What is the nominal moisture return rate of textile fibers respectively

Nominal moisture return rate of main fabric fibers.

Fibers Nominal moisture return rate

Cotton 8.5%

Polyester 0.4%

Ramie 13%

Nylon 4.5%

Wool 15-16%

Vinylon 5%

Silk 11%

Polyacrylonitrile 2%

Viscose 13%

Chlorlon 0%

Polypropylene 0%

Fabric materials include raw fabric materials and semi-finished fabric products that are finished into fabric products, such as various fibers, strips, spun yarns, fabrics, etc. The moisture absorption of fabric materials is an important characteristic related to the material performance and finishing process. The moisture absorption of fabric material is usually expressed by moisture regain rate, fabric material nominal moisture regain rate test nominal moisture regain rate, these basic quality indicators play a very important role in the commercial trade of fabric material, performance test and in fabric finishing. Test methods of fabric materials' nominal moisture return rate test methods (1) direct measurement method (2) indirect measurement method.

Moisture recovery rate and the nominal moisture recovery rate: The moisture recovery rate of fabric material is the percentage of the water absorbed in the specimen to the dry weight of the specimen. From time to time, the moisture content of the fabric material is different from its weight. In order to remove the different weight caused by the moisture rate, to meet the needs of the trade and inspection of fabric materials, the state of various fabric material moisture rate provides the corresponding standard, known as the fair moisture rate, it is numerically close to the equilibrium moisture rate measured under standard temperature and humidity conditions. It should be noted that the provisions of the fabric material's nominal moisture return rate are often based on the actual situation in each country, so it is not entirely consistent.

There are various methods for testing the moisture content of fabric materials

(1) direct measurement method: first weigh the sample, then remove the moisture, and then weigh the dry weight of the sample to calculate the actual moisture recovery rate. According to the different methods of removing moisture, direct measurement methods are: oven method, infrared radiation method, high frequency electric field heating method, vacuum drying method and hygroscopic agent drying method. In industrial production is often adopted in the oven method and infrared radiation method. The advantage of the oven method is that the measurement results are more accurate, the disadvantage is that the speed is slow, low efficiency. The advantage of infrared radiation method is fast, high efficiency, energy saving, the disadvantage is that the temperature is not easy to grasp, the results of the determination of fluctuations.

(2) indirect measurement method: is the use of certain properties of fibers and the relationship between the moisture return rate indirectly deduced from the fiber moisture return rate. The advantage of this method is fast and efficient, but the relevant properties of the fiber and the relationship between the rate of return to determine the value still need to use the direct method. Indirect method can be divided into resistance method, capacitance method, infrared extraction method and microwave method. China mostly uses the resistance method to determine the moisture of raw cotton. The microwave method is fast, continuous, non-contact, non-destructive, etc. It can be used for continuous measurement and automatic manipulation, and is a new technology that is still in progress recently.

Introduction of common oven method: It is through the resistance heating in the oven, so that the temperature of the air in the oven to a certain value, and maintain this temperature throughout the drying, and then the wet weight of the fabric material specimens have been weighed into the constant temperature oven for drying, so that the moisture in the fabric material constantly evaporated in the hot air, and the use of the oven's exhaust device will be constantly hot and humid air out of the box, for the moisture contained in the fabric material The drying process is carried out in the oven to make the moisture in the fabric evaporate in the hot air. As the fabric material moisture constantly evaporates and dissipates, the weight is constantly reduced, when the weight is dried to the same, that is, the dry weight of the fabric material. At this time, the method of hot weighing in the box can be adopted to weigh the dry weight of the specimen, and then the wet weight and dry weight of the specimen can be used to obtain the moisture recovery rate of the fabric material. In the oven method, the specified drying temperature is 105℃±3℃ for cotton; 105~110℃ for wool and most chemical fibers; 140~145℃ for silk. Drying time is generally 90min.

In addition, can also adopt the resistance wet method and so on to determine the moisture return rate of the fabric material. The resistance wet method is based on the fabric material has different resistance under different moisture return rate, so as to determine the moisture contained in the fabric material. For dry moisture content unstable goods, such as wool, raw silk, cotton, etc., in order to accurately calculate the weight of such goods, the international usually adopt the method of calculation by the metric (Conditioned weight), that is, to determine the actual moisture content of goods (moisture content) to calculate the clean weight of goods, and then converted into the weight of the metric moisture content.

Calculation formula is as follows: Metric weight = [actual weight of goods / (1 + actual moisture content)] ╳(1 + metric moisture content) = clean weight of goods ╳ (1 + metric moisture content)



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