A moisture-absorbing and quick-drying polypropylene fiber with a gradient structure and its preparation method

Abstract

The present invention belongs to the technical field of moisture-absorbing and quick-drying polypropylene fibers, and relates to a moisture-absorbing and quick-drying polypropylene fiber with a gradient structure and a preparation method thereof. After the matrix phase and the dispersed phase are mixed to obtain a mixture, melt blending and spinning are carried out to obtain a moisture-absorbing and quick-drying polypropylene fiber with a gradient structure; the matrix phase is polypropylene, and the dispersed phase is a hydrophilic polymer; the gradient structure refers to a surface enrichment type gradient structure or an internal enrichment type gradient structure; the surface enrichment type gradient structure means that the particle size of the dispersed phase gradually increases from the center to the outside on the fiber cross-section; the internal enrichment type gradient structure means that the particle size of the dispersed phase gradually decreases from the center to the outside on the fiber cross-section; the moisture-absorbing and quick-drying polypropylene fiber with a gradient structure has a groove structure on the surface, and the area occupied by the groove structure is 0.5-30% of the fiber surface area. The preparation method of the present invention is simple, and the obtained moisture-absorbing and quick-drying polypropylene fiber with a gradient structure has good moisture-absorbing and quick-drying properties and unidirectional moisture-conducting properties.

Description

Technical Field

[0001] The present invention belongs to the technical field of moisture-absorbing and quick-drying polypropylene fibers, and relates to a moisture-absorbing and quick-drying polypropylene fiber with a gradient structure and a preparation method thereof. Background Art

[0002] Whether outdoors or indoors, when the core body temperature of a human exceeds the high-temperature threshold, sweat is released from the body surface for evaporative heat dissipation. However, in a high-temperature and high-humidity environment, the amount of sweat produced is easily greater than the amount of evaporation. At this time, a large amount of sweat will accumulate on the skin surface and inside the fibers, causing discomfort to the human body. To prevent sweat accumulation, the design of functional fibers and fabrics must synergistically optimize their moisture-absorbing and quick-drying properties and improve the conduction and evaporation performance of the fibers for sweat.

[0003] Currently, fiber fabrics with moisture-absorbing and quick-drying properties on the market generally use fibers with a certain moisture-absorbing property as raw materials. However, the moisture-absorbing effect of chemical fibers is limited and the quick-drying effect is poor. When the amount of sweat on the body surface is large, it cannot be discharged in time, thus failing to meet the requirements of the human body for the comfort of fibers. Based on this, it is necessary to improve the moisture-absorbing and quick-drying properties of fiber materials by designing the macroscopic structure of the fibers and surface hydrophilic finishing.

[0004] (1) In the development of the macroscopic structure of fibers, mainly the physical structures of polypropylene, polyester or polyamide fibers are designed and developed, including fine-denier fibers, hollow porous fibers, and profiled cross-section fibers (such as "cross", "Y", "H", etc.). The surface of the profiled structure fibers provides a richer moisture transmission channel. The groove structure or porosity of the fibers can quickly conduct the inner-layer sweat or moisture to the outer layer for evaporation, promoting moisture transfer, and its moisture-absorbing and quick-drying performance is significantly better than that of circular fiber fabrics.

[0005] (2) In the development of surface hydrophilic finishing, hydrophilic groups (such as hydroxyl, carboxyl, amino, and amide groups) are introduced into the fiber macromolecular structure, or a melt blending method is used with hydrophilic raw materials to further enhance the moisture absorption and quick-drying performance of fiber fabrics by taking advantage of the hydrophilic and moisture-conducting characteristics of two-phase polymers. For example, moisture-absorbing and sweat-releasing fibers produced by grafting silk compounds onto polyester, or polyamide ester synthetic fibers produced by copolymerizing polyester and polyamide macromolecules. DuPont in the United States used radiation-induced polymerization to graft copolymerize hydrophilic components onto nylon 66 to obtain highly hygroscopic fibers. Sophista developed by Kuraray is a two-component core-shell composite fiber mainly developed from ethylene-vinyl alcohol copolymer (EVOH) and polyester (PET). Among them, hydrophobic PET as the core layer hardly absorbs moisture, and EVOH with hydrophilic groups as the skin layer has excellent wetting performance. Toyobo in Japan blended polypropylene ester with polyester spinning solution to produce Ekslive moisture-absorbing and quick-drying fibers. Patent CN119061556A discloses a moisture-absorbing, quick-drying and comfortable polyamide fabric, a spinning melt, and a preparation method of the spinning melt. The polyamide fabric is woven from nylon yarn and spandex yarn. The composition of the nylon yarn includes 1% - 8% of silk fibroin and 0.9% - 6% of polyvinylpyrrolidone. This method improves the capillary effect and air permeability of the fiber fabric and reduces the stuffy feeling during wearing.

[0006] However, the moisture absorption and quick-drying properties of the above-mentioned prior art still need to be improved. In order to further enhance the moisture absorption and quick-drying properties and reduce the problem of limited quick-drying properties of hydrophilic fibers when the human body is in a high temperature and high humidity environment, a fiber material with unidirectional moisture conduction can be obtained by constructing an asymmetric wettability gradient on both sides of the fiber fabric. Because there is a wetting transition from hydrophobic to hydrophilic in the thickness direction, sweat can be spontaneously transferred from the hydrophobic surface to the hydrophilic surface, while blocking sweat penetration in the opposite direction. Generally, the preparation method can be divided into two types according to the formation mode of the wetting gradient: layer-by-layer composite preparation and single-sided modification. The first type, in terms of the step wettability gradient structure based on layer-by-layer composite preparation, hydrophilic natural fibers (cotton, wool, viscose) and hydrophobic synthetic fibers (polyester, polypropylene) are used. The composite fabric can also be given excellent unidirectional liquid conduction properties through the reasonable design of fiber, yarn, and fabric structure. A double-layer unidirectional liquid conduction fabric was prepared using polyester / viscose blended yarn as the inner layer of the fabric and viscose yarn as the outer layer. The blended inner layer can conduct sweat to the outer layer by means of the wicking effect between the fibers and yarns, and the unidirectional moisture conduction index (R) can reach up to 372%. The second type, in terms of the gradual wetting gradient structure based on single-sided modification, a layer of hydrophobic titanium dioxide-silicon dioxide hybrid nanoparticles was deposited on the polyester fabric by solution coating, and then one side of the coated superhydrophobic fabric was exposed to ultraviolet light beam irradiation. Due to the photocatalytic degradation of alkyl groups by titanium dioxide and the introduction of oxygen-containing hydrophilic groups, the front side of the fabric after irradiation becomes hydrophilic, while the back side remains superhydrophobic. The fabric exhibits excellent unidirectional liquid conduction properties, with forward and reverse osmotic pressures of 2cm H2O and 18cm H2O, respectively.

[0007] At present, the preparation of moisture-absorbing and quick-drying fibers is generally achieved by regulating the fiber macrostructure and carrying out surface hydrophilic finishing. In the process of regulating the fiber macrostructure, it is often necessary to use complex production processes and equip specific professional equipment, which undoubtedly greatly increases the production cost. Moreover, relying solely on the design of the fiber cross-section (optimizing the water conduction path and increasing the fiber specific surface area) can only play a limited role in improving the fiber's hygroscopicity, making it difficult to achieve a more ideal hygroscopic effect, while reducing the fiber's mechanical properties.

[0008] For example, Coolmax fiber is known for its moisture absorption and perspiration function, but its ability to absorb water is relatively limited. It mainly conducts sweat quickly to the fabric surface through the special cross-sectional structure of the fiber (enhancing the capillary effect in the fiber), rather than absorbing a large amount of water like natural fibers (such as cotton fibers). In the case of heavy sweating, it may not be possible to discharge all the sweat in time, causing the wearer to still feel local dampness. In the process of surface hydrophilic finishing to improve the moisture absorption and quick drying of fibers, additional chemical reagents need to be added, which destroys the balance of the ecological structure and reduces the wearing comfort of the human body.

[0009] For example, in patent CN117488435A, a moisture-absorbing quick-drying fiber and a preparation method thereof are prepared by mixing cotton fiber and modified polyester fiber, wherein the modified polyester fiber is prepared by the following steps: tertiary amine modified nano zinc oxide reacts with p-chloroaniline to obtain modified nano zinc oxide; modified nano zinc oxide, formaldehyde polybutylene terephthalate solution and diethylamine react to obtain modified polybutylene terephthalate, and the modified polybutylene terephthalate is melted, spun, stretched and shaped to obtain modified polyester fiber. Although this modification process combines the advantages of cotton fiber and modified polyester fiber, allowing water to diffuse rapidly around and improving the water absorption rate, drip diffusion time, evaporation rate and moisture permeability of the fiber, since both phases are hydrophilic substances, they will interact with water molecules to reduce the movement rate of water molecules, which results in reducing the evaporation rate while increasing the water absorption rate. At the same time, this patent has a complex preparation process, increases the process cost, and is not suitable for mass production in industrial processes.

[0010] In patent CN118979315A, an anti-ultraviolet moisture-absorbing fiber and its preparation method are described. After Cu2O is coated on gold nanorods, ZnO is grown on the surface to obtain Au@Cu2O / ZnO composite material; Au@Cu2O / ZnO composite material is reacted with ethylene glycol, isosorbide, and terephthalic acid to obtain modified PET; modified PET is mixed with anti-ultraviolet additives and melt-spun to obtain modified PET fiber, which is then treated to obtain activated PET fiber; 2-[(2-aminoethyl)amino]ethanesulfonic acid sodium salt is reacted with silane coupling agent KH560 to obtain a hydrophilic modifier; the hydrophilic modifier and epigallocatechin gallate are grafted on the activated PET fiber to obtain an anti-ultraviolet moisture-absorbing fiber. The results show that the hydrophilicity of PET is improved based on the fiber surface, and at the same time, it is endowed with good antibacterial and anti-ultraviolet properties. However, this process has harsh reaction conditions, cumbersome multi-step reactions, and it is difficult to maintain the uniformity and stability of grafting.

