Mechanical behavior of tetrafunctional/phenol novolac epoxy mixtures cured with a diamine

An amine-cured epoxy system based on tetraglycidyldiaminodiphenyl-methane and a novolac glycidyl ether resin was studied. Epoxies were prepared by varying the cure schedules and using the isothermal time-temperature-transformation diagram of the system. The materials were characterized using dynamic-mechanical analysis (DMA), tensile stress-strain tests over a range of temperatures and testing speeds, impact, and hardness tests. Optical microscopy was used to study the fracture surfaces of the samples. Some interrelations between the behavior and the microstructure of the system are discussed. In addition, the effect of thermal aging on the mechanical properties has been studied. DMA analysis seemed to reveal a structure that tended to be less heterogeneous with increasing the crosslink density. The advance in the etherification reactions or the thermal aging has reduced the mechanical properties related with the consumption of energy to break. The optimal cure schedule according to the global properties has been established. The morphology of fractured surfaces by optical microscopy showed a clear correlation with the variation of the tensile properties.