Ph.D. Chemist Explains 3D Printer Resin

welcome to goober town hobbies my name is brent and i love to print and paint resin models so today i'm going to talk a little bit about how 3d printers work but i'm going to talk a lot about how resin works these printers turn liquid resin into solid plastic figures they print one layer at a time a motor moves the build plate above an lcd screen and a vat of resin the resin vat has a clear bottom uv light from the lcd screen goes through the bottom of the vat and polymerizes a layer of resin on the other side the screens have a resolution similar to a modern cell phone so the polymerization is precise and the models come out with really nice detail part of what makes these printers so cool is how simple they are just one linear actuator and one lcd screen and that's about it so the technology that's in these bottles is just as amazing you hit them with a little bit of uv light and they harden up just where you want them to and they stay liquid everywhere else so how does that work okay the building blocks of polymers are monomers these are small molecules that have the potential to form chemical chains just like building blocks they have structural features that allow them to connect if we initiate polymerization the monomers will start to link up to form dimers and trimers and tetramers and beyond these short chains are called oligomers once the chains get longer they're called polymers a single chain can contain hundreds or even thousands of monomer subunits nearby chains get tangled with each other and by now the whole thing is normally a solid the properties of a solid depend on things like what monomer you started with and what the average chain length is something else to know about polymers is that they can contain multiple ingredients most of these liquid resins use a proprietary blend of different chemicals us folks who 3d print as a hobby are always comparing notes about different resins you know which ones are hard or soft or brittle or hold detail really well and in broad strokes it's the same thing going on in all these bottles it's all acrylate chemistry acrylate polymerization but in the details there are actually a lot of differences between these different blends and that's what we're going to talk about it is perfectly reasonable to mix two or more different monomers together when this mixture polymerizes we'll end up with a copolymer that'll have different properties from what we get from either of the monomers alone these copolymer chains won't always have a nice alternating pattern between monomer a and monomer b sometimes you'll get a whole bunch of one type in a row and sometimes a whole bunch of the other so this is one place where the building block analogy of polymers is misleading with something like lego bricks we can determine where each piece goes really precisely but with chemicals they are so small that as humans on our size scale all we can do is decide which chemicals to mix together and whether or not to heat them and whether or not to shine uv light at them everything else is up to physics and chemistry and statistics [Music] for the type of polymerization reaction that we're talking about today the ingredients don't get placed precisely into polymer chains but as long as you shake the bottle of resin really well before you use it statistics will make sure that the properties of the solid are nice and reliable so far we've been talking about this reaction with these cutesy little cartoons with the stylized ball and socket joints now obviously this is an exaggeration but for somebody with a trained eye we absolutely can look at a molecule and see connection points places where new bonds can be made this here is methyl methacrylate it is the monomer in plexiglas and this acrylate group is really important to the chemistry of these resins so to my eye these two carbons over here are really important i look at this and i see connection points you know in in the cutesy terms i see a ball and a socket places where we can bind more monomers to this one so this is methylmethacrylate it's a monomer but we can also have larger molecules that have that acrylate group so in this molecule we have an acrylate group over here and one over here and so that means this molecule has two different places where we can be making connections so ball and socket here ball and socket here and that means this molecule can be involved in two polymer chains at the same time this is something known as a cross linker let's get back to the cartoons and talk about cross-linkers some larger molecules have multiple connection points if we mix them in with some monomers we can link the chains together this changes the macroscopic qualities of the polymer often cross-linked polymers are more rigid and more durable i've been using this little ball and socket drawing as a cute way to depict acrylates and polyacrylates of course there are lots of other polymers out there polyamides polycarbonates polyvinyls the biggest difference between these families is the type of bond that links the monomer units into the polymer chains in cute picture format instead of a round peg and a round hole maybe we've got square pegs and square holes or maybe triangles sure for 3d printer resin it's still the acrylic chemistry that's the most important but when we look at the ingredient