Overview
ISO 23713:2005 - "Pulps - Determination of fibre coarseness by automated optical analysis - Polarized light method" specifies an automated optical test for measuring fibre coarseness in pulps that polarize light. The method uses a polarized light setup to discriminate birefringent cellulose fibres from non-birefringent particles (air bubbles, fillers). Fibrous particles shorter than 0.2 mm are treated as fines and are excluded from results.
Keywords: ISO 23713:2005, fibre coarseness, polarized light method, automated optical analysis, pulp testing, birefringence.
Key topics and technical requirements
- Principle: Suspended fibres are passed through a fibre-orienting cell (FOC); projected fibre lengths are measured automatically. Crossed polarizers exploit birefringence of cellulose to separate fibres from non-fibrous material.
- Sample preparation:
- Disintegration per relevant ISO methods (chemical or mechanical pulps).
- Removal of fines by forming and rinsing a wet laboratory sheet (approx. 0.50 g oven-dry) and selecting debris-free portions.
- Prepare multiple test portions with controlled concentration and oven-dry mass.
- Instrumentation:
- Fibre length analyzer conforming to ISO 16065-1 (polarized light method).
- Standard lab equipment: disintegrator, sheet former, precision balances, vials; use of a reference pulp for verification.
- Calculations:
- Total fibre length LT = sum of individual fibre lengths.
- Fibre coarseness C (mg/m) = oven-dry mass of fibres in test portion / LT.
- Mean coarseness is the average of test portions.
- Verification & precision:
- Calibration check weekly; performance check monthly using a reference pulp.
- Published precision: repeatability CV ≈ 4% (hardwood/softwood); reproducibility CV varies (e.g., hardwood ~10.5%, softwood ~5.1%).
Applications and who uses it
- Quality control and process monitoring in the pulp and paper industry.
- R&D and product development for furnish selection, pulp treatment, and refining studies.
- Independent testing laboratories validating pulp properties.
- Instrument manufacturers and service providers supplying automated fibre analyzers.
Practical benefits include objective, repeatable measurement of coarseness to support pulp characterization and downstream paper performance assessments.
Related standards
- ISO 16065-1 - Fibre length by automated optical analysis (polarized light)
- ISO 5263-1 / -2 / -3 - Laboratory wet disintegration (chemical/mechanical pulps)
- ISO 5269-1 - Preparation of laboratory sheets
- ISO 638 - Dry matter content
- ISO 4119 - Stock concentration
- ISO 7213 - Sampling for testing
ISO 23713:2005 is a targeted, standardized procedure for laboratories and industry professionals needing reliable, automated measurements of fibre coarseness using the polarized light technique.
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