I want to spray n propyl bromide onto a vertical surface to remove an
eva coating using airless equipment.  (Proper breathing equipment is
used of course).

The trouble is that the n proply bromide evaporates very quickly.  I
need to find some way of thickening the solvent so that it stays on
the coating long enough to work.  I have tried fumed ("fluffy") silica
but this just blocks up the hoses and filters on the airless pump.  It
has been suggested to me that I add about 3% parafin wax to the n
proply bromide to slow down the evaporation rate and this sounds like
a good idea.  I still need to thicken it though.  I picked a chemist's
brains at one company and he suggested thickening it with a
surfactant.   I have tried a couple of companies and I can't find
anyone who can tell me anything sensible about this.   Albion
chemicals in the UK were suggested to me but it seems like they cannot
be bothered to help me with this.   One of their boffins suggested
thickening the npb with coco diethanine with glycerine.   It only
thickens it a little bit though.  I really want to thicken it a lot.  
(getting a sample from Albion was like drawing a tooth and their
"surfactant specialist" just could not be bothered to help me.)

To summarize:

I need to find a thickener which will work with n propyl bromide.   It
cannot be any kind of  mineral though because this just blocks up the
lines and filters on my airless pump.  I think some kind of surfactant
may be ideal because would also help break down the eva so there would
be some synergy with the npb.

Note:  $100 will be paid when a sample of suggested thickener has been
received and is found to work.

Cheers Chris Parkinson

chrissyboy-ga:  There are many methods for thickening organic
solvents. (I have 30 years experience as a paint chemist.) If you can
obtain a sample of dry napalm from Monsanto (Probably not) it will
thicken organic solvents, such as gasoline and many others, at room
temperature. I know because I once used it in a non-military project.
Aluminum stearare and calcium sterate also work, but require some
heating. Why not simply add a thick grease to your solvent?
  Then there are polybutylene polymers which thicken most any organic
solvent. Union Carbide used to make them.  Adding wax is not a bad
idea. Dissolve paraffin in mineral spirits with heat, add 5% or so to
your solvent. It should skin over and retard evaporation.
monroe22

Dear chrissyboy-ga:

Maybe adjusting engineering-type parameters, such as flow rate, or
other spraying parameters might be of help?

One often-times simple but wise approach to problems is the following:
 The best way to get rid of a problem, is to eliminate the problem. 
As such, would a possibility be the simplest of all--try it with no
solvent at all, i.e. just neat n-propyl bromide liquid?  In this case,
now you don't have to worry about solvent evaporation rate!

Failing this, perhaps I might suggest your trying to examine the
solvent itself which you are using.  Rather than seeking additives to
your existing solvent, perhaps you could change it to a different
solvent which is, itself, more viscous and thus "thicker."  I don't
really have any suggestions right off the top of my head right now for
an alternative solvent though (I don't even know what your present
solvent is), but an alternative solvent must, of course be something
compatable with the quite reactive primary alkyl bromide. (By the way,
I sincerely hope your safety equipment for preventing exposure to this
material and the like is very, very, very effective, as this stuff and
the like is very dangerous to be getting exposed to at low levels over
time, not to mention at moderate levels acutely).

However, a more innovative suggestion which I would really be
interested in seeing how well might work for your application,
relative to n-propyl bromide, would be to try another reagent,
alternative to n-propyl bromide.  It seems a little experimental and
somewhat "researchy," but nonetheless, the rationale for trying some
alternatives to n-propyl bromide would be that n-propyl bromide is a
primary alkyl bromide, and as such, a chemical structurally-related
compound might also have similar reactivity and thus maybe perform a
same or similar overall molecular function as your current n-propyl
bromide reagent.  For example, would the following also perform your
same function, yet also fulfill your other
application/viscosity/thickness parameters?  (with or without solvent,
as per my above commentary):

methyl bromide
ethyl bromide
butyl bromide
pentyl bromide
hexyl bromide
or even perhaps also worth a try might be some of the alkyl
dibromides, such as ethylene dibromide (aka 1,2-dibromoethane)?

Anyway, perhaps these and the like would have the same reactivity
you're seeking for your purposes, but might themselves be appropriate,
that is, without solvent.  Now, as for the solvent for each of these,
perhaps you could get away with no solvent, as I hypothesized above
for the n-propyl bromide, or trying various combinations, etc., but
that gets into numbers of possibilities which grow geometrically, real
quick.

So, anyhow, I wish you really very well in your endeavours and hope
you find a good "solution" for your current issues.

Kind Regards,

CarboCation.

Hi Monroe,

These suggestions sound as if they are on the right track.  I have
ordered some samples of polybutylene which will be arriving soon.  One
thing that worries me is that apparently polybutylene can be added to
a solvent to act as an adhesive.  What I don't want to end up with is
something which I spray on to get rid of the existing substrate only
to find that I am adding an even more tenacious substrate!

You say "why not simply add a thick grease to your solvent?"  Is that
not going to  reduce the degreasing effect of the solvent?   I am
spraying the solvent on to remove an eva sythetic wax/grease.  Surely
adding grease to the solvent is going to reduce its effectiveness?

Is it not possible to thicken the solvent by adding some kind of
surfactant?  I do add a surfactant at the moment but the solvent is so
thin and volatile that even with the fairly thick surfactant added, 
the resultant mixture is still very thin and volatile.   Is there not
a really thick surfactant or detergent that I could add?

Cheers Chris

Carbocation,

you say:

"As such, would a possibility be the simplest of all--try it with no
solvent at all, i.e. just neat n-propyl bromide liquid?  In this case,
now you don't have to worry about solvent evaporation rate!"

The n-propyl bromide IS the solvent!

Cheers Chris

Dear Chris
I used to make a paint stripper for metals with vertical surfaces.
This was a methylene chloride based product. We used paraffin to
retard evaporation but we used Methocel (made by Dow) as a thickener.
Most furniture style paint strippers used caustic soda or ammonia or
other water based activators for the paint stripper or they were made
with alcohols and ketones. So, they used the more hydrophilic
Methocels as the thickener (F4M K4M etc.). The gels weren't very good
or stable. We found a grade of Methocel that would swell with just an
addition of alcohol proportionate to the amount of thickener used. Try
Methocel OS. I believe it was called Methocel HB back when we used it.
Recommended concentrations would be 1-2% with about 5-8% Methanol or a
glycol ether as the activator for the thickener. The balance is your
n-propyl bromide (as I said earlier we used methylene chloride). You
should get a clear, stable, viscous result with proper aggitation. We
added formic acid as an accelreator- used it to strip epoxy- nasty
stuff.

Good luck