Preparation and characterization of vinylsilane crosslinked thermoplastic composites filled with nanoclays
Sibeko, Motshabi Alinah
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The effects of dicumyl peroxide/vinyltriethoxysilane (DCP/VTES) treatment, nanoclay content and the nature of the nanoclay were investigated for low-density polyethylene (LDPE)/clay and high-density polyethylene (HDPE)/clay nanocomposites. LDPE was treated with 0.1 phr of DCP with respectively 1 phr and 3 phr VTES (System A), and with 0.2 phr of DCP with the same amounts of VTES, and then mixed with different contents (1, 3, and 5 wt. %) of modified (Cloisite 15A) and unmodified (calcium montmorillonite) clay. The HDPE nanocomposites were prepared according to System A, using Cloisite 15A. The polymer-clay nanocomposites were prepared through melt mixing in a Brabender Plastograph internal mixer, and were characterized for their morphology, thermal properties, mechanical properties, thermomechanical properties and the extent of grafting/crosslinking. FTIR analysis clearly showed that grafting in System A was not very effective, and that the ‘grafted’ LDPE contained an appreciable amount of ungrafted (pure or hydrolysed) VTES. However, sufficient grafting was achieved in System B, but there was also a higher extent of crosslinking. The XRD and TEM results showed that C15A was more intercalated than Ca2+MMT showed, and also slightly exfoliated. Nanocomposites prepared according to System A showed intercalated structures, while those prepared according to System B showed partially exfoliated structures. The DSC results showed that the presence of DCP/VTES decreased the melting temperature and crystallinity of both the polymer matrices due to a decrease in lamellar thickness as a result of crosslinking between the polymer chains, in addition to VTES grafting. The addition of clay and its nature had no significant influence on the melting temperature and crystallinity of both polymers. The TGA results showed an improvement in the thermal stability of all the nanocomposites, but the silane treated C15A nanocomposites showed a higher degradation rate at higher clay contents. The mechanical and thermomechanical properties of the untreated nanocomposites were better than those of the treated nanocomposites at the same clay loading.