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NWSP 160.1 Lint (Gelbo)

Standard:

NWSP

Method:

NWSP 160.1

Title:

Resistance to Linting of Nonwoven Fabrics (Dry)

Scope

The NWSP 160.1 Lint test is applicable for determining the relative propensity of fabrics to generate particles when flexed and twisted by a particle generator. The size and number of these particles are then counted by a particle counter

SI values are regarded as the official standard system of measurement for this standard procedure. If other systems of measurement are used in place of SI units (including inch-pound) their values must be reported independently. Systems of measurement must not be combined in any way, but shall be regarded and reported separately.

Principle

This procedure should be conducted in a laminar flow hood or in a room where the air is class 100 clean room quality or better.

This procedure describes a test to determine the relative number of particles released from a fabric when it is subjected to a continuous flexing and twisting movement. During the flexing, air is withdrawn from the flexing chamber at 1 CFM (cubic foot per minute) or 0,0283 cubic meters/min and examined for particulates using a laser particle counter. The particle counter differentiates the particles by size using six or more channels. These channels will capture various ranges of particle sizes from 0.3 to 10 micrometers. These particles can be reported using three methods: (1) Counting the total particles over ten consecutive 30 s periods; (2) Reporting the average of the ten data points. The particles may originate as air-borne debris (dust) or as fragments from fibers, binders or process treatments. The test is applicable to both woven and nonwoven fabrics and may be used to assess the lint generating potential of the fabric or its composites.

In this procedure a 23 x 23 cm specimen is clamped between two holders which have a flexing stroke of 119.8 mm. There is a twist to the shaft of 180° and a stroke rate of about 60 cycles per minute. An isokinetic intake probe is affixed to the base of the Gelbo unit directly under the specimen. The probe is connected to the particle counter by a 102 cm long section of tubing (provided with the machine).

Generally, dry flexing results in release of only a small part of the total available particles, so individual results can be variable. However, multiple sampling/testing allows good relative measurements of products and processes and their tendency to generate particles. This means that lab to lab and time to time reproducibility is only fair in absolute numbers but very good in rankings.

It was found that many types of fabrics using different kinds of fibers have similar particle generation characteristics, indicating that a common mechanism governs the process of particle generation and counting. It is believed that particle generation originates from one of two mechanical processes. The first process demonstrates that particles are released from the fabric as it is being flexed, which slowly diffuse to the particle counter inlet. Diffusion reaches a maximum then diminishes as the five minute test time elapses. The second process results in particle generation by destruction of the fabric itself as it is being flexed. In general this component continues to increase with time.

Since almost all of the fabrics tested peaked within five minutes, it was decided to use five minutes as the standard flexing time and count particles every 30 s to obtain a total of ten data points per specimen. Because of the nature of particle collection, it appears that one or more of the following three methods would be the appropriate way to report the total count of particles from a fabric:

a) Report the highest count of the ten data points minus the average type “B” background count.
b) Report the combined total of the ten data points minus the total type “B” background count for a given time period 30 s x 10 = 5 minutes.
c) Report the average and the range of the ten data points minus the average type “B” background count.

 

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