Standard Test Methods for Moisture in Textiles

Importancia y uso:

5.1 Test Methods D2654, Procedure 1, is used in the trade as a basis for rejecting abnormally wet material, but it is not recommended for routine acceptance testing of commercial shipment. Procedure 2 is used by the trade and is recommended for acceptance testing of commercial shipments except as stated in Note 1 . Procedure 3 is used to determine the moisture in a material in a given moisture-equilibrium situation and is not used for acceptance testing of commercial shipments. Procedure 4 is for research and development and is recommended for determining the standard moisture regain of a material although there will usually be a bias between buyer and producer data because the produce is usually able to obtain material without surface material, mostly finishes.

5.1.1 In case of a dispute arising from differences in reported test results when using Test Method D2654 for acceptance testing of commercial shipments, the purchaser and the supplier shall 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 shall take a group of test specimens that are as homogeneous as possible and that are from a lot of material of the type in question. The test specimens shall then be randomly assigned in equal numbers to each laboratory for testing. The average results from the two laboratories shall be compared using student's l-test for unpaired data and an acceptable probability level chosen by the two parties before the testing is begun. 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 in the light of the known bias.

5.2 The measurement of moisture is important for several reasons, including the following:

5.2.1 Large quantities of fibers and manufactured textile products containing some water are bought and sold on the basis of mass. The value of a particular commodity varies over a significant range with a variation in the amount of water it contains.

5.2.2 Besides the effect of the moisture present when the material is received, the moisture present at the time of testing and subsequent handling and processing can be quite important.

5.2.2.1 Some textile fibers, particularly cellulosic fibers and wool, have physical properties that vary significantly with the amount of moisture present, such as tensile strength, crimp, torsional rigidity, etc.

5.2.2.2 Optimum conditions for processing, such as in carding, include moisture as an important parameter.

5.2.2.3 Control of blends during processing is sometimes critically dependent on the moisture present in the components.

5.2.2.4 Production of textile products to meet specifications for mass per unit area of fabric and the linear density of yarn depends on control of moisture.

5.2.2.5 Quantitative analysis of fiber mixtures requires information on moisture present. (See Test Methods D629.)

5.3 Between Procedures 1 and 2, the choice for use is dependent primarily on the degree of accuracy required in the result. They are oven-drying procedures and have the virtue of simplicity and economy, with Procedure 1 having the added feature of not requiring a special drying atmosphere for the oven. Both are subject to certain limitations, however, that are avoided by toluene distillation (Note 2).

5.3.1 Because Procedure 1 uses ambient air and Procedure 2 uses air from the standard atmosphere for testing textiles, the mass of the oven-dry specimen is somewhat greater than it would be if the air were without water. This is due to the establishment of moisture-equilibrium between the moisture in the air supply and the moisture in the specimen. The error is usually slight, but in the case of wool dried at 105 °C with the use of ambient air that is hot and humid, the residual moisture in the oven-dry specimen can be as high as 1 % or more (see Tables 1 and 2 of Test Method D584). When the temperature and relative humidity of the ambient air are known, the amount of moisture retained by a specimen of wool, cotton, silk, viscose rayon, cuprammonium rayon, or acetate shall be estimated data.4 An additional source of potential error in oven-drying is the loss of volatile matter other than water when such material is present.

5.4 It is sometimes possible, and preferable, when sampling a material for the determination of moisture to select sampling units of a size which coincide with the size required by the method for a test specimen. In these instances, the mass shall be determined immediately, and if the mass of the oven-dry material is to be determined, no intermediate steps are necessary. However, in other instances, it will be necessary to perform some intermediate manipulation with the material, such as compositing or subsampling. For such instances to circumvent the problem of moisture loss or gain after sampling, provisions are made in these methods to stabilize the material in the working laboratory atmosphere, and equations are provided with correction terms to relate the measured moisture to the amount which existed at the time when the sample was taken.

5.5 While moisture regain is not a frequently tested property, it has an importance, once established. Commercial moisture regains (see Table 1 in D1909) are values adopted for use in determining commercial mass and fiber blends which meet government regulations. These values are usually slightly higher than experimental standard moisture regain values or an average for a class which has a range.

5.6 The measurement of moisture regain of a fiber is affected by any surface material present, the procedure (technique, solvent) used to remove the material, the dryness achieved and the atmosphere (temperature, humidity) in which the dry material is conditioned.

Subcomité:

D13.51

Referida por:

D2462-22, D2495-07R24, D1576-22

Volúmen:

07.01

Número ICS:

59.080.30 (Textile fabrics)

Palabras clave:

measurement of moisture; moisture content; textile materials;