The effect of the milling degree on the structure and molar mass of MWL preparations Grigory Zinovyev,* [a] Ivan Sumerskii, [a] Mikhail Balakshin, [a,b] Thomas Rosenau [a] & Antje Potthast [a] [a] Division of Chemistry of Renewable Resources, Department of Chemistry, University of Natural Resources and Life Sciences, Konrad-Lorenz-Strasse 24, A-3430 Tulln, Austria grigory.zinovyev@boku.ac.at [b] Department of Bioproducts and Biosystems, School of Chemical Engineering, Aalto University, P.O. Box 16300, Aalto FI-00076 Finland mikhail.balakshin@aalto.fi ABSTRACT In the present study, the effect of milling expressed as the yield of milled wood lignin (MWL) on the structure and molar mass of the crude milled wood preparation (MWLc) was studied to better understand the requirements of the protocol and to find optimal conditions for MWL isolation, i.e. to obtain the most representative sample with minimal degradation. Keywords: carbohydrates, crude MWL, functional groups, lignin isolation, molar mass INTRODUCTION Isolation of lignin from lignocellulosic biomass is an important step in lignin characterization. Currently, MWL is a common preparation used to mimic native lignin. However, classical MWL with a yield range between 20-30% based on the total amount of lignin in wood might not be fully representative for the whole lignin in wood. On the other hand, increasing the yield of MWL by extending the milling intensity may result in additional changes in lignin structure. The well-known Björkman's procedure (1954) developed for lignin isolation and based on the extraction of extensively ball milled wood by neutral solvents at room temperature was further elaborated (Chang et al., 1975; Ikeda et al., 2002). Still, all methods require ball milling of wood to isolate the lignin. As the degree of lignin degradation does not depend whether aerobic or anaerobic conditions are used, the major effects are related to the actual milling (Fujimoto et al., 2005). As mentioned above, the overall yield had to be increased in order to represent the entire structure of wood lignin. Hence, significant efforts were made to boost the yield of the isolated lignins. In the current study, crude MWL preparations with a range of 20-75% yield have been isolated and characterized with regard to their molar mass distribution (SEC), hydroxyl groups of different types ( 31 P NMR) and sugar composition (based on methanolysis). The classical MWL purification was not used to access the whole extracted lignin.