For the cure process of a thermoset/thermoplastic blend, tetrafunctional epoxy resin/poly(ether sulfone)/dicyandiamide (100/25/5), we established a new time-temperature-transformation (TTT) cure diagram. The transformation here involves (1) onset of phase separation, (2) gelation, (3) fixation of the dimension of phase-separated structure, (4) end of phase separation and (5) vitrification. The onset and end of phase separation were characterized by the time variation of the invariant of light scattering (V 0 and the spatial fixation of phase-separated structure was by levelling off the decrease of scattering peak angle. The gelation and vitrification points were determined conventionally by rheological measurements, i.e. by a cross-over of dynamic storage modulus and dynamic loss modulus curves, and by torsional braid analysis curve, respectively. The epoxy/poly(ether sulfone) mixture was shown to exhibit lower critical solution temperature (LCST)-type phase behaviour (LCST= 265°C). In the early stage of curing, the ternary system was at a single-phase regime. After an induction period, phase separation started by the spinodal decomposition mode, then the domain spacing increased with time, i.e. the structure grew self-similarly. When the system was gelled, the spacing simultaneously ceased to increase. Even after that, the invariant still continued to increase, implying further growth in concentration fluctuation. The invariant then levelled off and finally the whole system was vitrified by the increase in glass transition temperature of the epoxy-rich phase. This situation was described in terms of the new TTT cure diagram in wide ranges of cure temperature (130-250°C) and cure time (6 h).
Посилання на статтю:
A new time-temperature-transformation cure diagram for thermoset/thermoplastic blend: tetrafunctional epoxy/poly(ether sulfone) / Bong Sup Kim, Tsuneo Chiba and Takashi Inoue // Polymer. – 1993. – Vol 34. – P. 2809-2815.