Phase morphology, crystallinity and mechanical properties of binary blendsof 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-co ntaining ionomer have been characterized in terms of phase morphology, crys tallinity and mechanical properties by DSC, WAXS, DMA, SEM, microhardness ( MH) and tensile testing. Such blends are claimed by manufacturers to improv e the thermo-formability characteristics of EVOH while retaining/improving its high gas barrier under high relative humidity conditions. From the resu lts, it becomes apparent that the miscibility of this high barrier EVOH gra de with the amorphous PA is very poor, and clear phase segregation througho ut composition was shown by DSC, DMA and SEM. Factors like geometric hindra nce and chain stiffness of the amorphous PA could be responsible for this b ehavior. A lack of good interaction between EVOH/PA blend components was fu rther supported by the negative deviation from the simple additive rule see n in the mechanical properties of these blends. A two phase structure was a lso observed in the EVOH/ionomer blends, but from the results a better phas e compatibility was inferred. This compatibility increased in the ionomer r ich blends and was thought to be enhanced by the presence of crystalline Ny lon in the formulation of the ionomer. An increased in flexibility and toug hness was measured in the mechanical properties of these EVOH/ionomer blend s. 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.