Molar Mass Characterization of Crude Lignosulfonates by Asymmetric Flow Field-Flow Fractionation

Lignosulfonates (LSs) are the main components of the byproduct of sulfite pulping processes accumulated in large quantities of hundreds of kilotons per year. Furthermore, they are currently the most widely utilized form of lignin due to their chemical and physical properties. LS molar mass characteristics determine their functional properties; however, there is a lack of fast and precise methods for LS molar mass analysis. The complex LS structure after pulping as well as the presence of considerable amounts of impurities in the raw sulfite spent liquor require tedious and time-consuming sample purification steps if conventional size exclusion chromatography (SEC) is to be used for analysis. Asymmetric flow field-flow fractionation (AsFlFFF) represents a good alternative to the conventional SEC technique, as the absence of a stationary phase allows purification and molar mass analysis of nonpurified industrial black liquors in one step, resulting in a drastically simplified procedure. The method's applicability was tested with various industrial lignin samples. The results demonstrated that the AsFlFFF approach in combination with multiangle laser light scattering (MALLS) detection is an efficient tool for rapid screening of the molar mass of technical LS. The essential parameters of the AsFlFFF/MALLS approach are presented in this paper. For chromatographic setups that do not have MALLS detection available, a calibration approach is provided.