Moisture-absorbing and quick-drying polypropylene fiber with gradient structure and preparation method of moisture-absorbing and quick-drying polypropylene fiber

Abstract

The 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, a matrix phase and a dispersion phase are mixed to obtain a mixture, and the mixture is subjected to melt blending spinning to obtain the moisture-absorbing and quick-drying polypropylene fiber with the gradient structure; the matrix phase is polypropylene, and the dispersion 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 on the fiber section is gradually increased from the center to the outside; the internal enrichment type gradient structure means that the particle size of the dispersed phase on the fiber section is gradually reduced from the center to the outside; the surface of the moisture-absorbing and quick-drying polypropylene fiber with the gradient structure is provided with a groove structure, and the area occupied by the groove structure is 0.5-30% of the surface area of the fiber. The preparation method disclosed by the invention is simple, and the prepared moisture-absorbing and quick-drying polypropylene fiber with the gradient structure has good moisture-absorbing and quick-drying performance and one-way moisture guiding performance.

Description

Technical Field

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

[0002] Whether outdoors or indoors, when the core temperature of the human body exceeds the high temperature threshold, the body surface will release sweat for evaporation and heat dissipation. However, in a high temperature and high humidity environment, the amount of sweat can easily exceed the amount of evaporation. At this time, a large amount of sweat will accumulate on the skin surface and inside the fiber, causing discomfort to the human body. To prevent sweat accumulation, the design of functional fibers and fabrics must coordinately optimize their moisture absorption and quick-drying properties to improve the fiber's conduction and evaporation performance of sweat.

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

[0004] (1) In terms of the development of fiber macrostructure, the main focus is on the design and development of the physical structure of polypropylene, polyester or nylon fibers, including fine denier fibers, hollow porous fibers, and special-shaped cross-section fibers (such as "cross", "Y", "H", etc.). The fiber surface with special-shaped structures provides more abundant water transfer channels. The groove structure or porosity of the fiber can quickly conduct sweat or moisture from the inner layer to the outer layer for evaporation, promoting moisture transfer. Its moisture absorption and quick-drying performance is significantly better than that of round fiber fabrics.

[0005] (2) In the development of surface hydrophilic finishing, hydrophilic groups (hydroxyl, carboxyl, amino and amide groups, etc.) are introduced into the fiber macromolecular structure or hydrophilic raw materials are melt-blended to utilize the advantages of the hydrophilic and moisture-conducting properties of the two-phase polymers to further enhance the moisture absorption and quick-drying properties of the fiber fabric. For example, moisture-absorbing and perspiration-wicking fibers produced by grafting silk compounds onto polyester or polyamide-based synthetic fibers produced by copolymerization of polyester and polyamide macromolecules. DuPont in the United States uses radiation-induced polymerization to graft and copolymerize hydrophilic components onto nylon 66 to obtain highly hygroscopic fibers. Sophista, publicly released by Kuraray, is a two-component core-skin composite fiber developed with ethylene-vinyl alcohol copolymer (EVOH) and polyester (PET) as the main raw materials. The hydrophobic PET as the core layer is almost non-hygroscopic, and the EVOH with hydrophilic groups as the skin layer has excellent wetting properties. Toyobo of Japan blended polypropionate with polyester stock solution to produce Ekslive moisture-absorbing and quick-drying fibers. Patent CN119061556A discloses a moisture-absorbing, quick-drying, comfortable polyamide fabric, a spinning melt, and a method for preparing the spinning melt. The polyamide fabric is woven from nylon yarn and spandex yarn. The composition of the nylon yarn includes 1% to 8% silk fibroin and 0.9% to 6% polyvinyl pyrrolidone. The method improves the capillary effect and air permeability of the fiber fabric and reduces the stuffiness when worn.

[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 inner layer of the blend 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 became hydrophilic, while the back side remained superhydrophobic. The fabric exhibited excellent unidirectional liquid conduction properties, with forward and reverse osmotic pressures of 2 cm H 2 O and 18 cm H 2 O.

[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 the patent CN118979315A, a UV-resistant moisture-absorbing fiber and its preparation method, Cu is coated on the gold nanorods. 2 O, and then ZnO was grown on its surface to obtain Au@Cu 2 O / ZnO composites; Au@Cu 2 O / ZnO composite material reacts 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 fibers, which are then treated to obtain activated PET fibers; 2-[(2-aminoethyl)amino]ethanesulfonic acid sodium salt reacts with silane coupling agent KH560 to obtain a hydrophilic modifier; the hydrophilic modifier and epigallocatechin gallate are grafted onto the activated PET fibers to obtain anti-ultraviolet hygroscopic fibers. 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 method for preparing Janus fabric by electrospinning in patent CN119041038A, Janus fabric is prepared by electrospinning. First, a certain concentration of PU spinning solution is prepared, and then hydrophilic medical gauze is used as a collector, and the parameters of electrospinning (voltage, flow rate and time, etc.) are fixed, and finally the Janus fabric is dried. The invention utilizes the differences in hydrophilicity, hydrophobicity and wettability on both sides of the fabric. The Janus fabric can achieve unidirectional wettability, laying the foundation for its controllable moisture collection and other aspects. The Janus fabric prepared by this method has a slow drip diffusion rate (6s) and has unidirectional moisture conduction characteristics, but this result is far from meeting 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 is not suitable for large-scale commercial production. In addition, in the patent CN115583084A, a multi-dimensional moisture-conducting and deodorizing knitted fabric and its application, a hydrophilic layer, a water-conducting layer and a hydrophobic layer are constructed in sequence by designing the fabric structure, and at the same time, the fiber fineness increases from the inside to the outside, and the fiber diameter decreases in sequence. The special thing is that the surface of the yarn after plasma surface treatment produces small particles with different concave and convex shapes, and its number and depth increase significantly. There are obvious etching marks on the surface of the yarn, and the surface roughness of the yarn increases significantly, thereby causing the increase of the specific surface area of ​​the yarn, and finally increasing the surface wettability, and its contact angle is 0 °. The multi-dimensional moisture-conducting fabric prepared by this method does not have a good moisture-conducting effect. The highest one-way transfer index is 200%, and the one-way transfer index after 120s is only about 70%, which is not conducive to the complete diffusion of water on the body surface. Its evaporation rate of water is only 0.24g / h at most, and its quick-drying property is poor.

