Design and Properties of Low-Viscosity Mixed Anhydride Cured Epoxy Resins

Epoxy resin has many advantages. However, as a matrix resin for composites, epoxy resin has the weakness of high viscosity, poor fluidity and low processing time. Considering the high viscosity and poor storage ability of the traditional epoxy prepolymer, we designed an epoxy resin formulation possessing both certain mechanical strength and fluidity. We utilized a low-viscosity trifunctional epoxy compound, N,N-diglycidyl-4-glycidyloxyaniline (AFG), and a solid-liquid mixture of low-eutectic anhydrides, specifically 4-methyl tetrahydro phthalic anhydride and 1,2,3,6-tetrahydrophthalic anhydride, as the epoxy monomers and curing agents, respectively. More importantly, when stored at room temperature for 3 h, this mixture exhibited a low viscosity (1000 mPa·s), which was attributed to the solid-liquid mixed anhydrides remaining in a liquid state at room temperature without recrystallizing. Then, a series of epoxy resins were designed by controlling the mole ratio of epoxide groups to anhydride groups. These resins were analyzed through mechanical property experiments and thermal analysis. The results showed a wide range of adjustable crosslink density in the epoxy resin, from 2 000 mol/m³ to 6 000 mol/m³, and the establishment of a relationship between network, mechanical, and thermal properties of the epoxy resin. This epoxy resin was successfully applied to prepare composites by the unidirectional tape prepreg process. Moreover, the ester bonds can be triggered with transesterification behavior under the zinc(Ⅱ) acetylacetonate catalyst with hydroxyl group. Therefore, epoxy resins can be completely degraded by ethylene glycol at 180 ℃ for 6 h. A wide range of mechanical and thermal properties can be achieved by controlling the ratio of epoxide groups to anhydride groups in epoxy resins, which provides a certain reference for the development of low-viscosity epoxy resins.