Study of blends of nylon 6 with EVOH and carboxyl-modified EVOH and a preliminary approach to films for packaging applications

Blends of nylon 6 (Ny6) with ethylene-co-vinyl alcohol (EVOH) and EVOH modified with the introduction of carboxyl groups (EVOH-COOH) have been studied by Fourier transform infrared spectroscopy, scanning electron microscopy, differential scanning calorimetry, and dynamic-mechanical thermal analysis. The thermal and thermomechanical analyses of the blends show that the melting, crystallization, and relaxational behavior are affected by the blend composition and the presence of carboxyl groups on the EVOH chains. Nevertheless, microscopic and thermal investigations demonstrate the biphasic nature of the two-blend systems. Selective solvent extraction of the EVOH or EVOH-COOH phase in their blends and Fourier transform infrared analysis of the residual products indicates the occurrence of ionic linkages between the amino groups of the polyamide and the carboxyl groups of the modified EVOH, whereas specific interactions are evidenced for Ny6/EVOH blends. Tests performed on extruded Ny6/EVOH films show that the addition of EVOH effectively reduces the gas permeability of Nylon, whereas the addition of small amounts of EVOH-COOH helps to control and stabilize melt rheology