Aromatic Epoxy from Caffeic Acid: Mechanical Properties and Flame Retardancy
Shuai Wang, Fei Sun, Zhongbin Ni, Yan Lyu, Tatsuo Kaneko, Weifu Dong, Mingqing Chen, Dongjian Shi
Abstract
The preparation of biobased epoxy resins with superior mechanical properties and flame retardancy is a significant challenge, and the development of caffeic acid epoxy resins (CFAE) from plant-derived caffeic acid that has a conjugate rigidity group and reactive double carbon and hydroxyl groups represents a promising advancement in this field. The epoxy resins with different cross-linking densities, such as CFAE 1 GEFA n and CFAE 1 FD n, can be obtained from CFAE through Diels–Alder reaction with Glycidyl Ether of Furfuryl Alcohol (GEFA) and 2-difuran disulfide (FD), followed by curing with 4,4′-diaminodiphenylmethane (DDM). The tensile strength of caffeic acid-based epoxy resins ranges from 73.8 to 106.5 MPa, much higher than that of bisphenol A diglycidyl ether-based epoxy/DDM (56.6 MPa). In addition, CFAE/DDM is rated V-0 in the UL-94 test and has a high limiting oxygen index of 31% and a very low peak heat release rate of 83.1 W g –1, suggesting excellent intrinsic flame-retardant properties. Additionally, the reduced smoke production rate of 0.14 m 2 s –1, total smoke production of 12.1 m 2, and total heat release of 62.2 MJ m – 2 of the CFAE-based epoxy indicate a decreased risk of toxic fumes and massive exothermic heat released during combustion. Overall, the resultant CFAE-based epoxy resins with sustainable and enhanced mechanical and flame-retardant properties have potential applications to electronic packaging, construction, decoration, and aerospace fields.