[0011] Based on the above advantages and disadvantages, in order to further enhance the moisture absorption and quick-drying performance, a fiber fabric with unidirectional moisture conduction function has been developed. In the patent CN119041038A, a method for preparing Janus fabric by electrospinning, the Janus fabric is prepared by electrospinning. First, a certain concentration of PU spinning solution is prepared, and then a hydrophilic medical gauze is used as a collector to fix the electrospinning parameters (voltage, flow rate, time, etc.). Finally, the Janus fabric is obtained by drying. This invention utilizes the differences in hydrophilicity, hydrophobicity, and wettability on both sides of the fabric. The Janus fabric can achieve unidirectional wettability, laying a foundation for its application in controllable water collection and other aspects. The water droplet diffusion rate of the Janus fabric prepared by this method is slow (6 s) and has the characteristics of unidirectional moisture conduction. However, this result far fails to meet the national requirements for moisture absorption and quick-drying fabrics (GB / T 21655.1-2023). At the same time, the electrospinning rate is slow and not suitable for large-scale commercial production. In addition, in the patent CN115583084A, a knitted fabric with multi-dimensional moisture conduction and deodorization and its application, by designing the fabric structure, a hydrophilic layer, a water-conducting layer, and a hydrophobic layer are constructed in sequence, and at the same time, there is a trend that the fiber fineness increases in turn from the inside to the outside and the fiber diameter decreases in turn. The special thing is that after the yarn is treated by plasma surface treatment, small particles with different concavities and convexities are generated on the yarn surface, the number and depth of which are significantly increased, obvious etching marks exist on the yarn surface, and the surface roughness of the yarn is significantly increased, thus causing an increase in the specific surface area of the yarn and finally increasing the surface wettability, and its contact angle is 0°. The multi-dimensional moisture conduction fabric prepared by this method does not have a good moisture conduction effect. The unidirectional transfer index is at most 200% at the highest, and only about 70% after 120 s, which is not conducive to the complete diffusion of moisture on the body surface. Its evaporation rate of moisture is at most only 0.24 g / h, and its quick-drying property is poor.

[0012] Therefore, it is of great significance to study a moisture absorption and quick-drying polypropylene fiber with a gradient structure and its preparation method to solve the problems existing in the prior art. Summary of the Invention

[0013] The purpose of the present invention is to solve the problems existing in the prior art and provide a preparation method for a moisture absorption and quick-drying polypropylene fiber with a gradient structure.

[0014] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0015] A moisture absorption and quick-drying polypropylene fiber with a gradient structure is prepared by melt blending and spinning after mixing a matrix phase and a dispersed phase to obtain a mixture;

[0016] The matrix phase is polypropylene, and the dispersed phase is a hydrophilic polymer;

[0017] The gradient structure refers to a surface-enriched gradient structure or an internal-enriched gradient structure;

[0018] The surface-enriched gradient structure means that the particle size of the dispersed phase gradually increases from the center to the outside on the fiber cross-section, that is, the enrichment degree of the dispersed phase on the fiber surface is greater than that in the fiber interior;

[0019] The internal-enriched gradient structure means that the particle size of the dispersed phase gradually decreases from the center to the outside on the fiber cross-section, that is, the enrichment degree of the dispersed phase in the fiber interior is greater than that on the fiber surface;

[0020] The moisture-absorbing and quick-drying polypropylene fiber with a gradient structure has a groove structure on its surface. The groove structure refers to the part that is recessed downward relative to the flat body surface of the fiber. Since it is similar to the groove by the roadside, it is called the groove structure. The groove structure is formed due to the phase separation of the dispersed phase and the matrix phase. During the melt spinning process, when the sum of the shear stress, tensile stress and the adhesion between the two phases is higher than the adhesion between the two phases, the two phases undergo phase separation on the fiber surface, so a groove structure will be generated on the fiber surface. The groove structure is distributed on the surface of the fiber and is controlled by controlling the spinning speed, draw ratio, zero-shear viscosity of the dispersed phase, content of the dispersed phase, molecular weight distribution of the dispersed phase and the aperture of the spinneret hole during the melt spinning process (reference can be made to CN116043362A; CN116043360A).

[0021] For the surface-enriched gradient structure, due to the enrichment of the hydrophilic polymer on the fiber surface, the hydrophilicity of the fiber can be significantly increased. The hydrophilic fiber surface is more likely to interact with water molecules, enabling the water molecules to be quickly adsorbed by the fiber surface. Due to the presence of the groove structure on the fiber surface, the capillary action of the fiber will be further enhanced. Due to the humidity and temperature gradients between the skin and the outside air, moisture can diffuse rapidly in the vertical direction of the fiber and in the fiber layer direction (such as Figure 2As shown in the figure, the rapid diffusion of moisture in the vertical direction depends on the free diffusion of water molecules. The water molecules migrate from the high-concentration region to the low-concentration region, realizing the evaporation and diffusion of moisture from the fiber core layer to the low-humidity outside. The principle of moisture diffusion around the fiber surface is based on the strong intermolecular force and hydrogen bond force of the hydrophilic polymer on water molecules. Under the influence of this strong force, the transfer of water molecules between the hydrophilic polymers is increased, thereby realizing the diffusion of moisture around the fiber surface. At the same time, relying on the free diffusion of water molecules, a large amount of moisture is conducted from the high-humidity condition to the low-humidity direction. Since there are fewer hydrophilic polymers in the fiber core layer, the force and absorption of moisture are less. Therefore, during the drying process of the fiber, the content and time of moisture diffusing from the core layer to the surface layer are reduced, and based on this, the quick-drying effect of the fiber is achieved. In addition, since there are fewer dispersed phases in the fiber and the interfacial tension of the two-phase polymer is lower (as is well known in the art, when the interfacial tension increases during the two-phase blending, the mechanical properties will decline rapidly), the inside of the fiber can be regarded as a strut core to enhance the mechanical properties of the blended fiber.

[0022] For the internal enrichment type gradient structure, we designed a fiber surface with hydrophobic and groove structures. The hydrophobic structure surface can prevent penetration into the fiber interior (core layer) at low humidity. At the same time, under high-humidity conditions, due to the capillary effect on the fiber surface, as well as the intermolecular force and hydrogen bond force between the fiber surface and water molecules, the groove structure on the fiber surface and the hydrophilic polymer inside make the moisture be inhaled from the outer surface of the fiber into the fiber core layer (vertical diffusion), and form diffusion in the fiber core layer (such as Figure 4 the stretching direction of the water droplet shown, that is, the lateral diffusion of the fiber). At the same time, through the free diffusion effect, the water molecules migrate from the high-concentration region to the low-concentration region, realizing the evaporation and diffusion of moisture from the fiber core layer to the low-humidity outside. This diffusion path prevents the sweat from re-infiltrating when the human body sweats a lot, and at the same time endows the fiber with the ability of one-way moisture conduction. The whole process is as shown in Figure 4 the figure. At the same time, this structure (locking a small amount of moisture in the fiber core layer) also endows the fiber with a certain water retention rate (the moisture regain increases). When the outside is dry, due to the free diffusion of moisture, the moisture inside the fiber will slowly release to the fiber surface, finally improving the moisture absorption, quick-drying, one-way moisture conduction and moisture retention effects of the fiber and fabric.

[0023] As a preferred technical solution:

[0024] A moisture-absorbing and quick-drying polypropylene fiber with a gradient structure as described above, the area occupied by the groove structure is 0.5-30% of the fiber surface area, the length of the groove structure is 70-7500 nm, the width is 0.8-10 nm, the aspect ratio is 87.5-2500, and the depth is 1 nm-25 nm. The distribution of the groove structure is relatively random, but the number, length and width of the groove structure can be controlled. The specific control methods are as follows (the viscosities mentioned herein all refer to zero-shear viscosities):

[0025] Internally enriched fibers: The number of groove structures on the fiber surface can be achieved by reducing the zero-shear viscosity of the dispersed phase, increasing the viscosity ratio of the two phases (matrix phase: dispersed phase > 1), and increasing the content of the dispersed phase. The number of groove structures on the fiber surface can be controlled by controlling the zero-shear viscosity ratio of the polymer dispersed phase and the matrix phase. When the viscosity ratio of the two phases (matrix phase: dispersed phase > 1) is larger, in the non-isothermal uniaxial tensile flow field during melt spinning, due to the existence of shear stress and tensile stress, the dispersed phase with high fluidity (i.e., low viscosity) will wrap the matrix phase with low fluidity (i.e., high viscosity). Therefore, outward migration, tensile deformation and coalescence of the dispersed phase occur. When the content of the dispersed phase increases, the number of dispersed phases migrating to the surface increases, so the number of grooves increases. The length of the groove structure on the fiber surface can be achieved by the spinning speed and the draw ratio. The faster the spinning speed and the larger the draw ratio, the longer the length of the groove structure. The width of the groove structure on the fiber surface can be controlled by controlling the content of the dispersed phase and the aperture of the spinneret hole. When the content of the dispersed phase is more and the aperture of the spinneret hole is larger, the coalescence phenomenon of the dispersed phase increases, and the increase in particle size leads to an increase in the width of the groove structure.

