ASTM D7025-09(2021)e1

5.1 This test method for determining fineness of cleaned flax fibers is considered satisfactory for acceptance testing of commercial shipments when the levels are controlled by use of a range of calibration standards.

5.2 The resistance that a plug of flax fibers offers to the flow of air is measured as an approximate indication of the average relative fineness of the fibers.

5.3 Instruments are available to indicate the resistance to air flow using either compressed air or a vacuum; and are constructed (1) to measure airflow under constant pressure drop across the plug, (2) to measure pressure drop when a constant flow of air is maintained, or (3) to indicate resistance to air flow from both a balanced and unbalanced Wheatstone bridge.

5.4 The reliability of the results of any test method depends primarily upon how well the specimens tested represent the original source material. Flax fibers are different from many textile fibers, such as cotton or synthetic ones, in that they are not individual filaments but bundles of fibrous material that may or may not be completely separated into individual filaments and therefore have a high degree of variability. While cleaning and processing can produce separation and changes in length, there is no certainty of fibrillation of the fibrous material.

5.5 The specific surface index of flax fibers may be a function of fineness, degree of retting, cleanliness, variety, bundle separation, and plant maturity harvest date. This fineness of flax fibers affects their mill processing and spinning performance as well as contributes significantly to the appearance and strength of the yarns produced.

5.6 The accuracy of weighing can be controlled by the number of fibers composing the bundle. However, with short fiber of low linear density the number of fibers to be counted becomes prohibitive unless the bundle mass is kept low.

1.1 This test method provides two options that cover the determination of the fineness of clean loose flax fibers by: Option 1, measuring the specific surface area by the resistance of a plug of flax fibers to air flow under prescribed conditions, or Option 2, estimating the mass per unit length.

1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.