2.2.3. Conductometric and Polyelectrolyte Titration of CNF

The content of carboxyl groups of the CNFs was determined by conductometric titration as described by Saito et al. [22]. CNF was dispersed rigorously in deionized H₂O and 0.01 M HCl (Sigma Aldrich, Munich, Germany). The suspension was titrated with 0.5 M NaOH (Sigma Aldrich, Munich, Germany). Titration conductivity values were plotted against volume of NaOH added. The carboxyl content S (µMol/g) was calculated using Equation (1).

where V_NaOH is the added volume of NaOH, C_NaOH is the concentration of NaOH solution and W_CNF is the weight of dispersed CNF.

The surface charge of CNF was also characterized for cationic demand, which was determined by polyelectrolyte titration using a Mütek PCD04 (BTG SL, UK) charger analyzer. The titration was performed through surface adsorption of diallyldimethylammonium chloride, poly-DADMAC, (Sigma Aldrich, Munich, Germany, molecular weight: 107 kDa) and the excess was titrated with polyethenesodiumsulphonate, PES-Na, (BTG, Éclépens, Switzerland) an anionic standard polymer.