Synthesis of Sustainable Polymeric Materials from Biobased Building-Blocks and Their Recycling or Reprocessing

To reach sustainable polymeric materials and a circular plastic economy, the choice of resources and synthetic methodology as well as product consumption, use and the end-of-life handling need to be scrutinized. To add to the complexity, the polymeric material groups portray inherent strengths and weaknesses and, thereby, an array of solutions to reach sustainable polymeric materials are required. Here, examples of our contribution to the field will be presented focusing on the utilization of renewable building-blocks, their polymerization methodologies where the principles of green chemistry are central, and the chemical structure design to achieve both functionality and a predetermined end-of-life handling choice.<br/>Aliphatic polyesters have been identified as valuable examples where chemical recycling to monomer (CRM) is a viable option. This relates to a combination of a possible pathway to revert back to monomer in combination with the appropriate thermodynamic prerequisites for achieving depolymerization using a realistic energy consumption. Yet, achieving a balance of reasonable temperature used for CRM while retaining polymer stability, for example during processing, is difficult. We have demonstrated a methodology to solve this problem by copolymerization and thereby extending the use of naturally occurring 6-membered lactones. When copolymerized with other more thermodynamically stable lactones, the kinetics can be utilized to achieve “end-capping” of the formed polyester, hindering their actual propensity to depolymerize at comparably low temperatures, and at the same time chemical recyclability was achieved.<br/>Thermosets are a group of polymeric materials where the end-of-life handling is inherently challenging, due to their network structure. In this context, the concept of covalently adaptable networks (CANs) is considered a potential future solution, as CANs have mechanical stability and chemical resistance but can, upon applying an external stimulus such as heat, rearrange bonds and thereby portray interesting properties such as self-healing and most importantly - they can be reprocessed. In this area we contribute by utilizing renewable building-blocks and applying the green chemistry principles in the CAN synthesis, achieving functionality and reprocessability for e.g. polyamide networks.