Molecular Dynamics Simulation For Polyurethane Elastomer Based On HTPB/MDI

Polyurethane elastomer is an important polymer adhesive,forming its molecular bonds based on urethane group.The flexible soft segment and hard segment in molecular structure,making the adhesives with wide hardness range,high strength and excellent low temperature performance.Firstly,the molecular dynamics method is used to analyze the radial distribution function of the atoms in the system,exploring the formation of the molecular bonds in the synthesis of polyurethane,analyzing the relationship between the radial distribution function and the microstructure of the different atoms under the temperature field.Secondly,the changes of mechanical properties and internal structure of polyurethane elastomers under uniaxial tension at different tensile rates,temperatures and pressures are explored.The radial distribution function between Diphenyl-methane-diisocyanate(MDI),1,4-butanediol(BDO)and HTPB/MDI based polyurethane elastomer was investigated by molecular dynamics method.The results verify that the formation of chemical bond of HTPB/MDI based polyurethane elastomer: when the polyurethane is synthesized,the nitrogen and carbon double bonds in functional groups of diisocyanate are opened,and the addition reaction occurs with the hydrogen atom on the hydroxyl group(-OH).The distribution function of polyurethane elastomer and its microdeformation mechanism were analyzed at different temperatures using the pressure of 0 atm.The results show that the peak value of radial distribution function of C-N,N-H,C-O and O-H decrease with the increasing temperature,and the peak position is slightly shifted to the right.With the increase of temperature,the rotational degree of freedom of the chemical bond inside the molecule increase,which results in the decrease of the radial distribution function.At this time,the temperature of the synthetic polyurethane is conducive to the progress of the curing reaction.In order to explore the tensile deformation characteristics and microscopic failure mechanism of the polyurethane elastomer,the stress-strain curve of polyurethane elastomer during uniaxial tension was analyzed.The results show that the deformation process contains four stages,quasi-elastic,plastic,hardening and slipping(fracture)regime.The influence of strain rate,temperature and pressure on the tensile process of polyurethane elastomer are calculated and analyzed.The results show that the internalstructure of polyurethane elastomer did not break at the end of the hardening deformation,only showing slippage between the molecules.With the increase of tensile rate,the yield strength and tensile modulus of polyurethane elastomer show an increasing trend,but decrease with the increase of temperature.