Preparation and properties of starch thermoplastics modified with waterborne polyurethane from renewable resources

A waterborne polyurethane (PU) aqueous dispersion was synthesized from castor oil, and blended with thermoplastic starch (TPS) to obtain a novel biodegradable plastic with improved physical properties. The effect of PU content on the morphology, miscibility and physical properties of the resulting blends was well investigated by scanning electron microscopy, differential scanning calorimetry, dynamic mechanical thermal analysis and measurements of mechanical properties and water sensitivity. The research results show that the blends exhibit a higher miscibility when PU content is lower than 15 wt% due to the hydrogen bonding interaction between urethane groups and hydroxyl groups on starch, whereas obviously phase separation occurs in the blends with more than 15 wt% PU. Incorporating PU of 4-20 wt% in TPS results in the blends with improved Young's modulus (40-75 MPa), tensile strength (3.4-5.1 MPa), elongation at break (116-176%). Further, PU also plays an important role in improving the surface- and bulk-hydrophobicity and water resistance of the resulting blends.