2.2. Modification of Carboxymethylcellulose Sodium

The modification of CMC with hydrazine groups was carried out by a previous method [20]. Briefly, 1 g CMC was dissolved in 200 mL of deionized water and 3 g adipic dihydrazide was added. The mixed solution was continuously stirred to make it evenly dispersed at temperature room. Next, HOBt (258 mg suspended in 2 mL of a dimethylsulfoxide: water (1:1) mixture) was added and followed by EDC (262 mg in 2 mL of a dimethylsulfoxide: water (1:1) mixture). If necessary, keep the pH at 6.8 by adding 0.1 M NaOH and stir overnight. After the reaction, the solution was dialyzed with deionized water (8000 MWCO membranes) for 3 days. The final product was obtained by lyophilization. The lyophilized product was subjected to elemental analysis with an elemental analyzer (Vario MACRO cube. Elementar, Langenselbold, Germany) to calculate the degree of modification.