Interlayer destabilization process of natural and commercial bentonite incorporated Ethylene Vinyl Acetate (EVA) nanocomposite with hybrid silicate nanofillers

Abstract

Natural and commercial bentonites can act as efficient fillers to reinforce a polymer matrix if their strong interlayer binding forces are weakened to reduce tactoid formation. In this research, interlayers destabilization process was applied to gain a loosely packed, swelled and disorganized clay layered structure for better polymer intercalation and filler dispersion during the polymer/clay composite fabrication. Three different destabilization methods were applied to the natural and commercial bentonites and their effects on swelling and platelets ordering/stacking of the clays were observed. The pristine and destabilized natural and commercial bentonites were characterized and compared based on their chemical component (XRF), chemical structure (XRD and FTIR) and morphology (FESEM). Chemical analysis revealed that mineralogical and chemical compositions of both types of bentonite affect their structure and swelling capability during the destabilization process. XRD results suggest that basal spacing (d001) of both natural and commercial bentonites reduced when single destabilization process (by salt addition) was applied but increased when destabilization was done by the combination of pH control and salt addition processes. The increment of basal spacing was seen to be ~0.04 nm for both natural and commercial bentonites showing that the destabilization process through combination of pH control and salt addition is more efficient in swelling both natural and commercial bentonite clays. This is supported by FESEM analysis where smaller, more loosely packed and uniform platelets were observed due to swelling and weakening of the interlayer binding forces of both natural and commercial bentonite clays. The ‘destabilized’ bentonites were used as co-nanofiller with the organically modified montmorillonite (OMMT) to form hybrid silicate nanofillers for EVA copolymer matrix reinforcement. Results show that the ‘destabilized’ bentonite prepared by the combination of pH control and salt addition is most efficient in reinforcing the EVA matrix when combined with the OMMT by allowing 124.9% increment in tensile strength, 13.5% in elongation at break and 190.8% in toughness values. Furthermore, thermal stability of the EVA nanocomposite was also improved. This could be related to the improved dispersion of bentonite upon the destabilization process that allows greater matrix-filler interactions in the nanocomposite system. In summary, destabilization process through pH control and salt addition is the promising and practical technique to improve the dispersion of bentonite throughout the polymer matrix. Without the use of expensive and toxic chemicals, it can be adopted as a new approach to swell bentonite for more environmental friendly nanocomposite technology.