Concentration-sensitive control of the stabilization-degradation balance in poly(butylene succinate-co-adipate) films via calcium lignosulfonate and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane.

Balancing durability during use with predictable biodegradation after disposal remains a major challenge in the design of biodegradable polyesters. Herein, poly(butylene succinate-co-adipate) (PBSA) films were modified with calcium lignosulfonate (LS) and the organic peroxide 2,5-dimethyl-2,5-di(tert-butylperoxy) hexane (DBPH) to elucidate how concentration-dependent intermolecular interactions and radical-mediated processes influence crystallinity, photooxidation, and soil biodegradation. Solvent-cast films were characterized by ATR-FTIR, DSC, XRD, SEM, AFM, accelerated UV ageing, and ISO 17556 soil biodegradation. ATR-FTIR suggested intermolecular interactions, including possible hydrogen bonding, between LS hydroxyl/sulfonate groups and PBSA carbonyl moieties, restricting chain mobility and increasing the glass transition temperature from -44.1 °C for neat PBSA to -40.8 °C at the highest LS content. DSC and XRD indicated a concentration-dependent dual role of LS, initially disrupting crystalline organization and, at higher concentrations, promoting heterogeneous nucleation, increasing crystallinity from 38.2% to 40.2%. DBPH increased the average crystallite size from 6.23 to 9.22 nm at moderate loading, whereas higher concentrations promoted greater microstructural heterogeneity, consistent with competing chain-extension and crosslinking reactions. Under UV irradiation, LS exhibited a concentration-dependent dual photochemical effect, while DBPH modulated the photooxidative response through competing chain scission and crosslinking processes. Soil biodegradation showed a transient inhibition stage followed by recovery of microbial mineralization. Overall, the combined use of LS and DBPH provides a concentration-dependent strategy to tailor PBSA microstructure, photooxidative stability, and biodegradation, enabling biodegradable materials with improved durability during use and predictable degradation after disposal.