Multicycling of Epoxy Thermoset Through a Two‐Step Strategy of Alcoholysis and Hydrolysis using a Self‐Separating Catalysis System

Abstract

Plastic has now become a contradiction between civilization and pollution that human society has to resolve. The recycling of thermosetting plastics in waste plastics is a huge challenge since they are difficult to remold like thermoplastic plastics due to their high crosslinking density. Here, a new strategy was developed to achieve multicycling of anhydride‐cured epoxy thermosets. The process consisted of mild and high‐efficiency alcoholysis catalyzed by potassium phosphate/low‐boiling alcohol system, and subsequent fast hydrolysis to obtain degradation products rich of carboxyl groups. The degradation products were reused as curing agent to prepare new anhydride‐cured epoxy thermosets without sacrifice of high strength and stability. Moreover, the new epoxy thermosets could still be repeatedly recycled using the same protocol. The insolubility of potassium phosphate in ethanol at room temperature made the separation and reuse of the catalyst more convenient. The use of low‐boiling alcohol not only allowed high‐efficiency degradation but also enabled easy separation from the degradation products. The excellent degradation performance was attributed to the improved swelling of the thermoset and the increased solubility of potassium phosphate induced by small amounts of water in the alcohol. This research provides a recycling method that can reintegrate thermoset waste plastics into remodeling ones under the background of circular economy.

Probing the Solubility of Imine-Based Covalent Adaptable Networks

“…For example, ester-based CANs could be dissolved using alcohols as solvent, , disulfide-based CANs could be dissolved by using thiols as the solvent, , and imine-based CANs could be dissolved using primary amines as the solvent. , As mentioned before though, this technique of solvent-assisted dissolution does, by definition, not dissolve the actual polymer but rather cuts it into small soluble end-capped pieces or monomers. It could, therefore, perhaps better be described as a practice of degradation or depolymerization …”

“…It could, therefore, perhaps better be described as a practice of degradation or depolymerization. 65 We were, however, able to fully recycle our polyimine CANs via dissolution without requiring primary amines to break down the polyimine network, but simply by dissolving the CANs in pure THF. For this recycling test, PI-30 materials were synthesized and their material properties were determined using rheology.…”

Microbial Enzyme Biotechnology to Reach Plastic Waste Circularity: Current Status, Problems and Perspectives

“…Thermosets are composed of branched polymeric chains that form a crosslinked three-dimensional network when heated. As these cross links are made up of covalent bonds, after their formation, these plastics cannot be recycled by melting and reforming [ 49 ]. In compliance with EU plastic demand distribution by resin type ( Table 2 ), thermoplastics (about 85%) dominate over thermosets (around 15%), with crystalline thermoplastics being the most requested (up to 50%).…”

“…A synergy with promising methods of abiotic secondary and tertiary PUR depolymerization approaches could allow for depolymerization of recalcitrant PUR waste, but no method has been tested on real PUR waste to date [ 49 , 165 , 168 , 194 , 195 ].…”

Affinity of K+to organic matter promotes reactions: degradation of super stable phenolic epoxy vinyl ester resin to value-added chemicals

“…[6][7][8][9][10] The alcohol solvents in the super/sub-critical state are demonstrated to be efficient for degrading thermoset resins, but harsh conditions, such as high reaction temperature and pressure, are commonly required. 11,12 Amines usually have good solubility and strong nucleophilicity and can interact with the carbonyl group of resins to depolymerize them under mild conditions. [13][14][15][16][17] However, the high cost of amines and their physiological and environmental toxicity limit their application.…”