The Power of Plastics: Polymers Past, Present and Future (Dr Rachel Platel – Chemistry)

so yeah I just want to say it’s a pleasure to be here tonight to talk to you thanks all for coming out to see this talk and I don’t know if any of you have been to any of the rest of the series but I hear it’s been a great success so hopefully I can give you something exciting to think about tonight as well so the talk I’m going to give you is it’s split into two parts first of all we’re going to look at polymers in general we’re going to look at their properties and think about why there’s such as put an important material to us what properties do they have that mean we use them every day and that they’ve invaded almost every area of our life and then in the second part I’m going to move on to talk more about my research which is in the area of biodegradable polymers so yeah so first of all what we need to do is define what we mean when we say polymer and a good definition the broadest definition is that it’s a large macromolecule it’s a large molecule that’s made up of lots of repeats units and the nice way to demonstrate this is with a paperclip chain so if we have one paperclip we can make that one off now we can make that our repeat unit and then we have if we join lots of them together we have a polymer it’s made up of lots of paperclips but it’s a much larger molecule than just the paperclip on its own and again we can have we can have just one long chain like that or we can have something branched we can have something in a circle there are lots of different structures for polymers and the word polymer comes from the Greek polis and Mareth meaning many or much and parts so it means with as many parts this polymer so now we’ve defined what a polymer is let’s think a bit more about the structure of one because although we’ve got this chain how does it really build up into the materia Reles that we have that we have before us everyday and so yeah so looking at this some some polythene some polyethylene wrap that you might use on your food if we kind of zoom in zoom right in on that there then and I’m sorry this is not showed up very well but you can see we’ve got a real network of have changed there if you can see the pale blue and you can imagine you can imagine that all of these individual chains are all randomly interlinked there’s not much order to them we call it a name office material and if we zoom in even further say on just on just on one of the chains then then we see that we’ve got these individual chains here which is what we were looking at with the paper clips again and each one of those is the same each one of those is the same and if we do one more zoom in on one of those molecules in this case you can see that we’ve got two carbon atoms and they’re bonded together as a chemical bond between them and then each one of those then has another chemical bond which goes on to form the chain so so that the the individual molecules of the chain are bonded together by chemical bonds to form this very strong material and so you can see that all the way down from the macro scale we can follow that all the way down to to the molecular scale of the polymer and and in the end that’s what chemistry and polymer chemistry is all about it’s about looking at the properties we have right up here that we see in that we use and then following the chain all the way down to see what exactly happens on the scale of molecules to make these properties up here and I’ve just put in this circle here just some of the some of the words that I think people would use describe plastics and some of the reasons may be that we that we use plastics rather than just relying on metals and wood and other natural materials and I think flexibility and elasticity is one of the main properties that we that we like in plastics I’ve put we’ve got a good strength to weight ratio as well and of course you know that for the same often for the same

weight as metal or something you can have a piece of plastic that it’s just as strong it does the job just as well but it’s much lighter and so it’s very well suited to the application and something like transparency is another is another quite good property that we like in polymers so so what is it that makes polymers special what property is it that that makes them flexible that makes them elastic to think about this question we need to think about states of matter a bit so first of all let’s just think about about something like water which we all know and we’re all familiar with the different states of matter as applied to water so below zero water exists as ice of course so got some ice cubes up here and and you know that if you hit those ice cubes with a hammer they’re very brittle they’ll smash on a molecular level the the molecules of water are sitting in a very ordered manner and they’re all they all have forces which hold them in place and they’re joined to their nearest neighbors on this side and this side on this side and so it’s a very rigid material when it’s a solid and then if we go through zero degrees the water will melt we’ll get to the liquid state and in that liquid state you know that water well here’s some water here it’s it flows it will hold the vault it will take the volume it set her it will take the shape of the container it’s in and and again on a molecular level we’ve broken some of those forces the ones that were really rigidly holding the molecules in place but there are still lots of forces holding the the molecules together but they can they can move somewhat through the liquid and and then