Thoughts about polymers

I was reading the post on Arcylates and decided that my answer needed a seperate post since I was getting too far afield.

Arcylates are great polymers for industrial uses, the problem is that the momoners are dangerous. They have a high rate of allery development when handled without proper protection, and they STINK. Stink as in your neighbors will be looking to kill you if you put a bath full of arcylates in your garage. There is a reason the name so closely resembles the word arcid. If you purchase a acrylate heavy enough not to stink you will be paying a great deal for the privilage.

That being said, laser prototyped acrylates give amazing dimensional stability, and they can produce better thin section detail than anyother technique I have ever seen. I always hit the laser booth at CastExpo just to gap at the detail.

They also do polystyrene laser cured prototyping, its used to produce a positive for lost foam casing. Again the detail is unbelieveable, and would likley be the best bet for eventually casting microchip scale electronic connections. I dont know what the cost of polystyrene nor what photoinitiators are used, although I imagine it is rather unique and expensive since free radical cure is very hard to control.

That however is a long way off, and not necessaryily the way that we want to go at least to start. I would much rather see some work done with Furfural type polymer, since they are the cheapest momoners available ($0.60/lbs), are dead simple to produce, and being bio-polymers are complete oil independant and carbon neutral. They take fillers wonderfully and are also a thermoset commonly used for making steel pouring molds, so pouring crude wiring should be rather simple. Furfur aldehyde uses straight sulfuric acid as the catayst, and has to be heated in order to get the reaction to advance, but that would require only the replacement of the heater coil with a heat lamp pointed at the work table.

Mike

The email is spam trap, ask if you want a real address.

Mike, your knowledge in this area is incredible. I sure hope you stick around to experiment with these ideas after we get to 1.0!

Great to read about this Furfural! It's important that we have as much detailed data on every polymer that we can think of.
After seeing the pricetags of the photoinitiators on Acryles I got quite a cold shower. It's very expensive and I'm also concerned about the toxicity of the blends. Triethylamine is some nasty stuff too and stinks probably even worse than acryles.
I think that the biggest issues with that polymer apart from the cost are the risks at manipulation.

I have been looking around and it seems that if we can get the Furfural to polymerise with an acid (can it be HCl instead of sulfuric acid? it's less of a hazard in my experience) and we can get a heat-source to focus enough on the printout (IR heating lamps), this would be a far easier option.

On styrene, i'll have a look around to see what could make it to polymerise fast and cheaply. I wager that the price of styrene is similar to the acryles, but it doesn't smell bad at all (at least for me). Technical grade styrene must be quite cheaper, but i have a distant memory of a warning concerning explosive polimerisation due to impurities, maybe I was having nightmares in the lab...

wow, i agree with corey that you know your stuff... i looked up furfural on wikipedia and found this:

Furfural, as well as its derivative furfuryl alcohol, can be used either by themselves or in together with phenol, acetone, or urea to make solid resins. Such resins are used in making fiberglass, some aircraft components, and automotive brakes.

thats super cool! should be some fun stuff to play with.

Polymers I know (being an organic chemist), but I will be leaning heavily on the group when I try and build a printer (not being an engineer). Mine will have to be the pressure pot variety, since I intend to try every type of polymer I can think of.

Free radical cure mechanisms like polystyrene are very difficult to control, although adding filler USUALLY is enough to prevent that from happening. I would imagine that they use a low molecular weight wax as the filler in commercial systems.

HCL will catalyize furfural just fine, H2SO4 just has twice the acidity per pound (which is the reason it is so dangerous) and is usally cheaper per pound so ends up costing about half as much. Most places premix the catayst onto the filler to reduce exposure.

I would skip furfural alcohol, it will exploisively polymerize if acid is added to the pure alcohol. Premixed with filler is the only way I ever handle it. Furfural doesnt react as quickly so that isnt a major issue. The orginal Bakelite was furfural based if memory serves. Both make relatively brittle polymers (just ask anyone who has broken a piece of bakelite).

Both materials are very filler friendly and will actually partially crosslink with cellulose fillers like sawdust (the filler in bakelite). The most common filler is sand since that has high enough heat resistance to pour metal with.

The most important reason that I think furfural is a great material to look at is the production method. Its produced by distilling agricultural waste in the presence of acid (usally sulfuric) and doesnt need any purification prior to use. If you use nitric acid the left over sludge can be neutralized and used as fertilizer, and the still can go back to producing ethanol (although I would have one still for fuel ethanol and one for drinking grade). The yeild is about 10% of the weight of the agricultural waste.

