The data includes the following datasets: dn_dc_for_Q_factor_determination: refractive indexes of lignin solutions measured at different concentrations (g/L) of lignin at different wavelengths (nm) of incoming light. The linear fit function in excel was used to determine the dn/dc from the presented data. The fit data can be found in the SI of the article. Filtration: Contains experimental results of crossflow filtration measurements for pure water permeability, 90% molecular weight cut off (MWCO) data based on polyethylene glycol (PEG) retentions (100-10000 g/mol) as measured by Gell permeation chromatography (GPC), and MgSO4 retention data. Measured quantities are: active fibre length (m), average [inlet and outlet] pressure (bar), permeate mass (g) [filled beaker-empty beaker], permeation time (s), feed and permeate conductivity (microS/cm). Fourier transform infrared spectroscopy data (FTIR): From the 3 different cationic lignin batches used in the article, the lignosulfonates and the unmodified Kraft lignin. batch number 1 was used for figure 2 in the article; batch number 2 was used for the salt stability, pH stability and biodegradability experiments (Figure 4, 5 and 6 of the main article and figure S4, S6, S7 and S9 of the SI); batch number 3 was used for the reflectometry and layer growth experiments at different NaCl concentrations (figure 3 in the article). the wavelength (cm-1) and signal intensity (a.u.) are presented. H-NMR: 1H-NMR data of the different cationic lignin batches, lignosulfonate and unmodified Kraft lignin. The chemical shift (ppm) and signal intensity (a.u.) are presented P-NMR: 31P-NMR data of the unmodified Kraft lignin and lignosulfonate. To calculate the OH content of the lignin from this data the MestreNova software was used. The chemical shift (ppm) and signal intensity (a.u.) are presented SEM: FESEM images of the bare support and the support coated with 9.5 or 10.0 bilayers of lignin Reflectometry: Reflectometry data for the lignins coated from 5, 50 and 500 mM NaCl solutions onto a silicon waver. The Q factors as determined from the dn/dc data and the professor Huygens software are presented together with the signal (S) base signal (So) and calculated adsorption (Ads) in mg/m2.