Enhancement of adhesion between the polymeric liner and the metallic connector of high-pressure hydrogen storage tank

The importance of manufacturing of hydrogen fuel tanks due to the application of hydrogen fuels in clean and recyclable energy is one of the most important issues of substituting the petroleum fuels. They consist of two main parts: Plastic liner, as a barrier escape of hydrogen and Carbon Fiber Reinforced Polymer (CFRP) layer to strengthen tanks. The liner plastic could be manufactured by rotational molding or blow molding. In rotational molding, the metallic boss embedded into the mold directly and stick on the polymer before wrapping step. However, in blow molding, the metallic boss is welded to liner polymer. By comparing these two methods, rotational molding demonstrates better feedback because of its capability in assembling boss and liner part, and also manufacturing the piece simultaneously, without the defect arising from welding. Moreover, improvement in the adhesion capacity of polymer to metal could be obtained by effective surface treatments. Therefore, good knowledge of adhesion concept could be useful in these regards. In this work, the possible treatments on Aluminum (metal) and medium density polyethylene (liner) which could be applied in rotational molding is proposed and the adhesion behavior of them has been compared. These surface treatments are anodizing, flaming, sandblasting with different average size of sand particles, and coating with polyethylene grafted (PEG) (CEA patent n°FR3035173). Despite of the mechanical test results, it was found that the sandblasting treatment (with higher roughness value) combined with PEG coating performed higher adhesion at the interface of metal/polymer in compare with other possible methods in rotational molding. Microstructures of these different surface treatments confirmed the obtained mechanical results.