Dilute solution properties of cellulose diacetate in mixed solvents

Abstract

In this paper the dilute solution properties of cellulose diacetate (CDA) in single solvents (acetone (A), N,N-dimethylformamide (DMF)) and in mixed solvents (acetone with DMF, N-methyl formamide (NMF) and formamide (F), respectively) were investigated by the low-angle laser light scattering method, as well as by the dilute solution viscometry method. The main experimental results comprised apparent weight average molar mass values, M2∗ and limiting viscosity number values, [η]H. The results were interpreted in terms of specific interactions of solution components. Basic solvents (acetone and DMF) primarily solvate hydroxyl groups of CDA and both the intensity and the direction of preferential solvation are determined by the preferred heteroassociation of solvent molecules (dipole interactions). Acidic solvents (formamide, NMF) primarily solvate acetyl groups of CDA. In this case the preferential solvation behaviour is determined by the autoassociation properties of acidic solvents (H-bonding). The autoassociaton of acidic solvent molecules is responsible for the intramolecular and intermolecular bridging of CDA-molecules as well. This phenomenon gives rise to the structuring of more concentrated CDA-solutions, which is of key importance when technical CDA-membranes are to be prepared. Within the framework of this paper it is proved that preliminary studies of the structuring of CDA-solutions may be performed in dilute solutions. On the basis of preliminary studies a suitable range of solvent compositions may be chosen and necessary but rather complex investigations in mid-concentration range may then be performed only in that, quite restricted composition range.