Why are there standard atmospheric requirements for textile testing?

As a textile testing lab researcher, the term “standard atmosphere” is commonly involved in your daily work. In a fabric test report, you can always find this term. Many fabric material tests must be conducted under a standard atmosphere. So, what is the relationship between the atmosphere and textile materials?

Moisture absorption&mechanical properties

Atmospheric conditions affect the amount of moisture absorption, which in turn affects the mechanical properties of textiles.
The amount of moisture absorbed mainly depends on the internal structure of the fiber. Atmospheric conditions (temperature, relative humidity, atmospheric pressure) also impact the amount of moisture absorbed. The same type of fiber can exhibit changes in mechanical properties due to fluctuations in atmospheric conditions, such as weight, strength, elongation, stiffness, electrical properties, and surface friction. To ensure the comparability of the tested performance of textile materials, it is necessary to uniformly specify the atmospheric conditions during testing, i.e., standard atmospheric conditions.

Equilibrium moisture regain rate

Furthermore, since the moisture absorption or desorption equilibrium of textile materials requires a certain amount of time, the equilibrium moisture regain rate achieved by absorption is often less than that achieved by desorption, and this error in the equilibrium moisture regain rate due to the lag in moisture absorption can also affect the test results of textile material performance. Therefore, it is not only necessary to specify the standard atmospheric conditions during textile lab testing, but also to require that before testing, the sample must be placed under standard atmospheric conditions for a certain period to achieve equilibrium moisture regain through moisture absorption. This process is called conditioning.
Suppose the actual moisture regain rate of the textile material before conditioning is high (close to or higher than the equilibrium moisture regain rate of the standard atmosphere). In that case, the sample must also undergo pre-conditioning: i.e., drying at a low temperature for a certain period to reduce its actual moisture regain rate, to ensure that conditioning proceeds by moisture absorption.

International standards have stipulated the pre-conditioning, conditioning, and testing standard atmospheric conditions for various textile materials.

The standard atmospheric conditions

Temperature of 20°C (for tropics 27°C)

Relative humidity of 65%

Atmospheric pressure of 86~106kPa

The difference between temperate standard atmosphere and tropical standard atmosphere lies in the temperature, the former being 20°C and the latter 27°C, with other conditions being the same.

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