Crosslinked PVA based polymer coatings with shear-thinning behaviour and ultralow hydrogen permeability to prevent hydrogen embrittlement

An economic transition from natural gas to a hydrogen economy will require redeployment of steel pipelines and other infrastructure. Mechanisms are urgently needed to prevent embrittlement of the steel in hydrogen service. In this work, we show that poly vinyl alcohol (PVA) and poly (ethylene glycol) diglycidyl ether (PEGDGE) crosslinked polymer materials can be used as internal coatings to dramatically reduce hydrogen permeation to the steel surface. Unlike other crosslinked PVA systems, these materials are shear-thinning and thixotropic, which is an essential requirement for facile, in situ application onto existing infrastructure. A hydrogen permeability of 0.01 Barrer is achieved, which is up to 100 times lower than commercially available coating materials. Experiments show that increasing concentrations of the alkali catalyst (KOH) do not impact the permeability of the crosslinked films but can benefit the rheology by shortening the reaction time. Higher reaction ratios of PVA to PEGDGE give lower hydrogen permeability due to a higher degree of polymer crystallinity, but less favorable rheology due to slower reaction kinetics. PVA with higher molecular weight gives lower hydrogen permeability and promotes shear-thinning behaviour, while PEGDGE with higher molecular weight increased the film permeability but enhances the shear-thinning behavior with shorter reaction times.