Degradation of Thermal-Mechanically Stable Epoxy Thermosets, Recycling of Carbon Fiber, and Reapplication of the Degraded Products

Abstract

Conventional epoxy resins can meet the requirement for engineering applications in which high glass transition and thermal stability are essential, but they show no degradability or recyclability. Vitrimers, with covalent adaptable networks, provide reprocessability and degradability. However, the thermally activated bond-exchange reactions prevent the composites from being thermal-mechanically stable at high temperatures. Therefore, developing epoxy/carbon fiber composites with thermal stability and degradability is attractive for industrial applications and environmental sustainability. In this work, we report the degradability of two thermal-mechanically stable epoxy networks derived from self-curing of two eugenol-based epoxy resins: bis­(2-methoxy-4-(oxiran-2-ylmethyl)­phenyl) succinate (II) and tris­(2-methoxy-4-(oxiran-2-ylmethyl)­phenyl)­benzene-1,3,5-tricarboxylate (III). Degradation can be proceeded through aminolysis of aliphatic esters in the networks at a mild condition. The exact structures of degraded products were precisely analyzed by 1H NMR spectra. An epoxy/carbon fiber composite based on III/carbon fiber was prepared. After degrading the epoxy network, the carbon fiber was recycled. Scanning electron microscopy (SEM) pictures show that the recycled carbon fiber is intact and looks the same as the virgin one. Furthermore, we modified the degraded product of epoxy networks for reapplication. One of the degraded products, oligo­(1-oxy-3-(3-methoxy-4-phenylene)­propan-2-ol) (IIc), was further reacted with methacrylic anhydride to obtain oligo­(1-oxy-3-(3-methoxy-4-phenylene)­propan-2-methacrylate) (IId). IId was further thermally cross-linked to a thermoset (IIe) with a T g value of 170 °C. The successful degradation and reapplication of thermal-mechanically stable epoxy networks and the recycling of carbon fibers are well demonstrated.

Characteristics and Application of Eugenol in the Production of Epoxy and Thermosetting Resin Composites: A Review

“…Reddy et al used eugenol-based epoxy resin to prepare epoxy composites with carbon fiber [ 67 ]. Eugenol, triethylamine, and dichloromethane (DCM) were added to a flask with a nitrogen inlet, stirrer, and thermocouple.…”

“…The description of the synthesis of these compounds can be found in the section describing the properties of the composites. eugenol-benzoxazine monomer (EBUz) monomer thiourea reaction [64] hetero structured benzoxazine monomer (HSBBz) monomer diphenyldiaminomethane reaction [65] organosilicon-modified epoxy monomer monomer melting polymerization of the epoxy group and amidogen with the disulfide bond [66] eugenol-based epoxy resins monomer -triethylamine and dichloromethane reaction, -1,3,5-Benzenetricarbonyl trichloride reaction -meta-chloroperoxybenzoic acid reaction [67] diepoxy-isoeugenol phenyl phosphate (DEpiEPP) flame retardant -condensation of isoeugenol (iEu) and phenyldichlorophosphate in toluene with triethylamine, -epoxidation by oxone [68] eugenol-based flame retardant containing phosphorus (P) and silicon (Si) flame retardant -Williamson etherification reaction of eugenol and triethylamine in tetrahydrofuran i diphenylphosphinyl chloride, -silane reaction [69] eugenol monoglycidyl ether (GE) diluent glycidylation reaction [70] diamine-allyl-eugenol (DAAE) curing agent -Williamson reaction, thiol−ene radical reaction [71,72]…”

“…These studies showed that eugenol glycidyl ether (GE) could be successfully used as a reactive diluent of DGEDP epoxy ester resins, allowing them to be processed by vacuum infusion for the production of fiber-reinforced composites. Reddy et al used eugenol-based epoxy resin to prepare epoxy composites with carbon fiber [67]. Eugenol, triethylamine, and dichloromethane (DCM) were added to a flask with a nitrogen inlet, stirrer, and thermocouple.…”

Bio-based epoxy functionalized MQ silicone resins: from synthesis to toughened epoxy composites with good mechanical properties, thermal resistance and transparency

“…23 At the same time, to promote sustainability, natural monomeric phenols such as vanillin, 24 lignin derivatives, 25,26 eugenol 27,28 and cardanol 29 are important promising bio-based building blocks to construct sustainable high-performance thermosetting polymers. 30,31 Eugenol is an essential oil of relatively low cost and it has many reactive functionalities, such as phenolic hydroxyl, allyl, and active sites on its aromatic ring. In our previous work, eugenol glycidyl ether (EG) was synthesized in excellent yield and purity, and then the allyl groups of EG were successfully connected with different small-molecular silicone linkers to afford epoxy monomers with excellent yield and purity.…”

Recycling of Carbon Fiber Reinforced Polymers in a Subcritical Acetic Acid Solution

“…Acids, bases, alcohols, and other solvents have been explored with varied success. [15][16][17] Water has been used as a solvent at high-temperature, high-pressure (HTHP) conditions. CFRP recycling has been explored in both subcritical (<374 °C) and supercritical water (SCW) environments, which both can be effective at decomposing organic compounds [18][19] and recalcitrant chemicals.…”