finally if we take the the water above a hundred degrees we get steam which is the gaseous state of water and and here we’ve broken all of the intermolecular forces really and those molecules are very far apart and they’re moving very fast they’ve got a lot of energy and so so then if we if we move on to think about polymers why is it for instance if I take I just take this piece of plastic it’s a solid I think you’d all agree it’s a solid but but it bends and so if we’ve said that that things as a solid are very rigidly held together how does this Bend like this now the answer is to do with the fact that we’ve got long chains long chains of molecules of repeat units so again this is hard to see I’m sorry the pale blue is the network that you could see before and then I’ve put one I’ve highlighted one of the polymer chains in red and what you can see is that there’s lots of different points where that polymer chain meets another polymer chain and so there’s lots of points where there’s a force with another polymer chain and and what we find is that when when the poem is in the solid state if it’s above a certain temperature it’s actually it has the chains have enough energy to move and and break some of those forces when you when you’re putting stress on it and make new forces with other chains so they’re able to move a bit even though it’s in the solid state and and we call this a solid rubbery phase so so it’s a bit like you might imagine rubber it’s flexible but it’s still solid still very much solid and if we call a plastic down then we get to what’s known as a solid glassy state and that as you might imagine is when the material becomes like glass so if you were to hit it with a hammer it would smash it’s not flexible at all you can’t bend it and that’s because these chains now don’t have as much energy as they had when we had a bit more heat so so they’re no longer able to move against each other and take up new positions as we put stress on them and so there’s another good analogy if you think about snakes in a snake pit snakes are cold-blooded animals and when it’s very cold they’ll all lie intertwined in the

snake pit but they won’t they won’t move and so if you were to drive a bulldozer through that snake pit then you would either either the bulldozer wouldn’t be able to get through if the snakes were too strong or it would cut right through them whereas if it was a sunny day the snakes would have some energy from the Sun and they would be warm they’d all be slithering over each other rather than still and so if you drove that bulldozer through they would all be able to slither out the way or slither around to let something through so that’s just another way to think about these two these two solid states that polymers have and again when we go to the liquid of a polymer now it’s melted it’s it has it has the properties of a liquid but not a liquid like water because again with these long chains we’ve got lots and lots of forces to overcome and so if you were pouring a liquid polymer would be very very viscous and actually when we’re close to the melting temperature it’s often still a solid but just a mole all one and this is something I’m going to demonstrate in a minute so I just put some things in there so so now I am going to demonstrate some polymer properties for you first of all we’re going to use a milk carton now as you can see this as it is I think you would agree is it’s fairly flexible so are you happy that that this is in a solid rubbery state rather than a solid glassy state yeah and in fact this is polyethylene and the the glass transition temperature the temperature at which this plastic goes from being solid and glassy to solid and rubbery is is around minus 135 I think so we’re safely we’re safely in the solid rubbery phase now I’m going to first of all show you a video of what happens when we put that this into the solid glassy phase when we cool it down and then I’m going to show you what we can do when we melt it so here so here I am dipping it into some liquid nitrogen that’s a hundred minus 196 degrees Celsius so it’s cooling down hopefully it’s moving over to the bench and I’m gonna whack it really hard and you can see can’t see very well it’s going back in anyway it wasn’t quite cool enough so hopefully you’ll see you’re going on on the next one so what you should be able to see is as I hit it then it smashes it shatters because it’s at this glassy it’s below this glass transition temperature there you are jumping back and forth here should have bought some liquid nitrogen here oh look at that pull paused on the on the shot you can see there’s a small piece which was shattered off here and shattered there and actually what I can do is show you this is what happened this is the actual carton and you can see a shatter at the top and if we try to do it with this then it would just squeeze it there’s no way it would shatter so now let’s see let’s see what we can do when we melt it I’m going to heat this carton with this heat gun I can’t talk while it’s on because it’s quite noisy so I’ll explain what I’m going to do now the melting temperature of of polyethylene is about 120 degrees so we’re just going to melt very small corner here and and then I’m going to blow into the neck and and demonstrate one of the industrial methods of processing polymers which is where we melt the polymer but because it’s so viscous we can then blow it into the shape we need it’s called extrude extrusion blow molding okay so let’s put my safety

