Methods were adapted to investigate the salt tolerance of sodium lignosulfonates and their emulsion stabilization efficiency. In addition, droplet size distributions and lignosulfonate effect on IFT were studied. The results were furthermore discussed with respect to the analytical data provided with the samples, more specifically hydrophobicity and average molecular weight.
The trend in salt tolerance among lignosulfonate samples was opposite to the emulsion stabilization efficiency; that is, samples with lower salt tolerance yielded on average more stable emulsions and vice versa. This observation was further matched by the hydrophobic characteristic of the lignosulfonates, where high hydrophobicity facilitated better emulsion stabilization and low hydrophobicity encompassed better salt tolerance. Recent developments have diversified the hydrophobicity scale of lignosulfonates, which is corroborated by the availability of more specialized products.
With respect to the type of added salt, lignosulfonate salting-out followed both the Hofmeister series and the Schulze–Hardy rule. Lignosulfonate-stabilized emulsions showed overall similar droplet size distributions. The IFT decreased as a logarithmic function when increasing lignosulfonate concentration from 0.01 to 10 g/L. A general tendency was found in that lignosulfonates with lower average molecular weight also induced larger decreases in IFT.
In conclusion, the adapted methods allowed more detailed assessment of lignosulfonate emulsion stabilization and salting-out phenomena. In addition, it was found that the suitability of sodium lignosulfonates for technical applications can be predicted by the analytical data to some extent.