A NEW TIME-TEMPERATURE TRANSFORMATION CURE DIAGRAM FOR THERMOSET THERMOPLASTIC BLEND - TETRAFUNCTIONAL EPOXY POLY(ETHER SULFONE)

For the cure process of a thermoset/thermoplastic blend, tetrafunction al epoxy resin/poly(ether sulfone)/dicyandiamide (100/25/5), we establ ished a new time-temperature-transformation (TTT) cure diagram. The tr ansformation 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 o f light scattering (V(v)) 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 b y rheological measurements, i.e. by a cross-over of dynamic storage mo dulus 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 behav iour (LCST = 265-degrees-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 domai n spacing increased with time, i.e. the structure grew self-similarly. When the system was gelled, the spacing simultaneously ceased to incr ease. Even after that, the invariant still continued to increase, impl ying further growth in concentration fluctuation. The invariant then l evelled off and finally the whole system was vitrified by the increase in glass transition temperature of the epoxy-rich phase. This situati on was described in terms of the new TTT cure diagram in wide ranges o f cure temperature (130-250-degrees-C) and cure time (6 h).