[0026] Surface-enriched fibers: The number of groove structures on the fiber surface can be achieved by increasing the molecular weight distribution of the dispersed phase and the content of the dispersed phase. Since the dispersed phase with a high zero-shear viscosity ratio has a relatively high molecular weight, the dispersed phase with a relatively wide molecular weight distribution contains a small amount of dispersed phase with a relatively low molecular weight, that is, a relatively low viscosity. These dispersed phases with a relatively low viscosity migrate to the fiber surface. When the molecular weight distribution of the dispersed phase increases and the content of the dispersed phase increases, the number of dispersed phases with a relatively low molecular weight increases, so the number of grooves on the fiber surface can be increased. The length of the groove structure on the fiber surface can be achieved by the spinning speed and the draw ratio. The faster the spinning speed and the larger the draw ratio, the greater the degree of droplet breakage and microfibrillation of the dispersed phase, and the longer the length of the groove structure. The width of the groove structure on the fiber surface can be controlled by controlling the molecular weight distribution of the dispersed phase, the content of the dispersed phase and the aperture of the spinneret hole. When the aperture of the spinneret hole is larger, the molecular weight distribution of the dispersed phase becomes wider and the content increases, the degree of droplet breakage and microfibrillation of the dispersed phase on the fiber surface weakens, so the width of the groove structure can be increased; when the aperture of the spinneret hole is smaller, the molecular weight distribution of the dispersed phase becomes narrower and the content decreases, the degree of droplet breakage and microfibrillation of the dispersed phase on the fiber surface increases, so the width of the groove structure can be decreased.

[0027] A moisture-absorbing and quick-drying polypropylene fiber with a gradient structure as described above, where the hydrophilic polymer is polyamide 6 (PA6).

[0028] For the surface-enriched gradient structure of the moisture-absorbing and quick-drying polypropylene fiber with a gradient structure as described above, the fiber cross-section is sequentially divided into concentric circular regions I, annular regions II, annular regions III, and annular regions IV from the center outwards. The particle size ranges of the dispersed phase in circular region I, annular region II, annular region III, and annular region IV are 30 - 600 nm, 50 - 1100 nm, 100 - 2500 nm, and 200 - 2700 nm respectively. The areas occupied by the dispersed phase in circular region I, annular region II, annular region III, and annular region IV are 1 - 2.5%, 2.2 - 3.5%, 2.5 - 6%, and 3.5 - 10% respectively. The enrichment degree is represented by the percentage of the hydrophilic dispersed phase in this region. If the proportion of the dispersed phase in this region is higher (i.e., the area proportion of the dispersed phase in the corresponding region is larger), it indicates a greater enrichment degree.

[0029] For the internal-enriched gradient structure, the fiber cross-section is sequentially divided into concentric circular regions I, annular regions II, annular regions III, and annular regions IV from the center outwards. The particle size ranges of the dispersed phase in circular region I, annular region II, annular region III, and annular region IV are 200 - 2700 nm, 150 - 2300 nm, 100 - 1800 nm, and 50 - 1500 nm respectively. The areas occupied by the dispersed phase in circular region I, annular region II, annular region III, and annular region IV are 1.6 - 10%, 1 - 8%, 0.5 - 5%, and 0.1 - 4% respectively.

[0030] For the surface-enriched gradient structure of the moisture-absorbing and quick-drying polypropylene fiber with a gradient structure as described above, the instantaneous water contact angle of the fabric prepared from the moisture-absorbing and quick-drying polypropylene fiber with a gradient structure is 15° - 55º, the water droplet diffusion time is 0.12 - 1.17 s, the wicking height is 10.5 - 12.6 cm, and the drying rate is 0.504 - 0.522 g / h.

[0031] For the internal-enriched gradient structure, the instantaneous water contact angle of the fabric prepared from the moisture-absorbing and quick-drying polypropylene fiber with a gradient structure is 72° - 105º, the water droplet diffusion time is 0.33 - 8.2 s, the wicking height is 7.5 - 11.6 cm, the drying rate is 0.37 - 0.521 g / h, and the unidirectional moisture conduction coefficient is 20.12 - 479.23%.

[0032] The present invention also provides a method for preparing a moisture-absorbing and quick-drying polypropylene fiber with a gradient structure, which is used to prepare a moisture-absorbing and quick-drying polypropylene fiber with a gradient structure as described in any one of the above. After the matrix phase and the dispersed phase are mixed to obtain a mixture, melt blending and spinning are carried out to obtain a moisture-absorbing and quick-drying polypropylene fiber with a gradient structure;

[0033] When the gradient structure is a surface enrichment type gradient structure, the zero-shear viscosity ratio of the matrix phase to the dispersed phase is 1.429 - 5.667:1, the content of the dispersed phase in the mixture is 10 - 20 wt%, the molecular weight distribution index of the dispersed phase is 4.1 - 4.5, the relaxation time of the dispersed phase is 2.1 - 4.5 s, and the relaxation time of the matrix phase is 4.7 - 8.3 s;

[0034] When the gradient structure is an internal enrichment type gradient structure, the zero-shear viscosity ratio of the matrix phase to the dispersed phase is 1:1.3 - 6, the content of the dispersed phase in the mixture is 5 - 25 wt%, the molecular weight distribution index of the dispersed phase is 4.1 - 4.5, the relaxation time of the dispersed phase is 2.1 - 7.4 s, and the relaxation time of the matrix phase is 0.5 - 0.8 s.

[0035] By regulating the morphology and distribution of the hydrophilic dispersed phase through melt blending and spinning, a gradient structure change in the enrichment degree of the dispersed phase is achieved, thereby improving the fiber properties. The formation of the gradient structure is caused by droplet migration, breakup, and coalescence.

[0036] In the droplet migration theory: During the melt spinning process, when the polymer flows in the gap of the screw, due to the existence of the stress field, a gradient shear stress is formed, resulting in a velocity gradient of the polymer. Different polymers have different relaxation times (the motion characteristics of polymer chains) during this process. When the polymer relaxation time is short, it indicates that the polymer chain segments move faster, and the chain segments are more likely to migrate to the region with a larger shear stress; when the polymer relaxation time is long, it means that the polymer chain segments move slower, and the chain segments are retained in the region with a lower shear stress. As the polymer molecular weight increases, the zero-shear viscosity of the polymer increases and the relaxation time increases, so it is more difficult to migrate to the region with a larger stress. In the pipe, the polymer is restricted by the pipe wall, and the flow velocity gradually increases from the pipe wall to the center of the pipe. According to Newton's law of internal friction, the shear stress is proportional to the velocity gradient. At the pipe wall, since the flow velocity is close to zero and the velocity gradient is the largest, the shear stress is the largest. Therefore, polymers with a higher molecular weight or a larger viscosity tend to flow towards the center, and polymers with a smaller viscosity or a lower molecular weight tend to flow towards the outside, based on which a surface-enriched gradient structure or an internal-enriched gradient structure is formed. The dispersed phase with a small amount of high molecular weight, that is, high viscosity, has a slower migration rate due to its longer relaxation time, so it will be retained in the low-stress region, that is, the inner side of the surface-enriched gradient structure; when the molecular weight distribution of the dispersed phase polymer is wide, the dispersed phase with a small amount of low molecular weight, that is, low viscosity, has a faster migration rate due to its shorter relaxation time, so it will migrate to the high-stress region, that is, the outside of the internal-enriched gradient structure. By regulating the above mechanism and polymer parameters, it is possible to regulate the area ratio (content) of the dispersed phase polymer to the matrix phase polymer in different regions of the fiber cross-section. The theory of the particle size and enrichment degree of the gradient structure dispersed phase is caused by the breakup, migration, and coalescence of droplets. Due to the incompatible characteristics of the dispersed phase and the matrix phase, during the spinning process, the droplets have different flow rates and flow directions. As the content of the dispersed phase polymer in the matrix increases, the dispersed phase migrates to different positions (when the zero-shear viscosity is high, it migrates towards the inside of the fiber; when the zero-shear viscosity is low, it migrates towards the outside of the fiber). During the migration process, the collision frequency increases and the coalescence probability increases, so the size of the dispersed phase increases accordingly, forming a gradient distribution of particle sizes. At the same time, the breakup mechanism of the fiber is based on Taylor's droplet deformation theory to propose the Taylor number (Ca), also known as the capillary number. The capillary number is proportional to the zero-shear viscosity, shear rate, and droplet radius of the surrounding fluid, and inversely proportional to the interfacial tension between the droplet and the surrounding fluid. When the capillary number is small, the interfacial tension dominates, and the droplet tends to maintain a spherical shape; as the capillary number increases, the influence of the viscous force gradually increases, and the droplet begins to deform. According to Taylor's capillary theory, when the dispersed phase deforms in a simple shear flow field, when the viscous force exceeds a critical value (the viscous force dominates compared to the interfacial tension, Ca > Ca c), the droplet will break until the interfacial tension is sufficient to maintain the balance with the viscous force. According to the formula summarized by Grace, the critical capillary number Ca of the dispersed phase in the shear flow field c Relationship with the zero-shear viscosity ratio P of the two phases:

[0037] ;

[0038] Therefore, droplet breakup can be divided into three mechanisms: stepwise droplet breakup, fiber transient breakup, and edge breakup. The stepwise droplet breakup mechanism occurs when the capillary number is small. When the flow field strength increases and the Ca of the system exceeds Ca c , the droplet splits into two, breaking into two smaller sub-droplets of equal volume. Huneault proposed using the reduced capillary number (Ca* = Ca / Ca c ) as a criterion to judge whether the droplet deforms or breaks and what kind of deformation mechanism occurs:

[0039] (1) When Ca* < 0.1, there is no deformation;

[0040] (2) When 0.1 ≤ Ca* < 1, deformation occurs without breakup. At this time, the droplet volume remains unchanged and the shape changes;

[0041] (3) When 1 ≤ Ca* < 4, deformation occurs and stepwise droplet breakup occurs, breaking into two smaller sub-droplets of equal volume;

[0042] (4) When Ca* ≥ 4, the droplet and the matrix phase undergo affine deformation together, following the fiber transient breakup and edge breakup mechanisms to form stable continuous microfibers.

