The influence of moisture regain on dyed fabrics

The influence of moisture regain on dyed fabrics
The moisture regain of textile materials when they reach equilibrium in the standard atmosphere is called the standard moisture regain. The actual moisture regain of each fiber and its products varies with the temperature and humidity conditions. In order to compare the moisture absorption capacity of various textile materials, the moisture regain measured after a specified time (equilibrium) is placed under a unified standard atmospheric condition ( Standard moisture regain) for comparison.

1. The impact on weight
The change in the moisture regain will of course cause the weight of the textile material to change. It should be emphasized here that the standard weight is used as the basis of the payment in the trade, otherwise the buyer will suffer (the material is damp) or the seller (the material will be dry) Loss of trade fairness is also one of the main reasons for trade disputes; in production, weight control per unit length (quantitative control) is carried out, and the weight of fiber materials increases proportionally with the increase in the amount of absorbed water.

2. Influence on length and cross-sectional area
The increase in moisture regain will cause the fiber volume to expand, and the lateral expansion is much greater than the longitudinal expansion.
the reason
The macromolecules are arranged along the axial direction, the molecular distance increases after moisture absorption, but the length of the macromolecules will not increase

The moisture swelling of the fiber is not only the thickening and hardening of the fiber, but also one of the reasons for the shrinkage (shrinkage) of the fabric. After the fabric enters the water, the fiber absorbs moisture and expands, which makes the diameter of the yarn thicker, and the degree of bending of the yarn in the fabric increases. At the same time, the fabric needs to occupy longer yarns in the warp or weft direction than before it absorbs moisture. The result is to shrink the fabric. However, the moisture swelling of the fiber also has a positive side. For example, water hoses and raincoats can use them to absorb moisture and thicken the fabric when they meet with water to make the fabric tighter and make it more difficult for water to pass. Swelling is also an important factor in the process of fabric wrinkling, drying and dyeing

3. Influence on density: The density of fiber increases first and then decreases with the increase of moisture regain.

4. Impact on mechanical properties
For most fibers, their strength decreases with the increase in moisture regain, a few fibers remain almost unchanged, and the strength of individual fibers (cotton, hemp) increases. The elongation at break of most fibers increases with the increase in moisture regain, and a few fibers are almost unchanged. This is mainly due to the fact that the crosslinks between the macromolecules are broken after the water molecules enter, the intermolecular force is reduced, and the macromolecules are easy to slip off, so the strength is reduced.
With the increase of moisture regain, the fiber becomes soft and easy to deform, the modulus decreases, and it is easy to entangle, while the denser fabric becomes stiff due to the support of the fiber; the friction factor of the fiber surface changes with the increase of the moisture regain Big.
Changes in moisture regain lead to changes in fiber mechanical properties, and changes in mechanical properties affect textile processing and product quality. If the moisture regain is too low, the fiber will become more rigid and brittle, easy to break during processing, and static electricity will be obvious; if the moisture regain is too high, the fiber will be difficult to loosen, and the impurities in it will be difficult to remove and entangled. Kink is easy to wind around the parts on the machine, which will cause fluctuations in carding, drafting, weaving and other processes. The change of cohesion will also change the structure of the yarn and the quality of the fabric, which will cause the instability or change of the yarn strength, hairiness, evenness, fabric size, fabric density, etc.

5. Influence on thermal properties
With the increase of moisture regain, the thermal insulation performance of textile materials gradually decreases, the cold feeling increases, the ignition temperature rises, the glass transition temperature decreases, the heat shrinkage rate rises, and the anti-melting hole ability is improved. The change of moisture regain has a great influence on the thermal properties of materials.

6. Impact on electrical properties
Textile materials are insulating materials, but their insulating properties will decrease with the increase in moisture regain, dielectric loss will increase, and static electricity will decrease.

7. Impact on optical properties
When the moisture regain increases, the optical refractive index of the fiber decreases. The absorption of light will increase, the color will become darker, and photodegradation and aging will increase.