Study of the reversion/degradation of CAN

Grant Agreement number: 101058371 Project acronym: ESTELLA Project title: Design of bio-based thermoset polymer with recycling capability by dynamic bonds for bio-composite manufacturing DELIVERABLE 2.3 Study of the reversion/ degradation of CAN Contractual Date of Delivery: 31/12/2024 Actual Date of Delivery: 30/12/2024 Lead contractor for this deliverable: WR Author(s): (ICSO), Giorgio Tofani, Filipa A. Vicente (NIC), Ghazal Tavakoli, Arijana Susa, Willem Vogelzang, Wouter Teunissen, Ian Jansen, Herman Beukelaer (WR) Participants(s): WR, ICSO, NIC WP contributing to the deliverable: WP2 Nature: Confidential Version V. 3 Grant Agreement 101058371 Project ESTELLA Final-ESTELLA_D2.3-v.3.docx 5 Executive Summary This report provides a summary of the work conducted under Task 2.3 of the ESTELLA project, which focused on studying the reversion and degradation of Covalent Adaptable Networks (CANs) and investigating the reprocessability and recycling efficiency of various CAN-based materials. NIC concentrated on the reprocessability of bio-epoxy resins containing associative CANs, analysing their recycling efficiency and the material properties post-recycling. ICSO focused on the degradation of the epoxy vitrimer materials also incorporating associative CANs by subjecting the materials to dissolution and depolymerization in the presence of solvents via transesterification at high temperatures. Capability of re-crosslinking of the thermosets was also analysed. Meanwhile, WR carried out a comprehensive study on the reversion and degradation of thermosets containing Diels-Alder (DA) functionalities, examining the parameters that influence the reprocessability of dissociative CANs. The research yielded important findings on the reversion and degradation behaviours of both associative and dissociative CAN-based resins, providing valuable insights into their reprocessability and potential for sustainable applications. Below are the summary of the main findings of the research performed on reversion and degradation of associative and dissociative resins. Associative bio-based epoxy from lignin with CAN [NIC] NIC has been studying the recycling and reprocessing of lignin-based epoxy resin containing associative CAN. The reversion and/or degradation studies of epoxy resins with CANs was only performed for one type of lignin-based epoxy resin instead of two, due to the suboptimal properties obtained for the other developed epoxy resins, their limited possibility for scalability, and/or findings covered in the Safe and sustainable by design (SSbD) report. This applies to the resin obtained through the functionalisation of higher molecular weight (MW) lignin fractions and crosslinked with 1,4-butanediol diglycidyl ether to form the final epoxy resin. Considering the reprocessability, two approaches were studied. In the first one, the epoxy resin was dissolved in green solvents, and the reshaping was tested. In this case, it was possible to reshape the epoxy resin. However, the recycled material was too brittle compared to the original one. The second method tested the self-healing properties of the epoxy resin by hot pressing in the presence and absence of pure fresh epoxide (1,4 butanediol diglycidyl ether). The results showed that the hot pressing did not support the self-healing of the epoxy resin sample. Grant Agreement 101058371 Project ESTELLA Final-ESTELLA_D2.3-v.3.docx 6 Associative fossil epoxy resins with CAN [ICSO] ICSO reports the successful development, characterisation and recycling of epoxy vitrimer materials tailored to meet both high performance criteria and sustainability goals. By selectively combining petrochemical epoxy resins with bio-based modifiers and optimising the curing agent composition (specifically containing both acid and anhydride), the research team has achieved mechanical properties and glass transition temperatures (Tg) that meet the project requirements. A key achievement is the demonstration of a cost-effective chemical recycling process using propylene glycol as a solvent. This approach enables cured epoxy materials to be dissolved and the raw components recovered for reuse. Incorporating 15-20% recycled material into the new formulations retained the desired properties while reducing material waste. These findings highlight the potential for industrial-scale implementation, advancing the principles of a closed-loop economy in the polymer industry. Dissociative biobased DA-containing resins [WR] WR presents the main findings of their research in the context of studying the reversion and degradation of Diels-Alder (DA) bonds and parameters influencing the reprocessability of the dissociative CANs. Accordingly, the "back-tomonomer" retro-Diels-Alder (rDA) process of the selected formulation in response to heat as stimulus was studied in detail. The WR-selected thermoset demonstrated excellent reprocessability, successfully undergoing extrusion for at least five cycles while maintaining a high recovery rate of thermal and mechanical properties. Compression moulding proved to be a less preferred approach for the reprocessing of some of the formulations. Remarkably, temperature was shown to play a crucial role on the successful reprocessability of the DA-containing thermosets. Accordingly, it was noticed that at higher temperatures, the extent of the viscosity drop required for reprocessing of material, is lowered more drastically after every cycle. In addition, even though the minimum viscosity recorded at lower temperatures was higher (making reprocessing less convenient), the degree of the restoration of DA bonds seemed to be greater, and the degree of degradation of rDA functionality seemed to be much smaller. These findings highlight the importance of optimizing reprocessing temperatures to balance recycling efficiency and material longevity. A systematic study of factors affecting DA bond reversibility and thermoset reprocessability was also performed and revealed: Grant Agreement 101058371 Project ESTELLA Final-ESTELLA_D2.3-v.3.docx 7 - Increasing DA bond concentration improves flow behaviour above the rDA threshold but requires an optimal level to balance thermal/mechanical properties with reprocessability. Excess concentration compromises performance. - Crosslink density has a strong influence on the reprocessability as well as thermal and mechanical properties of materials. The competition between crosslink density and DA bond cleavage significantly affects material reprocessability and properties. Our studies revealed that beyond a certain crosslink density, the material's flow behaviour becomes independent of DA bonds. Therefore, the balance between these factors must be carefully tailored to achieve desired outcomes. - The position of DA bonds also impacts reprocessability. DA bonds in the crosslinker appear to enhance reprocessability, though further studies are required for comprehensive understanding. These insights collectively support the development of more recyclable DAcontaining thermosets with extended usability. Taken together, the D2.3 deliverable has successfully met all outlined objectives, scope or impact, as specified in the Grant Agreement. However, a minor delay in submission has occurred due to the extended timelines in preceding interconnected tasks and the upscaling activities of certain partners.