Relationship between viscosity and molecular weight in an andosol humic acid

Abstract

Viscosity and molecular weight of particle size fractions obtained from an Andosol humic acid (HA) were determined. Viscosity was determined both in solutions with and without the addition of 0.1 M NaCl (Cs 0.1 and Cs 0, respectively) at pH 7.0. Polyelectrolytic character was observed in the particle size fractions based on the changes in the concentration dependence of reduced viscosity with NaCI concentrations. The use of a Cs 0.1 solution was suitable for the determination of the values of intrinsic viscosity ([η]) of the particle size fractions. The [η] value increased with increasing weight average molecular weight ( M _w) determined by gel permeation chromatography (GPC), and ranged from 4.3 to 12.9 X 10-3 (L g^-1) in the Cs 0 solution and from 3.5 to 6.6 × 10^-3 (L g^-1) in the Cs 0.1 solution. A linear relationship between [η] in the Cs 0.1 solution and M _w on a logarithmic scale, which was similar to the MarkHouwink equation, was observed. The value of the constant a calculated from the relationship, which reflected the polymer morphology, was 0.75 in the Cs 0.1 solution, and it corresponded to a polymer with flexible chains.

Key Words:

• GPC
• homologous series
• humic acid
• polyelectrolyte
• viscosity