Overview
EN ISO 1833-7:2017 (ISO 1833-7:2017) describes a quantitative chemical analysis method for determining the mass percentage of polyamide in textile mixtures. The standard uses an aqueous formic acid technique to dissolve polyamide from a known dry mass of the specimen; the remaining residue is recovered, dried and weighed to calculate polyamide content by difference. The method applies to mixtures of polyamide with a wide range of other fibres (cotton, viscose, cupro, modal, lyocell, polyester, polypropylene, chlorofibre, acrylic, glass fibre, elastomultiester, elastolefin, melamine), and to wool or animal hair fibres when wool ≤ 25% (if wool > 25% use ISO 1833-4).
Key topics and technical requirements
- Scope: Determination of polyamide mass percentage after removal of non‑fibrous matter; not for wool content > 25% (see ISO 1833-4).
- Principle: Dissolve polyamide in aqueous formic acid, filter, wash, dry and weigh residue; calculate polyamide fraction by difference.
- Reagents: Formic acid ~80% (mass fraction; acceptable range 77–83%); dilute ammonia solution.
- Test conditions: Add 100 ml formic acid per gram of specimen; allow to stand ~15 minutes at room temperature with intermittent shaking.
- Washing sequence: filter and wash residue successively with formic acid, hot water, dilute ammonia, and cold water; drain under gravity before suction.
- Apparatus: Use apparatus per ISO 1833-1 plus a glass-stoppered conical flask (min. 200 ml) and a weighed filter crucible.
- Calculation: Follow general calculation rules in ISO 1833-1; note special d-factor = 1.01 for melamine (1.00 otherwise).
- Precision: For homogeneous mixtures, confidence limits are not greater than ±1 percentage point (95% confidence).
Applications and users
This standard is essential for:
- Textile testing laboratories performing quantitative fibre analysis
- Quality control teams in textile and apparel manufacturing
- Raw material verification and supplier auditing
- R&D teams developing blended fibre products
- Certification bodies and regulators requiring standardized composition data
Use cases include product labelling verification, claims substantiation (e.g., polyamide content), blend composition troubleshooting, and incoming material inspection.
Related standards
- ISO 1833-1 - General principles for quantitative chemical analysis of textiles (referenced for reagents, apparatus and calculation rules).
- ISO 1833-4 - Applicable for mixtures where wool content exceeds 25% (hypochlorite method).
Keywords: EN ISO 1833-7:2017, ISO 1833-7:2017, textiles quantitative chemical analysis, polyamide mixtures, formic acid method, fibre composition testing, textile laboratory.
