Ultra-high gas barrier composites with aligned graphene flakes and polyethylene molecules for high-pressure gas storage tanks

Despite polymers have great advantage in improving the energy density of hydrogen storage containers due to their lightweight characteristic, the production of high gas barrier polymers in a low-cost and high-efficiency manner remains a challenge. Here, polyethylene/graphene flakes (PE/GFs) composite films with ultra-high gas barrier properties were produced by no-boundary constraints hot-pressing method. Theoretical analysis showed that an extensional-shear coupled flow was generated inside the polymer melts and the shear-flow force near the polymer melts surface is always higher than that inside the melts during this process, which is responsible for the alignment of GFs and PE molecules. The DSC results indicated that the crystallinity of the composites after hot-pressing is increased by about 10%. The quantitative results of positron annihilation lifetime spectrum (PALS) showed that the fractional free volume of composites is reduced from 6.52 vol% to 5.43 vol%. As a consequence of the synergistic effect of the above aspects, the barrier performance of the composites has been significantly improved, and the helium leak rate of the composites reached an astonishing 3.92 x 10(-9) Pa.m(3)/s with only 0.5 wt% GFs, outperforming unoriented pure PE with a decrease of 98.6%. Moreover, the tensile strength and Young's modulus of the oriented composites were increased by 31.4% and 21.1%, respectively. The work presented here demonstrates that the simple, fast, and economical preparation method can be readily used to produce composites with superior barrier performance, which will provide great reference for the processing technology of hydrogen storage containers.

Automated summary

Polyethylene/graphene flakes composite films with ultra-high gas barrier properties were produced by no-boundary constraints hot-pressing method. The barrier performance of the composites has been significantly improved, with a helium leak rate reaching an astonishing 3.92 x 10(-9) Pa.m(3)/s. The tensile strength and Young's modulus of the oriented composites were also increased by 31.4% and 21.1%, respectively, showcasing potential for superior barrier performance in hydrogen storage containers.