A Fourier transform infra-red spectroscopic analysis of the character of hydrogen bonds in amorphous cellulose

Hydrogen-bonding formation in amorphous cellulose was characterized by the analysis of Fourier transform infra-red (FT i.r.) spectra. Films of regioselectively substituted methylcelluloses were used to model components of amorphous cellulose. An artificial infra-red (i.r.) spectrum for amorphous cellulose was quantitatively synthesized by a suitable mathematical combination of the i.r. spectra obtained for the methylcellulose model compounds. A comparison between the i.r. spectrum for an amorphous film blend composed of 2,3-di-O- and 6-O-methylcelluloses and the artificial spectrum showed an almost complete overlap in the OH frequency region, indicating that after mixing there is no interaction between the OH groups of each component in the film blend. In other words, the OH bands in the artificial spectrum were considered to be simply a sum of hydrogen-bond absorptions contributed by each individual spectrum. The artificial spectrum was then compared to an experimental spectrum for an amorphous cellulose sample. The difference between the two spectra (real-artificial) was then analysed and interpreted by using results from a previous i.r. study on hydrogen bonding in alcohols and our own assumptions about the probable hydrogen bonds formed in amorphous cellulose. These analyses revealed that while the hydroxyl groups at the C(2) and C(3) positions in a glucose repeating unit are isotropically involved in intermolecular hydrogen bonding in amorphous cellulose, the hydroxyl group at the C(6) position is favourably engaged in an interchain hydrogen bonding that results in the formation of a crystalline state. Thus we conclude that amorphous cellulose might be composed, at least to some extent, by randomly distributed domains formed by intermolecular hydrogen bonds.