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

[0013] The purpose of the invention is to solve the problems existing in the prior art and provide a method for preparing moisture-absorbing 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-absorbing quick-drying polypropylene fiber with a gradient structure is prepared by mixing a matrix phase and a dispersed phase to obtain a mixture and then performing melt blending spinning;

[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] Surface-enriched gradient structure refers to the gradual increase in the particle size of the dispersed phase from the center to the outside of the fiber cross section, that is, the enrichment of the dispersed phase on the fiber surface is greater than that inside the fiber;

[0019] Internally enriched gradient structure refers to the gradual decrease in the particle size of the dispersed phase from the center to the outside of the fiber cross section, that is, the enrichment of the dispersed phase inside the fiber is greater than that on the fiber surface;

[0020] The surface of the moisture-absorbing quick-drying polypropylene fiber with a gradient structure has a groove structure. The groove structure refers to the part that is depressed downward relative to the flat body surface of the fiber. Because it is similar to the grooves on the roadside, it is called a groove structure. The groove structure is formed by 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 bonding force between the two phases is higher than the bonding force between the two phases, the two phases separate on the fiber surface, so a groove structure is generated on the fiber surface. The groove structure is distributed on the surface of the fiber and is controlled by controlling the spinning speed, stretch ratio, zero shear viscosity of the dispersed phase, dispersed phase content, dispersed phase molecular weight distribution and spinneret aperture during the melt spinning process (refer to CN116043362A; CN116043360A).

[0021] For the surface-enriched gradient structure, the hydrophilicity of the fiber can be significantly increased due to the enrichment of the hydrophilic polymer on the fiber surface. The hydrophilic fiber surface is more likely to interact with water molecules, allowing water molecules to be quickly adsorbed by the fiber surface. The presence of grooves on the fiber surface will further enhance the capillary effect of the fiber. Due to the humidity and temperature gradient between the skin and the outside air, water can diffuse rapidly in the vertical direction of the fiber and in the direction of the fiber layer (such as Figure 2As shown in the figure, the rapid diffusion of water in the vertical direction depends on the free diffusion of water molecules. Water molecules migrate from high concentration to low concentration areas, and the water evaporates and diffuses from the fiber core layer to the low humidity outside. The principle of water diffusion around the fiber surface is based on the strong intermolecular force and hydrogen bond force of hydrophilic polymers on water molecules. Under the influence of this strong force, the transfer of water molecules between hydrophilic polymers is increased, thereby achieving the diffusion of water around the fiber surface. At the same time, relying on the free diffusion of water molecules, a large amount of water is transferred from high humidity conditions to low humidity directions. Since there are fewer hydrophilic polymers in the fiber core layer, the force and absorption of water are less. Therefore, in the process of fiber drying, the content and time of water diffusion from the core layer to the surface layer are reduced, and the quick-drying effect of the fiber is achieved based on this. In addition, since there are fewer dispersed phases inside the fiber, the interfacial tension of the two-phase polymer is low (it is well known in the art that when the two phases are blended, the interfacial tension increases, which will cause the mechanical properties to decrease rapidly), the fiber interior can be regarded as a pillar core to enhance the mechanical properties of the blended fiber.

[0022] For the internal enrichment gradient structure, we designed a fiber surface with hydrophobic and groove structures. The hydrophobic surface structure can prevent water from penetrating into the fiber interior (core layer) at low humidity. At the same time, under high humidity conditions, the groove structure on the fiber surface and the hydrophilic polymer inside, due to the wicking effect of the fiber surface, as well as the intermolecular force and hydrogen bonding force between the water molecules, allow water to be absorbed from the outer surface of the fiber into the fiber core layer (vertical diffusion), and form a diffusion in the fiber core layer (such as Figure 4 The water droplet stretching direction is shown in the figure, that is, the lateral diffusion of the fiber). At the same time, through free diffusion, water molecules migrate from high concentration to low concentration areas, and the water evaporates and diffuses from the fiber core layer to the low humidity outside. This diffusion path prevents the reverse osmosis of sweat when the human body sweats a lot, and at the same time gives the fiber unidirectional moisture conduction ability. The whole process is as follows Figure 4 At the same time, this structure (locking a small amount of water in the fiber core) also gives the fiber a certain water retention rate (increased moisture regain). When the outside is dry, due to the free diffusion of water, the water inside the fiber will slowly release to the fiber surface, ultimately improving the moisture absorption, quick drying, one-way moisture conduction and moisturizing effects of the fiber and fabric.

