Unzipping polymers significantly enhance energy flux of aluminized composites

Abstract

This paper describes a new approach to enhancing the energy delivery rate of pyrotechnics by employing an unzipping polymer. The basic strategy is to localize the heat feedback to just near the reaction front by driving the endothermic chemistry of unzipping. This should then liberate gas near the flame front and propel particles away from the burning surface, to minimize agglomeration and sintering. In this study, polypropylene carbonate (PPC) is employed to load 90 wt% Al and CuO nanoparticles (NPs) via direct ink-writing. The results show a >1500% faster energy release rate from the aluminothermic reaction compared to a conventional polymer binder. Through in-operando microscopy, we observed a 6X thinner flame front and smaller combustion products, revealing significantly lower agglomeration of Al NPs with the unzipping polymer. Fast-heating Time-of-Flight Mass Spectrometry confirms that the unzipping polymer decomposes to low-molecular-weight gasses at a relatively low temperature, which significantly reduces the sintering of Al NPs. The thinner flame implies that heat feedback to the unreacted materials is more localized and drives the endothermic unzipping reaction for gas generation. This study provides a new approach to substantially increasing the energy release rate of nanoscale metallic fuels.