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.

Effect of Salts on Laccase‐Catalyzed Polymerization of Lignosulfonate

“…These results were found to largely follow the Hofmeister series and are also widely consistent with the reactivity of LS in aqueous salt solutions as found by Myrvold [49] . Further, it was reported that PO 4 3− (HPO 4 2− herein) had the strongest salting‐out effect on LS followed by SO 4 2−[49] which was also found in the present study.…”

“…While in saline solutions, the added ions will lower the charges on the LS molecule leading to less electrostatic repulsion resulting in the formation of denser‐packed oblate ellipsoid spheres. Depending on the pH, the presence of ions and on their concentrations, these spheres are more or less densely packed [48–53] . At low pH, LS is present as a dense, tightly packed spheroid molecule tending to precipitate.…”

Light scattering characterization of lignosulfonate structure in saline solutions

“…For polyelectrolytes, the origin of the fast mode is attributed to the translational self-diffusion of NaLS molecules, but that of the slow mode is still in debate, but probably Coulomb interactions are one of the main driving forces behind it (Förster et al 1990;Nyström et al 1993;Sedlák 1993;Sedlák 1995). Aggregate formation by means of hydrophobic interaction or hydrogen bonding Yan et al 2010;Myrvold 2013a) is also in discussion.…”

A Critical Review of the Physicochemical Properties of Lignosulfonates: Chemical Structure and Behavior in Aqueous Solution, at Surfaces and Interfaces

“…One report stated that lignosulfonate aggregates are nearly spherical [119], whereas another report illustrated a hollow configuration [121]. As Myrvold demonstrated, aggregation and disaggregation of lignosulfonate is highly dependent on the preparation method and parameters, such as temperature, pH, equilibration time, and concentration [122]. Both a condensed nearly spherical and an open-hollow configuration are therefore realistic.…”

“…Rana [121]; however, the validity of this measurement is questionable, since UV-spectrometry does not provide a linear response (absorbance increase per concentration increment) at high lignosulfonate concentrations. Overall, lignosulfonate aggregation and de-aggregation is a kinetic process that is especially affected by the origin and composition of the sample [122]. A certain difference in CAC is therefore to be expected between authors, who performed their measurements on dissimilar samples.…”