Humidity Resistant Biodegradable Starch Foams Reinforced with Polyvinyl Butyral (PVB) and Chitosan

In this study, water-insoluble, moisture-resistant starch foams were prepared using an optimized one-step extrusion-foaming process in a ZSK-30 twin screw extruder. The extrusion parameters, including temperature, screw configuration, die diameter, water content, and feeding rates, were optimized to achieve foams with the lowest density and controlled expansion. A screw configuration made up of three kneading sections was found to be the most effective for better mixing and foaming. Polyvinyl butyral (PVB) acted as a plasticizer, resulting in foams with a density of 21 kg/m³ and an expansion ratio of 38.7, while chitosan served as a nucleating agent, reducing cell size and promoting a uniform cell size distribution. The addition of PVB and chitosan reduced the moisture sensitivity of the foams, rendering them hydrophobic and water-insoluble. The contact angle increased from 0° for control foams to 101.5° for foams containing 10% chitosan and 10% PVB. Confocal laser scanning microscopy (CLSM) confirmed the migration of chitosan to the foam surface, enhancing hydrophobicity. Aqueous biodegradation tests, conducted at 30 °C in accordance with ISO 14852 standards, demonstrated that despite enhanced moisture resistance, the foams remained readily biodegradable, achieving approximately 80% biodegradation within 80 days. These modified starch foams present a sustainable solution for packaging and insulation applications that demand long-term humidity resistance.