Multiple Cross-Linking-Enhanced Wastepaper-Based Foams with Hydrophobicity and Thermal Insulation Performance

Conventional petroleum-derived polymeric foams impose substantial environmental burdens during production and disposal, underscoring the need for renewable and biodegradable alternatives. Herein, this study proposes a low-cost strategy for fabricating wastepaper-based foams reinforced through a multiple cross-linking network. Without requiring chemical pretreatment, wastepaper fibers were integrated with a modified soybean meal adhesive (SMA) and poly(vinyl alcohol) (PVA), generating a cooperative hydrogen-bonded and covalently cross-linked structure that enhanced interfiber interfacial cohesion and mechanical integrity. The resulting foams, produced via microwave foaming followed by low temperature drying, exhibited a lightweight porous morphology and demonstrated substantial improvements in energy adsorption per unit volume, with increases of 246% and 125% at 50% and 70% strain, respectively. Incorporation of n-eicosane phase change materials imparted reversible thermal-regulation functionality, yielding a high latent heat of 206.37 J g–1, reducing peak temperature of 10.7 °C, and prolonging thermal-buffering duration of 2.7 times. Moreover, a polydimethylsiloxane (PDMS) coating conferred robust hydrophobicity and excellent humidity resistance, with the moisture adsorption can be reduced to 10% under 98% RH. By leveraging the renewability of wastepaper fibers, this study offers a sustainable upcycling pathway for wastepaper resources and highlights the applicability of the resulting foams in green building insulation and energy-efficient thermal management.