Epoxy Thermosets Designed for Chemical Recycling

Abstract

Epoxy thermosets constitute a significant portion of high-performance plastics, as they possess excellent thermal and mechanical properties that are applicable in a wide range of industries. Nevertheless, traditional epoxy networks show strict limitations regarding chemical recycling due to their covalently crosslinked structures. Although existing methods provide partial solutions for the recycling of epoxy networks, it is urgent to develop more effective, sustainable, and permanent strategies that will solve the problem at hand. For this purpose, developing smart monomers with functional groups that enable the synthesis and development of fully recyclable polymers is of great importance. This review highlights recent advancements in chemically recyclable epoxy systems and their potential to support a circular plastic economy. Moreover, we evaluate the practicality of polymer syntheses and recycling techniques, and assess the applicability of these networks in industry.

Perspective on the Development of Monomer Recovery Technologies from Plastics Designed to Last

“…Introducing certain molecular functionalities that will disconnect under specific trigger conditions, will allow tailored resins to be easily removed from fibers while maintaining favorable properties. 30,31,87 In 2012, US-based company Connora Technologies launched a thermoset epoxy resin system tailored for disassembly. By incorporating an acidsensitive ketal group into the backbone of alkyl amines within the curing agent, referred to as recyclamine, fibers could cleanly be recovered from composite materials using mild acidic conditions.…”

“…While the issue of legacy materials in circulation and production is not addressed as of now, developing new formulations of resins designed for disassembly at their end-of-life is a promising approach to ease future waste handling. Introducing certain molecular functionalities that will disconnect under specific trigger conditions, will allow tailored resins to be easily removed from fibers while maintaining favorable properties. ,, In 2012, US-based company Connora Technologies launched a thermoset epoxy resin system tailored for disassembly. By incorporating an acid-sensitive ketal group into the backbone of alkyl amines within the curing agent, referred to as recyclamine, fibers could cleanly be recovered from composite materials using mild acidic conditions. , In 2019, Connora Technologies, together with its recyclamine process, was acquired by the Indian chemical company Aditya Birla .…”

“…As such, recycling of both the polymer and the fibers could be achieved. Many of the disassembly processes, including the one commercialized by Siemens-Gamesa and Aditya Birla, rely on aqueous acidic conditions to trigger the fragmentation of the polymer matrix. ,,, Therefore, we aimed at developing a robust reaction system that would tolerate residues of water and acid within the resin fraction. While originally envisioning a catalytic dehydrogenation in tandem with a nucleophilic substitution on the resulting ketone in basic media, serendipity led us to a much simpler protocol .…”

“…With an increasing focus on the identification of more sustainable thermoset plastics, advancements have mainly been focused on the use of biobased monomers − and designing recyclable polymers containing dynamic covalent bonds that deconstruct upon external stimuli. − A transition to new materials tailored for disassembly will likely be an important part of reaching a more sustainable future. Nonetheless, the introduction of new polymers as a substitute for current thermoset materials does not provide a solution to the lack of recycling technologies for existing materials.…”

Closing the loop: polyimine thermosets from furfural derived bioresources

“…Consequently, the generated plastic waste is either incinerated or landfilled thereby imposing a substantial environmental burden. 3,4 Furthermore, the prevalent utilization of petroleum-derived monomers in the production of commercial thermosets contributes to increased resource depletion. Therefore, there is a pressing demand to supplant conventional petroleum-based thermosets with biobased alternatives, ideally equipped for closed-loop recycling to recover constituent monomers for reuse in fresh thermoset production.…”