The relationship between moisture absorption and fiber properties

After the fiber is wet, the mass, volume, density and physical and mechanical properties of the fiber will be changed. The main relationships among them are as follows:

1. Influence on quality

The quality of the fiber was increased after the moisture absorption. The quality of fiber or textile products, are actually a resurgence of quality rate, so the correct representation of textile materials or concerned with the quality of some indicators, such as fiber or yarn linear density, fabric density and surface quality is square meters, should be set to the standard moisture regain quality quality.

Two. Hygroscopic expansion

After the fiber is hygroscopic, its longitudinal and transverse expansion and volume increase, and the lateral expansion is large and the longitudinal expansion is small. Therefore, when the fabric is water absorbent, the diameter of the yarns will become rough, which will make the fabric shrink. It will also make the softer fabric hard and tough, such as viscose fiber fabric. For example, if the fabric has high density, it will become an impermeable fabric after expansion after moisture absorption.

Fiber moisture expansion is anisotropic, the fiber axial transverse expansion rate was significantly greater than the fiber expansion rate, which is due to the orientation of fiber in long chain molecules, water molecules into the amorphous area, open the connection point of long chain molecules (hydrogen bonds and van Edward), the distance between the long-chain molecules increases the fiber tends to thicken, lateral. As for the fiber length direction, it is due to the incomplete orientation of macromolecules and the existence of a conformational conformation, which leads to conformational changes between water molecules and the increase of fiber length direction, but its expansion rate is far less than the lateral expansion rate. The expansion rate of various fibers in water is shown as follows:

Three. Influence on fiber line density

When a small amount of water is absorbed, the volume of the fiber changes little. The water molecules adsorb on the pores between the macromolecules. The volume and mass of the unit fiber increase with the increase of moisture absorption, and increase the fiber density. Most fibers have the highest density when the moisture regain is 4-6%. After the water molecules are filled with the pores, the moisture absorbs and the fiber volume expands significantly, making the fiber density decrease.

Four. Influence on the mechanical properties of fiber

Most fibers decreased strongly with the increase of moisture regain, especially viscose, but the strength of natural cellulose fibers such as cotton and linen increased with the increase of moisture regain. The elongation at break of all fibers increased with the increase of the moisture regain. With the increase of the moisture regain, the plastic deformation of the fiber increases and the surface friction coefficient of the fiber becomes larger. The changes in the mechanical properties of these fibers are mainly due to the change in the binding state between the molecules of the fiber after the water molecules enter the fiber.