Ageing of Elastomeric Polyurethanes Based on Hydroxy‐Terminated Polybutadiene (HTPB) and its Service Life: A Short Review

This review examines the ageing and service life of hydroxy‐terminated polybutadiene (HTPB)‐based polyurethane elastomers used as binders in solid composite propellants. Ageing is primarily governed by thermo‐oxidative degradation of the unsaturated polybutadiene backbone, which proceeds via a free‐radical oxidation mechanism and leads predominantly to additional crosslinking within the polymer network. As a consequence, the material progressively hardens, showing reduced elongation and loss of elasticity, with degradation initiating at relatively low temperatures (60–80°C). The ageing behavior is strongly influenced by formulation variables, including polymer microstructure, NCO/OH ratio, hydroxyl functionality, and curing chemistry. Accelerated ageing studies typically predict service lifetimes ranging from 5 to 15 years at room temperature, while the incorporation of antioxidants is essential to delay oxidative degradation. Despite these advances, existing research remains fragmented across individual studies, highlighting the need for integrated structure–property–ageing correlations. Future research should therefore focus on diffusion‐limited oxidation modeling and formulation strategies that combine controlled microstructure with optimized antioxidant systems to improve lifetime prediction accuracy. Although this review does not address full propellant systems, it is important to note that binder behavior may differ due to compatibility issues among propellant ingredients.