Modified polypropylene fiber short fiber suitable for wet-process use environment and preparation method of modified polypropylene fiber short fiber

Abstract

The invention provides a modified polypropylene staple fiber suitable for a wet process use environment and a preparation method thereof, the modified polypropylene staple fiber comprises a maleic anhydride grafted polypropylene staple fiber and a hydrophilic layer coating the surface of the maleic anhydride grafted polypropylene staple fiber, and the hydrophilic layer is obtained by crosslinking a hydrophilic polymer and a hydrophilic filler. According to the modified polypropylene short fiber, a compact hydrophilic layer formed by synergistic crosslinking of a hydrophilic polymer and a hydrophilic filler is constructed on the surface of the modified polypropylene short fiber, so that the modified polypropylene short fiber has good and stable hydrophilicity, and the dispersity, interface adaptability and hydrophilic layer stability of the polypropylene short fiber in a wet system are remarkably improved; according to the present invention, the prepared polypropylene fiber short fiber can maintain the good dispersion state in the wet-process system, and can be adhered and combined with the hydrophilic component in the wet-process system, such that the application effect of the traditional polypropylene fiber short fiber in the wet-process use environment is significantly improved, and the polypropylene fiber short fiber can be well suitable for the wet-process papermaking, the cement reinforcement and other typical wet-process processing scenes.

Description

Technical Field

[0001] The present application relates to the technical field of functional polypropylene staple fibers, and in particular to a modified polypropylene staple fiber suitable for wet use environments and a preparation method thereof. Background Art

[0002] Polypropylene (PP) staple fibers have excellent chemical stability, tensile strength, and corrosion resistance, and are widely used in a variety of fields, including concrete reinforcement, papermaking reinforcement fibers, wet-laid nonwovens, and filter substrates. Polypropylene staple fibers, due to their low cost, low specific gravity, low water absorption, and excellent mechanical properties, have great potential as reinforcing and modifying components in wet-laid processing systems.

[0003] However, since polypropylene itself is a non-polar polyolefin material and lacks polar groups on its surface, it exhibits poor wettability and extremely weak interfacial adsorption capacity in the aqueous phase system, resulting in the following problems in wet use environments such as coniferous pulp, cement mortar, and wet-laid mesh systems: poor hydrophilicity and difficulty in dispersion cause PP staple fibers to easily aggregate and settle in the aqueous phase and cannot be evenly distributed within the system, affecting the reinforcement efficiency; weak interfacial adsorption leads to a lack of sufficient adsorption between PP staple fibers and other materials (such as cellulose) in the wet use environment, and delamination or shedding is likely to occur after meshing; the adsorption interface between PP staple fibers and the matrix is unstable during the dehydration, pressing, and drying processes, resulting in unsustainable reinforcement effects.

[0004] To improve the performance of polypropylene staple fibers in wet-process applications, related technologies typically employ methods such as plasma treatment, grafting polar monomers, or blending hydrophilic components to enhance their surface hydrophilicity and dispersibility. However, these methods still present the following challenges: Due to the weak polarity of polypropylene staple fibers, direct grafting polar monomers or blending hydrophilic components has limited effectiveness in enhancing their hydrophilicity, resulting in poor dispersion stability in wet-process applications. Furthermore, blending hydrophilic components may compromise the strength of the polypropylene staple fibers themselves, thereby affecting their performance as reinforcement materials.

[0005] For example, patent CN119465431A discloses an antibacterial chitosan-modified polypropylene fiber. This method uses chitosan as a modifier to treat polypropylene with antibacterial agents. By introducing chitosan and quaternary ammonium salt structures, the antibacterial properties and a certain degree of hydrophilicity of polypropylene are enhanced. Furthermore, maleic anhydride is grafted onto PP to achieve blending enhancement. While this method improves the fiber's modification function, its structure focuses more on antibacterial and dyeing finishing, and the modification process relies on high-temperature melt blending. This method does not effectively control the dispersion stability and inherent properties of the PP staple fibers, thus significantly limiting its adaptability to wet-process applications.

