Controlling the morphology in epoxy/thermoplastic systems

Thermosets are frequently toughened by a high-Tg thermoplastic (TP). Blend morphologies obtained by curing induced phase separation with scales of a few hundreds of nanometers are relevant for high-performance applications, but no quantitative description for obtaining these morphologies exists yet. We propose such a quantitative approach for predicting and controlling the final morphology. The key is the degree of curing and the corresponding Tg of the blend and both phases when phase separation takes place. It is controlled by the Flory interaction parameter χ of the constituents and their respective Tg’s. We show that if phase separation takes place too early during curing, the Tg is too low and the morphologies grow to reach sizes of a few micrometers or more. Our study of different systems allows us to propose the relevant range of Flory interaction parameter χ and temperature window T–Tg for which the sizes of interest may be obtained. Our work opens the way for devising thermoplastics–thermosets couples with the appropriate affinity and Tg’s in order to make blends with tailored morphologies.