Evidence for a very slow disaggregation of lignosulfonates

Abstract

There is still a challenging question about how lignosulfonates (LS), such as non-sulfonated lignins, aggregate and disaggregate in solution. In the literature, the reported critical aggregation concentration (CAC) of LS varies by orders of magnitude. In the present work, the aggregation of a purified sodium LS (NaLS) from a softwood has been studied by size exclusion chromatography and capillary viscometry. It was found that intermolecular aggregates form at relatively high concentrations. Disaggregation is an extremely slow process for spray dried samples and proceeds for several weeks. The process can be speeded up by increasing the pH and/or temperature. The very slow disaggregation may explain the strongly varying (and sometimes very low) CAC values reported in the literature. An interaction energy of about 8 kJ mol-1 monomer was calculated.