Overview
ISO 6989:1981 specifies procedures for determining the length and length distribution of staple textile fibres by measuring single fibres. The standard describes three measurement routes: Method A (reference manual method on a graduated plate using light tension and forceps with grease), Method B (measurement of an enlarged projected image using an opisometer), and Method C (use of a semi-mechanical or semi-automatic device). The scope covers discontinuous textile fibres, except where strong inherent crimp makes single-fibre straightening impractical; it excludes fibrous bundles of bast fibres.
ISO 6989:1981 was issued to replace previous International Standards ISO 270 and ISO 1822 and provides a harmonized approach to single-fibre length measurement for textiles, wool and man-made staple fibres.
Key Topics
-
Three measurement methods
- Method A: Straightened fibre on a graduated glass plate, light tension, pointed forceps and white petroleum jelly or liquid paraffin. This method serves as the reference method and is used in disputes unless crimp prevents straightening.
- Method B: Fibre mounted on a projector slide, image enlarged on a screen and measured with an opisometer; requires calibration of magnification and use of oil to hold fibres on the slide.
- Method C: Semi-mechanical apparatus for controlled-tension measurement and automatic classification (annex describes a representative machine). Useful for higher throughput and automatic classing into fixed intervals (e.g., 5 mm groups).
-
Conditioning and sampling: Fibres must be conditioned and tested in the standard atmosphere defined in ISO 139. Laboratory sampling and selection of test specimens are to follow ISO 1130 procedures.
-
Test size and statistics: A nominal test comprises 500 fibres; sample size can be increased to achieve desired precision. Results include mean length, modal class, length-biased mean, coefficient of variation (CV), and 95% confidence limits.
-
Reporting and expression: Frequencies can be shown as histograms or cumulative frequency diagrams. Results must report the method used, apparatus type (if Method C), class intervals, any excluded classes, and any incidents affecting outcome.
Applications
- Quality control and acceptance testing of textile lots
- Fibre classification and labelling for spinning and textile processing
- Comparative research and dispute resolution (Method A as reference)
- Process optimisation in wool and man-made staple fibre production
Related Standards
This standard is practical for laboratories and manufacturers seeking reproducible single-fibre length data for classification, process control and reporting in textile testing.