Re-processing of recycling thermoset resins

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 4.2 Re-processing of recycled thermoset resins Contractual Date of Delivery: 30/11/2024 Actual Date of Delivery: 29/11/2024 Lead contractor for this deliverable: NIC Author(s): Giorgio Tofani, Filipa A. Vicente, Damian Ghazal Tavakoli Gheinani, Arijana Susa, Willem Vogelzang, Wouter Teunissen, Ian Jansen, Herman Beukelaer Participants(s): W P contributing to the deliverable: WP4 Nature: Confidential Version V. 3 Grant Agreement 101058371 Project ESTELLA ESTELLA_D4.2_v3 5 The recovered thermoset resin formulations after the recycling processes will be used as raw material to demonstrate the ability of epoxy resins to be reprocessed. NIC and ICSO will use the recovered epoxy resins to develop new thermoset materials with CAN as it was performed in T2.2. Recovered resin will be used in composition with fresh resin with CAN to determine the maximum amount of recovered resin that can be imparted without significant deterioration of the -Alder resins using typical thermoplastic melt processing technologies such as extrusion. Processing parameters will be optimised. After processing, the degree and rate of restoration of Diels-Alder bonds will be determined. Below are the main findings of the research performed by the involved partners: Considering the development of associative bio-based epoxy resins from lignin with CANs, two approaches of re-processing were studied. In the first one, the epoxy resin dissolved under cyrene treatment was reshaped in silicon molds (Figure 0). The second one consists of testing the self-healing properties of the epoxy resin by hot pressing in presence and absence of fresh epoxide (1,4 butanediol diglycidyl ether). The results showed that, during the first approach, it was possible to reshape the epoxy resin. However, the recycled material was too brittle with respect to the original one. Instead, the hot pressing did not allow the self-healing of the epoxy resin sample despite heating at 160 °C and 200 °C. Figure 0. From left to right: original NIC resin, recycled resin, remoulded samples 1 and 2. Regarding the development of associative fossil-based epoxy resins, materials based on commercial epoxy resin were chemically recycled by dissolving them in an organic solvent at elevated temperature. The process has been designed to effectively dissolve the material, enabling the separation of the component compositions (including the fibres from the resin matrix) and thus their subsequent reprocessing. The high temperature and appropriately chosen solvents promoted efficient decomposition of the polymer network, enabling the recovery of monomers/oligomers, which were reused in the synthesis of new materials. Next to the above-mentioned efforts, WR has investigated the reprocessability of two DA-containing thermosets using both extrusion and compression molding techniques. The processing parameters were optimized, and the thermal and mechanical properties of the materials before and after each reprocessing cycle were assessed using different analytical methods such as DSC, FTIR, tensile tests, and rheology measurements. These analyses allowed for determining the degree and rate of recovery of the DA bonds in each case. It was observed that while a desired drop in viscosity can be achieved at elevated temperatures due to the rDA reaction and the resulting breakdown of the crosslinked network, higher reprocessing temperatures could lead to a side Grant Agreement 101058371 Project ESTELLA ESTELLA_D4.2_v3 6 reaction namely, the homopolymerization of maleimide rings in BMI-689. This issue could also arise if the material is maintained at high temperatures for extended periods, increasing the likelihood of homopolymer formation. Thus, extrusion appears to be a preferable method for reprocessing DAcontaining thermosets, as it minimizes exposure time to high temperatures. This reduction in exposure lowers the risk of maleimide homopolymerization, thereby preserving the recyclability and reprocessing efficiency over multiple cycles. The D4.2 deliverable has fully met its objectives. However, it had to be postponed 3 months, which has been updated in the amendment of the Grant Agreement.