TSDC studies of the effects of plasticizer and water on the sub-T g relaxations of an epoxy resin system |
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Authors: | C. Maggana P. Pissis |
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Affiliation: | 1. National Technical University of Athens, Department of Theoretical and Applied Mechanics Zografou Campus GR , 15773, Athens, Greece;2. National Technical University of Athens, Department of Physics Zografou Campus, GR , 15713, Athens, Greece |
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Abstract: | 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 γ relaxation at about 150 K, the β relaxation at 160 K to 200 K and the ω 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 β relaxation reflects the heterogeneous structure of the material. The activation energies of the γ and β relaxations were calculated using the thermal sampling technique. Physical aging strongly influenced the TSDC thermogram of the ω 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 β relaxation toward lower temperatures. The mode of water absorption (immersion in water or exposure to humid environment) also influenced the evolution of the ω relaxation. |
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