Closed-loop recycling of polyethylene-like materials

Abstract

Plastics are a key component of virtually any technology today. Although their production consumes enormous feedstock resources, plastics are largely disposed of after their useful service life. In terms of a circular economy, 1-8 desirable re-utilisation of post-consumer sorted polymers ('mechanical recycling') is hampered by deterioration of materials performance. 9,10 Chemical recycling 1,11 via depolymerisation to monomer offers an alternative to retain high performance properties. The linear hydrocarbon chains of polyethylene 12 enable crystalline packing and provide excellent materials properties. 13 Their inert nature hinders chemical recycling, however, necessitating temperatures > 600 °C and recovering ethylene with < 10 % yield. 3,11,14 Here, we show that renewable polycarbonates and polyesters with a low-density of in-chain functional groups as break points in a polyethylene chain can be recycled chemically by solvolysis with > 96 % recovery. At the same time, the break points do not disturb the crystalline polyethylene structure, and the HDPE (high density polyethylene)-like materials properties are fully retained upon recycling. Processing can be performed by common injection moulding and the materials are well-suited for additive manufacturing. Selective removal from model polymer waste streams is possible. The virgin polymers result from polycondensation of long-chain building

Circularity in Mixed Plastics Chemical Recycling Enabled by Variable Rates of Polydiketoenamine Hydrolysis

“…Recycling efforts are further challenged when such products also include metals or glass, e.g., as complex assemblies bonded together using adhesives or fixtures (4)(5)(6). The inability to recover valuable chemical and materials resources from these products at end-of-useful-life is both wasteful and unsustainable (7)(8)(9)(10)(11)(12). Furthermore, the accumulation and leakage of non-recyclable mixedpolymer and mixed-material waste in the environment continues to strain global ecosystems (13)(14)(15)(16)(17).…”

The Novel Application of Asphalt in Cross-Linked Polyethylene Composite

“…2(a) show that they all have common characteristic bands: there are three strong absorption peaks at 2920cm − 1 , 1470cm − 1 , and 722cm − 1 , which belong to the expansion, bending, and swing vibrations of C-H, all of which are the infrared characteristic absorption peaks of polyethylene. And 722cm − 1 belongs to the absorption peak of amorphous PE [7], indicating that the WP-XLPE after S3M treatment has a de-crosslinked part. It is worth noting that as the number of milling cycles increases, there are obvious characteristic absorption peaks at 1740cm − 1 and 1240cm − 1 , which are carbonyl (-C = O) and C-O stretching vibrations, respectively.…”

“…Conventional direct incineration and land ll caused the leakage of waste liquid, the emission of waste gas, and pollute the land [7,8]. They are not in line with the current concept of sustainable green development [9].…”

Reversibly growing crosslinked polymers with programmable sizes and properties

“…Many strategies have been developed to build dynamic mechanisms into soft materials to enable them to reshape [20][21][22][23] , self-heal [24][25][26][27][28][29][30][31] , re-assemble [32][33][34] , be recycled [35][36][37][38][39] , change various properties 40,41 , etc. These material systems are sophisticated, but their transformations are predesigned and are not changeable beyond this design because the materials lack mechanisms to absorb external 'nutrients' to grow and to open new functions.…”