Question about ABS plastic yellowing

[lisq199]

From what I understand, white ABS plastic will yellow over time due to exposure to UV light, and yellowed ABS plastic not only looks bad, but is weaker as well.
So here's my question: Is dark colored ABS plastic immune to this problem?

[nubbinator]

No, it is not; however, modern plastic is less susceptible to yellowing as it does not contain the bromine that caused excessive yellowing in older ABS products.

[BlueNalgene]

This really depends on the the additive.

Polymers generally all come as white/colorless.  If they are in their pure form, the are rather unstable.  This is because UV light initiates a free radical oxidation step.  Some of the symptoms of this step include color change and enfeeblement.  Check out how yellow this historical sample of PE got in the past 80 years:


As we started producing plastics more often, we started including other chemicals in the melt called stabilizers.  We include these chemicals which are designed to absorb UV photons that would affect the polymer.  These chemicals are usually rather large "small molecules" with lots of conjugated loops double carbon bonds.  Here is one that I picked blindly from google images:


For ABS, which is unstable over the ranges of 300nm-310nm and 370nm-385nm, we need to add something to mask these wavelength regions.  So we add chemicals that mask these regions.  I led up to this with the long intro because it is important.  The colorant used in the polymer does not necessarily block UV light.  Say you have a plastic with a red additive with peak absorbance at 633nm.  That would probably not block UV photons. 

So, back to your question.  Is black plastic immune to this problem?  Probably.  Most black plastic is made from adding carbon black to the sample.  The carbon black absorbs over a wide range of wavelengths.  There is a simple white paper about this here.  We can assume that if the plastic is made with carbon black, then it is built to last in the sun.  I hedge my answer by saying "probably" because without some in depth analysis, we can't tell if the plastic was made with carbon black or something else.

I hope that is a satisfactory answer to your question.

[chyros]

Literature actually suggests the opposite. Stabilisers are more susceptible to UV absorption than ABS is, and accelerate the decomposition process. This would also suggest that black plastics are more susceptible as well.

Nubs; please don't bring up the damn bromine again xD .

[BlueNalgene]

Literature actually suggests the opposite. Stabilisers are more susceptible to UV absorption than ABS is, and accelerate the decomposition process. This would also suggest that black plastics are more susceptible as well.

Nubs; please don't bring up the damn bromine again xD .

Oh, I tried to explain that the stabilizers DO absorb it.  I apologize if I didn't make that clear.  Absorbing the UV photons is their purpose as they are less likely to produce the free radicals that cause the decomposition than the rest of the polymer.  If I'm wrong, I would be happy to edit.  Can link your source?

[chyros]

Literature actually suggests the opposite. Stabilisers are more susceptible to UV absorption than ABS is, and accelerate the decomposition process. This would also suggest that black plastics are more susceptible as well.

Nubs; please don't bring up the damn bromine again xD .

Oh, I tried to explain that the stabilizers DO absorb it.  I apologize if I didn't make that clear.  Absorbing the UV photons is their purpose as they are less likely to produce the free radicals that cause the decomposition than the rest of the polymer.  If I'm wrong, I would be happy to edit.  Can link your source?

-Piton et al., Polym. Degrad. Stab. 55, 1997
-David et al., Polym. Degrad. Stab. 84, 2004
-Pickett et al., Polym. Degrad. Stab. 85, 2004
-Rajan et al., J. Appl. Polym. Sci. 124, 2012
and others

[BlueNalgene]

Literature actually suggests the opposite. Stabilisers are more susceptible to UV absorption than ABS is, and accelerate the decomposition process. This would also suggest that black plastics are more susceptible as well.

Nubs; please don't bring up the damn bromine again xD .

Oh, I tried to explain that the stabilizers DO absorb it.  I apologize if I didn't make that clear.  Absorbing the UV photons is their purpose as they are less likely to produce the free radicals that cause the decomposition than the rest of the polymer.  If I'm wrong, I would be happy to edit.  Can link your source?

-Piton et al., Polym. Degrad. Stab. 55, 1997
-David et al., Polym. Degrad. Stab. 84, 2004
-Pickett et al., Polym. Degrad. Stab. 85, 2004
-Rajan et al., J. Appl. Polym. Sci. 124, 2012
and others

Piton et al. does not contradict my claim.  The radical transfer mechanism they describe occurs from one polymer chain to another, where the two chains are different in a copolymer mix.  The experimental section says they removed the anti-oxidants (the additives I refer to), and so they are not testing for that.

David et al. I can't find.  Do you have the title of this paper?

