Well, I'm parroting. Time to do some research.
"Tetrabromobisphenol A is also used as an additive in acrylonitrile butadiene styrene (ABS)."
Source:
https://en.wikipedia.org/wiki/Brominate ... _retardant
So we know it's in there.
However, the industry *knows* there are issues with UV stability in brominated plastics.
Next on the list is a document from ICL Industrial products. Admittedly, this is a PBT datasheet.
"FR-1410 (decabromodiphenyl ethane - 82% bromine) is cost efficient in
PBT but has limited UV stability and is not melt blendable during injection
molding."
Source:
http://icl-ip.com/wp-content/uploads/20 ... 130729.pdf
The datasheet and article lead me to believe that less bromine strongly correlates with greater UV stability and weathering endurance, though the plastic itself can also be a large factor.
"The plastics most commonly used to make the structural cases for electronic equipment are polypropylene, impact styrene, and ABS," replied Deanin. "These all tend to discolor and embrittle gradually when exposed to UV and/or heat. They become oxidized and develop conjugated unsaturation, which produces color. They crosslink or degrade, which causes brittleness."
Source: Article where a guy actually talked with an expert --
http://www.vintagecomputing.com/index.php/archives/189
SNES Systems, according to a Nintendo official reply, yellowed due to fire retardants.
"Deanin weighed in on the flame retardant issue only by saying that most retardants are harmless, but certain "aliphatic bromine compounds" are unstable to heat and UV, and should be avoided. Flame retardants unstable to heat! How ironic."
PBT had bromines added to it -- the explanation for the long term color difference likely lies in the different manufacturing processes or chemical makeups of the plastics. ABS is known for being "weak" to UV light, meaning it could break down and release bromine compounds for reaction much faster than PBT.
My conclusion is that ABS plastic, when coupled with bromine, is the perfect storm for yellowing. Oxidation is likely the primary yellowing factor, but it seems that bromine fire retardants act as an accelerant in the process. I don't know if the yellow color of bromine is part of the extreme yellowing shown in ABS, but I think it could be a contributing factor due to the breakdown of the plastic and the reactivity of bromine (which is off the charts).
