Thermokinetic studies of polyurethanes based on hydroxyl-terminated polybutadiene prepolymer

Three different polyurethane compositions were prepared based on hydroxyl-terminated polybutadiene (HTPB) prepolymer with different curative types. The employed curatives were hexamethylene diisocyanate (HMDI), isophorone diisocyanate (IPDI) and dicyclohexylmethane-4,4'-diisocyanate. These compositions serve as candidate binders for composite rocket propellants. TG/DTG experiments were executed to study the thermal decomposition behavior of the prepared compositions. Thermal analysis experiments were performed at four different heating rates 2, 5, 10 and 20 A degrees C min(-1) at temperature from ambient up to 500 A degrees C in a nitrogen atmosphere. The investigated compositions show two main decomposition stages: the first one from 300 to 420 A degrees C and the second one beyond 420 A degrees C. Two non-isothermal kinetic methods, Kissinger and Flynn-Wall-Ozawa, were employed to calculate the kinetic parameters of the decomposition for both stages. Results show that the order of thermal stability is HMDI-cured HTPB > IPDI-cured HTPB > H12MDI-cured HTPB over the range 300-420 A degrees C. This was manifested through the thermal analysis behavior and confirmed by the activation energy values calculated using the mentioned kinetic methods.