Biodegradable Foam Synthesized from Lignin-Rich Brewer’s Spent Grain Waste with Potential Use as a Sustainable Alternative for Packaging Applications

Abstract

Biodegradable foams derived from agroindustrial residues provide a sustainable alternative to existing petroleum-based packaging, while supporting circular bioeconomy objectives. In this study, biofoams were synthesized using raw brewer’s spent grain (BSG1) and lignin-enriched residues (BSG2 and BSG3) obtained postfermentation for ethanol production. Chemical composition analysis of all BSG biomasses revealed that BSG1 contained 18.72% total lignin, whereas BSG2 and BSG3 exhibited substantially higher lignin contents of 78.28 and 83.69%, respectively, representing nearly a 4-fold increase. SEM (scanning electron microscopy) analysis showed an increase in biofoam porosity from BSG1 (0.4%) to BSG2 (7.8%) and BSG3 (13.4%), which correlated with enhanced compressive strength (0.49–0.50 MPa) and improved thickness recovery under uniaxial cyclic compression. It also exhibited reduced water absorption, from 20% in BSG1 to 7 and 11% in BSG2 and BSG3, respectively. The enhanced lignin content may have contributed to the strength and moisture resistance of the biofoams, whereas the relatively low water absorption of the processed BSG likely supported its degradation in the environment. The foams exhibited high solubility in river and seawater (48–70%) and near-complete soil degradation within 7–10 weeks, highlighting their rapid environmental decomposition. Thermal analysis (TG/DTG) confirmed the multistage degradation typical of lignocellulosic materials, with higher residual char in BSG2 and BSG3 reflecting their lignin-rich composition. Collectively, these results demonstrated that lignin-rich BSG residues can be transformed into mechanically robust, moderately porous, thermally stable, and rapidly biodegradable biofoams, combining enhanced strength, controlled hydrophilicity, and environmental compatibility. This work establishes a zero-waste cascade valorization strategy in which lignin-rich fermentation residues are upcycled into biodegradable biofoams, providing a sustainable pathway for replacing petroleum-based packaging materials.