TSDC STUDIES OF THE EFFECTS OF PLASTICIZER AND WATER ON THE SUB-T-G RELAXATIONS OF AN EPOXY-RESIN SYSTEM

The sub-glass-transition-temperature (sub-T-g) relaxations of an epoxy resin system based on diglycidyl ether of bisphenol-A (DGEBA) and cur ed with triethylenetetramine (TETA) were investigated by means of the thermally stimulated depolarization current (TSDC) technique in the te mperature range 77 K to 300 K. Three relaxation regions were observed: the gamma relaxation at about 150 K, the beta relaxation at 160 K to 200 K and the omega relaxation at 240 K to 270 K. The plasticization e ffect on the aforementioned relaxations of a plasticizer chemically co nnected to the epoxy resin network was investigated. The amount of pla sticizer (commercial name THIOCOL LP3) was varied between 0% and 60% b y weight of the epoxy. The broad range of the beta relaxation reflects the heterogeneous structure of the material. The activation energies of the gamma and beta relaxations were calculated using the thermal sa mpling technique. Physical aging strongly influenced the TSDC thermogr am of the omega relaxation, indicating phase separation during the agi ng procedure. Water effects were systematically investigated from dry samples to water-saturated samples (water content, 2.5%). In all speci mens, water induced plasticization, which is expressed by the shifting of the beta relaxation toward lower temperatures. The mode of water a bsorption (immersion in water or exposure to humid environment) also i nfluenced the evolution of the omega relaxation.