Phase-inversion investigations of rubber-modified epoxies by electron microscopy and X-ray diffraction

Abstract

The phase-inversion phenomena of diglycidyl ether of bisphenol A (DGEBA) incorporated with a carboxy-terminated butadiene-acrylonitrile (CTBN) containing 17 wt% bound acrylonitrile after curing with ethylene diamine (EDA) in a stoichiometric ratio were investigated by scanning and transmission electron microscopy (SEM and TEM), and wide-angle X-ray scattering (WAXS). The results of the SEM studies revealed that the rubber-rich phases in a size range of 1–30 Μm, which originally dispersed in an epoxy-rich matrix, gradually transformed to a co-continuous phase as the CTBN content reached 30 phr. As the CTBN content was increased to 50 phr, that phase inversion, as the continuous epoxy-rich phase transformed to a dispersed phase, took place. However, because the transformed dispersed phase was very small, the phase inversion could only be observed by TEM in specimens stained by osmium tetraoxide (OsO₄). On the other hand, we also found that the phase inversion could be detected by WAXS, and this showed the absence of a characterization peak of the epoxy resin at the scattering vector,Q=4.1 nm⁻¹. To the best of our knowledge, this was the first time in the literature that WAXS has been employed to detect a phase inversion.