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by Matthew JonesAnd University of Bath And Jack PayneAnd University of Bath
It is impossible to imagine everyday life without plastic. Lightweight, durable and cheap, this material outperforms many other materials in Variety of applications.
Plastics have brought about positive change in ways that we often overlook. For example, developing plastic components in electronic devices, like the one you’re using to read this article, means that we’ve never been more connected to the world around us before.
But our love for plastic has come at an environmental cost. It was estimated that from 8.3 billion tons of plastic Between 1950 and 2015, more than 75% is now waste, with 79% accumulating either in a landfill or in the natural environment.
For scale, this is more than All living things On Earth and our oceans Drowning in plastic. For this reason, recent research efforts have focused on addressing these growing environmental concerns. One of these is chemical recycling.
Plastic value
To overcome the huge environmental concerns caused by plastic, we need to start evaluating plastic waste as a resource. After all, plastic waste contains value in the form of stable chemical bonds, so at least we should try to recover that energy. In fact, it is the stability of these bonds that is the reason why plastics remain so long in the environment.
In addition to burning plastic to recover this energy, we can also recycle plastic. The world is currently relying on Mechanical recycling, Where the plastic is sorted, melted and reshaped to mainly produce low grade plastic products. But this process is limited. The harsh conditions involved mean that every time a piece of plastic is recycled, its performance characteristics are adversely affected. This limits the number of times a piece of plastic can be recycled.
To make sure plastic retains its value in the long term, we need alternative recycling strategies. Chemical recycling It provides infinite recycling potential. But the challenge is to achieve it in a sustainable and economical manner on a large scale. Traditional methods are usually expensive and consume a lot of energy or resources, which has limited their widespread use.
Chemical recycling
Plastic consists of long-chain molecules known as polymers, which are made up of smaller, repeating building blocks called monomers. These monomers come in different shapes and sizes, and the bonding between them determines the properties of the plastic – such as its melting temperature and durability – which affects the way it is used.
While mechanical recycling involves smelting, chemical recycling relies on chemical transformation and thus breaking the bonds between monomers. Chemical recycling breaks down plastic at A. Molecular level. This means that The monomer can be recovered In what is called closed recycling, or plastic waste can be converted to another High value chemicals In open loop recycling. For many plastics, it is possible to recover monomers or other useful substances.
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Some plastics, such as polyolefins – the material in a polyethylene plastic bag – do not have weak single bonds, making them difficult to recycle chemically. In such cases, a A process called pyrolysis It is a different process from incineration, and relies on high reaction temperatures to produce fuel and wax.
Catalysis
Catalysts are used throughout 90% of industrial chemical processes. They make the process more efficient by providing the reaction in an alternate way, much like how Google Maps improves your journey. It can also allow us to be selective about the product being created and reduce waste. These benefits are essential to ensuring that the chemical can be recycled sustainably and economically on an industrial scale.
The enzymes that were working tirelessly during your last meal are naturally occurring stimuli that play an important role in digestion. Enzymes can Cracking plastic Has been reported.
However, these processes are limited By their productivity And require Specific practical conditions – such as the right temperature and pH – to maintain enzyme activity. But given the speed at which this field is advancing, the use of naturally occurring stimuli may be commercially viable in the future.
We have developed high efficiency Metal catalysts For the chemical recycling of polylactic acid (PLA), a plastic made from plant starch. This work used abundant inexpensive minerals – such as zinc or magnesium – that target chemicals called lactate esters, which are A possible green alternative For petroleum solvents.
This area is still in its infancy, but we expect important developments, particularly in process improvement, as the field gains momentum. This is actually a general endeavor in this area because conventional methods typically use harsh chemicals, and they can be resource- and energy-intensive.
Outside of PLA, there is a possibility to “update” other plastics, such as Polyethylene terephthalate (PET), Which is used for plastic bottles. Recent examples include The building blocks for high performance materials And Antibiotics and corrosion inhibitors From PET waste.
Our Last work He also investigated the chemical recycling of PET, which is being used on a much larger scale. PET is widely used in plastic bottles and food containers, while PLA occupies a much smaller market share, and is mostly used for 3D printing, biomedical devices, and certain packaging applications.
I look forward
Because societies use diverse plastics, a one-size-fits-all approach is not possible. Diverse and tailored recycling strategies are needed for existing and new emerging plastics. However, Chemical recycling operations on a commercial scale slave-woman.
In the future, we expect chemical recycling to complement its mechanical counterpart, especially for hard-to-recycle materials like Thin films. One thing is for sure, plastic is here to stay. With production expected to exceed Billion tons by 2050Recycling of chemicals promises to be an exciting space to watch.
Matthew Jones, Professor, Department of Chemistry, University of Bath, University of Bath And Jack Payne, PhD candidate, Center for Sustainable and Circular Technologies, University of Bath
This article was republished from Conversation Under a Creative Commons license. Read the The original article.
Top photo: Mountains of Plastic. Shutterstock / Mohamed Abdel-Rahim
