NIR FT Raman Spectroscopy–a Rapid Analytical Tool for Detecting the Transformation of Cellulose Polymorphs

Abstract

This is a report of the combined use of NIR FT Raman spectroscopy and X-ray diffraction measurements (WAXS) to investigate the polymorphic transformation of cellulose I into cellulose II. For this reason samples of cellulose I were swelled in different concentrations of NaOH and dissolved in different molten inorganic salts hydrates (LiCl·2ZnCl2·6H2O, LiClO4·3H2O, LiSCN·2,5H2O and ZnCl2·4H2O). NIR FT Raman spectra of the alkali treated samples were recorded. They characterize the pure modifications cellulose I and II as well as mixtures of the two polymorphic phases. The results of the Raman measurements were confirmed by X-ray scattering. The paper demonstrates that FT Raman vibrational spectroscopy is a powerful, rapid analytical method which may be used to follow the polymorphic transformation of cellulose I into cellulose II.