Oxidizability Enhancement of Hydroxyl Terminated Polyether Polyurethane Elastomers via Fluoroalcohols Grafting

Abstract

A series of fluoroalcohol grafted hydroxyl-terminated polyether (HTPE) polyurethanes (PU) elastomers were synthesized by a two-step method. The reaction progress was investigated by chemical titration and Fourier transform infrared spectroscopy (FTIR). The glass transition temperature (Tg), mechanical properties, morphology, and thermal decomposition behavior were determined for the preliminary analysis of PUs; the oxidizability property was tested by the decomposition of PU/Al composites. The results of mechanical and morphology properties demonstrated that the mechanical strength of modified PU elastomers was effectively improved for microphase separation of the hard segment. The PU film with the optimized fluoroalcohol content shows excellent performance of 17.7 MPa (tensile strength) and 547 % (elongation at break) at room temperature. Analysis of the thermal behaviors suggests that the oxidation ability of the modified PU is enhanced by the strong electronegativity of fluorine. The oxidizing gas HF, CF x , released during fluoroalcohol decomposition reacts with the alumina shell, releasing internal reactive Al, which improves the activity of the aluminum. This study might provide a new idea for utilizing high-performance polymer binders in composite solid propellants and casting explosives.

Enhancing energy release of aluminized propellants and explosives through fluorinated binder

“…In contrast, the combustion of P 1 generated fewer residues. According to our previous work [26], the decomposition of fluorine‐modified HTPE produces highly oxidizing fluorine fragments. These fragments react with Al to produce AlF 3 with a low boiling point, which serves to reduce the agglomeration of molten Al particles [29].…”

“…The P1 combustion products exhibited a lower number percentage of agglomerates (4.20 %) and mass percentage (42.17 wt%). According to the reported literature [17,24,25] [26]. However, given the low boiling point of AlF 3 (1275 °C), any formation is accompanied by evaporation into the gas phase, and no peak due to AlF 3 is observed in XRD analysis.…”

“…Ammonium perchlorate (AP, with two types of particle sizes, coarse: 111–170 μm, fine: 26–55 μm), cyclotetramethylene tetranitramine (HMX, coarse: 125–200 μm, fine: 20–56 μm), hydroxyl terminated polyether (HTPE), bis (2,2‐dinitropropyl) acetal/bis‐(2, 2‐dinitropropyl)‐formal (BDNPA/F, also known as A3) and N‐butyl nitroxyethyl nitramine (Bu‐NENA) were provided from Chongqing Hongyu Precision Industry Co., Ltd. Aluminum powder (Al, 99.0 % purity, D 50 =15 μm) was obtained from Yuanyang Aluminum Industry Co., LTD. Fluorine‐containing binder matrix (named HFN‐PU) was synthesized according to our previous study [26].…”

“…In contrast to P0, the P1 propellant undergoes a more complex process due to the presence of fluorine. The fluorine-modified HTPE binder can release HF directly and fluorine fragment ions, such as C x F y , during decomposition [26]. These high-active gases react with Al and the alumina shell to generate gaseous AlOF and AlF 3 , as illustrated by the following reactions:…”

“…In previous work [26], we synthesized a fluorine‐modified HTPE binder that exhibited promising application prospects. In this experimental study, we have replaced the HTPE binder with the fluorine‐modified binder and examined its effectiveness in propellants and casting explosives.…”