Group contribution Modelling of hydrogen solubility in polyamides for hydrogen transport application

Green hydrogen is central to the energy transition, but its use in fuel-cell electric vehicles depends on storage at pressures up to 70 MPa in Type IV composite pressure vessels, in which a polymer liner provides the primary gas containment barrier. Permeation through that liner is governed by hydrogen solubility and diffusivity, so the amount of hydrogen the polymer dissolves controls both leakage in service and the damage associated with rapid gas decompression. Measuring solubility at these pressures requires blast-rated equipment and characterises one material at a time. This thesis develops a group contribution thermodynamic model that predicts hydrogen solubility in aliphatic polyamides from their chemical structure. It is built in three stages around the Sanchez-Lacombe equation of state. The equation is first fitted to pressure-volume-temperature data for twelve polyamides in the equilibrium melt up to 200 MPa, reproducing the measurements to a mean absolute percentage error of 0.17%. Each characteristic parameter is then expressed as a linear function of the structural ratio Rs, the number of amide groups per methylene group in the repeat unit, which collapses the thirty-six individual constants into six universal coefficients and reconstructs the same experimental surfaces with an overall error of 0.31%. The framework is finally extended to binary hydrogen-polyamide mixtures through the Sanchez-Lacombe mixing rules, with a single binary interaction parameter calibrated on the PA6 sorption isotherm at 298 K, and predicts solubility for the whole series up to 70 MPa. A comparison with PA11 measurements shows that the model overstates the spread of the family, so the predictions are to be read as a relative ranking rather than as absolute uptakes. The result is a structure-to-performance screening tool that needs minimal experimental input and reaches polyamides for which no high-pressure data exist, among them the bio-based PA4.10.