[0006] Therefore, there is an urgent need for a new modification method that can give polypropylene staple fibers good hydrophilicity, dispersibility and wet interface stability while maintaining their bulk properties, so as to meet their enhancement needs in wet use environments. Summary of the Invention

[0007] The present application provides a modified polypropylene staple fiber suitable for wet-process use and a preparation method thereof. The modified polypropylene staple fiber constructs a stable hydrophilic layer formed by cross-linking a hydrophilic polymer and a surface-modified hydrophilic filler on the surface of the maleic anhydride-grafted polypropylene staple fiber, thereby solving the problems of poor dispersibility of the polypropylene staple fiber in wet-process applications, weak adsorption force with the matrix interface, and easy attenuation of the reinforcement effect after drying.

[0008] In the first aspect, the present application provides a modified polypropylene staple fiber suitable for wet use environment, comprising: maleic anhydride grafted polypropylene staple fiber, and a hydrophilic layer coated on the surface of the maleic anhydride grafted polypropylene staple fiber, wherein the hydrophilic layer is obtained by cross-linking a hydrophilic polymer and a hydrophilic filler.

[0009] According to the present application, the modified polypropylene staple fiber has good and stable hydrophilicity by constructing a dense hydrophilic layer formed by the synergistic cross-linking of hydrophilic polymers and hydrophilic fillers on its surface, thereby significantly improving the dispersibility, interface adaptability and hydrophilic layer stability of the polypropylene staple fiber in the wet system. It can maintain a good dispersion state in the wet system and can adhere to and combine with the hydrophilic components in the wet system, significantly improving the application effect of traditional polypropylene staple fibers in wet use environments, and making the polypropylene staple fibers better suitable for typical wet processing scenarios such as wet papermaking and cement reinforcement.

[0010] Specifically, the inventors found that in related technologies, the hydrophilicity of polypropylene staple fibers is often improved by separate grafting or surface treatment. However, in a wet use environment, the interfacial adsorption structure must not only have initial wetting ability, but also remain stable during dynamic processes such as slurry forming, pressing, and drying. If there is a lack of effective structural support and synergistic adsorption mechanism, the hydrophilic layer is prone to fall off or the interface delaminates, resulting in a decrease in enhanced performance. In this application, maleic anhydride grafted polypropylene staple fiber is used as the base fiber, which can provide polar groups (such as -COOH) on its surface, so that the subsequent hydrophilic polymer and hydrophilic filler can be stably adsorbed on the fiber surface through electrostatic action, hydrogen bonding or cross-linking, to construct a basic adhesion layer, and provide a basic anchoring interface for the construction of the hydrophilic layer; the hydrophilic layer is collaboratively constructed by the hydrophilic polymer and the hydrophilic filler, wherein the hydrophilic polymer has good flexibility and hydration, and can form a hydrophilic network structure that continuously absorbs water in an aqueous environment, and initially adsorbs and combines with the surface of the maleic anhydride grafted polypropylene staple fiber, and can form a continuous coating layer on the fiber surface, thereby improving its wettability and dispersibility in the aqueous phase. In the process of forming the continuous coating layer, the surface of the hydrophilic filler is generally It contains polar groups and can self-assemble in the continuous coating layer through intermolecular interactions such as hydrogen bonds. Subsequently, the hydrophilic polymers in the continuous coating layer are cross-linked by the corresponding cross-linking agent to form a network structure, so that the hydrophilic fillers are fixed to the continuous coating layer through the network structure, thereby obtaining a stable hydrophilic layer; on the one hand, the hydrophilic fillers in the hydrophilic layer can also serve as a microscopic anchoring skeleton due to their own rigid structure, which can improve the physical stability of the hydrophilic layer (such as water washing resistance, shear resistance and structural integrity during the drying process); on the other hand, the protrusions of the hydrophilic fillers can increase the roughness of the surface of the hydrophilic layer, thereby improving the interface contact efficiency between the modified polypropylene staple fiber and other hydrophilic materials in the wet system, so that it has stronger interface bonding ability in the wet system.

[0011] Therefore, this application collaboratively constructs a hydrophilic layer through the method of "hydrophilic polymer + hydrophilic filler + cross-linking structure". On the basis of maintaining the original mechanical properties of polypropylene, the fiber obtains stronger water-phase adaptability and more stable interface bonding ability, thereby achieving a balance between the dispersion enhancement effect and durability of short fibers in a wet use environment.

