Nanocomposite silicate layer polymer

Examples of filled polymer compositions are discussed, where the role of the preparation method has been clearly identified in relation to compound structure and end properties. Particular attention is also given to recent developments in the field of natural fibre-filled composites, supercritical fluid assisted processing of filled polymers, re-use of thermoset recyclate fillers and silicate layer polymer nanocomposites. 

J.A. Lander, Structure Development in Silicate-Layered Polymer Nanocomposites, Brunei University, Uxbridge, UK, 2002. [PhD Thesis]. 

XRD was used to investigate the spacings of silicate layers of montmorillonite (from 1.9 to 4nm) in PP/montmorillonite (MMT) nanocomposites prepared by in situ graft-intercalation in the presence of acrylamide [331]. Similarly, XRD and TEM were used to study the dispersibility of PP/MMT nanocomposites prepared by melt intercalation using organo-montmorillonite and conventional twin screw extrusion [332]. Various delaminated and intercalated polymer (PA6, PA 12, PS,... 

Galgali and his colleagues [46] have also shown that the typical rheological response in nanocomposites arises from frictional interactions between the silicate layers and not from the immobilization of confined polymer chains between the silicate layers. They have also shown a dramatic decrease in the creep compliance for the PP-based nanocomposite with 9 wt% MMT. They showed a dramatic three orders of magnitude drop in the zero shear viscosity beyond the apparent yield stress, suggesting that the solid-like behavior in the quiescent state is a result of the percolated structure of the layered silicate. 

PDMS nanocomposites with layered mica-type silicates were also reported.374 A two-step sol-gel process of the in situ precipitation of silica led to the development of siloxane-based nanocomposites with particularly high transparencies.3 5 Some unusual nanocomposites prepared by threading polymer chains through zeolites, mesoporous silica, or silica nanotubes were reviewed.3 6 Poly(4-vinylpyridine) nanocross-linked by octa(propylglycidyl ether) polyhedral oligomeric silsesquioxane was reported.377... 

Fig. 20. Schematic diagram describing the end-tethered nanocomposites. The layered silicates are highly anisotropic with a thickness of lnm and lateral dimensions (length and width) ranging from -100 nm to a few microns. The polymer chains are tethered to the surface via ionic interactions between the silicate layer and the polymer-end. Adapted from Ref. [54].

On a global scale, the linear viscoelastic behavior of the polymer chains in the nanocomposites, as detected by conventional rheometry, is dramatically altered when the chains are tethered to the surface of the silicate or are in close proximity to the silicate layers as in intercalated nanocomposites. Some of these systems show close analogies to other intrinsically anisotropic materials such as block copolymers and smectic liquid crystalline polymers and provide model systems to understand the dynamics of polymer brushes. Finally, the polymer melt-brushes exhibit intriguing non-linear viscoelastic behavior, which shows strainhardening with a characteric critical strain amplitude that is only a function of the interlayer distance. These results provide complementary information to that obtained for solution brushes using the SFA, and are attributed to chain stretching associated with the space-filling requirements of a melt brush. 

Besides metal ions and hydrogen ions, other cationic substances (e.g., cationic organic molecules or cationic tensides) can also be exchanged in the external and internal surfaces. Cationic tensides can make the surface hydrophobic (Lagaly and Dekany 2005). Furthermore, the distance between the layers is widened, enabling polymer chains to move in. This is an important condition in the preparation of nanocomposites containing layer silicates. Recently, the production and application of nanocomposites has become widespread, and many papers have been presented in this field (e.g., Paiva et al. 2008 Pavlidoua and Papaspyrides 2008). 

Special attention in studying nanocomposite properties usually attracts to allocation of organomodified layered silicates on polymer matrix which plays important part due to depending of this properties on allocation. 

Pavhdou, S. and C. D. Papaspyrides. 2008. A review on polymer-layered silicate nanocomposites. Progress in Polymer Science 33 1119-1198. 

Messersmith, P. B., Giannelis, E. R, Synthesis and barrier properties of poly(e-caprolactone)-layered silicate nanocomposites. loumal of Polymer Science Part A Polymer Chemistry. 7, 1047-1057 (1995), DOI 10.1002/pola.l995.080330707. 

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