Core-shell gradient magnetic composite fiber and spinning method thereof

Abstract

The invention relates to the field of composite fibers, in particular to a core-shell type gradient magnetic composite fiber and a spinning method thereof.The core-shell type gradient magnetic composite fiber comprises a magnetic core layer and a magnetic core layer which are sequentially compounded from inside to outside, and the magnetic core layer comprises a thermoplastic polymer matrix and first magnetic particles dispersed in the thermoplastic polymer matrix; the middle transition layer is formed by coating the magnetic core layer with an elastomer material, and second magnetic particles are dispersed in the middle transition layer; the outer functional layer is composed of an antibacterial skin-friendly polymer; wherein the weight percentage of the first magnetic particles is higher than that of the second magnetic particles, and a magnetic intensity gradient decreasing structure from the core layer to the outer layer is formed. By means of the innovative core-shell gradient structure design, the technical problem that the mechanical property of traditional magnetic fibers is sharply reduced under the high magnetic content is successfully solved.

Description

Technical Field

[0001] The present invention relates to the field of composite fibers, and particularly to a core-shell type gradient magnetic composite fiber and a spinning method thereof. Background Art

[0002] Magnetic composite fibers are a new type of functional fibers that combine magnetic functional materials with polymer matrices. By dispersing magnetic particles in a polymer matrix, the fibers are given specific magnetic response characteristics. Such materials show important application values in fields such as smart textiles, biomedicine, and electromagnetic shielding. For example, in wearable medical devices, magnetic fibers can promote local blood circulation through precisely regulated magnetic field stimulation, showing unique advantages in rehabilitation therapy; in the field of smart clothing, magnetic fibers can work in cooperation with other electronic components to achieve energy harvesting or signal sensing functions. However, the preparation of traditional magnetic fibers faces the core contradiction that it is difficult to balance magnetic properties and mechanical properties. When increasing the content of magnetic particles to enhance the magnetic response ability, it often leads to an increase in fiber brittleness and a decrease in flexibility. This fundamental defect severely restricts their practical applications.

[0003] Currently, the preparation technologies of magnetic composite fibers mainly include three categories: melt spinning method, wet spinning method, and electrospinning method. The melt spinning method extrudes and forms by melt-blending magnetic particles with thermoplastic polymers (such as polyester and polyamide). Its advantage lies in the mature process and suitability for continuous production. However, a high content of magnetic particles will cause a sharp increase in the melt viscosity, resulting in uneven fiber diameters and particle distribution gradients during the spinning process. The wet spinning method uses a polymer solution blended with magnetic particles and then forms through a coagulation bath. Although it can improve the particle dispersion, the problem of solvent residue often leads to pore defects inside the fibers, and the production efficiency is relatively low. Electrospinning technology can prepare ultrafine fibers and achieve the directional arrangement of nanoscale magnetic particles, but the mechanical strength of the obtained fibers is generally low and difficult to meet the requirements of textile processing. In recent years, some researchers have tried to introduce a multi-layer composite structure into the design of magnetic fibers. For example, a functional coating is coated on the fiber surface. However, the existing processes are difficult to precisely control the thickness of each layer and the interfacial bonding strength, often resulting in problems such as interlayer peeling or functional layer rupture.

[0004] The main deficiencies of the existing preparation methods are reflected in two dimensions: material properties and process feasibility. In terms of material properties, the poor interfacial compatibility between magnetic particles and polymer matrix is a common technical bottleneck. Since most magnetic particles have a high surface energy and weak affinity with organic polymers, even after surface modification treatment with silane coupling agents, particle agglomeration is still likely to occur during processing, resulting in stress concentration inside the fiber. Experimental data shows that when the content of magnetic particles exceeds 30%, the elongation at break of the fiber usually drops to less than 5%, and the deterioration of the anti-bending fatigue performance is more significant. After thousands of bending cycles, the magnetic performance attenuation can reach more than 20%. In addition, the fibers prepared by the existing processes generally have the problem of uneven spatial distribution of magnetic properties. The magnetic particles are randomly distributed in the fiber cross-section, resulting in large fluctuations in the magnetic field strength in the axial and radial directions of the fiber, which is difficult to meet the stringent requirements for magnetic field uniformity in the medical field.

[0005] From the perspective of process control, the existing technologies have insufficient ability to finely control the fiber structure. Taking the melt spinning method as an example, under high-temperature and high-shear conditions, magnetic particles are prone to migrate and form local enrichment areas. This non-uniformity of the microstructure not only affects the stability of magnetic properties but also causes problems such as yarn breakage in subsequent textile processing. Although the wet spinning method can obtain a relatively uniform particle distribution, it is limited by the rheological properties of the solution and is difficult to achieve stable dispersion of magnetic particles with a high solid content (>40%). Moreover, shrinkage stress is easily generated during the drying process, resulting in fiber deformation. More prominently, most of the existing preparation methods are limited to a single material system and are difficult to achieve multi-functional integration. For example, in an application scenario that requires both antibacterial and magnetic response properties, the traditional blending method will lead to mutual restriction of properties due to the interaction of different functional components - the addition of antibacterial agents may exacerbate the oxidation of magnetic particles, while the presence of magnetic particles may affect the stability of antibacterial agents.

