Evaluation of starch-PE multilayers:: Processing and properties

Adhesion tests performed on various plasticized starch-polyethylene multi-layer systems led to the selection of a suitable combination of polymers compatible with the starch-based layer. The compatibility of starch and polyethylene was better achieved through maleic anhydride functionalized polyethylene (PEg) than chemically modifying starch. The PEg method proved efficient provided that the water content, and the plasticizer nature and contents of the starch layer were carefully chosen. Computed shear viscosity allowed us to select a suitable botanical origin of starch such that the interfacial instabilities of the coextrusion process were minimized. The use of a multilayer structure (PE/PEg/starch/PEg/PE) improved gas barrier properties at high relative humidity. The higher quantity of water sorbed by thermoplastic starch (as compared to EVOH) coupled with starch's specific water sorption isotherm lengthened the water equilibration time in the hydrophilic inner layer significantly. As a result the gas barrier properties of the starch based multiplayer systems were enhanced as compared to existing commercial multiplayer systems (PE/PEg/EVOH/PEg/PE). This specific "water-buffering property" of the starch inner layer should prove useful in packaging applications of perishables with extended shelf life in environments of varying relative humidity. (C) 2005 Society of Plastics Engineers.