How to dissolve coloured transparent ABS Lego bricks?

I think these translucent Lego bricks are not ABS, as ABS is naturally opaque in colour. It's most likely MBS, or another translucent polymer (perhaps PC or PMMA). Very easy to find out with a simple burn test.

Wouter.

I'm no chemist, but have had a go at burning a sample anyway. Resulted in immediate black smoke, very fine soot particles floating in the air. If anything, slightly reluctant to catch alight and didn't burn for long unless in direct contact with flame. Of the examples shown here:

looks similar to the PC sample.

I've had a sample soaking in butanone for 24 hours now. Possibly some slight swelling taking place, hard to be sure, but corners are clearly splitting apart. Still no softening of the plastic though.

If it is PC, do you know what solvent I should be using?

Methylene Chloride

That is typical for styrenics (ABS, PS, MBS, ...), not really for PC.

PC will show small but distinct foaming and creates quite some ash on the burn place. And PC smells sweeter than ABS. Styrenics have a very characteristic smell of their own. Smell is the most telling right after burning.

Wouter.

OK, I'll have a further burn and sniff to compare with ABS .....

What fun...Lego brick barbeque! Unfortunately, results were somewhat inconclusive, but I'll report back anyway:

Plain white ABS brick - lots of smoke and sooty floaters. Not unpleasant smell. I know that this is ABS - just needed to watch it burn :)

Colourless transparent (clear) brick - some black smoke but no sooty floaters, slightly unpleasant smell, some frothy foaming. I'm assuming that this may be PC so will try Billy Hiebert's recommendation (thanks Billy).

Transparent light blue windscreen element - difficult to light and seemed to be extinguishing my pilot flame. Didn't really burn, but quickly formed a charred surface. Indistinct smell.

I think that Lego must be using more than a few polymer types / mixes depending on type / colour of element as 4 burns have produce 4 different outcomes. Unfortunately, I just don't have the necessary experience to differentiate PS, MBS, PC etc by smell, so perhaps the best route is simply to try various solvents until one works. Given that dichloromethane is the solvent of choice for PC, what should I try in the event that I'm dealing with MBS or PS for that matter?

Wouter.

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I am really disappointed that I can't be sure what Lego bricks are made from - I must have lost my childhood, finally. Are there not a couple of other "clear" possible materials?

- pvc - this might fit the description:

The only problem is that pvc has an acrid acidic after-smell. Tetrahydrofuran is a solvent.

- pp - particularly random copolymer. My experience with pp is that it does burn with a very small blue flame, with a slight yellow tinge at the top and sometimes a very slightly sweet smell - it usually isn't like polythene. No solvent!

- so-called "clear ABS", which I think is MABS. I can't say that I've burned this, but I would expect it to behave like ABS. I would expect solvents for ABS would work.

Regards, Bill

PVC has a very, very distinct smell. Very strong; one of the easiest if not the easiest to recognise.

If you're not sure: cable insulation is very often PVC (or PE; but that smells like candles). You can also test PVC the following way: take a clean copper wire (about 10 cm or so is enough), heat it in a gas flame such as from your furnace (a rather strong, colourless flame is preferred), then with the heated copper touch the sample to put a little molten plastic on the copper wire, and hold it in the flame again. PVC (and other chlorinated materials) causes a very distinct green coloured flame.

PP, unless you're talking about BOPP, is far from transparent. BOPP is film.

I don't know the chemical make-up of MBS (=M-ABS or MABS); anyway I wouldn't count too much on that. Polymers tend to have very few (often only one) solvents. And what solves one polymer easily, may merely weaken its cousin.

Wouter.

Are these "old" bricks? I looked on Lego's site and could not find any transparent bricks. Lego's were originally made from Cellulose acetate, more recently from ABS. Are these transparent ones a special category?

Not particularly old or special. They can turn up in all manner of Lego sets since the 1970's.

Just received my dichloromethane order today and am delighted to say that it did the job (nips the eyes a bit though!). Lego dissolved completely and the solvent remained crystal clear. Result!

Problem now is that once the solvent evaporates, the remaining product turns cloudy! Dammit, how did that happen? Or rather, how does one prevent that from happening? Two steps forward, one back :)

Could be the rubber content, or possibly the absorbed water. Someone on the group will probably know.

More likely absorbed solvent. I wouldn't be surprised if you find the volume of your plastic has increased a little bit.

By the way, why are you trying to make a solution of these bricks?

Wouter.

I'm attempting to make an accurate colour chart. There are over 100 diferent colors, many of which are quite similar and therefore difficult to identify correctly. Can't get a better colour match than that provided by the original material. Transparents are puting up a fight though :) Should I start a separate thread for the "cloudy after evaporation" dilema or is that considered bad form here?

Aha - possibly found the answer in this thread:

bottom line: if you want to make amorphous PC from dichloromethane solutions, make a thin film and slow down the evaporation rate.