[0006] In summary, although magnetic composite fibers show great application potential in many fields, the existing preparation technologies still have systematic defects such as the imbalance between magnetic and mechanical properties, low functional integration degree, and insufficient durability. Therefore, developing new composite structure design and preparation processes to achieve the spatial orderly distribution of magnetic particles, stable bonding of multi-material interfaces, and multi-functional synergistic effect has become the key research direction to break through the current technical bottlenecks. Summary of the Invention

[0007] The present invention aims to overcome the systematic defects of existing magnetic fibers, such as the imbalance between magnetic and mechanical properties, low functional integration degree, and insufficient durability. A core-shell type gradient magnetic composite fiber and its spinning method are provided to overcome the above deficiencies.

[0008] To achieve the above invention objectives, the present invention is realized through the following technical solutions: In a first aspect, the present application first provides a core-shell gradient magnetic composite fiber, which includes, from the inside to the outside in sequence: A magnetic core layer, comprising a thermoplastic polymer matrix and first magnetic particles dispersed therein; An intermediate transition layer, in which the magnetic core layer is coated with an elastomeric material and second magnetic particles are dispersed; An outer functional layer, which is composed of an antibacterial and skin-friendly polymer; Wherein, the weight percentage of the first magnetic particles is higher than that of the second magnetic particles, forming a structure with a decreasing magnetic intensity gradient from the core layer to the outer layer.

[0009] In the prior art, the development of magnetic composite fibers has been limited by a fundamental contradiction for a long time, that is, increasing the content of magnetic particles can improve magnetic properties, but will seriously damage the flexibility and durability of the material. Traditional solutions often adopt a compromise strategy, either sacrificing magnetic properties for mechanical properties, or tolerating brittleness for high magnetic response. This dilemma has severely restricted the application of magnetic fibers in high-end fields. Facing this pain point in the industry, the innovative design of the core-shell gradient magnetic composite fiber in the present application came into being. Its core breakthrough lies in breaking through the thinking limitation of a single material system and achieving the synergistic optimization of performance through a carefully designed multi-layer structure.

[0010] By deeply analyzing this innovative design, the present application finds that its subtlety is first reflected in the hierarchical construction of the material system. Different from the homogeneous structure of traditional magnetic fibers, this design creatively adopts a three-layer composite architecture, and each layer undertakes specific functions and cooperates with each other. The innermost magnetic core layer adopts a high-density magnetic particle distribution to ensure the basic magnetic properties while maintaining the structural integrity through the thermoplastic polymer matrix. The design of the intermediate transition layer is particularly crucial. The selection of the elastomeric material not only plays a role in coating and protecting, but more importantly, as a stress buffer layer, it effectively alleviates the interfacial stress caused by the modulus difference between the inner and outer layer materials. The antibacterial and skin-friendly characteristics of the outer functional layer fully consider the actual application requirements, enabling the material to meet the ergonomic requirements while exerting magnetic functions. This progressive design idea makes the performance indicators that originally restricted each other achieve harmonious unity.

[0011] In addition, in this application, the magnetic strength gradient decreases from the core layer to the outer layer. The reason is that by controlling the content of magnetic particles in each layer, the magnetic induction intensity shows a decreasing distribution from the inside to the outside. This non-uniform arrangement has the following multiple advantages: on the one hand, the continuous magnetic path formed by the high-concentration magnetic particles inside ensures the overall magnetic performance; on the other hand, the reduction of magnetic particles in the outer layer not only reduces the surface magnetic field interference but also improves the flexibility of the material. More importantly, this gradient change is not a simple linear decrease, but an optimized design based on the principle of magnetic circuit closure and the characteristics of stress distribution, making the magnetic field distribution more uniform and controllable, providing the possibility for special applications such as precision medicine.

[0012] The actual application effects prove that this innovative design has brought all-round performance improvement. In terms of mechanical properties, due to the stress buffering effect of the middle elastic layer, the flexibility and fatigue resistance of the fiber are significantly improved, and good processability is still maintained even under high magnetic content conditions. The gradient distribution of magnetic properties not only improves the magnetic field uniformity but also realizes the controllable adjustment of the external magnetic field, which has special value in the field of medical rehabilitation. In terms of function integration, the antibacterial and skin-friendly characteristics of the outer layer complement the magnetic function of the inner core, enabling the material to meet the dual requirements of high-end medical textiles for hygiene safety and comfort. These performance improvements are not simple quantitative changes but qualitative changes caused by structural innovation, reflecting the systematic effect that the whole is greater than the sum of its parts.

