Study On Preparation And Modification Of Azodicarbonamide

Azodicarbonamide (trade name: blowing agent ADC), a chemical blowing agent with a broad use, is a nontoxic, tasteless, non-polluting, saffron azo-blowing agent. One of its much obvious features has a group of -N=N-. When heated, it will release large amounts of N2. Its gas evolution reaches 200²50ml/g. The current process of ADC is as follows: biurea is synthesized from hydrazine hydrate and urea by means of acid condensation reaction, and azodicarbonamide is synthesized from biurea through oxidation reaction. The acid method is through adding a large number of sulphuric acid to the reaction system to adjust pH value of the system, which seriously corrodes the reaction equipment. Besides, it is difficult to collect and dispose the ammonium sulfate byproduct in the process. We adjust the pH value of hydrazine hydrate till weak alkaline with hydrochloric acid, rather than adjust the pH value of reaction system to reduce the adding amount of hydrochloric acid. It was investigated that hydrazodicarbonamide was directly synthesized from hydrazine hydrate with a high concentration and urea. Acid was not used in the process. So the corrosion of equipment is little, and the process is friendly to the environment. Orthogonal test was used to optimize the synthesis conditions of azodicarbonamide. Under the optimum conditions, the gas volume of azodicarbonamide was improved by ultrasonic method.Decomposition temperature of azodicarbonamide is 195²20℃, which is far beyond melt-processing temperature of PVC resin in the range of 170¹75℃. Therefore, an activator of azodicarbonamide is applied to reduce the decomposition temperature of the azodicarbonamide to meet the processing requirements of the PVC resin. Zinc oxide is a good activator. Zinc ion in zinc oxide has the ability to accept the lone pair electrons of nitrogen atom and carbonyl oxygen to decrease the decomposition temperature of azodicarbonamide. The ZnO-SiO₂ nanopowder was synthesized by sol-gel process, and applied in the prepared azodicarbonamide to obtain the composite blowing agent for PVC resin. The composite blowing agent has lower decomposition temperature and higher gas evolution. It is suitable for the processing of PVC foam in the future application.