Stability and characterization of GAP bonded ADN-propellant - the problem of gas formation during curing with isocyanates

摘要

During the development of a GAP-ADN formulations in the framework of HISP~*) - program a porous structure in the formulations was encountered. The pores are caused by gas formation during curing of the propellant mix, in some part also already mixing or kneading. This pore formation is very disadvantages with respect to mechanical properties and burning behaviour. The conditions of pore formation and the possible causes should be clarified in order to avoid or at least to reduce the pore formation below a critical extent. The origin of the gas formation was assumed to result in decomposition of ADN itself or the reaction between ADN and the isocyanate Desmodur™ E503, which was used to form the polyurethane based binder in the formulation. Mainly gas evolution at several temperatures, 50°C, 60°C and 70°C at function of measurement time was used to characterize the gas evolution rates. Besides Desmodur™ E503 also the isocyanate IPDI (iso-phorone diisocyanate) was included in this investigation. The gas evolution was followed with two methods. One was IR absorption of the concentration increase of N_2O, a decomposition product of AND. This was done only with E503, because of to high vapour pressure of IPDI. The other method was the determination of the total gas evolution using the vacuum stability apparatus produced by Czech company OZM, which follows the gas pressure by pressure transducers. With IPDI also the anomalous decomposition behaviour of ADN was observed. The obtained results suggest that the decomposition of ADN is the cause of the gas formation and that the control of temperature during propellant preparation, mix and especially curing, plays a key role to avoid the formation of bubbles and pores in the cured formulation.