[FlowolF]

Hi there knowledgable folks!

I use dissolved resins and/or plastics on a small scale as part of a wood stabilisation technique (vacuum impregnate softened woods for working), but have been encountering a problem when I use my styrene solutions - the solvents used are various ketone mix based solvents.

After using the solution once or twice, the styrene starts to clump and settle out of solution, eventually forming a very thick clump of goo about the consistency of chewing gum - harsh agitation will tend to take it back into a more dispersed state again, but not for very long, and certainly not long enough or well enough to run a vac. impreg. process properly, and needs to then be disposed of and replaced ',;~{~

As a small scale (unemployed!) user trying to get into business with my work, this is getting costly, not to mention enviromentally unfriendly!

Could this be due to the solution taking on moisture from the wood/will 'trace' amounts of water do this to dissolved styrene?

And if so, is there a way round this/a way to 'dry' the mixture to force it back to a solution or such?

TIA for any help or advice folks - much appreciated - I hope tis is the right place to ask!

Be well all,

Shaun/FW

[Stepan]

When you say "styrene", do you mean chemically pure styrene (monomeric), or polymer - polystyrene?

[FlowolF]

Hi Stephan - thanks for the reply.

I'm sorry - I meant polymer/polystyrene - I reclaim old polystyrene foam packaging for this.

Thanks again, and be well!

Shaun/FW

[Stepan]

Hi Flowolf. I agree with your guess. It is very likely that solvent adsorbed moisture and polystyrene solubility dropped. There is also a possibility that solvent extracts rosin from wood. Rosin also precipitate from ketone/water mixture. Most likely you can remove some water by using desiccant, but this will make everything quite expensive.

You may explore if you can:
-use dry wood to keep solvent dry;
-use all solvent at once, i.e. apply as much as you need for treatment;
-use solvent which does not adsorb water (toluene, naphtha, heavy ketones, .)   

[fledarmus]

I think Stepan is on the right track with his second possibility. I would guess that the solvents are leaching materials out of the wood which are acting as flocculants on the dissolved polystyrene.

If you look at the structure of polystyrene, it looks like a very long alkane chain with a benzene ring attached to every other carbon. Think of a long string with electron-rich coins hanging on it at regular intervals. These chains will interact with each other to form the solid polystyrene, but the interactions can be broken up by the ketone molecules so the polystyrene will dissolve. However, the benzene ring can also interact with other structures like aromatics, alkaloids, or metals which are present in the wood, and these interactions are not as easily disrupted. If enough material leaches from the wood, the polystyrene will form clumps around the impurities and drop out from your solution.

You might be able to minimize your problems by pre-soaking your wood in solvent containing no polystyrene. Stepan's suggestion to use only as much solution as will treat one batch of wood (in other words, treating in a container only slightly larger than the wood) might also help. Another suggestion would be to just allow the mixture to settle and decant off the clear solution, leaving the contaminated polystyrene behind and accepting the loss, rather than discarding the entire solution. You might even be able to recover the gummy polystyrene by treatment with other solvents which would remove the impurities and leave the clean polystyrene behind. Extraction using toluene and water might remove any ionic species, an additional wash with dilute acid might remove any alkaloids.

It would be fairly easy to test whether absorption of water is the issue, but I don't think it is. Just take a couple of mason jars and fill them with you solution, add a little water to one of them, and let them sit for a while. See if anything comes out. The same test can be made by soaking some pieces of your wood for a while in your ketone solvent (no polystyrene), then filtering out the wood and adding the solvent to a container of your polystyrene solution. This will determine whether it is material leaching from the wood that is causing your polystyrene to gum out of your solution.

[FlowolF]

Thanks Stepan (sorry for the feral 'h' that found it's way into your name last reply!) and Fledarmus much help indeed! - even asking the question gave me cause and direction with which to do some more solo-research -

 - I found me a a couple or so ounces of silica balls, dried them well in the oven and added them to one of the pots of gummed up mixture - so far no real change, but then again, our heating broke down and the jar has been sat in the cold, but I take the advice to try adding a few drops of water to a fresh solution sample and will do that asap - simple check - why didn't I think of that earlier?!? - I have the jar with silica gel added warming in front of a gentle heater right now to see if this helps though...

Also in my 'research' ('web-bashing'), I learned just how cosy these types of ketones are with water - will have to try toluene/'naptha'/similar less polar solvent in the future - pity I get the ketone blends for free, eh!

Also been trying to devise a way of reducing the size of the solution container, but not so easy with almost each piece to be treated being of a different size - may have to try some form of solvent resistant poly-bagging, or some such...

As for having the wood dry beforehand, well I do try in most cases, but often this treatment is the first stage to getting the wood dry quickly, and stabilised against cracking - I think the pretreatment with solvent is probably also a good idea too, and is actually one I had been mulling-over myself - aother solvent I can often get for free (and have some stock of right now) is isopropyly alcohol, and this is often used to help dry even 'green' woods, so I assume this *may* at least *help* my situation!

