A density functional theory study of the structural and electronic properties of pure and H2 doped polyethylene under high pressure and high temperature conditions of earth layers

Plastics have brought enormous conveniences to our everyday lives, but at the same time, they are causing detrimental environmental impacts. Plastics have recently been discovered in deep ocean trenches—proving their capabilities of traveling into the Earth’s inner layers. Of these plastics, polyethylene enjoys commercial popularity and widespread applications. We systematically study polyethylene at various pressures and temperatures to figure out its physical and chemical stability and further on its degradability, by performing first-principle calculations in the frame of the density functional theory. Results show that lattice constants and bond lengths decrease under high pressure applications, while marginal increases occur under high temperatures. The effect of the dopant H2 is also evaluated due to its abundance within the inner layers of the Earth. Our relaxation calculations show that H2 doped polyethylene exhibits greater decrease rates in structural parameters. The electronic structures of both the pure and doped polyethylene illustrate metallic transitions at pressures around 140 GPa, which is in good agreement with other theoretical studies. Throughout this paper, atomic and electronic structure changes under high pressures and temperatures are analyzed and discussed in more depth. We conclude that high pressure and temperature applications are potential factors that can be considered for future sustainable degradation methods.