A Quercetin-Derived Polybasic Acid Hardener for Reprocessable and Degradable Epoxy Resins Based on Transesterification

Abstract

The development of recyclable thermosets with high performance from renewable resources is highly desirable from the concerns of environmental and resource economics. Here, a full biobased carboxyl-containing epoxy hardener (CF-quercetin) was prepared from quercetin and succinic anhydride (starch/sugar derivative) through a mild one-step reaction. The epoxy resin cured by CFquercetin shows tensile strength (92 MPa) comparable with commercial counterparts and high storage modulus (3800 MPa) at room temperature. Owing to the high content of dynamic ester bonds in the epoxy networks, the cured epoxy resin can be repeatedly reprocessed like thermoplastics, and 91% recovery of tensile strength from the first reprocessing cycle can be achieved. Meanwhile, the glass-transition temperature and thermal stability of the reprocessed epoxy resin remain almost constant compared with the original epoxy resin. Furthermore, the epoxy resin cured by CF-quercetin presents rapid degradation in alkali aqueous solution (NaOH, 1 M) within 6 h at room temperature, but it is fully nondegradable in acidic and neutral solutions over a period of 120 days. The cured epoxy resin also shows acceptable stability in many conventional organic solvents. Taken together, our work provides a simple method to prepare a universal quercetin-based hardener for epoxy resins with reprocessability, degradability, and high mechanical performance.

Synthesis of Renewable, Recyclable, Degradable Thermosets Endowed with Highly Branched Polymeric Structures and Reinforced with Carbon Fibers

“…Bio-based thermosets that consist of biogenic carbons can be a solution because their use can reduce fossil fuel consumption and the carbon footprint . In particular, with the help of dynamic covalent chemistry, they are reprocessable and chemically recyclable; thus, they constitute bio-based covalent adaptable networks. , A variety of biomasses have been exploited for this purpose: vegetable oils − (including vanillin, − eugenol, , and cardanol , ), natural acids, − flavonoids, , and biopolymers, for example, polysaccharides, natural resins, and lignins. − Most of them contain β-hydroxy ester bonds that are commonly derived from epoxide, promoting transesterification due to the presence of free hydroxyl groups adjacent to the esters . Moreover, dynamic covalent bonds such as imine, disulfide, hindered urea, , acetal, boronic ester, and carbamate have been applied to build renewable dynamic networks.…”

“…2 In particular, with the help of dynamic covalent chemistry, 3 they are reprocessable and chemically recyclable; thus, they constitute bio-based covalent adaptable networks. 4,5 A variety of biomasses have been exploited for this purpose: vegetable oils 6−11 (including vanillin, 12−14 eugenol, 15,16 and cardanol 17,18 ), natural acids, 19−21 flavonoids, 22,23 and biopolymers, for example, polysaccharides, natural resins, and lignins. 24−30 Most of them contain β-hydroxy ester bonds that are commonly derived from epoxide, promoting transesterification due to the presence of free hydroxyl groups adjacent to the esters.…”

Recyclable and Degradable Vinylogous Urethane Epoxy Thermosets with Tunable Mechanical Properties from Isosorbide and Vanillic Acid

“…To date, a large amount of dynamic reversible bonds or structures have been incorporated into thermoset polymers, such as imine bonds, , Diels–Alder addition structures, , ester bonds, , disulfide bonds, − vinylogous urethane bonds, − carbonate linkages, , and so on. Cross-linked networks with dynamic bonds or structures reorganize in response to stimuli such as heat, UV light, or pH, resulting in the distinction between dynamic cross-linked polymers and traditional thermosets. Various dynamic reversible bonds or structures have experienced exponential growth of research interests in the past few decades, and they endow polymers with inherently recyclable, self-healing, and degradable properties.…”

Developing Easy Processable, Recyclable, and Self-Healable Biobased Epoxy Resin through Dynamic Covalent Imine Bonds

“…In that case, once exposed to heat, the reverse ester bonds are dynamically exchanged and the cross-linked arrangement remains intact, allowing the polymer to be recycled and repaired like a thermoplastic. There are several types of triggerable dynamic bonds such as Diels–Alder (DA), , disulfide bonds, , imine bonds, ,, and ester bonds. , Among them, imine bonds are extremely impressive for epoxy resins as they can perform multiple reversible reactions, including transimination, imine metathesis, and imine condensation, without a catalyst. , In addition, Liu and coworkers prepared fully biomass polyimine vitrimers with outstanding recyclability, degradability, and adhesion properties using vanillin-based aldehydes and aliphatic amines . However, the reported vitrimer exhibited very poor mechanical (∼5 MPa) and thermal properties ( T g ∼ 30 °C).…”

“…There are several types of triggerable dynamic bonds such as Diels−Alder (DA), 15,16 disulfide bonds, 17,18 imine bonds, 3,12,13 and ester bonds. 19,20 Among them, imine bonds are extremely impressive for epoxy resins as they can perform multiple reversible reactions, including transimination, imine metathesis, and imine condensation, without a catalyst. 21,22 In addition, Liu and coworkers prepared fully biomass polyimine vitrimers with outstanding recyclability, degradability, and adhesion properties using vanillin-based aldehydes and aliphatic amines.…”