Acceleration of epoxy resin curing by using a combination of aliphatic and aromatic amines

Curing of epoxy resins with aromatic amines, which provides an excellent combination of physical and mechanical properties, requires high temperatures. In this research, the amidoamine adduct of tall oil with triethylenetetramine have been used for acceleration of the reaction of the aromatic amine (diaminodiphenyl sulfone, DDS) with the diglycidyl ether of bisphenol A (DGEBA) epoxy resin. The kinetics of the curing reaction of DGEBA with a mixture of two hardeners was investigated by the non-isothermal DSC method. It was shown that the activation energy of curing decreased from similar to 68 to similar to 59 kJ/mole at amidoamine introduction. Nevertheless, there were no new bands in the IR-spectra of the cured epoxy resins. The acceleration of the curing reaction of the aromatic amine was apparently due to the autocatalytic action of the hydroxyl groups formed by the reaction of the epoxy resin with the amidoamine. Besides acceleration of curing, use of the hardener mixture significantly increased the rubbery-plateau modulus, while not influencing on the value of the elasticity modulus of the cured resin in the glassy state. A disadvantage of using amidoamine for accelerating the curing was lowering of the glass transition temperature of the cured polymer.