What Is Acetate?

How is acetate made?

Acetate is made by chemically converting plant cellulose into cellulose acetate, dissolving it in a solvent and spinning the solution into fibre. The cellulose comes from wood or from linters, the short fibres that cling to cotton seeds.

1. Acetylation. Purified cellulose is treated with acetic acid, then with acetic anhydride, using a catalyst such as sulphuric acid.
2. Partial reversal. Adding water partly reverses the reaction and gives cellulose diacetate, the form used for most acetate fibre.
3. Dissolving. Flakes of diacetate are dissolved in acetone.
4. Dry spinning. The solution is extruded through spinnerets, the fine nozzles that shape the fibre, and dry-spun into filaments.

The fibre that results is still cellulose acetate. That is the key difference from viscose, where the cellulose is regenerated: turned back into cellulose.

A short history

Cellulose acetate was prepared as early as 1865. During the First World War, the Swiss brothers Henri and Camille Dreyfus made cellulose diacetate in England as a coating for aircraft wings. After the war they turned it into fibre. Sources differ on the date: Britannica says their company, British Celanese, began commercial manufacture in 1921, while the Museum of Fine Arts, Boston's CAMEO database says it was first sold in the UK as an artificial silk called Celanese in 1919. DuPont began making acetate fibre in the United States in 1929.

Acetate was originally called rayon and was given its own category in 1952. Its production has declined since the mid-20th century, partly because of competition from polyester.

What are the properties of acetate?

Acetate is a soft, lustrous fibre with good drape, but it is weak when wet, sensitive to heat and dissolved by acetone. The main properties, with figures where the sources give them:

• Look and handle: silky in appearance and feel, with a high sheen. It drapes well and takes rich dye colours.
• Strength: CAMEO gives a tenacity of 1.1–1.4 g/denier dry and 0.65–0.75 g/denier wet, so it loses between about a third and a half of its strength when wet. It also has poor abrasion resistance.
• Moisture: a moisture regain of 6.5 per cent. It dries quickly.
• Heat: diacetate melts at about 230 °C. Cornell Cooperative Extension says it softens, sticks and shrinks at about 177 °C (350 °F), well within the range of a domestic iron.
• Pleats: it cannot be heat set, because the heat needed to set a crease damages the fabric.
• Light and air: it degrades faster than most fibres in continuous sunlight, and some dyes on acetate can fade or change colour from fumes in the air.
• Pests: it resists moths and mildew.
• Pilling: Cornell Cooperative Extension says acetate does not pill.

Sources disagree on creasing. Britannica and CAMEO describe acetate as wrinkle resistant; Cornell Cooperative Extension says it wrinkles easily during wear.

How is acetate different from triacetate and viscose?

Acetate and triacetate are both cellulose acetate, differing in how far the cellulose is acetylated, while viscose is regenerated cellulose made by a different process. Both US and EU labelling rules separate the two by how many of the cellulose's hydroxyl groups are acetylated.

Triacetate was marketed as Tricel by Courtaulds and British Celanese, and as Arnel in the United States. Two other regenerated cellulose fibres, modal and lyocell, are also defined separately in the EU, so a label can tell all four apart.

How does acetate appear on a clothing label?

Acetate appears on labels as "acetate", or as "triacetate" when at least 92 per cent of the cellulose's hydroxyl groups are acetylated.

• Under US law, the Federal Trade Commission defines acetate as a manufactured fibre whose fibre-forming substance is cellulose acetate. The name "triacetate" may be used where at least 92 per cent of the hydroxyl groups are acetylated.
• In the EU, Regulation (EU) No 1007/2011 sets the same 92 per cent line and adds a floor: the name acetate covers 74 to under 92 per cent acetylation. Only the names in the regulation's Annex I may describe fibre content.
• Percentages: in the EU, with limited exceptions, every fibre must be listed by percentage of weight, in descending order. "100 %", "pure" or "all" may be used only for a product made entirely of one fibre, allowing up to 2 per cent of unavoidable extraneous fibres.

Read acetate and triacetate as different instructions, not different spellings: one usually wants dry cleaning, the other can usually go in the machine. On vintage pieces, remember that acetate was once grouped with rayon, so older descriptions may not separate the two.

How do you tell good acetate from poor acetate?

You judge acetate by checking the label, the stress points and the signs of heat or light damage, because the fibre's weaknesses show up in predictable places.

1. Read the sewn-in label first. Check whether it says acetate or triacetate, and whether a lining has its own fibre line. Acetate is still used for linings because of its sheen.
2. Look at the rubbing points. Turn the garment inside out and check underarms, cuffs and the seat of a lined skirt or trouser. Because acetate resists abrasion poorly, fraying or thinning there is the first sign of wear.
3. Tilt it under a light. Look for glazed or stiffened patches where an iron has been. Acetate softens and sticks at about 177 °C, so a hot iron leaves its mark on the surface.
4. Compare colour on exposed areas. On a vintage piece, a shade change across the shoulders or outer surfaces, compared with the inside of a seam, points to fume fading or light damage.
5. Check pleats against the label. Acetate cannot be heat set to hold permanent pleats; triacetate can.
6. Test a loose thread, never the garment. Acetone, the main ingredient of many nail polish removers, dissolves acetate, so a stray thread from the seam allowance that dissolves in a drop points to acetate. Cornell Cooperative Extension uses acetone as a test for acetate, but the University of Georgia warns that triacetate can dissolve too, so read the result alongside the label.

Red flags: "silk-look" descriptions with no fibre content given; a satin weave sold as "silk satin" whose label says acetate; and glazed patches on secondhand pieces.

How do you care for acetate?

Follow the care label, and where it gives a choice, have acetate dry cleaned. Extension guides from the University of Georgia and Cornell advise:

• If you wash it, squeeze it gently by hand in lukewarm water with mild suds.
• Do not wring or twist. Blot or roll it in a towel, then drip dry or lay it flat at room temperature.
• Press it while damp, on the wrong side, with the iron on its lowest setting and a press cloth over the right side.
• Keep nail polish remover away from it. Acetone, acetic acid and alcohol all damage acetate, so let perfume dry before you dress.
• Store it out of direct sun.

Triacetate is easier: it can usually be machine washed and tumble dried, and ironed on the wool setting. Sources disagree on whether acetone harms it. Britannica says triacetate dissolves in a limited range of solvents, usually methylene chloride, and Cornell says it does not dissolve in acetone; the University of Georgia warns that acetone and some perfumes dissolve it. Treat it with the same caution.

Is acetate sustainable?

Acetate starts from plant cellulose, but it is chemically processed and breaks down slowly, so it is not automatically a low-impact choice. The cellulose comes from wood pulp or cotton linters. Turning it into fibre uses acetic anhydride and solvents such as acetone.

Biodegradation is slow. A 2023 laboratory study in Polymers found that cellulose acetate tow and film lost less than 3 per cent of their weight after 16 weeks in river water or seawater. The same paper reports that the higher the degree of substitution, the worse the biodegradability. The fibre name on a label says nothing about where the pulp came from, so any sustainability claim rests on evidence the seller supplies.