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Molecular Weight and Molecular Weight Distribution of Kraft Lignins

Published online by Cambridge University Press:  16 February 2011

Wolfgang Schmidl ,
Daojie Dong  and
Arthur L. Fricke
Wolfgang Schmidl
Affiliation:
University of Florida, Department of Chemical Engineering, Gainesville, FL 32611
Daojie Dong
Affiliation:
University of Florida, Department of Chemical Engineering, Gainesville, FL 32611
Arthur L. Fricke
Affiliation:
University of Florida, Department of Chemical Engineering, Gainesville, FL 32611
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Abstract

Kraft lignins are the lignin degradation products from kraft pulping. They are complex, heterogeneous polymers with some polar character. The molecular weight of kraft lignins greatly affect the physical properties of black liquors, and are of primary importance in separation from black liquor and in evaluating potential uses.

Several purified kraft lignins from slash pine were analyzed for number average molecular weight by vapor pressure osmometry (VPO), for weight average molecular weight by low angle laser light scattering (LALLS), and for the molecular weight distribution by high temperature size exclusion chromatography (SEC). The lignins were run in Tetrahydrofuran (THF), N, N-Dimethyl Formamide (DMF), DMF with 0.1M LiBr, and pyridine at conditions above the Theta temperature. Experimental methods are discussed.

The results show that VPO may be used to determine Mn for kraft lignins if the purity of the lignins and the identity of the impurities are known. LALLS can be used to determine Mw for kraft lignins if measurements are made at or above the Theta temperature of the lignin-solvent pair. SEC should be used at temperatures at, or above, the Theta temperature of the lignin-solvent pair. Size separation is highly dependent on the solvent used, and DMF is a much better solvent than THF for high temperature SEC. Future work using moment resolution procedures to derive an accurate calibration curve are also discussed.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 197: Symposium U – Materials Interactions Relevant to the Pulp, Paper and Wood Industries , 1990 , 21
Copyright
Copyright © Materials Research Society 1990

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References

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