Ethylene vinyl acetate/cellulose composites: functional modification, morphology and phase interactions

M. MINHAZ-UL HAQUE; VERA ALVAREZ; MARIANO PRACELLA

Dresden

Congreso; 10th European Symposium on Polymer Blends; 2010

Incorporation of cellulosic fibres into polymers matrices offers the possibility to design new composite materials with reduced environmental impact, due to the biodegradability, renewability and low cost of natural fillers. Indeed, good dispersion of fibres in the polymer matrix and good adhesion is an important prerequisite for obtaining good mechanical properties of the resulting composites. To increase the compatibility of the components, improving the interfacial adhesion and fibre dispersion within the polymer matrix, either surface modification of fibre and/or matrix are necessary [1-2]. The present communication is aimed at analysing the effect of compatibilization processes of ethylene vinyl acetate (EVA) composites with natural fibres, such as cellulose and hemp, on the morphological, thermal and mechanical properties. The composites were obtained by melt mixing EVA copolymers of different types with fibre contents in the range of 20-50 wt% using a Brabender internal mixer. Commercial samples of EVA (28 wt.% vinyl acetate), maleic anhydride grafted EVA (EVA-MA) and glycidyl methacrylate modified EVA (EVA-GMA) were used. The effect of polymer functionalization, fibre treatment and content, on the composite properties was then examined by SEM, FT-IR, NMR, DMTA, DSC, TGA and tensile mechanical tests. FT-IR spectroscopy demonstrated the occurrence of chemical interactions between the functional groups (MA, GMA) of EVA and the hydroxyl groups of cellulose. Accordingly, SEM microscopy pointed out a strong interfacial adhesion in both EVA-MA/Cell and EVA-GMA/Cell composites, as compared to EVA/Cell composites. DSC data indicated that the crystallization temperature of the polymer matrix increases in the presence of cellulose fibres, supporting a nucleating effect of cellulose on the growth of polymer crystals from the melt. Glass transition behaviour and filler effectiveness (FE) were analysed by DMTA [3]. Cellulose was found to be more effective filler for EVA-GMA (FE= 0.02) compared to EVA-MA (FE= 0.22). Tg of EVA and EVA-GMA was changed by the incorporation of cellulose fibre markedly. Tensile tests pointed out a consistent increase of elastic modulus (> 700%) with the filler content for all examined systems. Samples containing GMA grafted copolymers displayed larger changes of tensile strength and failure strength. Finally, significant changes of tensile parameters were also observed for composites of EVA-MA with esterified hemp fibres, supporting the occurrence of enhanced fibre-matrix interactions in the presence of anhydride groups on EVA copolymers.