Precipitation and activation of Eucalyptus kraft lignin in a single step

Abstract This study examines the impact of precipitation conditions, specifically pH and temperature, on the production of Eucalyptus kraft lignin from black liquor, focusing on the resulting chemical properties. Additionally, the process of hydroxymethylation of lignin during precipitation in a single step was investigated. Lignins were characterized using wet chemical analyses, which included the determination of phenolic hydroxyl group content, carboxylic group content, syringyl-to-guaiacyl ratio, molecular weight distribution, and glass transition temperature. Additionally, ATR-FTIR spectra were recorded, and prediction models between these spectra and lignin descriptive parameters were established: phenolic OH content, carboxyl group content, S/G ratio, glass transition temperature, and molecular weight distribution. The results demonstrate that the properties of the precipitated lignin are influenced by both pH and temperature during precipitation, with the precipitation yield exhibiting the most pronounced variation. The study also concludes that lignin activation during precipitation is achievable, with the most favourable outcomes observed at pH 9 and 80 °C.