What plastic cement?

Even the stuff that does trends to contain oil that;s counterproductive to sticking stuff together.

It's certainly very "heady" stuff, even using it outside I would say use a facemask with appropriate cartridge, but it doesn't contain acetone, that would dissolve your windows, not clean them.

The MSDS seems to show various light fractions of petroleum

If you want to buy acetone, get foam gun cleaner

I think polystyrene has a characteristic smell when burnt, which might indicate whether the plastic is that or not. I recently repaired my laptop case corner which broke off owing to the ridiculous force put on it by the stiff screen hinge. (The hinges have to be somewhat stiff to keep the screen in position, and I had already weakened them a bit by removing one of the springs). I first tried Araldite as it used to set rock hard, but now it's not made by Ciba-Gigy it hardened to a spongy flexible state. I then tried JB Plastic Weld, which was a lot better and even smelt the same as old Araldite, but it still hardened very slightly flexible, so I bolted on extra metal bracketry.

Yep, I've got a can and a half left over from a foaming job. Just be aware that it does nothing once the foam has cured.

I also have a 1 litre bottle of acetone purchased from Ebay may years ago. Currently around 7 quid for 1 litre.

Try superglue and sprinkle baking powder on it. I just repaired the side of a drill bit holder that broke off a segment when it droped on the floor. Ihe broken bit was part of the case had a hole into which the bit holding bit was forcedc into to form as hinge. I had no expectation that it would survive the prsessure. It did.