Study On High Energy Propellant Based On Energetic Thermoplastic Elastomers

The continuing demand for high performance and low vulnerability of ammunition in the advanced weapon system makes insensitive high energy propellants the most promising trend of gun propellants and charges in the21st century. The sensitivity of traditional propellant is determined by the thermal decomposition characteristics of nitrocellulose and nitroglycerine. So getting some new high energy additives and binders with low sensitivity which can alternative the normal energetic materials such as nitrocellulose and nitroglycerine plays a key role in the development of insensitive high energy propellant.However, some crosslinking binders needing curing agent to mold are the main energetic binders in current domestic research of insensitive high energy propellant instead of energetic thermoplastic elastomers (ETPE) with excellent performance due to technical reasons.The sensitivity of high energy additives particles can be reduced by surface coating, and the coating materials should be energetic as far as possible to avoid energy loss. Unfortunately, both of the two problems remain to be solved.To solve the problems, the thesis designed a high energy propellant based on GAP-ETPE, containing GAP-ETPE as binder and RDX which is coated by GAP-ETPE as high energy additive.The propellants with good mechanical strength stable combustion were prepared via several steps:formulation design, energy analysis, particle size gradation, surface coating of high energy additives and molding process study.The components of the propellants were seclected according to the properties, resources, cost, etc. RDX is the main energy source of the propellant while CL-20can be used as the assisted high energy additive. GAP-based energetic thermoplastic elastomers and nitrocellulose were chosen to be the energetic binder, and different energetic plasticizers can be used in different conditions.The analysis of energy characteristics of the propellant formulations were carried out by the programmed energy calculation software. The higher the ETPE content is, the higher the specific volume and the lower the explosion temperature are when formulations with the same impetus. The impetus can be more than1190kJ-kg"1when the RDX content of propellant RDX/ETPE/NC/A3(ETPE/NC=50/50)is70%and the explosion temperature is around3210K. The impetus of the propellant RDX/ETPE/NC/BTTN (ETPE/NC=70/30) can reach1200kJ·kg-1within a wide range.The study of RDX particle size gradation was carried out by tap density tester. In binary packing mixtures, the packing efficiency can reach the maximum value when the volume fraction of coarse-fine RDX particles is7:3. The packing efficiency can reach the maximum value when the volume fraction of coarse-middle-fine glass beads is7:1:2or6:1:3in ternary packing mixtures.GAP-based energetic polyurethane elastomer was introduced to coat RDX by liquid precipitation method. Coating conditions were as follows:coating amount(1%), coating time(30min), coating temperature(30℃), precipitant(1.5ml).It is found that the flowability improves obviously compared to uncoated RDX. It is experimentally shown that coating degree R is72.5%and the mass fraction of coating layer is0.98%, which agrees well with the initial value(1%). By coating of RDX with1%GAP-ETPE, the characteristic height of impact sensitivity (H50) of RDX particles is increased from25.6cm to47.9cm, and the friction probability is reduced from72%to40%.The dynamic viscosity of propellant slurry is lower when containing coated RDX.The thesis prepared binder particles by using NC as a carrier to absorb ETPE which is greatly improving the uniformity of mixing propellant materials, and then the ETPE-based high energy propellants with high RDX content(>70%) were prepared via solvent method and extrusion. The compression strength of the propellants can be above30Mpa and the impetus is from1170KJ·kg-1to1210kJ·kg-1. In constant-volume combustion experiments, the higher RDX content is, the faster burning speed is. The fluctuation of the pressure is not obvious during the burning process and the propellants have different burning rate pressure exponents in different pressure ranges.The measured impetus of the propellant formulations RDX/ETPE/NC (77.9/10.9/10.9) and RDX/CL-20/ETPE/NC (64.7/10.3/12.4/12.4) are1215kJ·kg-1and1251kJ·kg-1, respe-ctively. In constant-volume combustion experiments, the dp/dt-t and L-B curves showed that the burning process of the propellants were both fairly stable, and considering their better mechanical strength, the further research of the propellant formulations is meaningful.