glueshooter
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Phenol / Formaldehyde reactions in DI H2O
Hello all, let me apologize by saying this may be long, but it's because I want to be clear. Second, though I am a physics guy, I'm no chemist.
I want to make a stable aqueous solution of phenol - formaldehyde to later convert into some form of bakelite. I've searched the board extensively,
read some of library books, but something still isn't clear to me. I have access to all the raw materials: pure DI H2O, phenol crystals, 37%
formaldehyde solution (stabilized with methanol). And I have the acids. But the thing is, I don't want to actually react it.
I'd rather do something like this. Wiki says the max solubility of Ph is 8.4g/100ml. I'd like there to be some excess solubility, so I'll limit the
amount to 6g in 100ml.
To keep it simple, I'll imagine I want to make novolac. In theory then, I guess, I'd want to add an equal number of moles of the formalin to the
phenol solution. That's easy enough to calculate for any batch size, and I guess I just have to adjust the calculated amount to compensate for the
presence of methanol.
So here are my questions.
First, is this going to blow up on me, or will it be basically stable? In all of the material I gathered, there was always a step involving glacial
acetic acid and the hydrochloric acid to make it go 'boom!' Heat was often involved too. If I never add those acids and I keep it at room temperature,
can I keep it from reacting by using more methanol?
Why do you need or use both acids? Or is that for effect in videos and stuff like that? I'd like to react it later, but I'd like to have it in a
stable liquid form until then.
Phenol is a weak acid. Would I benefit by neutralizing it with NaOH prior to adding the formalin? If I neutralize it now, will it be able to react
later in the presence of an acid catalyst?
Should I dilute the formaldehyde solution prior to adding it? Formalin has a pKa of 13.3. Is it mildly basic then? Do I need to do anything about
that?
If the system is pH sensitive, do I need to worry about CO2, and should I bubble N2 thru the water first? Maybe even pull a vacuum on it prior to
that?
I've read about 1-Propanol being used as a stabilizer, but I've never seen a reference to anything other than methanol being used to stabilize
formaldehyde in water. Does it have to be methanol? Is the 3C chain on 1-P too long?
Can simple glycols, like propylene glycol, be added to these systems? Or do they interfere with cross-linking? Or do they initiate it?
If I keep my temps cool, like under 30C, will that help?
In the final reaction, do you have to have both acids, or will any strong acid do?
Thanks if you've stayed with me this long, and thanks again if you can provide any insight. - D
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kecskesajt
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IIRC, the acids are just catalyst.So if you mix phenol and CH2O,you get phenol-formaldehyd wich is capable of explosive polymerisation.
https://www.youtube.com/watch?v=Vlh0YDRmZ0I <-----Watch this video.
You are into physics more than chem?Be carefull with 37% formalin,my 25% formalin just burns my throat and eyes,makes a hard cough.Open outside,get a
face shield.Phenol is also toxic,causes skin irritation and peeling.
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Thaekross
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Why must it be a pre-made solution, pray tell?
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Thaekross
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Oh and, basifying Phenol produces a Phenoxide anion which will react with the Sodium cation formed from the proton exchange (Phenol acting as an acid)
and produce Sodium Phenoxide.
The reaction can be base-catalyzed any-who, so just mix 94g of Phenol and 40g of Sodium Hydroxide together in some water and slowly add 120mls of
Formaldehyde drop-wise with constant stirring and keep at about 70 degrees C. Someone correct me if I'm wrong.
It's an odd reaction to perform as it forms a poly-chem 
P.S. Try to keep at the same viscosity and heat it to 120 for about half an hour
...Perhaps an excess of NaOH?
[Edited on 31-7-2015 by Thaekross]
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glueshooter
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That's one of the videos I watched. But like I say, there's a step where they add both heat and acetic acid. He even says, "And that will sit there
happily, and nothing will happen until we add this, concentrated hydrochloric acid." And I notice too, he's not doing what I'm proposing, that is,
dissolving the phenol in water first; he just adds formalin straight to the phenol crystals.
And I can't tell exactly, but it looks like the phenol completely dissolved in however much formalin and acetic acid he added. If he did add excess
water, it was edited out. Maybe the acetic acid was very dilute instead of being glacial. Or I suppose, maybe the formaldehyde isn't the full 37%
variety. I wish they gave some numbers and specs to what they're using. But I suppose if I used the 20% variety, I wouldn't need to add as much water.
So I'm still confused about whether or not I can make this. And do I have to use the acetic acid? Is it used just because it's a better solvent for
phenol than water is? Why, and maybe this is outside the scope, but why is HCl a catalyst and acetic isn't? What does that mean for dissolved CO2 and
carbonic acid?
