Hi! My name’s Brad and I’ve just started a PhD at the University of Nottingham, where I’ll be researching new technologies that can be used to recycle plastics. Most of the last few months have been filled by me reading about all the ways that we can recycle plastics, both now and how it could be done in the future. I’d like to share with you a little of what I’ve read so far.
If you’ve found the website this blog post is on, then you’re probably already familiar with the circular economy. It is really important to increase the amount of plastic we recycle, as we transition to a circular economy, because it is one of the most commonly used materials in the world. Toothbrushes, drinks bottles, the clothes you’re wearing right now-they all contain at least one, usually several, types of plastics and they will all end up in a bin at some point.
But what happens to it after going in the bin?
Most plastic that is recycled is processed through mechanical recycling. This involves breaking down plastic waste by shredding, grinding or milling, followed by melting the plastic and re-forming it. If you think this sounds like a rough ride for the plastic, you’re right. In fact, it’s so rough that the plastic can be slightly damaged, which presents a problem. Mechanical recycling is also called “downcycling”, as the plastic is often damaged and can only be used for a lesser purpose afterwards. For example, clothing can be so damaged by the shredding in its recycling process that is “downcycled” into mattress stuffing or industrial cleaning rags, instead of new clothes.
So, how can we make it better?
What we really need is a way to recycle plastic without seriously damaging it. By looking at the molecular structure of each plastic, we can work out ways to break it down in such a way that the material’s quality is retained. Plastics are made from a group of chemicals called polymers. Polymers are very long chains of repeating units, called monomers. The repeating nature of their structure means there is potential to break them down by targeting a specific chemical bond. This is known as chemical recycling, and the clear advantage of it over existing methods is that the recycled material is close to the original in quality.
Let’s consider water bottles.
Many of them are made up of a polymer called poly(ethylene terephthalate). Many different chemical systems have already been developed that break down the polymer to its monomers (BHET or MHET), and one particularly elegant system is able to do this and then reversibly reform the polymer, a perfect circular system.
Different methods have been found for many other plastics, so there is definitely a future for chemical recycling. There are still problems, like what to do with the chemicals after the plastic has been broken down, but a lot of work is going into tackling them. There are ideas that use special solvents, or no solvents at all, which I’ll probably write a little bit about in the future - and this is likely to be something which my PhD will involve in the future.
By the time I do my next bit of blogging, I will have written a review of the research going on which could go on for as long as 10,000 words. This makes me confident that there’ll be a lot more for me to say next time!