[0013] The value of this innovative design is also reflected in solving multiple contradictory relationships that have long troubled the industry. The most prominent one is breaking the traditional understanding that magnetic properties and mechanical properties are in a trade-off relationship. Through the gradient structure design, the two are synergistically improved. Another important breakthrough is solving the problem of performance conflicts caused by function superposition. Through the strategy of spatial isolation, different functional components can each get their own place without interference. In addition, this design also well balances the relationship between short-term performance and long-term stability, significantly improving the environmental tolerance of the material system and extending the service life of the product. With the continuous improvement of technology, this core-shell gradient magnetic composite fiber is expected to play a greater role in fields such as intelligent medicine and flexible electronics, promoting the technological upgrading of related industries.

[0014] Preferably, the weight percentage of the first magnetic particles in the magnetic core layer is 30% - 60%, the average particle size is 0.5 - 10 μm, and it is selected from at least one of neodymium iron boron, samarium cobalt, or aluminum nickel cobalt.

[0015] Preferably, the thermoplastic polymer matrix is polyamide, polypropylene, or polyethylene terephthalate, and the first magnetic particles are surface-modified with a silane coupling agent.

[0016] In this application, polyamide, polypropylene or polyethylene terephthalate is used as the matrix material. Not only the good processing properties of these thermoplastic polymers are considered, but more importantly, their compatibility with magnetic particles and stability within a specific temperature range are valued. This material combination ensures the feasibility of the spinning process and provides the necessary mechanical strength for the fibers. The detailed design of surface modification of the first magnetic particles with a silane coupling agent is particularly crucial. It effectively improves the interfacial bonding condition between the inorganic magnetic particles and the organic polymer matrix, significantly reduces the interfacial energy through chemical bonding, enabling a high content of magnetic particles to be evenly dispersed without agglomeration. This dual optimization strategy produces a significant synergistic effect: on the one hand, the selection of the matrix material ensures that the processing window matches the thermal stability of the magnetic particles, avoiding high-temperature degradation; on the other hand, the surface modification treatment not only improves the particle dispersibility but also enhances the interfacial stress transfer efficiency, resulting in significant improvement in the mechanical properties of the composite material while maintaining high magnetic properties, especially key indicators such as tensile strength and elongation at break have been significantly improved, laying a solid foundation for subsequent textile processing and practical applications.

[0017] Preferably, the elastomeric material of the intermediate transition layer is silicone rubber, polyurethane elastomer or styrene-butadiene rubber, its elastic modulus is 0.5 - 5 MPa, the weight percentage of the second magnetic particles is 10% - 25%, and the particle size is smaller than that of the first magnetic particles.

[0018] This application achieves a double breakthrough in structural stability and functional durability through precise control of the transition layer thickness and particle surface treatment process. First, the thickness of the intermediate transition layer is limited within the range of 10 - 50 μm, which not only ensures sufficient thickness to buffer the stress difference between the inner and outer layers but also avoids a decrease in fiber flexibility due to excessive thickness. This optimal range is the best solution obtained through a large number of experiments and can provide the best protection effect without affecting the overall performance of the fiber. When ferrite or neodymium iron boron is selected as the second magnetic particle, an innovative silica isolation layer is coated on its surface. This treatment not only effectively prevents the oxidation failure of the magnetic particles but more importantly, establishes an interface with better chemical compatibility between the particles and the elastic matrix. The silicon-oxygen bonding between the silica layer and elastomers such as silicone rubber significantly enhances the interfacial bonding force. The direct advantage brought by this design is that the transition layer can maintain stable elastic properties during long-term use and ensure that the magnetic particles do not degrade in performance due to environmental factors or mechanical stress, enabling the composite fiber to maintain excellent magnetic-force coupling performance under repeated bending and complex environmental conditions, which is particularly suitable for high-end application scenarios such as medical rehabilitation and intelligent wear that require long-term reliability.

[0019] Preferably, the outer functional layer includes quaternary ammonium salt-modified polyurethane, chitosan copolymer or silver-based antibacterial agent-modified polymer.

[0020] Preferably, nano-silver particles or zinc oxide particles are also dispersed in the outer functional layer, with a weight percentage of 0.1% - 1% and an average particle size of 20 - 100 nm.

[0021] In a second aspect, the present invention also provides a method for preparing the core-shell type gradient magnetic composite fiber, comprising the following steps: (a) Melting and blending a thermoplastic polymer with first magnetic particles and degassing to form a core layer melt; (b) Blending an elastomeric material with second magnetic particles to form an intermediate layer colloid; (c) Formulating an outer functional solution; (d) Synchronously extruding the core layer melt, the intermediate layer colloid, and the outer functional solution through a three-channel spinning device; (e) Gradient curing treatment: Performing gradient curing treatment on the intermediate layer and the outer layer to obtain a core-shell type gradient magnetic composite fiber comprising a magnetic core layer, an intermediate transition layer, and an outer functional layer.

