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hello and welcome to Technically Speaking where scientists and engineers come together to chat about a common interest share knowledge and satisfy some curiosity I'm Antonia and I'm joined by Laura to talk about a new process being developed to dissolve common plastics found in clothing So Laura why does this excite you uh well you know we talked about essentially we saw about glass recycling uh in an episode a little while ago and how glass isn't necessarily going to be included
in a deposit return scheme in the UK and we looked at how recycling glass compares to recycling plastic And I was astounded that they only use mechanical methods for recycling plastic not chemical ones This is a chemical method that's being developed And the difference between this and other methods is that it seems to be able to separate out lots of different fibers So you don't need to pre- sort your plastic You can just shove your clothing fibers in there and it goes to work in theory I
mean this is lab scale at the minute but chemical methods are like the holy grail of plastic recycling So it sounds like a really promising way to go Yeah separating does seem to be one of the challenges with recycling in general That might even include color Yeah exactly We've mentioned in episodes previously that plastics come in a variety of types and they have lots of different additives added to them can't say that word Things and this sounds like a process
that could get around a lot of that and not to mention just contaminants because people don't exactly keep their waste in a nice shelter It might not have been clean to start with So yeah if uh we can dissolve the plastic maybe we can actually recover and recycle more of it So should we look into this published research then yes So it came out I think it was summer last year and they essentially use a zinc oxide catalyst and ethylene glycol to turn poly ethylene tetrathalate or pet polyester
in clothing into another tetrathalate the monomer form of the polymer and they use some microwaves and some heat to make the reaction happen really efficiently They put clothing fibers in there mixed fibers Uh and the cotton and nylon weren't really affected by this process Although the nylon did degrade a little bit but they can still separate all these different components out I mean this sounds good to me cuz the first thing when you said zinc oxide I thought oh that's a fairly easy catalyst
and fairly cheap compared to some other processes which are catalyzed with say platinum not as cheap And this is why people like sealing catalytic converters from cars isn't it cuz of platinum Yes I have been a victim Ah story for another time Yes And ethylene glycol I think is antifreeze Oh okay So quite common as well Yeah And a microwave So what I'm learning here is could I do this at home um it's worth giving it a go isn't it yeah In the research article they use an
off-the-shelf microwave reactor So these are things that you would find in a lab So you use the microwaves to help you synthesize chemicals usually or break them down It would turn out It did have quite a tiny capacity and I don't know how much control you'd need over the um I don't know how you're applying the microwaves or how fine control over the heat you'd need You said it's a special reactor not not just a microwave And the tiny amount What how small amounts can I
can I put in it when I being a massive geek looked at the technical specs for the microwave reactor they were using Of course Yeah why not got to look up spec sheets 20 ml vials They were using just half a gram of textile material in 5 mil of ethylene glycol and five milligrams of the catalyst So really tiny amounts they were working with No reason why you couldn't stick that in your microwave at home I suppose Yeah maybe I'll be able to afford like 5 mg of very very good quality zinc oxide
not just stuff that was in my sunscreen I was going to say zinc oxidizing quite a lot of cosmetic products isn't it so could you just like stick some moisturizer in there with your antifreeze in your clothing i suspect there would be some safety implications of that I don't know what sort of fumes should be getting given off then There are like too many other components then aren't there if I just microwave moisturizer plus metal plus plus some fabric I think that might
start a fire Or maybe I mean you need to get it at a temperature I think they used 210° C for 15 minutes in their optimal reaction scheme So you'll need to get your components up to that temperature as well I don't know what temperature a microwave normally gets to because I suppose it's not really Yeah it's not really a controlled temperature thing It's just trying to vibrate water molecules and so however hot that gets Yeah So we usually want to boil water I
guess 100° so probably not hot enough I don't know I mean we should do some experiments I mean we are using tiny amounts here Half a gram of um material Um maybe I'll leave it to to someone with better resources better fume cupboards and things like that Makes sense Never mind the the home experiment Um let's go back to the actual research I think that would be quite a good idea All right Then when most research looks at just breaking down pure PET they did that But they also looked at what
happens when you take some just clothing they got from a charity shop or Goodwill and put that in their microwave reactor with these other chemicals And they looked at like the dyes that came off and whether different coatings on the fabric affected the efficiency of the reaction So they found that ones that were UV resistant or fire retardant didn't dissolve quite so well which kind of makes sense because they're putting this at 210° C so the fire retardant would [ __ ] any reaction Is that how
fire retardants work i've never actually thought about it Yeah I covered this with roa when we were talking about things to do with fire ages ago And um the chemicals that are used to treat fabrics they basically just kind of melt over the surface of the fabric preventing things from getting to it So if you've got a fire and you've got oxygen in the room feeding the fire the oxygen can't get to your flammable materials So yeah if you wanted to do any sort of reaction not just combustion
