Amid mounting considerations over the state of the local weather and atmosphere, vital efforts have been spent creating progressive options to reduce plastic waste and capture carbon dioxide from the environment — most addressing one disaster at a time.
Nevertheless, researchers have lately devised a sustainable, closed-loop course of for producing and recycling polycarbonate plastic whereas additionally capturing carbon, successfully addressing the 2 challenges concurrently.
Typical plastics recycling is a mechanical course of that includes sorting, cleansing, and granulating the plastic into flakes earlier than heating it at excessive temperature, and never all plastics will be recycled on this means — although it’s extra environmentally pleasant than incineration or landfill disposal.
“Nevertheless, [mechanical recycling] has a important concern as a result of repeated publicity to excessive warmth may cause everlasting modifications within the chemical construction of the plastic, leading to poor-quality recycled plastics,” defined Hoyong Chung, a professor at Florida State College and scientist on the present study.
Utilizing lignin waste to make new plastics
The recycling methodology developed by Chung and his post-doctoral researcher, Arijit Ghorai, essentially differs from mechanical recycling. It includes changing polycarbonate into its unique constructing blocks in a course of referred to as depolymerization.
Key to this course of is lignin, a significant element of biomass which is now being acknowledged for its potential to not less than partially change fossil fuels within the manufacturing of plastics and different business merchandise owing to its renewability, broad market, and low price. It’s additionally a significant undesirable byproduct of the biofuel and pulp and paper industries, the place the latter generates roughly 50–70 billion tons of lignin yearly. A lot of this lignin goes to waste.
The “waste to wealth” idea isn’t new. Scientists have been turning every kind of usually discarded particles, similar to avocado pruning residue and metal shavings, into helpful merchandise like plastics and hydrogen gas.
Chemists have additionally identified for many years that carbon dioxide will be remodeled into polycarbonate plastics, however the conventional course of isn’t probably the most sustainable. Usually, carbon dioxide is reacted with fossil fuel-derived compounds, and the response not solely requires excessive temperatures and pressures — that means excessive vitality expenditure — but additionally meticulously designed steel catalysts, which provides complexity to the method and likewise financial prices, relying on the steel used.
To make this course of extra sustainable, Chung and Ghorai used lignin as an alternative of a fossil fuel-derived beginning materials in addition to a metal-free catalyst. Lignin is an effective different as a result of its chemical construction is wealthy in purposeful teams that may react with carbon dioxide within the presence of an acceptable catalyst.
This response, which the researchers catalyzed utilizing an natural molecule, produces cyclic carbonate, the constructing block or “monomer” of polycarbonate. The second step, the polymerization of cyclic carbonate into polycarbonate, will be completed at room temperature and regular atmospheric strain — a lot milder circumstances than these required for the standard synthesis.
By adjusting the catalyst, catalyst quantity, and response time, the properties of the plastic, similar to its thermal stability and energy, will be managed, permitting the polycarbonate to be custom-made for particular purposes. After its supposed use, it might then be recycled through depolymerization, the place the plastic is transformed again into its monomer.
A round plastic financial system
Chemical recycling, the umbrella time period for depolymerization and different applied sciences that convert plastic waste into its primary models to recreate the identical product, and chemical upcycling, which is the conversion of plastic waste into merchandise of upper worth, appear to be the lacking hyperlink in transitioning to a round plastics financial system.
Chung and Ghorai’s chemical recycling method was comparatively easy — to acquire the unique cyclic carbonate, they heated polycarbonate at 90 °C for 12 hours utilizing the identical natural catalyst to hurry up the depolymerization response.
“We are able to use these recycled monomers to resynthesize the unique, high-quality polymer,” Ghorai defined. “By adopting this methodology, we will keep away from any degradation in polymer high quality after recycling.”
“[Ideally], the developed polycarbonates are able to present process [repeated] closed-loop recycling with out compromising their unique properties,” he identified.
Ghorai and Chung confirmed by means of analyses that the properties of the recycled polymer have been similar to these of the unique, pristine polymer. Nevertheless, extra checks are wanted to find out what number of instances the polymer can really be recycled with out degrading.
The feasibility, security, and effectivity of the method additionally must be studied outdoors the lab on a a lot bigger scale, however the researchers hope it is going to finally be used to supply high-value chemical substances and specialised polymers for biomedical and energy-storage purposes.
“Within the brief time period, the polymer can be utilized for low-cost, short-term plastic merchandise in sectors similar to building, agriculture, packaging, cosmetics, textiles, diapers, and disposable kitchenware,” Chung mentioned.
The examine didn’t quantitatively assess how a lot carbon dioxide was captured by lignin, however the researchers instructed us these experiments are underway. In addition they plan to course of the polycarbonate — which they ready as a powder — into totally different types, similar to movies, for business use.
Regardless of the work that also must be completed, this examine demonstrates {that a} round plastics financial system for polycarbonate could possibly be attainable.
Reference: Arijit Ghorai and Hoyong Chung, CO2 and Lignin-Based Sustainable Polymers with Closed-Loop Chemical Recycling, Superior Practical Supplies (2024). DOI: 10.1002/adfm.202403035
Characteristic picture credit score: Claudio Schwarz on Unsplash
