Heat-Sealing Properties of Compression-Molded Wheat Gluten Films

The impulse heat-sealing properties of wheat gluten films were investigated. Films containing 30 wt% glycerol were compression molded at 100–130 °C and then sealed in a lap-shear or peel-test geometry at 120–175 °C. The tensile properties of the pristine films and the lap-shear and peel strength of the sealed films were evaluated and the seals were examined by scanning electron microscopy. Glycerol was added to the film surfaces prior to sealing in an attempt to enhance the seal strength. It was observed that the wheat gluten films were readily sealable. At a 120 °C sealing temperature and without glycerol as adhesive, the lap-shear strength was greater than or similar to that of polyethylene film, although the peel strength was poorer. The sealing temperature had a negligible effect on the lap-shear strength, but the peel strength increased with sealing temperature. The lap-shear strength increased with increasing mold temperature and the failure mode changed, especially in the absence of glycerol adhesive, from a cohesive (material failure) to an adhesive type. From previous results, it is known that the high-temperature (130 °C) compression-molded film was highly cross-linked and aggregated, and this prevents molecular interdiffusion and entanglement and thus leads to incomplete seal fusion and, in general, adhesive failure. The presence of glycerol adhesive had a beneficial affect on the peel strength but no, or only a minor, effect on the lap-shear strength.