Phase morphology, crystallinity and mechanical properties of binary blends of high barrier ethylene-vinyl alcohol copolymer and amorphous polyamide and a polyamide-containing ionomer

A number of dry melt-mixed binary blends of 32 mol% ethylene vinyl-alcohol copolymer (EVOH) and an amorphous polyamide (PA) and a crystalline Nylon-containing ionomer have been characterized in terms of phase morphology, crystallinity and mechanical properties by DSC, WAXS, DMA, SEM, microhardness (MH) and tensile testing. Such blends are claimed by manufacturers to improve the thermo-formability characteristics of EVOH while retaining/improving its high gas barrier under high relative humidity conditions. From the results, it becomes apparent that the miscibility of this high barrier EVOH grade with the amorphous PA is very poor, and clear phase segregation throughout composition was shown by DSC, DMA and SEM. Factors like geometric hindrance and chain stiffness of the amorphous PA could be responsible for this behavior. A lack of good interaction between EVOH/PA blend components was further supported by the negative deviation from the simple additive rule seen in the mechanical properties of these blends. A two phase structure was also observed in the EVOH/ionomer blends, but from the results a better phase compatibility was inferred. This compatibility increased in the ionomer rich blends and was thought to be enhanced by the presence of crystalline Nylon in the formulation of the ionomer. An increased in flexibility and toughness was measured in the mechanical properties of these EVOH/ionomer blends. The flexibility rose with increasing strain rate in extruded films. The overall crystallinity of the blends was lower than that of neat EVOH, ought to the amorphous condition of the PA and the lower crystallinity exhibited by the ionomer. (C) 2001 Elsevier Science Ltd. All rights reserved.