Chitosan intrinsic viscosity

The possibility of using viscosimetry methods and the determination of reducing carbohydrates concentration in investigation of chitosan enzymatic destruction have been discussed. It has been demonstrated that the change of chitosan intrinsic viscosity can result both from the rearrangement of the polymer supermolecular stmcture and from its hydrolysis. In this connection the direct method of determination of the reducing carbohydrates concentration seems to be much more eorrect at investigating the chitosan enzymatic destmction. 

Chen R.H., Tsaih M.L. 1998. Effect of temperature on the intrinsic viscosity and conformation of chitosans in dilute HCl solution. International Journal of Biological Macromolecules 23,135-141. 

Table 19.1 Intrinsic viscosity and viscosity average molecular weights of different grades of chitosan...

Figure 19.11 Intrinsic viscosity of different grades of chitosan solutions [50].

Figure 19.38 Particle size of chitosan as a function of intrinsic viscosity [148].

Viscosimetry is the mostly utilized method to determine the molecular weight of chitosan due to its simplicity. The method has the disadvantage of not being absolute because it relies on the correlation between the values of intrinsic viscosity with those of molecular weight, as determined hy an absolute method for fractions of a given polymer. This relationship is given by the well-known Mark—Houwink—Sakurada equation. 

There is no doubt that the characterization of chitin and chitosan materials has been the subject of much work and debate. Molecular weight and the degree of acetylation (D.A.) or deacetylation (D.D.) remain the primary properties of interest. Residual protein, other impurities and ash content are some of the other information sought. The use of GPC and intrinsic viscosity measurements for molecular weights persist, while NMR, IR, UV, and elemental analysis have all been used to report on the D.A. and D.D. (Kasaai 2009). It is now clear that where possible, NMR is the method of choice to evaluate D.A. and D.D., while IR, UV, and elemental analysis are still used where the sample mode does not permit easy access for NMR elucidation. 

The molecular weight of chitosan can be conveniently measured by the viscosity method. The viscosity of chitosan is measured at 25°C 0.1°C in O.lmol/L CH3COOH/O.2mol/L NaCl buffer solution with a capillary viscometer. The intrinsic viscosity [r ] is calculated according to an empirical equation (31.7) (Fan et al. 2002) ... 

The viscosity of CM-chitosan can be determined by the viscometric method with an Ubbelohde capillary viscometer. A One-Point method equation was used to calculate the intrinsic viscosity (Fan et al. 2002) ... 

Zhao, Z. H., Sun, H. Z., Sun, M. K. 2002. Single point method to determinate the intrinsic viscosity of carboxymethylated chitosan. Marine Fisheries Research Chinese) 23 41-43. 

A possibility of using the viscosimetiy and sedimentation and diffusion methods in studying the process of enzyme chitosan hydrolysis is discussed in the chapter. It is shown that a change in the intrinsic viscosity of chitosan may be determined by both the hydrolysis process in the glycoside bonds and transformation of the supramolecule stmcture of the polymer. Thus, for setting the hydrolysis process it is necessary to use an absolute method for molecular weight determination. 

The intrinsic viscosity of chitosan was determined in a buffer solution of 0.3 m. of acetic acid and 0.2 m. of sodium acetate, whereas the relative viscosity was established for polymer solutions of 1% acetic acid by the standard method [8] in 25 °C. 

The observed changes in the values of characteristic and intrinsic viscosity in the absence of enzyme agents are probably coimected with structural transformations such as destruction of chitosan associates in the acetic acid solution. As a XRD analysis shows, the source chitosan and the one dissolved in the acetic acid have different supramolecular organization (Fig. 8.3). 

FIGURE 1 The dependence of the intrinsic viscosity of chitosan extracted from 1% acetic acid solution containing trypsin (1), lidase (2), collagenase (3) and pepsin (4) on the time of chitosan standing in solution. 

The initial rate of enzymatic destruction of chitosan evaluated on the linear part by the drop in its intrinsic viscosity [tj] and calculated by the formula [2] ... 

Since ethanol is a precipitator for chitosan, its introduction into solutions of chitosan must degrade the thermodynamic quality of the solvent and increase the degree of stracturing and dynamic viscosity of concentrated polymer solutions. A monotonic decrease of the intrinsic viscosity and growth of Huggins constant in the studied range the ethanol ratio water (curves 1 and 2 in Figure 1, respectively) confirm the conclusion about the deterioration of the thermodynamic quality of mixture acetic acid-ethanol solvent. 

The chitosan solvent is important also when molecular weight has to be calculated from intrinsic viscosity the Mark Houwink relationship... 

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