Schematic illustration of the structures of the functional chemcail groups OSO₃ (H⁺) on CNCs, COO^-(H⁺) on TCNFs and lignin residues on CNCs. Exact protonated or deprotonated form of the group will depend on the pH condition [42]. Zeta potential results depicting three nanocellulose and BSA (0.5 mg\ml) suspension samples obtained in PBS buffer solutions at pH 3.5 and 7.2, respectively.