Overview
ISO 1136:2015 specifies an air‑permeability method for determining the mean diameter of wool fibres. The standard describes how a controlled current of air is passed through a compacted bundle (sliver) of wool fibres packed in a constant‑volume chamber; the resulting flow/pressure relationship is used, after calibration, to give an estimate of average fibre diameter. ISO 1136:2015 is particularly suitable for clean, unmedullated wool in an open, dispersed state (for example combed slivers). The method is indirect and calibrated against reference slivers.
Key topics and requirements
- Applicability
- Intended for clean, unmedullated wool dispersed uniformly (combed or card slivers).
- Dichloromethane extractable matter of the specimen must not exceed 1.0%.
- Applicable to oil‑combed slivers after cleaning with an organic solvent.
- Less accurate for lambswool, appreciably medullated wool, and heavily dyed wool (see Annex D).
- Principle
- Air flow through a packed fibre mass relates to total fibre surface area; for non‑medullated, near‑circular fibres this relates to mean diameter.
- Apparatus must be calibrated against known reference slivers (Annex E).
- Apparatus
- Two forms: constant flow (specimen mass ~1.5 g) and constant pressure (specimen mass ~2.5 g).
- Main components: constant volume chamber (base, plunger, cap), manometer, flowmeter, suction pump, and connecting tubing.
- Specimen preparation & conditioning
- Specimens must be cleaned and conditioned to a standard atmosphere (see ISO 139) before testing.
- Test specimens are prepared from a representative laboratory sample and weighed with defined accuracy.
- Corrections for testing atmosphere humidity are provided (Annex C).
- Calibration & accuracy
- Calibration using reference slivers is required; method is less precise for special wool types (Annex D). Reproducibility guidance appears in Annex B.
Applications and users
- Textile and wool testing laboratories performing quality control and mill testing.
- Wool scouring and processing mills monitoring fibre diameter for product specification and blending.
- Research groups and instrument manufacturers validating or calibrating air‑permeability diameter instruments.
- Trade and certification bodies requiring standardized fibre diameter reporting.
Related standards
- ISO 139 - Standard atmospheres for conditioning and testing (referenced for specimen conditioning).
- ISO 1136:2015 is based on IWTO test methods (IWTO‑6‑98) and integrates calibration and humidity correction annexes.
Keywords: ISO 1136:2015, wool fibre diameter, air permeability method, mean diameter, combed slivers, wool testing, calibration, ISO 139, textile quality control.