Cellulose Acetate

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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Portions of this monograph that are national USP text, and are not part of the harmonized text, are marked with symbols (^⧫ _⧫) to specify this fact.

Cellulose acetate;

Cellulose, diacetate CAS RN^®: 9035-69-2.

Cellulose, triacetate

CAS RN^®: 9012-09-3.

1 DEFINITION

Cellulose Acetate is partially or completely acetylated cellulose. It contains NLT 29.0% and NMT 44.8%, by weight, of acetyl (C₂H₂O) groups, calculated on the dried basis. Its acetyl content is NLT 90.0% and NMT 110.0% of that indicated on the label.

2 IDENTIFICATION

2.1 A. INFRARED ABSORPTION

Sample solution: Prepare a 20 mg/mL solution of Cellulose Acetate, previously dried, in acetone (mono- and diester) or in methylene chloride (di- and triester).

Analysis: Spread 1 drop of the Sample solution on a sodium chloride plate, place a second sodium chloride plate over it, and spread the specimen between the plates. Separate the plates, heat them both at 105° for 1 h, and reassemble the dried plates.

Acceptance criteria: The IR absorption spectrum exhibits maxima only at the same wavelengths as those of a similar preparation of USP Cellulose Acetate RS, treated in the same manner.

3 ASSAY

3.1 CONTENT OF ACETYL

3.1.1 For Cellulose Acetate labeled to contain NMT 42.0% of acetyl groups

Sample: 2 g of Cellulose Acetate

Titrimetric system

(See Titrimetry (541).)

Mode: Residual titration

Titrant: 1.0 N sodium hydroxide VS

Back-titrant: 1.0 N sulfuric acid VS

Endpoint detection: Visual

Analysis: Transfer the Sample to a 500-mL flask. Add 100 mL of acetone and 5-10 mL of water to the flask, insert the stopper into the flask, and stir with a magnetic stirrer until solution is complete. Pipet 30 mL of Titrant to the solution, with constant stirring. A finely divided precipitate of regenerated cellulose, free from lumps, is obtained. Insert the stopper into the flask, and stir with a magnetic stirrer for 30 min. Add 100 mL of water that has been preheated to 80", washing down the sides of the flask. Stir for 2 min, and cool to room temperature. Titrate the excess sodium hydroxide solution with Back-titrant to a phenolphthalein endpoint. Treat a blank in the same manner.

Calculate the percentage of acetyl in the portion of Cellulose Acetate taken:

                  Result = (V_B - V_S)/W x 4.305

V_B= Back-titrant volume consumed by the blank (mL)

V_S = Back-titrant volume consumed by Cellulose Acetate (mL)

W = weight of Cellulose Acetate taken, calculated on the dried basis (g)

Acceptance criteria: 29.0%-44.8% by weight of acetyl (C₂H₂O) groups on the dried basis

3.1.2 For Cellulose Acetate labeled to contain more than 42.0% of acetyl groups

Sample: 2 g of Cellulose Acetate

Titrimetric system

(See Titrimetry (541).)

Mode: Residual titration

Titrant: 0.5 N hydrochloric acid VS

Back-titrant: 0.5 N sodium hydroxide VS

Endpoint detection: Visual

Analysis: Transfer the Sample to a 500-mL conical flask. Add 30.0 mL of Dimethyl sulfoxide and 100 mL of acetone, and stir for 16 h with the aid of a magnetic stirrer. Pipet 30 mL of 1 N sodium hydroxide VS slowly into the flask, with constant stirring. Insert the stopper into the flask, and stir for 6 min. Allow to stand without stirring for 60 min. Resume stirring, and add 100 mL of water that has been preheated to 80", washing down the sides of the flask. Stir for 2 min, and cool to room temperature. Add 4-5 drops of phenolphthalein TS, and titrate the excess sodium hydroxide solution with Titrant. Add an excess of 0.5 mL of Titrant. Stir for 5 min. Allow to stand for 30 min. Titrate with Back-titrant to a persistent pink endpoint, using a magnetic stirrer for agitation. Calculate the net number of milliequivalents of sodium hydroxide consumed, and correct this value by use of the average of two blank determinations run concomitantly through the entire procedure.

Calculate the percentage of acetyl in the portion of Cellulose Acetate taken:

                 Result = (n/W) x 4.305

n = corrected value of the net number of milliequivalents of sodium hydroxide consumed

W = weight of Cellulose Acetate taken, calculated on the dried basis (g)

Acceptance criteria: 29.0%-44.8% by weight of acetyl (C₂H₃O) groups on the dried basis

4 IMPURITIES

RESIDUE ON IGNITION (281): NMT 0.1%

LIMIT OF FREE ACID

Sample: 5 g

Titrimetric system

(See Titrimetry (541).)

Mode: Direct titration

Titrant: 0.01 N sodium hydroxide VS

Endpoint detection: Visual

Analysis: Transfer the Sample to a 250-mL flask. Add 150 mL of freshly boiled, cooled water. Insert the stopper into the flask, swirl the suspension gently, and allow it to stand for 3 h. Filter through paper, and wash the flask and the filter with freshly boiled, cooled water, adding the washings to the filtrate. Add phenolphthalein TS, and titrate the combined filtrate and washings with the Titrant. Calculate the percentage of free acid in the portion of Cellulose Acetate taken:

                  Result = (V/W) x 0.06005

V = Titrant volume consumed (mL)

W = weight of Cellulose Acetate taken, calculated on the dried basis (g)

Acceptance criteria: NMT 0.1%, calculated as acetic acid

5 SPECIFIC TESTS

LOSS ON DRYING (731)

Analysis: Dry at 105° for 3 h.

Acceptance criteria: NMT 5.0%

MICROBIAL ENUMERATION TESTS (61) and TESTS FOR SPECIFIED MICROORGANISMS (62): The total aerobic microbial count is NMT 103 cfu/g, and the total combined molds and yeasts count is NMT 102 cfu/g. It meets the requirements of the tests for absence of Escherichia coli and Salmonella species.

6 ADDITIONAL REQUIREMENTS

PACKAGING AND STORAGE: Preserve in tight containers.

• Labeling: The labeling states the nominal percentage content of acetyl.

• USP Reference Standards 〈11〉

USP Cellulose Acetate RS