Understanding the Effects of Processing Conditions on the Properties and Durability of Poly(Butylene Succinate)

Abstract

This study investigates the effect of processing conditions on the structural, mechanical, and degradation behavior of poly(bu- tylene succinate) (PBS), a promising biodegradable polyester. PBS was processed using a micro-­ compounder by varying screw speeds (20 and 60 rpm) and residence times (2 and 5 min). Considering that the processing conditions for biopolymers in a mi- crocompounder are typically around 60 rpm with a residence time of approximately 5 min, this work attempts to minimize the thermo-­ mechanical degradation undergone during the PBS processing by reducing the screw speed by about three times (from 60 to 20 rpm) and the processing times by about 2.5 times (from 5 to 2 min). Characterization was performed by using thermal, mechanical, and rheological analyses. A lower screw speed (20 rpm) resulted in a higher degree of crystallinity (~62%), about 5% greater than that of samples processed at 60 rpm. The mechanical properties at break (e.g., tensile strength and elongation at break) and the rheological properties remained unchanged when the processing conditions were changed. It is worth noting that at 60 rpm, increasing residence time led to a 12.7% increase in elastic modulus. Degradation behavior was evaluated under photo-­ oxidative and hydrolytic conditions. After 96 h of UV exposure, samples processed at a lower speed (20 rpm) showed lower hydroxyl, carbonyl, and vinyl indices, indicating better resistance to photo-­ oxidation due to their higher crystallinity. Hydrolytic degradation was carried out at high and low environmental temperatures. Hydrolysis of all PBS samples at low temperature (25°C) occurred more slowly than at high temperature (70°C). These results highlight the critical role of processing parameters in tuning PBS crystallinity and stiffness, as well as degradation behavior. The PBS processed at low speed (20 rpm) for a short time (2 min) has been successfully processed, consuming lower energy and resulting in improved properties and reduced thermo-mechanical degradation. Overall, prolonged processing of PBS (at 5 min) appears to result in materials with poorer properties and lower degradation resistance, particularly at high screw speeds. These are key aspects of its application in sustainable materials and biodegradable packaging.