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Calculation Of Mark–Houwink–Sakurada (MHS) Equation Viscometric Constants For Chitosan In Any Solvent–temperature System Using Experimental Reported Viscometric Constants Data
Published 2007 · Chemistry
Abstract Mark–Houwink–Sakurada (MHS) equation constants, a and K, for chitosan in several solvent–temperature systems have been already reported. In this article, two equations are proposed to determine, a and K, for chitosan in any solvent–temperature system using the previous reported viscometric constants data. This study resulted in two following equations: Exponent a = 0.6202 + 0.699 x / ( 0.4806 + x ) log K · 10 - 5 = - 5.7676 · Exponent a + 5.9232 where x equals to [DA/pH·μ], with DA, degree of acetylation of chitosan, pH of chitosan solution in a solvent with ionic strength of μ. The two equations are used to determine the constants of chitosan solution without urea between 20 and 30 °C. The validity of prediction of the constants from the knowledge of the DA, pH and ionic strength were examined using the above equations. The constants were obtained by a deviation in the range of ±0.40–29.0% for the exponent a, and ±6–71% for most of K values. The deviation of experimental and calculation data is reasonable. This is because several factors affecting the correct values for the constants were not taken into consideration by authors whose reported experimental data. The effects of temperature and urea on the constants have been described and taken into consideration in this article. The author of this manuscript described the various parameters affecting the constants. The procedures to determine the correct values of the constants for chitosan were also explained. The author of this study introduced the empirical function for chitin/chitosan chain conformation, (DA/μ·pH), as a measure of chain stiffness in solution. The empirical value or hydrodynamic volume of the polyelectrolyte molecule in solution increased with an increase in DA and a decrease in μ of solvent and pH of solution. The quality of different solvents was compared using the latter empirical parameter. Different solvents, which were used to determine the intrinsic viscosities and the viscometric constants, a and K (published in the literature for chitosan), were compared. The latter empirical parameter was also compared with B-parameter defined by Smidsrord & Haug as chain stiffness; d ln [η]/d(1/T), and d ln [η]/dT as chain flexibility of the polymer.