Marine Degradable, Ion-Responsive Thermoplastic Starch-Based Film via Ionic Bonding between Laurate and Quaternary Ammonium

Starch is a biobased, low-cost polymer whose poor mechanical strength and difficult processability hinder its engineering applications. To address this, we design a simple method to form thermoplastic starch with excellent marine degradability. The cationic starch was prepared with a high degree of substitution (DS) and paired its cationic sites with hydrophobic long-chain alkyl anions through ionic bonding to form the ionic complex (CS-L), boosting hydrophobicity and imparting thermoplastic properties. Through the heat-pressing process, the CS-L ionic complex powder was transformed into a homogeneous film. Incorporating 2 wt % lauric acid into ionic complex (CS-L (2%)), which enhances its water resistance and flexibility, yields a tensile strength of 2.42 MPa and 94.6% elongation at break. The film shows rapid marine degradability, fully disintegrating in artificial seawater within 3 days, and exhibits a high degree of biodegradability in the BOD test. It also dissolves quickly under acidic conditions, demonstrating a material that successfully combines practical processability with strong biodegradability. This study presents a viable strategy for applying starch in engineering contexts, advancing the development of next-generation single-use plastics that align with the sustainability requirements of marine ecosystems.