Dilute solution properties of cellulose diacetate in mixed solvents

In this paper the dilute solution properties of cellulose diacetate (CDA) i n single solvents (acetone (A), N,N-dimethylformamide (DMF)) and in mixed s olvents (acetone with DMF, N-methyl formamide (NMF) and formamide (F), resp ectively) 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, (M) over bar( 2)(*) and limiting viscosity number values, [eta](H). The results were inte rpreted in terms of specific interactions of solution components. Basic sol vents (acetone and DMF) primarily solvate hydroxyl groups of CDA and both t he 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. I n this case the preferential solvation behaviour is determined by the autoa ssociation properties of acidic solvents (H-bonding). The autoassociaton of acidic solvent molecules is responsible for the intramolecular and intermo lecular bridging of CDA-molecules as well. This phenomenon gives rise to th e structuring of more concentrated CDA-solutions, which is of key importanc e 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 necessa ry but rather complex investigations in mid-concentration range may then be performed only in that, quite restricted composition range. (C) 2000 Elsev ier Science B.V. All rights reserved.