Characterizing Permeation Properties of Epoxy Resin for Enhanced Hydrogen Storage Tanks for Aviation Applications

This study investigates how different curing conditions affect the hydrogen gas permeation behavior of an epoxy resin system (LR285/LH287) certified for aerospace applications. The central research question addresses how the permeation coefficient of the material changes under varying thermal curing and postcuring regimes. To answer this, a dedicated experimental setup featuring a sample holder was developed. Unlike conventional tubular sample geometries, this design accommodates disc-shaped specimens, which greatly simplifies sample fabrication and handling. The influence of specimen thickness on the measured permeation coefficient and on the duration of the experiment was first evaluated to validate the test procedure. Permeation coefficients determined at 23 °C ranged from 6.55 × 10–16 to 7.24 × 10–16 mol s–1 Pa–1 m–1 with a scatter of approximately 4%. These values are in reasonable agreement with the few data points available in the literature, confirming that the developed setup is suitable for reliable measurements. The results also demonstrate that specimen thickness affects only the time required to reach steady-state permeation but not the intrinsic transport coefficient. In the second part of the study, the specimen geometry was kept constant while the curing and postcuring parameters were systematically varied. Temperature-dependent permeation data were evaluated using Arrhenius plots obtained from stepwise heating experiments. All specimens exhibited the expected Arrhenius-type increase of the permeation coefficient with temperature. Notably, slow curing at room temperature without subsequent postcuring led to the highest barrier performance against gaseous hydrogen. Increasing the curing temperature to 40 °C and applying postcures at 80 °C (RLB) or 100 °C (RLC) resulted in higher permeability, indicating a reduction in barrier effectiveness. This trend contrasts with the differential scanning calorimetry results, where samples with higher postcuring temperatures exhibited higher glass transition temperatures (Tg). Thus, while higher curing and tempering temperatures improve the thermal stability and mechanical robustness of the resin, they simultaneously diminish its gas barrier properties. Overall, the findings highlight a trade-off between thermal/mechanical optimization and hydrogen impermeability in aerospace-grade epoxy systems.