[2lrigbal]

Hello All,

I was wondering if anyone might be able to suggest a solvent to break down polyurethane prepolymers?  To be specific, the components on the profile are the following:

Ethyl acetate (5-10%) 
Polyurethane prepolymer (90-95%)
4,4 Diphenylmethane diisocynate (0.1-1%)

It seems like the polyurethane prepolymer was  used to bind the ethyl acetate, a solvent, with the 4,4 diphenylmethane diisocynate as a catalyst, is this right?  I only have the final product and the above list of materials that are supposed to comprise it.  I need to find something that will break it down or, better, dissolve it.  The only information that I have been able to find is the process of making polyurethane prepolymers, where to obtain more, and the uses of the material. 

Acetic acid or acetone soften the material, but I was hoping to find something that might work better.

Thanks!

[P]

I think the isocyanate causes crosslinking. Depending on the degree of x-linking the polymer will be harder to dissolve. 

With the acetone - you say it is softening rather than dissolving. How long have you left it?  Can you try breaking it up a bit with a spatula and stirring and then leaving it overnight to soften/dissolve a bit more? Then try more stirring and time to allow the solvent to really work its way in. (amount of time will depend on the degree of the x-linking).

Failing that, you could try some more potent solvents  -  maybe Toluene, or if all else fails THF is on of the stronger ones for dissolving up polymer  -  again -  it can take time if the degree of x-links are high.

[macman104]

I did some browsing and a site suggested possibly methyl vinyl ketone.  I always like DCM as well...

[P]

I did some browsing and a site suggested possibly methyl vinyl ketone. 

would the mvk be much better than the acetone?

I always like DCM as well...

Yea, I nearly suggested that as well!         When I worked in a polymer lab though, THF was our 'magic' solvent for the stuff that didn't want to dissolve.  We found that with most polymers, if THF wouldn't dissolve it then nothing else we had in the lab would.


Some people seem to think dissolving something is like magic (like acetone on expanded polystyrene)  -  you pour it on and the solid disappears.  This doesn't always happen - especially with highly cros-linked stuff.  You sometimes need elevated temperature, stirring and time for the solvent to seep deep into the solid and untangle the polymer chains.  Sometimes things can take a couple of days even to fully dissolve in a solvent, especially if the solution is near saturation point.

[2lrigbal]

P,

Yes, I left a sample in acetone overnight, and it was softened enough for me to break it up this morning.   The problem is that there is a rather large amount that will need to be broken down.  So that is why I was looking for something that might work better, or faster really.  If time is what it takes, however, that's how I will work with it.  Much thanks!

[DrCMS]

Ethyl acetate (5-10%) 
Polyurethane prepolymer (90-95%)
4,4 Diphenylmethane diisocynate (0.1-1%)

It seems like the polyurethane prepolymer was  used to bind the ethyl acetate, a solvent, with the 4,4 diphenylmethane diisocynate as a catalyst, is this right?

No its not.

I think the isocyanate causes crosslinking.

No it does not.  Its a diisocyanate so it forms linear chains.

Polyurethane prepolymers are made from the reaction of diols with diisocyanates, in this case the diisocyanate is MDI or 4,4 Diphenylmethane diisocynate . 

If the prepolymer is made with an excess of isocyanate as in this case it moisture cures.

The ethyl acetate is there as a solvent to reduce the viscosity to a more manageable level.

Cross linking is usually introduced with a triol.

As for dissolving the stuff if it has been kept dry try adding more ethyl acetate.  if its got wet and cured then it's a lot harder to shift.  To clean our reactors we use acetone followed by 5-10% aqueous caustic.

[macman104]

would the mvk be much better than the acetone?

Can't say.  I was just stating what I had read...

[P]

 If time is what it takes, however, that's how I will work with it.  Much thanks!

No worries  -  try the THF, it will be alot quicker by my guess.

[Mitch]

ethyl acetate is a solvent.

[Greener living]

In my experience, mix a bit of plasticizer with your solvent.  The plasticizer will help swell the polyurethane film, which then allows the solvent to solvate the film.  5-10 wt% of a common polyurethane plasticizer like DIDP, DOP, DINP, BBP, etc, will work wonders.

Good Luck.  Once polyurethane's crosslink, they are very tricky to get back into solutions, by design.

Also, I would agree with a previous post, the acetate is a solvent in this system.  I would try using the acetate with the plasticizer.

[rubberguy424]

Hi

I have been using a dimethylsiloxane for sometime and I too need to break this down further into a liquid.  I have found that Hexane is definately the way forward.  By aggitating the reaction, simply by stiring, I have the compund broken down in less than a minute.  You may have some luck trying this

Cheers

[ultraultra2001]

I am looking for a catalyst in order to accelerate the curing of one component polyurethane binder. This binder used to bound rubber granule in order to make product such as playground area tiles and also in the pour in place product such as running track.

 

two type of binder produced and used for these application,

1- is 1 on component binder who I think it is a prepolymer and after mixing with rubber granule in a mixer poured in a hot press and curing take place normally in 15 minute under high pressure and also 130 degree centigrade hot plates.

 

2- is the same binder which is used in pour in place projects such as running tracks. in this method the rubber and binder mixed and pour on the ground and level it and with a very low pressure compacted. the curing in this type is slow and also final curing take place may be after 24 hour.

 

i don't have any experience in chemical but i know these materials and working with them. I know that cutting in such binder accelerate with humidity but i need to reduce curing time more, such as 6 minute in the first application (hot press)

 

I know some catalyst used in PU applications such as DOBCO and now I use lead octoate (liquid metallic catalyst ) but  using this catalyst make the final product weak and also brittle.

I think the two type of above binder is the same but a catalyst used in factory in order to make the first one faster than the other. So I am looking for such catalyst which I  can add to binder in order to make it faster.