1. Foreword
Magnetic materials and their applications have been developed as early as ancient times. At present, magnetic materials come in many types and specifications and are used in huge amounts. They are widely used in many industries such as instruments, meters, electronics, aerospace, and in various fields such as household, animal husbandry, fishery, medical care, health care, medicine, environmental protection, and biotechnology. It plays an increasingly important role and people pay more attention to it.
Due to differences in chemistry, physical structure, particle size and magnetic industry, the magnetic properties of the material are different depending on whether the induced magnetic field of the material changes synchronously with the external magnetic field, whether its direction is the same, the magnitude of the magnetic susceptibility and coercive force, etc. . Therefore, different magnetic materials have different uses after being made into various products. Therefore, the magnetic materials can also be processed into different shapes according to the needs of the application, such as block, film, granular, powder, fiber, etc. for use.
Human cells are microscopic bodies with certain magnetism, and the human body has a biological magnetic field. Therefore, the external magnetic field affects the physiological activities of the human body, causing changes in charge, potential, molecular structure, biochemical and physiological functions through the nervous and humoral systems, which can adjust the body’s body functions and improve disease resistance, and has a medical and health care effect.
Magnetic fiber is a fibrous magnetic material. It can be divided into magnetic textile fibers and non-textile fibers. Magnetic non-textile fibers have been reported more than ten years ago. For example, magnetic alloy fibers are used to make magnetic composite materials and magnetic coating materials, and magnetic lignocellulose fibers are used to make magnetic paper. Magnetic products made from them can be used in many aspects such as magnetic recording, memory, electromagnetic conversion, shielding, protection, medical and biotechnology, separation and purification, etc. What is needed for the textile industry is magnetic textile fibers. It should be a material that has both textile fiber properties and magnetic properties. It has magnetism that other textile fibers do not have, and it also has some physical forms that other magnetic materials do not have in the past (diameter of several microns to tens of microns, length generally greater than 10 mm, aspect ratio generally above 500) and properties, such as softness , elastic, etc., and can also be made into yarns, fabrics or processed into non-woven fabrics and products of various shapes through textile processing.
2. Preparation method of magnetic fibers
Magnetic fibers can be divided into metal (or alloy) magnetic fibers, organic magnetic fibers (the matrix is organic fibers) and inorganic magnetic fibers (the matrix is inorganic fibers) according to the material of the matrix fiber. The mechanical properties of metallic magnetic fibers are approximately the same as those of the corresponding matrix fibers. The mechanical properties of inorganic magnetic fibers are similar to or slightly lower than those of the corresponding matrix fibers. The mechanical properties of organic magnetic fibers, such as strength, are generally lower than those of corresponding matrix fibers. The difference varies with different preparation methods and the content of magnetic particles in the fibers.
According to literature and patent reports, there are roughly two ways to prepare magnetic fibers (including textile fibers and non-textile fibers): one is to prepare magnetic fibers through direct shaping, and the other is to prepare magnetic fibers through chemical and physical modification of matrix fibers.
1. Direct forming method of magnetic fibers
Direct forming of magnetic fibers can be used to prepare metal or alloy magnetic fibers and various magnetic organic fibers. The fiber forming and processing methods can be divided into the following three types.
(1) Traditional manufacturing method of metal fiber
The preparation of magnetic metal fibers or magnetic alloy fibers started early. They are generally prepared by certain manufacturing methods similar to those for manufacturing metal fibers, such as drawing, melt extrusion, jet cooling, melt extraction, cutting, crystallization, etc. Since the late 1970s, metal magnetic fibers have been mostly used to prepare composite materials and are also used to make magnetic coatings.