As for why I'm trying to start so close to the bone, Thaekross, it's because I haven't been able to purchase a suitable formula that can be modified
to suit my needs. They come as partially pre-reacted mixtures, and I'm having all kinds of problems with batch to batch uniformity. I have to thin it
with so much IPA that the fluids are phase separating.
I just want to start at the beginning and come up with a good base formula for the printing operation I'm trying to do. Whether or not I would ever
make it long term, I don't know, but I feel like my suppliers don't understand what I'm asking for, and neither do I. So I just want to build up some
experience so we can all talk more intelligently. But I don't want to blow up my lab for that.
And let me just say again, I don't want to react it in the bottle. What I want to do is prepare a surface with a catalyst, and print onto it. I don't
want it to react until it hits the substrate. But I want to stay fresh in the bottle as long as possible, but not do so much to keep it fresh that it
won't ever react.
Thanks again, D
[Edited on 31-7-2015 by glueshooter]
[Edited on 31-7-2015 by glueshooter]
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Pumukli
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I'm just reading J. Frederick Walker - Formaldehyde (1944), maybe it is in the SM library, not sure.
Anyways, in chapter 12 "Reactions of formaldehyde with phenols" it says a few interesting things.
E.g.:
"When trioxane crystals are mixed with crystallyne phenol at ordinary temperatures, liquefaction takes place, heat is absorbed, and a colorless
solution is obtained. Reaction takes place only when a strongly acidic depolymerization catalyst is added to the phenol-trioxane solution."
Or:
"... as a result, acid condensations may attain a violence which cannot be equalled under alkaline conditions."
Or:
"Saligenin is a crystalline compound melting at 82 C. On heating alone or in the presence of an acid it is converted to resinous products... Saligenin
is synthesized by the method of Manasse." - which is not a too complicated procedure.
I suggest you consult this book if you want to explore these phenol-formaldehyde polymers!
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Thaekross
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There isn't really a way to mix phenol and formaldehyde as they will always react slowly. The ions that are formed in this acid-base reaction will
always react together.
As far as I am concerned; This is impossible, at in the manor you want it.
I would suggest, If you need to do this so much, that you just perform the reaction and melt the poly-resin to liquid, mix with wood-flour and keep
heated until printing. At printing, cool it down slowly and then print before it cools to hardness
The poly-resin should be stable enough to keep in storage.
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Nicodem
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Thread Moved
1-8-2015 at 01:31 |
glueshooter
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Thanks for that tip, Pumukli. I'd been downloading the O-Chem books looking for chapters on Phenol, and I didn't think to read the Formaldehyde book.
It is in the library, great call.
And Thaekross, I think that's what I'm wondering. Is it constantly reacting, just really slowly instead of violently. And I wonder how slow you can
keep the reaction before you have a solid resin filled bottle. I only need to measure shelf-life in months, so as long as the reaction is very slow, I
might be able to get away with it.
Thanks again, back to the reading. - D
[Edited on 4-8-2015 by glueshooter]
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glueshooter
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I think I'm just going to buy some materials and go for it. I've found several formulas that all seem to suggest that the reaction can be either
slowed or neutralized. I still don't understand exactly why the acetic acid is used, and I will probably leave it out. I really don't think it's a
catalyst, but I'm not sure if it's supposed to be a cosolvent or what.
I can't find a solid reference for the maximum solubility of sodium phenoxide (sodium phenylate). The only number I could find was on
thegoodscentscompany.com, and I'm not 100% confident in anything they're publishing. Anyway, it said 1x10^6g/L, or 1g/cc. That just seems a little
high to me, not that I would know.
So I'm thinking some aqueous NaOH, add Phenol slowly while stirring to convert it to Na.Ph, add some N-Propyl alcohol, then add the methanol
stabilized formalin and see what happens. At a very small scale, of course, less than 10g of phenol crystals to start. Put it in a bottle and leave it
on the shelf for a few days. I'm really thinking that I can keep it from reacting violently.
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WGTR
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Please forgive me if I'm overlooking an important detail about your application. I don't quite understand why you want to mix the reagents together,
but don't want them to react until a later time.
Bakelite can be made from phenol and formaldehyde, as you already know. Acid or base catalysts can be used. Using some archaic terminology, the
initial result after some heating with an ammonia catalyst is the "A" phase. It's a liquid resin that separates out from the water and sinks to the
bottom. At this point it is soluble in acetone, and can be thinned out for spraying. Further heating gives the "B" phase (and some more water), that
isn't soluble in acetone, but can be softened and fused together under heat and pressure. Heating at higher temperatures, or for a very prolonged
time at lower ones, results in the "C" phase. This is impervious to many solvents, is brittle, and doesn't soften under temperature. It's the
precursor to glassy carbon, in fact.
