This may come as a shock to the younger readers of this blog, but there once was a time in ancient history when animation was created without the use of digital technology. Using analog technology, humans created animation by rendering drawings one frame at a time, with many of the drawings first being created on clear plastic films of cellulose nitrate. Theses were called "cels" for short. Cellulose acetate was eventually used as a replacement for the nitrates.
As an even larger shock, most of the movies created with this technique were well received and are fondly remembered by the public. The cels, no longer serving a useful purpose, are being recognized for their artistic value by collectors and curators. But there is a problem: cellulose nitrate, besides being flammable , the material doesn't age well. Many of the cels are starting to seriously degrade. The Getty Conservation Institute and Disney are now working together to better understand the degradation and finds steps to further reduce it.
We have and continue to do lots of work here at Aspen Research regarding polymer degradation, so I can firmly stand by the last two words of the previous sentence - they will be able to slow degradation down, but it can never be stopped, especially after it has started. Nitrogen blanketing is a likely option, as are other inert gases (argon is quite common); low light conditions and even avoiding certain wavelengths  altogether are also important. I would imagine that all the film stock is not of the same quality and some impurities are going to cause more problems than others. It's a fascinating project, and I wish I was involved.
 The flammability of cellulose nitrate served as an important plot aid in the films (Nuovo)Cinema Paradiso (one of my all time favorites - the kissing montage at the end of the movie is so poignant) and Quentin Tarantino's "Inglourious Basterds" [sic].
 It is often assumed that shorter wavelengths, being of higher energy are more destructive than longer wavelengths. This is not always the case (we've made lots of money from people who believed otherwise). See for instance: A. L. Andrady, Advances in Polymer Science, 128, 1997, 47-94