Preparation And Properties Of Fluoro-Hydroxyl-Terminated Polybutadiene Solid Propellant

Hydroxy-terminated polybutadiene(HTPB)has low viscosity,low explosive damage,and strong storage capacity.Therefore,butylated propellant has become the best series of composite solid propellant,and it has been widely used in the military field at home and abroad.Polyvinylidene fluoride(PVDF)has strong polar fluorine atoms,stable chemical properties,and reliable mechanical properties,and is generally used as a propylene propylene propellant.Nowadays,the focus of improved solid propellants is generally on coating or constructing fluorine-containing substances on the surface of aluminum powder,or grafting high-energy groups on HTPB,but the former has uneven fluorine dispersion,resulting in uneven energy release during combustion.Affect the use of propellant,the latter is easy to cause the decline of HTPB mechanical properties.Therefore,PVDF with excellent mechanical properties was grafted to HTPB to prepare fluorine-terminated hydroxy-polybutadiene materials and applied it to the propellant,which solved the problems of uncontrollable burning rate,easy sintering,and many residues.To improve the combustion performance and increase the heat released by combustion without affecting the mechanical properties of HTPB propellant,it is of great significance for the preparation of high-energy solid propellant with controllable burning rate.The PVDF containing double bonds was designed and synthesized,and the formation of polymer double bonds was determined by means of FT-IR and ~1H-NMR.The modified PVDF was grafted to HTPB to prepare fluorine-terminated hydroxy-polybutadiene materials.At the same time,FT-IR and GPC were used to determine the successful polymerization of the two polymers produced by chemical modification.The results of thermal analysis(TG-DSC)show that the grafting of fluorine has little effect on the thermodynamic properties of HTPB,and the thermal stability is stronger.Compared with physical blending,it is found that the material produced by chemical modification is still very hydrophobic,and the elongation change during unidirectional stretching is smaller,which is close to that of pure HTPB,and the tensile strength and elastic modulus are improved.SEM characterization found that the5% fluorine-doped materials had the smallest tensile fracture surface defects and a very small number.Further,the synthetic fluorine-based hydroxyl-terminated polybutadiene material was applied to the solid propellant to test its application performance.The test of the comprehensive analysis system of ignition and combustion found that when the fluorine doping content is 5%,the flames of the two propellants are brighter than the traditional butylated propellant,and the ignition delay time is greatly shortened.the burning rate of the pellets produced by physical blending F-HTPB-Phys composite material,chemically modified F-HTPB-Chem material increased by ? 30% and ? 41%,respectively.It is proved that the grafting of F in HTPB promotes the rapid ignition of the pellet,and the effect of increasing the burning rate is remarkable.The flame temperature of the propellant is higher during the entire combustion process,and the uniform dispersion of fluorine makes the propellant burning rate controllable.The combustion heat test results showed that the combustion heat of the 5%-F-HTPB-Phys and 5%-F-HTPB-Chem grains increased by ? 3.31% and ? 3.50% compared with the pure grains.According to the morphology of the combustion residue,the small particle size of the residue is observed and the combustion is sufficient,which shows that the introduction of PVDF solves the problems of easy sintering of Al powder and large particle size of the residue.But this research also requires research scholars to do more exploration in strictly controlling the number of PVDF grafted on HTPB.