Effects of Sizing Agents and Resin-Formulated Matrices with Varying Stiffness–Toughness Ratios on the Properties of Carbon Fiber Epoxy Resin Composites

Abstract

Interlaminar shear strength (ILSS) and compressive strength are two of the most critical properties of carbon fiber-reinforced polymer (CFRP). In this report, three types of epoxy resins-4,4'-diaminodiphenylmethane epoxy resin (AG-80), bisphenol A epoxy resin (E-1NT), and novolac epoxy (EPN)-were studied. E-1NT is characterized by low viscosity and low cost but exhibits poor mechanical properties, while AG-80 offers better wetting with carbon fiber. These two epoxy resins were mixed in various mass ratios. The study revealed that as the AG-80 content increased, the ILSS of the composite also increased, reaching a maximum of 94.04 MPa when the AG-80 content reached 60%. Beyond this point, further increases in AG-80 did not enhance the ILSS. Conversely, the compressive strength initially increased but then declined sharply as the AG-80 ratio increased. The maximum compressive strength was recorded at 748.52 MPa when the AG-80 content reached 60%, which was 21% higher than pure AG-80 and 32% higher than pure E-1NT. Additionally, the study examined three different types of ionic sizing agents and four different resin matrices (E-1NT/DDS, AG-80/DDS, AG-80/E-1NT/DDS, EPN/DDS). Among them, the 60% AG-80/40% E-1NT/DDS/CF formulation demonstrated the best balance in both ILSS and compressive strength.