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Current research on the compatibility between plastic liners utilized in Type IV high-pressure hydrogen storage containers and hydrogen remains insufficiently comprehensive. Therefore, further exploration into how the high-pressure hydrogen storage process influences the crystalline phase transition of polymers is essential to improve the applicability and safety of plastic lining materials. This study primarily investigated the preparation of polyamide 1012 (PA1012) and polyamide 11 (PA11) through rotational molding and injection molding, denoted as Roto-PA1012/Roto-PA11 and In-PA1012/In-PA11, respectively. Considering the operational parameters of the 70 MPa Type IV hydrogen storage tank, we conducted hydrogen cycling experiment using the long carbon chain polyamide (LCPA) liner materials and comprehensively analyzed the morphology, crystal structure, grain size, mechanical properties and hydrogen barrier properties of polyamide materials before and after hydrogen cycling. The results showed that after hydrogen cycling, no significant changes were observed in Roto-PA1012/Roto-PA11, while In-PA1012/In-PA11 demonstrated severe foaming. Rotational molding of LCPA maintained stable mechanical and hydrogen barrier properties throughout the hydrogen cycle, which can be attributed to the favorable thermodynamic stability of the α' form achieved during rotational molding, leading to uniform and stable crystal sizes. In conclusion, this study provides a theoretical foundation for future investigations into the molding process and material selection of high-barrier polymer liners, as well as the actual production and utilization of Type IV hydrogen storage tanks. • This research examines the effects of hydrogen circulation on the properties of long carbon chain polyamide (LCPA). • LCPA produced through rotational molding demonstrates better hydrogen compatibility compared to injection molding. • The study explores structural changes in LCPA during hydrogen absorption and desorption. [ABSTRACT FROM AUTHOR]

Weak interfacial bonding properties between thermoplastic liners and carbon fiber‐reinforced composites (CFRP) can easily lead to debonding failure, which is a major challenge in development of type IV composite hydrogen storage vessels. We optimized Box–Behnken design atmospheric‐pressure plasma process parameters for maximizing interfacial bonding properties between thermoplastic liner (PA11 liner) and CFRP using Design‐Expert software. From various designs, plasma process parameters, including time (t), nozzle‐to‐specimen distance (d) and gas flow rate (r) of treatment were selected for optimization to assess the effects of their interactions on climbing drum peel (CDP), flatwise tensile (FWT) and asymmetric double cantilever beams (ADCB). The CDP strength, FWT strength and strain energy release rate (GADCB) of untreated samples were 4.2 N·mm/mm, 0.26 MPa and 87.2 J/m2, respectively. After the plasma treatment, optimum process parameters of t = 200 s, d = 12.5 mm, and r = 700 L/h were used to achieve 33.8 N·mm/mm, 2.97 MPa and 1008.4 J/m2, respectively, which were 8.0, 11.4 and 11.6 times that of untreated PA11 surface, respectively. This method has the potential for guiding thermoplastic liner surface treatment of type IV hydrogen storage vessels before winding. [ABSTRACT FROM AUTHOR]

The rapid development of hydrogen fuel cells has been paralleled by increased demand for lightweight type IV hydrogen storage vessels with high hydrogen storage density, which raises the performance requirements of internal plastic liners. An appropriate manufacturing process is important to improve the quality of polymer liners. In this paper, DSC, WAXD, a universal testing machine and a differential pressure gas permeameter were used to investigate the effect of the cooling rate of the rotational molding polyamide 11 on the thermal, crystallization, mechanical and barrier properties. The cooling rate is formulated according to the cooling rate that can be achieved in actual production. The results suggest that two PA11 liner materials initially exhibited two-dimensional (circular) growth under non-isothermal crystallization conditions and shifted to one-dimensional space growth due to spherulite collision and crowding during the secondary crystallization stage. The slower the cooling process, the greater the crystallinity of the specimen. The increase in crystallinity significantly improved the barrier properties of the two PA11 liner materials, and the gas permeability coefficient was 2-3-fold higher than at low crystallinity. Moreover, the tensile strength, the tensile modulus, the flexural strength, and the flexural modulus increased, and the elongation at break decreased as the crystallinity increased. [ABSTRACT FROM AUTHOR]