Deterioration
All plastic is subject to deterioration through physical or chemical means, and thus, motion picture film is subject to the same deterioration. Cellulose nitrate, cellulose diacetate and triacetate are known to be unstable mediums: improperly preserved film can deteriorate in a period of time much faster than many photographs or other visual presentations.
Cellulose nitrate, because of its unstable chemistry, eventually breaks down, releasing nitric acid, further catalyzing the decomposition. In the final stages of celluloid decomposition, the film turns into a rust-like powder.
Likewise, tri-acetate stock is also vulnerable to deterioration. Because of the small gauge of the film, owners of home-made films often find that their film can become shrunken and brittle to the point where the film is unwatchable in the space of a few years. In general, decaying acetate film breaks down into acetic acid, and similar to celluloid decomposition, leads to an auto-catylictic breakdown of the base that cannot be reversed. The result of the acetic acid released is a strong odor of vinegar, which is why the decay process in the archival community is known as "vinegar syndrome".
Modern polyester-based stocks are far more stable by comparison and are rated to last hundreds of years.
Read more about this topic: Film Stock