PHYSICOCHEMICAL STUDIES OF ALKALI LIGNINS: III. SIZE AND SHAPE OF THE MACROMOLECULE

Abstract

Light-scattering measurements were made on the alkali lignin fractions described in a previous paper. The range of molecular weights found was from 50,000 to 48 x 106. The usual logarithmic graph of intrinsic viscosity and molecular weight was linear and gave a value of 0.32 for the exponent. From the logarithmic sedimentation coefficient[long dash]molecular weight relationship, the exponent was found as 0.52. Flory''s hydrodynamic parameter [PHI] 1/2 p-1 was 2.3 x 106. These results suggested that the configuration of the alkali lignin macromolecule conformed to a structure between that of a random coil and an Einstein''s sphere impenetrable to solvent. The branching parameter, g, introduced by Zimm and Stockmayer, decreased with an increase in molecular weight as expected. Most of the values of Huggins'' constant, k,'' were between 1 and 2 which indicated a compact particle. A marked increase in k'' was noted for fractions of low or very high molecular weight. The significance of the data is discussed and a model tentatively suggested for the macromolecule.