Abstract
The paper presents the results of thermal analysis of polymer material in the form of starch derivatives in the form of sodium carboxymethyl starch (CMS–Na) with degree of substitution (DS) in the range 0.2–0.9 for the preparation of foundry binder. In this work, the thermal behavior of the modified starch and qualitative assessment of degradation products released during pyrolysis were determined and comprised. The analysis of the course of progressive decomposition of the starch material under controlled heating in the range of 25–1000 °C in anaerobic atmosphere was based on the results of thermal analysis methods (TG–DTG–DSC) in combination with the results of pyrolysis–gas chromatography–mass spectrometry (Py–GC/MS). The detailed TG–DTG–DSC analysis allowed to determine and compare the temperature at which the process of decomposition of carboxymethyl starches sodium salts with different degrees of substitution begins and to determine the course of its degradation under conditions corresponding to the contact of the foundry binder in the form of starch material with liquid metal (conditions like in foundry mold). Thermogravimetric analysis shows that decomposition processes are multistage, and dehydration is the first step of decomposition. Moreover, TG–DTG–DSC analyses indicate that the thermal stability and the decomposition path of tested compounds depend on the DS. Results of Py–GC/MS studies showed that the formation of decomposition products (including cyclic and aromatic hydrocarbons) in a predetermined temperature range is lower in the case of CMS–Na with high DS.
Highlights
In the foundry industry in the production cycle, it is possible to use organic, inorganic and mineral substances, which, as binding materials, ensure obtaining durable casting forms based on the mineral matrix, at the same time giving the possibility of making castings with the reduction in their defects
Thermal degradation properties and effect of pyrolysis of carboxymethyl starch with different degree of substitution (DS) were analyzed and compared: 1. The results of the TG–DTG–differential scanning calorimetry (DSC) analyses of starch binder CMS–Na show that its thermal decomposition was a multistage process
The subsequent mass losses at temperature range 25–1000 °C are determined as evaporation of water adsorbed in molecule, sodium carboxymethyl starch dehydration, breakage of glycosidic bonds in the polymer chains and intensify the fragmentation of chain
Summary
In the foundry industry in the production cycle, it is possible to use organic, inorganic and mineral substances, which, as binding materials, ensure obtaining durable casting forms based on the mineral matrix, at the same time giving the possibility of making castings with the reduction in their defects. Binders in sand molds are a key component determining their properties and produced castings quality by the binding strength of the of the matrix grains of sand. Faculty of Foundry Engineering, AGH University of Science and Technology, Reymonta 23, 30 059 Kraków, Poland The influence of the modification method, e.g., on the thermal properties of binders in the form of modified starch in relation to the application in foundry processes, is still studied
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