Improving molar mass analysis of cellulose samples with limited solubility

Abstract

Fully dissolved cellulose samples are a requirement for reliable size exclusion chromatography (SEC). Although most of the standard dissolving pulps can be completely dissolved in the N,N-dimethylacetamide/lithium chloride (DMAc/LiCl) solvent system, some cellulose samples (e.g., regenerated cellulose fibers) have poor solubility and therefore have a limited access to molar mass measurements. For improving the latter, different activation steps have been developed.In order to obtain complete solutions for subsequent SEC analysis, the scope of this study was to further improve established methods by elucidating the major influential factors of sample preparation. In addition, the degree of stretching in artificial fibers was examined for viscose fibers. Therefore, activation steps in DMAc or dimethyl sulfoxide (DMSO) and subsequent dissolution in DMAc/LiCl were analyzed with swelling and dissolution kinetics. The time needed for maximum swelling was found to be the optimum activation time. Turbidity measurement was introduced to observe dissolution kinetics as an indicator of dissolution quality. Thus, the duration, as well as the number of steps toward dissolution, was optimized to enhance the throughput in the overall analysis of a large variety of hitherto poorly soluble cellulose samples. A comparison of the MMDs of completely soluble reference materials obtained with the intensified conventional method, and the developed method demonstrated that the latter has no adverse influence on the results.