Improvement of mechanical properties of in situ-prepared HTPE binder in propellants

A new type of hydroxyl-terminal block copolymer (HTPE) binder with excellent mechanical properties was prepared using an in situ preparation method. Compared with traditional HTPE binder preparation, this method involves relatively simple operations, which not only reduces costs, but also does not require a complicated synthesis process to prepare the HTPE prepolymer intermediate. Thus, it is expected to replace the binder for HTPE propellants. The mechanical properties, crosslinking density, hydrogen bonding, and thermal performances of the prepared HTPE binders were investigated through tensile testing, low-field nuclear magnetic resonance (LF-NMR), Fourier-transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC) analysis. The ultimate tensile strength (σm) of the in situ-prepared HTPE binder was 1.83 MPa, the fracture elongation (eb) was 371.61%, and the strength increased by 80% compared to the HTPE binders. The crosslink density (Ve) decreased with an increasing content of PEG and/or TDI. The proportion of H-bonds formed by the imino groups increased with the content of PEG and TDI and reached 81.49% at PEG and TDI contents of 50% and 80%, respectively, indicating a positive correlation between the H-bonds and σm. Based on the statistical theory of elasticity, the integrity of the curing networks showed that the contents of PEG and TDI affected the integrity of the curing networks. The DSC data of the in situ-prepared HTPE binder showed a lower glass transition temperature. Finally, compared to HTPE propellant, the strength and elongation of the in situ-prepared HTPE propellant increased by 206% and 135%, respectively. This exciting result greatly enhances the feasibility of the in situ HTPE preparation method.