Picket, J. only mentions a single additive, titanium dioxide.  This is probably one of the poorest UV stabilizers you could use because it is so reflective.  While this paper is very interesting regarding the continued radical reaction caused by the initial UV exposure, it does not refute my argument regarding stabilizing agents.

Rajan et al. actually supports my claims.  The UV stabilizing agents actually do reduce the transmission of UV wavelengths through the samples in the UV/Vis experiments.  I believe your argument is best summed up and then dismissed by this direct quote below figure 5:

It is observed that the rate of oxidation for unprotected sample is much higher in the initial aging hours and afterwards it get decreased whereas for protected sample the rate of oxidation is much slower in the initial hours but sustains the same rate of oxidation for a longer aging period and finally it enters into a plateau region. Even though the protected sample has a prolonged linear region of oxidation before it reaches a plateau still it has lower overall oxidation level at all stages of aging compared to the unprotected sample.

While this paper may be useful for explaining why the yellowed plastics continue to be a problem, especially for older parts like classic keyboards, it does not imply that stabilizers accelerate the decomposition.


Granted, this was just a quick read of the papers.  I have plans tonight, so I need to go to the liquor store.  I just wanted to respond before I go get drunk.

[nubbinator]

No, it is not; however, modern plastic is less susceptible to yellowing as it does not contain the bromine that caused excessive yellowing in older ABS products.

Pourque?  Everything I've seen states that bromine and UV exposure are the main cause of yellowing in plastics.  I'll gladly not mention that if that has been proven to not be the case.

Note, I am not discussing the change in composition and plastic being made more brittle by UV exposure, just the yellowing.

[BlueNalgene]

No, it is not; however, modern plastic is less susceptible to yellowing as it does not contain the bromine that caused excessive yellowing in older ABS products.

Pourque?  Everything I've seen states that bromine and UV exposure are the main cause of yellowing in plastics.  I'll gladly not mention that if that has been proven to not be the case.

Note, I am not discussing the change in composition and plastic being made more brittle by UV exposure, just the yellowing.

I can't tell who you are intending to quote there.  I can't comment on the Br thing since I don't know enough about it from my experience.  The yellowing does happen without bromine present though.  The Pickett paper is probably the best for explaining that.

[chyros]

Literature actually suggests the opposite. Stabilisers are more susceptible to UV absorption than ABS is, and accelerate the decomposition process. This would also suggest that black plastics are more susceptible as well.

Nubs; please don't bring up the damn bromine again xD .

Oh, I tried to explain that the stabilizers DO absorb it.  I apologize if I didn't make that clear.  Absorbing the UV photons is their purpose as they are less likely to produce the free radicals that cause the decomposition than the rest of the polymer.  If I'm wrong, I would be happy to edit.  Can link your source?

-Piton et al., Polym. Degrad. Stab. 55, 1997
-David et al., Polym. Degrad. Stab. 84, 2004
-Pickett et al., Polym. Degrad. Stab. 85, 2004
-Rajan et al., J. Appl. Polym. Sci. 124, 2012
and others

Piton et al. does not contradict my claim.  The radical transfer mechanism they describe occurs from one polymer chain to another, where the two chains are different in a copolymer mix.  The experimental section says they removed the anti-oxidants (the additives I refer to), and so they are not testing for that.

David et al. I can't find.  Do you have the title of this paper?

Picket, J. only mentions a single additive, titanium dioxide.  This is probably one of the poorest UV stabilizers you could use because it is so reflective.  While this paper is very interesting regarding the continued radical reaction caused by the initial UV exposure, it does not refute my argument regarding stabilizing agents.

Rajan et al. actually supports my claims.  The UV stabilizing agents actually do reduce the transmission of UV wavelengths through the samples in the UV/Vis experiments.  I believe your argument is best summed up and then dismissed by this direct quote below figure 5:

It is observed that the rate of oxidation for unprotected sample is much higher in the initial aging hours and afterwards it get decreased whereas for protected sample the rate of oxidation is much slower in the initial hours but sustains the same rate of oxidation for a longer aging period and finally it enters into a plateau region. Even though the protected sample has a prolonged linear region of oxidation before it reaches a plateau still it has lower overall oxidation level at all stages of aging compared to the unprotected sample.

While this paper may be useful for explaining why the yellowed plastics continue to be a problem, especially for older parts like classic keyboards, it does not imply that stabilizers accelerate the decomposition.


Granted, this was just a quick read of the papers.  I have plans tonight, so I need to go to the liquor store.  I just wanted to respond before I go get drunk.

I think I might've mistook your "stabilisers" for fire retardants and other additives, which is what the articles are about iirc. The original thread I posted in was about Retrobright, I just quoted the sources I used for that discussion.