Humidity response of poly(butylene adipate-co-butylene terephthalate) copolyesters and their composites with wood flour determined by dynamic mechanical analysis

• Hygrothermal stability of biodegradable copolyesters was estimated.
• Hygrothermal aging was simulated by dynamic mechanical analysis.
• Viscoelastic properties of P(BA-co-BT) rely on an aromatic moiety and reinforcement.
• Humidity combined with heating deteriorates viscoelastic properties of copolyesters.

This study investigated the mechanical and viscoelastic properties of poly(butylene adipate-co-butylene terephthalate) copolyesters, P(BA-co-BT)s and their composites, P(BA-co-BT)–WF with 20 vol.% of beech wood flour (WF) at dry (N2) and in humid atmosphere (50% RH) using a large temperature range from 20 to 90 °C. The melting behaviour of P(BA-co-BT) copolyesters were studied with differential scanning calorimetry (DSC) and wide-angle X-ray analysis. The increase of the aromatic moiety as well as reinforcement with WF improved stiffness of copolyesters. The ambient testing environment with the increased temperature negatively impacted the stiffness and strain properties of P(BA-co-BT)s as well as P(BA-co-BT)–WF composites. The loss of mechanical properties was accelerated in humid atmosphere due to hydrolytic degradation of the ester linkage in copolymers. It was determined that wood flour used as a reinforcement slightly contributed to the hygrothermal aging of P(BA-co-BT) composites. Understanding the effect of humid atmosphere combined with dynamic changed temperature provides useful information for the assessment of the hygrothermal stability of biodegradable polyesters.