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Aftermath of a wildfire-coins in plastic!

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stickle:
Everyone,

My in-laws lost their home in the recent Camp Fire in Northern California.  In picking through the wreckage we discovered two related problems that we could use your knowledge to solve.

They had silver coins in a "fireproof" safe.  The lining of the safe was black plastic.  The plastic melted and encased the coins.  Is there a solvent that will remove the plastic?

They had some other coins stored in ziplock bags.  These melted together with the plastic from the coin tubes.  Is there a solvent that will remove this plastic?

Is there a completely different way to go?  The black plastic gets soft at around 300 degrees F. but just smears. 

Your wisdom would mean a great deal to a couple of elderly fire refugees. 

Thank you.

S

wildfyr:
I would try a good soak in paint thinner, aka toluene first.

If that doesn't work, then next I would try dichloromethane which is bought as paint Stripper in some places.

Be careful with both and DO NOT work with in enclosed spaces.

Enthalpy:
Dissolving a polymer thicker than a paint layer tends to take very long. Nice if it works, but often discouraging. Ultrasound, like in a jewellery cleaner, often helps.

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An alternative might be an acetylene+oxygen torch. The flame burns the plastic away quickly, more so with an excess of oxygen. It may melt the coins too, depending on how it's done, but the silver in the coins has often the same value as the coins.

Molten silver is just more difficult to sell than a silver coin. Such a coin is basically a stamping meant to guarantee a silver amount and purity.

If you try the torch:
- Blow pure oxygen once the plastic burns. The flame will be less hot than with acetylene.
- Do that outside! Nearly all burning plastics are toxic for real.
- Maybe air suffices.

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Possibly a strong ultraviolet source would degrade the plastic at interesting pace, so it can be broken and brushed away, but I doubt it. Sunlight takes its time, especially if the plastic is black, thick, and resides between the coins. Some sources, like arc lamps, are stronger.

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As most chemical methods get slower with the plastic thickness, it wouldn't be bad to first separate the coins with a chisel, hammer (and vice), leaving just thin plastic on them.

After that, just a barbecue fire followed by brushing may suffice. De-oxidising the tarnished silver is standard practice.

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Hey chemists, would there be some compound (A bleach on steroids? Ozone? Percarbonate?) that oxidises the plastic away? That should be faster than a dissolution.

Or one that makes the plastic fragile (again an oxidizer?) so it can be hammered and brushed away?

Would a strong base be worth trying? Breaking the polymer chemically must be faster than dissolving it.

wildfyr:
Pirahna solution? Highly dangerous but would fit the bill.

We don't know what polymer it is, and without FTIR or some manufacturer info we probably never will. If its polyester then KOH would be great. If its polypropylene then its useless.

Corribus:
It's all blind speculation without knowing better what kind of polymer it is.  Polypropylene and polyethylene have much different stability to, e.g., UV light. I have no idea what a safe liner would be made from but plastic bags are almost certainly polyethylene, which is unfortunately very difficult to dissolve in anything, at least not without destroying the coin underneath as well. There's a caterpillar that can eat polyethyelene: https://www.nature.com/articles/d41586-017-00593-y

Honestly I think enthalpy's suggestion of controlled burning is probably the best bet. Silver's melting point is about 960 deg. C and manycommon organic polymers decompose at around 400-600 deg. C. If you could control the furnace temperature to be safely below the silver melting point but above the polymer decomposition temperature, you may be able to burn away the polymer while leaving the coins intact. Then clean whatever reside remains with a strong solvent. I wouldn't expect any kind of mint condition coin left over at the end though.

This does seem to defeat the purpose of a fireproof safe.

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