Approximately 60 - 80% of the lignin of various hardwoods (poplar, maple, birch, etc.) was found to have a Mw of 1600 - 2000 and a Mn of 900 when isolated from pulping liquors of the Alcell ® process. The remaining 20 - 40% consists of low molecular weight lignin fragments remaining soluble during the precipitation procedure. Extending the cooking time up to 16 hours does not materially reduce the molecular weight or change the chemical structure. Molecular weight data on lignin isolated from thousands of semi-commercial cooks shows the same molecular weight phenomena suggestive of a carbon-carbon linked "core" of about seven to ten units which remains after cleavage of all alpha and beta ether linked monomers. The implication of these findings is that biosynthesis of hardwood lignin is under genetic control and is not the totally random process advocated by Freudenberg and others.
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