okay did you see there everyone got a chance to see that stare this side of it I just popped anyway hopefully you had a chance to see how how that really blew out and you can imagine if you had if this whole thing was molten then you then you’d get a really good effect and it would all blow into a bubble and anyway now I just want to just touch that for me and what what does it feel like what sort of plastic yeah slightly sticky but does it remind you of any plastic material plastic bag may be one of those one of those food bags yeah the guy that really took the girl to open yeah and so this is this is a method that’s used to make to make carrier bags you blow giant sheets of plastic from a big blower down below and the polymer is continuously rolled up and up it’s amazing to see anyway this was just a small demo now what I’d also like to show you in a another demonstration is is we’ve got some polymer beads here now this is this is just a commercially available polymer it’s called polycaprolactone and it’s melting temperature it’s just 60 degrees so we can melt it really easily and and then form it form it with our hands basically so it’s just so if you see if you look here you can see that the polymer beads are clear and then I can scrunch them and mold them into a ball like that you’ve got to be quick because it might it it comes below 60 degrees quite quickly again but you can see how whereas that’s clear so that’s definitely in the in the liquid state or it was these beads how we receive the polymer are transparent so you can tell that they’re in the solid state and this is the liquid state and even when when something like this cools down you can see we’re still above the glass transition temperature and that’s minus 57 for this polymer and because you can see we’ve still got that flex I’ve been talking too much we still know that flex here which gives us which shows that we are in that solid rubbery States rather than the solid glassy state just kind of screen back on now my final demonstration some of you as you came in could see we were messing around with some milk and vinegar at the front here there may even be some a little raft of vinegar that went that went around but what we were doing was making a very simple polymer which can be made from from milk and vinegar and some very early plastics were made in this way we took some milk shown there by glass of milk and then we added some vinegar which was acid and and I think you probably know instinctively what happens when you do that the milk we call it curdling but you form a solid lump don’t you and and actually what this is I’ve got some here here’s some knife I scooped out and then I’ve dried off and this is this is a very basic form of polymer and you can squeeze it with your

hands and rolled it into a shape in true blue pizza style here’s what I made earlier here’s what I did last night and it’s now hardened and again if we think about what’s happened on the on a molecular level then we started with some milk and in milk there are lots of proteins which are polymers they’re made up of chains of amino acids but they’re quite short chains and so in the glass of milk they’re able to be suspended as as the chains and and you still see the milk as a flowing liquid but it does contain these chains now when we add the vinegar then that causes chemical bonds to be formed between some of the units on the chains and so then you get something which is much bigger in mass than than these shorter chains here and so it’s no longer able to dissolve or be suspended in in the milk and it comes out as this lump which then hardens to this kind of resin and this is an example of what we call a thermoset polymer so instead of as in the case of of this caprolactone i just showed you or the polyethylene that i showed you with the milk we can continually remount reform recall and melt and form and cool as many times as we want because we’re only physically changing the plastic we’re changing the state of matter but in this case of this case in we are actually chemically changing the material and so you can’t go back from this we can’t heat this up and come back to the glass of milk because these chemical bonds that we’ve formed are permanent and so there’s some other nice examples of of plastics like this casein itself actually was used in the early 1900s to make buttons and jewelry and ornaments and another example is something like vulcanized rubber where it was natural rubber and sulfur was added to crosslink it into a much less tacky a better material to use so this is one of the classes of polymers and the other class is the thermoplastics which are the ones I showed you before where you can melt and solidify as many times as you want okay so that actually concludes the first bit of the talk and now I’m just going to briefly tell you something about the research that I do and so although I’ve been talking a lot about about how how great plastics are I’m now going to tell you that there are some problems with plastics as we know them I’m sure all of you have seen some sort of photograph like this one as well you’ve been on a train ride maybe and been passed to some trees that are just coated in in bags it’s a lot of landfill problems with plastics as the use of plastics has grown so the amount of waste that we have from plastics has also grown there’s also a problem because many of the plastics that we use every day come from oil and gas reserves which of course are finite resources tip to run out but even even if you want to argue that they’re not going to be running out anytime soon the price of oil is certainly not going to be going down I