Life cycle assessment of chemical and mechanical recycling of polyethylene waste: enhancing the sustainability of chemical routes

Plastic industry plays an important role in modern society, but its growing production raises significant environmental concerns, particularly regarding end-of-life disposal. To solve these problems and create a circular economy, recycling is essential, This Master’s thesis investigates the environmental performance of high-density polyethylene (HDPE) waste recycling through a Life Cycle Assessment (LCA), comparing mechanical and chemical recycling (via pyrolysis). Two gate-to-gate systems were modeled in SimaPro, applying system expansion to account for the displacement of virgin HDPE and energy recovery from sorting residues. Environmental impacts were assessed using the ReCiPe Midpoint (H) method. The results show that mechanical recycling exhibits lower environmental impacts across most categories, particularly in global warming potential. This is primarily due to its lower energy requirements and the favorable substitution factor of 0.9 applied in this study. It should be noted that the environmental benefits attributed to mechanical recycling are highly influenced by this assumed substitution factor. On the other hand, chemical recycling despite its higher environmental impacts due to energy-intensive processes such as steam cracking and pyrolysis produces a high-quality output comparable to virgin HDPE. The sustainability of chemical recycling could improve significantly with the use of renewable energy as the result of the sensitivity analysis reveals that relying on renewable energy sources can significantly reduce the overall impact results; for example, the global warming impact of chemical recycling is reduced by approximately 21%. These improvements not only enhance environmental performance but also support alignment with circular economy principles by enabling the recovery of high-quality materials from plastic waste while minimizing emissions and resource use.