Moisture Regain in Textile

 



The moisture regain of textile materials when they reach equilibrium under standard atmosphere is called standard moisture regain. The actual moisture regain of each fiber and its products varies with temperature and humidity conditions. In order to compare the moisture absorption capacity of various textile materials, the moisture regain (standard moisture regain) measured after a specified period of time (equilibration) under uniform standard atmospheric conditions is compared.

Calculation formula

Moisture regain is the difference between the wet weight and dry weight of the sample as a percentage of the dry weight. Suppose the dry weight of the sample is G0 and the wet weight of the sample is G, then the moisture regain W is W=(G-G0) / G0 × 100%

Factors affecting moisture regain rate

Internal factors
  • The role of hydrophilic groups: In fiber molecules, the number of hydrophilic groups and the strength of hydrophilicity can affect its hygroscopic performance. The more hydrophilic groups there are, the stronger the hydrophilicity and the better the hygroscopicity; fibers with low macromolecular polymerization degree will have stronger hygroscopicity if the macromolecular end groups are hydrophilic groups.
  • Crystallinity of fiber: The lower the crystallinity, the stronger the moisture absorption capacity.
  • Fiber specific surface area and voids: The larger the fiber specific surface area, the stronger the surface adsorption capacity, and the better the moisture absorption capacity; the more pores in the fiber, the stronger the moisture absorption capacity.
  • Accompanying organisms and impurities: Different organisms and impurities have different effects. The cotton wax in cotton fiber and the oil in wool fiber weaken the moisture absorption capacity; the pectin in hemp fiber and the sericin in silk enhance the moisture absorption capacity.
External factors
  • Relative humidity: Under certain temperature conditions, the greater the relative humidity, the better the hygroscopicity of the fiber.
  • Temperature effect: In general, as the temperature of the air and fiber materials increases, the equilibrium moisture regain of the fiber will decrease.
  • Air flow rate: When the air flow rate is fast, the equilibrium moisture regain of the fiber will decrease.

Test Methods

Direct measurement method
The direct test method is to first weigh the wet weight of the textile fiber material, then remove the moisture in the textile fiber material, weigh the dry weight, and calculate the moisture regain of the textile fiber material according to the formula defining moisture regain.
According to different methods of removing moisture from textile fiber materials, it can be divided into oven drying method, infrared drying method, vacuum drying method, high-frequency heating drying method, hygroscopic agent drying method, etc.
Indirect determination method
Using the principle that the amount of water in textile materials is closely related to certain properties, the moisture content or moisture regain can be inferred by testing these properties.
This type of method tests quickly and does not damage the sample, but there are many influencing factors, which affects the stability and accuracy of the test results to a certain extent. Some of these methods do not contact the sample and can be used for continuous testing in production, so they show great advantages in automatic moisture monitoring.
According to different testing working principles, there are testing methods such as resistance moisture measurement method, capacitive moisture measurement method, microwave moisture measurement method and infrared spectrum moisture measurement method. At present, the most commonly used method is the resistance moisture measurement method, which uses fibers to have different resistance values under different moisture regains (or moisture contents).
Click to learn more about digital moisture meter
The digital moisture meter, which combines temperature and moisture testing capabilities, is extensively used in the moisture testing of pure cotton bobbin yarn, mixed bobbin yarn, and other chemical yarn.
This meter was created in accordance with the electric properties of fibers; the electric resistance of the sample should be in the range of 3.8×104Ω～2×1012Ω.
Moisture regain represents moisture absorption ability; the greater the moisture regain, the lower the electric resistance. By applying a voltage between fibers and measuring the resultant current, electric resistance values may be calculated.

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