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Name: John
Status: other
Grade: other
Location: VA
Country: N/A
Date: January 2007

Question:
I accidentally discovered an strange phenomena. I had laid a plastic tape recorder touching a toy rubber mouse. The plastic in contact with the rubber mouse melted. No distortion of the rubber mouse at all. I tried a dozen other plastic objects in contact with the rubber mouse and all but one melted (a plastic highlighter did not melt). What could be in the rubber toy mouse that could melt plastic like this without any damage to itself. It only will take a day for the melting to be visible. The melting will look like a hot soldering iron was placed on the plastic.



Replies:
John,

I am intrigued by your observation and I wish I could replicate it. Could you send me some information of what this toy rubber mouse is or how I might get my own? Without knowing much more than what you said in your query I can only speculate that there must be some solvent, outgassing substance, organic substance, or pet slobber on the toy mouse that is causing this effect. Some plastics are indeed more soluble than others and it is entirely possible that the toy mouse can remain intact while causing other nearby plastics to dissolve.

Let me know,

Greg (Roberto Gregorius)


Wow. That rubber has a huge plasticizer percentage. Plasticizer is a liquid that dissolves into a solid, helping it to be rubbery instead of brittle. Plasticizers for polystyrene tend to dissolve most plastics. There are polystyene gels and ABS gels these days. Or maybe it is a more rubber-like compound, such as isoprene.

Your highlighter tube is made of poly-ethylene, or at least poly-propylene, which hardly dissolve in anything, if they did it would be in a different liquid which dissolves styrene.

Look up "solvent parameter". Solvent-liquids range from "light" to "heavy", meaning not density but their own internal self-cohesion energy. Due to thermal mass-action laws, like dissolves like on this scale.

Energy is optimized when lightly-adhering molecules are mixed together in one blob, and all the heavily-adherent molecules are together in another. Roughly speaking. You will notice that melted wax is not really very sticky. (iffy point) Wax and hydrocarbon oils are very light solvents and low-parameter substances.

Acetone is a typical heavy solvent. It gets most plastics, but cannot touch polyethylene (like your marker pen) I guess that is why they make marker-pens out of it. the ink is a solid dye and plastic, dissolved in heavier solvents like alcohols and glycol ethers

Teflon and related liquids (Fomblin) are the ultimate low-parameter substances. Silicone comes close.

On the other end, DMSO and methyl-pyrolidone are heavier, higher-parameter, than acetone. Not sure what they dissolve or ignore.

I bet if you heated that mouse to 60C for a year, it would be 30% smaller. Or ten years in cold running water. All the plasticizer liquid would creep out and away, and it would shrink. Get harder, too.

By the way, most plasticizers are reputed to be not too good for the body, if ingested in significant amounts or exposed repeatedly.

Oh, by the way, the reason the mouse doesn't melt from all it's plasticizer: it is cross linked. The molecules are chained together in long tangled polymer strings, and the strings are occasionally glued to each other too. The last is "cross-linking". So the whole mess can get bloated with liquid molecules and be flimsy, but it cannot ever really turn inside out or be scrambled, no matter how dissolved it gets. It has a permanent large-scale shape, until the day harsh chemical reactions break all those links between strings, or mechanical shredding occurs.

Jim Swenson



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