Overview
ISO 3073:1975 - Wool - Determination of acid content specifies a chemical test method to quantify the acid content of wool. The method is applicable to undyed wool in any form (loose fibre, sliver, yarn or fabric) and may be used for dyed wool provided that dye extracted during the test does not interfere with titration end‑point detection. Results are reported as a percentage by mass of the dry sample.
Key topics and technical requirements
- Principle: acids are extracted from a known mass of wool using a dilute pyridine solution; the extracted acid is determined by titration with standardized 0.1 N sodium hydroxide.
- Reagents: pyridine solution (5 g/L), NaOH 0.1 N (standardized against potassium hydrogen phthalate), phenolphthalein indicator (ethanolic solution).
- Apparatus: conical flasks with ground stoppers (250 ml), pipettes (50 and 100 ml), burette (25 ml), analytical balance (precision 0.0005 g), ventilated oven for drying at 105 ± 3 °C, desiccator, glass beakers, glass‑wool filter.
- Sampling and sample size: follow ISO 1130 for representative sampling; the standard calls for at least two test portions of approximately 2.000 g (±0.001 g) and one 1.000 g portion for moisture/dry mass determination.
- Procedure highlights: dry and determine the dry mass; extract each test portion with 100 ml pyridine solution (mechanical agitation for 1 hour or overnight after initial wetting); decant and filter; pipette 50 ml aliquots and titrate with NaOH using phenolphthalein to a faint persistent pink.
- Expression of results: results are calculated from titration normality and titrant volume, expressed as percentage by mass of the dry sample. The standard provides conversion constants (k) to report results as equivalents of common acids (example values: HCl 3.65; formic 4.6; H2SO4 4.9; acetic 6.0).
- Quality notes: average of duplicate determinations is used; potentiometric end‑point determination may be used as an alternative.
Applications and users
- Textile testing laboratories performing routine quality control on raw and processed wool.
- Wool processors and scouring plants assessing acidity related to processing chemistry or contamination.
- Research and development groups studying fibre chemistry, dyeing interactions, or finishing treatments.
- Regulatory and standards bodies requiring documented measurement methods for specification compliance.
Related standards
- ISO 1130 (textile sampling procedures) - referenced for representative sampling.
- ISO 3073 derives from the Fédération Lainière Internationale method (FLI‑3‑65); see local standards bodies for any updated or successor methods.
Keywords: ISO 3073, wool acid content, acid determination in wool, pyridine extraction, titration method, textile testing, wool quality control.
