Comparative Kinetic Evaluation of Thermal Degradation Pathways in Biodegradable Polyesters – PLLA, PBS, PBAT, and PHBV

• Thermal degradation of PLLA, PBS, PBAT, and PHBV studied by thermogravimetry. • Isoconversional and model kinetic analysis reveal distinct degradation mechanisms. • PHBV shows rapid one-step degradation with low activation energy. • PLLA, PBS, and PBAT display multi-step pathways with rising E α . • Isothermal lifetime predictions link kinetics to processing limits. The thermal degradation of biodegradable polymers strongly influences their processing, stability, and recyclability. This study investigates the kinetics of poly(butylene adipate-co-terephthalate) (PBAT), poly(butylene succinate) (PBS), poly(lactic acid) (PLLA), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) using thermogravimetric analysis (TGA) combined with Advanced Isoconversional Kinetic Analysis (AIKA) and Model-Based Kinetic Analysis (MBKA). Effective activation energies ( E α ), reaction model functions ( f(α) ), and mechanistic schemes were determined, and predictive isothermal simulations were performed. PHBV exhibited the lowest stability, degrading near 280°C through a rapid, mainly single-step process. In contrast, PLLA, PBS, and PBAT decomposed above 350°C, following multi-step pathways. Contrary to predictions based on melting temperature, PHBV emerged as an outlier, while PLLA, PBS, and PBAT showed overlapping thermal resistance. AIKA confirmed this distinction: PHBV displayed nearly constant E α , whereas PBS and PBAT showed increasing values, reflecting secondary reactions. MBKA supported these findings, identifying initial autocatalytic steps followed by first-order processes. Predictive simulations validated the models and provided lifetime estimations under processing conditions. These results demonstrate that thermal stability is governed by structure and degradation pathway complexity rather than melting temperature and highlight the value of combining model-free and model-based kinetics to guide the processing and design of thermally stable biodegradable polyesters.