The mechanical properties of HTPE/PEG interpenetrating polymer network (IPN) binders were systemically studied with molecular dynamics (MDs) simulations and experiments. In this study, an algorithm was used to construct the crosslinking interpenetrating polymer network models and then the mechanical behaviors of Hydroxyl-terminated polyethylene glycol-tetrahydrofuran co-polyether/poly ethylene glycol (HTPE/PEG) IPN models were analyzed at a molecular scale. Firstly, glass transition temperatures (T_g), mean square displacement (MSD) and mechanical properties of IPN crosslinked model simulations showed that better thermomechanical parameters appeared at low temperatures, which were in good agreement with the experimental methods, including dynamic mechanical analysis and uniaxial tensile. Then bond-length distribution was performed to verify the crosslinked structures between prepolymers and curing agents. FTIR-ATR spectra analysis of four IPN binder specimens also gave a convictive result to the special interpenetrating polymer network of polyether polyurethane binders. Cohesive energy density and friction-free volume explained how the micro-structures of IPN crosslinked models and the force of inter-molecule chains affected the mechanical behaviors of the HTPE/PEG polyurethane matrix. Lastly, the morphology of IPN binder specimen tensile fracture indicated the mechanism at different temperatures. These studies were helpful in understanding the mechanical properties of HTPE/PEG interpenetrating polymer network binders and provide molecular insight into mechanisms of mechanical behaviors, which would guide the property improvement of HTPE propellant.

The mechanical properties of HTPE binders have been systemically studied through combining the microstructure molecular simulations with macroscopic experiments. In this study, the crosslinking structures of HTPE binders were established by a computational procedure. Based on the optimized crosslinking models, the mechanical properties and the glass transition temperatures (T_g) of HTPE/N-100, HTPE/HDI, HTPE/TDI, and HTPE/IPDI binder systems were simulated; specifically, the T_g were 245.758 K, 244.573 K, 254.877 K, and 240.588 K, respectively. Then the bond-length distributions, conformation properties, cohesive energy densities, and fraction free volume were investigated to analyze how the microstructures of the crosslinking models influenced the mechanical properties of HTPE binders. Simultaneously, FTIR-ATR spectra analysis of HTPE binders proved that the special peaks, such as -NH and -NCO, could be seen in the crosslinking polyurethane structures synthesized between prepolymers and curing agents. The dynamic mechanical analysis was carried out, and it found that the T_g of HTPE/N-100, HTPE/HDI, HTPE/TDI, and HTPE/IPDI binder systems were −68.18 °C, −68.63 °C, −65.67 °C, and −68.66 °C, respectively. In addition, the uniaxial tension verified that both the ultimate stress and Young’s modulus of HTPE binder systems declined with the rising temperatures, while the strains at break presented a fluctuant variation. When it was closer to glass temperatures, especially −40 °C, the mechanical properties of HTPE binders were more prominent. The morphology of the fractured surface revealed that the failure modes of HTPE binders were mainly intermolecular slipping and molecular chain breakage. In a word, the experimental results were prospectively satisfied using the simulations, which confirmed the accuracy of the crosslinking models between prepolymers and curing agents. This study could provide a scientific option for the HTPE binder systems and guide the design of polyurethanes for composite solid propellant applications.

In this study, the crosslinking structures of nitrate ester plasticized polyether (NEPE) binders were constructed by a computational procedure. Based on the final crosslinking models, the glass transition temperatures, mechanical properties, and thermal expansion coefficients of polyethylene glycol400/multi-functional isocyanate (PEG400/N-100), polyethylene glycol400/toluene diisocyanate (PEG400/HDI), polyethylene glycol400/hexamethylene diisocyanate (PEG400/TDI) and polyethylene glycol400/isophorone diisocyanate (PEG400/IPDI) models were simulated by molecular dynamics, and could be confirmed by experiments. Then the bond-length distributions, conformation properties and cohesive energy densities were used to analyze in detail how the different cured structures influenced the mechanical and thermal properties. Furthermore, the radial distribution function, mean square radius of gyration, volume shrinkage and fraction free volume were calculated, which could directly explain the relationships between the intermolecular chains and macroscopical properties of the NEPE binders. Lastly, PEG400/N-100 and PEG400/HDI systems were chosen for the experiments. The dynamic mechanical analysis results explained that PEG400-HDI showed better flexibility and its T_g value was 45 °C lower than that of PEG400-N100. The mechanical properties illustrated that the ultimate tensile strength and Young's modulus of PEG400/N-100 were both to an extent higher than that of PEG400/HDI in the temperature range of −40 °C to 50 °C, according to the results provided by a universal tensile test machine. The experimental results were in good agreement with the simulation analysis. This work can help us to have an efficient comprehension on the crosslinking structures and micro-property relationships of the NEPE binders and act as a guidance for designing applicable polyurethanes in propellant applications.