Thermal degradation studies of a polyurethane propellant binder

The thermal oxidative aging of a crosslinked hydroxy-terminated polybutadie ne (HTPB)/isophorone diisocyanate (IPDI) based polyurethane rubber used as a polymeric binder in solid propellant grain, was investigated at temperatu res from 25 to 125 degreesC. The changes in tensile elongation, polymer net work properties and chain dynamics, mechanical hardening and density were d etermined with a range of techniques including modulus profiling, solvent s welling, NMR relaxation and O-2 permeability measurements. We critically ev aluated the Arrhenius methodology that is commonly used with a linear extra polation of high temperature aging data using extensive data superposition and highly sensitive oxygen consumption experiments. The effects of other c onstituents in the propellant formulation on aging were also investigated. We conclude that crosslinking is the dominant process at higher temperature s and that the degradation involves only limited hardening in the bulk of t he material. Significant curvature in the Arrhenius diagram of the oxidatio n rates was observed, This is similar to results for other rubber materials .