(Dr. Jonathan Colton, advisor)
"Effects Of Processing and Of Environmental Conditions on the Properties of Epoxy Materials"
The first part of this study investigates the effects of microwave and thermal curing on the aging of epoxies. Neat epoxy samples were cured by microwave and by conventional thermal processing. Cured samples were aged in a ventilated oven at 150°C. Mechanical properties show a significant drop between the first and the second day of aging for both kinds of samples. The reason for that is the occurrence of products of oxidation on the surface of the material. Due to the uneveness of the cooling in curing processes, some evidence of physical aging on both kinds of samples has been also observed.
In the second part of this study, three state-of-the-art, epoxy-based materials, representative of materials used for rapid tooling applications, were selected to investigate their aging behavior under different storage environments. Four different conditions, each one characterized by a specific relative humidity, were used to perform a 7-week-long aging study. Temperature was kept constant at 30°C for all conditions. The main trend observed here was a drop in mechanical properties and in the glass transition temperatures in wet environments, whereas aging time showed no influence on these properties. Moisture intake is assumed to be mainly responsible for that behavior and coefficients of diffusion were determined in order to confirm this assumption. A simple empirical model has been elaborated in order to predict the mechanical behavior observed here.