Polyolefins and Polystyrene as Chemical Resources for a Sustainable Future: Challenges, Advances, and Prospects

Abstract

Nonbiodegradable plastics with inert and saturated C−C backbones comprise the majority of global annual plastics produced, including the ubiquitous polyolefins (polyethylene and polypropylene) and polystyrene. Unlike polymers with cleavable bonds, such as polyesters, polyurethanes, and polycarbonates, these inert plastics are the most challenging to upcycle and cannot be easily broken down by chemical or enzymatic means. Thus, they mostly end up in landfills or are incinerated to produce copious amounts of greenhouse emissions. In recent years, increased research effort has been focused toward the upcycling of low-value plastic waste to give them a new lease of life. However, the unreactive C−C polymer backbones of these plastics have posed formidable challenges for attempts at post-synthetic chemical functionalization and conversion into commodity chemicals. In this Perspective, we discuss these inert plastics as large untapped resources for the production of new functional polymeric materials and valuable industrially relevant feedstock, such as dicarboxylic acids and aromatic compounds. The exciting pioneering work featured herein will hopefully inspire a change in the way we view these waste plastics from a chemical deadend to versatile raw materials, forming the basis of a more sustainable materials economy.

Sustainable chemical upcycling of waste polyolefins by heterogeneous catalysis

“…Different from the primary recycling, secondary recycling refers to mechanical recycling in which the recovered wastes are utilized to construct other products for different applications, achieving open-loop recycling. 16 The waste polyolefins always undergo the following steps 17 : (1) separation and sorting on the basis of the size, shape, density, and other properties; (2) baling and transport; (3) washing to remove the contaminants; (4) grinding to form the plastic flakes; (5) compounding and pelletizing to meet the converter standard; and (6) extrusion. In the extrusion process, the polymers can be plasticized or softened by the heat and rotating screws, followed by the production of fixed cross-section extrudate via the temperature-controlled barrel sections.…”

“…3,4 Present statistics and estimations indicated that the global plastic production reached about 360 million tons (Mt) in 2019, and the annual output of plastics by 2050 would exceed 500 Mt. 5 However, the service lives of most plastics are limited and usually below 1 month due to their disposable applications. This phenomenon leads to the excessive discharge of waste plastics.…”

“…Finally, we proposed the potential enhancement approaches for efficient and selective recovery of polyolefins in the view of polymer modification and the design of catalysis or catalyst. Compared to other published reviews, 5,[12][13][14] we highlight more investigations on the structure-performance relationships and the design of catalysis or catalysts, which are less discussed before. In addition, the comparison and discussion on different strategies from the perspective of a specific product can give some new insights and complementation for the catalysis and catalyst design.…”

“…Plastics are a crucial and indispensable component of modern society and human life, 1,2 and are widely used in agriculture, transportation, packaging, chemical, and construction industries due to their excellent physicochemical properties 3,4 . Present statistics and estimations indicated that the global plastic production reached about 360 million tons (Mt) in 2019, and the annual output of plastics by 2050 would exceed 500 Mt 5 . However, the service lives of most plastics are limited and usually below 1 month due to their disposable applications.…”

Expanding Plastics Recycling Technologies: Chemical Aspects, Technology Status and Challenges

“…to these polymers via chemical methods (e.g., oxidation, halogenation, esterification, metathesis etc.) [896][897] as depicted in Figure 49. The products include polymers with new properties, 898 liquid fuels, 899 waxes, 900 and platform molecules.…”