Ethanol-assisted alkyl ketene dimer surface modification for enhanced moisture stability of starch-based foams

Starch-based foams are promising sustainable materials, but their application is hindered by moisture sensitivity and humidity-induced mechanical deterioration. This study developed an ethanol-assisted alkyl ketene dimer (AKD) surface modification strategy to enhance the hygro-mechanical stability of starch-based foam boards and to elucidate the roles of surface esterification and physical coating. Foam boards were fabricated via a two-step extrusion foaming process, followed by AKD treatment with or without ethanol post-treatment to regulate the interfacial organization. FTIR analysis confirmed that esterification introduced limited chemical anchoring, while ethanol treatment reconstructed the coated surface into a more uniform morphology with increased roughness, as revealed by SEM and 3D profilometry. The optimal sample (SF-AKD0.8-E) exhibited a water contact angle of 145.61° (compared to 60.32° for the unmodified foam) and a reduction in equilibrium water absorption from 7.84 to 0.64 g·g^-1. The glass transition temperature increased from 48.35 to 67.59 °C, accompanied by improved mechanical retention under 87% RH. These findings demonstrate that moisture stability is governed by the interfacial organization of AKD, rather than its loading amount, providing a surface-engineering strategy for biodegradable polysaccharide foams.