Polymer nanocomposites polyamide

At present time the great attention is given to the study of properties of polymeric nanocomposites produced on the basis of well known thermoplastics (PP, PE, PS, PMMA, polycarbonates, and polyamides) and caibon nanotubes (CN). The CNs are considered to have the wide set of important properties like thermal stabihty, reduced combustibility, electroconductivity, and so on [1-7]. Thermoplastic polymer nanocomposites are generally produced with the use of melting technique [1-12]. 

This chapter focuses on the blends and multilayers of a variety of nanoparticles and conjugated polymers. However, it must be mentioned that there has been a large amount of research in the last two decades on nanocomposites of conventional polymers [19]. Polymer nanocomposites in this context are generally defined as the combination of a polymer matrix resin and inorganic particles that have at least one dimension, i.e., length, width, or thickness, in the nanometre size range. Typical of this class of materials is the nanocomposite which researchers at Toyota Co., discovered in the 1980s polyamide 6... 

Koo and co-workers [78] attempted to develop polyamides 11 and 12 with enhanced flame retardancy and thermal and mechanical properties by the incorporation of montmorillonite clays, silica and carbon fibre-polymer nanocomposites. Flammability properties of the nanocomposites were compared with those of the virgin polyamides, using cone calorimetry with an external heat flux of 50 kW/m. Cone calorimetry was also used in an evaluation of polyamide 6 - anion modified Mg/Al interlayer formulation [79]. The data from the cone calorimeter shows that the heat production rate (HPR) and mass loss weight of the sample with 5 wt% MgAl(H-DS) decrease considerably to 664 kW/mVs and 0.161 g/mVs from 1064 kW/mVs and 0.252 g/mVs... 

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. 

Polymer nanocomposites find their first application in car hoods, which are easily attacked by NO pollutants since they are exposed to the exterior environment. NO at standard atmosphere and pressure is 29.5% NO and 70.5% N O. Polyamide-6 is highly sensitive to such pollutants. The infusion of nano-clay platelets in the polyamide matrix in general decreases the diffusivity and permeability of the nanocomposites to atmospheric oxygen... 

It was the pioneering work of Toyota researchers toward the development of polymeric nanocomposites in the early 90s [1, 2], in which electrostahcally held 1-nm-thick layers of the layered aluminosilicates were dispersed in the polyamide matrix on a nanometer level, which led to an exponenhal growth in the research in these layered silicate nanocomposites. These nanocomposites were based on the in-situ synthesis approach in which monomer or monomer solution was used to swell the filler interlayers followed by polymerizahon. Subsequently, GianneUs and CO workers [3, 4] also reported the route of melt intercalation for the synthesis of polymer nanocomposites. 

In-situ intercalation method was reported by Toyota researchers for the synthesis of polyamide nanocomposites that led to the exponential growth in the nanocomposites research. For generation of polymer nanocomposites by this method, the layered silicate mineral is swollen in monomer. After swelling, the polymerization of the monomer is initiated. As monomer is present in and out of the filler interlayers, therefore, the generated stmcture is exfoUated or significantly intercalated. As the rate or mechanism of polymerization in and out of the filler interlayers... 

The main uses of montmorillonite stem from its characteristic expansion, and it is used to control viscosity or impart thixotropy to a variety of liquid polymers based on unsaturated polyesters, PVC plastisols, polysulfides, alkyds, etc. It has also been reported to control the melt rheology of thermoplastics and to reinforce polyamides. There has, over the last few years, been enormous industrial and research interest, with many papers and patents, published on montmorillonite, especially as an organoclay as the basis of polymer nanocomposites. Because of the delamination process described above plastic-organoclay nanocomposites have been reported to have very high rigidity, low permeability to fluids, and fire resistance. This subject is covered in more detail in Chapter 10. 

In the case of polymer/clay nanocomposites, alkylammonium exchange species influence the affinity between the polymer and the clay surface. For example, it was reported that clays treated with dialkyl dimethylammonium halides, in particular with two chains of about 18 carbon atoms, have a surface energy similar to poly(olefins) such as polypropylene (PP) and polyethylene (PE) [27]. Polar polymers as polyamides (PA) have been recommended to get better interactions as reported by Toyota [8]. The alkyl chain length is related with increase in interlayer space required for the intercalation of polymer chains. Because of the nonpolar nature of their chains, they reduce the electrostatic interactions between the silicate layers and lower the surface energy of the layered silicates. As a consequence, an optimal diffusion of the polymer to dissociate the stacked clay layers, that is, an exfoliation process, can be obtained. Despite the compatibility of MMT modified by long alkyl chain quaternary ammonium with hydrophobic polymers (PE and PP), conventional alkylammonium ions show low thermal stability, that is, an onset decomposition temperature is close to 180°C.This poor thermal stability could limit their use in the preparation of PLS with matrices processed at high temperatures such as PA, poly(ethylene terephthalate) (PET), and poly(ether ether ketone) (PEEK) [30]. 

Althongh nanocomposite matrix materials may be metals and ceramics, the most common matrices are polymers. For these polymer nanocomposites, a large number of thermoplastic, thermosetting, and elastomeric matrices are used, including epoxy resins, polynrethanes, polypropylene, polycarbonate, poly(ethylene terephthalate), silicone resins, poly(methyl methacrylate), polyamides (nylons), poly(vinylidene chloride), ethylene vinyl alcohol, butyl rubber, and natural rubber. 

The first commercial application of nanoclay polymer nanocomposites was a timing-belt cover made of polyamide nanocomposite by Toyota Motors in the 90s. Since then, CPN grabbed great attention and the research about their properties and applications experienced a vast boost. 

This can be performed by co-condensation of monomer and precursor vapors. The main advantages of this mediod are a high homogeneity and a strong polymer-particle binding. It is frequently used for nanocomposites of metals in polyamides, polyimides, polystyrene or Teflon. Co-condensation at low temperature in combination with gamma or UV irradiation yield metal-polymer nanocomposites of variable partiele size and high partiele density. 

This book covers both fundamental and applied research associated with polymer-based nanocomposites, and presents possible directions for further development of high performanee nanocomposites. It has two main parts. Part I has 12 chapters which are entirely dedicated to those polymer nanocomposites containing layered silicates (clay) as an additive. Many thermoplastics, thermosets, and elastomers are included, such as polyamide (Chapter 1), polypropylene (Chapter 4), polystyrene (Chapter 5), poly(butylene terephthalate) (Chapter 9), poly(ethyl acrylate) (Chapter 6), epoxy resin (Chapter 2), biodegradable polymers (Chapter 3), water soluble polymers (Chapter 8), acrylate photopolymers (Chapter 7) and rubbers (Chapter 12). In addition to synthesis and structural characterisation of polymer/clay nanocomposites, their unique physical properties like flame retardancy (Chapter 10) and gas/liquid barrier (Chapter 11) properties are also discussed. Furthermore, the crystallisation behaviour of polymer/clay nanocomposites and the significance of chemical compatibility between a polymer and clay in affecting clay dispersion are also considered. 

Practically all the polymers can be processed to make nanocomposites. This emerging technology is developing in polyamide andTPO nanocomposites with applications in the automotive industry, and there are experiments with saturated polyesters, acrylics, polystyrenes... 

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