Structure and properties of casting films blended with starch and waterborne polyurethane

A series of casting films blended from starch and waterborne polyurethane ( STPU) in aqueous solution were prepared. The structure and properties of th e films were investigated by infrared spectroscopy, ultraviolet spectroscop y, scanning electron micrography, strength test, thermogravimetric analysis , and different scanning calorimetry. The results showed that the tensile s trength and modules of air-dried STPU blend films increased with the increa se of starch content, while elongation decreased. When starch content was i n the range from 80 to 90 wt %, the blend films showed significantly higher tensile strength, breaking elongation, water resistivity, and light transm ittance than that of pure starch film, resulting from the miscibility betwe en starch and waterborne polyurethane. Moreover, the STPU films containing 90 wt % starch have higher thermal stability than pure waterborne polyureth ane film, and their light transmittance was close to the polyurethane, due to the existence of a strong intermolecular hydrogen bonding between starch and polyurethane. (C) 2001 John Wiley & Sons, Inc.