Identification and mitigation of antioxidant induced rheological and ballistic anomalies in composite solid propellant processing and performance

Hydroxyl terminated‐polybutadiene‐based composite solid propellants are highly sensitive to variations in raw material quality and even trace impurities can adversely affect processing and ballistic performance. In the present study, an abnormal increase in slurry viscosity accompanied by burn‐rate suppression was observed during production of a composite solid propellant segment despite all major formulation ingredients meeting routine acceptance criteria. A systematic root‐cause investigation was undertaken to identify the origin of the anomaly and establish its impact on propellant processing and performance. A stepwise evaluation of raw materials, process variables and propellant properties indicated that the anomaly was associated with a specific lot of the antioxidant N ‐phenyl‐β‐naphthylamine (PBNA). Multi‐technique analytical characterization revealed the presence of sulfanilic acid, resin‐like oligomer, residual synthesis byproducts and elevated metallic impurities in the affected PBNA lot. These impurities were found to increase slurry viscosity without significantly altering cure kinetics and were also associated with reduced burn‐rate performance in catalysed propellant compositions. Controlled simulation trials confirmed that replacement of the affected PBNA lot restored normal rheological and ballistic behaviour, thereby establishing the critical influence of PBNA quality on propellant processing and performance. Based on the analytical findings, an improved purification strategy was developed and implemented at the vendor level. The purified PBNA exhibited substantially reduced impurity levels and successfully restored normal processing and performance characteristics in subsequent production batches. The study highlights the critical influence of trace level antioxidant impurities on composite propellant manufacture and demonstrates the importance of comprehensive impurity profiling beyond conventional qualification tests for ensuring process reliability and ballistic consistency.