Viscometric study of chitosan degradation in organic acid solvents
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1Shandong Provincial Key Laboratory of Molecular Engineering, School of Chemistry and Pharmaceutical Engineering, Qilu University of Technology (Shandong Academy of Sciences), Jinan, China 250353
2Department of Textile and Polymer Engineering, Yazd Branch, Islamic Azad University, Yazd, Iran.
Chitosan is, nowadays, one of the mostly used biopolymers throughout the world. Organic acid solvents are highly used for preparation of chitosan solutions. In this study, we examined the changes in chitosan solution viscosity dissolved in acetic acid, formic acid and hydrochloric acid (HCl) as the most common organic acid solvents. To consider the effect of acid concentration, chitosan was dissolved in dilute (1%v/v) and concentrated acid (50% for acetic acid and formic acid and 37% for HCl). The chitosan concentration was kept constant to be 1%w/v in all of the solutions. The solutions were stored at room temperature for 7, 17, 31 and 44 days and the viscosities were measured by a Brookfield viscometer. Among the solvents, the viscosity of the initial solution was highest for acetic acid 50% and lowest for HCl 1%. For acetic and formic acid, the viscosity was increased by increasing the concentration of the acid while in case of HCl, the trend was reverse and the viscosity of chitosan solution in the concentrated HCl was lower than dilute HCl. The viscosity reduction was highest for dilute acetic acid solution and lowest for HCl in all of the time points of measurement. Finally, by modeling the viscosity-time data, a 3rd degree polynomial was fitted to the data and the parameters are reported. Results of this study shows that although acetic acid is used in most of research works for preparation of chitosan solutions, it highly reduces the viscosity compared to formic acid and HCl.