Performance of lignin as filler in composites of low density-polyethylene (LDPE) and lignosulfonate

Low-density polyethylene (LDPE) composites were developed using unmodified kraft lignin and lignosulfonate at varying mass ratios to evaluate their effects on mechanical, thermal, and environmental performance. At low filler content, lignin enhanced LDPE crystallinity and stiffness due to improved dispersion and interfacial interaction. However, higher lignin loadings led to particle agglomeration and reduced thermal stability between 100 and 400 °C. Tensile strength increased with lignin content, though no notable difference was observed between LL7.5 and LL10, which was likely due to aggregation. All composites exhibited a consistent melting point at 107 °C. Thermogravimetric analysis revealed that lignin degraded between 200 and 400 °C, while LDPE decomposed at 400 to 500 °C. Melt Flow Rate (MFR) declined with increasing filler content, from 4.92 g/10 min (LL0) to 3.53 g/10 min (LL10). FTIR analysis before and after 30 days of sunlight exposure showed no significant chemical changes, suggesting good environmental stability. These results demonstrated that unmodified lignin-based fillers can enhance the stiffness and environmental resilience of LDPE composites, although thermal stability may be compromised at higher loadings. The study offers insights into the balance between biofiller content and composite performance, supporting the development of sustainable materials for industrial use.