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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Wed, 30 May 2001 23:49:26 GMT
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Viewed:
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3240 times
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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 has 1 Reply:
 | | Re: why parts yellow (was Re: Sopwith Camel pictures)
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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 (...) (24 years ago, 31-May-01, to lugnet.general)
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Message is in Reply To:
| | why parts yellow (was Re: Sopwith Camel pictures)
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| Frank Filz showed me a brick out of a sealed set from the 70's that had yellowed in the box, once opened over twenty years later. The box may have been near or in a store window, so it may have gotten UV through the box, but the parts in the same (...) (24 years ago, 30-May-01, to lugnet.general)
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