Overview
ISO 20920:2018 specifies a standardized laboratory method for determining the dye uptake of cationic dyeable modified polyester fibres using a cationic dye. The method applies to cationic dyeable polyester (CDP) and easy cationic dyeable polyester (ECDP) fibres, including staple fibres and filament yarns, but excludes polyester partially oriented yarns. The test evaluates how much dye is absorbed by fibre specimens by spectrophotometric comparison of residual dye in solution.
Key topics and technical requirements
- Principle: Dye specimens with a defined cationic dye solution, measure the residual dye absorbance spectrophotometrically, and calculate dye uptake by comparison with a blank.
- Reagents & materials:
- Grade 3 water (ISO 3696)
- Cationic red X‑GRL (10 g/L stock solution; prepared by dissolving 1 g dye in 100 ml water)
- Acetate buffer (pH 5), soap per ISO 105‑C10
- Apparatus & conditions:
- Spectrophotometer with 1 cm cuvette; measure at peak wavelength (532 nm)
- Dyeing machine capable of (100 ± 3) °C; heating rate (1.5 ± 0.5) °C/min
- Liquor ratios: pre-wash 50:1; dyeing 100:1
- Procedure essentials:
- Two specimens of 1.5 g each are tested.
- Prepare an 80 mg/L working dye solution (dilution of the 10 g/L stock with buffer).
- Dye at 100 °C for 60 minutes, cool, dilute solutions to absorbance between 0.1–0.5, and measure at 532 nm.
- Calculate uptake: ω = (1 − (Ai·ni) / (A0·n0)) × 100 (%) and report the arithmetic mean of two specimens to 0.1%.
- Pre-treatment & conditioning:
- Launder to remove oils (optional if oil content is shown not to affect results); condition per ISO 139.
- Quality & precision:
- Annex A provides precision data (repeatability and reproducibility). Example values: CDP staple fibre r = 3.62%, R = 4.94%; ECDP staple fibre r = 2.42%, R = 2.49%.
- Traceability: Record specimen ID, mass, dye concentration, test date and any anomalies in the test report.
Applications and who uses it
- Textile fibre and yarn manufacturers evaluating dyeability of modified polyester (CDP, ECDP)
- Dyeing and finishing laboratories performing quality control and R&D
- Raw material suppliers, procurement teams, and compliance/technical buyers assessing dye uptake performance
- Test houses requiring a reproducible, comparable method for internal QC, product specifications and supplier acceptance
Related standards
- ISO 139 - Standard atmospheres for conditioning and testing
- ISO 3696 - Water for analytical laboratory use
- ISO 105‑C10 - Colour fastness to washing (soap)
- ISO 5725‑2 - Precision of measurement methods (used for precision analysis in Annex A)
Keywords: ISO 20920, dye uptake, cationic dyeable polyester, CDP, ECDP, textile testing, spectrophotometer, cationic dye, dyeing procedure, laboratory method.
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