Cellulose and cellulose derivatives: Recent advances in physical chemistry

Abstract

This article reviews a recent progress on the physical chemistry of cellulose and cellulose derivatives (CD) and their applications to some industrial fields. Average degree of substitution for each hydroxyl groups attached to carbon 2, 3, and 6 in a pyranose ring «f k » (k=2, 3, 6) could be estimated by 1H-and 13C-NMR methods and distribution of total degree of substitution of some CD was evaluated by thin-layer chromatography. «f k » correlated closely with the anticoagulant activity of sodium cellulose sulfate and also with the absorbency against aqueous liquid of sodium carboxymethyl cellulose. Successive solution fractionation method afforded us to prepare CD samples with relatively narrow molecular weight distribution. Light scattering measurements on the gel-free CD solutions were carried out and the number-average molecular weight of cellulose acetate (CA) was determined by membrane and vapor pressure osmometry and gel-permiation chromatography. Lower and upper critical solution temperatures were determined for CA-solvent systems. The pore forming mechanism in the CA-solvent casting process was discribed relating to critical phenomena. The solvation was verified by the chemical shift in NMR spectra and by the adiabatic compressibility. The significant contribution of the draining effect on the hydrodynamic properties was experimentally confirmed. The excluded volume effect in CA solutions was very small. The rigidity of CD molecules in the unperturbed state was estimated by various methods based on the pearl necklace and wormlike chain models. The unperturbed chain dimension of CA molecules in the solutions was decided by the polarity of the solvent and the total degree of substitution. Cellulose dissolved in a hypotherical non-polar solvent behaves as almost a freely rotating chain and the low degree of flexibility of the cellulose chain deduced from the physical properties of cellulose solution and solid, is caused by the solvation or intra-or inter-molecular hydrogen bond. The solubility of cellulose in the aqueous alkali solution was discussed.