What causes plastic to yellow?

[promethuem5]

Hi all,

I'm a big old school toy person, and I was wondering what causes plastic to yellow. I'd look it up for myself, but its a snow day and Ive got HW to catch up on...so Im kinda busy. I was hoping one of you smart guys here chould answer my question, or direct me to the answer.

Thanks a bunch!

Ben

[do not disturb]

ahhh this age old topic again.

so far, theres no actual scientific proof that explains yellowing. some say sunlight, some say UV rays, some say humidity levels, some say it depends on the chemicals used to make the plastic, but no one really knows?

i had a MPC(dodges bricks) once and i had it boxed up in a closet away from all sunlight. after a few months i opened the box and BAM! yellowing on the wing! now this toy hadn't seen the light of day since the day i got it. i opened the box, saw how crappy it was, and i was ashamed to put it on display. so back in the box it went. there was no good reason for the yellowing whatsoever. no sunlight, no UV rays, little to no humidity, WTF???

some say, if your toy yellows, that direct sunlight will get rid of the yellowing but i have yet to see someone prove it. all i can tell you is try your best to keep it away from sunlight and and other outside factors(smoke) and your toys should stay good as new.

[Mechamaniac]

FATE

[the white drew carey]

Pee.

[do not disturb]

wow, the extensive knowledge about the topic at hand and willingness to help is just amazing.

[promethuem5]

Im impressed by the umm....well thought out answers to my question. Thanks for the real answer haterist....weird.

[justvinnie]

One simple answer: oxidation.

Oxidation is a chemical process whereby a compound loses electrons. We live in an oxidative environment. That's why metals rust. Our biochemistry is tuned to take advantage of the oxidative nature of the air we breathe. Guess what oxygen does? Exposure to ordinary air alone will cause all plastics to yellow. The stripping of electrons will make the plastic breakdown and change color.

Plastics are polymers, in other words long chains of carbon. This opens up even another source for oxidation to occur in plastics. UV light is easily absorbed by plastic. UV is extremely high energy and can cause electrons to be ejected. This causes the formation of free radicals that cause chemical reactions to break the plastic down.

All plastics will yellow over time in the environment. White plastic will exhibit the most obvious yellowing while colored plastics will be masked by pigments. Some plastics yellow more rapidly than others. I have no doubt that Toynami opted for cheap plastic that yellows easily. The only real way to prevent yellowing is to lock your toy in a vault that is flushed with inert gases and bury it underground.

vinnie

[Lynx7725]

One simple answer: oxidation.

Uhm Vinnie, which degree do I need to take to know all this?

I have no doubt that Toynami opted for cheap plastic that yellows easily. The only real way to prevent yellowing is to lock your toy in a vault that is flushed with inert gases and bury it underground.

Of course, there is the alternative solution of launching it into space, where the concentration of oxygen is sufficient low that oxidation is less of an issue...

EDIT: Of course, UV would still be a problem, but I guess a orbit around Pluto should be sufficient to retard the process sufficiently...

Edited January 6, 2005 by Lynx7725

[promethuem5]

Thanks alot Vinnie! Im taking chem right now...so I probably shoulda know that

[Montarvillois]

Pee.

Yup !

Definitly pee.

[F360°]

well, if you smoke then it will yellow at light speed.

[Kin]

Well... plastic is made out of oil... right? Maybe it's the combi of sun and oil..... sun tan!

[promethuem5]

No smoking in my house, so thats not an issue! SMoking is gross and should be banned

[do not disturb]

well, if you smoke then it will yellow at light speed.

not true at all. i know some smokers and there stuff is fine.

[F360°]

well, if you smoke then it will yellow at light speed.

not true at all. i know some smokers and there stuff is fine.

I mean smoking near their toys,, like in the same room. If you smoke in a different room then it doesn't really matter much.

[do not disturb]

well, if you smoke then it will yellow at light speed.

not true at all. i know some smokers and there stuff is fine.

I mean smoking near their toys,, like in the same room. If you smoke in a different room then it doesn't really matter much.

well of course, but they smoke like chimneys(atleast a pack a day) and smokers tend to smoke throughout their homes....there isn't a room without an ashtray.

[Kin]

Ey... anyone tried bleech to get rid of the yellow color?

[zeo-mare]

Ey... anyone tried bleech to get rid of the yellow color?

uhhh i have never tried that before and it does not seem really like a good idea

[promethuem5]

Im pretty sure bleach would eat away most plastics Kin, so I wouldn't recommend it...

[Zentrandude]

thinking too hard around plastic will yellow them.

to get rid of it guess bleach or for the overkill types vat of acid and melt the sucker in it.

or you can paint it if your real good.

[nightmareB4macross]

I was doing some research...

