Curing Viscosity of HTPB-Based Binder Embedding Micro and Nano-Aluminum Particles

Aluminum is used as a metal fuel in energetic materials for the improvement of propulsion performance and density. Both nano-sized and micrometer-sized activated powders represent valuable options in order to improve metal combustion properties, each possessing advantages and drawbacks. These ingredients bear peculiar properties (namely, higher specific surface, coatings, or surface characteristics) which generate high mixing viscosity once suspended in a polymer as well as altered mechanical properties of the final product. Four different powders dispersed in a polymer binder are taken into consideration and the evolution of viscosity in time during the curing process is investigated. The suspending medium is represented by a mixture of hydroxyl-terminated polybutadiene (HTPB), isophorone diisocyanate (IPDI) and dioctyl adipate (DOA). Viscosity was measured for 5h on samples under isothermal curing at 60°C. Non-isothermal DSC kinetic analyses were also performed using the Kissinger method. It was found that, for the test conditions, a size reduction of metal particles slowed down the increment rate of curing viscosity while some peculiar coatings, such as fatty acids, introduced opposite trends.