TECHNOLOGICAL ASPECTS OF NITRATION OF STARCH WITH NITROGEN-SULFUR ACID MIXTURE

Aim. To establish patterns of starch nitration process, allowing to justify the choice of the composition of the nitrating mixture and the regime parameters of nitration. Methods. The degree of nitration was expressed in terms of the nitrogen content in the resulting starch nitrate, which was determined by the ferrosulfate method. We also carried out an assessment of the surface state of the starch grains and starch nitrate at a 300-fold magnification using an optical microscope. Results. It was established that the dependences of the nitrogen content in starch nitrate on the composition of the nitrating mixture and the operating parameters of the process pass through maxima. At certain values of the composition of the nitrous mixture, the nitration process is disturbed, which is associated with side reactions. When starch is nitrated with a nitrogen-sulfuric acid mixture, the resulting starch nitrate retains the granular structure of the original starch, but characteristic defects are formed on the surface of its grains. Conclusions. The maximum nitrogen content in starch nitrate is achieved at H2SO4/HNO3 approximate to 3, a water concentration in the nitrating mixture 8-10% temperature 35-40 degrees C, nitration time 30-35 minutes and nitration module 30-40. The ratio of the rates of the nitration process and side reactions determines the stability of the nitration process. It is broken when H2SO4/HNO3 <= 0.5 and H2SO4/HNO3 >= 7.0 as well as when the concentration of water in the nitrous mixture C-H2O >= 20 %. The surface defects of starch nitrate grains are associated with dissolution and extraction into a nitrating mixture of amylose nitrate, as a result of which one should expect changes in the internal structure of starch nitrate grains.