Effect of nm-THIN Inorganic Layered Fillers on the Crystallization of Polymer Nanocomposites
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EFFECT OF nm-THIN INORGANIC LAYERED FILLERS ON THE CRYSTALLIZATION OF POLYMER NANOCOMPOSITES H. Nakajima, Z.M. Wang, K. Strawhecker, and E. Manias 1 Materials Science and Engineering Department, Pennsylvania State University, 325-D Steidle Bldg, University Park, PA 16801 ABSTRACT The crystallization behavior of polymers in nanocomposites with inorganic fillers (montmorillonite layered silicate, MMT) is reviewed. Various different polymers are comparatively discussed [poly(vinyl alcohol) (PVA), polypropylene (PP), syndiotactic-polystyrene (sPS), and poly(ethylene oxide) (PEO)] representing three types of filler/matrix interactions: strong specific interactions (PVA/MMT), weak/negligible interactions (sPS and PP/o-MMT), and “unfavorable” (PEO/MMT). In the case of PVA/MMT, crystallization of PVA is strongly promoted by MMT, also stabilizing a new crystal form not found in bulk PVA. For sPS and PP/o-MMT, crystallization is only moderately affected, exhibiting traces of simple heterogeneous nucleation and mostly bulk-like crystal structures, with very small traces on non-bulk crystals. For PEO, crystallization is impeded near the MMT surfaces, due to coordination of the surface cations to the PEO. In all cases smaller spherulite sizes develop when filler is added, independent of the size of the bulk polymer spherulites, whereas the crystallization temperature changes reflect the strength of the polymer/surface interactions. INTRODUCTION The very large commercial importance of polymers has been driving an intense investigation of polymeric composites reinforced by particulates, fibers, and layered inorganic fillers. In particular, in the case of layered inorganic fillers, talc and mica have traditionally attracted the most interest. However, recent advances in polymer/clay and polymer/layered-silicate nanocomposite materials 1,2 have inspired efforts to disperse clay-based fillers in almost any polymer available, usually expecting that complete exfoliation of the inorganic fillers in the polymer would yield the best performing systems 2. At the same time, the crystallization of polymers next to these inorganic surfaces has not been studied as extensively, and not beyond a few systems (e.g. nylon-6 and montmorillonite 3 ). The nylon-6/montmorillonite studies have shown a nucleating and epitaxial effect of the inorganic surfaces, which stabilizing a surface-induced crystalline phase 3 (γ crystal), that is rarely found in the bulk polymer. This effect has been used to enhance the mechanical and thermal properties of the polymer, since the surface nucleated crystalline phase has better mechanical and thermal characteristics than the bulk crystal phases. For the nylon-6 case, the current opinion is that the origin of this substantial effect on the polymer 1
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Q4.10.2
crystallization lies in the manner that amide interact with the inorganic aluminosilicates, through strong hydrogen-bonding interactions. The aim of this work is to reveal the general effects of the dispersion o
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