The influence of water on the intercalation of epoxy monomers in Na-montmorillonite

The intercalation of a typical UV-curable epoxy monomer (CE) in unmodified montmorillonite and the effect of hydration on the intercalation reaction are studied. Montmorillonite in the sodium form was submitted to a controlled hydration/dehydration cycle and the water content was checked by TGA/XRD analyses. The structure of the hydrated Na+-montmorillonite was determined from the values of the basal spacings and from the water content of the hydrated form: a coordination of four water molecules per Na ion was found, corresponding to a minimum of energy calculated by molecular dynamics simulation. When dispersing the clay in the CE monomer, the anhydrous Na+-montmorillonite did not show any intercalation; on the contrary the hydrated form showed an increase of the basal spacing. A possible mechanism to explain the intercalation of the CE monomers is proposed.

Graphical abstractXRD spectra of sodium montmorillonite dispersions in an epoxy monomer (5% w/w): when the clay is anhydrous (d-spacing = 9.6 Å), no intercalation occurs (blue curve); the hydrated form of the montmorillonite (d-spacing = 12.1 Å) shows an increase in basal spacing from 12.1 to 14.7 Å (the wide halo derives from the amorphous scattering of the liquid monomer).Figure optionsDownload full-size imageDownload as PowerPoint slide