Pre-dispersing process of organo-montmorillonite nanofiller: influence to the toughness, flexibility and thermal stability of ethylene vinyl acetate (EVA) nanocomposites

In these new millennia, further advances in new generation medical devices are restricted due to more stringent requirements of biomedical materials for use in more sophisticated and comprehensive biomedical treatment and procedures. Scientists are therefore, keeping an effort to develop new and improved materials for the growth of this biomedical industry. This research intends to develop a new biocompatible material with excellent flexibility, toughness and thermal stability as future candidate for biomedical applications. Ethylene Vinyl Acetate nanocomposites containing 5wt% organo-MMT were produced by melt compounding method, to be relevant with the industrial manufacturing process. A new processing procedure, the so called 'predispersing' process was introduced in order to facilitate the organo-montmorillonite nanofiller dispersion in the matrix, and at the same time provide the plasticizing effect to the host EVA copolymer. Toluene and water liquids were used as pre-dispersing medium and their efficiency to enhance the mechanical and thermal performance of the EVA nanocomposites was investigated. Furthermore, several pre-dispersing parameters were employed involving different types of dispersing method and time. The structureproperty-processing relationships of the EVA nanocomposites were studied and the best pre-dispersing medium and parameters were determined. Based on the morphological, mechanical and thermal studies by FTIR, SEM, tensile test, DMT A, DSC and TGA, the organo-MMT nanofiller pre-dispersed by ultrasonication in water medium for 2 minutes (MMT(W)2m_u) gives the most significant plasticizing effect to the EVA copolymer. The FTIR analysis evidenced the 'destabilizing effect' of the pre-dispersing process to the binding energy within the organo-MMT inter-galleries. This destabilization effect facilitated the organo-MMT exfoliation and dispersion inside the EVA, enhanced the distribution of onium ions at the nanoplatelet-polymer interfaces, and subsequently promoted relaxation of EVA copolymer chains during conformation and deformation process. As a result, plasticized EVA nanocomposite was obtained. When subjected to tensile deformation, the lowering of modulus of elasticity was accompanied by an increased in elongation at break and toughness. DMT A analysis has further proved this plasticizing effect as the storage modulus of the EVA was seen to reduce in the region of -40° to 45°C when incorporated with the MMT(W)2m_u nanofiller. Based on the damping behaviour, one could suggest that the compatibility of the polyethylene (PE) and polyvinyl acetate (PV A) of the EVA copolymer was enhanced when the MMT(W)2m_u nanofiller was added. All these factors led to the enhancement in thermal stability of the EVA nanocomposite as can be observed in TGA. In conclusion, the pre-dispersing process of organo-MMT nanofiller can bring beneficial effects to the overall performance of the EVA nanocomposite, as a candidate for biomedical material.