TTT diagram and phase structure control of 2/4 functional epoxy blends used in advanced composites

Abstract

A 2/4 functional epoxy blend system (DGEBA/TGMDA) cured with 4,4′-diamino diphenyl sulphone (DDS) was used as the raw material in this research. Round disk compression mode DMA (dynamic mechanical analyzer) was employed to study the gelation at the different temperatures, and the relationship between gel-time (tgel) and temperature was obtained. The cure kinetics was studied by dynamic DSC (differential scanning calorimetry) analysis, and the parameters of the cure reaction were obtained to establish a phenomenological model. The relationship between glass transition temperature (Tg) and cure degree (α) was analyzed by an isothermal plus dynamic DSC method based on the DiBenedetto equation, which gave a mathematical description of Tg as a function of both time and temperature. Characteristic temperatures such as Tg0, gelTg and Tg∞ were also determined. The cure degree at gelation turned out to be 0.4539, while the temperature at which vitrification line and gel line transected was found to be 70.2°C. The time-temperature-transition (TTT) diagram was plotted based on the work above, which served as a tool for process optimization in the manufacture of advanced composites. A new cure procedure of this practical thermosetting system was extracted from the TTT diagram by prolonging the pre-gel time to restrict the diffusion ability and the flow ability of the solution. The final phase structure was proved by SEM to be ex-situ phase morphology compared with the traditional in-situ phase structure by exerting different cure procedures.