list for some of these commercially available resins we'll see words like polyurethane acrylate in cartoon form here's a chain of polyurethane urethane monomers bound together into a polymer chemical engineers and synthetic chemists can stick acrylate groups onto the ends of this polymer this is polyurethane acrylate and for our purposes it's just a big old cross-linker the term resin is a bit vague generally it's a liquid that can be hardened into a solid polymer so everything in our bottles of printer juice is resin but a narrower definition is pretty much what we're looking at here a thick liquid of short polymer chains that could be hardened into a cross-linked solid what we're looking at here is a big cross-linker and a stereotypical resin we are almost ready to understand the ingredient list for what's going on in these printer resins so we've talked about monomers and cross linkers also in these bottles can be pigments or dies these are often colored not always but often also in here we can have straight up filler and by that i mean molecules that don't end up directly bound into the polymer they sit in between the polymer chains and the final solid matrix they still play a role but they're not directly bound in and these you know filler molecules also can play a role in keeping the resin nice and viscous during the printing process some of these fillers are known as plasticizers they give some plasticity to the solid and keep it from becoming too brittle last but certainly not least every one of these bottles needs to contain some photo initiator this is the stuff that absorbs uv light from the printer and uses that energy to start the polymerization reaction here's a little cheat sheet for the things that could be in these bottles of resin monomers the basic building blocks of polymers cross linkers molecules that can join two or more polymer chains together plasticizers other stuff that gets tangled into the polymer matrix photo initiators to get the reaction going pigments to make the models we print look cool the manufacturers of these resins are required to put out safety information in the form of safety data sheets now for trade secret reasons they try to be a little bit vague about the ingredient list but if we know what we're looking for we can figure out what's going on here's one from form labs white resin they list methacrylated oligomer methac related monomer and a third ingredient which is a photo initiator you can see that they're koi with the exact percentages and even the precise identity of some of the ingredients but they give you enough information to gauge the risks of working with this stuff we'll talk about safety in a moment but for now i look at this list and i see crosslinker monomer and initiator here's one from elegoo epoxy acrylate resin monomer color pigment and photo initiators again the main ingredient is a large cross linker type resin followed by monomer and then pigment and photo initiator here's another one acrylate monomer polyurethane acrylate and photo initiator onto any cubic white resin polyurethane acrylate acrylate monomer photo initiator for fun here's one from global 3d they list five different acrylate monomers each somewhere between zero and forty percent and they lose two acrylic cross-linking resins somewhere between ten and fifty percent each i just thought this one was fun because of how vague those percentages were some companies really guard their trade secrets alright i think we've got the general idea of the type of stuff that goes into these resins so now let's focus in on just one of these this is any cubic eco resin it is a resin i've used a fair bit before and i like it but more importantly on the sds sheet they actually list all the chemicals that are in there and their exact percentages so that is very handy we've got epoxidized butyl esters of fatty acids derived from soybeans 45 iso-octal acrylate 30 very long name that ends in acrylate fifteen percent two other molecules at five percent each so that's five listed ingredients and the percentages add up to one hundred percent this is a good start the sheet doesn't spell out the role of each chemical though so the fun part is figuring out what each of these does here are the structures let's see what we can see first i see some acrylate groups iso-octal acrylate is a monomer if i drew it as a cartoon the ball and socket would be here where the acrylate is and it would have a big side group where the isooctyl is this bigger molecule has four acrylate groups this is definitely a crosslinker and in theory it could be a link in four different polymer chains at the same time next polychloro-copper phthalocyanine this big ring compound has actually appeared on this channel before it's one of my favorite materials that i use in this hobby do you recognize it this is green pigment number seven green pigment number seven phthalo green in a previous hobby science video i talked about common pigments and phthalo green is a big one the stuff that makes a lot of our paints and inks green is the same molecule that makes this model of baby yoda green you know i love doing these hobby science videos because every time we learn new things some of those things start to connect and the world makes a little more sense and that's a beautiful thing back to the list of ingredients 45 percent of the material