Development of bicontinuous morphologies in polysulfone-epoxy blends

The development of bicontinuous morphologies in 10 wt% polysulfone (PSu)-ep oxy (DGEBA)/anhydride (MTHPA) blends, was followed by optical and scanning electron microscopy. Blends cured at 80 degrees C revealed the formation of large epoxy-rich domains surrounded by a PSu-rich matrix, soon after the c loud point. Advancing the cure led to an increase in the volume fraction an d the coalescence of epoxy-rich domains. A bicontinuous primary morpholcgy was thus generated. A secondary phase separation was observed in both prima ry phases from the very beginning of the phase-separation process. While sp inodal demixing was clearly the mechanism by which the primary morphology w as generated, nucleation-growth could be responsible of the secondary phase separation. Postcure steps produced a change in the composition of phases as revealed by DMA, and in the secondary morphology as observed by SEM. A p ostcure at 120 degrees C led to a single T-g at 115 degrees C with a small shoulder at higher temperatures. A postcure at 200 degrees C led to a T-g a t 108 degrees C for the epoxy-rich phase and a T-g at 137 degrees C for the PSu-rich phase. The partial purification of the thermoplastic phase produc ed a significant enhancement of toughness. K-IC was increased from 0.65 MPa m(1/2) for the neat thermoset to 1.10 MPa m(1/2) for the blend postcured a t 200 degrees C. (C) 1999 Elsevier Science Ltd. All rights reserved.