[0022] In the prior art, when producing multi-layer composite fibers, problems such as mismatched processing parameters of each layer of materials and poor interfacial bonding are often faced, resulting in unstable product performance. To address these issues, this method innovatively develops a complete gradient preparation process, the core of which lies in achieving the stable preparation of complex structures by precisely controlling the material processing and forming conditions at each stage. In the initial material processing stage, a special degassing treatment is carried out on the core layer melt. This seemingly simple step is actually crucial, as it effectively eliminates the bubble defects brought by high-content magnetic particles and provides a uniform melt basis for subsequent spinning. The formulation of the intermediate layer colloid is also carefully designed. The blending of the elastomeric material and the magnetic particles is not a simple physical mixing, but rather through specific process conditions to ensure uniform dispersion of the particles without damaging the network structure of the elastomer.

[0023] The three-channel synchronous extrusion process is another innovative highlight of this method. Traditional multi-layer spinning often adopts sequential extrusion or post-composite methods, which are prone to interfacial defects. However, this technology ensures the tight bonding between layers by precisely regulating the extrusion parameters of the three channels to enable synchronous composite of materials with different properties in the optimal state. Particularly worth mentioning is the design of the gradient curing treatment. It is not a simple overall curing, but rather a targeted curing strategy based on the characteristic differences of each layer of materials. Rapid curing is performed on the intermediate layer to stabilize the structure, while mild curing conditions are used for the outer layer to ensure surface performance. This differential treatment method not only improves production efficiency but also ensures the full play of the performance of each layer of materials.

[0024] In terms of actual effects, this set of preparation methods has brought significant performance improvements and production advantages. Due to the composite of each layer of materials under optimal conditions, the interfacial bonding strength of the obtained fibers has been significantly improved, and the problem of interlayer delamination has been fundamentally solved. The application of the gradient curing process endows the product with a more uniform structure and more stable performance, and the batch consistency has been significantly improved. In terms of production efficiency, the combined design of synchronous extrusion and gradient curing shortens the production cycle and reduces energy consumption on the premise of ensuring quality. The most prominent value of this method lies in its successful transformation of the complex core-shell type gradient structure from a laboratory concept into a mature process that can be scaled up for production, clearing the technical obstacles for the industrial application of high-performance magnetic composite fibers. This idea of combining material design with process innovation is not only applicable to the field of magnetic fibers but also has important reference significance for the development of other multifunctional composite materials.

[0025] Preferably, the extrusion temperature of the core layer is 220 - 280 °C; The extrusion temperature of the intermediate layer colloid is 30 - 80 °C lower than that of the core layer; The extrusion temperature of the outer layer solution is 50 - 100 °C lower than that of the core layer, and the extrusion speed ratio of the core layer, intermediate layer, and outer layer is = 1:(0.8 - 1.2):(1.5 - 2.5).

[0026] The optimized design of the process parameters in this application demonstrates the subtlety of the coordinated control of temperature and speed in the preparation process. Precisely controlling the core layer temperature within the range of 220 - 280 °C not only ensures the full melting of the thermoplastic polymer and its uniform mixing with magnetic particles but also avoids the risk of material degradation caused by high temperatures; setting the intermediate layer temperature 30 - 80 °C lower than the core layer cleverly balances the relationship between the fluidity of the elastomer and the stability of magnetic particles. Too low a temperature will lead to difficult extrusion, and too high a temperature may damage the molecular structure of the elastomer; the treatment of the outer layer solution with a larger temperature drop (50 - 100 °C) fully considers the viscosity characteristics of the functional polymer solution and the requirements for surface forming quality. More importantly, the specific ratio design of the extrusion speeds of the three layers, with a speed ratio of 1:(0.8 - 1.2):(1.5 - 2.5), creatively solves the common problem of layer thickness control in multi-layer composites - the core layer maintains the reference speed to ensure structural stability, the intermediate layer with a similar speed ensures uniform coating, and the relatively faster speed of the outer layer is conducive to forming a complete functional surface. This process scheme with the coordination of temperature gradient and speed gradient enables three materials with very different properties to achieve perfect composite in the best state, not only solving problems such as insufficient interlayer bonding force and uneven thickness in traditional processes but also significantly improving the consistency and yield rate of products, providing a reliable technical guarantee for industrial production.

[0027] Preferably, ultraviolet curing and thermal curing are performed on the intermediate layer colloid and the outer layer functional solution; The ultraviolet curing uses ultraviolet light with a wavelength of 365 nm and an intensity of 50 - 200 mW / cm 2 to irradiate for 10 - 60 seconds; The thermal crosslinking curing is carried out at 80 - 120 °C for 5 - 30 minutes.

