Fiber cohesion is related to the resistance to drafting encountered during textile processing and is affected by such fiber properties as surface lubrication, linear density, surface configuration, fiber length, and crimp.

Fiber cohesion is affected by the alignment of fiber in sliver in addition to the factors listed in 5.1. A half turn of twist in a 140-mm specimen has been found to increase the breaking force by 30 % and a full turn by 60 %. For this reason, care must be exercised in precise mounting of specimens.

For the same reason given in 5.2, card sliver gives a different breaking tenacity than draw sliver of the same fiber. Fibers are more aligned in draw sliver, resulting in lower cohesion.

Increasing the gage length of test specimens reduces the breaking force and apparent cohesion.

The mathematical relationship between the observed value for breaking tenacity and processability has not been established, but the observed values can be used in comparing various fiber characteristics on a relative basis.

This method for measuring fiber cohesion in sliver or top (static tests) is not recommended for acceptance testing because it is an empirical method which must be followed explicitly. Results obtained under other conditions cannot be expected to be comparable.

In some cases, the purchaser and the supplier may have to test a commercial shipment of one or more specific materials by the best available method, even though the method has not been recommended for acceptance testing of commercial shipments. In case of dispute arising from differences in reported test results when using this test method for acceptance testing of commercial shipments, the purchaser and supplier should conduct comparative tests to determine if there is a statistical bias between their laboratories. Competent statistical assistance is recommended for the investigation of bias. As a minimum, the two parties should take a group of test specimens, which are as homogeneous as possible and which are from a lot of material of the type in question. Test specimens then should be randomly assigned in equal numbers to each laboratory for testing. The average results from the two laboratories should be compared using appropriate statistical analysis and a probability level chosen by the two parties prior to testing. If a bias is found, either its cause must be found and corrected or the purchaser and the supplier must agree to interpret future test results with consideration to the known bias.

1.1 This test method describes the measurement of fiber cohesion as the force required to cause initial drafting in a bundle of fibers in sliver and top. The observed cohesive force required to separate the fibers is converted to cohesive tenacity based on the linear density of the specimen.

Note 1—For determination of fiber cohesion in dynamic tests, refer to Test Method D4120.

1.2 The values stated in SI units are to be regarded as standard. Inch-pound units appear in parentheses for information only.

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.