I'm currently working with lignin solutions in sodium hydroxyde and I've collected data on the solutions' viscosity at different NaOH and lignin concentration. The viscosity seems to be correlated mainly with lignin concentration by a power model (the viscosity is proportional to the fourth power of the concentration), yet it still shows some deviations for simillar lignin concentrations at different NaOH concentrations. I've tried working with relative, specific, and reduced viscosity, with the pH, and with lots of different variations of this power model that I inicially proposed, but none of them solved these minor discrepancies. Having in sight that lignin is considered to behave as a branched polyelectrolyte in NaOH solutions, is there a general model that can be tried? One that counts the ionic strength or something simillar? I found quite hard to find any simple model that could be used, yet I think it's quite hard that none has been proposed this far.