Overview
EN ISO 1833-4:2023 specifies a quantitative chemical method (hypochlorite method) for determining the mass percentage of protein fibres in textile mixtures after removal of non‑fibrous matter. The procedure dissolves protein fibres (wool, other animal hair such as cashmere or mohair, and silk) selectively with an alkaline hypochlorite reagent, leaving a residue of non‑protein fibres that is collected, washed, dried and weighed. The protein fraction is calculated by difference from the known dry mass of the test specimen.
Keywords: EN ISO 1833-4, textiles, quantitative chemical analysis, protein fibres, hypochlorite method, wool, silk, cotton, viscose.
Key topics and technical requirements
- Scope of applicability: mixtures of protein fibres (wool, animal hair, silk) with non‑protein fibres including cotton, cupro, viscose, modal, acrylic, chlorofibres, polyamide, polyester, polypropylene, glass, elastane, elastomultiester, elastolefin, melamine and PP/PA bicomponent.
- Principle: selective dissolution of protein fibres with alkaline hypochlorite; residue mass measured and protein content obtained by difference.
- Reagents:
- Hypochlorite solution prepared from sodium or lithium hypochlorite; sodium hypochlorite must be checked iodometrically (target ~0.9–1.1 mol/L before dilution), lithium hypochlorite provides more stable active‑chlorine content.
- Sodium hydroxide and dilute acetic acid for reagent preparation and washing.
- Apparatus & conditions:
- Conical flask (≥250 ml), filter crucible, water bath maintained at (20 ± 2) °C.
- Use 100 ml hypochlorite solution per gram of specimen; agitation for 40 minutes at specified temperature.
- Controlled washing (water, dilute acetic acid) and drying prior to weighing.
- Accuracy and precision: confidence limits on homogeneous mixtures are ±1 percentage point at a 95% confidence level.
- Edition: Third edition (2023), supersedes EN ISO 1833-4:2017.
Practical applications
- Textile testing and quality control: routine laboratory determination of fibre composition for incoming materials, production checks and finished‑product verification.
- Label compliance and consumer protection: verification of declared wool/silk content on labels and certificates.
- Procurement & supply chain: raw material inspection for mills, converters and garment manufacturers.
- R&D and failure analysis: material characterization in product development or dispute resolution.
Who uses this standard
- Textile testing laboratories and accredited fiber analysis labs
- Manufacturers, spinners, and knitwear/weaving mills
- Quality assurance and compliance teams
- Regulatory bodies and customs authorities
Related standards
- ISO 1833-1 (General principles of quantitative chemical analysis for textiles) - referenced normative guidance for test procedure and reporting.
This standard is essential when accurate, repeatable chemical quantification of protein fibre content is required in mixed‑fibre textiles.
