Back-to-monomer recycling of polycondensation polymers: opportunities for chemicals and enzymes

Abstract

This review highlights the promising strategies developed to break down polycondensate polymers back to monomers using chemicals and enzymes. Our aim is to create a renewed awareness to valorize plastic waste into virgin plastics.

Fermentation for the production of biobased chemicals in a circular economy: a perspective for the period 2022–2050

“…hydrolysis or glycolysis) and for certain specific vinyl polymers like polystyrene (PS) and polymethyl methacrylate (PMMA) via pyrolysis. [330][331][332][333][334] The focus on back-to-monomer chemical recycling is based on the principle that mechanical recycling options (to initial application quality, such as food packaging) are limited for mixed, polluted, contaminated and or ( partially) degraded materials. Chemical recycling allows for (extensive) purification of the monomers, followed by de-novo production of virgin polymer for highly demanding applications, including food packaging.…”

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.…”

“…[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. [527] PET bottle waste is industrially available on a large scale, and only high-purity PET recyclate qualifies for reuse as food-contact material via back-to-monomer molecular recycling of PET by hydrolysis. As a result, methanolysis, glycolysis, and aminolysis have made significant progress as alternatives to mechanical downcycling.…”

“…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 ]…”

Precisely Tailoring and Renewing Polymers: An Efficient Strategy for Polymer Recycling

“…One most extensively studied method is the depolymerization of the plastic -back into their parent chemicals or valuable monomers, which could be repolymerized to virgin-quality polymers (so-called back-to-monomer recycling). [10,[16][17][18][19] This approach provides complements of the finite raw materials, and the polymers produced from recovered monomer exhibits no loss in properties. However, these processes are often energy consuming.…”