[0023] As the preferred technical solution:

[0024] In the above-mentioned moisture-absorbing quick-drying polypropylene fiber with a gradient structure, the area occupied by the groove structure is 0.5-30% of the fiber surface area, the length of the groove structure is 70-7500nm, the width is 0.8-10nm, the aspect ratio is 87.5-2500, and the depth is 1nm-25nm. 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 method is as follows (the viscosity mentioned refers to the zero shear viscosity):

[0025] Internally enriched fiber: The number of groove structures on the fiber surface can be achieved by reducing the zero shear viscosity of the dispersed phase, increasing the two-phase viscosity ratio (matrix phase: dispersed phase>1), and increasing the dispersed phase content. The number of groove structures on the fiber surface can be achieved by controlling the zero shear viscosity ratio of the polymer dispersed phase to the matrix phase. When the two-phase viscosity ratio (matrix phase: dispersed phase>1) is larger, in the non-isothermal uniaxial tensile flow field of the melt spinning process, due to the presence 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), so the dispersed phase migrates outward, stretches and deforms, and aggregates. When the dispersed phase content increases, the more dispersed phase migrates to the surface, the more grooves there are. The length of the groove structure on the fiber surface can be achieved by spinning speed and stretch ratio. The faster the spinning speed, the larger the stretch ratio, and the longer the groove structure. The width of the groove structure on the fiber surface can be controlled by controlling the dispersed phase content and the spinneret aperture. When the dispersed phase content is higher and the spinneret aperture is larger, the aggregation 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 wider molecular weight distribution contains a small amount of dispersed phase with a lower molecular weight, that is, a lower viscosity. These dispersed phases with lower 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 lower molecular weight increases, thereby increasing the number of grooves on the fiber surface. The length of the groove structure on the fiber surface can be achieved by spinning speed and stretching ratio. The faster the spinning speed and the larger the stretching ratio, the greater the degree of rupture and microfibrillation of the dispersed phase droplets, and the longer the groove structure length. 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. When the spinneret aperture is larger, the molecular weight distribution of the dispersed phase becomes wider and the content increases, the droplet rupture and microfibrillation degree generated by the dispersed phase on the fiber surface are weakened, thereby increasing the width of the groove structure; when the spinneret aperture is smaller, the molecular weight distribution of the dispersed phase becomes narrower and the content decreases, the droplet rupture and microfibrillation degree generated by the dispersed phase on the fiber surface are increased, thereby reducing the width of the groove structure.

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

[0028] For a surface-enriched gradient structure of a 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 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. 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. 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 larger (i.e., the area proportion of the dispersed phase in the corresponding region is larger), it indicates a greater enrichment degree.

[0029] For an 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 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. 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.

[0030] For a surface-enriched gradient structure of a 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 an 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 quick-drying polypropylene fiber with a gradient structure, which is used to prepare a moisture-absorbing quick-drying polypropylene fiber with a gradient structure as described in any one of the above items, wherein a matrix phase and a dispersed phase are mixed to obtain a mixture, and then melt-blended and spun to obtain the moisture-absorbing quick-drying polypropylene fiber with a gradient structure;

[0033] 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 10-20wt%, the molecular weight distribution index of the dispersed phase is 4.1-4.5, the relaxation time of the dispersed phase is 2.1-4.5s, and the relaxation time of the matrix phase is 4.7-8.3s;

[0034] When the gradient structure is an internally enriched 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 5~25wt%, the molecular weight distribution index of the dispersed phase is 4.1~4.5, the relaxation time of the dispersed phase is 2.1~7.4s, and the relaxation time of the matrix phase is 0.5~0.8s.

[0035] By regulating the morphology and distribution of the hydrophilic dispersed phase through blending melt spinning, a gradient structure change in the degree of dispersed phase enrichment was achieved, thereby improving fiber properties. The formation of the gradient structure is caused by droplet migration, rupture 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, which causes the polymer to have a velocity gradient. Different polymers have different relaxation times (motion characteristics of polymer chains) in this process. When the polymer relaxation time is short, it means that the polymer chain segments move faster and the segments are easier to migrate to the area with greater shear stress; when the polymer relaxation time is long, it means that the polymer chain segments move slower and the segments are retained in the area with lower shear stress. As the molecular weight of the polymer increases, the zero shear viscosity of the polymer increases and the relaxation time increases, so it is more difficult to migrate to the area with greater stress. In the pipe, the polymer is constrained by the pipe wall, and the flow rate 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 rate is close to zero, the velocity gradient is the largest, so the shear stress is the largest. Therefore, polymers with higher molecular weight or higher viscosity tend to flow to the center, and polymers with lower viscosity or lower molecular weight tend to flow to the outside, based on which a surface-enriched gradient structure or an internally enriched gradient structure is formed. The dispersed phase with a small amount of high molecular weight or high viscosity will be retained in the low stress area, i.e., the inner side of the surface-enriched gradient structure, due to the long relaxation time and slow migration rate; when the molecular weight distribution of the dispersed phase polymer is wide, the dispersed phase with a small amount of low molecular weight or low viscosity will migrate to the high stress area, i.e., the outer side of the internally enriched gradient structure, due to the short relaxation time and fast migration rate. By regulating the above mechanism and polymer parameters, the area ratio (content) of the dispersed phase polymer to the matrix phase polymer in different areas of the fiber cross section can be regulated. The theory of the particle size and enrichment degree of the dispersed phase in the gradient structure is caused by the rupture, migration and coalescence of droplets. Due to the incompatibility of the dispersed phase and the matrix phase, during the spinning process, the droplets have different flow rates and 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 to the inside of the fiber; when the zero shear viscosity is low, it migrates to the outside of the fiber). During the migration process, the collision frequency increases and the probability of aggregation increases. Therefore, the size of the dispersed phase increases accordingly to form a gradient distribution of particle size. At the same time, the fiber rupture mechanism is based on the Taylor drop deformation theory. The Taylor number (Ca), also known as the capillary number, is proportional to the zero shear viscosity, shear rate and droplet radius of the surrounding fluid, and is 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 remain spherical; 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 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 is c Relationship with the two-phase zero shear viscosity ratio P:

[0037] ;

[0038] Therefore, droplet breakup can be divided into three mechanisms: droplet breakup, fiber transient breakup and edge breakage. The droplet breakup mechanism occurs when the capillary number is small. When the flow field intensity increases, the system Ca exceeds Ca c When the droplet is split into two, it breaks into two smaller droplets of equal volume. Huneault proposed the reduced capillary number (Ca* =Ca / Ca c ) is used as a criterion to determine whether the droplet is deformed or broken, and what kind of deformation mechanism occurs:

[0039] (1) No deformation occurs when Ca*< 0.1;

[0040] (2) When 0.1≤Ca*<1, deformation occurs but no rupture occurs. At this time, the droplet volume remains unchanged but the shape changes.

