In this research, a group of segmented polyurethane (PU) copolymers with different hard segment (HS) contents were successfully synthesized. The microstructure of the PU copolymers was characterized via Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and small-angle neutron scattering (SANS). Then, the PU copolymers were selected as polymer binder for coating an insensitive high explosive 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) to prepare polymer bonded explosives (PBXs). When the HS concentration of PU copolymers increased from 14 to 34 wt %, a 14.6 times increase in the creep rupture time of PBXs under 60 °C/3 MPa and a 52.3% decrease in the steady-state creep strain rate under 60 °C/1 MPa were observed. The experimental results indicated that a wide variety of structure and properties of PU copolymer could be customizable through the adjustment of the HS contents, and consequently, provided an efficient route to tune the creep performance of the PBXs over a wide range.
As important parts in weapon systems, polymer bonded explosives (PBX) are often subjected to different external stimuli, e.g. compression, tension and impact during manufacturing, transportation and handling. Hence, sufficient mechanical property is necessary to ensure the security and reliability. However, weak interfacial interactions always restrict and weaken the properties of the PBX, especially for the mechanical property. Conventional surface modifications can hardly achieve a desired result, due to the inadequacy for solving the low surface energy, smooth and poor adhesive performance of high-quality explosives. To solve this problem, herein, we reported a novel multi-scale surface modification strategy of explosive crystals to strengthen interfacial properties. The surface of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) was in-situ grafted by a crosslinked high-strength polymer network consisting of hyperbranched polyurethane (HBPU) and graphene oxide (GO), which significantly improved the interfacial bonding, interlocking and mechanical strength of interface layer itself. Beneficial from this multi-scale surface modification, a high-efficiency mechanical enhancement of PBX was achieved. With only 0.5 wt% network content, the maximum tensile and compressive strength PBX composites were both significantly improved, which were 59% and 26% higher than those of pure PBX, respectively. This approach of constructing multi-scale surfaces aiming at low surface wettability and weak interface of explosives potentially provided a creative opportunity for design and fabrication of high performance PBX, and might raise potential of interest to the communities in energetic materials.
Herein, the effect of fluoropolymer binders on the properties of polymer-bonded explosives (PBXs) was comprehensively investigated. To this end, fluorinated semi-interpenetrating polymer networks (semi-IPNs) were prepared using different catalyst amounts (denoted as F23-CLF-30-D). The involved curing and phase separation processes were monitored using Fourier-transform infrared spectroscopy, differential scanning calorimetry, a haze meter and a rheometer. Curing rate constant and activation energy were calculated using a theoretical model and numerical method, respectively. Results revealed that owing to its co-continuous micro-phase separation structure, the F23-CLF-30-D3 semi-IPN exhibited considerably higher tensile strength and elongation at break than pure fluororubber F2314 and the F23-CLF-30-D0 semi-IPN because the phase separation and curing rates matched in the initial stage of curing. An arc Brazilian test revealed that F23-CLF-30-D-based composites used as mock materials for PBXs exhibited excellent mechanical performance and storage stability. Thus, the matched curing and phase separation rates play a crucial role during the fabrication of high-performance semi-IPNs; these factors can be feasibly controlled using an appropriate catalyst amount.
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