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

Abstract

Thermoset polymers with permanently cross-linked networks via thermally reversible covalent bonds have outstanding self-healing and adaptable properties, combined with very good mechanical properties and solvent resistance. This work reports in...

Influence of the Presence of Disulphide Bonds in Aromatic or Aliphatic Dicarboxylic Acid Hardeners Used to Produce Reprocessable Epoxidized Thermosets

“…From these results, we notice that the higher reaction enthalpies were obtained for R e/a = 1, with the exception of the ESFO/DTBA system, thus this ratio was selected as optimal and used for the future studies. This result supports the reported investigations where the equimolar ratio R e/a = 1 gave the optimal results in terms of reactivity [ 22 , 24 ].…”

“…The prepared EVOs thermosets were submitted to mechanical recycling (reprocessing) and the thus obtained recycled materials were characterized by DSC analysis to determine the T g temperature values. In this manner, both the virgin and recycled thermosets were compared [ 22 ]. The thermosets prepared with DTBA show the temperature of this transition from ~49 °C, in the ESFO/DTBA resin, to 91 °C, for EPLO/DTBA.…”

“…The polymer networks were prepared by reacting the EVOs with diacid hardeners in different R e/a functional ratios epoxy groups/acid groups: R e/a = 2 (e/a = 1/0.5), R e/a = 1.25 (e/a = 1/0.8) and R e/a = 1 (e/a = 1/1). In all the formulations, IM was used as the initiator as we recently showed its good selectivity on epoxy/acid copolymerization and also the positive effect on the thermoset’s recyclability [ 20 , 21 , 22 , 23 , 24 ]. According to previous results [ 21 ], the initiator was used in 1 wt.% of the total amount of the reactive mixture, as the optimal amount for curing.…”

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

“…When the tertiary amine and nonphenolic hydroxyl coexisted in the curing system, they formed a complex with the anhydride, which further enhanced the reactivity between the epoxy group and the anhydride ( Figure 2 d) [ 57 ]. When anhydride is insufficient in the system, homopolymerization and/or etherification of epoxy monomer may occur at high temperature [ 24 ], which is unfavorable to the dissolution of epoxy resins. Here we think that the copolymerization of epoxy and anhydride forming ester bonds is dominant, and the effects of secondary reactions are not considered.…”

“…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.…”