Effects of promoter and curing process on exfoliation behavior of epoxy/clay nanocomposites

The effects of a catalyst and coupling agent as well as a curing process on exfoliation behavior of CH₃(CH₂)₁₅NH₃+-montmorillonite clay in an anhydride-cured epoxy-clay system have been investigated by XRD, DSC, and TEM. The results have shown that the organoclay is easily intercalated by the epoxy precursor during the mixing process, and the clay galleries continue to expand during the curing process, but the Na⁺-montmorillonite clay is not intercalated during either the mixing or the curing process. The results also suggest that in the cured system without any promoter although partial exfoliated clay layers have already formed, an amount of the intercalation structure still remains. Although addition of a promoter or coupling agent into the cured system significantly lowers the maximum reaction temperature, and during the curing process the layered organoclay can be gradually broken into nanoscale structures, in which no d₀₀₁ diffraction peaks are observed, the complete exfoliation is achieved at gel time or before. The possible mechanism for the complete exfoliation is discussed on the thermodynamic and kinetic point of view.