[ad_1]
The world is drowning in plastic. About 60% of the more than 8.7 billion metric tons of plastic that were manufactured are no longer used, but are primarily stored in landfills or released to the environment. That equates to more than 400 kg of plastic waste for each of the 7.6 billion people on the planet.
One reason for this is that many plastics are not recyclable in our current system. And even those that are recyclable still go to the landfill eventually.
Plastics cannot be infinitely recycled, at least without using traditional techniques. Most are only given a new lease on life before ending up on land, in the ocean, or in an incinerator. But there is hope in a different form of recycling known as chemical recycling.
Traditional physical or mechanical recycling generally crushes plastic into smaller pieces that are then mixed and molded to create lower quality plastic products. Chemical recycling, on the other hand, breaks down plastic at the molecular level, making “platform molecules” available that can then be used to make other materials. These are the first days for this idea, but, in principle, it could open up a wide range of opportunities.
Plastics are a broad classification of materials known as polymers, which are made of small “monomer” building block molecules made up primarily of carbon and hydrogen. The challenge of chemically recycling plastic is finding the right techniques to decompose and reconstitute the material into a variety of end products while minimizing waste.
All of this must be done productively, economically, on a large scale and without carbon emissions. The final solution should create less harm than the problem you are trying to solve.
The monomers that make up plastics can take a variety of shapes and sizes: some are straight lines, some are branched, and some have rings. How they bond determines the properties of the plastic material, including the ease with which they decompose, their melting temperatures, etc.
In the simplest terms, breaking chemical bonds is a matter of energy. Plastics are largely very stable materials, so they generally require a large amount of energy to break them down, usually in the form of heat to trigger a process called pyrolysis. You can have more precise control over decomposition using the right catalyst, a material that triggers the chemical reaction from a specific location in the polymer chain.
An example of a catalyst is the type of biological molecule known as an enzyme. These occur in living organisms and play a vital role in processes in the body such as digestion. There are up to 50 microorganisms known as “plastivores” that can digest plastic because they contain enzymes that help break it down.
But using these natural processes can be challenging because it must keep biological organisms alive, so they require very specific conditions, such as temperature and pH levels, and often take a long time to complete. However, with more research, they could be used commercially in the future.
Other catalysts can work fairly quickly. For example, my colleagues and I have shown that it is possible to use iron nanoparticles to help convert black plastic (one of the most difficult types to recycle) to carbon nanotubes in seconds. Then we were able to use this new material to build electrical components like data cables to transmit information to a speaker system to play music.
New techniques
There is a global effort in this growing field to develop new techniques. Research has shown that you can chemically recycle old cooking oil (a natural polymer) into a biodegradable resin for use in 3D printers. Other waste materials such as food, rubber, and plastics can be used to rapidly produce graphene (a one-atom-thick form of carbon). Scientists have also developed a way to repeatedly recycle bioplastics rather than allowing them to slowly biodegrade and release carbon dioxide.
Chemical recycling could complement mechanical recycling, especially for problematic materials in physical recycling such as thin films and microplastics. These become trapped in the grinding machinery due to their small size and strength, causing the entire system to jam, slow down, or even come to a complete stop and need cleaning. Mills cannot work on thin films, much less on microplastic materials that are hundreds of times smaller.
Many of these techniques have been demonstrated in the laboratory and there are several companies that now do it commercially. These processes require time, experience, and money. But until we stop using plastics, this is a growing field of opportunity for investment to develop a circular carbon economy through the use of chemical plastics recycling.
This article is republished from The Conversation by Alvin Orbaek White, Senior Lecturer, University of Swansea School of Engineering, under a Creative Commons license. Read the original article.
Crown coverage
Read our daily coverage on how the tech industry is responding to coronavirus and subscribe to our weekly Coronavirus in Context newsletter.
For tips and tricks on how to work remotely, check out our Growth Quarters articles here or follow us on Twitter.
[ad_2]
