Depolymerization within a Circular Plastics System

Abstract

The societal importance of plastics contrasts with the carelessness with which they are disposed. Their superlative properties lead to economic and environmental efficiency, but the linearity of plastics puts the climate, human health, and global ecosystems at risk. Recycling is fundamental to transitioning this linear model into a more sustainable, circular economy. Among recycling technologies, chemical depolymerization offers a route to virgin quality recycled plastics, especially when valorizing complex waste streams poorly served by mechanical methods. However, chemical depolymerization exists in a complex and interlinked system of end-of-life fates, with the complementarity of each approach key to environmental, economic, and societal sustainability. This review explores the recent progress made into the depolymerization of five commercial polymers: poly­(ethylene terephthalate), polycarbonates, polyamides, aliphatic polyesters, and polyurethanes. Attention is paid not only to the catalytic technologies used to enhance depolymerization efficiencies but also to the interrelationship with other recycling technologies and to the systemic constraints imposed by a global economy. Novel polymers, designed for chemical depolymerization, are also concisely reviewed in terms of their underlying chemistry and potential for integration with current plastic systems.

Chemically Recyclable and Biodegradable Vulcanized Rubber

“…While the recycling conditions studied here are certainly not optimum for larger-scale operations due to the long reaction time, they can be easily improved by the use of a catalyst . Methanolysis of PET, for example, is usually performed with KOH as the catalyst at 180–280 °C and is still the topic of numerous ongoing studies. , Note that both the methanolysis of PET and dimer acid purification via distillation are established procedures on an industrial scale.…”

“… 34 Methanolysis of PET, for example, is usually performed with KOH as the catalyst at 180–280 °C 36 and is still the topic of numerous ongoing studies. 37 , 38 Note that both the methanolysis of PET 39 and dimer acid purification via distillation 40 are established procedures on an industrial scale.…”

Electrochemical recycling of polymeric materials

“…7a), which are extensively used as thermoplastic or thermosetting materials. 17 They find a wide range of applications from rigid/flexible foams to coatings, fibers, adhesives, and elastomers. 64,65 In Europe in 2017, the end-of-life management of this class of polymeric materials principally consisted of landfilling (0.9 Mt per year), incinerating (0.6 Mt per year) and recycling (mechanical and chemical, 0.5 Mt per year).…”

“…Polyesters and polycarbonates represent a major class of polymeric materials with versatile physical properties making them ubiquitous to a large range of applications from construction materials to medical applications. 17 Among the polyester family, PET is the third most produced and discarded plastic worldwide. 1 It is a semi-crystalline polymer and its thermochemical depolymerization has been widely studied.…”

Micelles Cascade Assembly to Tandem Porous Catalyst for Waste Plastics Upcycling

“…[11][12][13] As an alternative, catalytic cracking of polyolefins into their original monomers or value-added chemicals has recently been considered the most promising route. [14][15][16][17][18][19][20][21] Both homogeneous and heterogeneous catalytic systems have been designed and developed for the catalytic cracking of polyolefin recycling, facilitating the generation of a circular economy. [22][23][24][25][26][27][28][29][30][31][32] Thereinto, heterogeneous systems are more widely studied due to the easy separation of the fluid mixture from the catalyst, their large capacity and strong adaptability to industrially used processes and instruments.…”