Overview
ISO 5267-2:2001 defines the “Canadian Standard” freeness method for determining the drainability of pulp suspensions. The standard quantifies freeness as the volume (millilitres) of filtrate collected from the side orifice of a dedicated freeness tester. It is applicable in principle to all types of pulp in aqueous suspension and is widely used in pulp and paper laboratory testing, process control and quality assurance.
Key topics and requirements
- Principle: Drainage through a fibre mat formed on a perforated screen is measured as the volume of filtrate from the side orifice.
- Apparatus: Requires the Canadian Standard freeness tester (two designs exist: original and modified), calibrated measuring cylinders, an accurate balance, and ISO standard water (ISO 14487). Annex A describes the tester; Annex B covers maintenance; Annex C covers calibration.
- Sample preparation:
- Stock concentration: 0.30% ± 0.01% (mass), temperature 20.0 °C ± 0.5 °C.
- Typical sample transfer: 1 000 ml ± 5 ml of homogeneous suspension.
- Avoid air bubbles; recirculate filtrate when thickening to preserve fines.
- Note: treatments producing many fines can cause false freeness, typically below 100 ml.
- Procedure: Pour the conditioned 1 000 ml sample into the chamber, start flow by opening valves as specified, then measure filtrate volume from the side orifice. Two determinations are required; report the mean. Duplicates differing by more than 2% must be repeated.
- Expression and reporting: Mean freeness in ml, test temperature/concentration (if different), funnel type (modified or original), and any unusual conditions. Full reporting items are listed in clause 9.
Practical applications and users
- Who uses it:
- Laboratory technicians in pulp and paper testing labs
- Process control engineers and mill quality teams
- Equipment manufacturers and calibration/authorized laboratories
- R&D groups assessing mechanical treatment, fibre swelling or refining effects
- Typical uses:
- Monitoring pulp drainability during refining and stock preparation
- Comparing effects of mechanical or chemical treatments on fibre properties
- Quality control and specification checks during pulp production
Note: ISO 5267-2 results are a laboratory index and may not directly predict drainage on a commercial paper machine.
Related standards
Keywords: ISO 5267-2, Canadian Standard freeness, pulp drainability, freeness tester, pulp suspension, stock concentration, freeness calibration, pulp testing.