Insights into Chemical Recycling and Upgrading Strategies for Polyolefin-Based Plastics

Plastic waste, particularly the dominant polyolefins, presents a growing environmental issue due to its chemical stability and low recycling rates. Although various methods are proposed to address plastic waste, the strong carbon–carbon bonds within polyolefins, as well as the degradation of mechanical strength and additional value by conventional recycling methods, pose great challenges to their downstream usage. With this regard, this paper emphasizes the chemical recycling of polyolefins into renewable resources, including carbon materials, liquid fuels, and various hydrocarbon chemicals, by thermal catalytic methods. An in-depth discussion on the feasibility and limitations of promising chemical recycling techniques is provided, such as the association between the reactor design, process optimization, catalyst preparation, and the product distribution. Specifically, the structure–function relationship over different catalysts was highlighted, including the molecular sieve, precious metal, transition metal, and ion liquid. In addition, the future challenge regarding the simultaneous treatment of mixed plastics is also summarized, along with the copyrolysis of waste plastic and biomass. As such, this paper underscores sustainable and scalable solutions for polyolefin upcycling, which may shed light upon the industrial application of plastic resources.