I think that the plastic between the two layers of glass deteriorates, thus
causing the fogging. I seen fogged windshields on my '63 MGB and '53
International Truck, both of which have very little plastic in the dashes. Of
course if you are talking about the fogging of the interior glass (as opposed
to between the layers of glass), then the plastisizer is probably the culprit.
Kevin Brown
Odessa, MO
Matt Milkevitch wrote:
> Fellow Listers,
>
> To the best of my knowledge, the fogging we observe on
> our MG windshields is due to the slow "evaporation" of plastisizer
> from our plastic dashboards. The function of a plastisizer is to
> make the plastic flexible...for example, PVC (poly(vinyl chloride) is
> fairly brittle, but the addition of a carboxylic acid ester softens
> it up a bit, making it a suitable material for garden hoses, plastic
> covers, and so forth. Carboxylic acid esters are organic compounds
> which are derivatives of carboxylic acids, which have a variety of
> uses from flavorings and solvents, to plastisizers. In addition,
> other compounds are used as plastisizers, but we've come to the end
> of my knowledge base here.
>
> Typically, for the plastic in our dashboards, a non-volatile
> plastisizer should be used, however given the fact that our cars are
> typically exposed to sunlight (and therefore high interior temperatures),
> over time this supposed non-volatile plastisizer can "evaporate"
> ...thus leeching out and forming on the windshield. From here,
> I imagine it can become baked on and would therefore be
> somewhat difficult to remove.
>
> As far as removal goes, I heard somewhere that a
> concentrated solution of ammonia does the trick...but I have not
> experimented with this myself and therefore don't know if it works.
> If anyone chooses to try this, I would remind them that even though
> supermarket-grade ammonia is only about a 5% solution, it will
> produce strong vapors, and these vapors are exceedingly irritating.
> Adequate ventilation and suitable skin protechion (read, gloves)
> would therefore be required.
>
> If anyone tries this, let me know if it works!! I have
> some "fog" I'd like to get rid of!!
>
> Best Regards,
>
> Matt Milkevitch
> Matthew Milkevitch
> Graduate Student, Ph.D. Candidate
> Dr. Karen J. Brewer(Chem), Advisor
> Dr. Brenda W. Shirley(Biol), Co-Advisor
> Va. Tech
> Blacksburg, VA 24061
> (540) 231-4708
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