Localized freezing to remove plastic from textile

I have just received 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 melted onto the object's
surface. I am now trying to remove the plastic (probably PE). Tests
with a soldering needle set at 65 deg. 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 dissolved plastic
completely and thus plasticizing the fibres.

I am now evaluating localized freezing, hoping that the PE will
become brittle and could be broken down into minute pieces and thus
removed. As I do not know of a way to locally and in a controlled
manner 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-Tetrafluorethane (which *is* a
fluorocarbon) and seem to be able to cool a surface down to -40 deg.
C to -60 deg. C. (e.g. see

    <URL:http://www.microcare.com/product/pdf/PS-50-FRZ-DST.pdf>

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 (i.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
advertisement proclaims there to be no residues at all)?

Does anybody know of a different spray cooling down to such low
temperatures but using less harmful substances? Might this chilling
method work at all for embrittling PE?

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

Karin von Lerber
Prevart GmbH
Oberseenerstr. 93
CH-8405 Winterthur
+41 52 233 12 54
Fax: +41 52 233 12 57


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                  Conservation DistList Instance 19:58
                  Distributed: Thursday, June 1, 2006
                       Message Id: cdl-19-58-007
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