Effect of primary-secondary synergistic system on the aging resistance of Salix psammophila/polylactic acid composites

Abstract

To enhance the hydrothermal aging resistance of Salix psammophila wood flour/polylactic acid (PLA) composites, a primary–secondary synergistic anti-aging system was constructed using antioxidant 1010 as the primary antioxidant and distearyl thiodipropionate (DSTP) as the auxiliary antioxidant, with maleic anhydride as an interfacial compatibilizer. The composites were fabricated by hot-pressing, and the effects of the synergistic system on mechanical performance and hydrothermal aging behavior were investigated. Static mechanical results showed that the 1010/DSTP system enhanced the initial mechanical properties and effectively mitigated mechanical degradation after aging. After hydrothermal aging (60 °C, 96 h), the synergistically modified composite (WPC-1/D) retained 47.38% of its flexural strength, representing a 56.54% increase compared to the aged, unmodified control. Stress–strain behavior indicated improved deformation coordination and delayed damage evolution, suggesting enhanced interfacial stability under hydrothermal conditions. Dynamic mechanical analysis further confirmed the synergistic effect, as WPC-1/D exhibited a high storage modulus of 1295.43 MPa in the glassy region after aging, together with increased loss modulus and loss factor peaks, reflecting restricted molecular chain mobility and enhanced energy dissipation. A static-dynamic mechanical correlation model was established to quantitatively describe the relationship between macroscopic mechanical degradation and viscoelastic response during hydrothermal aging. Microscopic observations revealed a multi-scale progressive aging process from damage initiation to damage penetration, clarifying the aging damage pathways. Chemical analysis showed that the O–H absorption peak of WPC-1/D shifted most slowly from 3332 cm⁻¹ to 3422 cm⁻¹, the ester CO group exhibited only slight displacement, and no new CH₃-related absorption peaks emerged; meanwhile, the carbon content increased from 73.88% to 80.03% and the oxygen content decreased from 25.92% to 18.80%, indicating suppressed hydrolysis–oxidation degradation. This study elucidates the anti-aging mechanism of the primary–secondary synergistic system and provides empirical insights and experimental evidence for improving the durability of fully biodegradable composites.