Its actually a major goal in production of ethanol from cellulose to get the furfural out without damaging the end yeild, since furfural is worth more per pound than ethanol is.

So as cellulose ethanol production expands, so should the availablity of furfural. Most furfural currently is changed into furfural alcohol for use in metal casting because furfural alcohol reacts a lot quicker in the absence of additional heat.

Mike

The email is a spam trap, ask if you want a real address

Yup, organic chemist here too, allthough my speciallity is more in IR analysis and synthesis methods. I'm sure i will have tons of questions for you on polymer chemistry!

A comment on Styrene. If we are going to use that polymer, we must go the way of copolymerisation with butadiene or such, as pure polystyrene is very brittle and has poor mechanical qualities. Maybe you know cheaper copolymeres and ones that mix better with styrene? Maybe a good filler would do the trick of improving it's mechanical qualities?

On the other hand, the more i read about furfural the more i like it!
I'm going to inquire for the price of the ready-to-use mix. The composition generally used i think is a mix of furfural alcohol, silica filler and phenol, but if we can get a good, ready-made mix delivered, i'm sure non-chemist would prefer it a lot and it would give us a standard blend to work with. if it allready has the H2SO4 mixed in, ok.. it really is a better reactant than HCl. I'm just concerned that high enough concentrations of it could have bad effects on the gear, as it attacks anything that isn't glass or stainless steel or polyethylene or such... HCl is less demanding on the equipment.

It is so cool to have some honest to goodness organic chemists on board here at RepRap. Are either of you two interested in the chemistry of producing polyactic acid (PLA) from cornstarch? Vik down in Auckland is having some commercially produced PLA made into filament for his 3D printer to see how RepRap friendly it will be. There has been a great deal of amateur interest in confecting a methodology for making small batches of usuable PLA.

Forrest Higgs Wrote:
-------------------------------------------------------
> Are either of you two interested in the chemistry of
> producing polyactic acid (PLA) from cornstarch?
> Vik down in Auckland is having some commercially
> produced PLA made into filament for his 3D printer
> to see how RepRap friendly it will be. There has
> been a great deal of amateur interest in
> confecting a methodology for making small batches
> of usuable PLA.

Hi Forrest!

I can look into this, but for starters, polylactic acid is a polymer of lactic acid, which doesn't derive directly from starch or sugars. It is the processing from sugars or starches by living organisms that creates the lactic acid. This turns the production process of PLA from starch in quite a heavy-duty endeavour (involving yeasts or bacteria and fermentation tanks and whatnot). Maybe you would be interested to know about the synthesis of PLA monomer from lactic acid? Lactic acid is cheap (i've seen 0.7 to 3

I will make a couple of calls as well. I work for one of the largest producers of the premade blends, Ashland Inc. The problem is that I work for the research and development area not sales. So while I work every day with the materials themselves, I order from the factory for free and have no clue about retail availablity and pricing. I actually tried to get Ashland to pour some test castings for reprap in our onsite foundry but wasnt able to drum up any interest.

My synthesis is rather weak these days, I specialize in product development and alternate material testing. So once I get a printer I have ALOT of ideas about possibilites. I have got some beautiful light/cheap poly-ceramic composites that I would use if I could get my hands on molds for the parts.

Mike

I'm amazed at the fantastic mix of skilled people we have here!
Mike, you having knowledge of polymer blends is incredibly helpful! And hearing the word "poly-ceramic"... i'm salivating over my keyboard allready!!

What if we make a short document with the crucial parameters a RepRap polymer would handle, so that we could start categorising the polymers and their blends and modifications. This way we could make non-chemists understand what control they could gain over these polymers and they could start thinking on what devices and software they may devise to take full advantage of the crazy blends you come up with!

To list a few categories, no order here:

* Type of polymer: thermoplasts/non-thermoplasts/dissolved polymers/double composite/unstable monomer...
* Fast setting/slow setting
* Setting parameters: melting/polymerising temperature, time to workable set, time to complete hardening, light-activation, temperature activation, catalytic activation, volume expansion/contraction after setting
* viscosity
* mechanic properties of freshly printed polymer
* mechanic properties of hardened polymer
* solubility
* accepts fillers
* availability/price
* safety

whatddayathink?

that would be really cool. we have some pages detailing types of materials that can be used in the wiki... its pretty decent, but could definitely use some sprucing up.

personally, i dont know much about chemistry... so i cant do it myself, but it would be amazing if one of you guys wanted to take a crack at it.

we hid the wiki registration link to keep the spambots out, but send me a PM and i'll send you the link to register.

