Uniaxial Tensile Behavior and Thermoforming Characteristics of High Barrier EVOH-Based Blends of Interest in Food Packaging

摘要

The uniaxial tensile characteristics of blends of an ethylene-vinyl alcohol copoly-mer (EVOH-32 mol% ethylene) with an amorphous PA and/or a nylon-containing ionomer, used as barrier layer in multilayer food packaging structures, was assessed in this paper. The stress-strain behavior of these materials at elevated temperatures and at different strain rates was examined. The stress-strain curves obtained were used to understand the influence of temperature and strain rate on the uniaxial deformation process of the materials, these being of general importance during typical processing steps including thermoforming. A male mold for deep-draw was used to assess the thermoforming (biaxial deformation in nature) behavior of extruded sheets at 100, 120, 140 and 150degC, and the results were broadly found to be in agreement with results from simple uniaxial tensile tests. From the preliminary thermoforming results, it was found that EVOH/aPA extruded blends did not improve the poor formability of EVOH alone. In contrast, significant improvement in thermoformability was achieved by blending EVOH with a compat-ibilized ionomer. Optimum forming capacity was achieved in a ternary blend by addition of a compatibilized ionomer to an EVOH/aPA blend in the range of 140degC-150degC. The ternary blend showed a lower reduction of thickness in the sidewalls, as well as a higher dimensional uniformity in the thermoformed part.