Importance of atmospheric conditions and relative humidity in the textile testing and standard atmospheric conditions

Importance of atmospheric conditions and relative humidity in the textile testing:

The regain of any textile material gets dependent upon dampness in the surrounding air and the dampness of air depends upon the climatic conditions. If there is much moisture present in the air, the moisture regains of the textile material increases. If the surrounding air is too much dry, the moisture regains of textile material decreases. The amount of moisture per unit volume of air present in the surrounding air greatly influences the moisture regain of textile material. The dampness of the atmosphere is described in terms of humidity. There are two kinds of humidities that are calculated:

Absolute humidity:

The weight of the moisture present in a unit volume of the moist air is called absolute humidity. Absolute humidity is measured in grains/ cubic foot or grams/ cubic metre.

Relative humidity: 

The ratio of the actual vapour to the saturated vapour pressure at the same temperature, expressed in terms of percentage is called relative humidity. 

We can also say that the ratio of the absolute humidity of the air to that of saturated air with water vapour at the same temperature and pressure expressed in the term of percentage is called relative humidity.
The regain of the textile material appears to depend upon the relative humidity rather than the actual amount of water vapour present. Now, we have understood that the moisture regain of textile material depends upon the relative humidity and the moisture regain of textile material affects textile material properties. Thus it is necessary to specify the atmospheric conditions in which the textile material testing should be carried out.

Standard atmospheric conditions:

An atmosphere pre-vailing barometric pressure with a relative humidity of 65% and a temperature of 20 degrees centigrade is called the standard atmospheric condition. Certain tolerances are allowed 

Testing atmospheric conditions:

The atmosphere with a relative humidity of 65% plus or minus 2% and temperature of 20 degrees centigrade plus or minus 2 degrees centigrade is called testing atmospheric conditions.

In tropical and sub-tropical areas, difficulties appear to achieve the 20 degrees centigrade temperature. A higher temperature is used in these regions. The testing temperature is kept 27 degrees centigrade plus or minus 2 degrees centigrade.