The swelling of microcrystalline cellulose by the use of polar protic solvents such as ethanol or methanol enables the penetration of benzophenone into submicroscopic pores of the natural polymer, while solvents such as benzene or dichloromethane do not open the polymer chains, thus not producing any entrapped benzophenone. Ground-state diffuse reflectance studies revealed a dramatic blue shift in the 350-nm absorption of benzophenone in the former case, in accordance with a strong interaction of the hydroxyl groups of cellulose with the ketone. Diffuse reflectance laser flash photolysis studies of benzophenone adsorbed on microcrystalline cellulose showed, in cases where benzophenone is entrapped in the polymer chain, the formation of a transient which decays nonexponentially and exhibits a maximum absorption at about 530 nm, assigned to triplet benzophenone. After ca. 25 ps, this transient generates another species with an absorption maximum at 545 nm. We assigned this new species to the diphenylketyl radical. In all cases where the solvent does not swell cellulose, a different behavior was observed typical for benzophenone microcrystals triplet decay. The ketyl radical formation is greatly reduced in this case. Triplet benzophenone decays by complex kinetics and lives about 10 ps when adsorbed onto microcrystalline cellulose, while the ketyl radical, when formed, lives 1 order of magnitude longer than the triplet. Samples which exhibit a high yield of ketyl radical formation also have a smaller phosphorescence emission in accordance with the fact that large amount of triplet molecules were consumed in the process of hydrogen abstraction from the matrix, involving hydrogens linked to carbons bearing a hydroxyl group.

Unpolished specimens with a more developed surface have lower color stability. Specimens stored in water develop some changes in their visual appearance. The presently proposed methods are effective in evaluating the luminescence of dental materials. Luminescence needs to be tested in addition to color, as the two characteristics are uncorrelated. It is important to further improve the color and luminescence stability of dental materials.

The structures of different celluloses (microcrystalline and native) were characterized by diffuse reflectance infrared spectroscopy (DRIFT), analyzing the bands due to O−H stretching, C−O stretching, and C−H bending modes. The respective crystallinities were determined as 73 ± 2% and 40 ± 2%, and the crystalline structure in both was characterized as type Iβ. 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 stretching 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 adsorbed at the cellulose surface. By deconvolution of spectra and subsequent analysis of the main components' relative intensities, it has been possible to calculate the approximate amounts of entrapped molecules per gram of cellulose as a function of total benzophenone concentration. These results show that, for low benzophenone concentrations, adsorption occurs preferentially in crystalline domains of cellulose, independently from its crystallinity. On the contrary, as concentration is increased, crystallinity has a determinant role on the total amount of adsorbed benzophenone and on its molecular distribution in the different domains of cellulose.

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