Plastic remains soft after paint stripping

[Twinsen]

Hey guys,

I have recently stripped the paint from a couple of rather old and thin PVC model parts (30-ish years old), using what I have always used in the last 15 years : floor wax stripper. Never had any issues with it, works wonders. I just submerge the parts in a sealed container of stripper for a few days and then the paint just slides off and leaves a clean raw surface.

But this time something strange is happening : the paint came off like a breeze, as it always does, but the plastic was left somewhat soft. I let it dry for 3 weeks and to my surprise it’s still soft.

I mean, it holds its original shape and is rigid but if I put my fingernail in it, it leaves a mark. Same with a toothbrush, I can imprint the bristles onto the surface if I press hard enough.

I tried heating it with a heat gun, putting it in hot water, cold water, rinsing it a million times, nothing seems to work.

Do you guys think the actual structure of the plastic could have been altered? Meaning it will never go back to normal?

I’m open to any ideas to try and save thr parts…

 

[rbeach84]

What is the brand of the floor stripper? Perhaps the safety sheet for it can offer a clue.
I'm assuming you've done PVC like this previously...
R/ Robert

 

[TazMan2000]

I think it's pretty obvious that the stripper changed the plastic's properties. It could be that the formula of the stripper changed or it just could be the thin PVC just being more reactive. Perhaps even the PVC is made with a different recipe that what you usually use. It is possible that the material would "sweat out" or off-gas enough to make the PVC more resilient after several months, but this could be permanent.
You could try isopropyl, but at this stage with the material changing, isopropyl could even cause more damage.

I don't think there is much else you can try. You could spray an area with paint, to see how that sticks, but pending the characteristics of the plastic now, perhaps even the solvents in the paint could do damage.

TazMan2000

 

[Twinsen]

Welp, I think you are correct. It definitely altered the chemical structure of the plastic... I put the parts in (very) hot water again, just like I did pre-paint stripping to remove some old stickers, but this time the parts turned from white to yellow/orange and buckled at every corner and the surface started to get crusty and disintegrate. It is now safe to say the parts are FUBAR and headed to the trash.

For clarification, the stripper is called Glanzer and contains ammonia. I've been using it for over 15 years to strip paint from model kit parts, plastic figures, plastic car parts... You name it. It has always removed every sort of paint and left the surface unharmed and ready to be painted again. Until today.

Thank you for your suggestions, the damage was indeed permanent... Lesson learned, be extremely careful with very old plastics!

 

[Too Much Garlic]

I am not certain, but I don't think you should use ammonia based products on pvc.

Sorry to hear that the model was ruined. But the stripping agent definitely penetrated the plastic and affected it. You might have needed to use a degreaser instead of hot water or heat. Very hot water by itself can ruin pvc, so do not use it too much.

You should put it in hasardous material disposal.

 

[TazMan2000]

Castrol Super Clean works well for me. I haven't found a plastic that it is rough on and it removes chrome coating from plastic parts well. Some say that Easy Off Oven Cleaner works well, but I've never tried that. Some people complain about the Easy Off smell.

TazMan2000

 

[division 6]

I've had Super Clean soften thin resin parts.

 

[TazMan2000]

I've had Super Clean soften thin resin parts.

Was it permanent or did the resin harden up later?

TazMan2000

 

[division 6]

It stiffened up but it took a while .
It was after market viper canopy frames.