in this mixture is derived from soy oil that's a filler and a plasticizer we'll talk about that in a moment and then we have this molecule weighing in at five percent of the mix this is the photo initiator this is the molecule that absorbs uv radiation from the printer and initiates polymerization okay it's time to talk about how this reaction actually works now in a liquid molecules are constantly floating around and bouncing off of each other now most of the time when molecules collide nothing happens but if two molecules collide at just the right angle and there's enough energy involved it is possible for a chemical reaction to occur now for the reaction that's going on in 3d printing you don't have to be a chemist to understand it we can think about this polymerization through the lens of even and odd numbers okay check this out all organic molecules have an even number of electrons at some point you've probably heard about electron pairs and valence electron shells and something about atoms want to have full electron shells well all of that kind of boils down to the fact that all stable organic molecules have an even number of electrons so everything in this bottle all of the molecules in this bottle have an even number of electrons and for the most part those are not too reactive but if we were to have a species that had an odd number of electrons those are called radicals those are unstable and reactive and indeed that's going to be what happens in this reaction so in this reaction when we hit the photo initiator with light we're going to generate radicals that have odd number of electrons and start reacting with molecules that have even number of electrons back to the cartoons for a moment here's the initiator molecule sometimes when it absorbs uv radiation it fragments photons of ultraviolet light have more energy than visible light normally visible light can't start chemical reactions but sometimes uv light can that's why us humans need to be careful with uv light to avoid sunburns and cancer and all that the photo initiator starts as a molecule with an even number of electrons and it fragments into two radicals each with an odd number of electrons these radicals are highly reactive and they really get the polymerization going so now there's a small percentage of radicals floating around in our liquid resin and they're bumping into things just like all the molecules are but when radicals collide with something they're more reactive and so there's a higher chance of a chemical reaction occurring now statistically they are most likely to collide with a molecule so we have a situation where a radical is colliding with a molecule now here's the key bit when an odd number is added to an even number the result is an odd number so if a reaction occurs between a radical and a molecule the product is going to be another radical which is still reactive so the initiator fragments and the fragments are radicals when the radical collides with a monomer or crosslinker the two can bind together but the product of the reaction is still a radical it's still highly reactive the radical keeps floating around in solution and colliding with things and when it collides with monomers or cross-linkers at just the right angle a reaction can occur odd plus even yields odd so we keep getting a larger and larger radical this chain reaction is called radical chain polymerization now eventually a radical will collide with another radical odd plus odd yields even and that reaction will give a stable product since we know the ingredients of the any eco resin i'll show you what's going on with a real example the initiator molecule here starts with 188 electrons even number covalent chemical bonds are the sharing of a pair of electrons uv light can cause a cleavage of this carbon-carbon bond that leaves one of the two bonding electrons with the big fragment and one with the smaller fragment there's a lot of carbon-carbon bonds in the resin mix but the reason that this photolytic cleavage can occur is that these radicals are just stable enough to get formed that being said these fragments are still quite reactive so when this radical collides with an acrylate group a reaction can occur these arrows show the movement of electrons during a reaction that unpaired electron on the radical and one electron from that double bond in the acrylate group get together to form a new carbon-carbon single bond that links the radical to the monomer but it also leaves behind a new unpaired electron our product is still a radical and it's still reactive the chain reaction has begun monomer or crosslinker units keep getting added to the chain and that unpaired electron stays around once you get these chain reactions started they really go on their own for a little while polymer chains often end up being hundreds or thousands of units long a reasonable question is why doesn't the chain reaction cause the whole vat of resin to turn into a solid chunk well molecules are really small a monomer is very roughly one nanometer long when the lcd screen on the printer lights up a pixel of uv light that pixel is a little square approximately 50 000 nanometers long so it's possible for the chain reaction to propagate outside the lit region a little bit but it won't get far enough for us to actually notice it's actually more likely for the uv light itself