Nanothermite composites with a novel cast curable fluoropolymer

Abstract

Structural nanoenergetic (SNE) composites consisting of nanothermites dispersed in a polymer binder are attractive for combustion applications due to their substantially higher volumetric energy, density, and tailorable energy release characteristics. Cast curing is an extensively utilized, safe, and economical method for processing energetic materials into structural composites possessing macroscale geometries. The use of cast curing as a route for processing SNE composites is limited by the lack of suitable binder systems. The widely used cast curable binder such as hydroxyl terminated polybutadiene (HTPB) if used for this purpose will render the SNE composites thermally non-ignitable. Fluoropolymers have emerged as energetic binders for aluminum containing nanothermites due to their capability to induce pre-ignition reaction and sustain the ignitability of composites. Herein, we report the synthesis of a novel cast curable fluoropolymer (FP) with 58 wt% fluorine content produced through the cationic ring opening polymerization of 3-Perfluorohexyl-1, 2-epoxypropane. We demonstrate the utility of the synthesized FP as a cast curable binder for aluminum/copper oxide (Al/CuO) nanothermite to prepare SNE composites. The SNE composites were cast cured as cylindrically shaped specimens with the FP content ranging from 30 to 50% by weight. All the SNE composites were observed to be thermally ignitable even under an inert environment, suggestive of the unique role of FP on promoting the ignitability of SNE composites. SNE composite containing 40 wt% FP recorded the highest energetic performance in terms of heat of reaction (880 cal/g) and pressure generation characteristics (pressurization rate = 3.81kPsi/s; time to maximum pressure = 340 ms). Additionally, the 40 wt% FP SNE composite generates time averaged combustion temperature of 2530 K as estimated by spectroscopic technique.