INFRARED APPROACH TO THE STUDY OF ADSORPTION ON CELLULOSE - INFLUENCEOF CELLULOSE CRYSTALLINITY ON THE ADSORPTION OF BENZOPHENONE

The structures of different celluloses (microcrystalline and native) w ere characterized by diffuse reflectance infrared spectroscopy (DRIFT) , analyzing the bands due to O-H stretching, C-O stretching, and C-H b ending modes. The respective crystallinities were determined as 73 +/- 2% and 40 +/- 2%, and the crystalline structure in both was character ized as type I beta. A comparative study of adsorption of an aromatic ketone, benzophenone, on these two substrates was made, using the same technique. Through the modifications observed in the carbonyl stretch ing band of benzophenone, it was possible to distinguish adsorption in three different environments: entrapped between the glycosidic chains in crystalline domains, in amorphous domains, and as crystallites ads orbed at the cellulose surface. By deconvolution of spectra and subseq uent analysis of the main components' relative intensities, it has bee n possible to calculate the approximate amounts of entrapped molecules per gram of cellulose as a function of total benzophenone concentrati on. These results show that, for low benzophenone concentrations, adso rption occurs preferentially in crystalline domains of cellulose, inde pendently from its crystallinity. On the contrary, as concentration is increased, crystallinity has a determinant role on the total amount o f adsorbed benzophenone and on its molecular distribution in the diffe rent domains of cellulose.