[0041] (3) When 1≤Ca*<4, deformation occurs and the droplet breaks up step by step into two smaller droplets of equal volume;

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

[0043] Since 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) A method for preparing a moisture-absorbing quick-drying polypropylene fiber with a gradient structure according to the present invention. The fiber prepared by this method can achieve gradient moisture conduction, thereby preventing the phenomenon that the "core" part of the core-shell fiber has insufficient moisture absorption capacity so that moisture cannot break through the "shell".

[0052] (3) The moisture-absorbing and quick-drying polypropylene fiber with a gradient structure of 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 absorption and quick-drying properties of the fiber. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0054] Figure 2 It is the moisture transport pathway of surface-enriched fibers;

[0055] Figure 3 This is a cross-sectional view of the internally enriched fiber;

[0056] Figure 4 This is a diagram of the moisture transfer pathway and unidirectional moisture conduction mechanism of the internally enriched fiber;

[0057] Figure 5 It is the fiber cross-section area division diagram;

[0058] Figure 6 The surface SEM images of the moisture-absorbing and quick-drying polypropylene fibers of Examples 1 to 12;

[0059] Figure 7 The cross-sectional SEM comparison diagrams of the internally enriched moisture-absorbing and quick-drying polypropylene fibers of Example 5, Example 7, and Example 8;

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

[0061] Fig. 9 The cross-sectional SEM comparison diagram of the moisture-absorbing and quick-drying polypropylene fibers of Example 5, Example 11, and Example 12;

[0062] Fig.10 It is a cross-sectional binary analysis comparison diagram of the moisture-absorbing and quick-drying polypropylene fibers of Example 5, Example 11, and Example 12;

[0063] Fig.11 Polypropylene (PP 1 ) evaporation of water in an environment with a relative humidity of 40% by the moisture-absorbing quick-drying polypropylene fibers of Examples 2 to 8;

[0064] Fig.12 This is the unidirectional moisture conduction test curve of the internally enriched moisture-absorbing and quick-drying polypropylene fiber of Example 8. DETAILED DESCRIPTION

[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 are not intended 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 fall within the scope limited by the appended claims of the application equally.

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

[0067] Breaking strength and breaking elongation: The mechanical properties of the fiber were tested using the XL-2 filament yarn strength and elongation tester. A pretension of 5.0 cN was applied to the bottom of the fiber, the length between the two clamps was set to 250 mm, the stretching speed was set to 500 mm / min, and the average of 10 test results was taken for each sample; the coefficient of variation refers to the error range of each test.

[0068] SEM image: The morphology of the obtained fibers was observed using a scanning electron microscope (SEM, SU8010, Hitachi).

[0069] Friction coefficient: XCF fiber friction coefficient tester is used to test the friction coefficient of chemical fibers in accordance with the group standard TCSTM 00522-2022.

[0070] Moisture regain: According to the national standard GB / T 9994-2018, the moisture regain of fibers and fabrics is tested.

[0071] The single-layer machine-made fabric was prepared using the SGA598 fully automatic rapier sampling loom of Jiangyin Tongyuan Textile Machinery Co., Ltd. using moisture-absorbing and quick-drying polypropylene fibers with a gradient structure. In the fabric structure, the same type of fiber was used for both the warp and weft yarns. The warp yarn density was 160 strands / inch, and the weft yarn density was 210 strands / inch. A plain fabric with a length of 200±5mm, a width of 200±5mm, and a thickness of 0.91±0.05mm was obtained to test its water contact angle, moisture absorption and quick-drying properties, and unidirectional moisture conductivity.

[0072] Water contact angle: Analyze using a water contact angle tester (model JC2000D). Place the fabric in the center of the platform and place a sampling needle filled with distilled water on the upper shelf. Take an image of the moment when distilled water contacts the microfiltration membrane as the main basis for calculating the water contact angle. Drop a 5μL droplet on the sample surface and test the contact angle between the droplet and the sample surface. Randomly select at least 6 different locations on the sample for testing and finally take the average value.

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

[0074] Unidirectional moisture conductivity coefficient: According to the standard AATCC TM-195, the unidirectional moisture conductivity of the sample at 120s is tested using a liquid moisture management tester (Model M290, SDL Atlas, USA). The sample is placed horizontally between the upper and lower resistance sensors, and 0.2g of water is dropped on the center of the sample. When water is conducted through the sample, the resistance change between the upper and lower surfaces of the sample will be recorded and converted into relative moisture content according to the algorithm. This test will provide a quantitative unidirectional moisture conductivity index (R) to characterize the unidirectional liquid conductivity performance of the sample, which is defined as the difference between the cumulative relative moisture content of the upper and lower surfaces of the sample:

[0075] ;

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

[0077] Embodiment PP of the present invention 1 / PA6 1 -PP in 5% 1 / PA6 1 For PP 1 and PA6 1 Blended slices, 5% is the mass fraction of the dispersed phase in the mixture; PP 0 PP 1 PP 2 PP 3 The numbers in the code are used to distinguish the four types of PP, PA6 1 、PA6 2 、PA6 3 The numbers in the table are used to distinguish the three types of PA6.