[0028] In summary, the present application has the following beneficial effects: Through the innovative core - shell type gradient structure design, the present invention successfully solves the technical problem that the mechanical properties of traditional magnetic fibers sharply decline at high magnetic content. In its three - layer composite structure, the high - density magnetic core layer ensures excellent magnetic properties, the elastic intermediate transition layer effectively buffers stress concentration, and the outer functional material provides good antibacterial and skin - friendly properties. The unique gradient magnetic distribution design enables the magnetic field strength to show a controllable change, meeting the special application requirements such as precision medicine. The developed synchronous extrusion and gradient curing process realizes the stable preparation of complex structures, enabling the product to have a fracture elongation rate increased by more than 3 times while maintaining high magnetic properties, significantly improving the anti - bending fatigue performance, and controlling the magnetic property attenuation within 5% after tens of thousands of cycles. This design concept that combines material innovation and process breakthrough not only provides new ideas for the development of high - performance magnetic fibers but also opens up an effective way for the research and development of other multifunctional composite materials. Detailed implementation manners

[0029] The following further describes the present invention with reference to specific embodiments. Those of ordinary skill in the art will be able to implement the present invention based on these descriptions. In addition, the embodiments of the present invention involved in the following description are usually only a part of the embodiments of the present invention, rather than all of the embodiments. Therefore, all other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments of the present invention shall fall within the scope of protection of the present invention.

[0030]

First magnetic particles

[0031] (2) Preparation of coupling agent solution: Prepare a mixed solvent according to a volume ratio of ethanol: deionized water = 95:5, add 3 - aminopropyltriethoxysilane (KH - 550), control the concentration of the silane coupling agent to be 1.5 wt%, and magnetically stir for 10 minutes to fully hydrolyze it (adjust the solution pH value to 4.5 - 5.5 with acetic acid).

[0032] (3) Surface modification: The dried NdFeB powder was added to the coupling agent solution at a solid-liquid ratio of 1:10, heated in a water bath to 60°C, and ultrasonically dispersed (power 300W, frequency 40kHz) for 30 minutes, then transferred to a constant temperature stirring reactor and mechanically stirred (speed 500rpm) for 4 hours. (4) Post-treatment process: After the reaction is completed, the particles are washed by centrifugation (8000 rpm, 10 min) three times with anhydrous ethanol, and then dried under vacuum at 60°C for 6 hours and sieved through a 325-mesh sieve to obtain the first magnetic particles (a) surface-modified with a silane coupling agent.

[0033] The surface modification method of the first magnetic particle (b) comprises the following steps: (1) Pretreatment process: Place the ferrite powder (Fe3O4, average particle size 5-10μm) in a vacuum drying oven and dry it at 100℃ for 3 hours to completely remove the surface adsorbed water.

[0034] (2) Preparation of coupling agent solution: Prepare the modified solution: isopropanol / water mixed solvent (volume ratio 9:1), add γ-methacryloxypropyltrimethoxysilane (KH-570) at a concentration of 2.0wt%, then adjust the pH to 4.0-5.0 with acetic acid, and stir magnetically for 30 minutes to complete the hydrolysis.

[0035] (3) Surface modification: dry ferrite powder was added to the modified solution at a solid-liquid ratio of 1:8, and ultrasonic-mechanical stirring was used for synergistic treatment: first ultrasonic dispersion (400 W, 35 kHz) for 45 minutes, then transferred to a three-necked flask, refluxed in an 80 °C oil bath, and mechanically stirred (600 rpm) for 6 hours.

[0036] (4) Post-treatment process: After the reaction is completed, the particles are centrifugally washed with acetone (10,000 rpm, 15 minutes) for 4 times, vacuum dried at 70°C for 8 hours, and passed through a 400-mesh sieve to obtain the modified first magnetic particles (b).

[0037]

Second magnetic particles

[0038] (2) Silane coupling agent pretreatment: prepare an ethanol / water mixed solvent (volume ratio 8:2), then add 3-aminopropyltriethoxysilane (KH-550) at a concentration of 1.0wt%, adjust the pH to 9.0-10.0 with ammonia water, add the dried magnetic particles (solid-liquid ratio 1:10), ultrasonically treat in a 60℃ water bath (power 350W) for 2 hours, centrifuge and wash, and dry at 80℃ for 6 hours (3) Silica Coating by Stöber Method: Solution Preparation: A mixed solvent of ethanol / water (volume ratio 7:3) was added with 0.5 M ammonia water as a catalyst, and then 1.0 wt% cetyltrimethylammonium bromide (CTAB) was added as a surfactant; Coating Reaction: The pretreated magnetic particles were dispersed in the above solution (solid-liquid ratio 1:15), and then tetraethyl orthosilicate (TEOS) was slowly added dropwise. The mass ratio of TEOS to magnetic particles was 1:5, and the reaction was carried out at a constant temperature of 40 °C for 12 hours with mechanical stirring (300 rpm). After the reaction was completed, it was centrifugally washed with ethanol (8000 rpm, 10 minutes) 3 times, and finally dried in vacuum at 60 °C for 8 hours. (4) High-temperature Heat Treatment: The coated particles were placed in a tube furnace and under nitrogen protection, heated to 500 °C at a rate of 5 °C / min, and then held for 2 hours to densify the silica layer, and naturally cooled to room temperature to obtain the second magnetic particles with silica-coated surface.

