Dielectric Study of the Time-Temperature-Transformation (TTT) Diagram of DGEBA Epoxy Resins Cured with DDS (Diaminodiphenylsulfone).

摘要

Microdielectrometry and differential scanning calorimetry have been used to study the isothermal cure of EPON 825 with diaminodiphenylsulfone (DDS). The results are compared with published torsional braid analysis (TBA) studies of the same system using a time-temperature-transformation diagram. The dielectric measurements were made at temperatures between 100 and 220 C using measurement frequencies between 0.1 Hz and 10,000 Hz. The DSC was operated in an isothermal mode to determine extent of conversion at temperatures between 137 and 177 C. Two mechanics of charge transport are responsible for the observed dielectric response; an ionic conductivity early in cure that decreases as the reaction proceeds, and a Debye-type dipole relaxation later in cure. The time to reach 60% conversion determined by DSC correlates with the TBA gelation loss peak, as would be expected from the Flory theory of gelation, but there is no clear dielectric event at 60% conversion. The peak in dielectric loss factor identified with the dipole relaxation correlates with the TBA vitrification loss peak. (Author)