Investigating the Aging Behavior of High-Density Polyethylene and Polyketone in a Liquid Organic Hydrogen Carrier

Hydrogen is recognized as a significant potential energy source and energy carrier for the future. On the one hand, storing hydrogen is a challenging task due to its low volumetric density, on the other hand, a particular type of hydrogen in the form of a liquid can be used to store large quantities of hydrogen at ambient conditions in thermoplastic tanks. But storing hydrogen in this form for a long time in polymer tanks affects the physical and chemical properties of the liner. In the current automotive industry, high-density polyethylene (HDPE) has already been used in existing fuel tank applications. However long-term exposure to fuels leads to the permeation of hydrocarbons into the polymers, resulting in a loss of mechanical properties and reducing the efficiency of fuel cells (FC) in automotive applications. Additionally, facing material shortages and a limited supply of resin leads to an increase in the cost of the material. Therefore, an alternative material is being searched for, especially for hydrogen fuel tank applications. In this study, two semi-crystalline thermoplastics, HDPE and polyketone (POK), were compared, which were exposed to a selected liquid organic hydrogen carrier (LOHC) at 25 °C and 60 °C for up to 500 h in an enclosed chamber, to measure their fuel up-take. A short analysis was carried out using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and mechanical testing to understand the influence of the LOHC on the polymer over time. Fuel sorption and tensile properties showed a plasticizing effect on HDPE. The material degradation was more pronounced for the aged samples of HDPE in comparison to POK. As expected, thermal aging was increased at 60 °C. The fuel absorption of POK was lower compared to HDPE. A slight increase in crystallinity was observed in POK due to the aging process that led to changes in mechanical properties. Both HDPE and POK samples did not show any chemical changes during the aging process in the oven at 25 °C and 60 °C.

Enhanced flame retardancy and toughness of eco-friendly polyhydroxyalkanoate/bentonite composites based on in situ intercalation of P-N-containing hyperbranched macromolecules

Polyhydroxyalkanoates (PHA) is a biodegradable polyester, and its application range is limited by the poor flame retardancy and low modulus. Bentonite (BNT) as a green inorganic filler can improve the modulus and flame retardancy of PHA to a certain extent. An in situ polymerization method was designed to intercalate P-N-containing hyperbranched macromolecules (HBM) among BNT layers (HBM-B) and to improve the flame retardancy while improving the dispersion of BNT in the PHA matrix. The layer spacing of BNT was increased from 1.2 nm to 4.5 nm. The effect law of the joint action of in situ intercalation of BNT and the HBM on flame retardancy and mechanical properties of PHA was systematically studied. The HBM-B showed stronger flame retardancy when the mass ratio of HBM to BNT was 75/25. The limiting oxygen index (LOI) of the PHA/HBM-B composite was increased to 27.6 % while maintaining good toughness. Compared to the physical blend of HBM and BNT (HBM/B), the elongation at break of PHA/HBM-B₂₅ composites can be increased by up to 10 times. When the content of HBM-B is up to 15 wt%, the LOI of PHA-Based composites can reach 29.6 % and the UL-94 rating reaches V-0, which meets the standard of flame-retardant material. Therefore, the present work is expected to expand the application of PHA-based composites in the field of flame retardancy.

Synthesis of a phosphoramidate flame retardant and its flame retardancy on cotton fabrics

A phosphoramidate flame retardant (dimethyl N,N-bis(2-hydroxyletheyl)phosphoramidate, DMBHP) was synthesized and applied to cotton fabrics for enhancing the flame retardancy. The structure of DMBHP was characterized by FT-IR and NMR. The flame retardancy and combustion behavior of the treated cotton fabrics were evaluated using the vertical flammability test (VFT), limiting oxygen index (LOI), and the cone calorimetric test. Moreover, to further analyze the flame retardant action of DMBHP in cotton fabrics, thermal degradability of the treated fabrics, as well as the chemical structure, surface morphology, and element contents of the char residue of the DMBHP-treated fabrics were also evaluated. The results show that, after treating with DMBHP, the cotton fabrics acquired a LOI value from 18.1 to 31.1 with the concentration increasing to 30% and self-extinguished in VFT tests when treated with up to 15% DMBHP. Besides, the total heat release and the peak heat release rate of DMBHP (30%)-treated fabric decreased obviously compared with the pure cotton along with more residue retained. TG, SEM, and EDS results of treated cotton fabric and the corresponding residue after burning showed that DMBHP has the capability of enhancing char formation. In addition, DMBHP will confer cotton fabrics a certain durability against washing with the help of 1,2,3,4-butanetetracarboxylic acid (BTCA) and citric acid (CA).