to leak outside of its designated square and that's why sometimes clear resins give different prints from solid color resins so the specific resin that we've been doing a deeper dive on is this anycubic eco resin now this stuff is sold as being sourced from nature and biodegradable and a little bit safer so let's talk about those claims a little bit before we go any further i do like this stuff i do use it but yeah let's talk about those claims a little bit this is the marketing that any cubic has been using soybeans processed into resin then back to nature the marketing on this looks good and from personal experience it definitely does have less of a chemical smell than other resins that i've used this is the ingredient list processed soybean oil monomer crosslinker pigment and photo initiator okay so that 45 ingredient does come from soy one way you can tell is because soya is in the title but also there's a really big clue in the fact that some of the other words are pluralized butyl esters fatty acids now in soy the plant and the bean there are thousands of different molecules and if you squeeze a soybean to get the oil out that oil is still going to be a blend of a whole bunch of different stuff so not isolated individual molecules that you can give a singular name to but you know a blend of different fatty acids for example that's not a bad thing that blend can absolutely be useful to us and it's also kind of a hint that this ingredient is not too many steps away from actually coming from a plant which is cool and is as advertised so this ingredient is soybean oil that's had a couple of chemical modifications to it fats and plants and animals often exist as triglycerides the three ester linkages over here are an easy place to make chemical modifications for example if you treat fat with lye like in fight club you can cleave the ester and make these long chain carboxylates with a hydrophilic end and a hydrophobic end missible with grease and miscible with water soap just like fight club the neutral protonated form of this is called a fatty acid if the carbon chain has no double bonds that means the molecule is saturated with hydrogen atoms and it's called a saturated fatty acid if the carbon chain does have carbon-carbon double bonds it's an unsaturated fatty acid this soy oil has lots of unsaturated fatty acids depending on what decade you live in this is called the good fat now the sds sheet says that our bottle contains butyl esters there we go again that side of the molecule is easy to modify as part of the processing it seems like they converted triglycerides or fatty acids into butyl esters presumably the viscosity of the butyl esters works well here another modification is epoxidation if this molecule is hit with an oxidizer the carbon-carbon double bonds will get converted into epoxides the ingredient list says that the resin contains 45 fatty acids soya epoxidized butyl esters so i read that as a bunch of structurally related molecules similar to this epoxidized soybean oils are becoming more and more common as plasticizers in the final polymer it's filler but it's filler that keeps the plastic from being too brittle this stuff is probably also useful in the liquid resin to keep everything in the blend suspended as a liquid mixture with the right viscosity okay what about the other ingredients i don't know for sure where they sourced each of these but i don't think they came from soybeans the fact that each of these is reported as a pure single compound and not as a blend or an extract is a big hint that they've been on a long journey since the last time that they were part of nature i'm sure that all of this material was part of a plant at some point but that may have been millions of years ago and they may have spent time as a petroleum product in the meantime okay so 45 of this stuff does come from soybean oil after a couple rounds of chemical modification now the other 55 i don't know for sure but it is very similar to the stuff that's in all the other brands of resin i think it's much more likely that that other 55 came from petroleum products but you know that being said i think it's awesome that nearly half of this came from natural renewable sources that's great and it does have less of an odor than other resins have so that's great too that being said the marketing is a little bit misleading there's there's images of people composting this and it's somehow turning back into drinking water and i'll just say do not spread this on your garden um and that image of it you know decomposing into drinking water is just wildly irresponsible but yeah there you go i think it's cool that you know half of this did not need to be sourced from petroleum products that's great okay this brings us to safety we've spent some time looking through safety data sheets and most of them say that this can be a skin irritant and a respiratory irritant it's also poisonous if you drink it and it's poisonous to wildlife if you pour it down the drain that being said there are lots of differences between the precise ingredients used between different brands and different companies so be sure to read up on the one that you're using if a google search doesn't get you an sds sheet you should be able to email the company and get them to send you a pdf of that safety sheet the safety hazards for chemicals are