Cross-linking network structures and mechanical properties of novel HTPE/PCL binder for solid propellant

A series of cross-linked hydroxyl-terminated polyether and poly(ε-caprolactone) HTPE/PCL binders were prepared by varying the relative mass contents of PCL to HTPE. The correlations between the microstructures and macroscopic mechanical properties of HTPE/PCL binders at a wide temperature range of − 50 to 70 °C were investigated. The cross-linking network structures of HTPE/PCL binders were analyzed by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and low-field nuclear magnetic resonance (LF-NMR), and the universal testing machine was used to characterize the mechanical properties of HTPE/PCL binders. It is found that the influence of adding PCL on the physical cross-linking network structures is not obvious, but it reduces the degree of microphase separation. For the chemical cross-linking network structures of HTPE/PCL binders, the cross-linking density (V_e) demonstrates an increasing tendency with enhancing PCL mass content, but the molecular weight between the cross-linking points (M_c) shows an opposite change trend. The addition of PCL can improve the maximum tensile strength (σ_m) of HTPE/PCL binders under the wide temperature range of − 50  to 70 °C. The HTPE/PCL binder with 40 wt% PCL possesses the better mechanical properties; its σ_m increases from 0.63 to 0.81 MPa at 20 °C, 1.64 to 3.06 MPa at − 50 °C and 0.57 to 0.68 MPa at 70 °C separately comparing with the HTPE binder.