Structural studies (FTIR, DRIFT) of CMS-Na0.6 etherified starch for applications in moulding sands technology

Structural (FTIR) and thermo-analytic (DRIFT) studies were conducted on modified starch in the form of sodium salt of carboxymethyl starch (CMS-Na_0.6) in the initial state, i.e. a colloidal solution, and in a cross-linked form prepared by physical means (temperature, microwave radiation). Modified starch CMS-Na_0.6 was obtained by way of etherification of potato starch. The first part of the article presents the structural analysis of CMS-Na_0.6 before and after cross-linking by means of physical factors based on the results of infrared spectroscopy tests (FTIR) obtained with the use of the transmission technique. The second part identifies the structural changes in the etherified starch with the use of Diffuse Reflectance Infrared Fourier Transform spectroscopy (DRIFT), recording the spectra in the temperature range of 25-500°C. Based on the courses of the obtained IR spectra, it was established that during the operation of physical factors (temperature, microwave radiation), cross-linking of the colloid CMS-Na_0.6 was observed as a result of total evaporation of the solvent water and next dehydration and formation of intra- and intermolecular cross-linking hydrogen bonds. The spectroscopic method DRIFT was applied to determine the progress of the thermal decomposition of CMS-Na_0.6 during a controlled temperature increase in the range of 25-500°C. It was established that the process of thermal degradation begins already at 280°C. The performed analysis of the obtained structural test results constitutes a complementation of the research conducted in the scope of applying etherified starch as a binder in moulding sand technology.

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