I have just recieved a textile object which has been left on a oven
bench together with a folded plastic sheet, with the result that upon
heating of the oven the plastic has molten onto the objects surface.
I am now trying to remove the plastic (probably PE). Tests with a
soldering needle set at 65°C are somewhat successful, but under the
microscope the fibres are visibly stuck together with molten plastic,
probably caused when trying to remove it with the needle.
Solvents (Toluol) soften the plastic, but make the plastic creep into
the fibres further; the plastic cannot be removed as a sheet, even if
the solvent is applied to the interface of fibres and plastic. I do know
that PE can be solved in Hydrofluorocarbons, but I hesitate trying this
for health reasons as well as because I am concerned that I will not be
able to remove the disolved plasic completely and thus plasticizing the
fibres.

I am now evaluating localized freezing, hoping that the PE will become
brittle and could be broken down in minute pieces and thus removed.
As I do not know of a whay to locally and in a controlled mannor use
fluid Nitrogen, I did some research in freezing sprays. They are used
for testing broken fuses in electronics or adjusting thermostats of
freezers. They all seem to consist of 1,1,1,2-Tetrafluorethan (which *is
* a Fluorocarbon) and seem to be able to cool a surface down to -40°C -
-60°C. E.g. see <www.microcare.com/product/pdf/PS-50-FRZ-DST.pdf>

My questions are:
Has anybody used such freezing sprays in conservation (I could not find
any literature about such use. I guess the frequently cited chewing-gum
removal works with the less chilly temperature of medical cooling
sprays, which are different)? How will the cold Hydrofluorocarbon gas
interact with the plastic? The same as in liquid form 8i.e. solubilise it) ?
Will there be any residues from the spray (the bottle is under pressure,
so I assume the gas will be propelled out without a carrier, and the
advertisment proclaims there to be no residues at all)?
Does anybody know of a different spray cooling down to such low
temperatures but using less harmfull substances?
Might this chilling method work at all for embrittling PE?

Are there any suggestions / ideas of how to approach above conservation
problem with a different method?

Thanks for any comments and remarks.

Karin von Lerber
--
Karin von Lerber
Prevart GmbH
Oberseenerstr. 93
CH-8405 Winterthur
Tel. +41 (0)52-233 12 54
Fax. +41 (0)52-233 12 57
e-mail: [log in to unmask]
www.prevart.ch