[0043] Since when the zero-shear viscosity ratio P = 1, Ca cThe minimum, so a small and uniform dispersed phase morphology can be obtained by matching the zero shear viscosity ratio. However, step-by-step rupture rarely occurs in the actual blending process, and the step-by-step rupture mechanism also lacks consideration of the rupture time. The fiber transient rupture is closer to the rupture of the dispersed phase in actual conditions. When the blended polymer melt passes through the capillary, due to the convergence of the inlet area, the polymer molecular chain is simultaneously subjected to tensile and shear stresses, and the dispersed phase with a smaller molecular weight or less content will be deformed into an ellipsoid, rod, and microfibril. When the deformed dispersed phase flows through the capillary, when the corresponding microrheological behavior conditions are met, the dispersed phase will deform and rupture. After the polymer blend is extruded from the capillary, the microrheological behavior of the dispersed phase is mainly affected by tensile stress. Since the dispersed phase presents a certain molecular weight distribution, the dispersed phase with a smaller molecular weight (smaller zero shear viscosity) is retained in the area with a smaller flow rate, presenting a microfibril shape in the fiber. These theoretical foundations provide a theoretical basis for the realization of gradient structure in fibers. Therefore, the dispersed phase deforms to varying degrees along the radial direction, which is the main reason why the PA6 dispersed phase presents a gradient distribution morphology along the radial direction.

[0044] As the preferred technical solution:

[0045] The method for preparing a moisture-absorbing quick-drying polypropylene fiber with a gradient structure as described above, wherein the number average molecular weight of the dispersed phase is 80,000 to 100,000 g·mol -1 .

[0046] The method for preparing a moisture-absorbing quick-drying polypropylene fiber with a gradient structure as described above, wherein the number average molecular weight of the matrix phase is 75300-121000 g·mol -1 , the molecular weight distribution index is 1.7~4.5.

[0047] As described above, the preparation method of the moisture-absorbing quick-drying polypropylene fiber with a gradient structure, the process parameters of the melt blending spinning are: screw temperature 235~270℃, head, connecting pipe and box temperature 250~270℃, spinning speed 1000~1200m / min.

[0048] The preparation method of the moisture-absorbing quick-drying polypropylene fiber with a gradient structure as described above is characterized in that after spinning, heat stretching and shaping are performed, the stretching temperature is 50-120° C., and the stretching multiple is 2-4.

[0049] Beneficial effects:

[0050] (1) The present invention discloses a method for preparing a moisture-absorbing and quick-drying polypropylene fiber with a gradient structure, which uses polypropylene with excellent moisture conduction properties and nylon 6 with excellent moisture absorption properties as raw materials, and constructs a gradient structure inside the fiber through a melt spinning process during the processing, thereby achieving good moisture absorption and quick-drying properties and unidirectional moisture conduction properties of the polypropylene fiber.

[0051] (2) The preparation method of a moisture-absorbing and quick-drying polypropylene fiber with a gradient structure according to the present invention can achieve gradient moisture conduction through the fibers prepared by this method, preventing the phenomenon that the "core" part in the core-shell fiber has insufficient water suction force and the water cannot break through the "shell".

[0052] (3) The moisture-absorbing and quick-drying polypropylene fiber with a gradient structure according to the present invention has a groove structure on the surface, which can increase the specific surface area of the fiber, strengthen the capillary phenomenon, and further increase the moisture-absorbing and quick-drying performance of the fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 It is a cross-sectional view of a surface-enriched fiber;

[0054] Figure 2 It is the moisture transmission path of the surface-enriched fiber;

[0055] Figure 3 It is a cross-sectional view of an internal-enriched fiber;

[0056] Figure 4 It is the moisture transmission path and unidirectional moisture conduction mechanism diagram of the internal-enriched fiber;

[0057] Figure 5 It is a fiber cross-sectional area division diagram;

[0058] Figure 6 It is the surface SEM picture of the moisture-absorbing and quick-drying polypropylene fiber of Examples 1 to 12;

[0059] Figure 7 It is the cross-sectional SEM comparison diagram of the internal-enriched moisture-absorbing and quick-drying polypropylene fiber of Examples 5, 7, and 8;

[0060] Figure 8 It is the cross-sectional binary analysis comparison diagram of the internal-enriched moisture-absorbing and quick-drying polypropylene fiber of Examples 5, 7, and 8;

[0061] Figure 9 It is the cross-sectional SEM comparison diagram of the moisture-absorbing and quick-drying polypropylene fiber of Examples 5, 11, and 12;

[0062] Figure 10 It is the cross-sectional binary analysis comparison diagram of the moisture-absorbing and quick-drying polypropylene fiber of Examples 5, 11, and 12;

[0063] Figure 11 It is for polypropylene (PP 1 ) fiber and the moisture evaporation situation of the moisture-absorbing and quick-drying polypropylene fiber of Examples 2 to 8 in an environment with a relative humidity of 40%;

[0064] Figure 12 It is the one-way moisture conduction test curve of the internally enriched moisture-absorbing and quick-drying polypropylene fiber of Example 8. Specific embodiments

[0065] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0066] The test methods for the performance indicators in the embodiments and comparative examples of the present invention are as follows:

[0067] Tensile strength and elongation at break: The mechanical properties of the fiber were tested using an XL-2 type filament yarn strength and elongation tester. Apply a pre-tension of 5.0 cN at the bottom end of the fiber, set the length between the two clamps to 250 mm, and set the tensile speed to 500 mm / min. Take the average value of 10 measurement results for each sample; among them, the coefficient of variation refers to the error range of each test.

[0068] SEM image: The morphological structure of the obtained fiber was observed using a scanning electron microscope (SEM, SU8010 type, Hitachi).

[0069] Coefficient of friction: The coefficient of friction of chemical fibers was tested using an XCF type fiber friction coefficient tester in accordance with the group standard TCSTM 00522-2022.

[0070] Moisture regain: The moisture regain of the fiber and fabric was tested in accordance with the national standard GB / T 9994-2018.

[0071] Using the SGA598 full-automatic rapier sampling loom of Jiangyin Tongyuan Textile Machinery Co., Ltd., a single-layer machine-made fabric was prepared using the moisture-absorbing and quick-drying polypropylene fiber with a gradient structure. In the fabric structure, the warp and weft yarns both use the same type of fiber. The warp density is 160 ends per inch, and the weft density is 210 ends per inch. A plain fabric with a length of 200 ± 5 mm, a width of 200 ± 5 mm, and a thickness of 0.91 ± 0.05 mm was obtained to test its water contact angle, moisture absorption and quick-drying property, and one-way moisture conduction property.

[0072] Water contact angle: Analyzed using a water contact angle tester (model JC2000D). Place the fabric in the center of the platform, and place a syringe filled with distilled water on the upper shelf. Take a picture of the moment when the distilled water contacts the microfiltration membrane, which is the main basis for calculating the water contact angle. Drop 5 μL of liquid on the surface of the specimen, test the contact angle between the liquid drop and the sample surface, and randomly take at least 6 different position points on the sample for testing, and finally take the average value.

[0073] Water droplet diffusion time, drying rate, wicking height, water absorption rate: Tested in accordance with the national standard GB / T 21655.1-2023.

[0074] Unidirectional moisture permeability coefficient: In accordance with the standard AATCC TM-195, use a liquid moisture management tester (Model M290, SDLAtlas, USA) to test the unidirectional moisture permeability performance of the specimen at 120 s. Place the specimen horizontally between the upper and lower resistance sensors, and drop 0.2 g of water droplets at the center of the specimen. When the water conducts through the sample, the resistance changes on the upper and lower surfaces of the specimen will be recorded and converted into relative moisture content according to the algorithm. This test will provide a quantitative unidirectional moisture permeability index (R) to characterize the unidirectional liquid conduction performance of the specimen, which is defined as the difference in the cumulative relative moisture content between the upper and lower surfaces of the specimen:

[0075] ;

[0076] where T is the test time, U t and U b are the real-time relative moisture contents of the upper and lower surfaces of the specimen, respectively.

[0077] PP in the embodiment of the present invention 1 / PA6 1 -5% of the PP 1 / PA6 1 is the blend chips of PP 1 and PA6 1 , 5% is the mass fraction of the dispersed phase in the mixture; the numbers in PP 0 , PP 1 , PP 2 , PP 3 are used to distinguish four kinds of PP, and the numbers in PA6 1 , PA6 2 , PA6 3 are used to distinguish three kinds of PA6.

