One thing you typically don't want treasured museum artifacts to do is self-destruct.
You probably also don't want them to gain sentience and stage a violent coup, but the likelihood of that happening, I think, is fairly slim.
The self-destructing thing, though, happens all the time. Not quickly, not quite as dramatically as a cinematic Big Red Button. But the plastics and other materials that make up these artifacts sometimes need a little help through the decades.
I recently spoke with a research scientist at the Smithsonian Institution's Museum Conservation Institute about the museum's approach to slowing the deterioration of plastic artifacts. (The artifacts in question happen to be costumes from the “Star Wars” movies … you're welcome for filling that gaping hole in Plastics News' coverage.)
Odile Madden has a PhD in materials science and engineering and specializes in studying how plastics degrade. The material she studies most often, she said, is cellulose acetate. It's found in artifacts like World War II-era aviator goggles and, as it turns out, the eye lenses in stormtrooper helmets.
The thing about cellulose acetate is it has an inconvenient tendency to abruptly shatter.
This shattering phenomenon tends to happen to objects that are 60 or 70 years old, Madden said. What happens is that as the plasticizers migrate out of the material over time, they take mass out with them, causing shrinking and distortion in the plastic. At the same time, another degradation reaction, hydrolysis, is happening in the polymer, catalyzed by acetic acid released by the plastic as it tries to revert back to cellulose.
So over time the plastic becomes more brittle — maybe it discolors — it's under tension. And then one day the plastic decides it's had enough, and POW, it shatters.
That's not really something you want to happen to an irreplaceable emblem of culture.
It's possible in many cases to slow a plastic's deterioration, with careful storage and display procedures. But that's where things get tricky for cellulose acetate.
As Madden explained, sealing in the air around the object could help slow the migration of plasticizers out of the material. But then you have the acetic acid building up, and you might want to vent that off, which would involve an exchange of air … you see the problem.
Sounds like quite a conundrum for the cultural heritage community.
Fortunately, scientists like Madden are on the case.