Sustainable extraction of lignin from rice straw: utilizing fractionated lignin for antimicrobial functionalization of polymeric materials

Lignin extracted from rice straw via hydrothermal steam explosion and fractionated using acid-catalyzed organosolv treatment in previous work was incorporated into styrene–butadiene rubber (SBR) at 3 and 6 wt% to develop functionalized composites with antimicrobial properties. Antimicrobial testing demonstrated a 99.99% reduction in Staphylococcus aureus viability, with the lignin exhibiting a minimum inhibitory concentration of 0.5 mg mL⁻¹ against both S. aureus and Klebsiella pneumoniae. Mechanical characterization revealed improvements in elongation at break (+40.4%), tear resistance (+38.5%) and tensile strength (+16.8%) relative to unfilled SBR, while abrasion resistance remained within footwear industry standards. Thermal characterization through thermogravimetric analysis and differential scanning calorimetry revealed that lignin contributed to the thermal stability of the composites and behaved as a reinforcing filler, maintaining the integrity of the rubber matrix under processing conditions. This work demonstrates a sustainable and scalable approach to valorize rice straw lignin for the development of bio-based antimicrobial elastomeric materials, with potential for industrial implementation and future application in other rubber-based systems.