Development of multilayer barrier films of thermoplastic starch and low-density polyethylene

This study focuses on producing 3-layer films out of Low-Density Polyethylene (LDPE) and Thermoplastic Starch (TPS) using the latter to improve the film oxygen barrier properties. Potato and corn-based TPS, plasticized with glycerol, have been prepared and blended with LDPE using a twin-screw extruder. The TPS fraction was varied from 50 to 80 wt%. The effect of a maleated copolymer as blend compatibilizer was assessed by examining blend morphology using scanning electron microscopy. The aforementioned TPS/LDPE blend was used as a core layer in a 3-layer blown film with pure LDPE as outer layers. Natural and organo-modified clays were added to the TPS phase at concentrations up to 5 wt% to investigate their effect on blend morphology as well as on processability and physical properties of the film. X-ray diffraction experiments indicated significant exfoliation and a general orientation of non-exfoliated clay parallel to the film surface. Adding natural clay to the TPS was also found to improve processing and quality of the films. Highly transparent films with oxygen barrier 20 times higher than pure LDPE films were achieved while maintaining similar mechanical properties relative to pure LDPE. The multilayer TPS/LDPE film could therefore represent a low-cost bio-based alternative for food packaging requiring better oxygen protection in order to increase shelf-life.