[0039] [Preparation of Quaternary Ammonium Salt Modified Polyurethane] Preparation Method of Quaternary Ammonium Salt Modified Polyurethane: 1. Raw Material Preparation: Polyurethane Prepolymer: Poly(tetramethylene ether) glycol (PTMG, Mn = 2000) and isophorone diisocyanate (IPDI) were reacted at an NCO:OH molar ratio of 2:1 to prepare a terminal - NCO prepolymer (NCO content 5.2 wt%); Quaternary Ammonium Salt Monomer: Methacryloyloxyethyltrimethylammonium chloride (DMC, purity ≥ 99%); Chain Extender: 1,4 - butanediol (BDO); Catalyst: Dibutyltin dilaurate (DBTDL, 0.05 wt%); Solvent: N,N - dimethylformamide (DMF, anhydrous grade).

[0040] 2. Synthesis of Quaternary Ammonium Salt Modified Polyurethane (1) Preparation of Prepolymer: PTMG was dehydrated in vacuum at 110 °C for 2 hours to remove moisture, then cooled to 80 °C, and IPDI and DBTDL were added, and the reaction was carried out for 3 hours under nitrogen protection to obtain a terminal - NCO polyurethane prepolymer; (2) Quaternary Ammonium Salt Grafting Modification: The prepolymer was dissolved in DMF (solid content 30%), stirred and cooled to 60 °C, and BDO (NCO:OH = 1:1) was added for chain extension, and the reaction was carried out for 1 hour; (3) Post-treatment: After the reaction was completed, the system was cooled to 40 °C, poured into a polytetrafluoroethylene mold and cast into a film, dried in vacuum at 80 °C for 24 hours to completely remove the solvent, and finally soaked in deionized water for 48 hours to remove unreacted monomers. After drying at 60 °C, quaternary ammonium salt-modified polyurethane was obtained.

[0041]

Example

[0042] (S.2) Preparation of core layer melt: PA6 and the first magnetic particles (a) were added to a twin-screw extruder and melt-blended at 250 °C, with a screw speed of 200 rpm and vacuum degassing treatment for 30 minutes to obtain a uniform core layer melt.

[0043] (S.3) Preparation of intermediate layer colloid: LSR and the second magnetic particles were placed in a planetary mixer and dispersed at a high speed of 2000 rpm for 40 minutes to form a uniform colloid, which was left standing for defoaming and then used.

[0044] (S.4) Preparation of outer layer solution: The modified PU solution and silver nanoparticles were ultrasonically dispersed for 30 minutes (power 300 W), and passed through a 200-mesh sieve to remove aggregates.

[0045] (S.5) Coaxial electrospinning was carried out using a spinning device with a three-layer coaxial nozzle: Temperature setting: Core layer channel: 260 °C; Intermediate layer channel: 200 °C (60 °C lower than the core layer); Outer layer channel: 180 °C (80 °C lower than the core layer); Extrusion speed control: Core layer: 1.0 m / min (reference); Intermediate layer: 1.0 m / min (speed ratio 1:1); Outer layer: 2.0 m / min (speed ratio 1:2); Orifice diameter design of the spinneret plate: Core layer: 0.3 mm; Intermediate layer: 0.5 mm (coating gap); Outer layer: 0.8 mm (coating gap).

[0046] (S.6) Gradient curing treatment: Intermediate layer curing: Ultraviolet light irradiation (wavelength 365 nm, intensity 150 mW / cm2 ) 30 seconds; Outer layer curing: Through a 120 °C hot air circulation oven, with a residence time of 2 minutes; Final shaping: After water bath cooling (20 °C), winding is carried out to obtain fibers with a total diameter of 150 ± 10 μm.

[0047] Example 2 The difference between Example 2 and Example 1 is that step (S.1) is modified, and the remaining conditions are the same as those in Example 1.

