Molecular weight of lignins

The molecular weight of lignin in the wood, ie, of protolignin, is unknown. In addition to difficulties of isolation and purification, the polymer exhibits strong solvent, ionic, and associative effects in solution. An unequivocal method of measurement has not been developed. The polymer properties of lignin and its derivatives have been discussed (10,16). 

The various conflicting interpretations are attributed in part to the non-specific nature of the spectrum of lignin and more so to the fact that the. molecular weight of lignin is, as yet, unknown. Recently, Aulin-Erdtman (4) has successfully used the methoxyl content of various lignins instead of molecular weights in the determination of extinction coefficients. 

The advantage of the UF method over gel permeation chromatography is related to the retardation effect commonly associated with GPC that causes underestimation of the molecular weight of lignin (Chap. 8.1). By contrast, there is little interaction between lignin macromolecules and the thin UF membrane hence, in UF, true fractionation of the molecules based on molecular weight is obtained. 

High molecular weight (HMW) lignins behave like flexible polyelectroljrtes, whereas low molecular weight (LMW) lignins behave like colloids and dissociate or form micelles. The molecular weight of lignins used as expander components exerts an influence on battery... 

As the main substances of the root, stem, and leaf of the plant, the content of lignin approaches 70 %. The native structure of lignin remains unclear because no method has been established to isolate lignin from the plant in its native state. The molecular weight of lignin is 800-10,000 [4]. The structural fragment of lignin is as follows ... 

Molecular Weight and Polydispersity. Becanse it is not possible to isolate lignin from wood without degradation, the true molecular weight of lignin... 

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