classified as one two three or four one is pretty tame be careful with two be very careful with three and four you really shouldn't have in your home unless you have a very compelling reason most of the hazards in resins are ones and twos with drinking it being a four don't drink resin okay chemical safety i am a chemist i've spent many years working in laboratories i've worked with truly frightening things and tame things and everywhere in between and in some ways i guess that makes me not a great person to talk to because i've been sensitized to some risks and desensitized to others but i think the real take-home message here is that low risk it never means no risk you should treat all chemicals with respect um as for the stuff in these bottles even as a chemist even as a person who's read the sds sheets i do not fully understand all of the risks that are in this bottle nothing in here truly scares me but i do treat it with respect you know i always wear gloves when i work with this stuff first because it's icky but also i can cause skin irritation or even allergic reactions it is a good idea to wear eye protection certainly do not put this in a place where a child or a pet could ingest it and also i try to breathe the fumes as little as possible so i don't spend a lot of time in a room while a printer is actively working now another safety thing to talk about is ethanol or isopropanol so most people when they're cleaning their prints or just cleaning up around their work area those alcohols work very well as cleaning solvents but of course just just reminder alcohols the liquid and the fumes are very very flammable so be careful with them do not burn down your house and do not burn down your neighbor's house um other than that we don't need to be afraid of this stuff but to treat it with respect that's my that's my advice and now we can talk about disposal the correct answer is that you should contact your local waste management department and follow their instructions okay now let me tell you what i actually do now the solid is really quite safe and is fine to throw right in the trash as for the liquid a couple of things one it is very easy to turn the liquid into a solid and two the liquid is expensive you shouldn't be throwing away that much of it anyway so if you are done with your printer for a while you absolutely save the resin pour it back through the filter that came with the printer into the bottle seal up the bottle use it next time if you have a paper towel with you know resin soaked into it the best thing you can do is leave that out in the sun for a couple hours that resinol polymerize and that solid waste is really fine to go right into the landfill and uh if it's not sunny out just throw it in a bag and that's probably fine to go in the landfill as well now the most interesting waste that i generate or maybe the most tricky is the vat of alcohol that's kind of gotten resin mixed up in it from from rinsing off prints now that's you know kind of a lot of volume of alcohol that gets all nasty with the resin and so it's a little bit of a question of how to dispose of that properly so a couple of suggestions there one if you let that mixture settle out for a couple of weeks normally all the resin will soak to the bottom or sink to the bottom and then you can decant off the alcohol and use that again another possibility is if you are really done with that jar liquid is to let the alcohol evaporate and then deal with the sludge at the bottom after that's happened so in terms of alcohol evaporating again be careful that you're not going to burn down your house do that in an open area what have you but don't feel bad about evaporating alcohol it happens at hospitals and bars all the time you know for isopropanol and ethanol so really don't worry about that and for the most part you won't be losing too much of the resin stuff to the atmosphere don't worry about that either um and then once you have kind of a sludge at the bottom of your container you can either hit that with light and polymerize it or wipe it up uh get it onto a paper towel throw it in a couple of bags solid waste throw it right in the uh in the landfill so that's uh that's waste disposal uh again the the take-home message is that the solid is really not that harmful can go right in the trash and the liquid very easy to turn the liquid into a solid so here you go um don't pour it down the drain right that's that's the other thing none of the liquid should ever go down the drain not the alcohol not the alcohol soaked in resin never down the drain in the scheme of things we're generating small quantities of waste between evaporation and disposing of the remaining solids in the landfill my conscience is clear all right i think we're wrapping up here i was planning on this being a quick episode uh it wasn't but it was fun you know these episodes where we actually learned something are really gratifying to me and it's awesome how kind of the abstract chemistry comes together with practical considerations and if nothing else i hope i've convinced you to shake your bottles of resin really well so that the monomers and the crosslinkers and the initiators are all mixed in together the way they're supposed to be so yeah that's it for this time i hope you enjoyed this episode shake your resin and thank you so much for watching [Music] you