[0078] Example 1

[0079] A method for preparing a moisture-absorbing quick-drying polypropylene fiber with an internally enriched gradient structure, the specific steps are as follows:

[0080] (1) Preparation of raw materials:

[0081] Dispersed phase: PA6 1 , the number average molecular weight is 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 ;

[0082] Matrix phase: PP 0 , the number average molecular weight is 81200 g·mol -1 , molecular weight distribution index is 2.2, zero shear viscosity is 115Pa·s, melt index is 30g·10min -1 ; The interfacial tension between the matrix phase and the dispersed phase is 9mN·m -1 ;

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

[0084] (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 5wt%;

[0085] 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 235°C, 250°C, 260°C, 260°C, and 260°C respectively; the temperature of die head, pipe and box is 260°C; the spinning speed is 1200m / min;

[0086] (4) After spinning, GR1 and GR2 hot rollers are used for hot stretching and shaping. 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 stretching multiple is 4.

[0087] The final 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 aspect ratio is 87.5, and the depth is 1 nm; the relaxation time of the dispersed phase is 2.1s, and the relaxation time of the matrix phase is 0.8s; 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, the particle size ranges of the dispersed phase in circular area Ⅰ, circular area Ⅱ, circular area Ⅲ and circular area Ⅳ are 250-850nm, 200-750nm, 150-650nm and 80-450nm, respectively, and the areas occupied by the dispersed phase in circular area Ⅰ, circular area Ⅱ, circular area Ⅲ and circular area Ⅳ are 1.6%, 1.4%, 1.2% and 0.8%, respectively; the instantaneous water contact angle of the fabric made of hygroscopic quick-drying polypropylene fiber with internal enrichment gradient structure is 105º.

[0088] Example 2

[0089] A method for preparing a moisture-absorbing quick-drying polypropylene fiber with an internally enriched gradient structure, the specific steps are as follows:

[0090] (1) Preparation of raw materials:

[0091] Dispersed phase: PA6 1 , the number average molecular weight is 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 ;

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

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

[0094] (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 5wt%;

[0095] 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 235°C, 250°C, 260°C, 260°C, and 260°C respectively; the temperature of die head, pipe and box is 260°C; the spinning speed is 1200m / min;

[0096] (4) After spinning, GR1 and GR2 hot rollers are used for hot stretching and shaping. 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 stretching multiple is 4.

[0097] The final prepared moisture-absorbing quick-drying polypropylene fiber (PP 1 / PA6 1-5%) has a groove structure on its surface, 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 2.1s, 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, the particle size ranges of the dispersed phase in circular area Ⅰ, circular area Ⅱ, circular area Ⅲ and circular area Ⅳ are 200-800nm, 150-700nm, 100-600nm and 50-300nm, respectively, and the areas occupied by the dispersed phase in circular area Ⅰ, circular area Ⅱ, circular area Ⅲ and circular area Ⅳ are 2.5%, 1%, 0.5% and 0.1%, respectively; the instantaneous water contact angle of the fabric made of hygroscopic quick-drying polypropylene fiber with internal enrichment gradient structure is 100º.

[0098] Example 3

[0099] A method for preparing a moisture-absorbing 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 10 wt %.

[0100] The final prepared moisture-absorbing 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 divided into concentric circular area Ⅰ, circular area Ⅱ, circular area Ⅲ and circular area Ⅳ from the center to the outside, the particle size ranges of the dispersed phase in circular area Ⅰ, circular area Ⅱ, circular area Ⅲ and circular area Ⅳ are 250-1000 nm, 170-950 nm, 100-1100 nm and 60-800 nm, respectively, and the areas occupied by the dispersed phase in circular area Ⅰ, circular area Ⅱ, circular area Ⅲ and circular area Ⅳ are 3%, 2%, 3% and 2%, respectively; the instantaneous water contact angle of the fabric made of hygroscopic quick-drying polypropylene fiber with internal enrichment gradient structure is 93º.

[0101] Example 4

[0102] A method for preparing a moisture-absorbing quick-drying polypropylene fiber with an internally enriched gradient structure is basically the same as that in Example 2, except that the content of the dispersed phase in the mixture in step (3) is 15 wt %.

[0103] The final prepared moisture-absorbing 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 2000nm, the width is 4nm, the aspect ratio is 500, and the depth is 10nm; the relaxation time of the dispersed phase is 2.1s, and the relaxation time of the matrix phase is 0.5s; the fiber cross section is divided into concentric circular area Ⅰ, annular area Ⅱ, annular area Ⅲ and annular area Ⅳ from the center to the outside, the particle size ranges of the dispersed phase in circular area Ⅰ, annular area Ⅱ, annular area Ⅲ and annular area Ⅳ are 500~1700nm, 250~1600nm, 240~1500nm and 200~1400nm, respectively, and the areas occupied by the dispersed phase in circular area Ⅰ, annular area Ⅱ, annular area Ⅲ and annular area Ⅳ are 6%, 4%, 3% and 2% respectively; the instantaneous water contact angle of the fabric made of hygroscopic quick-drying polypropylene fiber with internal enrichment gradient structure is 88º.

