Overview
EN ISO 1061:1999 / ISO 1061:1990 specifies a standardized titration method for determining the free acidity of unplasticized cellulose acetate. The method measures acidity extractable by water plus acidic groups attached to the polymer (for example, carboxyl groups) and expresses results as grams of acetic acid per 100 g of dry cellulose acetate. This second edition supersedes ISO 1061:1975 with minor technical revisions. The method is not suitable for cellulose acetate containing additives that could interfere with the test.
Key topics and requirements
- Principle: Water extraction of a test portion followed by rapid titration of the aqueous extract with a sodium hydroxide solution using phenolphthalein as indicator.
- Sample preparation:
- Sample must be powdered to pass a 710 μm sieve (see ISO 565) or ground.
- Moisture content must be determined and results corrected to dry mass (see ISO 585).
- Apparatus:
- 250–300 ml glass flask with ground-glass stopper
- 250 ml graduated cylinder
- 25 ml burette (protected against CO2)
- Analytical balance accurate to 0.01 g
- Reagents:
- Distilled water (freshly boiled to remove dissolved CO2)
- Standard volumetric sodium hydroxide solution (as specified in the standard)
- Phenolphthalein indicator solution
- Procedure highlights:
- Typical test portion ≈ 10 g (or more depending on expected acidity)
- Add 150 ml distilled water; condition at 20–27 °C with shaking (3 h with intermittent shaking or 1 h continuous shaking)
- Titrate promptly to avoid saponification and CO2 absorption
- Perform a blank and two determinations; repeat if results differ by >10% of the mean
- Calculation & reporting:
- Free acidity reported as mass % (g acetic acid / 100 g dry cellulose acetate)
- Include reference to the standard, product identification, sample treatment, free acidity, and test date
- Precision: Inter-laboratory precision data are not available; use caution for contractual/specification disputes.
Applications and users
- Quality control laboratories in plastics and film manufacturing
- Suppliers and processors of unplasticized cellulose acetate
- R&D teams assessing polymer purity and hydrolytic degradation
- Contract testing and certification bodies verifying material specifications
Practical uses include monitoring raw material quality, assessing storage or processing effects on acidity, and supporting product compliance.
Related standards
- ISO 565 - Test sieves (mesh 710 μm reference)
- ISO 585 - Determination of moisture content for unplasticized cellulose acetate
Keywords: EN ISO 1061:1999, ISO 1061:1990, free acidity determination, unplasticized cellulose acetate, sodium hydroxide titration, phenolphthalein, moisture correction, ISO 585, ISO 565.
