The most common way plastics are recycled at the moment is mechanical recycling. This is where plastic waste is cleaned, melted and reformed into plastic pellets which can then be reformed into new products. Sounds great right? BUT...there’s a small problem. The intense heat and grinding of the plastic during the recycling process damages the material. This means that a lot of the plastic mechanically recycled cannot be used for its original purpose again. For this reason, mechanical recycling is also called “open-loop recycling” or “downcycling” as the plastic being damaged each time it’s recycled means that it will eventually become unusable and be sent to landfill or incinerated (which isn’t great really).
Chemical recycling is an opportunity to change this. Chemical reactions can selectively cleave the bonds in a polymer, breaking it down in a “gentler” way compared to mechanical recycling. The really important advantage chemical recycling has over mechanical is that it produces the original monomers that make up the polymer. A plastic can then be rebuilt from these monomers, making it possible to product plastic of as good quality as the original material fed into the recycling process. Chemical recycling is also known as “closed-loop recycling” because you can put a waste plastic in and produce a recycled plastic of identical quality out the other end, meaning it can be re-used for the original purpose. Sounds great right? BUT...there’s a small problem.
Chemical recycling is still very new, which means that there is still a lot of work to do. Researchers have found ways to chemically recycle lots of polymers: polyesters, polyurethanes, polystyrene and polycarbonates, but each individual polymer needs a different mix of chemicals to break it down. Throw in the fact that many plastics are made up of more than one polymer, and many also have additives included too, and it becomes obvious why there is still a reliance on mechanical recycling.
However, I am of the belief that chemical recycling will become increasingly important as we move towards the future. Last week I attended the Global Research and Innovation in Plastic Sustainability conference (GRIPS). I had the chance to see some exciting innovations currently happening in the chemical recycling field. The current preference for mechanical recycling arises from the fact that a lot of infrastructure already exists for it, and chemical recycling hasn’t become cheap enough to disrupt the current system. Just to be clear I’m not bashing mechanical recycling; I just think chemical recycling will be really important moving forward.
My PhD project will involve finding new ways to chemically recycle polymers (so yes, I am biased), hopefully in a way that will simplify the process, which could be quicker and cheaper than what’s been done so far. I’ll keep you posted.
Brad