Infrared spectroscopic evidence of a direct addition reaction between palygorskite and pyromellitic dianhydride

Palygorskite covalently grafted with pyromellitic dianhydride was investigated. Untreated and grafted samples were characterized by X-ray diffraction, thermogravimetry, and Fourier transform infrared spectroscopy. Infrared results showed the direct grafting of anhydride onto the bound water molecules on the external surfaces of the palygorskite. The grafting modification makes palygorskite more readily compatible with anhydride, resulting in substantial enhancements in the glass transition temperature and flexural strength of the anhydride-cured epoxy resin/palygorskite nanocomposites.