Natural rubber composites incorporating alkali lignin: Property characterization and functional evaluation

Conventional natural rubber (NR) fillers pose several environmental concerns. This study presents the sustainable development of NR composites incorporating sugarcane leaf (SCL)-derived alkali lignin and commercial alkali lignin as functional fillers. The primary objective was to evaluate the mechanical properties, aging resistance, thermal stability, and antimicrobial activity of the NR composites. Various NR composites were prepared by different filler types, including KOH-extracted SCL lignin, commercial alkali lignin, and butylated hydroxytoluene (BHT). The results show that NR composites containing KOH-extracted SCL lignin exhibited superior mechanical properties (crosslink density 126 mol/m³), improved aging resistance (aging coefficient 80.08 %), and enhanced thermal stability (the thermal degradation with 50 % weight loss (T₅₀) and the highest degradation rate occurs (T_d) of 394 and 383 °C, respectively) compared to all other samples. NR composites with commercial lignin demonstrated the highest reduction in Staphylococcus aureus populations (56.25 %). The NR composites with KOH-extracted SCL lignin displayed limited antimicrobial efficacy (37.78 %), suggesting that its primary contribution lies in mechanical and thermal reinforcement rather than microbial inhibition. These findings highlight the potential of eco-friendly lignin from SCL biomass as a sustainable bio-based filler for NR composites.