[0048] Step (S.1) is specifically as follows: Core layer material: Polyamide 6 (PA6) is selected as the thermoplastic polymer matrix and premixed with the first magnetic particles (a) at a mass ratio of 70:30; Intermediate layer material: Photocurable liquid silicone rubber (LSR) is mixed with the second magnetic particles at a mass ratio of 80:10; Outer layer material: Quaternary ammonium salt modified polyurethane (PU) is dissolved in DMF solvent to prepare a 25 wt% solution, and 0.1 wt% silver nanoparticles are added.

[0049] Example 3 The difference between Example 3 and Example 1 is that step (S.1) is modified, and the remaining conditions are the same as those in Example 1.

[0050] Step (S.1) is specifically as follows: Core layer material: Polyamide 6 (PA6) is selected as the thermoplastic polymer matrix and premixed with the first magnetic particles (a) at a mass ratio of 40:60; Intermediate layer material: Photocurable liquid silicone rubber (LSR) is mixed with the second magnetic particles at a mass ratio of 75:25; Outer layer material: Quaternary ammonium salt modified polyurethane (PU) is dissolved in DMF solvent to prepare a 25 wt% solution, and 1 wt% zinc oxide nanoparticles are added.

[0051] Example 4 The difference between Example 4 and Example 1 is that the first magnetic particles (a) are replaced by the first magnetic particles (b).

[0052] Example 5 The difference between Example 5 and Example 1 is that steps (S.5) and (S.6) are modified, and the remaining conditions are the same as those in Example 1.

[0053] Specifically: (S.5) Coaxial spinning is carried out using a spinning device with a three-layer coaxial nozzle: Temperature setting: Nuclear layer channel: 280 °C; Intermediate layer channel: 200 °C (80 °C lower than the nuclear layer); Outer layer channel: 180 °C (100 °C lower than the nuclear layer); Extrusion speed control: Nuclear layer: 1.0 m / min (benchmark); Intermediate layer: 0.8 m / min (speed ratio 1:0.8); Outer layer: 1.5 m / min (speed ratio 1:1.5); Spinneret hole diameter design: Nuclear layer: 0.3 mm; Intermediate layer: 0.5 mm (coating gap); Outer layer: 0.8 mm (coating gap).

[0054] (S.6) Gradient curing treatment: Intermediate layer curing: Ultraviolet light irradiation (wavelength 365 nm, intensity 200 mW / cm 2 ) for 10 seconds; Outer layer curing: Through an 80 °C hot air circulation oven, residence time 5 minutes; Final shaping: After water bath cooling (20 °C), winding is carried out to obtain fibers with a total diameter of 130 ± 10 μm.

[0055] Example 6 The difference between Example 6 and Example 1 is that steps (S.5) and (S.6) are modified, and the remaining conditions are the same as those in Example 1.

[0056] Specifically: (S.5) Coaxial spinning is carried out using a spinning device with a three-layer coaxial nozzle: Temperature setting: Nuclear layer channel: 220 °C; Intermediate layer channel: 190 °C (30 °C lower than the nuclear layer); Outer layer channel: 170 °C (50 °C lower than the nuclear layer); Extrusion speed control: Nuclear layer: 1.0 m / min (benchmark); Intermediate layer: 1.2 m / min (speed ratio 1:1.2); Outer layer: 2.5 m / min (speed ratio 1:1.5); Spinneret hole diameter design: Nuclear layer: 0.3 mm; Intermediate layer: 0.5 mm (coating gap); Outer layer: 0.8 mm (coating gap).

[0057] (S.6) Gradient curing treatment: Intermediate layer curing: Ultraviolet light irradiation (wavelength 365 nm, intensity 50 mW / cm 2 ) for 60 seconds; Outer layer curing: Through a 100 °C hot air circulation oven, residence time 3 minutes; Final shaping: After water bath cooling (20 °C), winding is carried out to obtain fibers with a total diameter of 130 ± 10 μm.

[0058] Comparative Example 1 The non-nuclear layer, middle layer, and outer layer are designed, all of which use the PA6 matrix of Example 1, and the magnetic particles are evenly dispersed (55 wt%).

[0059] Comparative Example 2 Only the nuclear layer (55 wt% magnetic particles) and the outer layer (containing 0.3 wt% nano silver) are retained, and the elastic middle layer is missing.

[0060] Comparative Example 3 The content of magnetic particles in the nuclear layer is 10 wt%, and the outer layer increases to 55 wt%, and other conditions are the same as in Example 1 Comparative Example 4 The magnetic particles in the nuclear layer were not treated with silane coupling agent, and the second particles in the middle layer were not coated with silica.

[0061] The fibers prepared in Examples 1-6 and Comparative Examples 1-4 were tested, and the test methods are as follows: 1. Magnetic property test Saturation magnetization intensity (Ms): Vibration sample magnetometer (VSM), magnetic field strength ±2T, room temperature; Residual magnetization (Br) and coercivity (Hc): B-H hysteresis loop measurement, pulsed magnetic field generator; Surface magnetic field distribution uniformity: Gaussmeter multi-point scanning (sampling every centimeter axially).