As for pouring off the solvent though to reclaim the PS - well, even though I get both for free, the solvent is *much* harder to come by than is the PS itself, which it seems my neghbours throw away in bulk every week LOL!

So, much to think about and to work on now - thanks very much once again folks!

I'll be sure to return with my results whatever they may turn out to be, though.

Be well!

Shaun/FW ',;~}~

[Arkcon]

You'll want your solvent scrupulously dry (that's moisture-removed, still 'fluid') before you add the polystyrene to avoid the future clumping, for starters.

Its very worthwhile to pre-dry the wood.  Your anhydrous (right?) isopropanol is a good idea, but a pre-soak in the ketone mix is a good idea, to remove contaminates from the wood, and to be sure the wood is full of the same ketone solution.

Since this is a diy procedure of yours, I'm wondering how clean your polystyrene is.  Just ground up packing material or coffee cups?  Because that stuff is polymerized by mixing with other reagents, that might still be there, and available to cause clumping later.  So the answer may require you to filter a few clumps and use your mix promptly.

If you've got some sort of home business, you can purchase pure styrene from a chemical wholesaler such as Sigma-Aldrich.  They'll just ask if you know what you're doing.  AFAIK, styrene isn't a controlled chemical.

[FlowolF]

Thanks Arkon.

The solvent is as it comes - in 5L sealed metal cans and it does dissolve the PS perfectly at first, and unused solution remains a solution even after a couple of weeks, and the ISO? - Well it's high purity/undiluted - most likely 99.8%+, but not sure it'll be technically 'anhydrous' - it all comes from old aerospace stock (they apparently have a 2 year imposed stocking/shelf-life yahsee).

And yes - the PS is just various bits of old PS packing material.

Home business? - Not quite yet! Still at the R&D/experimental stage and trying to get this off the ground, with just about zero funding ATM - in fact we are worse than broke LOL!

Anyways - gonna make a separate post in a mo. with my 'test' results - cheers again bud ',;~}~

Shaun/FW.

[FlowolF]

OK folks - after my chats here with Fledermus and Stepan, and a bit of web-digging I first got some silica gel balls and dried them right out in a hot oven, and mixed them into a jar of gummy PS clumps - nothing at first but the stuff had been sat cold - I heated the mix over the day yesterday and lo! - it started to dissolve again, heh...

However, it didn't return to full solution, least not yet...

After this I did what I 'obverously' shoulda done to start with - made up a fresh, small/sample batch of PS solution, then added just a couple of drops of water and agitated it - almost instantly the PS clumped and settled out into a gum at the base of the jar - so there ya has it - seems that moisture from the wood is at least the major culprit, d'oh!

I think I'll be trying to dry and pre-stabilise the woods (against cracking) with ISO in the vac. chamber, and also be looking out for a cheap or free source of less polar solvents such as the toluene or naptha suggested earlier in the thread, and in fact I'm now hypothesizing that the change in solvent alone will see an end to this bother - I certainly hven't got the time/space/energy/(pick-your-resource) to be pre-drying and re-drying solvents, certainly not yet!

So, thanks once again to all who've replied - you've been a great help indeed.

Take care, and be well, all!

Shaun/FW ',;~}~

 

[Stepan]

Silica gel is not the best desiccant for a liquid phase. For you purpose, try solid sodium sulfate or calcium chloride dried at 150-250C (300-400F).  I believe CaCl2 you sometimes can buy in hardware store as road deicing salt.

You can reuse it again and again if you dry it every time. Be careful with flammability of residual ketones in desiccant.

Also, try to use ketone solvent as fast as you can. With time it starts to accumulate peroxide which is quite dangerous. Use potassium iodide as an indicator on peroxide.

[FlowolF]

Silica gel is not the best desiccant for a liquid phase. For you purpose, try solid sodium sulfate or calcium chloride dried at 150-250C (300-400F).  I believe CaCl2 you sometimes can buy in hardware store as road deicing salt.

You can reuse it again and again if you dry it every time. Be careful with flammability of residual ketones in desiccant.

Also, try to use ketone solvent as fast as you can. With time it starts to accumulate peroxide which is quite dangerous. Use potassium iodide as an indicator on peroxide.

Thanks again Stepan,

Re: silica gel - aye bud - I looked up 'drying solvents' a few days ago (isn't the web a wonderful library!?!) , but a few ounces of silica gel was what I had to hand and it appeared it should have some positive effect, and that plus the test with a few drops of water showed me at least what was happening - I think I will be trying a change of base solvent as the prevention of this issue, rather than be trying to dry the ketones as a hassle of a cure though, if you see what I mean! - Friend of mine reckons he's spotted some toluene, or at least toluene mixed with another non-polar solvent, that he can probably get for me.

However, I will take a look at the hardware place in the meantime, and again - thanks very much for your helpful input S. - MUCH appreciated.

Be well!

Shaun/FW ',;~}~