[0104] Example 5

[0105] A method for preparing a moisture-absorbing 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 final 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 3000nm, the width is 8nm, the aspect ratio is 375, and the depth is 20nm; the relaxation time of the dispersed phase is 2.1s, and the relaxation time of the matrix phase is 0.5s; the fiber cross section is divided into concentric circular area I, annular area II, annular area III and annular area IV from the center to the outside, the particle size ranges of the dispersed phase in circular area I, annular area II, annular area III and annular area IV are 300-2000nm, 290-1800nm, 250-1750nm and 150-1250nm, respectively, and the areas occupied by the dispersed phase in circular area I, annular area II, annular area III and annular area IV are 7%, 5%, 4.5% and 3.5%, respectively; the instantaneous water contact angle of the fabric made of hygroscopic quick-drying polypropylene fiber with internal enrichment gradient structure is 82º.

[0107] Example 6

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

[0109] The final moisture-absorbing and quick-drying polypropylene fiber (PP 1 / PA6 1 -25%) 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 5000nm, the width is 2 nm, the aspect ratio is 2500, and the depth is 25nm; the relaxation time of the dispersed phase is 2.1s, 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, the particle size ranges of the dispersed phase in circular area Ⅰ, circular area Ⅱ, circular area Ⅲ and circular area Ⅳ are 350-2200nm, 300-2000nm, 220-1800nm ​​and 200-1500nm, respectively, and the areas occupied by the dispersed phase in circular area Ⅰ, circular area Ⅱ, circular area Ⅲ and circular area Ⅳ are 9%, 7%, 5% and 4%, respectively; the instantaneous water contact angle of the fabric made of hygroscopic quick-drying polypropylene fiber with internal enrichment gradient structure is 79º.

[0110] Example 7

[0111] A method for preparing a moisture-absorbing quick-drying polypropylene fiber with an internally enriched gradient structure, the specific steps are as follows:

[0112] (1) Preparation of raw materials:

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

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

[0115] (2) Drying the matrix phase and the dispersed phase separately in a rotary vacuum oven at 120°C for 24 hours to remove moisture;

[0116] (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%;

[0117] 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 240°C, 255°C, 265°C, 265°C, and 265°C respectively; the temperature of die head, pipe and box is 265°C; the spinning speed is 1200m / min;

[0118] (4) After spinning, GR1 and GR2 were used for hot stretching and shaping. The temperature of GR1 was 50°C, the speed of GR1 was 400 m / min, the temperature of GR2 was 100°C, the speed of GR2 was 1200 m / min, and the stretching multiple was 3.

[0119] The final moisture-absorbing and quick-drying polypropylene fiber (PP 1 / PA6 2 -20%) 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 2500nm, the width is 5nm, the aspect ratio is 500, and the depth is 16nm; the relaxation time of the dispersed phase is 4.2s, 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, the particle size ranges of the dispersed phase in circular area Ⅰ, circular area Ⅱ, circular area Ⅲ and circular area Ⅳ are 350-2500nm, 250-2200nm, 210-1600nm and 150-1100nm, respectively, and the areas occupied by the dispersed phase in circular area Ⅰ, circular area Ⅱ, circular area Ⅲ and circular area Ⅳ are 8%, 7%, 3% and 2%, respectively; the instantaneous water contact angle of the fabric made of hygroscopic quick-drying polypropylene fiber with internal enrichment gradient structure is 75º.

[0120] Example 8

[0121] A method for preparing a moisture-absorbing quick-drying polypropylene fiber with an internally enriched gradient structure, the specific steps are as follows:

[0122] (1) Preparation of raw materials:

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

[0124] Matrix phase: PP 1 , the number average molecular weight is 75300 g·mol -1 , molecular weight distribution index is 1.7, zero shear viscosity is 100Pa·s, melt index is 45g·10min -1 ; The interfacial tension between the matrix phase and the dispersed phase is 14mN·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 moisture-absorbing and 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. Fig.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 , molecular weight distribution index is 4.5, zero shear viscosity is 350Pa·s, melt index is 24g·10min -1 ;

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

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

[0136] (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 a surface-enriched gradient structure; the content of the dispersed phase in the mixture is 10wt%;

[0137] 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 240°C, 255°C, 265°C, 265°C, and 265°C respectively; the temperature of die head, pipe and box is 265°C; the spinning speed is 1200m / min;

[0138] (4) After spinning, GR1 and GR2 were used for hot stretching and shaping. The temperature of GR1 was 50°C, the speed of GR1 was 400 m / min, the temperature of GR2 was 100°C, the speed of GR2 was 1200 m / min, and the stretching multiple was 3.

[0139] The final prepared moisture-absorbing quick-drying polypropylene fiber (PP 2 / PA6 2-10%) has a groove structure on its surface, 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 aspect ratio is 1000, and the depth is 10 nm; the relaxation time of the dispersed phase is 4.5s, and the relaxation time of the matrix phase is 4.7s; 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, the particle size ranges of the dispersed phase in circular area Ⅰ, circular area Ⅱ, circular area Ⅲ and circular area Ⅳ are 30-400nm, 50-800nm, 100-1200nm and 200-2000nm, respectively, and the areas occupied by the dispersed phase in circular area Ⅰ, circular area Ⅱ, circular area Ⅲ and circular area Ⅳ are 1.8%, 2.2%, 2.5% and 3.5%, respectively; the instantaneous water contact angle of the fabric made of hygroscopic quick-drying polypropylene fiber with surface enriched gradient structure is 55º.