[0078] Example 1

[0079] A preparation method of a moisture-absorbing and quick-drying polypropylene fiber with an internal enrichment type gradient structure, the specific steps are as follows:

[0080] (1) Preparation of raw materials:

[0081] Dispersed phase: PA6 1 , with a number average molecular weight of 82000 g·mol -1 , a molecular weight distribution index of 4.1, a zero shear viscosity of 150 Pa·s, and a melt index of 38 g·10 min -1 ;

[0082] Matrix phase: PP 0 , with a number-average molecular weight of 81,200 g·mol -1 , a molecular weight distribution index of 2.2, a zero-shear viscosity of 115 Pa·s, and a melt index of 30 g / 10 min -1 ; The interfacial tension between the matrix phase and the dispersed phase is 9 mN·m -1 ;

[0083] (2) Dry the matrix phase and the dispersed phase separately in a rotary vacuum oven at 120 °C for 24 h to remove moisture;

[0084] (3) Mix the matrix phase and the dispersed phase treated in step (2) to obtain a mixture, and then perform melt blending and spinning to produce a moisture-absorbing and quick-drying polypropylene fiber with an internal enrichment-type gradient structure; the content of the dispersed phase in the mixture is 5 wt%;

[0085] The process parameters for melt blending and spinning are as follows: the temperatures of the first, second, third, sixth, and fifth zones of the screw are 235 °C, 250 °C, 260 °C, 260 °C, and 260 °C respectively, the temperatures of the head, the adapter, and the housing are 260 °C, and the spinning speed is 1200 m / min;

[0086] (4) After spinning, perform hot drawing and setting using GR1 and GR2 hot rolls. The temperature of GR1 is 50 °C, the speed of GR1 is 300 m / min, the temperature of GR2 is 90 °C, the speed of GR2 is 1200 m / min, and the draw ratio is 4.

[0087] The finally obtained moisture-absorbing and quick-drying polypropylene fiber (PP 0 / PA6 1 -5%) has a groove structure on its surface. The area occupied by the groove structure is 0.5% of the fiber surface area. The length of the groove structure is 70 nm, the width is 0.8 nm, the length-width ratio is 87.5, and the depth is 1 nm; the relaxation time of the dispersed phase is 2.1 s, and the relaxation time of the matrix phase is 0.8 s; the fiber cross-section is sequentially divided into concentric circular regions I, annular regions II, annular regions III, and annular regions IV from the center outwards. The particle size ranges of the dispersed phase in circular region I, annular region II, annular region III, and annular region IV are 250 - 850 nm, 200 - 750 nm, 150 - 650 nm, and 80 - 450 nm respectively. The areas occupied by the dispersed phase in circular region I, annular region II, annular region III, and annular region IV are 1.6%, 1.4%, 1.2%, and 0.8% respectively; the instantaneous water contact angle of the fabric made of the moisture-absorbing and quick-drying polypropylene fiber with an internal enrichment-type gradient structure is 105º.

[0088] Example 2

[0089] A preparation method of a moisture-absorbing and quick-drying polypropylene fiber with an internal enrichment-type gradient structure is as follows:

[0090] (1)Preparation of raw materials:

[0091] Dispersed phase: PA6 1 , with a number-average molecular weight of 82000 g·mol -1 , a molecular weight distribution index of 4.1, a zero-shear viscosity of 150 Pa·s, and a melt index of 38 g·10 min -1 ;

[0092] Matrix phase: PP 1 , with a number-average molecular weight of 75300 g·mol -1 , a molecular weight distribution index of 1.7, a zero-shear viscosity of 100 Pa·s, and a melt index of 45 g·10 min -1 ; The interfacial tension between the matrix phase and the dispersed phase is 8 mN·m -1 ;

[0093] (2)Dry the matrix phase and the dispersed phase separately in a rotary vacuum oven at 120 °C for 24 h to dry the moisture;

[0094] (3)Mix the matrix phase and the dispersed phase treated in step (2) to obtain a mixture, and then carry out melt blending and spinning to obtain a moisture-absorbing and quick-drying polypropylene fiber with an internal enrichment-type gradient structure; the content of the dispersed phase in the mixture is 5 wt%;

[0095] The process parameters of melt blending and spinning are: the temperatures of the screw zones I, II, III, VI, and V are 235 °C, 250 °C, 260 °C, 260 °C, and 260 °C respectively, the temperatures of the head, the adapter, and the housing are 260 °C, and the spinning speed is 1200 m / min;

[0096] (4)After spinning, use GR1 and GR2 hot rollers for hot drawing and setting. The temperature of GR1 is 50 °C, the speed of GR1 is 300 m / min, the temperature of GR2 is 90 °C, the speed of GR2 is 1200 m / min, and the drawing ratio is 4.

[0097] Finally, the obtained moisture-absorbing and quick-drying polypropylene fiber with an internal enrichment-type gradient structure (PP 1 / PA6 1The surface of the (PP / PA6 - 5%) has a groove structure. The area occupied by the groove structure is 1% of the fiber surface area. The length of the groove structure is 100 nm, the width is 1 nm, the aspect ratio is 100, and the depth is 3 nm. The relaxation time of the dispersed phase is 2.1 s, and the relaxation time of the matrix phase is 0.5 s. The fiber cross - section is sequentially divided into concentric circular regions Ⅰ, annular regions Ⅱ, annular regions Ⅲ, and annular regions Ⅳ from the center outwards. The particle size ranges of the dispersed phase in circular region Ⅰ, annular region Ⅱ, annular region Ⅲ, and annular region Ⅳ are 200 - 800 nm, 150 - 700 nm, 100 - 600 nm, and 50 - 300 nm respectively. The areas occupied by the dispersed phase in circular region Ⅰ, annular region Ⅱ, annular region Ⅲ, and annular region Ⅳ are 2.5%, 1%, 0.5%, and 0.1% respectively. The instantaneous water contact angle of the fabric made of the moisture - absorbent and quick - drying polypropylene fiber with an internal enrichment - type gradient structure is 100º.

[0098] Example 3

[0099] A preparation method of a moisture - absorbent and quick - drying polypropylene fiber with an internal enrichment - type gradient structure is basically the same as that of Example 2, except that the content of the dispersed phase in the mixture in step (3) is 10 wt%.

[0100] The finally obtained moisture - absorbent and quick - drying polypropylene fiber (PP 1 / PA6 1 -10%) has a groove structure on its surface. The area occupied by the groove structure is 5% of the fiber surface area. The length of the groove structure is 500 nm, the width is 1.5 nm, the aspect ratio is 333, and the depth is 3 nm. The relaxation time of the dispersed phase is 2.1 s, and the relaxation time of the matrix phase is 0.5 s. The fiber cross - section is sequentially divided into concentric circular regions Ⅰ, annular regions Ⅱ, annular regions Ⅲ, and annular regions Ⅳ from the center outwards. The particle size ranges of the dispersed phase in circular region Ⅰ, annular region Ⅱ, annular region Ⅲ, and annular region Ⅳ are 250 - 1000 nm, 170 - 950 nm, 100 - 1100 nm, and 60 - 800 nm respectively. The areas occupied by the dispersed phase in circular region Ⅰ, annular region Ⅱ, annular region Ⅲ, and annular region Ⅳ are 3%, 2%, 3%, and 2% respectively. The instantaneous water contact angle of the fabric made of the moisture - absorbent and quick - drying polypropylene fiber with an internal enrichment - type gradient structure is 93º.

[0101] Example 4

[0102] A preparation method of a moisture - absorbent and quick - drying polypropylene fiber with an internal enrichment - type gradient structure is basically the same as that of Example 2, except that the content of the dispersed phase in the mixture in step (3) is 15 wt%.

[0103] The finally obtained moisture - absorbent and quick - drying polypropylene fiber (PP1 / PA6 1 -15%) has a groove structure on its surface. The area occupied by the groove structure is 10% of the fiber surface area. The length of the groove structure is 2000 nm, the width is 4 nm, the length-width ratio is 500, and the depth is 10 nm. The relaxation time of the dispersed phase is 2.1 s, and the relaxation time of the matrix phase is 0.5 s. The fiber cross-section is sequentially divided into concentric circular regions I, annular regions II, annular regions III, and annular regions IV from the center outwards. The particle size ranges of the dispersed phase in circular region I, annular region II, annular region III, and annular region IV are 500 - 1700 nm, 250 - 1600 nm, 240 - 1500 nm, and 200 - 1400 nm respectively. The areas occupied by the dispersed phase in circular region I, annular region II, annular region III, and annular region IV are 6%, 4%, 3%, and 2% respectively. The instantaneous water contact angle of the fabric made of the moisture-absorbing and quick-drying polypropylene fiber with an internally enriched gradient structure is 88º.

[0104] Example 5

[0105] A preparation method of a moisture-absorbing and quick-drying polypropylene fiber with an internally enriched gradient structure is basically the same as that of Example 2, except that the content of the dispersed phase in the mixture in step (3) is 20 wt%.

[0106] The finally prepared moisture-absorbing and quick-drying polypropylene fiber (PP 1 / PA6 1 -20%) has a groove structure on its surface. The area occupied by the groove structure is 15% of the fiber surface area. The length of the groove structure is 3000 nm, the width is 8 nm, the length-width ratio is 375, and the depth is 20 nm. The relaxation time of the dispersed phase is 2.1 s, and the relaxation time of the matrix phase is 0.5 s. The fiber cross-section is sequentially divided into concentric circular regions I, annular regions II, annular regions III, and annular regions IV from the center outwards. The particle size ranges of the dispersed phase in circular region I, annular region II, annular region III, and annular region IV are 300 - 2000 nm, 290 - 1800 nm, 250 - 1750 nm, and 150 - 1250 nm respectively. The areas occupied by the dispersed phase in circular region I, annular region II, annular region III, and annular region IV are 7%, 5%, 4.5%, and 3.5% respectively. The instantaneous water contact angle of the fabric made of the moisture-absorbing and quick-drying polypropylene fiber with an internally enriched gradient structure is 82º.

[0107] Example 6

[0108] A preparation method of a moisture-absorbing and quick-drying polypropylene fiber with an internally enriched gradient structure is basically the same as that of Example 2, except that the content of the dispersed phase in the mixture in step (3) is 25 wt%.

