Research On Mechanical Properties Of GAP Based Composite Crosslinking System Based On Click Chemistry

Glycidyl azide polymer(GAP)has the advantages of high density,high enthalpy of formation,low friction sensitivity and low impact sensitivity,which has broad application prospects in high-energy composite solid propellants.Click chemical reaction has the advantages of harmless by-products and no affected by water,which is an effective means to replace isocyanate curing reaction.Hexanitrohexaazaisowurtzitane(CL-20)is a new energetic compound with high energy density and excellent detonation performance.With CL-20 added into the composite solid propellant,the energy performance of the propellant can be significantly improved.In this paper,the mechanical properties and influencing factors of GAP-BPS and GAP-BPS/CL-20 curing systems were studied with GAP as energetic binder,CL-20as high-energy explosive,and BPS as curing agent.The specific contents are as follows:(1)GAP-BPS(hereinafter referred to as GB)blend system and GAP-BPS/CL-20(hereinafter referred to as GB/CL-20)layered system were established by molecular dynamics.According to Huisgen cycloaddition reaction mechanism,Perl crosslinking script was written to‘crosslink'GB blend system and GB/CL-20 layered system,and the influence of curing parameters R value on crosslinking degree was studied.The results showed that when the R value was less than 0.3,the crosslinking degree of GB crosslinking system and GB/CL-20crosslinking system was 100%;When R value is greater than 0.3,the crosslinking degree of GB crosslinking system is greater than that of GB/CL-20 crosslinking system,and the crosslinking degree of GB/CL-20 crosslinking system is less than 100%.It shows that when the amount of BPS in the system is large,the addition of CL-20 will hinder the growth of GB interconnect network and is not conducive to the generation of interconnect network.(2)The mechanical properties of the cross-linked GB model and GB/CL-20 model were calculated by molecular dynamics.The results show that with the increase of R value,the fracture strength and resistance to elastic deformation of the two systems increase first and then decrease.When the R value is 0.3,the fracture strength and hardness of GB crosslinking system are the largest,and the system has the strongest resistance to elastic deformation and the best mechanical properties;When R value is 0.5,the hardness and elastic deformation resistance of GB/CL-20 crosslinking system are the strongest.At the same R value,the addition of CL-20reduces the fracture strength of the system and enhances the ability to resist elastic deformation and plastic deformation.(3)The tensile properties of GB crosslinking model and GB/CL-20 model after crosslinking were calculated by non-equilibrium molecular dynamics.The microscopic behavior of stretching showed that when the crosslinking degree of GB crosslinking system was 100%,the GAP molecular chain in the system was connected to crosslinking network through BPS,and most of them appeared in the crosslinking network during stretching,which was difficult to be pulled away.The tensile behavior of GB/CL-20 crosslinking system showed that cracks first appeared at the interface between GB crosslinking network and CL-20 crystal.With the tensile process,the cracks gradually expanded,and finally the GB/CL-20 crosslinking network was broken.Because of the non-chemical bond interactions such as hydrogen bond and van der Waals force between azide and CL-20 in GB cross-linked network,‘wire drawing'phenomenon will appear in the process of crack expansion,which will prevent the speed of crack expansion to a certain extent.After the cross-linking system of GB/CL-20 is broken,the‘silk'with non-chemical bond interaction with CL-20 will appear retraction phenomenon,which is due to the‘retraction'phenomenon conforms to the principle of energy minimization.At the same time,the non-equilibrium tensile simulation results are consistent with the elastic mechanics calculation results.When R value is 0.3,GB crosslinking system has the best ability to resist elastic deformation.When R value is 0.5,GB/CL-20 crosslinking system has the best resistance to elastic deformation.(4)Based on the simulation results,the mechanical properties of GB_0.3/CL-20,GB_0.4/CL-20,GB_0.5/CL-20 and GB_0.6/CL-20 films were tested by universal material testing machine,and the influence of R value on mechanical properties was studied.The results show that when R value is 0.5,the Young's modulus of GB_0.5/CL-20 sample is the largest,and with the increase of R value,the Young's modulus increases first and then decreases.Similar to the unbalanced uniaxial tension of GB/CL-20 crosslinking system,when the film is subjected to tensile force,cracks first appear at the edge of the film,and continue to expand with the tensile process until the film breaks.The results of laser confocal microscopy showed that GB_0.5/CL-20 had the largest surface roughness,indicating that the‘drawing'phenomenon was serious during the tensile process,and the intermolecular interaction between the two sections was strong.