[0140] Example 10

[0141] A method for preparing a moisture-absorbing quick-drying polypropylene fiber with a surface-enriched gradient structure, the specific steps are as follows:

[0142] (1) Preparation of raw materials:

[0143] Dispersed phase: PA6 1 , the number average molecular weight is 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 ;

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

[0145] (2) Drying the matrix phase and the dispersed phase separately in a rotary vacuum oven at 120°C for 24 hours to remove moisture;

[0146] (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 a surface-enriched gradient structure; the content of the dispersed phase in the mixture is 15wt%;

[0147] 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 240°C, 255°C, 265°C, 265°C, and 265°C respectively; the temperature of die head, pipe and box is 265°C; the spinning speed is 1200m / min;

[0148] (4) After spinning, GR1 and GR2 were used for hot stretching and shaping. The temperature of GR1 was 50°C, the speed of GR1 was 400 m / min, the temperature of GR2 was 100°C, the speed of GR2 was 1200 m / min, and the stretching multiple was 3.

[0149] The final prepared moisture-absorbing quick-drying polypropylene fiber (PP 2 / PA6 1 -15%) has a groove structure on its surface, 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 divided into concentric circular area Ⅰ, circular area Ⅱ, circular area Ⅲ and circular area Ⅳ from the center to the outside, the particle size ranges of the dispersed phase in circular area Ⅰ, circular area Ⅱ, circular area Ⅲ and circular area Ⅳ are 40-500nm, 55-850nm, 120-1800nm ​​and 250-2300nm, respectively, and the areas occupied by the dispersed phase in circular area Ⅰ, circular area Ⅱ, circular area Ⅲ and circular area Ⅳ are 2%, 3%, 4% and 6%, respectively; the instantaneous water contact angle of the fabric made of hygroscopic quick-drying polypropylene fiber with surface enriched gradient structure is 40º.

[0150] Embodiment 11

[0151] A method for preparing a moisture-absorbing quick-drying polypropylene fiber with a surface-enriched gradient structure, the specific steps are as follows:

[0152] (1) Preparation of raw materials:

[0153] Dispersed phase: PA6 1 , the number average molecular weight is 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 ;

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

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

[0156] (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 a surface-enriched gradient structure; the content of the dispersed phase in the mixture is 20wt%;

[0157] 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 240°C, 255°C, 265°C, 265°C, and 265°C respectively; the temperature of die head, pipe and box is 265°C; the spinning speed is 1200m / min;

[0158] (4) After spinning, GR1 and GR2 were used for hot stretching and shaping. The temperature of GR1 was 50°C, the speed of GR1 was 400 m / min, the temperature of GR2 was 100°C, the speed of GR2 was 1200 m / min, and the stretching multiple was 3.

[0159] The final prepared moisture-absorbing quick-drying polypropylene fiber (PP 2 / PA6 1 -20%) 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 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 2.1s, and the relaxation time of the matrix phase is 4.7s; 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, the particle size ranges of the dispersed phase in circular area Ⅰ, circular area Ⅱ, circular area Ⅲ and circular area Ⅳ are 50-600nm, 60-1000nm, 150-2400nm and 300-2600nm, respectively, and the areas occupied by the dispersed phase in circular area Ⅰ, circular area Ⅱ, circular area Ⅲ and circular area Ⅳ are 2.5%, 3.5%, 6% and 8%, respectively; the instantaneous water contact angle of the fabric made of hygroscopic quick-drying polypropylene fiber with surface enriched gradient structure is 25º.

[0160] Example 12

[0161] A method for preparing a moisture-absorbing quick-drying polypropylene fiber with a surface-enriched gradient structure, the specific steps are as follows:

[0162] (1) Preparation of raw materials:

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

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

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

[0166] (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 prepare 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%;

[0167] The process parameters of melt blending and spinning are: the temperatures of the screw zones I, II, III, VI, and V are 250°C, 260°C, 270°C, 270°C, and 270°C respectively, the temperatures of the head, the adapter, and the housing are 270°C, and the spinning speed is 1000 m / min;

[0168] (4) After spinning, perform hot drawing and setting with GR1 and GR2. The temperature of GR1 is 80°C, the speed of GR1 is 500 m / min, the temperature of GR2 is 120°C, the speed of GR2 is 1000 m / min, and the drawing ratio is 2.

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

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

[0171] Table 1

[0172]

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

[0174] Table 2

[0175]

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

[0177] Figure 7 The cross-sectional SEM comparison diagram of the internally enriched moisture-absorbing quick-drying polypropylene fiber of Example 5, Example 7, and Example 8 shows that after etching with formic acid, the position of the PA6 inside the fiber can be completely exposed, and the gradient structure of the fiber can be further observed. Figure 7 It can be seen that when the PA6 content inside the fiber is 20%, as the two-phase zero-shear viscosity ratio (PA6:PP) changes from 1.5:1 to 6:1, it can be clearly seen that with the increase of PA6 viscosity, the dispersed phase PA6 shows a trend of concentration inside the fiber and presents a PA6 internal enrichment phenomenon.

[0178] Figure 8 This is a cross-sectional binary analysis comparison diagram of the internally enriched moisture-absorbing quick-drying polypropylene fiber 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 binarized and statistically analyzed. Matlab was used to read, identify, and statistically analyze the image to obtain the size and number of the dispersed phase, which was divided into four regions (Ⅰ, Ⅱ, Ⅲ, and Ⅳ). The density of the dispersed phase in different regions was observed to more clearly observe the distribution structure of the dispersed phase. 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 with the increase of PA6 viscosity, the dispersed phase PA6 shows a trend of concentration inside the fiber, the content of the dispersed phase in zones I and II increases significantly, and the content in zone IV decreases significantly, showing a phenomenon of increased internal enrichment.

