Kristensen Steffan K, Ahrens Alexander, Donslund Bjarke S, Skrydstrup Troels
Interdisciplinary Nanoscience Center (iNANO), Aarhus University, Gustav Wieds Vej 14, 8000 Aarhus C, Denmark.
Carbon Dioxide Activation Center (CADIAC), Novo Nordisk Foundation CO2 Research Center, Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, 8000 Aarhus C, Denmark.
ACS Org Inorg Au. 2024 May 7;4(4):373-386. doi: 10.1021/acsorginorgau.4c00009. eCollection 2024 Aug 7.
In order to prevent the current unsustainable waste handling of the enormous volumes of end-of-use organic polymer material sent to landfilling or incineration, extensive research efforts have been devoted toward the development of appropriate solutions for the recycling of commercial thermoset polymers. The inability of such cross-linked polymers to be remelted once cured implies that mechanical recycling processes used for thermoplastic materials do not translate to the recycling of thermoset polymers. Moreover, the structural diversity within the materials from the use of different monomers as well as the use of such polymers for the fabrication of fiber-reinforced polymer composites make recycling of these materials highly challenging. In this Perspective, depolymerization strategies for thermoset polymers are discussed with an emphasis on recent advancements within our group on recovering polymer building blocks from polyurethane (PU) and epoxy-based materials. While these two represent the largest thermoset polymer groups with respect to the production volumes, the recycling landscapes for these classes of materials are vastly different. For PU, increased collaboration between academia and industry has resulted in major advancements within solvolysis, acidolysis, aminolysis, and split-phase glycolysis for polyol recovery, where several processes are being evaluated for further scaling studies. For epoxy-based materials, the molecular skeleton has no obvious target for chemical scission. Nevertheless, we have recently demonstrated the possibility of the disassembly of the epoxy polymer in fiber-reinforced composites for bisphenol A (BPA) recovery through catalytic C-O bond cleavage. Furthermore, a base promoted cleavage developed by us and others shows tremendous potential for the recovery of BPA from epoxy polymers. Further efforts are still required for evaluating the suitability of such monomer recovery strategies for epoxy materials at an industrial scale. Nonetheless, recent advancements as illustrated with the presented chemistry suggest that the future of thermoset polymer recycling could include processes that emphasize monomer recovery in an energy efficient manner for closed-loop recycling.
为了防止目前对大量废弃有机聚合物材料进行不可持续的填埋或焚烧处理，人们已投入大量研究工作，致力于开发适用于商业热固性聚合物回收利用的解决方案。这种交联聚合物一旦固化就无法再熔融，这意味着用于热塑性材料的机械回收工艺不适用于热固性聚合物的回收。此外，由于使用了不同单体导致材料结构多样，以及将此类聚合物用于制造纤维增强聚合物复合材料，使得这些材料的回收极具挑战性。在这篇展望文章中，我们讨论了热固性聚合物的解聚策略，重点介绍了我们团队在从聚氨酯（PU）和环氧基材料中回收聚合物结构单元方面的最新进展。虽然这两类聚合物在产量方面是最大的热固性聚合物类别，但它们的回收前景却大不相同。对于PU，学术界和工业界加强合作，在醇解、酸解、氨解和分相二醇解以回收多元醇方面取得了重大进展，目前正在对多个工艺进行进一步的扩大规模研究。对于环氧基材料，其分子骨架没有明显的化学断裂靶点。然而，我们最近证明了通过催化C-O键断裂从纤维增强复合材料中拆解环氧聚合物以回收双酚A（BPA）的可能性。此外，我们和其他人开发的碱促进裂解方法在从环氧聚合物中回收BPA方面显示出巨大潜力。仍需要进一步努力评估此类单体回收策略在工业规模上对环氧材料的适用性。尽管如此，本文所展示的化学方法的最新进展表明，热固性聚合物回收的未来可能包括以节能方式强调单体回收以实现闭环回收的工艺。
