Biobased Diels-Alder Engineered Network from Furfuryl Alcohol and Epoxy Resin: Preparation and Mechano-Physical Characteristics

Designing End-of-life Recyclable Polymers via Diels-Alder Chemistry: A Review on the Kinetics of Reversible Reactions

The purpose of this review is to critically assess the kinetic behaviour of the furan/maleimide Diels-Alder click reaction. The popularity of this reaction is evident and still continues to grow, which is likely attributed to its reversibility at temperatures above 100°C, and due to its bio-based "roots" in terms of raw materials. This chemistry has been used to form thermo-reversible crosslinks in polymer networks, and thus allows the polymer field to design strong, but also end-of-life recyclable thermosets and rubbers. In this context, the rate at which the forward reaction (Diels-Alder for crosslinking) and its reverse (retro Diels-Alder for de-crosslinking) proceed as function of temperature is of crucial importance in assessing the feasibility of the design in real-life products. Differences in kinetics based from various studies are not well understood, but are potentially caused by chemical side groups, mass transfer limitations, and on the analysis methods being employed. In this work we attempt to place all the relevant studies in perspective with respect to each other, and thereby offer a general guide on how to assess their recycling kinetics. This review sheds light on the kinetics on the furan/maleimide Diels-Alder reaction. This popular reaction opens up a path to develop end-of-life recyclable polymer networks with self-healing properties. The factors affecting reaction kinetics are discussed, and the importance of accurate reaction kinetics in the context of polymer reprocessing is highlighted. This article is protected by copyright. All rights reserved.

Thermally Healable and Recyclable Graphene-Nanoplate/Epoxy Composites Via an In-Situ Diels-Alder Reaction on the Graphene-Nanoplate Surface

In this work, thermally healable graphene-nanoplate/epoxy (GNP/EP) nanocomposites were investigated. GNPs were used as reinforcement and crosslinking platforms for the diglycidyl ether of bisphenol A-based epoxy resin (DGEBA) through the Diels-Alder (DA) reaction with furfurylamine (FA). The GNPs and FA could then be used as a derivative of diene and dienophile in the DA reaction. It was expected that the combination of GNPs and FA in DGEBA would produce composites based on the interfacial properties of the components. We confirmed the DA reaction of GNPs and FA at the interface during curing of the GNP/EP nanocomposites. This procedure is simple and solvent-free. DA and retro DA reactions of the obtained composites were demonstrated, and the thermal healing properties were evaluated. The behavior of the GNP/EP nanocomposites in the DA reaction is similar to that of thermosetting polymers at low temperatures due to crosslinking by the DA reaction, and the nanocomposites can be recycled by a retro DA reaction at high temperatures.

Simultaneous Recovery of Matrix and Fiber in Carbon Reinforced Composites through a Diels-Alder Solvolysis Process

Efficient and comprehensive recycling of fiber-reinforced thermosets is particularly challenging, since the irreversible degradation of the matrix component is necessary in order to separate the fiber component in high purity. In this work, a new approach to fully recyclable thermoset composites is presented, based on the thermal reversibility of an epoxy-based polymer network, crosslinked through Diels-Alder (DA) chemistry. Carbon fiber composites, fabricated by compression molding, were efficiently recycled through a simple solvolysis procedure in common solvents, under mild conditions, with no catalysts. Specifically, the purity of reclaimed fibers, assessed by thermogravimetric analysis and scanning electron microscopy, was very high (>95%) and allowed successful reprocessing into second generation composites. Moreover, the dissolved matrix residues were directly employed to prepare smart, thermally healable coatings. Overall, DA chemistry has been shown to provide a convenient strategy towards circular economy of thermoset composites.