A Review on the Potential and Limitations of Recyclable Thermosets for Structural Applications

Abstract

The outstanding performance of conventional thermosets arising from their covalently cross-linked networks directly results in a limited recyclability. The available commercial or close-to-commercial techniques facing this challenge can be divided into mechanical, thermal, and chemical processing. However, these methods typically require a high energy input and do not take the recycling of the thermoset matrix itself into account. Rather, they focus on retrieving the more valuable fibers, fillers, or substrates. To increase the circularity of thermoset products, many academic studies report potential solutions which require a reduced energy input by using degradable linkages or dynamic covalent bonds. However, the majority of these studies have limited potential for industrial implementation. This review aims to bridge the gap between the industrial and academic developments by focusing on those which are most relevant from a technological, sustainable and economic point of view. An overview is given of currently used approaches for the recycling of thermoset materials, the development of novel inherently recyclable thermosets and examples of possible applications that could reach the market in the near future.

Tough and Multi‐Recyclable Cross‐Linked Supramolecular Polyureas via Incorporating Noncovalent Bonds into Main‐Chains

“…[19] However, the use of catalyst and the generation of reactive species during the exchange of dynamic covalent bonds may bring potential risks on the decrease of mechanical properties and recyclability. [20] Besides dynamic covalent bonds, various noncovalent bonds have been used as cross-linking points to construct recyclable networks. [21][22][23][24][25][26][27][28][29][30][31] Compared with dynamic covalent bonds, the binding strength of noncovalent bonds is weaker and therefore noncovalent bonds are more likely to break and reform reversibly under facile conditions without catalysts.…”

The Use of Click-Type Reactions in the Preparation of Thermosets

“…This reaction occurs at moderate temperatures and has a reverse process (retro-Diels-Alder) at elevated temperatures. This reversibility, triggered under different conditions, facilitates not only the reworkability of thermosetting materials, but also the possibility of special applications such as remendable materials [153,154] and other smart technologies [155].…”

Estudo Da Viabilidade Técnica Do Processamento De Resíduos De Espuma Flexível De Poliuretano Por Um Moinho De Facas

“…Sendo assim, novas soluções em reciclagem estão sendo buscadas para solucionar este problema que cresce assim como o consumo do poliuretano. Segundo Post et al (2019) os termofixos, como o poliuretano, apesar de terem suas ligações cruzadas que limitam sua reciclabilidade, podem ser reciclados de forma mecânica, térmica ou química. Porém, de forma geral, isto requer muita energia e não se chega a matéria prima de origem, sendo então recomendado que esta família de materiais, no pós consumo, seja aplicado como carga, fibra ou substrato, como forma de reciclagem ou reaproveitamento.…”