Recent advances in molecuar and supermolecuar characterization of cellulose and cellulose derivatives

Recent advances between 1985 and early 1993 in the following topics of the characterization of molecular structure and molecular properties of cellulose and its derivates (CD) made in the authors' laboratories are briefly reviewed: (1) A theoretical basis of the assignment of carbonyl carbon peaks of ¹³C NMR spectra on cellulose acetate (CA) was given, especially when the total degree of substitution <> is below 3. (2) Molar fractions of 8 kinds of unsubstituted and partially or fully substituted anhydroglucopyranose units were successfully determined for CA and sodium cellulose sulfate (NaCS). (3) The sequence distribution of substituted and unsubstituted anhydroglucopyranose units along a water–soluble CA chain was evaluated. (4) C₆-substituted (i.e., 6-O-acetyl) CA and C₂- and C₆-substituted CA were synthesized, and the full assignment of the ¹³C NMR spetrum of the former was given and a new method for evaluating the degree of substitution at C₆ position was proposed. (5) By destructing the intramolecular hydrogen bonding, cellulose becomes soluble in aq. sodium hydroxide. The specific supermolecular structure of aq. sodium hydroxide, dissolving mechanism, dissolved state and molecular parameters of cellulose in aq. sodium hydroxide were discussed. (6) The solubility behavior of CA with a wide range of total degree of substitution in solvents including water, acetone/water and acetone is controlled by the distribution of substitution and the supermolecular structure. (7) The existence of O₃-H … O'₅ intramolecular hydrogen bonds in a water-in soluble cellulose derivative with hydrophilic substituent (NaCEC) was confirmed by CP/MAS ¹³C NMR and deuteration IR method. At a relatively low degree of substitution the solubility of the derivative in water or aqueous alkali was mainly governed by considerable destruction of the intramolecular hydrogen bonds. (8) The persistence length q, evaluated directly by small-angle X-ray scattering (SAXS) on CA with different total degree of substitution <> ranging from 0,8 to 2,9 confirmed definitely the conclusion drawn before by Kamide and Saito on the molecular rigidity of CD, especially the effect of <> on q. (9) C₆-substituted CA shows different solubility towards dimethylacetamide and water at 20°C, as compared with C₂- and C₃-subsituted CA and C₂-, C₃- and C₆- substituted CA, whose <> is ca. 0,6.