Overview
ISO 1833-4:2023 - Textiles - Quantitative chemical analysis - Part 4 defines a hypochlorite-based chemical method to determine the mass percentage of protein fibres in textile mixtures. The method quantifies protein fibres (wool, animal hair such as cashmere/mohair, silk) after removal of non-fibrous matter in mixtures with a wide range of non‑protein fibres (e.g., cotton, cupro, viscose, modal, acrylic, polyamide, polyester, polypropylene, glass, elastane, melamine and certain bicomponents).
This third edition (2023) updates preparation details for the hypochlorite reagent and aligns with general principles in ISO 1833-1.
Key topics and technical requirements
- Principle: Dissolve protein fibre selectively with alkaline hypochlorite; collect, wash, dry and weigh the insoluble residue. Protein content = initial dry mass − residue mass.
- Scope of fibres: Applies to mixtures of specified protein fibres with listed non-protein fibres (see scope for full list).
- Reagents:
- Sodium hypochlorite solution (active chlorine ~35 g/L; adjusted to 3.5% active chlorine for reagent) - requires iodometric checking of active chlorine.
- Lithium hypochlorite (solid) alternative - preferred for infrequent analyses because of constant hypochlorite content.
- Sodium hydroxide and dilute acetic acid for washing.
- Test procedure highlights:
- Use 100 mL of hypochlorite solution per gram of test specimen.
- Agitate continuously for 40 minutes in a water bath at (20 ± 2) °C.
- Filter, wash (water → dilute acetic acid → water), dry and weigh residue.
- Control water-bath temperature carefully - some dissolutions (e.g., wool) are exothermic and can affect results.
- Calculation details:
- Results calculated following ISO 1833-1 general instructions.
- Density correction factor d = 1.00 normally; raw cotton d = 1.03; cotton, viscose, modal, melamine d = 1.01.
- Precision: Confidence limits on homogeneous mixtures are not greater than ±1 percentage point at 95% confidence.
Applications and users
- Textile testing laboratories performing quantitative fibre composition analysis.
- Manufacturers and brand quality control teams verifying fibre declarations and compliance.
- Regulatory and inspection bodies investigating labeling disputes or fiber-content claims.
- Research groups studying blended-fabric behavior or recycling feedstock composition.
Keywords: ISO 1833-4:2023, hypochlorite method, textiles, protein fibres, quantitative chemical analysis, fibre composition, wool testing, viscose, textile quality control.
Related standards
- ISO 1833-1 - General principles of quantitative chemical analysis for textiles.
- Other parts of the ISO 1833 series for methods applicable to different fibre combinations (see ISO catalogue for the full series).
Open preview (PDF)Textiles — Quantitative chemical analysis — Part 4: Mixtures of certain protein fibres with certain other fibres (method using hypochlorite)
