Friday, September 11, 2015

Filtering Silly Putty

Years ago, probably about 1995 or thereabout, I hosted a 100lb Silly Putty group buy. I wrote a little web page using JSP, Perl, and Firebird, and used it to let dorks like myself sign up to buy Silly Putty in half-pound increments. I think I ended up with about 25 orders ranging from half a pound up to 15 pounds. Once we reached that magic 100lb aggregate, the minimum order quantity for Dow Corning® 3179 Dilatant Compound I had everyone mail me a check, and ordered a box of the stuff.

Not long after the boxes showed up I and one of the guys from the buy, a Cisco engineer from Austin, spent an evening dividing it up according to the order list and packing it into cardboard boxes for shipping. New 3179 Dilatant Compound is tough stuff, dividing it up is a tough forearm workout!

That was so successful I hosted a second buy for unpigmented translucent putty and a kilo of green glow powder to make glowing putty.

So, tl;dr: that's how I ended up with about 8 pounds of coral Silly Putty, several pounds of white putty, and a fist-sized blob of glowing putty.

The problem with Silly Putty is that over the years it collects lint and grit which makes it less fun to play with, and it darkens, especially if you like to use it to pull ink off of newspapers. So I was thinking of ways I could clean it. Picking out lint and grit is too slow to be realistic, but bulk filtering is impossible because it's a putty. But what if I dissolve it first and then filtered it?

I have a new bottle of Ronsonol lighter fluid that I bought as a home lab solvent a while back, so I figured I'd give it a job. I dropped a small blob of putty into a 20mm test tube, threw in a couple of tiny magnets to act as a stir bar, covered it in a few mL of lighter fluid and loaded it up on the stir plate:


I let it run for an hour or so, but the big chunk wasn't dissolving very fast, so I added a hot water bath to encourage it. Eventually, and with a little encouragement from a glass rod, it all dissolved into a clear solution and the coral pigment.

I centrifuged it and transferred the clear solution and the coral mess to evaporation dishes in the vent hood. After driving off the solvent I was left with unpigmented putty base and the coral pigment with it's contaminant load of lint and grit:


However, as you can see, the solids were a gummy mess. This is because I did not rinse the solids with clean solvent before evaporating the solution, which means that some of the putty base was left behind.

So I repeated the process with the gummy mess, this time rinsing, centrifuging, decanting twice more before drying the solids. The result is a very fine coral powder with some contaminants that I've halfheartedly manually separated. 


I don't have a good way to divide the coral powder to show how small the particle size is, but it's talc-like. If I can get it down to fine powder I will be able to run it through a mesh to remove the remaining lint, and then I can incorporate it back into the putty to achieve the original goal, filtered putty (with only a faint smell of lighter fluid). I may try this again with a different solvent, maybe something that smells nicer. I'm sure alcohol will work, and it's easier to evaporate.
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