[0109] Finally, the obtained moisture-absorbing and quick-drying polypropylene fiber (PP 1 / PA6 1 -25%) with an internal enrichment-type gradient structure has a groove structure on its surface. The area occupied by the groove structure is 20% of the fiber surface area. The length of the groove structure is 5000 nm, the width is 2 nm, the aspect ratio is 2500, and the depth is 25 nm. The relaxation time of the dispersed phase is 2.1 s, and the relaxation time of the matrix phase is 0.5 s. The cross-section of the fiber is sequentially divided into concentric circular regions Ⅰ, annular regions Ⅱ, annular regions Ⅲ, and annular regions Ⅳ from the center outwards. The particle size ranges of the dispersed phase in circular region Ⅰ, annular region Ⅱ, annular region Ⅲ, and annular region Ⅳ are 350 - 2200 nm, 300 - 2000 nm, 220 - 1800 nm, and 200 - 1500 nm respectively. The areas occupied by the dispersed phase in circular region Ⅰ, annular region Ⅱ, annular region Ⅲ, and annular region Ⅳ are 9%, 7%, 5%, and 4% respectively. The instantaneous water contact angle of the fabric made of the moisture-absorbing and quick-drying polypropylene fiber with an internal enrichment-type gradient structure is 79º.

[0110] Example 7

[0111] A preparation method of a moisture-absorbing and quick-drying polypropylene fiber with an internal enrichment-type gradient structure is as follows:

[0112] (1) Preparation of raw materials:

[0113] Dispersed phase: PA6 2 , with a number average molecular weight of 82000 g·mol -1 , a molecular weight distribution index of 4.5, a zero-shear viscosity of 350 Pa·s, and a melt index of 24 g·10 min -1 ;

[0114] Matrix phase: PP 1 , with a number average molecular weight of 75300 g·mol -1 , a molecular weight distribution index of 1.7, a zero-shear viscosity of 100 Pa·s, and a melt index of 45 g·10 min -1 ; The interfacial tension between the matrix phase and the dispersed phase is 12 mN·m -1 ;

[0115] (2) The matrix phase and the dispersed phase are respectively dried in a rotary vacuum oven at 120 °C for 24 h to dry the moisture;

[0116] (3) After mixing the matrix phase and the dispersed phase treated in step (2) to obtain a mixture, melt blending and spinning are carried out to obtain a moisture-absorbing and quick-drying polypropylene fiber with an internal enrichment-type gradient structure; the content of the dispersed phase in the mixture is 20 wt%;

[0117] The process parameters of melt blending and spinning are as follows: the temperatures of the first, second, third, fifth, and sixth zones of the screw are 240 °C, 255 °C, 265 °C, 265 °C, and 265 °C respectively, the temperatures of the head, the adapter, and the housing are 265 °C, and the spinning speed is 1200 m / min;

[0118] (4) After spinning, hot drawing and setting are carried out using GR1 and GR2. The temperature of GR1 is 50 °C, the speed of GR1 is 400 m / min, the temperature of GR2 is 100 °C, the speed of GR2 is 1200 m / min, and the draw ratio is 3.

[0119] Finally, the prepared moisture-absorbing and quick-drying polypropylene fiber (PP 1 / PA6 2 -20%) with an internal enrichment type gradient structure has a groove structure on its surface. The area occupied by the groove structure is 10% of the fiber surface area. The length of the groove structure is 2500 nm, the width is 5 nm, the aspect ratio is 500, and the depth is 16 nm; the relaxation time of the dispersed phase is 4.2 s, and the relaxation time of the matrix phase is 0.5 s; the fiber cross-section is successively divided into concentric circular regions I, annular regions II, annular regions III, and annular regions IV from the center outwards. The particle size ranges of the dispersed phase in circular region I, annular region II, annular region III, and annular region IV are 350 - 2500 nm, 250 - 2200 nm, 210 - 1600 nm, and 150 - 1100 nm respectively. The areas occupied by the dispersed phase in circular region I, annular region II, annular region III, and annular region IV are 8%, 7%, 3%, and 2% respectively; the instantaneous water contact angle of the fabric made of the moisture-absorbing and quick-drying polypropylene fiber with an internal enrichment type gradient structure is 75º.

[0120] Example 8

[0121] A preparation method of a moisture-absorbing and quick-drying polypropylene fiber with an internal enrichment type gradient structure comprises the following specific steps:

[0122] (1) Preparation of raw materials:

[0123] Dispersed phase: PA6 3 , with a number average molecular weight of 92400 g·mol -1 , a molecular weight distribution index of 4.2, a zero-shear viscosity of 600 Pa·s, and a melt index of 19 g·10 min -1 ;

[0124] Matrix phase: PP 1 , with a number average molecular weight of 75300 g·mol -1 , a molecular weight distribution index of 1.7, a zero-shear viscosity of 100 Pa·s, and a melt index of 45 g·10 min -1 ; the interfacial tension between the matrix phase and the dispersed phase is 14 mN·m-1 ;

[0125] (2) Drying the matrix phase and the dispersed phase separately in a rotary vacuum oven at 120°C for 24 hours to remove moisture;

[0126] (3) The matrix phase and the dispersed phase treated in step (2) are mixed to obtain a mixture, and then melt-blended and spun to obtain a moisture-absorbing quick-drying polypropylene fiber with an internally enriched gradient structure; the content of the dispersed phase in the mixture is 20wt%;

[0127] The process parameters of melt blending spinning are as follows: the temperatures of screw zone I, zone II, zone III, zone VI, and zone V are 245°C, 260°C, 270°C, 270°C, and 270°C respectively; the temperature of die head, nozzle, and box is 270°C; the spinning speed is 1000m / min;

[0128] (4) After spinning, GR1 and GR2 were used for hot stretching and shaping. The temperature of GR1 was 80°C, the speed of GR1 was 500 m / min, the temperature of GR2 was 120°C, the speed of GR2 was 1000 m / min, and the stretching multiple was 2.

[0129] The final prepared moisture-absorbing quick-drying polypropylene fiber (PP 1 / PA6 3 -20%) has a groove structure on the surface, the area occupied by the groove structure is 8% of the fiber surface area, the length of the groove structure is 1000nm, the width is 2nm, the aspect ratio is 500, and the depth is 10nm; the relaxation time of the dispersed phase is 7.4s, and the relaxation time of the matrix phase is 0.5s; the fiber cross section is divided into concentric circular area I, circular area II, circular area III and circular area IV from the center to the outside, and circular area I, circular area II, circular area III and The particle size ranges of the dispersed phase in the annular region IV are 500-2700nm, 200-2300nm, 100-1200nm and 50-500nm, respectively. The areas occupied by the dispersed phase in the annular region I, annular region II, annular region III and annular region IV are 10%, 8%, 1.5% and 0.5%, respectively. The instantaneous water contact angle of the fabric made of the hygroscopic quick-drying polypropylene fiber with an internal enriched gradient structure is 72°. The unidirectional moisture conduction performance test results are shown in FIG. Figure 12 shown.

[0130] Example 9

[0131] A method for preparing a moisture-absorbing quick-drying polypropylene fiber with a surface-enriched gradient structure, the specific steps are as follows:

[0132] (1) Preparation of raw materials:

[0133] Dispersed phase: PA6 2, the number-average molecular weight is 82000 g·mol -1 , the molecular weight distribution index is 4.5, the zero-shear viscosity is 350 Pa·s, and the melt index is 24 g·10 min -1 ;

[0134] Matrix phase: PP 2 , the number-average molecular weight is 107000 g·mol -1 , the molecular weight distribution index is 4.5, the zero-shear viscosity is 500 Pa·s, and the melt index is 15 g·10 min -1 ; The interfacial tension between the matrix phase and the dispersed phase is 13 mN·m -1 ;

[0135] (2) Dry the matrix phase and the dispersed phase separately in a rotary vacuum oven at 120 °C for 24 h to dry the moisture;

[0136] (3) Mix the matrix phase and the dispersed phase treated in step (2) to obtain a mixture, and then perform melt-blending spinning to obtain a moisture-absorbing and quick-drying polypropylene fiber with a surface-enriched gradient structure; the content of the dispersed phase in the mixture is 10 wt%;

[0137] The process parameters of the melt-blending spinning are: the temperatures of the first, second, third, sixth, and fifth zones of the screw are 240 °C, 255 °C, 265 °C, 265 °C, and 265 °C respectively, the temperatures of the head, the pipe, and the box are 265 °C, and the spinning speed is 1200 m / min;

[0138] (4) After spinning, perform hot drawing and setting with GR1 and GR2. The temperature of GR1 is 50 °C, the speed of GR1 is 400 m / min, the temperature of GR2 is 100 °C, the speed of GR2 is 1200 m / min, and the drawing ratio is 3.

[0139] Finally, a moisture-absorbing and quick-drying polypropylene fiber with a surface-enriched gradient structure (PP 2 / PA6 2The surface of (-10%) has a groove structure. The area occupied by the groove structure is 7% of the fiber surface area. The length of the groove structure is 3000 nm, the width is 3 nm, the length-width ratio is 1000, and the depth is 10 nm. The relaxation time of the dispersed phase is 4.5 s, and the relaxation time of the matrix phase is 4.7 s. The cross-section of the fiber is sequentially divided into concentric circular regions I, circular ring regions II, circular ring regions III, and circular ring regions IV from the center outwards. The particle size ranges of the dispersed phase in circular region I, circular ring regions II, circular ring regions III, and circular ring regions IV are 30-400 nm, 50-800 nm, 100-1200 nm, and 200-2000 nm respectively. The areas occupied by the dispersed phase in circular region I, circular ring regions II, circular ring regions III, and circular ring regions IV are 1.8%, 2.2%, 2.5%, and 3.5% respectively. The instantaneous water contact angle of the fabric made of the moisture-absorbing and quick-drying polypropylene fiber with a surface-enriched gradient structure is 55º.

