Mechanisms of moisture absorption

Mechanisms of moisture absorption 

• Moisture absorption in textile fibers occurs through the interaction of water molecules with polar groups within the structure (e.g. OH, -COOH). 
•  In ordered (crystalline) parts of the structure, these polar groups are not attached but in disordered (amorphous) regions there can be very free groups which can act as hooks with which the water molecules can link through hydrogen bonding. 
• Thus the absorption of moisture takes place in the amorphous regions only.

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. 

VAPOUR Pressure: 

• Water molecules evaporate from the bulk at a rate determined by the exposed surface area. And the temperature.
• The space above surface reaches a point where:

no. of molecules evaporating = condensing. 

Dew Point: The atmospheric temperature (varying according 

to pressure and humidity) below which water droplets begin 

to condense and dew can form. 

taken form google images

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 (i.e how much moisture it is capable of holding and this will decide whether the fibre will lose or gain moisture) rather than the actual amount of mositure present in the air.

• Standard Atmosphere: This is defined as an atmosphere at the prevailing barometric pressure with a relative humidity of 65 % and  temperature of  20 ± 2˚C   

photo taken form google images

• In tropical and sub tropical region a standard  temperature of     27± 2˚C is used.