hybrid nanocomposites intercalation by in situ polymerization, direct intercalation, and polymer melt intercalation. Each of these methods has its advantages and disadvantages. For example, the in situ polymerization works only in tiie... 

Despite the considerable number of studies concerned with the preparation of various types of polymer-silicate nanocomposites by the conventional emulsion technique, there has been no report on syntheses of novel polymer-silicate nanocomposites by the emulsifier-free emulsion method. The advantage of this method of polymerization is that a high concentration of surfactant/ emulsifier is considered to be one of the main drawbacks of emulsion polymerization due to difficulties in removing the residual emulsifier from the nanoparticle surface.The recently developed unconventional emulsifier-free emulsion polymerization enables the latter problem to be resolved and composite nanoparticles with tailored morphology to be synthesized. 

Ray SS, Okamoto M. Polymer/layered silicate composites a review from preparation to processing. Prog. Polym. Sci. 2003 28 1539-1641. 

Three main types of composites can be formed when the layered clay is incorporated with a polymer, as shown in Figure 2 (Alexandre and Dubois, 2000). Types of composites formed mostly depend on the nature of the components used (layered silicate, organic cation and polymer matrix) and the method of preparation. 

Plasticized PLA-based nano-composites were prepared and characterized with polyethylene glycol and MMT. It is reported that the organo-modified MMT-based composites show the possible competition between the polymer matrix and the plasticizer for the intercalation between the alumino-silicate layers (Paul et ah, 2002). 

Examples of known phosphazene polymer blends are those in which phosphazenes with methylamino, trifluoroethoxy, phenoxy, or oligo-ethyleneoxy side groups form blends with poly(vinyl chloride), polystyrene, poly(methyl methacrylate), or polyethylene oxide).97 100 IPNs have been produced from [NP(OCH2CH2OCH2CH2OCH3)2] (MEEP) and poly(methyl methacrylate).101-103 In addition, a special type of IPN has been reported in which a water-soluble polyphosphazene such as MEEP forms an IPN with a silicate or titanate network generated by hydrolysis of tetraethoxysilane or tetraalkoxytitanane.104 These materials are polyphosphazene/ceramic composites, which have been described as suitable materials for the preparation of antistatic layers in the manufacture of photographic film. 

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