Channel: Goobertown Hobbies

Views: 303,762

Keywords: resin, resin printer, 3d printer, sla, sla resin, photopolymerization, how do 3d printers work, 3dprinter, 3dprinting, 3d printing, printer, sla printer, slaprinter, sla 3d printer, anycubic, formlabs, elegoo, global3d, white resin, photoinitiator, crosslinker, acrylate, polyacrylate, printer resin, 3d printed minis, minis, miniatures, dnd, dungeons and dragons, dnd minis, warhammer, warhamer, 40k, 4k, warhammer40k, warhammer 40k, aos, warhammer aos, age of sigmar, warhammer age of sigmar, fantasy

Id: ht4tbCiFxeM

Length: 30min 43sec (1843 seconds)

Published: Thu Oct 01 2020

Reddit Comments

[u/PNDMike]

I love Goobertown Hobbies! He's the Bob Ross of mini painting and has a chemistry degree to boot. Thanks for sharing, I hadn't actually seen this one before. Definitely going to stop drinking resin, that's for sure.

[u/clamroll]

I feel like this video should be required watching for all printer owners. Time and again I've seen people with relevant degrees get ignored by people insisting that this stuff is so dangerous it's practically a war crime to use it. Good to hear a respected hobbyist who's a chemist lay it all out in digestible terms for those of us who went to art school 😄 If my dumb ass can understand this, hopefully others will too.

The one thing I wish he covered was that the fumes from isopropyl aren't just flammable, they're a neuro toxin. Probably not going to use it in quantities large enough for it to be a problem, but if you get headaches being around it, you'll probably want a good n95 mask. Check the msds for your alcohols, I guarantee you'll learn something.

[u/Universe_Becoming]

Excellent video! Thanks for posting! 😁

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One thing he kinda got wrong though was regarding UV light and how it relates to LCD printers. Everything he said about UV light is correct, however, LCD printers don't "technically" use UV light. There is an interesting story relating to this as well.

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LCD printers work just outside the UV spectrum. The UV spectrum starts at 400 nm and LCD printers work just outside of that at 400 nm and above. Most use 405 nm light. Why is that? It's because the LCD displays used cannot use light in the UV spectrum. This is because UV light destroys the liquid crystal in the displays. LCD stands for liquid crystal display. In fact, to prevent UV light from the sun or other sources from getting to the liquid crystal UV blockers are built into the displays.

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The interesting story surrounds the invention of LCD printers. The first 3D printer invented by Chuck Hull, founder of 3D Systems, was a printer that used a UV laser to photopolimerize the photopolymerizable liquid resin. He termed it stereolithography or SLA for stereolithography apparatus. These did work via UV light. Then, the next big invention was DLP or digital light processing, printers that also used UV light to photopolimerize the resin. Both of these types of printers were super expensive because of the hardware they used. But inventors knew if they could use LCD displays then they could be made for comparatively next to nothing. The problem was UV light! There were no resins readily available that could photopolimerize outside of the UV spectrum. Until so-called "daylight resins" started being experimented with. Daylight resins could photopolimerize in the UV spectrum but also well outside the UV spectrum! And that's what made LCD printers possible. And now, thanks to LCD printers, we can buy a resin printer for less than 200 USD. 😁

[u/berwyn52]

Great video. Only issue is his speak patterns make me want to pull my hair out. Ending every sentence on a low tone.....

[u/SandiestBlank]

All this time, Dr. Goobertown. Crazy. Also, a great video.

[u/neautika]

This is what we like to see when someone is surfing the line of our rules. Well done. I approve.

[u/Significant-Owl-3628]

How in the world did you get a mono x?