Physicochemical Studies of Alkali Lignins: Ii. Ultracentrifugal Sedimentation Analysis

Ultracentrifugal sedimentation of alkali lignin fractions revealed marked boundary spreading at low and high centrifugal fields. An analysis of the gradient diagrams indicated a wide distribution of sedimentation coefficients ranging from 0.5 to over 400 × 10−13 second. There was only a small decrease in the polydispersity on subfractionation. The distributions were continuous with a single peak and positive skewness. A linear relationship was found between the intrinsic viscosity and the standard deviation of the weight-average sedimentation coefficient. The sedimentation coefficient based on the movement of the maximum ordinate at a field of 11.5 × 103 g was several times greater than the corresponding coefficient for the same fraction at 200 × 103 g. A qualitative interpretation of this phenomenon is given in terms of the Faxen and the Archibald solution to the Lamm equation.