Nanofillers polymeric nanocomposites

Joshi, M. and Butola, B. S., Polymeric nanocomposites—polyhedral oligomeric silsesquioxanes (POSS) as hybrid nanofiller, J. Macromol. Sci., Polym. Rev. (2004), C44, 389M10. 

Recently, new approaches on flame retardancy deal often with nanofillers and in this section some examples of improvements of fire behavior of polymeric foams obtained by use of nanoclays or nanofibers will be shown. Much more details on flame retardancy of polymeric nanocomposite may be found elsewhere as for example in the book edited by A. B. Morgan and C. A. Wilkie105 or in scientific review.106 Polymer nanocomposites have enhanced char formation and showed significant decrease of PHRR and peak of mass loss rate (PMLR). In most cases the carbonaceous char yield was limited to few weight %, due to the low level of clays addition, and consequently the total HRR was not affected significantly. Hence, for polymer nanocomposites alone, where no additional flame-retardant is used, once the nanocomposite ignites, it burns slowly but does not self-extinguish... 

One more aspect of the model, concerns the determination of parameter b, which characterizes interfacial adhesion at the nanofiller - polymeric matrix level. The condition b = was accepted for the value of (Fig. 4.1), but this parameter can also be estimated more precisely according to Eq. (4.6) and Eq. (4.7), using experimental values E, E and (p. An independent estimation of the interfacial adhesion level for the nanocomposites studied, can be obtained with the aid of parameter A, determined according to the equation ... 

As the adduced above data have shown, the polymer nanocomposites with three main types of inorganic nanofiller and also polymer-polymeric nanocomposites melt viscosity caimot be described adequately within the fiamework of models, developed for the description of microcomposites melt viscosity. This task can be solved successfully within the framework of the fractal model of viscous liquid flow, if in it the used nanofiller special feature is taken into account correctly. Let us note that unlike microcomposites nanofiller cotents enhancement does not result in melt viscosity increase, but, on the contrary, reduces it. It is obvious, that this aspect is very important from the practical point of view. 

New families of nanofillers and nanocomposites are opening up performance reserves of plastics, rubbers and dispersions. Even very low nanofiller % by volume can suffice to alter the property profiles of polymeric materials and functional additives in significant ways. The application spectrum extends from new construction materials to a diversity of functional polymers [77, 106],... 

Polymeric nanocomposites can be obtained using one of the following methods solution casting, in situ polymerization or melt blending. Preparing nanocomposites by solution mixing gives nicely dispersed nanofiller in the polymer however the use of a solvent is sometimes limited. The second method (in situ) is based on... 

Surface modification of the nanofiller will be a challenge in the preparation of new types of rubber nanocomposites. Furthermore, the modification of various nanofillers using other nanofiUer systems will be a key to obtaining materials with designed properties. The interactions at the interface between the nanofillers and the matrix are one of the most important factors connected with the production of the new improved polymeric nanocomposites. Understanding the modification of the nanofiller in the polymer matrix, as well as the mechanical behavior in dynamic mode, leads to the possibility of producing new rubber nanocomposites, for example, for tire applications, where enhanced rolling resistance would improve traction [17]. 

The best performance of polymeric nanocomposites is achieved when the nanofiller is dispersed in the polymer matrix without any agglomeration. Currently, numerous procedures for the preparation of polymeric nanocomposites have been proposed using the following approaches (i) direct incorporation of nanoscale building blocks into a polymer melt or solution [6-9], (ii) in-situ generation of nanoscale building blocks in a polymer matrix vacuum... 

In conclusion, even if some very promising results have already been reached, a deeper understanding of the nanofiller-matrix interactions is certainly required in order to optimize the creep stability and fatigue resistance of both thermoplastic and thermosetting polymeric nanocomposites. 

The preparation of stable dispersion of a nanofiller in a monomer is the main problem when polymeric nanocomposite is obtained during polycondensation in-situ. Nanoparticles-monomer and particle-particle interactions strongly influence the quality of dispersion and the tendency to agglomerate. 

Several types of synthetic or semisynthetic layered materials have been described, partially applied to polycondensation or polymerization inside confined space in layered nanofillers. Model systems for confined polymers and polymer bmshes were presented in Reference 160. Polymeric nanocomposites based on polyamides can be obtained by polycondensation of monomers (by homo- or heteropolycondensation) with fluor-ohectorite in interlayer spacing of 1-2 nm. 

Most reviews deal with the effects of different nanofillers on the properties of polymer matrices. However, this work does not intend to be a comprehensive review on the thermal properties of polymeric nanocomposites, but rather aims to illustrate the versatile applications of thermal analysis (TA) in the emerging field of polymer nanomaterial research. Although analyzing bulk samples of several milligrams size, TA is also capable to provide information on the average structure of the nanocomposite even at the nanoscale. Therefore, this chapter will address the most relevant results obtained by TA that can be used to obtain indirect evidence of nanodispersion, highlighting the strong potential of such instruments, as low-cost techniques frequentiy available in most industrial and research laboratories. 

In this context, a smdy that evaluated obtaining and characterization of polymeric nanocomposites of polyaniline (PAni) with a variety of montmoriUonite (MMT) clays (Cloisite Na", lOA, 15A, 20A and 30B) was developed by Baldissera and coworkers [122]. The aim of obtaining these nanocomposites is to link the features provided by nanofiller with the characteristics of conducting polymers. 

ENGAGE is an ethylene-octene copolymer. Ray and Bhowmick [70] have prepared nanocomposites based on this copolymer. In this study, the nanoclay was modified in situ by polymerization of acrylate monomer inside the gallery gap of nanoclay. ENGAGE was then intercalated inside the increased gallery gap of the modified nanoclay. The nanocomposites prepared by this method have improved mechanical properties compared to that of the conventional counterparts. Preparation and properties of organically modified nanoclay and its nanocomposites with ethylene-octene copolymer were reported by Maiti et al. [71]. Excellent improvement in mechanical properties and storage modulus was noticed by the workers. The results were explained with the help of morphology, dispersion of the nanofiller, and its interaction with the mbber. 

Polymeric blends are popularly known to show desired properties based on the components. But their nanocomposites have been prepared to further modify the properties. Various blends like NR-ENR and PP-EPDM [188,189] with nanofillers have also been smdied. 

Up to now we considered pol5meric fiiactals behavior in Euclidean spaces only (for the most often realized in practice case fractals structure formation can occur in fractal spaces as well (fractal lattices in case of computer simulation), that influences essentially on polymeric fractals dimension value. This problem represents not only purely theoretical interest, but gives important practical applications. So, in case of polymer composites it has been shown [45] that particles (aggregates of particles) of filler form bulk network, having fractal dimension, changing within the wide enough limits. In its turn, this network defines composite polymer matrix structure, characterized by its fractal dimension polymer material properties. And on the contrary, the absence in particulate-filled polymer nanocomposites of such network results in polymer matrix structure invariability at nanofiller contents variation and its fractal dimension remains constant and equal to this parameter for matrix polymer [46]. 

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