Preparation of drug-montmorillonite UV-radiation protection compounds by gas-solid adsorption

Ethyl cinnamate/montmorillonite intercalation complexes were obtained by gaseous adsorption of the drug on the clay surface. They were characterized by powder X-ray diffraction, differential thermal and thermogravimetric analyses and by visible-UV and IR spectroscopies. It was found that after 1 day of adsorption, most of the drug enters the interlayer space of the clay by substitution of water molecules, and is removed only after heating at high temperature. In addition, a portion is physisorbed on the external surface of the crystallites, being removed easily below 100degreesC. The interlayer complex improves the protecting ability of the pure clay or the pure drug against ultraviolet radiation, specially in the so-called 'C' range (290-190 nm).