ISO 23713:2005

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.