Thermoprocessed starch-polyester bilayer films as affected by the addition of gellan or xanthan gum

Abstract

Monolayer films based on cassava starch (CS) or maize starch (MS), with and without 10% of gellan or xanthan gum, and PLA-PHBV (75:25) blend films, were obtained by melt-blending and compression moulding, using glycerol (for starch blends) and PEG 1000 (for polyester blends) as plasticisers. Bilayer films were obtained by thermo-compression of the different starch based sheets with the polyester sheet. Both mono and bilayers were characterised as to their mechanical and barrier properties, equilibrium moisture, water solubility and microstructure. The incorporation of gellan gum and xanthan gum improved the mechanical properties of starch-based films, especially in the case of MS, although the highest EM and TS values were obtained for CS-gum films. The incorporation of either gellan or xanthan gum decreased the water vapour and oxygen permeability of starch-based films; the CS films with gums being the least permeable to oxygen. The lowest changes in mechanical properties throughout storage were obtained in cassava starch-based films, especially those containing xanthan gum. Starch based-polyester bilayers presented a high oxygen and water vapour barrier capacity, as compared to their individual monolayers. Bilayer films with cassava starch including the gums showed the lowest OP and WVP values and the highest elastic modulus and tensile strength, with extensibility values in the range of the corresponding monolayers and slight changes in their physical properties throughout time. The bilayer formed with cassava starch with gellan gum and a PLA-PHBV appeared as the best option for food packaging purposes taking into account its functional properties and the good layer adhesion of the bilayer.