[0012] In some embodiments, the maleic anhydride grafted polypropylene staple fiber is obtained by melt spinning maleic anhydride grafted polypropylene and polypropylene.

[0013] In some of the above embodiments, compared with maleic anhydride grafted polypropylene fibers prepared by traditional methods such as solution grafting and plasma treatment, the present embodiment adopts a method of directly melt spinning after blending maleic anhydride grafted polypropylene (PP-g-MAH) with polypropylene, which can make the grafted groups tend to be enriched and distributed on the fiber surface during the melt spinning and cooling molding process. The polar functional groups formed have the advantages of more uniform distribution, more stable structure, and not easy to migrate or hydrolyze and inactivate, thereby providing a more continuous anchoring interface for the adsorption and cross-linking of hydrophilic polymers and hydrophilic fillers, thereby improving the structural integrity and water resistance of the hydrophilic layer in a wet application environment, and further enhancing the dispersion of the short fibers in the slurry and the interfacial adhesion performance with the hydrophilic matrix.

[0014] In some embodiments, the maleic anhydride grafted polypropylene has a maleic anhydride grafting rate of 0.5 wt% to 1.5 wt%, a weight-average molecular weight of 50,000 to 100,000, a weight-average molecular weight of 150,000 to 250,000, and a mass ratio of the maleic anhydride grafted polypropylene to the polypropylene of 0.1 to 0.3:1. For example, in one embodiment of the present application, the maleic anhydride grafted polypropylene has a maleic anhydride grafting rate of 1 wt%, a weight-average molecular weight of 80,000, a weight-average molecular weight of 200,000, and a mass ratio of the maleic anhydride grafted polypropylene to the polypropylene of 0.25:1.

[0015] In some embodiments, the melt spinning conditions include: using a screw extruder at 200-220°C and a screw speed of 100-200 rpm to perform melt mixing and then cooling and granulating, and then feeding the prepared granules into a melt spinning machine, spinning at a spinneret temperature of 230-240°C, and stretching at a stretching ratio of 3-5 times.

[0016] In some embodiments, the hydrophilic polymer includes chitosan and polylysine, and the mass ratio of chitosan to polylysine is 4-8:1.

[0017] In some of the above-mentioned embodiments, by compounding chitosan and polylysine in a mass ratio of 4 to 8:1 as the hydrophilic polymer component, it is possible to achieve a balanced regulation of structural stability and hydration adsorption capacity on the basis of ensuring that the hydrophilic layer as a whole is positively charged and has good hydrophilicity, thereby further improving the coating integrity and functional synergy of the hydrophilic layer in a wet use environment.

[0018] Specifically, chitosan has a natural polyhydroxyl and polyamine structure, is highly hydrophilic, and can provide good hydration ability and flexibility, but its cross-linking density is low and its mechanical support is poor. If used alone, the hydrophilic layer is prone to swelling, breaking or falling off during shearing or drying. Polylysine has a high density of amino groups and high cross-linking activity, and can form a dense cross-linked network with a cross-linking agent, but its chain segment rigidity is relatively large. If the ratio is too high, it can easily lead to increased brittleness of the hydrophilic layer and decreased water absorption. The inventors found through experiments that when the mass ratio of chitosan to polylysine is controlled within the range of 4 to 8:1, the hydrophilic layer can form a dual-functional network structure that is both flexible and conformable, and densely cross-linked, and has better interface adhesion and film-forming stability in a wet slurry environment, thereby further enhancing the dispersibility and peeling resistance of the short fibers and their structural integrity during the wet-dry cycle.

[0019] It can also be understood that the hydrophilic polymers used, chitosan and polylysine, are both positively charged, and both are more easily adsorbed on the maleic anhydride grafted polypropylene staple fibers to form a continuous coating layer, and also make the resulting hydrophilic layer positively charged, which can effectively inhibit the agglomeration and degradation of the modified polypropylene staple fibers in the wet system. It is also worth noting that in the wet system where polypropylene staple fibers are added as reinforcing fibers, such as concrete slurry and coniferous wood slurry, the matrix materials such as cement hydration particles and coniferous wood fiber surfaces are negatively charged, so the modified polypropylene staple fibers with positive surface charge can adhere to the matrix material in the system through electrostatic action, further improving the reinforcing effect of the modified polypropylene staple fibers in the wet system.

