Polymer-clay nanocomposites Melt intercalation

Benali, S. et al. 2008. Study of interlayer spacing collapse during polymer/clay nanocomposite melt intercalation. Journal of Nanoscience and Nanotechnology Letters 8 1707-1713. 

D. Polymer-Clay Nanocomposites Synthesized via Melt Intercalation... 

Lim, S.T. Lee, C.H. Choi, H.J. Jhon, M.S. Solidlike transition of melt-intercalated biodegradable polymer/clay nanocomposite. J. Polym. Sci. Part B Polym. Phys. 2003, 41, 2052-2061. 

The main techniques that can be used to prepare polymer/clay nanocomposites are (a) melt mixing the layered clay with polymer, (b) mixing the layered clay with solution of polymer followed by solvent removal, and (c) in situ intercalative polymerization, where the monomer is first intercalated in the clay and subsequently polymerized in situ. 

Funck, A. Kaminsky, W. (2007) Polypropylene carbon nanotube composites by in situ polymerization. Compos. Sci. Technol. Vol.67, No.5, pp.906-915 Garda-Leiner, M Lesser, A. (2003) Melt Intercalation in Polymer-Clay Nanocomposites Promoted by Supercritical Carbon Dioxide. Polym. Mater. Sci. Eng. VoL89, pp.649-650... 

Z. Shen, G.P. Simon, Y.-B. Cheng, Comparison of solution intercalation and melt intercalation of polymer-clay nanocomposites, Polymer 43 (2002) 4251—4260. 

Polymer/clay nanocomposites exhibit remarkable improvement in material properties relative to unfilled polymers or conventional composites. These improvements can include increased tensile modulus, mechanical strength, and heat resistance and reduced gas permeability and flammability [1], There are various methods of preparing polymer/clay nanocomposites (i) in situ polymerization, (ii) solution intercalation, (iii) melt intercalation, and (iv) in situ template synthesis [2],... 

This chapter is organized in the following way. First, we present some common techniques for characterizing the dispersion of nanoclays in polymer blends. The dispersion level has been shown to have a fundamental effect on the fire performance of polymer-clay nanocomposites (PCNs), as an exfoliated or intercalated polymer-clay system seems to enjoy reduced flammability. Second, the effects of nanoclays on the viscosity of polymer blends are discussed. With increased temperature in the condensed phase during combustion, most polymers (and hence polymer blends) have sufficiently low viscosity to flow under their own weight. This is highly undesirable, especially when the final products will be used in vertical orientation, because the melt can drip, having the potential to form a pool fire, which can increase fire spread. The results on thermal stability are presented next, followed by those for the cone calorimeter. The quantitative effects of nanoclays on the... 

Intercalation of polymers in layered hosts, such as layered silicates, has proven to be a successful approach to the synthesis of PLS nanocomposites. These polymer/ clay nanocomposites can be prepared in several ways, namely, solution exfoliation, melt intercalation, in situ polymerization, and template synthesis [9]. 

These materials, unlike the other nanophase materials described in this chapter, are nano-sized in only one dimension and thereby act as nanoplatelets that sandwich polymer chains in composites. Mont-morillonite (MMT) is a well-characterized layered silicate that can be made hydrophobic through either ionic exchange or modification with organic surfactant molecules to aid in dispersion [5,23]. Polymer-layered silicates may be synthesized by exfoliation adsorption, in situ intercalative polymerization, and melt intercalation to yield three general types of polymer/clay nanocomposites. Intercalated structures are characterized as alternating polymer and siHcate layers in an ordered pattern with a periodic space between layers of a few nanometers [13], ExfoHated or delaminated structure occurs when silicate layers are uniformly distributed throughout the polymer matrix. In some cases, the polymer does not intercalate... 

To achieve improved dispersibUity of nanoclay fillers within polymer systems, three familiar methods are commonly used, namely, melt intercalation, solution intercalation, and in situ polymerization. The melt-intercalation method is based on the melting point of polymer matrices and is applied by annealing above the melting point of the polymer (Reddy et al., 2013). This method has been chosen by industrial sectors to produce polymer/clay nanocomposites. However, it is not apphcable to the fabrication of biobased polymer/clay nanocomposites based on thermosetting materials such as epoxy and polyester due to their high viscosities (Wypych and Satyanarayana, 2005 Wang et al., 2014). Therefore, the fabrication of biobased thermosetting polymer/clay nanocomposites is mainly based on solution intercalation or in sim polymerization. 

Reference. [18] showed the strong infiuence of preparation route on the thermal properties of polystyrene (PS) nanocomposites. An appreciable reduction in Tg was observed only for composites obtained from solution, whereas the composites obtained by melt intercalation showed Tg values approximately equal to that of neat polymer. Some difficulties in detecting changes in Tg for polymer-clay nanocomposites occurring with the conventional DSC [19] method could be overcome using the TMDSC method. 

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... 

The imphcation from the above work is that polymer present in the galleries of montmorillonite through intercalation and exfoliation has enhanced thermal stability provided by a different thermal degradation mechanism when compared to the pure polymer. Calculations of the activation energy of polyurethane-imide-clay nanocomposites [37] utilizing the Broido [38] and Coats-Redfern equations were consistent with a mechanism that increased the thermal stability of the polymer-clay nanocomposite in relation to the pure polymer. An optimization of melt-blending processing that improved the exfoliation efficiency of polymer-clay nanocomposites resulted in increased thermal stability by TGA when compared to polymer-clay nanocomposites with inferior exfoliation, and pure polymer [39]. 

Ginzburg, V.V., Gendelman, O.V., and Manevitch, L.I. (2001) Simple kink model of melt intercalation in polymer-clay nanocomposites. Phys. Rev. Lett., 86, 5073-5075. 

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