Mapping of the Hydrophobic Composition of Lignosulfonates

Oliver Musl,Ivan Sumerskii,Irina Sulaeva,Jana Falkenhagen,Thomas Rosenau,Antje Potthast,Arnulf Kai Mahler

doi:10.1021/acssuschemeng.1c06469

Abstract

Lignosulfonates are industrial biorefinery products that are characterized by significant variability and heterogeneity in their structural composition. Typically, they exhibit high dispersities in molar mass (molar mass distribution─MMD) and in functionalities (functionality-type distribution─FTD), which crucially affect their material usage. In terms of FTD, state-of-the-art lignin analytics still rely mainly on the determination of functional group contents, which are statistical averages with limited explanatory power. In contrast, our online hydrophobic interaction chromatography–size-exclusion chromatography 2D-LC approach combines the determination of both MMD and FTD in a single measurement to provide a comprehensive picture of the characteristic composition of industrial lignosulfonates─information hitherto inaccessible by state-of-the-art lignin analytics. In this way, the complex inter-relationships between these two important structural parameters can be studied in an unprecedented manner. In this study, we reveal the considerable differences in terms of hydrophobic composition and its dispersity present in a range of different industrial lignosulfonates─data desperately needed in tailoring and refining of lignosulfonate composition for material usage.

Highlights

Lignosulfonates are derivatives of natural lignin polymers.Their common feature is the sulfonation of an otherwise hydrophobic lignin backbone, which allows for water solubility at any pH
This study provides data on the hydrophobic composition of different lignosulfonates in a comparable and reliable way, which is so far missing from the existing literature
We compiled a set of lignosulfonates that differ greatly in terms of origin to gain an overview of their prevalent variance in structural composition

Summary

Introduction

Lignosulfonates are derivatives of natural lignin polymers Their common feature is the sulfonation of an otherwise hydrophobic lignin backbone, which allows for water solubility at any pH. Their inherent amphiphilic character induced by the strongly polar sulfonic acid groups makes them attractive for any applications exploiting surface-active properties (e.g., dispersing agents, colloidal stabilizers, detergents, surfactants, etc.).[1−5] Lignosulfonates are important co-products from the sulfite pulping process and, as such, represent technical products with a certain structural diversity. Sulfite pulping processes can be distinguished by the used counter ion (Ca2+, Mg2+, Na+, or NH4+) and process pH (acidic, neutral, or alkaline), resulting in grave changes to the pulping reaction mechanisms and, inflicting changes in the native lignin structure.[2,8,9]

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