There are two factors affecting fiber moisture regain: internal and external.

Intrinsic factors include:

Chemical structure - the number of hydrophilic groups and the strength of polarity of fiber macromolecules;

Aggregate structure - the crystallinity of the fiber, the size and number of pores in the fiber;

Morphological structure - the size of the specific surface area of the fiber, the cross-sectional shape, thickness and surface roughness; the nature and content of the fiber companions.

External conditions include: temperature and humidity; air pressure; the size of the original moisture regain.

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Fiber Intrinsic Factors

1. The role of hydrophilic groups

In fiber macromolecules, the number of hydrophilic groups and the strength of polarity can affect the size of its moisture absorption capacity. The higher the number, the stronger the polarity, and the higher the moisture absorption capacity of the fiber. Various groups have a great influence on the water absorption of cellulose fibers, protein fibers, and synthetic fibers.

Such as: hydroxyl (-OH), amido (-NHCO-), carboxyl-COOH), amino (-NH2), etc. It has a great affinity with water molecules and can form chemically combined water (absorb water) with water molecules.

Cellulose Fiber

Such as cotton, viscose fiber, copper ammonia and other fibers, each glucose residue in the macromolecule contains 3 -OH, hydrogen bonds can be formed between water molecules and -OH, so the hygroscopicity is relatively large. Most of the hydroxyl groups in acetate fibers are replaced by acetate groups (-COCH3), and acetate groups have no strong attraction to water, so the hygroscopicity of acetate fibers is low.

protein fiber

The main chain contains hydrophilic amide groups, amino groups (-NH2), carboxyl groups (-COOH) and other hydrophilic groups, so it has good hygroscopicity, especially wool, and the side chains have more hydrophilic groups than silk , so its hygroscopicity is better than that of silk.

synthetic fiber

Vinylon: The macromolecule contains hydroxyl groups (one OH). After acetalization, some of the hydroxyl groups are blocked and the hygroscopicity is reduced, but its hygroscopicity is the best among synthetic fibers.

Nylon 6, Nylon 66: In the macromolecule, every 6 carbon atoms contains an amide group (-CONH-), so it also has a certain moisture absorption capacity.

Acrylic fiber: There is only a polar group cyano group (-CN) with weak hydrophilicity in the macromolecule, so the moisture absorption capacity is small.

Polyester, polypropylene: Due to the lack of hydrophilic groups, the moisture absorption capacity is extremely poor, especially polypropylene basically does not absorb moisture.