Subject:
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Re: why parts yellow (was Re: Sopwith Camel pictures)
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Newsgroups:
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lugnet.general
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Date:
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Thu, 31 May 2001 15:15:26 GMT
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Viewed:
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4437 times
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Recently I was checking some of my Classic Lego windows & doors for
yellowing. The older ABS white windows (from 1964-72) were quite prone to
yellowing. However, ALL of my Cellulose Acetate white windows had sustained
NO yellowing (I have hundreds of these). I have the feeling that ABS is much
more prone to yellowing than Cellulose Acetate is.
Gary Istok
"Kyle D. Jackson" wrote:
> In lugnet.general, Cary Clark writes:
> >
> > Show what do we know?
> > - ABS yellows. White, light grey and blue bricks show the yellowing most
> > visibly.
> > - Parts yellow with age, but not uniformly. Bricks faces against other
> > faces do not yellow.
> > - Sometimes the yellowing can be bleached out, but as Tom Stangl avows,
> > sometimes no amount of bleach can take the yellowing out.
> > - Parts do not uniformly yellow, even though all sides are exposed to
> > air. I have monorail track that is partially yellowed, but was
> > presumably completely air exposed.
> > - Parts that get sun exposure yellow faster. This is common lore; can
> > anyone dispute it?
> > - Parts in sealed boxes or in wooden drawers can yellow, apparently
> > faster than parts that get diffuse sunlight.
>
> According to our resident plastics expert at work, both ABS and
> CA (cellulose acetate) polymers will discolour from exposure to
> ultra-violet light. The UV energy directly "attacks" the molecular
> bonds of the polymers. And presumably this damage is cumulative---
> in other words, once there has been exposure, the plastics will
> begin to discolour over time. I would speculate that this is because
> each broken molecular bond releases more energy, further energizing
> the reaction, and so on. Technically it's really a long-term
> decomposition. Polymers in general have a useful life, over which
> their mechanical properties (strength, flexibility, etc.) degrade.
> This is hastened by UV exposure.
>
> Compare the areas of your "white" computer monitor cases that
> are exposed to light to those that aren't as much---you'll see
> it's yellowing, too, if it's old enough.
>
> Also, I was told that ABS should not outgas at atmospheric pressure
> unless heated up to it's softening point. Put it into a vacuum,
> however, and it's a different ballgame. For example even metals can
> outgas in space.
>
> I draw one conclusion from all of this: If your LEGO has ever
> seen light, and unfortunately all of it has (at the factory),
> then it will yellow. The only question is just how long it will
> take.
>
> KDJ
> ______________________________________________________
> Harbinger of LEGO Death #203, Windsor, Ontario, Canada
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Message is in Reply To:
 | | Re: why parts yellow (was Re: Sopwith Camel pictures)
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| (...) According to our resident plastics expert at work, both ABS and CA (cellulose acetate) polymers will discolour from exposure to ultra-violet light. The UV energy directly "attacks" the molecular bonds of the polymers. And presumably this (...) (25 years ago, 30-May-01, to lugnet.general)
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