(20e) A Study on the Gelation Kinetics and Chain Relaxation of Polybutylene Succinate (PBS) By Reactive Extrusion

Reactive extrusion has been applied to fabricate high compatibility blends with enhanced performance for decades. However, controlling the gelation of polymers in reactive extrusion is crucial to achieve stable processing and high-quality products. As a biodegradable polymer, polybutylene succinate (PBS) is likely to be attacked by the free radicals at high temperature, leading to chain branching or grafting with other functional groups to prepare the modified biomaterials. In this work, the peroxide concentration and temperature dependence of PBS critical gel kinetics and viscoelastic properties were determined by rheological studies. The gel time, relaxation exponent of the critical gel and activation energy for the gelation were also determined. As a result, it was found that the gelation is a complex reaction order was 0.67, which indicated a first-order reaction occurred with additional side reactions such as chain branching or decomposition. The relaxation exponent decreased as peroxide concentrations and temperature increased, suggesting that the cross-linking density of the critical gels increased during the real reactive extrusion. At 0.5 phr peroxide, the active energy reaches a maximal value of ~93.7 kJ/mol, which indicated there were difficulties within the relaxation of the reaction cross-link network, and should therefore be avoided during melt processing. The whole research demonstrates a theoretic predication on controlling the gelation and viscoelastic properties of bio-PBS in reactive extrusion.

Acknowledgment: This research is financially supported by the Ontario Research Fund, Research Excellence Program; Round-7 (ORF-RE07) from the Ontario Ministry of Research, Innovation and Science (MRIS) (Project # 052644 and 052665); the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA)/University of Guelph Gryphon’s LAAIR Program (Project # 298636); Agriculture and Agri-Food Canada (AAFC) and Competitive Green Technologies through AgriInnovation Program project (Project # 052882 and 051910); and the Natural Sciences and Engineering Research Council (NSERC), Canada Discovery Grants (Project # 401111 and 400320).