Title
Characterization of lignin dissolved during alkaline sodium borohydride and hydrogen peroxide pretreatments of sugar maple (Acer saccharum)
Authors
JONI LEHTO, ADRIAAN VAN HEININGEN, TERO HAAPALA, JARMO LOUHELAINEN, HANNU PAKKANEN and RAIMO ALÉN

Received November 16, 2023
Published Volume 58 Issue 1-2 January-February
Keywords hydrogen peroxide, lignin, molar mass distribution, pretreatment, sodium borohydride, sugar maple

Abstract
Sugar maple (Acer saccharum) wood chips were pretreated with aqueous sodium hydroxide, sodium borohydride, and hydrogen peroxide pretreatments, and the characterization (i.e., amount, molar masses, and molar mass distributions) of the lignin dissolved during the pretreatments was performed. Of the applied pretreatments, especially borohydride pretreatments were efficient in dissolving lignin from this feedstock, as 20% to 28% of the dissolved organics were found to consist of dissolved lignin, contributing to 3.4% to 9.0% of the initial wood lignin. Corresponding values for 2.5% and 5.0% alkaline peroxide pretreatments were from 5.9% to 9.2% dissolved lignin of the total dissolved organics and from 1.1% to 3.2% of the initial wood lignin. Additionally, determined molar masses and molar mass distributions indicated that borohydride pretreatments generally led to the formation of smaller-molar-mass lignin fragments when compared to reference pretreatments and to pretreatments conducted with alkaline peroxide process, indicating more efficient lignin degradation caused by borohydride addition. For example, Mn and Mw values of the analyzed reference effluents were 54%-62% and 66%-71% higher when compared to the corresponding borohydride effluents, respectively.