Effect of Dissolved Hydrogen on Polyamide 11: Observation During Hydrogen Desorption Process After Decompression at Atmospheric Pressure

ABSTRACT The effect of dissolved hydrogen on polyamide 11 (PA11) after decompression from a 90 MPa hydrogen gas environment was investigated. Structural analyses using wide‐angle X‐ray diffraction (WAXD) and Fourier transform near‐infrared (FT‐NIR) spectroscopy revealed no significant changes in the crystalline phase. Optical imaging and small‐angle X‐ray scattering (SAXS) also detected no visible or nanoscale internal damage (blistering). However, the flexural modulus () of PA11 decreased significantly after exposure, indicating reversible plasticization. The reduction in E f was found to correlate linearly with hydrogen concentration and is attributed to a temporary decrease in the glass transition temperature ( T g ) induced by dissolved hydrogen in the amorphous phase. Analysis of the equivalent volume generated by a single hydrogen molecule, together with the electron density correlation function (EDCF) of the SAXS patterns, suggested that penetrated hydrogen molecules create free‐volume‐like spaces that reduce intermolecular friction, thereby leading to the decrease in E f .