Curing chemistry of epoxidized soybean oil and its application for structural composite materials

Epoxidized Soybean Oil (EPO) was investigated for its cross-linking reaction with several different types of amines. The catalyst of boron trifluoride ethyl-amine complex was found not only to advance the curing reactions between EPO and the amines but also to improve the thermal and mechanical properties of the cured materials. The EPO polymer cured by the aliphatic amine, triethylene tetramine (TETA), was soft with a T_g of 15°C. The cycloaliphatic amine, bis (p-aminocyclohexyl) methane (PACM), cured EPO to obtain a hard, rigid polymer with the T_g of 58°C. The EPO cured by the cycloaliphatic multifunctional amine, Ancamine 2264, increased the T_g to 65°C. By studying the effect of different EPO/amine ratios on the mechanical properties of the cross-linked polymers, the highest flexural strength value of 950 psi was obtained using the EPO/PACM molar ratio of 0.53:1. The EPO was also studied for its potentials in blending with several other epoxy resins for the improvements of properties. A two-step blending method using EPO and diglydigyl ether of bisphenol A (DGEBA) was discovered, which gave the greatest improvement in increasing the flexural strength to 6,100 psi. This result was more than a 6 fold increase as compared to the pure EPO cured with the same amine. The epoxy-amine reaction mechanisms between the EPO and the amine were identified to be different from the reaction between the DGEBA and the amine. The EPO gave little reactivity with secondary amine. Based on the investigated resin formulations, a series of structural composites were prepared using the EPO as the main matrix and glass fiber as the reinforcing agent. The EPO composite was characterized to possess the same stiffness and 60% to 80% of the strength value as compared to the DGEBA based composites.