Innovative plasticized starch films modified with waterborne polyurethane from renewable resources

To develop biodegradable materials with high performance, we prepared a novel waterborne polyurethane (PU) from rapeseed oil based polyol, and then used it to modify the glycerol plasticized starch (PS) to overcome the intrinsic drawbacks of the starch materials, such as poor mechanical properties and water sensitivity. The blend films were successfully prepared by casting the aqueous dispersions of gelatinized starch and PU. The effect of PU content on the morphology, miscibility and physical properties of the resulting materials was detailed investigated by scanning electron microscopy, differential scanning calorimetry, dynamic mechanical thermal analysis and measurements of mechanical properties and water sensitivity. The results show that glycerol plasticized starch can mix with rapeseed oil based waterborne polyurethane at molecular level when PU content is lower than 20 wt%, whereas the phase separation occurs when the PU content further increases in the blends. The occurrence of hydrogen bonding interaction between starch and PU plays a key role in improvement of the material performance. Compared with the pure PS films, the PS/PU blends exhibit higher values of the elongation at break (85-480%), the toughness (1.8-7.1 MPa) and the tensile strength (2.8-4.1 MPa). Meanwhile, incorporating PU into the plasticized starch matrix leads to an improvement of surface and bulk-hydrophobation and a better water resistance of the resulting materials.