Overview
ISO 3072:1975 - Wool - Determination of solubility in alkali specifies a laboratory test method to measure the alkali solubility of wool. The test quantifies the loss in dry mass after immersion in a controlled sodium hydroxide solution and gives an index of chemical change caused by treatments (acid, oxidizing/reducing agents, heat, light or alkalis). The procedure is most useful for quality control and comparison with an untreated control.
Key topics and requirements
- Scope and applicability: Applies to wool in any form (loose fibre, sliver, roving, yarn, cloth). Best interpreted when an untreated control sample is available.
- Principle: Immersion of wool in 0.1 N sodium hydroxide under specified time, temperature and volume, followed by determination of mass loss as percentage of dry mass (alkali solubility). Acid-containing samples require a correction for acid content.
- Critical test conditions
- Alkali solution: 0.1 N sodium hydroxide, 100 ml per test specimen.
- Temperature control: water-bath at 65 ± 0.5 °C with stirring.
- Exposure: typically 1 hour with gentle shaking at intervals.
- Drying: ventilated oven at 105 ± 3 °C to constant mass before and after treatment.
- Sample preparation and pre‑extraction
- Remove fat and vegetable matter by Soxhlet extraction with dichloromethane (1 hour, ~6 cycles/hour). Note: dichloromethane is toxic - use adequate ventilation.
- Apparatus and accuracy
- Soxhlet extractor, thermostatic water-bath, 100 ml stoppered flasks, sintered-glass filtering crucibles (porosity 1), ventilated oven, analytical balance (accuracy 0.0002 g).
- Results
- Report alkali solubility as percentage loss of dry mass (S). For samples with acid (pH
