TSDC studies of the effects of plasticizer and water on the sub-T-g relaxations of an epoxy resin system

摘要

The sub-glass-transition-temperature (sub-T-g) relaxations of an epoxy resin system based on diglycidyl ether of bisphenol-A (DGEBA) and cured with triethylenetetramine (TETA) were investigated by means of the thermally stimulated depolarization current (TSDC) technique in the temperature 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 effect on the aforementioned relaxations of a plasticizer chemically connected to the epoxy resin network was investigated. The amount of plasticizer (commercial name THIOCOL LP3) was varied between 0% and 60% by 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 sampling technique. Physical aging strongly influenced the TSDC thermogram of the omega relaxation, indicating phase separation during the aging procedure. Water effects were systematically investigated from dry samples to water-saturated samples (water content, 2.5%). In all specimens, water induced plasticization, which is expressed by the shifting of the beta relaxation toward lower temperatures. The mode of water absorption (immersion in water or exposure to humid environment) also influenced the evolution of the omega relaxation.