[0140] Example 10

[0141] A preparation method of a moisture-absorbing and quick-drying polypropylene fiber with a surface-enriched gradient structure comprises the following specific steps:

[0142] (1) Preparation of raw materials:

[0143] Dispersed phase: PA6 1 , with a number average molecular weight of 82000 g·mol -1 , a molecular weight distribution index of 4.1, a zero shear viscosity of 150 Pa·s, and a melt index of 38 g·10 min -1 ;

[0144] Matrix phase: PP 2 , with a number average molecular weight of 107000 g·mol -1 , a molecular weight distribution index of 4.5, a zero shear viscosity of 500 Pa·s, and a melt index of 15 g·10 min -1 ; The interfacial tension between the matrix phase and the dispersed phase is 11 mN·m -1 ;

[0145] (2) Respectively drying the matrix phase and the dispersed phase in a rotary vacuum oven at 120 °C for 24 h to dry the moisture;

[0146] (3) Mixing the matrix phase and the dispersed phase treated in step (2) to obtain a mixture, and then performing melt-blending spinning to produce a moisture-absorbing and quick-drying polypropylene fiber with a surface-enriched gradient structure; the content of the dispersed phase in the mixture is 15 wt%;

[0147] The process parameters of melt blending and spinning are as follows: the temperatures of the screw zones I, II, III, VI, and V are 240 °C, 255 °C, 265 °C, 265 °C, and 265 °C respectively, the temperatures of the head, nozzle, and housing are 265 °C, and the spinning speed is 1200 m / min;

[0148] (4) After spinning, hot drawing and setting are carried out using GR1 and GR2. The temperature of GR1 is 50 °C, the speed of GR1 is 400 m / min, the temperature of GR2 is 100 °C, the speed of GR2 is 1200 m / min, and the draw ratio is 3.

[0149] Finally, the moisture-absorbing and quick-drying polypropylene fiber (PP 2 / PA6 1 -15%) with a surface-enriched gradient structure is obtained. The surface has a groove structure. The area occupied by the groove structure is 16% of the fiber surface area. The length of the groove structure is 5000 nm, the width is 3.5 nm, the aspect ratio is 1428, and the depth is 25 nm; the relaxation time of the dispersed phase is 2.1 s, and the relaxation time of the matrix phase is 4.7 s; the fiber cross-section is sequentially divided into concentric circular regions I, annular region II, annular region III, and annular region IV from the center outwards. The particle size ranges of the dispersed phase in circular region I, annular region II, annular region III, and annular region IV are 40 - 500 nm, 55 - 850 nm, 120 - 1800 nm, and 250 - 2300 nm respectively. The areas occupied by the dispersed phase in circular region I, annular region II, annular region III, and annular region IV are 2%, 3%, 4%, and 6% respectively; the instantaneous water contact angle of the fabric made of the moisture-absorbing and quick-drying polypropylene fiber with a surface-enriched gradient structure is 40º.

[0150] Example 11

[0151] A preparation method of a moisture-absorbing and quick-drying polypropylene fiber with a surface-enriched gradient structure is as follows:

[0152] (1) Preparation of raw materials:

[0153] Dispersed phase: PA6 1 , with a number-average molecular weight of 82000 g·mol -1 , a molecular weight distribution index of 4.1, a zero-shear viscosity of 150 Pa·s, and a melt index of 38 g·10 min -1 ;

[0154] Matrix phase: PP 2 , with a number-average molecular weight of 107000 g·mol -1 , a molecular weight distribution index of 4.5, a zero-shear viscosity of 500 Pa·s, and a melt index of 15 g·10 min -1 ; the interfacial tension between the matrix phase and the dispersed phase is 11 mN·m-1 ;

[0155] (2) Dry the matrix phase and the dispersed phase separately in a rotary vacuum oven at 120 °C for 24 h to remove moisture.

[0156] (3) Mix the matrix phase and the dispersed phase treated in step (2) to obtain a mixture, and then conduct melt blending and spinning to prepare moisture-absorbing and quick-drying polypropylene fibers with a surface-enriched gradient structure; the content of the dispersed phase in the mixture is 20 wt%.

[0157] The process parameters of melt blending and spinning are as follows: the temperatures of the first, second, third, sixth, and fifth zones of the screw are 240 °C, 255 °C, 265 °C, 265 °C, and 265 °C respectively, the temperatures of the head, the adapter, and the housing are 265 °C, and the spinning speed is 1200 m / min.

[0158] (4) After spinning, perform hot drawing and setting with GR1 and GR2. The temperature of GR1 is 50 °C, the speed of GR1 is 400 m / min, the temperature of GR2 is 100 °C, the speed of GR2 is 1200 m / min, and the draw ratio is 3.

[0159] The finally prepared moisture-absorbing and quick-drying polypropylene fibers (PP 2 / PA6 1 -20%) have a groove structure on the surface. The area occupied by the groove structure is 20% of the fiber surface area. The length of the groove structure is 6000 nm, the width is 4 nm, the aspect ratio is 1500, and the depth is 20 nm; the relaxation time of the dispersed phase is 2.1 s, and the relaxation time of the matrix phase is 4.7 s; the cross-section of the fiber is sequentially divided into concentric circular regions I, annular region II, annular region III, and annular region IV from the center outwards. The particle size ranges of the dispersed phase in circular region I, annular region II, annular region III, and annular region IV are 50 - 600 nm, 60 - 1000 nm, 150 - 2400 nm, and 300 - 2600 nm respectively, and the areas occupied by the dispersed phase in circular region I, annular region II, annular region III, and annular region IV are 2.5%, 3.5%, 6%, and 8% respectively; the instantaneous water contact angle of the fabric made of the moisture-absorbing and quick-drying polypropylene fibers with a surface-enriched gradient structure is 25º.

[0160] Example 12

[0161] A preparation method of moisture-absorbing and quick-drying polypropylene fibers with a surface-enriched gradient structure, the specific steps are as follows:

[0162] (1) Preparation of raw materials:

[0163] Dispersed phase: PA6 1 , with a number average molecular weight of 82000 g·mol -1, molecular weight distribution index is 4.1, zero shear viscosity is 150 Pa·s, and melt index is 38g·10min -1 ;

[0164] Matrix phase: PP 3 , the number average molecular weight is 121000 g·mol -1 , molecular weight distribution index is 3.4, zero shear viscosity is 850Pa·s, melt index is 4g·10min -1 ; The interfacial tension between the matrix phase and the dispersed phase is 17mN·m -1 ;

[0165] (2) Drying the matrix phase and the dispersed phase separately in a rotary vacuum oven at 120°C for 24 hours to remove moisture;

[0166] (3) The matrix phase and the dispersed phase treated in step (2) are mixed to obtain a mixture, and then melt-blended and spun to obtain a moisture-absorbing quick-drying polypropylene fiber with an internally enriched gradient structure; the content of the dispersed phase in the mixture is 20wt%;

[0167] The process parameters of melt blending spinning are as follows: the temperatures of screw zone I, zone II, zone III, zone VI, and zone V are 250°C, 260°C, 270°C, 270°C, and 270°C respectively; the temperature of die head, pipe and box is 270°C; the spinning speed is 1000m / min;

[0168] (4) After spinning, GR1 and GR2 were used for hot stretching and shaping. The temperature of GR1 was 80°C, the speed of GR1 was 500 m / min, the temperature of GR2 was 120°C, the speed of GR2 was 1000 m / min, and the stretching multiple was 2.

[0169] The final prepared moisture-absorbing quick-drying polypropylene fiber (PP 3 / PA6 1The surface of the (-20%) has a groove structure, and the area occupied by the groove structure is 30% of the fiber surface area. The length of the groove structure is 7500 nm, the width is 10 nm, the aspect ratio is 750, and the depth is 25 nm. The relaxation time of the dispersed phase is 2.1 s, and the relaxation time of the matrix phase is 8.3 s. The cross-section of the fiber is sequentially divided into concentric circular regions I, annular regions II, annular regions III, and annular regions IV from the center outwards. The particle size ranges of the dispersed phase in circular region I, annular region II, annular region III, and annular region IV are 30 - 500 nm, 100 - 1100 nm, 200 - 2500 nm, and 400 - 2700 nm respectively. The areas occupied by the dispersed phase in circular region I, annular region II, annular region III, and annular region IV are 1%, 3.5%, 5.5%, and 10% respectively. The instantaneous water contact angle of the fabric made of the moisture-absorbing and quick-drying polypropylene fiber with a surface enrichment type gradient structure is 15º.

[0170] The mechanical properties of the moisture-absorbing and quick-drying polypropylene fibers of Examples 1 - 12 are as shown in Table 1 below:

[0171] Table 1

[0172]

[0173] The friction properties of the moisture-absorbing and quick-drying polypropylene fibers of Examples 1 - 12 are as shown in Table 2, where F 静 is the static friction force, U 静 is the static friction coefficient, F 动 is the dynamic friction force, U 动 is the dynamic friction coefficient. These indexes can reflect the surface roughness indirectly.

[0174] Table 2

[0175]

[0176] The surface SEM images of the moisture-absorbing and quick-drying polypropylene fibers of Examples 1 - 12 are as shown in Figure 6 and it can be clearly seen from the figure the groove structure on the fiber surface.

[0177] Figure 7 Figure is the cross-section SEM comparison diagram of the internal enrichment type moisture-absorbing and quick-drying polypropylene fibers of Example 5, Example 7, and Example 8. After etching with formic acid, the positions of PA6 inside the fiber can be completely exposed, and the gradient structure of the fiber can be further observed. From Figure 7 it can be known that when the PA6 content inside the fiber is 20%, as the zero-shear viscosity ratio of the two phases (PA6:PP) changes from 1.5:1 to 6:1, it can be clearly seen that as the viscosity of PA6 increases, the dispersed phase PA6 shows a tendency to concentrate inside the fiber and presents the phenomenon of internal enrichment of PA6.

