Morphology layered-silicate polymer

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Finnigan B, Martin D, Halley P, Truss R, Campell K. Morphology and properties of thermoplastic polyurethane nanocomposites incorporating hydrophilic layered silicates. Polymer 2004 45 2249-2260. 

Okamoto K, Sinha Ray S, Okamoto M (2003), New poly(butylene succinate)/ layered silicate nanocomposites. 2. Effect of organically modified layered silicates on morphology, materials properties, melt rheology, and hiodegradahility , JPolym Sci Part B Polym Phys, 41, 3160-70. 

M. Kurian, A. Dasgupta, F. Beyer, M.E. Galvin, Investigation of the effect of silicate modification on polymer-layered silicate nanocomposites morphology , J. Polym. Sci, Polym. Physics Ed., 2004, 42, 4075-4083. 

In numerous works dealing with the combination of nanoparticles and FR compounds, surface modifications of nanoparticles were only aimed to promote good dispersion of the nanoparticles into the polymer matrix (with intercalated or exfoliated morphologies for layered silicates as nanoparticles), even in the presence of the usual FRs, for example ammonium polyphosphate (APP) or magnesium hydroxide (MH). The initial aim was to combine the individual effects of each component to achieve strong synergistic effects. 

Moreover, the development of new strategies for surface modifications of nanoparticles with compounds having FR activity could provide a new field of research on FR systems. The use of novel phosphorus-, nitrogen-, or halogen-containing modifiers, instead of alkylammonium ions, for layered silicates seems promising. FR action conferred by the surface modifier can be combined with action due to composite morphology, particularly when the host polymer is a polymer blend instead of a pure polymer. 

Samyn, F., Bourbigot, S., Jama, C., Bellayer, S., Nazare, S., Hull, R., Castrovinci, A., and Camino, G. (2008) Crossed characterisation of polymer-layered silicate (PLS) nanocomposite morphology TEM, x-ray diffraction, rheology and solid-state nuclear magnetic resonance measurements, European Polymer Journal 44(6) 1642-1653. 

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Fig. 29 Different morphologies encountered in polymer-layered silicate nanocomposites phase segregated left), intercalated middle), and exfoliated nanocomposites right)...

Pluta, M. Morphology and properties of polylactide modified by thermal treatment, filling with layered silicates and plasticization. Polymer 45, 8239-8251 (2004)... 

Asi Asif, A., Rao, V. L., Saseendran, V., Ninan, K. N. Thermoplastic toughened layered silicate epoxy ternary nanocomposites - Preparation, morphology, and thermomechanical properties. Polym. Eng. Sci. 49 (2009) 756-767. 

As illustrated in Fig. 1, layered silicate composite structures fall into three different classes (a) microcomposites with no interaction between the clay galleries and the polymer, (b) intercalated nanocomposites, where the silicate is well-dispersed in a polymer matrix with polymer chains inserted into the galleries between the parallel, sihcate platelets, and (c) exfohated nano composites with fully separated silicate platelets individually dispersed or delaminated within the polymer matrix [12]. However, these terms describe only ideal cases and most observed morphologies fall between the extremes. A more detailed nomenclature will be presented later in this review. 

As the field of thermosetting layered silicate nanocomposites is still relatively new, the major work to date has focused on the understanding of morphology, processing conditions and properties of less complex binary nanocomposite systems. However, the promising results reported for this new class of material have recently encouraged research in nanocomposites where it is a supplementary additive, used in combination with other phases such as fibres, rubbers or hyperbranched polymers. 

When electrical and electronic properties are also of interest apart from mechanical and thermal properties, carbon nanotubes can be of better advantages. Nanotubes are inert in nature and, therefore, also require surface modification in order to achieve compatibility with the polymer matrices. Thus, the nanoscale dispersion of the nanotubes is as important and challenging as the layered silicates as the properties are dependant on the generated morphology in the composites. In a representative study, Teng et al. 

On a thermodynamic ground, nanoscale mixing of layered silicates with polymers is only possible if the chemical structure of both components is such to grant favorable energetic interactions [4-8]. However, the morphology of experimental nanocomposites will be dependent on kinetics as well, and, consequently, on the pathway of their preparation. 

Koo, C. M., Kim, M. J., Choi, M. N., Kim, S. O., and Chung, I. J. 2003. Mechanical and rheological properties of the maleated p>olypropylene-layered silicate nanocomposites with different morphology. Journal cf Applied Polymer Science 88 1526-1535. 

Coiai, S., Scatto, M., Bertoldo, M., Conzatti, L., Andreotti, L., Sterner, M., Passaglia, E., Costa, G., and Ciardelli, R 2009. Study of the compounding process parameters for morphology control of LDPE/layered silicate nano-composites. e-Polymers, no. 050 1-18. http Hwww.e-polymers.org/ journal/papers/scoiai 280509.pdf... 

Xie, Y., Yu, D., Kong, J., Fan, X., and Qiao, W. 2006. Study on morphology, crystallization behaviors of highly filled maleated polyethylene-layered silicate nanocomposites. Journal of Applied Polymer Science 100 4004-4011. 

Depending on the nature of the filler distribution within the matrix, the morphology of the nanoeomposites can evolve from the so-called intercalated structure where a regular alternation of the layered silicates and polymer monolayers is observed, to the exfoliated (delaminated) structure where the layered silicates are randomly and homogeneously distributed within the polymer matrix. The easiest and technically most attractive way to produce these types of materials is to knead the polymer in the molten state with a modified layered silicate, such as montmorillonite. Compounding on different machines, such as a Buss ko-kneader or mills, still produces essentially the same morphology in the resulting nanoeomposites. 

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