As soon as I can get my email to see the registeration message I will pm you for the link. In the meantime I have been testing the possiblity of using one of the poly-ceramics as a base for a repstrap and was quite pleased with the results. I mixed up a sample today using our cheaper commercially available resins and used a wet catayst rather than a gas catayst. The result is a material that can be sculpted into almost any shape for the first 10 mins then worked with a knife for about 10 more mins after that point you need a file or saw. I used the same resin to then impregnate some of the pieces and I'll get tensile strengths off the different types tomorrow, I expect something with slightly less compresssion strength than concrete but with higher transverse and tensile strengths.

The end cost for this material should be less than $2 per pound even after impregnation (and a heafty markup from the wholesale costs) and the composite is so light that the end density is in the 0.7g/cc range. In addition because it has about 80% ceramic character and that ceramic is a refractory the heat resistance and castablity of any end product would be astromical. The great part is that since all of these materials are products that my employer sells, I figure to file it as a side project in new market development and get credit for it if I eventually arrange a sale.

Wow, sounds like a Win/Win. Better reprapping through chemistry!

cool! if you're in the USA and would like me to ship you some syringes and a few different needle sizes to test with i'd be happy to. or you could go to [www.researchsupply.com] but you'll have to buy a few boxes of needles to get different sizes. still pretty cheap ($3-4/box)

the biggest syringe i can find on the net is 100cc, but they only sell up to 60cc. anyone know where we can find larger syringes?

Just a crazy idea:
what about using a modified hand pump instead of a syringe?
The kind used for pumping bicycle wheels with.
How hard would it be to modify it so that the polymer doesn't leak over the piston?

These pumps exist in many volumes, and may have a long tube so that the pump doesn't have to be carried along the syringe-tip.

The thoughts and ideas expressed in this post do not reflect those of my employer and are intended only as communications between individuals. Any attempts at implement are at your own risk

Edited 1 time(s). Last edit at 09/12/2007 09:54PM by ohiomike.

What a brilliant idea!
This rig you describe is even perfect for testing polymers also. No need to finish building a whole Reprap to test mixes, viscosities, fillers, nozzels, tube-lengths!

You know, as nozzles i was thinking about polyethylene micro-pipette tips.
They can be wedged or screwed in on a threaded pipe that would connect the plastic tube you describe above. I have found several boxes of 12000 pipette nozzles for 30$ on ebay, here one example:

[cgi.ebay.com]

Its my hope to build a repstrap by constructing the polymer delievery system so that I can optimize the material and then using my hand as the robot to build the other pieces.

The simple pieces I can build with the poly ceramic using flat plates etc, the more complex I will use the paste extruder and my hand to make. I can control flow using my fingers as a pinch value until I can build the pinch value, etc, etc, etc.

My hope is that when I am finished I will have a very good idea of part configurations, as well as the viscosities and cure rates that will get the highest productivity out of the system.

Whenever weight isnt an issue I plan to substitue cast concrete to lower the price, increase durability and increase stability. The build table and the pressure pot come to mind.

Since all of the composites I am interested in can be cold cured with liquid catayst, baked for extra strength, and then impregnated if necessary, I think it might work.

Mike

The thoughts and ideas expressed in this post do not reflect those of my employer and are intended only as communications between individuals. Any attempts at implement are at your own risk

Edited 1 time(s). Last edit at 09/12/2007 09:55PM by ohiomike.

Mike, that ceramic blend you've got is so good it seems to be the philosophical element! )
And it probably has excellent thermal properties too, right?
How about being able to use it as a precision cast resin in a mold?

Here is why i ask: I have always thought that for the parts that need to be the toughest, we need to print out a mold which we would then fill out with a more liquid version of the resin and let it set. The mold could be disposable (wax, silicone...) and removed after the piece has set. This would achieve much better mechanic properties than having deposited the whole volume of the piece thread by thread.

Actually that is precisely the use these materials were orginally developed for. They are called nobake foundry resins when rammed into molds the way you are describing. For precision casting you would need to reduce the viscosity but that is easily done, in fact a lot of craft stores sell these types of resins pure for exactly that use.

I will do you one better and tell you about a process called cold-box core making where foundries make casting molds by injecting this material into core-boxes using compressed air and then inject triethylamine gas insead of using a liquid catayst. For all intents and purposes the reaction is instantous so the productivity is huge. Given molds of the parts I could turn out reprap kits by the dozens in a weekend. There is even a line of injection coremaking that uses the furfural type resins. Scrubber systems already exist that would allow the left over amine to be captured and reused.


This is the primary method that foundries use to make the sand cores that they then use to pour the metal parts with. Its very well understood 20year old technology.

