Acetyl Cellulose

acetates of cellulose, acetic acid esters of cellulose. Acetyl cellulose is usually obtained by the action on cellulose (cotton wool or, more rarely, refined wood-pulp cellulose) of acetic anhydride in the presence of various catalysts and solvents (or diluents):

[C₆H₇O₂(OH)₃]_n + 3_n(CH₃CO)₂O → [C₆H₇O₂(OCOOH₃)₃]_n + 3_nCH₃COOH

The final product of the reaction is cellulose triacetate, which in engineering is usually called primary acetate, or triacetylcellulose; it contains 62.5 percent bound acetic acid. So-called secondary acetate (up to 55 percent bound acetic acid) is obtained by fractional hydrolysis of triacetate.

Acetyl cellulose is a white, amorphous mass; its density is approximately 1,300 kg/m³. Acetyl cellulose is weakly water-absorbing (especially the triacetate) and photostable; it possesses good physicomechanical properties and is practically noncombustible. The thermostability of acetyl cellulose is insufficiently high: at temperatures as low as 190–210°C the color of the material changes, and at 230°C it begins to decompose. Alkalis and mineral acids gradually saponify acetyl cellulose. The primary acetate is soluble in acetic acid, methylene chloride, chloroform, dichlorethane, aniline, and pyridine; the secondary acetate dissolves also in acetone, mixtures of acetone and alcohol, ethyl acetate, dioxane, and other organic solvents. Acetyl cellulose is used in the manufacture of fibers, coatings (especially electro-insulating and motion-picture film), and plastics.