Overview
ISO 16065-1:2014 specifies an automated optical method for determining fibre length in pulps using the polarized light technique. Applicable to all kinds of pulp, the standard excludes fibrous particles shorter than 0.2 mm from results. The method uses a fibre orienting cell (FOC) and a crossed-polarizers setup to exploit birefringence of cellulosic fibres and to discriminate fibres from non-fibrous particles (e.g., air bubbles).
Key topics and requirements
- Principle: Fibres in water flow through an FOC; projected fibre lengths are measured by a photo sensor matrix while crossed polarizers transmit light only from birefringent fibres.
- Apparatus: Fibre-length analyser (FOC, uniform light source, photo sensor, polarizing optics), disintegrator, pipette, verification fibres, and reference pulp.
- Optical and detector specs:
- Analyzer resolution: ≤ 100 µm across 0–7 mm.
- Light extinction of crossed polarizers: >99%.
- Detection efficiency: 100% for fibres ≥ 0.100 mm.
- Flow path thickness: no thicker than 0.5 mm in light direction to ensure fibre straightening.
- Sampling & sample prep:
- Follow ISO 7213 for lot sampling.
- Disintegration procedures per ISO 5263 (with guidance on never-dried pulps and avoiding fibre shortening).
- Stock dilution ranges: 0.010–0.025% (softwood) and 0.004–0.010% (hardwood) mass fraction.
- Measurement protocol:
- Agitate suspension continuously; take 50 ml test portions with a 50 ml pipette (tip ≥5 mm).
- Minimum fibres measured: steady-state variance of 0.01 mm in average length, or at least 5 000 fibres if continuous monitoring not available.
- Verification & calibration:
- Calibration checks weekly with verification fibres (three lengths, ~0.5, 3.0, 7.0 mm).
- Monthly performance checks with a reference pulp; tolerance for length-weighted mean of chemical pulps: ±1.5%.
- Calculations: Number-, length- and mass-weighted mean lengths and fibre-length distributions are computed per the method.
Applications
- Quality control and process monitoring in pulp and paper production
- Comparative pulp characterization for mill-to-mill or supplier verification
- Research and development of pulping and refining processes
- Instrument performance verification and calibration
Who should use this standard
- Pulp and paper laboratory technicians and quality engineers
- Process engineers monitoring fibre quality
- Equipment manufacturers of fibre-length analysers
- Standards bodies, testing laboratories, and R&D teams
Related standards
Keywords: ISO 16065-1:2014, fibre length, polarized light, pulps, automated optical analysis, fibre orienting cell, birefringence, pulp testing.
Open preview (PDF)Pulps — Determination of fibre length by automated optical analysis — Part 1: Polarized light method