[0178] Figure 8 This is the cross-sectional binary analysis comparison diagram of the internal enrichment type moisture-absorbing and quick-drying polypropylene fibers of Example 5, Example 7, and Example 8. To further observe the gradient structure of the dispersed phase in the fiber cross-section, the image was subjected to binary processing and statistics. Using Matlab for image reading, recognition, and statistics, the size and number of the dispersed phase were obtained, and it was divided into four regions (Ⅰ, Ⅱ, Ⅲ, and Ⅳ). Observe the density of the dispersed phase in different regions to more clearly observe the distribution structure of the dispersed phase. From Figure 8 It can be seen that as the zero-shear viscosity ratio of the two phases changes from 1.5:1 to 6:1, it can be clearly seen that as the viscosity of PA6 increases, the dispersed phase PA6 shows a tendency to concentrate inside the fiber, and the content of the dispersed phase in regions Ⅰ and Ⅱ increases significantly, while the content in region Ⅳ decreases significantly, showing the phenomenon of increasing internal enrichment.

[0179] Figure 9 This is the cross-sectional SEM comparison diagram of the moisture-absorbing and quick-drying polypropylene fibers of Example 5, Example 11, and Example 12. After etching with formic acid, the position of PA6 inside the fiber can be completely exposed, and the gradient structure of the fiber can be further observed. From Figure 9 It can be known that when the content of PA6 inside the fiber is 20%, as the zero-shear viscosity ratio (PA6:PP) changes from 1.5:1 to 1.5:8.5, it can be clearly seen that as the viscosity of PP increases, the dispersed phase PA6 shows a tendency to concentrate on the surface of the fiber, and shows the phenomenon of surface enrichment of PA6.

[0180] Figure 10 This is the cross-sectional binary analysis comparison diagram of the moisture-absorbing and quick-drying polypropylene fibers of Example 5, Example 11, and Example 12. To further observe the gradient structure of the dispersed phase in the fiber cross-section, the image was subjected to binary processing and statistics. Using Matlab for image reading, recognition, and statistics, the size and number of the dispersed phase were obtained, and it was divided into four regions (Ⅰ, Ⅱ, Ⅲ, and Ⅳ). Observe the density of the dispersed phase in different regions to more clearly observe the distribution structure of the dispersed phase. From Figure 10 It can be seen that as the zero-shear viscosity ratio changes from 1.5:1 to 1.5:8.5, it can be clearly seen that as the viscosity of PP increases, the dispersed phase PA6 shows a tendency to concentrate outside the fiber, and the content of the dispersed phase in regions Ⅰ and Ⅱ decreases significantly, while the content in regions Ⅲ and Ⅳ increases significantly, showing the phenomenon of increasing surface enrichment.

[0181] The moisture-absorbing and quick-drying properties of the fabrics made from the moisture-absorbing and quick-drying polypropylene fibers in Examples 1 to 12 are as shown in Table 3 below:

[0182]

[0183] Based on the above-mentioned gradient structure with internal enrichment of the dispersed phase, the water-absorbing dispersed phase is concentrated inside the fiber and wrapped by hydrophobic polypropylene. This structure has a good internal storage effect on moisture. Based on this, the moisture regain of the fabric was measured under standard atmospheric pressure (temperature 20°C, relative humidity 65%).

[0184] As Figure 11 shown to observe the moisture retention effect of the fiber, after the fiber reaches equilibrium under standard atmosphere, the fabric was moved to a condition with a relative humidity of 40% and a temperature of 20°C to test the water evaporation situation. It can be seen from the figure that as the PA6 content in the fiber increases, the water evaporation duration and evaporation amount increase accordingly. When the PA6 1 content is 20%, the evaporation duration of the fiber is 80 minutes and the evaporation amount is 0.049 g. As the relative viscosity of the dispersed phase PA6 increases, the enrichment degree of the dispersed phase inside the fiber increases and the moisture retention effect improves. When the PA6 3 content is 20%, the evaporation duration of the fiber is 100 minutes and the evaporation amount is 0.072 g.

Claims

1. A moisture-absorbing and quick-drying polypropylene fiber with a gradient structure, characterized in that: It is prepared by melt blending and spinning after mixing the matrix phase and the dispersed phase to obtain a mixture; The matrix phase is polypropylene and the dispersed phase is a hydrophilic polymer; The gradient structure refers to a surface-enriched gradient structure or an internal-enriched gradient structure; The surface-enriched gradient structure means that the particle size of the dispersed phase gradually increases from the center to the outside on the fiber cross-section; The internal-enriched gradient structure means that the particle size of the dispersed phase gradually decreases from the center to the outside on the fiber cross-section; The moisture-absorbing and quick-drying polypropylene fiber with a gradient structure has a groove structure on its surface; The fiber cross-section is sequentially divided into concentric circular regions I, annular regions II, annular regions III, and annular regions IV from the center to the outside; For the surface-enriched gradient structure, the particle size ranges of the dispersed phase in the circular region I, annular region II, annular region III, and annular region IV are 30 - 600 nm, 50 - 1100 nm, 100 - 2500 nm, and 200 - 2700 nm respectively, and the areas occupied by the dispersed phase in the circular region I, annular region II, annular region III, and annular region IV are 1 - 2.5%, 2.2 - 3.5%, 2.5 - 6%, and 3.5 - 10% respectively; For the internal-enriched gradient structure, the particle size ranges of the dispersed phase in the circular region I, annular region II, annular region III, and annular region IV are 200 - 2700 nm, 150 - 2300 nm, 100 - 1800 nm, and 50 - 1500 nm respectively, and the areas occupied by the dispersed phase in the circular region I, annular region II, annular region III, and annular region IV are 1.6 - 10%, 1 - 8%, 0.5 - 5%, and 0.1 - 4% respectively; 2. The moisture-absorbing and quick-drying polypropylene fiber with a gradient structure according to claim 1, wherein, The area occupied by the groove structure is 0.5 - 30% of the fiber surface area, the length of the groove structure is 70 - 7500 nm, the width is 0.8 - 10 nm, the aspect ratio is 87.5 - 2500, and the depth is 1 nm - 25 nm; 3. The moisture-absorbing and quick-drying polypropylene fiber with a gradient structure according to claim 1, wherein, The hydrophilic polymer is polyamide 6; 4. A moisture-absorbing and quick-drying polypropylene fiber with a gradient structure according to claim 1, characterized in that, For the surface-enriched gradient structure, the instantaneous water contact angle of the fabric prepared from the moisture-absorbing and quick-drying polypropylene fiber with a gradient structure is 15° - 55°, the water drop diffusion time is 0.12 - 1.17 s, the wicking height is 10.5 - 12.6 cm, and the drying rate is 0.504 - 0.522 g / h; For the internal-enriched gradient structure, the instantaneous water contact angle of the fabric prepared from the moisture-absorbing and quick-drying polypropylene fiber with a gradient structure is 72° - 105°, the water drop diffusion time is 0.33 - 8.2 s, the wicking height is 7.5 - 11.6 cm, the drying rate is 0.37 - 0.521 g / h, and the unidirectional moisture transport coefficient is 20.12 - 479.23%; 5. A method for preparing a moisture-absorbing and quick-drying polypropylene fiber with a gradient structure, which is used to prepare a moisture-absorbing and quick-drying polypropylene fiber with a gradient structure as described in any one of claims 1 to 4, characterized in that: The moisture-absorbing and quick-drying polypropylene fiber with a gradient structure is prepared by melt blending and spinning after mixing the matrix phase and the dispersed phase; When the gradient structure is a surface-enriched gradient structure, the zero-shear viscosity ratio of the matrix phase to the dispersed phase is 1.429 - 5.667:1, the content of the dispersed phase in the mixture is 10 - 20 wt%, the molecular weight distribution index of the dispersed phase is 4.1 - 4.5, the relaxation time of the dispersed phase is 2.1 - 4.5 s, and the relaxation time of the matrix phase is 4.7 - 8.3 s; When the gradient structure is an internal enrichment type gradient structure, the zero shear viscosity ratio of the matrix phase to the dispersed phase is 1:1.3 - 6, the content of the dispersed phase in the mixture is 5 - 25 wt%, the molecular weight distribution index of the dispersed phase is 4.1 - 4.5, the relaxation time of the dispersed phase is 2.1 - 7.4 s, and the relaxation time of the matrix phase is 0.5 - 0.8 s.

6. The preparation method of a moisture-absorbing and quick-drying polypropylene fiber with a gradient structure according to claim 5, characterized in that, The number-average molecular weight of the dispersed phase is 80,000 to 100,000 g·mol -1 .

7. The preparation method of a moisture-absorbing and quick-drying polypropylene fiber with a gradient structure according to claim 5, characterized in that, The number-average molecular weight of the matrix phase is 75,300 to 121,000 g·mol -1 , and the molecular weight distribution index is 1.7 to 4.

5.

8. The preparation method of a moisture-absorbing and quick-drying polypropylene fiber with a gradient structure according to claim 5, characterized in that, The process parameters of melt blending and spinning are as follows: the screw temperature is 235 - 270 °C, the temperatures of the head, the pipe joint and the box body are 250 - 270 °C, and the spinning speed is 1000 - 1200 m / min.

9. The preparation method of a moisture-absorbing and quick-drying polypropylene fiber with a gradient structure according to claim 8, characterized in that, After spinning, hot drawing and setting are carried out. The drawing temperature is 50 - 120 °C, and the drawing ratio is 2 - 4.

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