Chemical upcycling of polymers

Abstract

As the production volume of polymers increases, so does the amount of plastic waste. Plastic recycling is one of the concepts to address in this issue. Unfortunately, only a small fraction of plastic waste is recycled. Even with the development of polymers for closed loop recycling that can be in theory reprocessed infinitely the inherent dilemma is that because of collection, cleaning and separation processes the obtained materials simply are not cost competitive with virgin materials. Chemical upcycling, the conversion of polymers to higher valuable products, either polymeric or monomeric, could mitigate this issue. In the following article, we highlight recent examples in this young but fast-growing field. This article is part of the theme issue 'Bio-derived and bioinspired sustainable advanced materials for emerging technologies (part 2)'.

Hydrogenative depolymerization of silicon-modified polyureas

“…The resilience and ubiquity of synthetic polymers (or simply ''plastic''), along with the high societal dependence on these materials, poses a paradoxical challenge, since they present a serious environmental threat, but their banning or full replacement with more benign alternatives is practically impossible. Thus, the development of technologies for recycling and upcycling of plastic waste has become increasingly important, [24][25][26] chemical recycling and depolymerization methods being particularly attractive. 27 In the case of polyureas, and particularly their silylated congeners, there are no reported methodologies for their end-of-life treatment or upcycling, and only very few methods for their depolymerization.…”

Closing the Carbon Loop in the Circular Plastics Economy

“…Several reviews have addressed back-to-monomer molecular recycling by thermal, chemical, and (bio)catalytic unzipping of polymer chains. [457,459,464,491,[511][512][513][514][515][516][517][518][519][520][521][522][523][524][525][526][527]72,79,80,82] Similarly to polymerization catalysis in industrial polymer manufacturing processes, depolymerization catalysis plays a key role in back-to-monomer molecular recycling. [80,468,491,515,526,528] In contrast to polymers such as polyolefins, acrylics, and vinyl polymers, all of which have hydrolytically stable C-C linkages in their backbones, polycondensation-and polyaddition-based polymers contain ester, amide, urethane, and carbonate groups that enable monomer recovery by hydrolysis and solvolysis.…”

“…Several reviews have addressed back‐to‐monomer molecular recycling by thermal, chemical, and (bio)catalytic unzipping of polymer chains. [ 457,459,464,491,511–527,72,79,80,82 ] Similarly to polymerization catalysis in industrial polymer manufacturing processes, depolymerization catalysis plays a key role in back‐to‐monomer molecular recycling. [ 80,468,491,515,526,528 ]…”

Integration of upcycling and closed-loop recycling through alternative cyclization–depolymerization

“…[7][8][9][10][11][12][13][14] Upcycling that converts end-of-life plastics to a product of higher quality or value than the original will be more acceptable by a market-oriented economy, hence improving the recycling ratio of waste plastics. [15][16][17][18][19][20] However, after the service period, the upcycled product will again face the end-oflife problem and may bring secondary pollution, leading to weak sustainability of the upcycling mode. Comparably, closed-loop recycling, which regenerates the same product with equal quality and value to the original polymer through a depolymerization-separation/purification-repolymerization process, is highly sustainable.…”