Patterns of the process of starch nitration with nitric acid

Abstract

The article presents the results of the experimental study on the starch nitration process with aqueous solutions of nitric acid. This nitrating medium has a number of advantages over the nitric and sulfuric acids mixture commonly used in industry, in particular it concerns the chemical stability of resulting starch nitrate. The aim of this work is to establish the dependence of nitration degree of starch on the nitration process parameters, taking into account changes in the chemical composition of its macromolecules. The experimental research method involved the use of ferrous sulfate method to determine the nitration degree of starch and IR-Fourier spectroscopy to analyze the macromolecules chemical composition. The parameters of the nitration process were changed in the following ranges: the mass fraction of water in acid solution of 0 to 35%, the temperature of 3.4 to 800С, the nitration module, as the ratio of the mass of the acid solution to the mass of potato starch of 1 to 40, and the nitration time of 1 to 180 min or 24 h. Based on the experimental results, it was found that the maximum degree of starch nitration is achieved with a water mass fraction in the nitrating solution of about 2%; a further increase in its content leads to a decrease in the starch nitration degree. The increase in the starch nitration degree to the maximum value in this case indicates the nucleophilic mechanism of starch nitration. It is shown that the temperature has a weak effect on the starch nitration degree, and nitrates of oxidized starch are formed under the conditions of high temperature. Increasing the nitration modulus leads to an increase in the starch nitration degree. The effect of nitration time on the starch nitration degree is related to the starch property to dissolve in nitric acid. The initial stage of starch nitration process proceeds at a high rate, which is a consequence of the acid intense penetration into the starch amorphous regions and their dissolution. In the following stages, the nitration process is slowed down due to the acid diffusion into the starch crystalline regions. If nitration is continued, a practically stable value of the nitration degree is achieved in the resulting starch nitrate. The obtained results allow choosing rational conditions for preparation of starch nitrate, which is a powerful explosive.