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.
Chamber Wall Channeling
Boundary Flow
Air bypass along the internal perimeter of a sample holder represents a common source of bias in airflow-based fiber fineness measurements. In linen testing, chamber wall channeling occurs when the compressed flax specimen does not adhere uniformly to the metal walls of the specimen cylinder. This creates a path of lower resistance for the gas stream, which distorts the calculated specific surface area of the fibers.
Error Severity
The consequence of this bypass is an overestimation of the average fiber diameter. Because the gas flows more easily around the edges, the measured resistance of the bed drops, leading the instrument to record a coarser grade than the actual fiber lot possesses. In high-precision spinning mills, such an error can lead to incorrect blending of flax with cotton.
A typical batch of combed flax sliver requires precise measurements to ensure spinning stability. When channeling remains undetected, the resulting yarn suffers from uneven density and increased breakages during high-speed spinning on the factory floor.
Corrective Action
Eliminating the bypass requires uniform packing of the specimen and the use of specialized sealing rings or specimen dimensions. Laboratory technicians must ensure that the linen fibers are randomized and evenly distributed to the very edges of the chamber. When the specimen is properly packed, the resistance of the bed remains uniform and the results are reliable.