Molecular Weight of Lignin Fractions Leached from Unbleached Kraft Pulp Fibers

Abstract

The molecular weights of lignin fractions leached from an unbleached kraft pulp were found to increase from 230,000 to 410,000 as washing of the pulp proceeded. The free diffusion coefficients for both a spherical and a disk-like conformation were calculated and were found to be seven orders of magnitude higher than the observed intrafiber diffusion coefficient. Also the change in the free diffusion coefficient with molecular weight was far less than the 100-fold polydispersity observed previously. A comparison of the molecular dimensions with the pore size indicated that a flat, disk-like conformation, rather than a spherical conformation, is appropriate for the lignin macromolecule.