Fractionation of Kraft Lignin for Production of Alkyd Resin for Bio-Based Coatings: Characterization of Low Molecular Weight Kraft Lignin Products of Aqueous Ethanol Fractionation for Application in Alkyd Resins

We have recently demonstrated a new pathway of successful utilization of low molecular weight kraft lignin obtained from aqueous ethanol fractionation of kraft lignin in the synthesis of bio-based alkyd resins for anti-corrosion coatings. However, these lignin fractions generated foul odors during the synthesis of alkyd resins, which could not be explained by the reported characteristics of these lignin materials. The current literature does not focus on investigating the odor characteristics of the low molecular weight lignin fractions in realistic conditions of alkyd resin production, even though this information can be highly important in developing an efficient, safe, and sustainable bio-based formulation of alkyd resin. The thermal degradation profile obtained in realistic conditions of alkyd resin synthesis can help determine the release of volatile organic compounds generating odor and/or hazards during the resin synthesis. In addition, the solubility behavior of low molecular weight kraft lignin in an aqueous solution of varying pH is not typically reported in the literature, which also prevents researchers from understanding the applicability of these lignin fractions in water-borne formulations of alkyd resin in mildly alkaline/acidic conditions. In this work, the pH-dependent solubility and thermal degradation profiles of the low molecular weight fractions of softwood kraft lignin (MW < 3000 g/mol), produced by aqueous ethanol fractionation at pilot scale, were explored. The production of volatile organic carbons (VOCs) including odor-releasing sulfur compounds and lignin derivatives was analyzed by thermal desorption combined with a gas chromatography method simulated at the condition of alkyd resin synthesis. Overall, this study presents new insights into the feasibility, limitations, and areas of improvement in utilizing the low molecular weight kraft lignin fractions produced by ethanol/water fractionation, which in turn could help this technology to grow in the sustainable coating industry.

Funding acknowledgment:
 
This research work was conducted as part of the LIGNICOAT project, which has received funding from the Bio Based Industries Joint Undertaking under the European Union’s Horizon 2020 research and innovation program under grant agreement No 101023342. The JU receives support from the European Union’s Horizon 2020 research and innovation programme and the Bio-based Industries Consortium. The authors gratefully acknowledge the above funding support for this project.