But don't different types of criteria affect different types of plastic?

What type of plastic are you refering to? ABS, PET, PVC, Styrene, etc?

[justvinnie]

Different plastics will be affected by UV and air oxidation at different rate. I don't keep up with plastic technology, bet I bet they do have plastics that are resistant to one or the other. Mind you resistant, not immune. Bullet proof glass is made from polycarbonate. They suggest you have it changed once a year because UV causes it to weaken and breakdown.

Of course, even with the most perfect storage possible, one cannot stop entropy from taking over...

vinnie

[do not disturb]

I was doing some research...

But don't different types of criteria affect different types of plastic?

What type of plastic are you refering to? ABS, PET, PVC, Styrene, etc?

the type of plastic doesn't make much of a difference since most if not all white plastics yellow over time. the only thing that varies is the speed/rate at which the yellowing occurs.

[nightmareB4macross]

It also depends if there are what type of plastic. Though all will yellow, with some exceptions to polymers.

[Agent ONE]

No smoking in my house, so thats not an issue! SMoking is gross and should be banned

I like to smoke cigars.. I blow the smoke in the faces of all the little girly men who are too sissy to stop their crying and pick up the weights.

[Montarvillois]

I read somewhere that you can soak yellowed plastic in denture cleaner and it'll do the job without damaging the plastic.

[nightmareB4macross]

I've read that as well, but it's only a myth.

There doesn't seem to be anything that would change the composite structure of the plastic, only topical remedies.

One thing I have tried is Fusion or Plastikote vynil/rubber sprays. It contains acids that actually allow the dye to permanently bond to the plastic. Only that once it has been sprayed on it tends to change the texture of the surface.

Fusion leaves the surface grainy, almost like the fast packs of the 1/48 Yammy Valks.

Plastikote on the other hand leaves a smoother texture that can easily be made smother with a polishing wheel.

The great thing about these mediums is that the are very resilient to chipping and scratches. But in order for this to be possible it takes about 1 week's time to really adhere.

Test these out, they just might surprise you.

[promethuem5]

Hmmm...Id be tempted to try that if it wasnt my first Gakken Cyclone

Sounds very interesting tho...I might have to look into that for some other stuff like customs....

[nightmareB4macross]

Prometheum,

You will be surprised, there are man different colors. You just have to seek out the color you want most colors are available but some must be special ordered. Believe me, I know.

Several things you will have to remember, clean the part extremely well with dish soap and warm water, then rubbing alcohol, let dry, and spray it on. There is no need to primer the surface, it melts on to it.

[promethuem5]

Wow! defenetaly sounds like good stuff for a custom Yammie....

[nightmareB4macross]

Prometheum,

I am currently using it on a 1/35 Gakken Legioss.

Believe it or not, the white is very clean and smooth, no details have been lost. I wish I could post pictures, I really need to get a new computer and digicam...hopefully this month (crosses fingers ).

[wolfx]

If white plastics yellow....do other color moulded plastics yellow too?

Just wondering.

And if paint was an easy remedy, is it too expensive to paint the stuff instead of moulding it and leaving it in color?

[nightmareB4macross]

All colors yellow to a certain degree, the color helps hide some of the yellowing. I believe it is part of the degregation process of plastic.

[Father Jack]

Ghosts

[CoryHolmes]

It also depends if there are what type of plastic.  Though all will yellow, with some exceptions to polymers.

Sorry to butt in like this, but ALL plastics are polymers. All of them. Every last one of them. I'm a polymer engineer, so I knoweth of what I speaketh.

Scrubbing and washing and cleaning won't do much more to help than possibly ripping off the top few layers of the toy, exposing the un-oxidized material to the air.

It's not a dirt or smear that you can clean off, it's an actual chemical change that the molecular chains are undergoing that's causing the poor yellow colour. It's also making your plastic much weaker, thus more prone to breaking.

Also, I'd bet that most of the toys out there aren't painted per se, but are actually coloured plastic. That is, the colour is moulded in with the plastic during the manufacturing process.

And yes, it IS possible to add in additives to retard the degrading process, but they're expensive and rather difficult to work with, nor are they 100% effective.

What type of plastic are you refering to? ABS, PET, PVC, Styrene, etc?

ABS will yellow with exposure to sunlight.

PET will discolour slightly with exposure to sunlight.

PVC has outstanding sunlight and other weather resistance, hence why it's use as siding is so popular.

Styrene is pretty robust as far as sunlight goes, but it will yellow. (this is what toys are usually made of, so use that as a reference for the upper two as to how much they'll yellow and discolour)

But take this list with a grain of salt, since as I said above, there are many thousands of possible additives that could be present in a particular plastic material, and each one of those will have an effect on the properties.

Edited January 7, 2005 by CoryHolmes