Determination of intrinsic viscosity-molecular weight relationship for cellulose in BmimAc/DMSO solutions

For simply and accurately determining molecular weight of cellulose, an ionic liquid mixed with a co-solvent, 1-butyl-3-methylimidazolium acetate/dimethyl sulfoxide (BmimAc/DMSO) (1:1, w/w) was used and dissolved cellulose well at ambient temperature. During the dissolution process no degradation of cellulose was observed, and all the resultant cellulose/BmimAc/DMSO solutions were transparent and stable. These advantages make it as an ideal solvent system to build a new characteristic method of cellulose's molecular weight by the measurement of the intrinsic viscosity [eta], which is significantly better than the currently used solvent systems. [eta] of solutions of nine cellulose samples was measured by using rheometer with cylinder fixture and Ubbelohde viscometer, respectively. The [eta] values obtained by these two methods were well consistent. The degree of polymerization (DP) of these cellulose samples was determined by Copper (II) ethylenediamine method. Then the molecular weight and its distribution of representative samples were cross-checked by gel permeation chromatography for soluble derivatives of cellulose. As a result, a relationship DP = 134 [eta](1.2) was built, suitable for DPs in the range of 220-1400. The uncertainty of this relationship was estimated to be 5 %. This work provided a simple, accurate and reliable method for determining [eta] and the molecular weight of cellulose.