Moisture Relation And Testing

Some of the most important properties of a textile fiber are closely related to its behavior in various  atmosphere condition .Most fiber are hygroscopic, that is they are able to absorb water vapour from a moist  atmosphere and, conversely, desorb or lose water in a dry atmosphere.Many physical properties of fiber are affected by the amount of water absorbed dimension.tensile strength,elastic recovery,electrical resistance,rigidity and so on.When in fabric from the moisture relationship of a fiber play a major part in deciding whether the fabric is unsuitable for a particular purpose .The important of this point is a appreciated when  fabrics for clothing, both outwear and underwear ,are considered .Additional factors arise in these cases since the structural details of the fabric can modify the apparent behavior of the fiber.For example ,fabrics woven from a hydrophobic material such as "Terylene" can pic up water by a "wicking" action along the fiber and yarn surface.
The mechanism of water absorption is a subject beyond the scope of this present volume  , but perhaps one or two points would be useful to bear in mind.In an orderly array of molecules the side chains will to be linked,but in a random arrangement a number of free links or hooks will be available, and if they are of a polar character possessing an attraction for polar chemicals groups such as hydroxide OH ,carboxyl    COOH ,carbonyl CO then water molecules can attach themselves. Orderly arrarys of molecules occur  in the crystalline region of the fiber structure and random array in the amorphous region.For a first approximation we could conclude that the absorption of water takes place in the amorphous region.This is of course, a simplified explanation of the absorption of water by fibers and the literature should be consulted for a detailed discussion.
An entertaining but nevertheless thought provoking article by Hearle is entitle "Moisture".
In this article the views of numerous workers in this branch of textile science are discussed,some of the apparent contradictions explained,and many confused ideas on fiber/ Moisture relations clarified.For a fuller treatment of the subject.