Closed-loop recycling of polyethylene-like materials

Plastics are key components of almost any technology today. Although their production consumes substantial feedstock resources, plastics are largely disposed of after their service life. In terms of a circular economy(1-8), reuse of post-consumer sorted polymers ('mechanical recycling') is hampered by deterioration of materials performance(9,10). Chemical recycling(1,11) via depolymerization to monomer offers an alternative that retains 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 above 600 degrees Celsius and recovering ethylene with a yield of less than 10 per cent(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 a recovery rate of more than 96 per cent. At the same time, the break points do not disturb the crystalline polyethylene structure, and the desirable materials properties (like those of high-density polyethylene) are fully retained upon recycling. Processing can be performed by common injection moulding and the materials are well-suited for additive manufacturing, such as 3D printing. Selective removal from model polymer waste streams is possible. In our approach, the initial polymers result from polycondensation of long-chain building blocks, derived by state-of-the-art catalytic schemes from common plant oil feedstocks, or microalgae oils(15). This allows closed-loop recycling of polyethylene-like materials. Polycarbonates and polyesters with materials properties like those of high-density polyethylene can be recycled chemically by depolymerization to their constituent monomers, re-polymerization yielding material with uncompromised processing and materials properties.