Effects of short-term thermal oxidation on the mechanical and thermal behavior of PA6 liner material for type IV hydrogen storage cylinders

The purpose of this study is to understand the changes in the performance of polyamide 6 (PA6) as a liner material under short-term thermal oxidation conditions. PA6 samples were subjected to oxidation at temperatures ranging from 90-150 °C for durations between 5-20 hours. Tensile, bending, and impact tests were conducted to evaluate changes in mechanical properties, while thermal analyses, including Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), and Differential Scanning Calorimetry (DSC), were performed to explore thermal stability and crystallization behavior. The results revealed that short-term thermal oxidation significantly influenced the ductility, tensile strength, and impact resistance of PA6, with marked decreases in these properties under higher oxidation temperatures and prolonged oxidation times. The material showed a clear embrittlement transition at 150 °C, with notable declines in tensile elongation and impact strength. The formation of carbonyl groups, particularly aldehydes and ketones, was accelerated by increased oxidation temperature and time, suggesting a correlation between thermal oxidation and chemical aging. Thermal analysis demonstrated a decline in thermal stability, characterized by reduced initial decomposition temperature (<i>T</i> _d5%), maximum decomposition rate temperature (<i>T</i> _dmax), and end decomposition temperature (<i>T</i> _end) with increased oxidation severity. Meanwhile, crystallinity and melting enthalpy increased due to partial recrystallization during the oxidation process. These findings highlight the sensitivity of PA6 to thermal oxidation, underlining the importance of controlling oxidative conditions to maintain material performance. The study suggests the necessity for thermal management strategies and antioxidant incorporation to enhance the durability of PA6 for hydrogen storage applications, where exposure to elevated temperatures is inevitable.