don’t think and currently it’s about 7% of of world oil supplies are used in plastics so what could we do to solve this problem and one of the solutions lots of people are looking at is using biodegradable and bio anĂ­bal plastics and so we can make a plastic from from sugar beet from corn if we ferment the corn or the sugar beet then we get out lactic acid most of you will know about lactic acid because you might exercise too hard and got a cramp and that’s a buildup of lactic acid in your muscles but as you know your body deals with it very well because if you just rest for a few moments it goes away and you can carry on so if we join together two of these lactide units we form this you don’t need to worry about any of this but you just see it’s a circular molecule and and if we open up this molecule if we break one of those bonds here then we can form a polymer which has a repeat unit of of this cycle basically and and

that polymer is actually has a lot of the properties that polymers have that are derived from oil and gas and it also has the added bonus of being able to be used in the body because as I just said if we can break it down back into this this lactic acid then your body knows how to deal with that and knows how to metabolize it so so here we are we’ve got some plastics that we made we do a reaction called hydrolysis which just means we add water and that water can break down some of these break some of these bonds here to form the lactic acid and then we can eventually convert all of that to carbon dioxide and water which then theoretically we could put the carbon dioxide back into growing some plants and that’s a closed carbon cycle for instance so as I’ve just said there’s many uses for these for these plastics polyketide and related plastics that you can use them for commodity uses but also there are these intriguing possibilities they’re already used in these process in these functions things like dissolvable stitches bone scaffolds if you shatter a bone badly instead of using metal pins and supports you can use something that will slowly degrade allowing your bone to regrow and there’s also the possibility to use them for delivering drugs in the body if you wanted a slow-release of a drug over over weeks or months then you could just put an implant in and it would slowly theoretically it would slowly release the drug over a period of time so it sounds the way I’m describing it it sounds like it’s all a done deal but of course as with lots of these things there are many improvements that we need to make now one of those concerns the way that Polly lactate and these plastics degrade in the body and there’s two main problems really the first one is that you remember I said we needed some water to to cause the polymer to biodegrade and well the problem is this polymer doesn’t really like water it’s quite we call it hydrophobic it doesn’t it doesn’t really let the water mix with it very well and so in that sense it’s not ideal to need water to biodegrade it and the other problem comes when we look at the way it might degrade in the body and release a drug and just drawn a cartoon here if you imagine the yellow is the polymer support and then the red is little little pockets of the drug then over time you would expect the the polymer to be broken down in the body and release those little balls of of the drugs took to then be taken by the bloodstream around the body until we until we have no polymer and all of the drug has been delivered now if we look at a graph of how these polymers tend to behave we’ve got polymer weight here and then time along the bottom and what you can see is that often we have this very steep drop in polymer weight in a very short amount of time at the beginning and as you can imagine what that does is give a burst of of whatever drug it is which can then mean that you get a bit of a hit of whatever it is right at the beginning which you might not want and then you can see it does it does steady off and gives a nice degradation over the remaining time but what we would really like is for there to be this slow predictable degradation all the way through the profile and so one of the one of the ways to to solve some of these problems is to take our poly our lactate monomer but then to add in some of these other monomers and you can see again I’m not I don’t need you to worry too much about the the molecules themselves but if you just see I’ve highlighted in red this group here and you can see that that’s what all of these have in common and that means that they can be they can be catalyzed and made into a polymer by the same types of catalysts because they have very similar structures but in fact the very small differences in structure which you can also see this one’s got more members in its ring and then this one hasn’t got these spikes they they actually create

