Cellulose acetate film (Sicherheitsfilm)

Cellulose acetate film, or safety film, is used in photography as a base material for photographic emulsions. It was introduced in the early 20th century by film manufacturers as a safe film base replacement for unstable and highly flammable nitrate film.

Beginning with cellulose diacetate in 1909, this innovation continued with cellulose acetate propionate and cellulose acetate butyrate in the 1930s, and finally in the late 1940s, cellulose triacetate was introduced, alongside polyester bases. These less flammable substitutes for nitrate film were called safety film.

The motion picture industry continued to use cellulose nitrate supports until the introduction of cellulose triacetate in 1948, which met the rigorous safety and performance standards set by the cinematographic industry. The chemical instability of cellulose nitrate material, unrecognized at the time of its introduction, has since become a major threat for film collections.

Decay and the "vinegar syndrome"
The first instance of cellulose triacetate degradation was reported to the Eastman Kodak Company within a decade of its introduction in 1948. The first report came from the Government of India, whose film was stored in hot, humid conditions. It was followed by further reports of degradation from collections stored in similar conditions. These observations resulted in continuing studies in the Kodak laboratories during the 1960s.

Beginning in the 1980s, there was a great deal of focus upon film stability following frequent reports of cellulose triacetate degradation. This material releases acetic acid, the key ingredient in vinegar and responsible for its acidic smell. The problem became known as the "vinegar syndrome."

Source: Wikipedia