(2) Organometallic complex decomposition method
This is one of the methods for preparing metal or alloy magnetic fibers. Metal iron, cobalt, etc. are heated in a rotating metal atom reactor in a high vacuum to cause the metal atoms to escape and react with low-temperature toluene to form a zero-valent metal complex of toluene, such as a toluene solution of xylene iron [0] . Then, the toluene solution of xylene iron [0] placed under low temperature and nitrogen protection flows through a heating pipe placed in an external magnetic field, which decomposes the xylene iron [0] and leads to the formation of a slurry containing magnet fibers. The diameter of the magnetic metal fibers made by this method can be controlled between 0.1 and 100 μm, and the aspect ratio of the fibers can be between 100 and 10,000 times. The slurry containing the magnetic metal fibers can be coated on the surface after ball milling and appropriate treatment. On polyester film, magnetic recording material is made.
(3) Blended spinning method
Most magnetic organic fibers can be prepared using this method. Usually, magnetic material particles with a particle size less than 1 micron are mixed into the solution or spinning solution of fiber-forming polymer, and magnetic fibers are made by melt spinning or wet spinning. The strength of the obtained magnetic fibers mainly depends on the amount and particle size of the added magnetic particles.
The advantage of the blended spinning method is that the magnetic powder mixed into the fiber can be hard magnetic material or soft magnetic material. It can be melt-spun or applied in some wet spinning or dry spinning situations. It can even prepare magnetic composite fibers or special-shaped fibers. fiber. The disadvantage is that the amount of magnetic powder mixed in is usually less than 18%, such as the following magnetic polyamide. When the magnetic powder mixed in is 13%, the strength of the magnetic polyamide fiber is only about 50% of the original polyamide fiber. In addition, when the magnetic field is strengthened outside the spinneret, a�The spinning equipment is complex and may cause magnetic pollution.
2. Chemical and physical modification method using fiber as matrix
This method is suitable for preparing magnetic organic fibers and magnetic inorganic fibers. According to the characteristics of the matrix fiber, the following different specific methods can be used.
(1) Intracavity filling method
According to reports, this method is mainly used for the preparation of magnetic lignocellulosic fibers. Because wood fibers have cells and there are channels on the walls between the cells, magnetic particles can be filled into the cells of the wood fibers through physical methods to make magnetic fibers, which can be used to make magnetic paper, etc. In principle, fibers with similar structural characteristics can be made into corresponding magnetic fibers using this method.
(2) Surface coating method
Magnetic fibers are made by coating magnetic substances on the surfaces of various fibers using appropriate methods. For example, the 1987 patent report by Takuro Moriki and others in Japan used surface deposition coating method to make magnetic potassium titanate fibers. The method is to add aqueous ferrous salt solution and alkaline solution under appropriate conditions and successively add potassium titanate fibers dispersed in a water medium system. After hydrolysis and air oxidation, the generated magnetic iron oxide is deposited on the surface of the fibers to obtain dark brown magnetic titanium. Potassium acid fiber, used in the manufacture of magnetic composite materials.
(3) Positioning synthesis method
Utilize the cation-exchangeable groups in certain fibers to exchange ferrous ions with them, and then undergo hydrolysis and oxidation to convert them into magnetic γ-Fe2O3 or Fe3O4 (collectively called ferrite) and deposit them on the surface of the fiber. In the setting zone, the position of the generated magnetic substances (particles) in the fiber is controlled by the position of the cation exchange group in the original fiber, so it is called a positional synthesis method. Since magnetic particles are formed in an amorphous area with a small space, their size is usually very small, generally between 2 and 60 mm. Usually more ferrite is formed on the fiber surface. Due to the small size of the ferrite produced, it can exhibit superparamagnetism.
If the matrix fiber does not have cation exchange groups, various methods of chemical fiber modification can be used. First, the cation exchange groups can be introduced into the matrix fiber, and then the positioning synthesis method can be used. However, as a result, the strength of the magnetic fiber decreases significantly. For some fibers, it can even be as low as 50 to 60 percent of the strength of the matrix fiber. Because the fiber undergoes two treatments of chemical denaturation and positioning synthesis, each treatment will cause a decrease in strength.
3. Prospects
Magnetic fibers, especially magnetic textile fibers, started late. In the past ten years, there have been very few reports on magnetic textile fibers. They have not yet formed large-scale production, and there are no magnetic textile fiber products on the market. Therefore, both their manufacturing methods and their practical applications have broad room for development.
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