High-elongation, water-weldable, and fully degradable biomass foams fabricated via oven drying

Biomass-based foams present a promising alternative to conventional plastic foams. However, many reported biomass-based foams are composed of nondegradable components and are mechanically weak and brittle. We proposed a hybrid biomass-driven foaming strategy that used specially designed cellulose nanofibers and sodium caseinate to synergistically create stable wet foams and form gas-impermeable bubble interfaces to prevent structural collapse during oven drying. The foams exhibited high tensile stress (~400 kPa) comparable to that of brittle foams and had excellent ductility, with an elongation of 137.0%. The foams also displayed outstanding cyclic elastic behavior, retaining more than 90% of their compressive stress after 100 cycles. In addition, the foams were water-weldable, recovering 87.3% of their original tensile stress and nearly 100% of their elongation, allowing them to be tailored into customized geometric structures. A roll-to-roll casting process was used to produce continuous foam rolls, demonstrating successful scalability. This study provides an advanced formulation for fabricating fully degradable biomass-based foams with superior mechanical properties.