From Dr. Baekeland himself:
Attachment: THE SYNTHESIS, CONSTITUTION, AND USES OF BAKELITE.pdf (1.3MB)
This file has been downloaded 387 times
I've had some "A" phase diluted in acetone for a week or so at room temperature, and it is quite happy to remain in its present clear yellow, low
viscosity, state. I've been using it to pot transformer windings and other things.
In a small test tube, 10mL of formalin (w/10-15% methyl alcohol) was mixed with 3.0g of phenol at room temperature. Everything dissolved to a clear
solution. 2.0 mL of 30% ammonia solution was added drop-wise. For the first few seconds, some vigorous bubbling was noted. Everything was mixed
together thoroughly, and the temperature was noted to rise. The test tube was stoppered loosely and placed into a water bath, and heated at 80°C for
15-30 minutes. The top part of the tube was above the water line, and it is there that some volatiles would condense.
The overall reaction had a similar appearance to a haloform reaction. The solution remained clear under heating for a significant amount of time, and
then it suddenly clouded up. Right at the point when the solution became cloudy, it was removed from heating and left to stand overnight. Slowly,
the product separated into two clear phases, with water on top.
The bottom phase was removed, and diluted with acetone to achieve the desired viscosity. Easy cheesy.
A drop of this stuff on a glass slide needed heating at 75°C overnight before it took on a hard surface at room temperature. Even then it cracked
when it cooled down, and heating at higher temperatures caused it to remelt. It wasn't until heating above 175°C for a few minutes that the resin
completely cured to a fully hard, clear, bright yellow "glass".
I recommend using ammonia solution as the catalyst. This avoids metal ion contamination, and the reaction is much less violent than the
acid-catalyzed version. If you want to know, my procedure was taken from DOI: 10.1002/masy.200900127.
http://onlinelibrary.wiley.com/doi/10.1002/masy.200900127/ab...
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glueshooter
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Thanks, WGTR, I guess I'm not explaining it enough. I need to be able to run this fluid through an industrial piezo printhead (think XAAR or Dimatix )
and it has to be low viscosity / low surface tension to work. Around 7cPs and 38 dyne/cm.
Why I say I need it to 'react later' is simple. I mean, it's a printing operation. Sometimes, you have lots to print, sometimes, you have little to
print. So, maybe you buy twelve gallons knowing that you'll use that up over the course of a month or two. Maybe even 6 months. So I need the fluid to
stay stable until you actually want to print it.
And I don't want it to harden 'in the printer', at least not exactly. I want the ink, on contact with the substrate, to be activated by the acid there
(that's mixed in to the substrate), and only then start its final setup.
It's like a single layer sand-casting (that's where I'm getting the inspiration, anyway). Say I take a piece of water repellent paper, and I print a
thick coating of this fluid on it. Then, I take some silica sand and mix it with some HCl, and really mix it to spread the acid all over the kernels.
Then I dump this 'activated sand' on the printed pattern. I let that react over night, or on a hot-plate, and then I shake off the excess sand, and
only the printed area remains covered in sand. It's like making patterned sand-paper.
Is heat just as important as acid? Will this whole idea never work cold?
Thanks, and I'm going to read this paper right now. - D
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WGTR
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OK, thanks. I understand what you're trying to do now.
This "A" phase that I'm describing is basically what is sold as "resole" now:
https://www.plenco.com/phenolic-novolac-resol-resins.htm
Shelf life:
https://www.plenco.com/customer-material-support.htm
Another idea is to access this book online:
http://link.springer.com/book/10.1007/978-3-642-04714-5
I was able to download the whole book through my university account. I can't post it here, but you can probably get it free by visiting your local
university. Chapter 4 (resin chemistry) explains what chemical reactions happen at various curing temperatures. I think it will answer a lot of your
questions.
Also, there is a paper that directly answers your question about shelf life:
http://onlinelibrary.wiley.com/doi/10.1002/pen.760271308/abs...
I'm not well acquainted with printing applications, so my help with that may not be very useful. I also work with only the simplest phenolic resins,
and don't have a wide breadth of knowledge in this area.
[Edited on 8-7-2015 by WGTR]
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glueshooter
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No, WGTR, you couldn't be more wrong. This is the EXACT kind of help I need. There's tons of information, but it's all so focused on getting to the
end product of resins.
Like you, I want to stick to the simplest forms possible, About the only thing special about my kind of ink formulation is that it's usually best if
you can make a true solution chemistry, as opposed to emulsions, suspensions, and colloids. Though it's true that all kinds of fluids can be printed,
for my particular realm, dissolvable solutions are best.
The one thing I can't quite wrap my head around is the acetic acid. It doesn't seem strong enough to be a catalyst, but it's a liquid, so maybe it's a
solvent? Or does it become one of the participants in the reactions once the HCl sets it off?
But thanks again, and thanks everyone. - D
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