Methyl hydroxyethylcellulose (MHEC) is widely used in pharmaceutical, nutritive and construction industries to give water-dispersible systems some of necessary properties as rheology, thixotropy, anti-sedimentation and water retention. The main application area of the aforementioned cellulose ether is creation of different construction compositions, in particular dry mixtures. Main structural parameters of methyl hydroxyethylcellulose that determine rheological, physical, and physicochemical properties of dry mortars are the degree of substitution (DS), the molar substitution (MS) and the degree of polymerization (DP). In this paper acid-catalyzed hydrolysis of different samples of MHEC under the influence of sulphuric acid is scrutinized. Optimal conditions of hydrolysis are established, and experimental technique is described. These conditions lead to the generation of various D-glucose derivatives, the structure of which is carefully analyzed by 13C NMR spectroscopy. Collation of signals in 13C NMR spectra is fulfilled based on the calculated values of carbon atoms chemical shifts with the use of BIOPSEL program. By analyzing integral intensity of the corresponding C-atoms signals in the products of hydrolysis the analysis of substitute-members distribution in anhydroglucose unit is conducted. The DS values in 2, 3, and 6 positions (DS?-2, DS?-3, DS?-6) are calculated, the amount of methoxyl (DSMe) and hydroxyethoxyl (DSHE) groups and the total degree of substitution (DStotal) were determined. The distribution of substitute members in accordance with different positions of glucopyranose unit shows the higher reactive capacity of the 2, 6 positions and hydroxyl in hydroxyethyl fragment. Within the method the DS is determined in four different MHEC samples. The comparative analysis between the obtained data and the data indicated by cellulose ethers manufacturers takes place. The results obtained confirm the high accuracy of the method under consideration.
Keywords— acid-catalyzed hydrolysis, anhydroglucose unit (AHU), degree of substitution (DS), distribution of substitute members, glucopyranose unit, integral intensity, methyl hydroxyethylcellulose (MHEC).
|
