Biodegradable antistatic starch foams via two-step extrusion: Linking additive effects, melt rheology, and cellular...

Developing biodegradable starch foams with antistatic functionality remains challenging because antistatic additives can simultaneously influence charge dissipation, melt viscoelasticity, and foam-structure formation. Herein, a hierarchical film-to-foam strategy was developed to separate additive-specific effects from changes introduced during two-step extrusion foaming of starch-based materials. Homogeneous hydroxypropyl starch (HPS) films were first used to screen additives with strong antistatic potential and favorable interactions with the starch matrix, while pellet rheology was further applied to evaluate whether these additive effects could be translated into a melt state suitable for stable foaming. Polyvinylpyrrolidone (PVP) and 1-ethyl-3-methylimidazolium acetate ([EMIM][Ac]) showed similarly strong antistatic potential in the film model, but generated different rheological responses in starch pellets. After foaming, high [EMIM][Ac] loading promoted expansion but weakened structural stability, whereas 1 wt% PVP provided the best overall balance, yielding low apparent density (21.26 kg·m^-3), relatively high expansion ratio (32.94), reduced resistivity (724.62 MΩ·cm), and improved compressive resilience (140.41%) and recovery (58.46%). These results show that the performance of antistatic starch foams is governed not by additive chemistry alone, but by the sequential coupling of additive-starch interactions, melt-state regulation, and foam-structure development. This work provides a useful basis for designing multifunctional biodegradable polysaccharide foams with balanced electrical and mechanical performance.