CP/MAS Carbon-13 NMR Study of Spin Relaxation Phenomena of Cellulose Containing Crystalline and Noncrystalline Components

Abstract

Cross-polarization, 13C rotating frame spin-lattice relaxation and 13C laboratory frame spin-lattice relaxation processes were studied for different cellulose samples by CP/MAS 13C NMR spectroscopy. The CP process apparently can be described by a simple thermodynamic model and relative intensities of the respective resonance lines are consistent with the atomic ratios for the spectra obtained at a contact time of .apprx. 1 ms. The observed rotating frame spin-lattice relaxation times .**GRAPHIC**. were dominately dependent of the time constant .**GRAPHIC**. by which 13C nuclei were coupled to the 1H dipolar spin system. It was, therefore, impossible to obtain information about molecular motion of cellulose from .**GRAPHIC**. On the other hand, spin-lattice relaxation times .**GRAPHIC**. in the laboratory frame were found to be useful for the characterization of the structure of the crystalline and noncrystalline components of cellulose. The resonance lines assignable to the respective components were selectively recorded by use of the difference in .**GRAPHIC**.