[0020] In some embodiments, the chitosan has a degree of deacetylation of 80% to 95% and a weight-average molecular weight of 100,000 to 300,000; the polylysine has a weight-average molecular weight of 5,000 to 10,000. For example, in one embodiment of the present application, the chitosan has a degree of deacetylation of 90% and a weight-average molecular weight of 150,000, and the polylysine has a weight-average molecular weight of 6,000.

[0021] In some embodiments, amino groups are grafted onto the surface of the hydrophilic filler.

[0022] In some of the above-mentioned embodiments, by grafting amino functional groups on the surface of the hydrophilic filler, it has good chemical reactivity and polar adsorption capacity, which can not only undergo cross-linking reaction with the hydrophilic polymer to enhance the structural density and stability of the hydrophilic layer, but also enhance the affinity between the hydrophilic filler and the surface of the maleic anhydride grafted polypropylene staple fiber, thereby further improving the adhesion performance and water resistance retention ability of the hydrophilic layer.

[0023] Specifically, amino functional groups can be adsorbed with hydrophilic polymers through hydrogen bonds. In the presence of a crosslinker, the amino functional groups can crosslink with the amine groups on chitosan and polylysine. As a result, the hydrophilic filler not only serves as a physical embedding point, but also participates in the construction of the solidified structure as part of the chemical network, effectively improving the structural integrity and shear stability of the hydrophilic layer in the aqueous system. Furthermore, amino functionalization imparts a certain degree of hydrophilicity and cationic charge to the filler surface, which helps it to be stably distributed in the aqueous dispersion system, prevents particle agglomeration and sedimentation, and facilitates the formation of a continuous and uniform composite coating with the hydrophilic polymer during the coating process.

[0024] Therefore, by introducing hydrophilic fillers with surface grafted amino groups, not only can the cross-linking ability between it and the polymer be enhanced, but also the overall stability and reinforcement performance of the hydrophilic layer can be improved from the two aspects of interfacial chemical bonding and microscopic distribution, further improving the dispersibility of the modified polypropylene staple fiber in the wet use environment, the interfacial adsorption strength and the reinforcement effect in the wet system.

[0025] In some embodiments, the hydrophilic layer is obtained by cross-linking the hydrophilic polymer and the hydrophilic filler with glutaraldehyde.

[0026] In some of the above-mentioned embodiments, by using glutaraldehyde as a cross-linking agent, a covalent cross-linking structure is formed between the hydrophilic polymer and the hydrophilic filler with surface grafted amino groups, which can effectively improve the structural stability, water retention and shear resistance of the hydrophilic layer, and further enhance the interfacial adhesion effect and durability of the modified polypropylene staple fiber in a wet use environment.

[0027] Specifically, the glutaraldehyde molecule contains two aldehyde groups, which can undergo an aldehyde-amine condensation reaction with primary or secondary amine groups on the surface of polymers or particles under mild aqueous conditions to generate a C=N structure (imine bond), forming a three-dimensional cross-linked network between the hydrophilic polymer and filler. Compared with simple physical adsorption or hydrogen bonding, the cross-linked structure has stronger chemical stability and anti-peeling ability.

[0028] Therefore, by using glutaraldehyde to cross-link the hydrophilic polymer and hydrophilic filler, not only the stable configuration connection between the organic-inorganic components in the hydrophilic layer is achieved, but also the hydrophilic layer's resistance to shear, hydrolysis and interfacial stress in the aqueous phase system is significantly enhanced, thereby further improving the reinforcement effect of the modified polypropylene staple fiber in the wet system.

[0029] In some embodiments, an imidazole ring is grafted onto the surface of the hydrophilic filler.

[0030] In some of the above embodiments, by further introducing an imidazole ring structure on the surface of the hydrophilic filler, the hydrophilic layer can be given stronger adaptability to the aqueous environment and higher interfacial binding stability. Especially in wet application systems, the imidazole structure can provide an enhancement effect that is different from conventional amino-modified fillers through its unique polar effect and metal ion coordination ability.

