Surface,Interface Features And Bonding Effects In PBT Propellants

AP/HMX/Al/PBT/A3 composite solid propellant is a kind of insensitive and high energy propellant.The surface characteristics of the main components and the filler-PBT matrix interface bonding characteristics are the key factors that affected the mechanical properties of the propellant.Improving the bonding strength of the filler-PBT matrix interface by adding bonding agents could improve the mechanical properties of the propellant.The aims of this paper are characterizing and improving the bonding property of filler-PBT matrix interface.By means of the contact angle test,the surface tension and its components of the PBT propellant’s main components were characterized,also the interface tension and the adhesion work of filler-PBT matrix were calculated.By means of the inverse gas chromatography（IGC）test,the surface acid-base property parameters of the PBT propellant’s main components were characterized,and the enthalpy of interfacial function.The interfacial adhesion properties were estimated by these surface/interface characterizing methods.The effects of the bonding agents to the mechanical properties of the simulated propellant were investigated.Combined with the fiber optical spectrum,FTIR and XPS,the bonding agents with better performances were selected.And the action principles of bonding agents were explored.The results of the contact angle tests show that,the order of the surface tension in the fillers of PBT propellant is AP>HMX>Al,the surface tension of PBT matrix is less than the fillers.The results of the IGC tests show that,the order of forming the covalent bond in the main components of PBT propellant is Al>HMX>AP>PBT matrix,the order of forming the electrostatic bond in the main components of PBT propellant is Al>AP>HMX>PBT matrix.The results of the contact angle and IGC tests show that,the order of the bonding strength is Al-PBT matrix>HMX-PBT matrix>AP-PBT matrix.Although AP-PBT matrix has the maximum interfacial adhesion work,but it gets the maximum interfacial tension,the minimum ratio of adhesion work and interfacial tension,and the minimum enthalpy of interfacial function,which indicate that AP-PBT matrix interface is the weakest interface in PBT propellant.DDBA5,DDBA7 and DDBA8 can improve the adhesion properties of AP-PBT matrix and AP-HMX matrix interface.Furthermore,when acted with TDI,these 3bonding agents show rapid reaction rate and high extent of reaction.In the PBT/A3liquid system,DDBA8 coats the surface of AP to 38.65%,and DDBA5 coats the surface of HMX to 60.43%.DDBA4 is the best bonding agent for improving the mechanical properties of single filler simulated propellant AP/PBT/A3.DDBA8 is the best bonding agent for improving the mechanical properties of single filler simulated propellant HMX/PBT/A3.DDBA5,DDBA7 and DDBA8 are the better bonding agents for improving the mechanical properties of PBT propellant.The action principles of the DDBA bonding agents in the PBT propellant was explored.There are polar groups such as-C=O,-C?N,-P=O in the molecules of DDBA5,DDBA7 and DDBA8.Polar adsorption can be easily formed between fillers（AP,HMX）and the polar groups.The-NR group in DDBA8 reacts with NH₄⁺in AP.The products of ammounium salt ions are adsorbed by AP.The coordination bond can be formed between the boron atom and the nitrogen atom of nitramine groups in HMX.The-OH groups in bonding agents show a strong activity to react with the isocyanate.The aziridine ring can react with active hydrogen which means the boding agents can be combined with the PBT matrix crosslinked network.A high modulus layer can be formed by the bonding agents reacted with isocyanate and the active hydrogen.