Study On Granule-Casting Process And Properties Of Elastomeric Modified Cast Double Base (EMCDB) Propellant

In this paper, granule-casting process had been first successfully applied to the shapingof EMCDB propellant. The propellant has higher energy, better mechanics property andburning plateau.Firstly, in EMCDB preparation, two kinds of formulations A and B were designed andinvestigated. The A formulation can be used to free-loaded motor charge, while the Bformulation is applicable to cast-bonded motor charge. The path of preparing process and thekey components of EMCDB propellant were established.Secondly, the curing process of EMCDB propellant was investigated systematically. Ineach period of curing, morphological change in curing process were observed by the opticalmicroscope. The influences of key components in the propellant and curing temperature onthe rate of crosslinking reaction were studied by means of FT-IR and Dinbutylamine titration.Meanwhile, the mechanism of crosslinking reaction was analyzed. The elementary curingmodel of EMCDB propellant was constructed, and the optimal curing conditions were found.The curing process includes two steps, which are solution and plastify of macromolecularbinder, and the curing reaction of the linking agent. The rate of solution and plastify ofmacromolecular binder depends on the solution property of binder in plasticizer with smallmolecular weight, the curing temperature, and some other factors. The process ofcrosslinking is that in which the crosslinked network can be formed. The rate of crosslinkingcuring reaction depends on the activity of curing agent, the activity of curing catalysts, curingtemperature and so on. The network integrity depends on the competition of solution andplastify of macromolecular binder with the curing reaction. And even, the mechanicalproperties of the propellants is also determined by the network integrity.Thirdly, the factors, such as the content of NC and PEG, the concentration of crosslink,particle size of RDX, bonding agent, combustion catalyst etc. played on tensile properties ofthe propellants under high or low temperature were studied. The glass temperatures (T_g) ofEMCDB propellants were measured by the way of DSC and DMA. After that, the dynamicmechanical properties of them were tested with the method of DMA. Finally, themicromorphology of break surface formed tensile was observed by SEM. The results of DSCand DMA showed that T_g of binding agent system decreased conspicuously when the contentof NC was reduced, or the molecular weight of PEG or its content was increased, or suitableantifr-plasticizing was added. When the T_g was lower, the ratio of elongation of EMCDBpropellants under low temperature was effectively enhance. The SEM observing resultsindicated that some elastic threads on the fracture surface were found in EMCDB with blinder agent, but the bare dry particles of RDX couldn't be observed there. It was shown that thebonding agents intensified the interface function between the filler particles and the binders,so the peak value of mechanical loss modulus (E") decreased when the interface functionwas intensified.Finally, the factors, such as the content of aluminum powder, binders, components ofcombustion catalyst, particle size of RDX, the way of dealing with the catalyst, etc played onthe combustion of the propellant were investigated too. The catalytic combustion mechanismof EMCDB propellants was probed by means of the single color frame amplificationphotography,Πmode miniature thermocouple, the scanning electron microscope and theLINK ISIS energy spectrum. The results provided the theoretical and practical base to how toadjust the combustion property of EMCDB propellants. The composite catalyst of lead saltwith cupric salt and carbon black can make EMCDB propellant occur plateau combustion inthe wider range between middle pressure and high pressure. The burning rate was enhancedwith the content of black carbon increased, and combustion platform was made wider andmoved to lower pressure range with the content of lead salt increased, while combustionplatform was moved to higher pressure segment with the content of copper salt increased. Thesmaller the particle size of catalyst is, the easier the combustion platform is formulated.Inducting the catalyst by the wet process is better than the dry process.With the decrease of particle size of RDX or increasing of the content of NC, the burningrate is increased. Furthermore, the pressure range of burning platform pressure was broadenedin this way. The flame structure of EMCDB propellants is similar to the typical modifieddouble-based propellants. The composite catalyst of lead salt with black carbon can restrainaggregation of the active components of catalyst, and effectively promote the catalysisefficiency. With the increase of pressure, temperature of the surface reaction zone, the darkzone and the flame zone were increased, while the surface reaction depth was decreased.