A Technique for the Characterization of Sorption States in Water—Cellulose Systems by Wide Line NMR

A technique is described by which the protons in water–cellulose sorption systems may be assigned to four categories. The protons are quantitatively divided into water- and cellulose-associated protons and these categories are further subdivided into interchanging and non-interchanging species. The relationships are derived on the assumption that the line narrowing observed in the NMR spectrum of celluloses on the addition of moisture is due to the rapid interchange of some of the water and cellulose protons (or their spins). The experiments were carried out at water–cellulose concentrations of about 7% on a variety of cellulose samples differing in supramolecular structure as characterized by crystalline fraction and lattice type. Data are presented which indicate that the larger the proportion of water protons involved in the interchange process, the larger the spin–spin relaxation time of those water protons not involved in the interchange. It is concluded that linewidth of the narrow component of the water–cellulose NMR signal is not related to sorption processes as simply as previously suggested.