Correlation between mechanical performance and structural evolution in PLA toughened with reactive polysiloxanes during accelerated aging

Polylactide (PLA) is a sustainable thermoplastic with considerable industrial potential; however, its limited durability under outdoor exposure restricts its broader use in engineering applications. This study investigates the effect of two reactive polysiloxane modifiers (MODs), denoted MOD1 and MOD2, incorporated at 1–5 wt%, on the mechanical performance and aging behavior of PLA under simulated outdoor conditions involving UV-B radiation, elevated temperature, and humidity. The incorporation of MOD1 and MOD2 substantially enhanced the initial ductility and impact toughness of PLA, with impact strength increasing by more than 100% relative to neat PLA for selected formulations. Despite progressive aging-induced embrittlement, the PLA/MOD formulations retained their mechanical performance more effectively than neat PLA. After 250 h of aging, PLA/MOD1 formulations retained ~90% of their initial tensile strength, whereas neat PLA exhibited an ~ 50% decrease. MOD1 provided more persistent ductility after prolonged exposure, whereas MOD2 exhibited superior photochemical stability, with the carbonyl index change after 500 h decreasing from 2.00 for neat PLA to 0.65 for PLA/MOD1 and 0.24 for PLA/MOD2. DSC and XRD analyses indicated that the deterioration of mechanical properties was closely associated with secondary crystallization and changes in the amorphous/α-crystalline phase balance of PLA. Use of reactive polysiloxane additives represents a promising strategy for developing tougher and more aging-resistant PLA materials for durable outdoor applications. Graphical Abstract