Poly(m-xylene adipamide)-montmorillonite nanocomposites: effect of organo-modifier structure on free volume and oxygen barrier properties

Abstract

It was shown that nanoparticle–polymer interactions that affect the free volume and oxygen barrier properties of poly(m-xylene adipamide)/clay nanocomposites can be tailored by the choice of organic modifier of montmorillonite clay. Three different organo-modified clay compounds based on montmorillonite (Cloisite 30B, 10A and 93A) were dispersed in the resin poly(m-xylene adipamide) at loading levels of 2 wt% clay. Samples were melt compounded and extruded using a laboratory scale twin screw micro compounder. Positron annihilation lifetime spectroscopy (PALS) was used to examine the free volume of the polymer nanocomposites. PALS results suggested that the Cloisite 10A additive should give the higher reduction in gas permeability as it results in the lowest free volume for the nylon resin when compared to all of the clay additives examined. Oxygen transmission rates (OTR) were measured on nanocomposite films and the Cloisite 10A additive was found to give the best oxygen barrier, showing a reduction of OTR of 66% compared to the neat resin. In all cases examined, PALS free volume data was found to have excellent correlation to the measured oxygen transmission rates. The addition of Cloisite 10A resulted in the highest crystallinity and an increase in glass transition temperature when compared to the neat resin. Results indicate that the improved barrier properties of the clay compounds is primarily due to an increase in the degree of crystallinity of the polymer, with the nanoparticles being more effective nucleating agents when favourable nanoparticle–polymer interactions are present.