[0062] 2. Mechanical property test Tensile strength and elongation at break: ASTM D3822, tensile rate 50 mm / min; Flexural fatigue resistance: MIT folding endurance tester (ASTM D2176), load 500g, angle ±90°, record magnetic attenuation rate.

[0063] 3. Functional characteristics Bacteriostatic rate: GB / T 20944.3-2008 (Staphylococcus aureus / Escherichia coli), 24h contact method; Skin-friendly property: Friction coefficient test (ASTM D1894), measured in an environment with a humidity of 65%.

[0064] The test results are shown in Table 1 below: Table 1 As can be seen from the data in the above table, the magnetic and mechanical properties of Examples 1-6 are significantly better than those of the comparative examples. Comparing Comparative Example 4 with Example 1, it can be seen that the silane coupling agent and the coating process improve the interfacial bonding ability, resulting in a significant increase in the elongation at break. At the same time, the reverse gradient of Comparative Example 3 verifies that the magnetic field uniformity highly depends on the decreasing design of the nuclear layer - outer shell.

[0065] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Those skilled in the art to which the present invention pertains may make various modifications or supplements to the described specific embodiments or use similar means for substitution, but will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A core-shell type gradient magnetic composite fiber, characterized in that: Including compound from inside to outside: A magnetic core layer comprising a thermoplastic polymer matrix and first magnetic particles dispersed therein; An intermediate transition layer, comprising an elastic material covering the magnetic core layer and having second magnetic particles dispersed therein; The outer functional layer is composed of antibacterial and skin-friendly polymers; The weight percentage of the first magnetic particles is higher than that of the second magnetic particles, forming a structure with a decreasing magnetic intensity gradient from the core layer to the outer layer.

2. A core-shell gradient magnetic composite fiber according to claim 1, characterized in that: The weight percentage of the first magnetic particles in the magnetic core layer is 30%-60%, the average particle size is 0.5-10 μm, and the particles are selected from at least one of neodymium iron boron, samarium cobalt, or aluminum nickel cobalt.

3. A core-shell type gradient magnetic composite fiber according to claim 2, characterized in that: The thermoplastic polymer matrix is ​​polyamide, polypropylene or polyethylene terephthalate, and the first magnetic particles are surface-modified with a silane coupling agent.

4. The core-shell gradient magnetic composite fiber according to claim 1, characterized in that: The elastic material of the intermediate transition layer is silicone rubber, polyurethane elastomer or styrene-butadiene rubber; The weight percentage of the second magnetic particles is 10%-25%.

5. A core-shell type gradient magnetic composite fiber according to claim 4, characterized in that: The second magnetic particles are ferrite or neodymium iron boron, and the surface of the second magnetic particles is coated with a silicon dioxide isolation layer.

6. The core-shell gradient magnetic composite fiber according to claim 1, characterized in that: The outer functional layer comprises quaternary ammonium salt modified polyurethane, chitosan copolymer or silver series antibacterial agent modified polymer.

7. A core-shell type gradient magnetic composite fiber according to claim 6, characterized in that: Nano silver particles or zinc oxide particles are also dispersed in the outer functional layer, and the weight percentage thereof is 0.1%-1%.

8. A method for preparing a core-shell type gradient magnetic composite fiber as claimed in any one of claims 1 to 7, characterized in that: The following steps are involved: (a) melt-blending a thermoplastic polymer with first magnetic particles and degassing to form a core layer melt; (b) blending the elastomeric material with the second magnetic particles to form an intermediate layer colloid; (c) preparing an outer layer functional solution; (d) Synchronously extruding the core layer melt, the middle layer colloid, and the outer layer functional solution through a three-channel spinning device; (e) Gradient solidification treatment: The intermediate layer and the outer layer are subjected to gradient solidification treatment to obtain a core-shell type gradient magnetic composite fiber comprising a magnetic core layer, an intermediate transition layer and an outer functional layer.

9. The method according to claim 8, characterized in that In the step (d): The core layer extrusion temperature is 220-280°C; The extrusion temperature of the middle layer colloid is 30-80℃ lower than that of the core layer; The extrusion temperature of the outer layer solution is 50-100℃ lower than that of the core layer. The extrusion speed ratio of the core layer, the middle layer and the outer layer is 1:(0.8-1.2):(1.5-2.5).

10. The method according to claim 8, characterized in that The gradient curing process in step (e) includes UV curing and thermal curing of the middle layer colloid and the outer layer functional solution in stages; The UV curing adopts a wavelength of 365nm and an intensity of 50-200mW / cm 2 UV light irradiation for 10-60 seconds; Thermal crosslinking curing is carried out at 80-120°C for 1-5 minutes.

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