Development of recyclable carbon fiber-reinforced plastics (CFRPs) with controlled degradability and stability using acetal linkage-containing epoxy resins

Recyclable carbon fiber-reinforced plastics (CFRPs) with controlled degradability and stability were developed by adding bisphenol A (BA)-type epoxy resins containing acid-degradable acetal linkages (BA-CHDMVG) to the matrix resins of CFRPs. BA-CHDMVG was synthesized by the reaction of the hydroxyl groups of BA with vinyl ether containing a glycidyl group (cyclohexane dimethanol vinyl glycidyl ether (CHDMVG)) and added to conventional BA-type epoxy resins (jER828 and jER1001). The acetal linkage-containing CFRPs (BA-CHDMVG-based CFRPs) were prepared using a mixture of these epoxy resins as the matrix. The obtained CFRPs exhibited almost the same tensile and thermal properties as those of the conventional BA-based CFRP (BA-based CFRP). One of the BA-CHDMVG-based CFRPs, (BA-CHDMVG) 40 -(jER1001) 60 -based CFRP (content in the matrix resin: BA-CHDMVG, 40 wt%; jER1001, 60 wt%), underwent smooth degradation through hydrolysis of the acetal linkages incorporated into the matrix resin upon treatment with 0.1 mol l −1 hydrochloric acid in a tetrahydrofuran (THF)/water (9/1 v/v) mixed solvent for 24 h at room temperature to produce strands of carbon fibers. On the other hand, there was no change in the appearance of the same BA-CHDMVG-based CFRP board upon acid treatment in water with no organic solvent. To determine their stability against aqueous acid, the BA-CHDMVG-based CFRP boards were immersed in 0.1 mol l −1 aqueous acetic acid solution at room temperature for 30 days and then subjected to tensile testing. The BA-CHDMVG-based CFRPs after the acid treatment exhibited almost the same tensile properties as those of the BA-CHDMVG-based CFRPs before the acid treatment. These results indicate that the BA-CHDMVG-based CFRPs are stable toward acid in the normal living environment, such as acid rain. Recyclable carbon fiber-reinforced plastics (CFRPs) with controlled degradability and stability were developed by using acid-degradable acetal linkage-containing epoxy resin (BA-CHDMVG). The obtained BA-CHDMVG-based CFRPs exhibited almost the same tensile and thermal properties as those of the conventional BA-based CFRPs and underwent smooth degradation through hydrolysis with the treatment of hydrochloric acid in a tetrahydrofuran (THF)/water (9/1) mixed solvent. On the other hand, in the absence of organic solvents, the BA-CHDMVG-based CFRPs have sufficient stability toward acid in the normal living environment.