the fire retardant coating would be in the way Yeah So they did say there may have to be some pre-treatment when they eventually get on to doing this industrial scale So it may be that you don't just stick whatever your fabrics are in your process And out pops some monomers of your PET and some cotton fibers and some nylon and some elastane monomers You'd have to do a little bit of pre-treatment which is a little bit disappointing because the aim is you can just stick whatever you want in there
but it's a step beyond what people have done so far So it's a step forward Yeah And I was surprised because the difference was still a 95% yield if it was completely just undyed material and dyed made it 80 at most 70% Which is good But yeah the fire retardant um material down to 10% Definitely needs some work Yeah and they did say that the dyes tended to end up in the ethylene glycol which you could then separate them back out you could potentially reuse them as well I think slightly
disappointing is that you may not be able to use the cotton fibers to make new clothing afterwards Unsurprisingly the synthetics can all be broken down into monomers and then put back into a process again But the natural fibers they're degrading anyway as people use them in their clothing Every time you wash your clothes the fibers get a little bit more fluffy and fragile don't they so you would normally throw cotton containing clothing out once it's completely worn out Well I do Some
people don't At which point the cotton fib was probably in great shape anyway So when they go into this process and they're cut up and they're heated again they get slightly more degraded And I think they said in the research article in the discussion that there are other things they could be used for But I don't think they said they could just be used for fertilizer for cotton fields which to me seems really obvious So it would still be circular in that respect
I suppose if it's all degraded it's come out of this recycling process It's not just going to be cotton It's going to be slightly ethylene glycoly with a bit of dye at that point Is that something we want to throw on a cotton field to try and grow more cotton well I think they said that the cotton could be washed to remove the reaction product so you would get just cotton back Oh okay Well or maybe just where the recycling plant is just isn't where the cotton is growing
Maybe not They did say there are lots of uses for it and maybe that's why they didn't suggest using it as fertilizer for cotton fields cuz there's no guarantee it would make sense But the idea definitely is promising isn't it you know your material sorry your waste material becomes your feed stock Exactly Yeah Working towards an actual circular economy where the thing you recycle actually gets recycled back into the same thing So we stick in whatever fabrics and then we get the monomers of
the PET and then it could just be anything It could be a plastic bottle not just clothing potentially Yeah So you would use it for I guess whatever was needed most I mean you would think if you're being circular you turn it back into clothing but I guess there's no reason that you have to of people suddenly start buying fewer items of clothing whereas for some strange reason the use of single-use plastic suddenly keeps increasing when we're meant to be decreasing it I wonder would it make
synthetic fabrics more popular if you know it can be recycled or natural fibers because they're almost more one use because they're less high quality at that point Yeah I've had the same thought as well So I've been trying to minimize buying synthetic fibers and going for like just a cotton t-shirt rather than a cotton t-shirt with spandex in it because I can cut it up and put it on my compost heat potentially if it's been dyed using water-based dyes Um or I can send it
back to the company it's come from because they're like "Yeah bring send it back It's organic cotton We want to keep
using it." That's a cool initiative Yeah But you're right If synthetics become more circular and more reusable maybe I would switch to that My only question then is well what about microplastics so every time you wash your synthetics little fibers break off and end up in the water supply Well and this a big area of research isn't it it's not a lot of known about what it does in biological systems Yeah I suppose if it was a waste water could we put the waste water through the chemical recycling
process otherwise I've heard of research where enzymes had actually developed in bacteria that could break down plastic So chuck in some bacteria Yeah I've heard a few things about this as well And I imagine if it's in a waste water stream there's not a really high concentration of microplastics So I don't know how effective the enzymes would be or if you'd want to concentrate the microplastic somehow first to make the reaction more efficient suppose if you just wanted to break it down or did
you want to actually try and recover then yeah you would want to concentrate it just simply get a filter to capture whatever was there then you're still going to have a lot of different things in your waste water I think that's the challenge from what uh another episode from a long time ago from our water engineer Gari was saying that it's difficult to get them out because there are so many other things in there I'd come across this as a attachment to a washing machine so you can get it sort
of at the source It's a filter that you attach onto the drain of your washing machine and when the filter comes blocked it puts it into bypass mode So instead of going through the filter it will go out into the waist stream but then it will flash up to tell you to change filter And this company that's developed it wants it to be an entirely circular process You send them the filter and they will recover the fibers off it and try and turn it into something new Ah very nice I do wonder
how many people just wouldn't bother doing that Like the waste pipe from my washing machine is really difficult to get to I'm not pulling the washing machine out every single time I want to change the filter Yeah I I was thinking this if I got it for myself where would I even put it your washing machine is in the kitchen right like most British houses Well a really small utility room adjacent to the kitchen Not really got any extra space unless I knock down the
