Enhancing the Recyclability of a Vegetable Oil-Based Epoxy Thermoset through Initiator Influence

Abstract

Bisphenol A-based epoxy thermosets involve both environmental and health risks. By reacting a vegetal oil-based epoxide with an aromatic diacid containing S–S bonds a thermoset is produced. Herein, reprocessable thermosets were synthesized, the recyclability being designed through a dual mechanism: that of disulfide metathesis and of transesterifications. To assess the feasibility of the reprocessing, a series of 10 initiators was tested to probe their effect not only on the cross-linking reaction but also on the recyclability. This study introduces for the first time the key role of the initiator on the material performance and on their reprocessing. A very good reprocessability was obtained for thermosets prepared using as initiator the imidazole. Moreover, the thermosets exhibit complete chemical recyclability in 1 N NaOH at 80 °C, after 3 days, without needing additional chemicals. The reprocessed materials have similar performance with the virgin ones, even after 10 cycles of reprocessing.

Building thermally and chemically reversible covalent bonds in vegetable oil based epoxy thermosets. Influence of epoxy–hardener ratio in promoting recyclability

“…Even if the E 0 values in the rubbery plateau are increased after the reprocessing, the crosslink density diminishes, except the system with R = 2 where the crosslink density augments after reprocessing from 0.28 to 0.59 mmol cm À3 . In our previous work, 21 we explained that this increase of the crosslink density can be attributed to the dual mechanism of the network's internal rearrangement occurring during reprocessing. ESO/DTBA systems revealed a similar trend to that of the ELO based systems (Table S4, ESI †), with lower crosslink (Table S4, ESI †), and again the ELO/ ESO/DTBA R = 1 thermoset has the higher crosslinking density.…”

“…2,2 0 -Dithiodibenzoic acid (DTBA) was used as a dynamic hardener. Our team already studied how the initiators influence the copolymerization of ELO/DTBA, 13,21 but, to the best of our knowledge, this study reports for the first time the effect of the ratio of the thermoset systems on the chemical recyclability and the thermal reprocessing properties. The epoxy/acid reactions were monitored via differential scanning calorimetry (DSC) and infrared spectroscopy (FT-IR) analyses.…”

Recyclable High-Performance Epoxy-Anhydride Resins with DMP-30 as the Catalyst of Transesterification Reactions

“…The widespread application of epoxy thermosets has brought a serious concern about their large amounts of waste, including leftover pieces, off-grade products, and end-of-service-life components. The initial disposal methods, including landfill and incineration, led to severe environmental pollution and waste of resources [ 6 , 7 , 8 , 9 ]. To achieve the recycling of epoxy resins, various technologies have been developed, such as pyrolysis, supercritical fluid method, and chemical solvolysis [ 7 , 10 , 11 ].…”

“…The development of vitrimers containing dynamic covalent bonds (DCBs) makes it possible to recycle thermosets under mild conditions [ 8 , 9 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ]. Over the past few decades, researchers have developed an array of vitrimers through incorporating various DCBs (e.g., disulfide [ 25 , 26 ], imine-amine exchange [ 27 ], and hindered urea bond [ 28 ]), among which epoxy vitrimer prepared from the curing reactions of epoxy-anhydride [ 29 , 30 , 31 ] or epoxy-carboxylic [ 32 , 33 , 34 ] is the most investigated vitrimer system.…”

“…One of the typical accelerators for epoxy resins is 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30), which can effectively reduce the curing temperature and speed up the curing process [ 8 , 52 ]. It can also be used alone as the curing agent [ 53 ].…”