Regain And Moisture Content

The amount of moisture in a sample of material may be expressed in terms of Regain or Moisture content.

Regain is defined as the weight of water  in a material expressed as a percentage of the oven dry  weight .Moisture content is the weight of water in a material expressed as percentage of the total weight

Let Oven dry weight   = D

Weight of water         = W

Regain                       = R

Moisture content       = M

Atmospheric Condition And Relative Humidity:

Among other thing , the regain of a textile material depends upon the amount of moisture present in the surrounding air.The dampness, of the atmosphere can be described in terms of humidity either absolute humidity or relative humidity.

Absolute Humidity : The weight of water present in a unit volume of moist air that is grains per cubic foot or grams per cubic meter .

Relative Humidity: The ratio of the actual vapour pressure to the saturated vapour pressure at the same temperature ,expressed as a percentage.

An alternative definition for relative humidity is the ratio of the absolute humidity of the air to that of air saturated with water vapour at the same temperature and pressure. This  ratio may then be expressed as a percentage.At ordinary temperatures such as those at which processing and  testing are carried out,the two ratio are almost identical.It is convenient to described a given atmosphere in terms of relative humidity rather than absolute humidity because the regain of textile materials appears to depend upon the relative humidity rather than the actual amount of water vapour present.Since the relative humidity affects the regain of a textile  material and since the properties of the material are influenced by the regain,it is necessary to specify the atmospheric condition in which testing should be carried out.

 
Standard Atmosphere: This is defined as an atmosphere at the prevailing barometric pressure with a relative humidity of 65 per cent and  temperature of  20 ± 2 degree centigrade  .

In tropical and sub tropical region the difficult of achieving a temperature of  20 degree C are understood and so a standard  temperature may be used   27± 2 degree centigrade.