wall Yeah So so we're probably going to have to just park that filter for at least for us to imagine a cocktail of bacteria that you chuck in to your waste water One to get rid of some of the the organic waste um and produce you know your bio gases to use for energy And then maybe you get your plastic fibers out using a different bacteria and then we just have clean water right in the future far from now is what we're aiming for I would say it's not that far in the future because
this enzymebased technique does have a pilot plant and they've got 100% fiberto fiber bio recycled clothing line and they've done it with Patagonia Puma and some other brands So they've done it They've made a t-shirt out of an old t-shirt So they it's like 100% efficient if you say fiber to fiber There's no loss at all from that process No I think what they mean is they didn't have to use any virgin material to make it Okay But they started off like an extra large
t-shirt and they came out with a small t-shirt I suppose um maybe maybe that Yeah But it's gone So this this pilot plant has been going since 2021 and they're actually thinking of making one in the UK as well So they're expanding and they're making a actual industrial scale one in France And this is chemical recycling So this is using an enzyme Okay But it's still breaking the polymer down into monomers to then Yes remake your polymer Correct Yes So the enzyme
the bacteria has two enzymes Sorry One is the one that breaks down PET so PET A And then that produces MH And the second enzyme is an MHA Aas And it produces ethylene glycol and terraic acid Okay So it's a two-step process That sounds like it could take a fair amount of time You would be correct It is a bit slow In one of the papers I read it took a few hours to convert like 9 g Okay Whereas this new research using the microwaves takes 15 minutes although it was only half a gram I don't know if
you'd scale it up if it'd still be 15 minutes still Well what um amazing other researchers have done is they got the structure of that bacteria which was Idonella psychis 2011 F6 Well that is a very exciting name Yeah you hear the sarcasm in my voice Call it Bob or Chris or something or Danny Yeah maybe there would be too many Danny's because they basically modeled it and then altered it so it would be faster So then what do they call that danny but faster Danny fast I don't know
Danny Danny go fast Yeah And then Danny gets super fast Danny Sonic Yeah I'm sure you could do some sort of video game type progression of your bacteria Level one Level two So yeah it it definitely was more promising that they could make it faster essentially whereas I think for chemical processes it's just make it hotter Yeah And then I guess you run into things like um I think this process that I was reading about at 210° C Um I think that's like the point at
which the nylon starts to break down or melt which isn't that great And then it got in the way I guess I think so Yeah and it turned this kind of goo that had to be separated out somehow which meant the nylon was degraded which then means you need to do more processing but it's all just chemicals right so you can develop a process to deal with most chemicals I think yeah yeah I was also under the impression that techniques that use um bacteria or enzymes they
don't work quite so well if you've got mixed fibers in there I can imagine that the enzyme or the bacterium likes to sit on a surface and if it's sitting on the surface of some ponds It's not going to do its job to break down the PET unless that PET also happens to be sitting on the surface of the garden I don't know if that's just my brain making things up though I'm trying to remember what I read about this cuz I think their aim was also for mixed fiber recycling Oh
okay So are they actually able to do mixed fiber recycling now or is it an aspiration i'm just going to make funny faces until I remember Okay If you don't know that's fine I mean the reason I ask is the research paper I was reading from June last year says that they're the first to do this sort of chemical decomposition without sorting the textiles first Yeah I just cannot remember what I had read Maybe we can revisit this in a later episode then and look at more enzyme based techniques and
how they work and how advanced they are I'm intrigued by this um industrial scale plant Was it industrial scale or pilot scale that you mentioned it was pilot scale and they're building an industrial scale The main focus of the research was identifying better bacteria containing these enzymes and which one was sort of the fastest and which had the best reaction mechanisms So no it wasn't really going into detail of what happens when you have mixed fibers Okay just the biological side But I was
under the impression that they could having extracted the enzyme they could then essentially synthesize the enzyme and tweak it to make it more efficient Yeah So I think they were comparing versions of them because I suppose enzymes are kind of named by what they uh react with I don't think that limits like what structure it actually takes This is where my biology fails me Do you mean that you could have enzymes with different structure but they would still break
down the same molecule yes that is what I mean Okay So they picked out different bacteria that also had enzymes that did the PET breaking down process Yeah They found different bacteria that eat PET essentially Okay And they've evolved to do this cuz there's a lot of plastic in the world and there's a lot of plastic in the environment Yes One of the scientists that discovered it was analyzing waste water with plastic in it and that's how they found the enzyme Ah
nice If we put the biological process aside this research paper that we started off with on the chemical recycling of mixed fibers I quite liked that this paper covered a lot of different topics that it almost was multiple papers built into one That they didn't just look at the reaction of zinc oxide and PET but they then looked further and how different fibers reacted And then even further they decided to see how would that actually look like if they built a chemical plant around it
