Determination of Bast Fiber Fineness via Standardized Low-Pressure Air Permeability
Low-pressure air permeability tests determine bast fiber fineness by measuring specific surface area across standardized compressed fiber plugs under ISO 2370.
Differential Pressure Drop
Resistance Magnitude
Airflow resistance measurement quantifies the energy lost as a gas moves through a porous medium. Workers use differential pressure drop to evaluate the permeability of flax fiber plugs within a test chamber. A steady stream of air passes through the specimen, and sensors detect the change in force between the inlet and the outlet.
Higher values indicate a denser or finer fiber arrangement that restricts movement more effectively. The physical quantity remains stable as long as the volume and velocity of the incoming air are held constant by the equipment.
Measurement Variable
Factors influencing the result include the density of the sample and the specific surface area of the individual strands. Monitoring differential pressure drop allows a lab technician to calculate the micronaire value or fineness of the raw material. If the flax is too coarse, air passes through easily with minimal resistance.
Compacted fibers or those with smaller diameters create a more tortuous path for the air.
Grading Outcome
Mill specifications often dictate a narrow range of acceptable results to ensure consistent spinning performance. An unexpected shift in differential pressure drop during testing signals a change in the batch quality or a failure in the sample preparation stage. This data is recorded on the quality certificate for every lot of scutched flax.