Enhancing Molar Mass Distributions of Lignosulfonates with Chemometry-Assisted Functional Group Profiling

Technical lignins are a coproduct of the pulp and paper industry in large quantities. Depending on the botanical origin, the pulping process, and the isolation protocol, their molar mass and content of functional groups vary. Moreover, the content of the functional groups differs among fractions of different molar masses. Functionalities significantly influence the properties of a lignin sample and, thus, its suitability for material applications. In this study, we present a new method for the fast quantification of different functional groups present in lignosulfonates across their molar mass distribution. By creation of a range of partial least squares regression (PLSR) models, based on a large FTIR spectral database and reference data obtained from conventional methods, it was possible to predict the content of several types of functional groups in the fractions of lignosulfonates with sufficient accuracy. The developed prediction models had coefficients of determination of up to 94%. Lignosulfonate fractions were obtained by aqueous size-exclusion chromatography (SEC). Utilizing the established PLSR models, molar mass-dependent profiles of functional groups were made available within short analysis times in offline mode. This rapid, robust, and affordable method is expected to become a routine analysis tool in industry for process and quality control, potentially advancing the value-added utilization of technical lignins.