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

[0180] Fig.10 This is a cross-sectional binary analysis comparison diagram of the moisture-absorbing quick-drying polypropylene fiber of Example 5, Example 11, and Example 12. In order to further observe the gradient structure of the dispersed phase in the fiber cross section, the image is binarized and counted. Matlab is used to read, identify, and count the image to obtain the size and number of the dispersed phase, and divide it into four regions (Ⅰ, Ⅱ, Ⅲ, and Ⅳ). The density of the dispersed phase in different regions is observed to more clearly observe the distribution structure of the dispersed phase. Fig.10 It can be seen that as the zero shear viscosity ratio of the two phases changes from 1.5:1 to 1.5:8.5, it can be clearly seen that with the increase of PP viscosity, the dispersed phase PA6 shows a trend of concentration outside the fiber, the content of the dispersed phase in zones I and II decreases significantly, and the content in zones III and IV increases significantly, showing a phenomenon of increased surface enrichment.

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

[0182]

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

[0184] like Fig.11 The figure shows the observation of the moisture retention effect of the fiber. After the fiber reaches equilibrium under the standard atmosphere, the fabric is moved to a relative humidity of 40% and a temperature of 20°C to test the evaporation of moisture. As can be seen from the figure, as the PA6 content in the fiber increases, the evaporation time and evaporation amount increase accordingly. 1 When the content is 20%, the evaporation time of the fiber is 80 minutes and the evaporation amount is 0.049g. As the relative viscosity of the dispersed phase PA6 increases, the enrichment of the dispersed phase inside the fiber increases, and the moisturizing effect is improved. 3 When the content is 20%, the evaporation time of the fiber is 100 minutes and the evaporation amount is 0.072g.

Claims

1. A moisture-absorbing quick-drying polypropylene fiber with a gradient structure, characterized in that: It is prepared by mixing the matrix phase and the dispersed phase to obtain a mixture and then melt-blending and spinning it; 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; Surface-enriched gradient structure refers to the gradual increase in the particle size of the dispersed phase from the center to the outside on the fiber cross section; Internally enriched gradient structure refers to the gradual decrease in the particle size of the dispersed phase from the center to the outside on the fiber cross section; The moisture-absorbing quick-drying polypropylene fiber with a gradient structure has a groove structure on its surface.

2. The moisture-absorbing quick-drying polypropylene fiber with a gradient structure according to claim 1, characterized in that: The area occupied by the groove structure is 0.5~30% of the fiber surface area. The length of the groove structure is 70~7500nm, the width is 0.8~10nm, the aspect ratio is 87.5~2500, and the depth is 1nm~25nm.

3. The moisture-absorbing and quick-drying polypropylene fiber with a gradient structure according to claim 1, characterized in that: The hydrophilic polymer is polyamide 6.

4. The moisture-absorbing quick-drying polypropylene fiber with a gradient structure according to claim 2 or 3, characterized in that: The fiber cross section is divided into concentric circular area I, annular area II, annular area III and annular area IV from the center outward; For the surface-enriched gradient structure, the particle size ranges of the dispersed phase in circular region I, circular region II, circular region III and circular region IV are 30-600nm, 50-1100nm, 100-2500nm and 200-2700nm, respectively, and the area occupied by the dispersed phase in circular region I, circular region II, circular region III and circular region IV is 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 circular region I, annular region II, annular region III and annular region IV are 200~2700nm, 150~2300nm, 100~1800nm ​​and 50~1500nm, respectively, and 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.

5. The moisture-absorbing quick-drying polypropylene fiber with a gradient structure according to claim 4, characterized in that: For the surface-enriched gradient structure, the instantaneous water contact angle of the fabric prepared by the moisture-absorbing quick-drying polypropylene fiber with a gradient structure is 15°~55º, the droplet diffusion time is 0.12~1.17s, the wicking height is 10.5~12.6cm, and the drying rate is 0.504~0.522g / h; For the internal enriched gradient structure, the instantaneous water contact angle of the fabric prepared using the hygroscopic quick-drying polypropylene fiber with a gradient structure is 72°~105º, the drip diffusion time is 0.33~8.2s, the wicking height is 7.5~11.6cm, the drying rate is 0.37~0.521g / h, and the unidirectional moisture conductivity coefficient is 20.12~479.23%.

6. A method for preparing a moisture-absorbing and quick-drying polypropylene fiber with a gradient structure, for preparing a moisture-absorbing and quick-drying polypropylene fiber with a gradient structure as claimed in any one of claims 1 to 5, characterized in that: The matrix phase and the dispersed phase are mixed to obtain a mixture, and then melt-blended and spun to obtain a moisture-absorbing quick-drying polypropylene fiber with a gradient structure; 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 10-20wt%, the molecular weight distribution index of the dispersed phase is 4.1-4.5, the relaxation time of the dispersed phase is 2.1-4.5s, and the relaxation time of the matrix phase is 4.7-8.3s; When the gradient structure is an internally enriched 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 5~25wt%, the molecular weight distribution index of the dispersed phase is 4.1~4.5, the relaxation time of the dispersed phase is 2.1~7.4s, and the relaxation time of the matrix phase is 0.5~0.8s.

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

8. The method for preparing a moisture-absorbing quick-drying polypropylene fiber with a gradient structure according to claim 6, characterized in that: The number average molecular weight of the matrix phase is 75300~121000g·mol -1 , the molecular weight distribution index is 1.7~4.

5.

9. The method for preparing a moisture-absorbing and quick-drying polypropylene fiber with a gradient structure according to claim 6, characterized in that: The process parameters of melt blending spinning are: screw temperature 235~270℃, head, connecting pipe and box temperature 250~270℃, spinning speed 1000~1200m / min.

10. The method for preparing a moisture-absorbing quick-drying polypropylene fiber with a gradient structure according to claim 9, characterized in that: After spinning, hot stretching is carried out, the stretching temperature is 50~120℃, and the stretching multiple is 2~4.

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