The synergistic effect of gamma irradiation and alkaline soaking at low temperature on the pre-deacetylation of α-chitin: Optimization by design of experiment.

The effect of gamma irradiation and alkaline soaking time at low temperature (4 °C) as a pretreatment of α-chitin before its N-deacetylation and the effect temperature, NaOH concentration and the reaction time traditionally used during the deacetylation process were studied by applying a factorial experimental design. The top and bottom levels applied for each factor were 1-25 kGy for γ irradiation dose, 2-18 hours for alkaline soaking time at low temperature (4 °C), 50-85 °C for temperature, 35-60% for NaOH concentration and 30-90 min for reaction time. The measured response of deacetylation degree (DD) was determined by FTIR. The pre-treated samples of α-chitin were characterized by X-ray diffraction, DSC and SEM to investigate physical and chemical modification. The obtained results showed that γ irradiation and alkaline soaking time at low temperature are significant factors. The most influential factor was the temperature during the deacetylation process. The equation of the predictive mathematical model for the DD was obtained as follows: DD(%)=-80.4825+0.4984A[NaOH]+1.1355AT°+0.1505Atime-0.1808ADose+0.9845Asoaktime X-ray diffraction, DSC and SEM revealed that the pre-treatment of α-chitin affected greatly its crystallinity and led to chemical and physical modification of its structure. The pretreatment consisting of γ irradiation and soaking time at 4 °C in alkaline medium played a synergistic effect during the deacetylation process.