Thermal decomposition of binder based on etherified starch to use in foundry industry

Abstract

In this work, the main purpose was the determination of the thermal stability of the modified starch: sodium carboxymethyl starch (CMS-Na) used in foundry technology as organic binder for molding sand. The analysis of the course of decomposition of the starch material under controlled heating in the range of 20-500°C was based on the results of thermal analysis methods (TG, DTG, DSC) in combination with the results of spectroscopic technology (DRIFT). The use of various methods of thermal analysis and spectroscopic methods was possible to determine more entirely the mechanism of the binder decomposition process comprising reactions at the molecular level with regard to the conditions prevailing in the mold. The onset temperature of degradation of the binder and at the same time the temperature at which it begins to lose binding properties were determined. It was found that the mechanism of the binder is multistage process. The decomposition of the starch binder CMS-Na involves the gradual evaporation of the water bound at a temperature of 20-120°C and water constitutional starch in the range of 120-200°C, degradation of the binder in the temperature range 200-342°C by breaking the glycosidic bonds in the polymer chains with the formation of volatile compounds and finally detaching the side groups and partial combustion of the starch material within a temperature range 342-500°C.

Archives of Foundry Engineering

“…At 320C band in the range of wavenumber 1800-1700 cm -1 (maximum of peak at 1664 cm -1 ; area 3) corresponding to the vibration of the carbonyl group forming a C=O is occurred. The recorded vibration of the C=O may be related to both the formation of aldehydes, ketones, esters from the sample [14,17,18]. Moreover, above 320C a new band appeared at 1601 cm -1 , the intensity of which increases and the maximum shifts to lower wavenumbers with increasing temperature.…”

Thermoanalytical studies (TG–DTG–DSC, Py–GC/MS) of sodium carboxymethyl starch with different degrees of substitution

“…From the point of view of pouring a liquid alloy casting into foundry sand molds, important issue is it is to determine the thermal stability of a binder during process. Namely, course of thermal decomposition of the organic binder in molding sand determines the result in the formation of significant casting defects, knock-out properties or adversely affect the efficiency of thermal reclamation methods of used molding sands [21][22][23][24][25]. In terms of environmental protection and the assessment of the binder's harmfulness, it is also important to determine the quality (composition) of the decomposition products of the binding material released during rapid heating.…”

Rapid Preparation of Oxidized Starch with High Carbonyl Contents Using NaBrO as Oxidizer

“…Starch is an abundant, affordable, and renewable resource and considered the cheapest and major source of energy for human beings in food products . However, in order to achieve a particular objective in food and non‐food products, such as thermoplastic starch, oxidized starch, etherified starch, crosslinked starch, grafted starch, et al starches need to be modified to improve its application scope due to its poor performance. For this purpose, starch can be modified via physical, chemical or enzymatic method to obtain modified starch with desired properties…”