An anhydrous methanol solution of each selected aldehyde
(10 mL) at the desired concentration (0.4–1M) was added into a
flask containing chitosan films (2 cm×2 cm) or particles (0.03 g).
After stirring for a given time at ambient temperature (∼28–30 ◦C),
NaBH4 (0.3 g, 0.8 mol) was added into the reaction mixture and
the solution was stirred for 24 h