Response surface methodology applied to the study of the microwave-assisted synthesis of quaternized chitosan

• Quaternized chitosan derivative is synthesized in acid medium under microwave irradiation.
• Modeling by response surface methodology to determine optimum reaction parameters is successfully achieved.
• Microwave-assisted derivatization of chitosan is much faster than conventional reaction.

A quaternized derivative of chitosan, namely N-(2-hydroxy)-propyl-3-trimethylammonium chitosan chloride (QCh), was synthesized by reacting glycidyltrimethylammonium chloride (GTMAC) and chitosan (Ch) in acid medium under microwave irradiation. Full-factorial 23 central composite design and response surface methodology (RSM) were applied to evaluate the effects of molar ratio GTMAC/Ch, reaction time and temperature on the reaction yield, average degree of quaternization (DQ¯) and intrinsic viscosity ([η  ]) of QCh. The molar ratio GTMAC/Ch was the most important factor affecting the response variables and RSM results showed that highly substituted QCh (DQ¯ = 71.1%) was produced at high yield (164%) when the reaction was carried out for 30 min. at 85 °C by using molar ratio GTMAC/Ch 6/1. Results showed that microwave-assisted synthesis is much faster (≤30 min.) as compared to conventional reaction procedures (>4 h) carried out in similar conditions except for the use of microwave irradiation.