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Cellulose diacetate, sometimes simply called diacetate, is a synthetic polymer made by treating cellulose with acetic acid. It consists of two acetyl functional groups on each unit of D-anhydroglucopyranose of the cellulose molecule. It was first developed in the United States.
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
It is fragile since it is based on cellulose. When cellulose diacetate deteriorates, it shrinks and releases acetic acid, causing a "vinegar syndrome".
Cellulose diacetate has been used to make fabrics, membranes, filaments, and many consumer products. From 1922 to 1957 it was used to make film stock, mainly in smaller formats such as 8 mm, 16 mm, 35 mm, and 70 mm.
In photography, a film substrate made from cellulose diacetate is called safety film.