Synthesis of hydrophilic synthetic fibers
According to the principle of fiber hydrophilicity, the methods to realize fiber hydrophilicity can be divided into chemical method and physical method.
(1) Chemical modification method
① Hydrophilization of fiber macromolecules
This is a method of introducing a large number of hydrophilic groups into the macromolecular structure of fibers by polymerization or copolymerization. For example, acrylic acid, vinylpyridine and dicarbonylpyrrole are introduced into acrylic fiber copolymerization to obtain acrylic fiber with good hygroscopicity. Or by chemical treatment, a part of the cyano group in the fiber is converted into amide group or carboxyl group. For nylon, the amount of methylene (- CH2 -) can be reduced in macromolecular structure. For example, the hygroscopicity of polyamide 4, polyamide 3, 2 and 1 can be greatly improved. In addition, through copolymerization, the regularity of macromolecular structure is changed, and the crystallinity is reduced to increase the number of amide groups that can associate with water to improve the hydrophilicity of the fiber.
② Graft copolymerization with hydrophilic substances
It is a successful example to obtain hydrophilic modified acrylic fiber by graft copolymerization of acrylonitrile and natural protein, such as Chinon fiber developed by Toyo textile company of Japan in 1969. Another example is the grafting of acrylic acid and methacrylic acid on polyester fiber, and the grafting of acrylic acid or maleic acid onto polyamide 66 fiber by DuPont company in the United States.
③ Hydrophilic treatment of fiber surface
The essence of treatment is to add a layer of hydrophilic compound (also known as hydrophilic finishing agent) on the surface of fiber or fabric. At present, there are two kinds of hydrophilic finishing agents: one is acrylic monomers, the other is surfactants with hydrophilic part and fixed part, which are processed by dipping and rolling.
The introduction of hydrophilic groups and graft copolymerization often lead to the loss of some of the original excellent properties of the fiber, such as decreased color fastness, handle hardening, etc. Therefore, the actual amount of hydrophilic groups added or grafted can only be limited, and the improvement of moisture absorption rate of fiber can not meet the ideal requirements. The hydrophilic surface treatment method is very simple, low cost, and can basically maintain the original characteristics of the fiber and increase the moisture absorption of the fiber, but the disadvantage is poor hydrophilic durability, especially poor washing resistance.
(2) Physical modification method
① Blending or compounding with hydrophilic substances
Blending is to mix hydrophilic material into spinning melt or solution before spinning, and then spinning according to conventional spinning method to obtain hydrophilic fiber. For example, DuPont company of the United States uses 4% - 25% n-hexane Propionamide and polyamide blended yarn, the moisture absorption rate of the fiber is 8% - 9%; the Japanese Imperial company uses fatty acids, aliphatic amines or aliphatic alcohols with carbon atom number more than 12, polyether and polyamide to blend with polyamide, use polyacrylamide and polyacrylonitrile to blend high moisture absorption acrylic fiber, and use polyethylene glycol to derive High hygroscopic polyester was prepared by blending hydrophilic polymers such as poly (ethylene glycol), poly (alkylene glycol) and polyester.
Composite fiber also belongs to the category of blending, mainly through the composite spinning of hydrophilic polymer and hydrophobic polymer to be modified, so that the fiber has both hydrophilicity and excellent characteristics of the original fiber. Eccentric (or parallel) composite fiber can also improve the crimp elasticity of the original fiber. For example, Asahi Chemical Co., Ltd. of Japan uses acrylonitrile copolymer as the skin layer and acrylonitrile copolymer containing carboxyl group as the core layer, and the water retention rate of hollow composite fiber can reach 30%. The polyester fiber with good hygroscopicity and antistatic property can be obtained by melt spinning with common polyester chips as the skin layer and polyether modified polyester chips as the core layer, and then saponified.
② Microporosization of fiber structure
By changing the morphological structure of the fiber, synthetic fiber also has many micropores which connect inside and outside, just like cotton fiber and wool. This kind of fiber also has the advantages of small density, fast drying, good warmth retention and dirt resistance. It is very obvious to improve the clothing comfort of people engaged in sports activities and physical labor. Since the successful development of porous acrylic dunova made by Bayer company in 1976, the United States, Japan, Italy and other countries have successively developed and researched microporous acrylic fiber and porous polyester. Microporous polyester is mainly produced by using microporous forming agent according to the principle of dissolution method. The micropores of microporous acrylic fiber can be obtained by dissolution method, hole fixation method and high polymer cophase separation method.
③ Profiled cross section and surface roughening of fiber
This is a simple and effective method to improve the hydrophilicity of fiber. For example, many pores can be formed between fibers of L-shaped cross section. With the increase of the surface roughness of the fiber, the apparent contact angle can be reduced, and the hydrophilicity of the fiber can be improved.
In addition, the hollow fiber was made from polyester and cationic modified polyester blended yarn, and then treated with NaOH solution, resulting in a large number of micropores on the fiber, and some of the micropores were interconnected and connected to the hollow part. With the increase of alkali concentration, the number of micropores increases, which greatly improves the hydrophilicity of polyester fiber.