Preparation and characterization of polyoxymethylene (POM)/organophilised montmorillonite (OMMT) nanocomposites

Agnieszka Leszczyńska, Krzysztof Pielichowski Politechnika Krakowska, Wydział Inżynierii i Technologii Chemicznej, Katedra Chemii i Technologii Tworzyw Sztucznych, ul. Warszawska 24, 31-155 Kraków, Poland

Quarterly No. 4, 2008 pages 338-343

DOI:

keywords: polyoxymethylene, montmorillonite, nanocomposites, mechanical properties

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abstract In this work preparation, structural analysis and mechanical properties of polyoxymethylene (POM)/ organically-modified montmorillonite (OMMT) nanocomposites were presented. POM/OMMT nanocomposites were obtained by melt blending of POM with organically modified montmorillonite. Cation exchange reaction was carried out with dimethyldioctadecyl ammonium chloride and sodium activated montmorillonite. The structure analysis by WAXD and TEM methods showed the formation of complex nanostructures, where the ordered (intercalated) areas form a spatial structure resembling the „house-of-cards” arrangements, which are typical for montmorillonite water-based suspensions. Mechanism of nanostructures formation through delamination of MMT stacks under the influence of shearing forces during homogenization of OMMT in polymer melt has been proposed. The SEM microphotographs of criofractured samples showed that in the modified polymer plate-like or rod-like crystals, oriented towards the melt flow direction during injection molding, were formed. No visible orientation was observed for injection moldings of pure POM and the crystals were in the form of spherulites. The SEM microphotographs of cracks formed during tensile tests revealed oriented morphology of polymer crystals in the nanocomposite material that could contribute to the improvement in mechanical properties. The results of dynamic mechanical analysis (DMA) showed that the E’ modulus of nanocomposites was significantly higher than that for pure POM in the temperature range from 100 to 100C. The glass transition temperature of nanocomposites was slightly moved toward higher temperatures as evidenced by DMA. This indicated the confinement of polymer chain dynamics by MMT layers and may indicate the nanocomposite formation. Under static deformation, the tensile strength and modulus of elasticity were significantly improved by the introduction of nanoparticles. The largest improvement was observed for nanocomposite material containing 1 wt. % of OMMT. With an increase of MMT content, the improvement in mechanical properties tended to decrease.