Organic chemical devulcanization of rubber vulcanizates in supercritical carbon dioxide and associated less eco-unfriendly approaches: A review

There is a growing need to recover raw materials from waste due to increasing environmental concerns and the widely adopted transition to circular economy. For waste tyres, it is necessary to continuously develop methods and processes that can devulcanize rubber vulcanizates into rubber products wit...

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Bibliographic Details
Published in:Waste Management & Research 2022-05, Vol.40 (5), p.490-503
Main Authors: Gumede, Jabulani I, Hlangothi, Buyiswa G, Woolard, Chris D, Hlangothi, Shanganyane P
Format: Article
Language:English
Subjects:
Carbon Dioxide
Chemical agents
Circular economy
Environmental impact
Literature reviews
Mechanical properties
Motor Vehicles
Natural rubber
Organic Chemicals
Organic chemistry
Raw materials
Rubber
Rubber products
Tires
Toxicity
Waste materials
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Summary:There is a growing need to recover raw materials from waste due to increasing environmental concerns and the widely adopted transition to circular economy. For waste tyres, it is necessary to continuously develop methods and processes that can devulcanize rubber vulcanizates into rubber products with qualities and properties that can closely match those of the virgin rubber. Currently, the most common, due to its efficiency and perceived eco-friendliness in recovering raw rubber from waste rubbers, such as tyres, is devulcanization in supercritical carbon dioxide (scCO2) using commercial and typical devulcanizing agents. The scCO2 has been generally accepted as an attractive alternative to the traditional liquid-based devulcanization media because of the resultant devulcanized rubber has relatively better quality than other processes. For instance, when scCO2 is employed to recover rubber from waste tyres (e.g. truck tyres) and the recovered rubber is blended with virgin natural rubber (NR) in various compositions, the curing and mechanical properties of the blends closely match those of virgin NR. The atmospheric toxicity and cost of the commonly used devulcanization materials like chemical agents, oils and solvents have enabled a shift towards utilization of greener (mainly organic) and readily available devulcanization chemical components. This literature review paper discusses the approaches, which have less negative impact on the environment, in chemical devulcanization of rubber vulcanizates. A special focus has been on thermo-chemical devulcanization of waste tyres in scCO2 using common organic devulcanizing agents.
ISSN:0734-242X
1096-3669
DOI:10.1177/0734242X211008515