Preparation and properties of thermoplastic starch-polyester laminate sheets by coextrusion

The effects of extrusion and formulation variables on the structure and pro perties of starch-polyester laminates were examined. Three-layer polyester/ starch/polyester sheets were prepared using a twin-screw extruder for the s tarch/water center layer, a single screw extruder for the outer polyester l ayers and a feedblock and coathanger type sheet die. Overall sheet and coat ing thicknesses were more uniform as coating polymer (poly(epsilon-caprolac tone), PCL) viscosity decreased (lower molecular weight), starch melt visco sity increased (lower moisture) and feedblock/die temperature increased. Pe el strengths were 1 to 2 orders of magnitude larger for high than low molec ular weight PCL. High peel strengths were associated with rough, wavy inter faces (interfacial instability). Addition of plasticizer such as glycerol a nd sorbitol to the starch decreased peel strengths. Peel strengths varied l ittle with type of polyester coating, except, perhaps, for polylactic acid and polyesteramide, which were more difficult to peel. Some possible applic ations of laminated starch sheets include food packaging and controlled rel ease of drugs, pesticides, insect diets, etc.