Synthesis of starch-based non-isocyanate polyurethane hybrids with hot-melt processability and enhanced performance

Biodegradable starch-based plastics are promising alternatives to petroleum-derived polymers, yet their poor melt processability and limited mechanical strength hinder industrial adoption. Here we propose a dual-modification-hybridization route: native corn starch is first esterified with citric acid (CA) and plasticized with glycerol (GLY) to obtain citric-acid-modified starch (CAS), and then hybridized with non-isocyanate polyurethane (NIPU) to yield melt-processable starch bioplastics. With 10 wt% NIPU relative to starch (CAS/NIPU-10), the material becomes melt-processable below 110 °C, whereas an analogous thermoplastic starch blend at the same ratio (TPS/NIPU-10) remains non-flowable upon heating. Concomitantly, tensile strength increases from 3.17 MPa (TPS/NIPU-10) to 6.54 MPa (CAS/NIPU-10), the elongation at break reaches 38.32%, and the specimens exhibited substantial visual degradation during outdoor soil exposure over 60 days. CA-GLY modification disrupts the starch double-helix, while a hydrogen-bond network between starch hydroxyls and the polar functional groups of NIPU relaxes the constraints of crystalline domains on chain-segment mobility. This environmentally benign route yields starch bioplastics that combine good melt processability, enhanced mechanical performance, and visual degradation under outdoor soil exposure, thereby bridging the technical gap between starch-based plastics and industrial thermoforming applications.