I spoke to my boss about the project and while he doesnt want me working on it during normal business hours, he has agree to allow me to use it to fill in down time, or to stay late (since I am salaried). The material costs are negligible and as far as he is concerned are part of me gaining a better understanding of the systems.

He is a metalurgist (with 30 years experience) so I was picking his brain on the castability of my material, he suggested that prior to casting thinner wiring I would want to pre-heat the part so that thermal differences would be less and gas pressure would be less likely to slow the formation of the wires. Also he thought aluminum wiring would generate less gas especially with the higher resin percentage I am looking at. But he thinks with careful design their isnt any real reason the wiring couldnt be cast into the part.

Its very unlikley that I will ever get permission to use the foundry given the huge backlog, but I actually know of a couple other test foundries that I have contacts in that I am going to ask.

Mike

The thoughts and ideas expressed in this post do not reflect those of my employer and are intended only as communications between individuals. Any attempts at implement are at your own risk

Edited 1 time(s). Last edit at 09/12/2007 09:52PM by ohiomike.

wow, thats great news. i love reading your thoughts and progress on this. its definitely an area i would have no idea about getting into... but it seems like a very promising area.

have you looked at backyard foundry sites for doing metal casting at home? apparently they are VERY easy and can do stuff like aluminum, brass, etc.

Till you crack a crucible. :-o

My thinking is that the most basic printer isnt a printer at all its a PEN. The first plotter style printers were basically just pens with automated holders. So the first step for me will be the development of a 3D pen. That way I can leave all of the robotics development to the engineers for the time being and work on what I am good at.

I am thinking about using a length of thin CPVC to stiffen the delivery tube with a stylus style opening so that I can shape the material as it extrudes. Then attach a threaded clamp on the hose above the stylus and just loosen the screw to start the flow and tighten to stop. I will worry about automation after I get the polymer delivery pen to work well and get a good feel for the material.

If I can make the pen simple enough a bare bones kit might just consist of instructions for building a pen, templates for the first parts in PDF and the materials list with ordering/construction info for materials like the boards, motors, resins and refractorys.

Mike

The thoughts and ideas expressed in this post do not reflect those of my employer and are intended only as communications between individuals. Any attempts at implement are at your own risk

Edited 1 time(s). Last edit at 09/12/2007 09:50PM by ohiomike.

The simplicity of casting aluminum is a major point in its favor. I will also scout for job shops that might be willing to toss a handful of castings onto the end of a larger aluminum pour for a $100 or so.

Lets not discuss broken crucibles/explosive devices.

Mike

The thoughts and ideas expressed in this post do not reflect those of my employer and are intended only as communications between individuals. Any attempts at implement are at your own risk

Edited 1 time(s). Last edit at 09/12/2007 09:49PM by ohiomike.

you may want to have a chat with adrian. i know he has done work on both a syringe based extruder and also a peristaltic pump based extruder. also, he has done some experimentation with that pressure pot style one you were talking about.

extruder heads will be super simple to make once we can print all the little parts for them. oh how i dream for post 1.0 days... =)

***Lets not discuss broken crucibles/explosive devices.***

Ah, so if we ignore the problems they will disappear, hey? right...

well, if your crucible breaks, you simply make another one. from what i've read, a properly constructed (and used) forge can last for years. as for the crucible itself... its just a steel container and can be easily replaced.

i'd rather worry about real problems =)

Sigh... My experience with crucibles and molten metal stems from comments gleaned from a long association with a family of artists in South Africa. One of the things that several of them do is casting statuary. On showing one of them the publication of of the Gingery Foundry I got in return the observation that metal casting was something that was quite dangerous even for people experienced in the technique. I was told bluntly that such publications that gave the impression that casting was a skill that just about anybody could undertake as a hobby was, how can I put it, irresponsible.

Indeed, on websites describing casting you regularly see this sort of caveat...

******************************
Working with metal (molten or otherwise) is inherently dangerous, and you run a very real risk of injury or even death if you have an accident. The information on this website is for entertainment purposes only, and I can't begin to describe a complete set of safety practices for working with metal. If you are a bit of a klutz, don't try working with metal! If you have an accident, don't blame me! Having said that- wear steel tipped work boots, wear coveralls, wear a full face mask and wear heavy leather welding gloves. Don't rush your work. Think carefully about what you need to do. Always be comfortable, attentive and calm. Don't work with or around people who are distracting or don't know what they're doing.
******************************

[www.mibot.com]

Okay, I've had my say. I won't trouble enthusiasts here again.

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