enough difference in the polymer that it allows the wound it also actually makes them more susceptible to a good degradation have you seen here of course when you put more than one monomer into the mix you do have the the possibility to form different sequences of polymer so before we just had one repeat unit and we could repeat that lots and lots of times but if we have two choices then we could have lots of one monomer and then lots of another monomer so that’s right at the beginning now the block copolymer we call it we could have a very random arrangement of the different units so you know two of one three of another two of more on one of the other or we could have an alternating arrangement where we where we alternate between the different monomers and and what’s been shown to be very good is to have this alternating arrangement because it actually all of the linkages you can see are blue to red so it’s blue to red and there’s red to blue which is the same as blue to red and blue to red and blue to red whereas here we’ve got blue blue blue blue red so here there’s there’s different kinds of linkages because we can have blue blue or blue red or red red whereas here you’ve only got blue red and so the breakdown when it happens is very very regular because there’s only one kind of bond to break now what I’m interested in is is actually the design of the of the catalysts which we use to make these polymers because in the end if we can if we can make a an alternating copolymer like this or if we can in any way control the way our monomers are going into a polymer then we can ultimately control the way it degrades in the end and the way it behaves for instance in the body or in any other use and so drawn quite a crude cartoon here but I think it makes the point so here’s a metal and that’s the the real workhorse of the catalyst it does all of the work and then we’ve got this kind of red scaffold around it and you can think of that as a support or or something that really keeps the metal from doing reactions that we don’t want keeps it from joining up with other metals and also influences the metal by by putting it in a certain environment and so we’ve then got atoms which join this scaffolding to the metal and we’ve also got some groups hanging off the scaffold and all of those can affect the way that the metal behaves that the catalyst behaves so there’s lots as you can see there’s lots and lots of areas in which we can investigate and see which are good catalysts for these processes and just very briefly if we look at the the metals that do this job very well this is a periodic table here and you can see we’ve just got pockets of metals over here anyone who don’t know anyone who’s doing chemistry at school got alkali metals here we’ve got some early transition metals and then zinc and aluminium might be familiar there and then something down here called the lanthanide series so there’s lots of different metals to choose from and then that’s before you’ve even started looking at any of the scaffold or any of the other groups so there’s there’s really a very wide variety of work that we can do in building catalysts for these processes and just here I just want to highlight this is a catalyst I’ve worked on and you can see how it mirrors the cartoon in purple in the center that’s an atrium at and that’s the metal that does the work in grey is the kind of supporting scaffold and then in blue and red we’ve got the atoms that join the scaffold that bond the scaffold to the metal okay so just very last very at the very end I just wants to say another way we can make these alternating polymers is to actually take a monomer that has a different group at the top to what it has at the bottom and so then if we were to simply use just that monomer it’s like having two halves of something different and again you can put those into a chain in an alternating fashion so that you have different groups to attack when you’re degrading that

polymer so some of you might have have watched that and then kind of thought but what about what about using corn for this because corn is a food source and is it really an ethical idea to to take a food source and use it to make a plastic when it could be feeding feeding people and so this is a problem and and I think in general the field is trying to move away from using food sources as as feedstocks for polymers and so here I just wanted to show you a couple of the of the ideas that are around things like vegetable oil and ground grounds from coffee all have valuable valuable molecules in them that can be used as feedstocks for polymers has also a molecule called limonene which can be extracted from orange peel which again is a waste product and we can we can do reactions on this molecule to then make it able to be incorporated into a polymer and actually this is also being investigated for use as a green solvent as an alternative to some solvents finally it’s a molecule called pi 9 which comes from resin and again we can use this double bond here to to put a chemical group on which can then mean it’s able to be incorporated into a polymer so I think in terms of the future there’s it’s certainly bright in terms of the variety of polymers we can we can make and I think their uses are just growing and growing so just to conclude I hope I hope you’ve you felt over the last 40 minutes or so that we’ve you’ve learned a lot about polymers we’ve looked at some of their different properties we’ve looked at why they’re really valuable and important in our lives and then we’ve also thought about how we can move forward in the future when we have reserves that are dwindling and the necessity to kind of look for new routes to these polymers and new routes to these materials so I’d like to just thank Allan Dara and Ross Malcolm they they come from the Faculty of Science and Technology at Lancaster and they’re the ones who have who have organized this series and they’ve been instrumental in its success so thanks very much I’d like to thank Mike for chairing the session and he’ll be taking some questions from you hopefully and Michael peach who helped me make the video I’d also like to thank members of the chemistry department at Lancaster it’s a great team we’ve got and they’ve been a great support over the last few months thanks very much