Study On Preparation, Structure And Properties Of Low Density Polyethylene/montmorillonite Nanocomposites

Polymer-layered silicate (PLS) nanocomposites have attracted great attention due to their academic and industrial importance. Fabrication of polyolefine/layered silicate nanocomposites has been considered to be one of the important methods of modification for poiyolefine. Owing to the abundant output and broad applications of poiyolefine, PLS nanocomposites based on poiyolefine have become an enormous commercial allure. The studies on the melt compounding of polymer / compatibilizer-layered silicates system and their structure and properties were carried out.1. Based on organo-montmorillonites (C16-MMTs) obtained by the surfactant cetyltrimethylammonium ion (CTA+) intercalated into the galleries of Na-montmorillonite (MMT), the conformation of the confined methylene chains in C16-MMTs were characterized by means of XRD, TGA and FTIR. The C16-MMT formed single sedimentation layer when CTA+ loading level was below 0.75CEC (cation exchange capacity) , in which the methylene chains of the CTA+ adopted lateral monlayer with some conformation freedoms; but stratified when its loading level beyond this value, in which the intercalated methylene chains in the upper sedimentation layer adopted a bimolecular, laterally layered arrangement, while the confined chains within the lower in the stratified precipitate formed a tilted interpenetrating bilayer arrangement with few gauche conformers.Besides, it was found that compared with CTA+, the confined geometry improves the thermal stabilization of methylene chains about 20 in the case of the gallery height less than 9.1 A and surfactant content less than 24.7 wt%, while the onset temperature of degradation reduces about 25 at high gallery heights and surfactant loadings. Based on an examination of TGA and DTG, the degradation of the intercalated methylene chains different from the crystalline bulk reflects that a multilayer arrangement of methylene chains.2. Intercalation and exfoliation behaviors of organo-MMTs in low density polyethylene (LDPE) and copolyethylene/MMT systems have been investigated. It was found that LDPE has certain intercalation capability, while ethylene vinyl-acetate copolymer (EVA) with polar groups exhibits some compatibilization and excellent intercalation capability. The dispersion of MMT and the properties of composites were basically determined by the nature of organo-MMT and the polarity of the polymer chains. The intercalated nanocomposites could be explained in terms of the formation of "ladder" structure due to the excessive polar groups on the polymer chains which adhere adjacent silicate sheets. XRD results revealed that EVA easily intercalated into the organo-MMT, and even drove MMT to exfoliate as increasing C16 loading level beyond 1.0 CEC. The mechanical properties indicated that the improved exfoliation degree of MMTs was essential for better properties of the nanocomposites, while the mechanical properties of intercalated nanocomposites were dependent on the structure of the organic modifiers3. By virtue of EVA, ethylene crylic-acid comolymer (EAA) and ethylene methacrylic-acid copolymer (EMA), LDPE/MMT nanocomposites have been prepared by melt intercalation. XRD results revealed that melt intercalation of compatibilizers into organo-MMT followed by blending with LDPE was preferred to the dispersion of the silicate layers in LDPE matrix. Moreover, the dispersion of MMT was dependent on the interaction among organo-MMT, surfactants andcompatibilizers. There were existed three effects for a compatibilizer: intercalation, miscibility and encapsulation, the effect of which was dependent on the compatibilizer loading, molecule weight /or melt index and molecule structure. TEM images revealed that the phase morphology of PLS composites were influenced by the interaction among the matrix, the compatibilizer and organo-MMT. Hence, a novel mesophase ""silicate sheet cluster" was also found in LDPE/EAA/MMT nanocomposite.The mechanical, barrier and thermal properties results of LDPE/MMT composites indicated that,...