Metal fuels such as aluminum (Al) have 3 times higher energy densities than the most powerful explosives - making Al particles the most commonly employed additive in energetic materials. Nanoscale metallic fuels have shown to be as much as 1000 times more reactive due to their high surface area to volume ratio. Unfortunately, due to significant sintering that occurs on a time scale often shorter than the combustion time, the initial nanoscale fuel is transformed into microscale particles. This increase in particle size slows down energy release rate and minimizes the advantages of employing nanoscale mtals. Strategies to mitigate this problem while showing considerable requires subsequent processing.
Prof. Zachariah and his team have developed a novel approach that utilizes a chain-unzipping polymer as a binder for energetic composites. The polymer (polypropylene carbonate - PPC) decomposes primarily through sequential monomer depolymerization. The strategy localizes the heat feedback to near the reaction front by driving the endothermic chemistry of unzipping. This then liberates the gas near the flame front and propels particles away from the burning surface to minimize agglomeration and sintering. The unzipping polymer decomposes into volatiles at a relatively low temperature which significantly reduces the sintering.
Conceptualization of unzipping versus traditional polymer binder.
Flame front temperature map and corresponding schematic of composites with PPC (on the left) and HPMC/PVDF (on the right).
The developed composite samples demonstrate:
Applications that use energetic materials such as propellants, solid fuels, thermites, etc.