Acetate safety film was first marketed on a large scale in the 1920s, due largely to a desire on the part of photographic manufacturers to sell 16mm home movies that did not pose a risk of fire in home projectors or hot attics. Non-flammable plastic supports were obtained by grafting the acetate group (CH 2 COOH), or other similar organic acids, onto the cellulose molecule. The initial 16mm cinema films (and some sheet film) were made with cellulose diacetate, that has an average of two out of a possible three sites acetylated (see diagram).
After the Second World War, cellulose triacitate replaced nitrate in 35mm motion picture films, as well as in x-ray and various roll films. Low flammability was achieved in all the acetate supports by virtue of the inherent nature of the side groups and by generous additions (10-15 per cent by weight) of fire-retardant substances known as plasticizers.
Cellulose acetate is manufactured by reacting cellulose with acetic anhydride using sulfuric acid as a catalyst. This slow burning base material is frequently used for motion picture films and in sheet form for overlay cells in animation.
Preservation of Safety Film: Final Report