This is what I quite like They're already thinking about that end point and how do we get to an industrial process They're not just sitting in the lab going "Well I've got my half gram of textile and I've made like 95% pure PET
out of this Job done." I suppose that's kind of what a chemical engineer does is there's the reaction but then okay what is actually the ultimate reaction pathway to make it a viable chemical plant i can see that there could be so many steps to your industrial process to start off with random clothing that people have tossed away to all your pure different components So your cotton your nylon spandex and your PET monomers And then if you even recycle the ethylene
glycol that you put in to then make your pet again Exactly What do you do with all the dyes and how do you deal with all the different um pre-treatment methods that have been applied to the fabrics like UV resistance that sort of thing So you need to think about all those different aspects if you want to see a real world result I mean it's like hard to imagine some of these things cuz until you win it you don't really understand that they were looking at a throughput of 500 kg per hour and the
operating cost being $92 million in what the same hour I don't think that's in an hour but if that was an annual cost that's a lot of investment requirement you said this research article the paper cover all these different aspects it sound like someone's entire PhD was my take on it cuz they looked at all the different variables and it definitely sounded like four years of work to me at least and then there was this technoeconomic assessment that you just mentioned that I kind of thought well
that seems really brief and I'm not an expert in this and I think I need some more detail to really understand what you've done there Here are some really big numbers It's all I got out of it Yeah like two different scenarios In one scenario you just kind of I don't know increased the resale value of your item by saying we're just going to charge as much per unit And I don't know if that's how these things work because surely the market has to be willing to pay that
price It's not really sciency or engineering at this point though economics Interestingly my chemical engineering degree did involve these kind of economic assessments of your process cuz then you'd then decide you know what I'm going to change which process step I'm going to take I'm going to actually not use that and find a different way or you know what purity do you aim for because of what selling price you have So funnily enough economics does fall into my degree a lot
Okay And maybe this is the the difference with it being an engineering degree Ah so you understood this part of the research article better than I did then I guess Yeah this kind of felt like my bread and butter much more than the biological enzyme process that I was reading there was a lot of um squiggly spiral models Whereas me being a scientist with a PhD in computational chemistry which is basically staring at squiggly spirals on a computer for 4 years I was much more at home with the
biological stuff Oh we we read the wrong papers But anyway yeah it definitely seems like a full study Questionable about the the price I don't know Maybe that needs more optimization They're at lab scale at the minute So I don't know how well considered those costs are if they'd be further refined the further along they get in the research That's how these things work right your costs get more accurate the further on you go through the work Definitely And maybe
there isn't even a market for recycled monomers yet Maybe everyone just buys the pure stuff and you have to kind of add that environmental green price tag Well that's it I mean I feel like there has to be some stronger motivation for stopping people from extracting fossil fuels and pushing them towards using recycled material We've extracted so many fossil fuels already It seems daft then just stick them in landfill I totally agree I saw a fact in one of the
articles we were reading as the prep and a study estimates that 8.3 billion tons of plastic have been made in the history of since we've been making plastic See I can't visualize that at all The only metric I have for any of this because I'm also a nuclear scientist is that all the nuclear waste that we've made in the UK so far that government wants to bury underground would fill Wembley Stadium Okay And every single year as household waste we produce a much bigger volume of
waste than Wembley Stadium Much much much bigger And plastic's just one part of that Where does it all go it's weird when you think about it isn't it cuz as an individual you probably don't produce that much waste but billions of people in the country that all adds up in the world Yeah Yeah And you hear stories of like lots of clothing like fast fashion ending up just floating around the Atakama desert because no one has anything else to do with it really So it
just gets dumped there Well hopefully with this pilot plant by Carbios and you know all the research into enzymes that we would be able to clean up some of our mixed waste or at least recover a PET I think this sounds like an emerging technology and I guess it's uh are we going to use enzymes to do all this work or are we going to use microwaves and catalysts to do it or can they work on separate waist streams it's definitely one to watch I think Yeah there could be
different applications for them Say one of them might have a better affinity for certain wastes Yeah So I think let's draw this conversation to a close We've discussed a great piece of research that looks into a chemical recycling method for PET fibers and it has the potential to work with other fabrics mixed together or fibers mixed together So it has great potential but it's still in the early stages of research Yes I'm going to pay more attention to this research I think
and see what happens next I agree I think we should definitely keep an eye on this topic Thanks for listening and see you next time The views expressed in this podcast belong entirely to the person that said them They do not represent any industry or organization If you enjoyed listening to these views it would really help us out if you could rate us leave a review and tell a friend This podcast was sponsored by no one but if you're interested in funding us to
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