Hygrothermal aging behavior of biochar-reinforced polylactide/wood plastic composites

• A 1% biochar loading is optimal for composite performance. • Biochar induces a homogeneous, Fickian-controlled water uptake. • The primary cause of strength loss is interfacial cracking from swelling. • Interfacial degradation is conclusively proven by dynamic mechanical analysis. Addressing the need for sustainable materials amid growing environmental concerns, this study investigates the development of biodegradable composites from landscaping waste (LW) and polylactic acid (PLA), enhanced with biochar (BC). The primary focus is on evaluating the impact of BC addition (0.5-4 wt%) on the mechanical performance and hygrothermal aging (water absorption and color stability) of LW/PLA composites. Furthermore, BC incorporation effectively mitigates aging: increasing BC content and exposure time lead to lower thickness swelling, reduced color fading, and less surface deterioration compared to BC-free composites. Water absorption kinetics followed the Fickian model, and saturation significantly degraded mechanical properties, primarily due to fiber swelling, interfacial micro-cracking, and debonding. Dynamic mechanical analysis confirmed that moisture saturation increased the loss factor and impaired interfacial stress transfer. This work demonstrates that BC, particularly at 1 %, is a highly effective modifier for enhancing the performance and durability of sustainable LW/PLA composites.