Ammonium dinitramide (ADN)-based hydroxyl-terminated polybutadiene (HTPB) propellant prepared by dimeryl diisocyanate (DDI)

Toluene diisocyanate (TDI) reacts with ammonium dinitramide (ADN), and isophorone diisocyanate (IPDI) adversely affects the thermal stability of ADN, which limits the application of ADN in hydroxyl‑terminated polybutadiene (HTPB) propellant. Due to the low toxicity and good physicochemical properties, dimeryl diisocyanate (DDI) is a good alternative for HTPB propellant. It was found that DDI is compatible with ADN, and HTPB/ammonium perchlorate (AP)/ADN/Al propellant cured by DDI was successfully prepared. Compared with HTPB/AP/Al and HTPB/AP/cyclotrimethylene trinitramine (RDX)/Al propellants, HTPB/AP/ADN/Al propellant has the lowest density, but the highest heat of combustion and theoretical specific impulse, which is related to the low density, high oxygen balance, high gas production and high energy of ADN. The addition of ADN promotes the low-temperature decomposition of AP in propellant, shortens the ignition delay time, and improves the burning rate and burning rate-pressure exponent. RDX and ADN have lower melting point and decomposition temperature, and release a lot of heat during decomposition, so it is easier to form a molten layer on the combustion surface, which promotes the Al agglomeration. However, the high gas production of ADN inhibits the Al agglomeration to some extent. The proportion of agglomerates in condensed combustion products of HTPB/AP/ADN/Al propellant is 5.11 % lower than that of HTPB/AP/RDX/Al propellant, and its size is also smaller. The Al content of condensed combustion products of HTPB/AP/ADN/Al propellant is nearly 1/3 lower than that of HTPB/AP/RDX/Al propellant. DDI is a curing agent suitable for ADN-based HTPB propellant, and compared with nitroamine explosives with negative oxygen balance such as RDX, ADN has many advantages in HTPB system.