[0031] Specifically, the imidazole ring is a polar nitrogen heteroaromatic ring structure with a conjugated electron system. On the one hand, it can form a stable polar hydration layer in the aqueous phase, improving the interfacial wettability and anti-agglomeration ability of the short fiber when dispersed in water; on the other hand, the nitrogen atom on its heterocyclic ring can react with multivalent cations (such as Ca 2+ 、Al 3+ ) chelate, thereby reducing the shielding interference of these ions on the electrostatic adsorption of the hydrophilic layer. Through the coordination bridge structure of "imidazole-metal ion-pulp fiber", an additional stable adsorption interface is established. Furthermore, the imidazole ring has excellent molecular planar flexibility and high polarity, and is independent of charge adsorption. It can maintain adsorption capacity on the fiber surface even when electrostatic adsorption weakens, effectively solving the problem of interfacial bonding attenuation caused by charge dissipation and decreased adsorption during wet forming and drying processes.

[0032] Therefore, by introducing the imidazole ring structure on the surface of the hydrophilic filler, not only the stability and adaptability of the hydrophilic layer in the aqueous phase are improved, but also the interfacial adsorption strength between the staple fiber and the hydrophilic matrix in the wet system is further enhanced through the synergistic effect of polar adsorption and metal ion coordination, which helps to improve the dispersibility of the modified polypropylene staple fiber in the wet system and the reinforcement effect in the wet system.

[0033] In some embodiments, the hydrophilic filler is obtained by modifying the filler with an aminosilane coupling agent and an imidazole silane coupling agent, wherein the mass ratio of the aminosilane coupling agent to the imidazole silane coupling agent is 1 to 3:1.

[0034] In some of the above embodiments, by using aminosilane coupling agents and imidazole silane coupling agents to synergistically modify the hydrophilic filler, amino functional groups and imidazole ring structures can be simultaneously introduced on the filler surface to construct a dual-functional surface with both cross-linking activity and interface adsorption function, wherein the mass ratio of aminosilane to imidazole silane is controlled at 1~3:1, which can ensure that the filler has good cross-linking ability while introducing a sufficient amount of imidazole ring structure, further giving the hydrophilic layer stable hydration adsorption capacity and adaptability to wet use environment, thereby achieving a balanced synergy between the structural stability of the hydrophilic layer and the interface functionality.

[0035] Specifically, the aminosilane coupling agent can provide the main chemical cross-linking sites in the presence of glutaraldehyde to form a cross-linked skeleton structure of the hydrophilic layer; while the imidazole silane coupling agent provides stable polar adsorption sites, enhances the interfacial affinity between the filler particles and the hydrophilic fibers in the slurry, and forms an adjustable additional adsorption channel through metal ion coordination.

[0036] The inventors further discovered that when the proportion of imidazole groups on the filler surface is low, while a cross-linked network can form, the hydrophilic layer's adaptability to wet-process environments is significantly reduced, impacting the durability of the modified polypropylene fiber's reinforcement. Excessive imidazole components can weaken the cross-linking density and reduce structural strength. Compounding aminosilane and imidazolesilane in a mass ratio of 1 to 3:1 can form a composite interface on the filler surface that possesses both a stable structure and synergistic adsorption capacity, facilitating the construction of a flexible, dense, and well-adherent hydrophilic coating in wet-process environments.

[0037] Therefore, the use of aminosilane and imidazole silane to modify the filler in a mass ratio of 1~3:1 can not only improve the structural integrity of the hydrophilic layer, but also improve the dispersion performance of the staple fiber in the aqueous phase system and the interfacial bonding efficiency in the slurry matrix, thereby further improving the reinforcement effect of the modified polypropylene staple fiber in the wet system.

[0038] It should be noted that aminosilane coupling agent and imidazole silane coupling agent have well-known meanings in the art, that is, aminosilane coupling agent refers to a silane coupling agent containing an amino group, and imidazole silane coupling agent refers to a silane coupling agent containing an imidazole group. As an example, in one embodiment of the present application, the aminosilane coupling agent is 3-aminopropyltrimethoxysilane, and the imidazole silane coupling agent is N-(trimethoxysilylpropyl)imidazole.

[0039] In some embodiments, the filler includes mesoporous silica and montmorillonite, and the mass ratio of the mesoporous silica to montmorillonite is 1~3:1; wherein the average particle size of the mesoporous silica is 100~200nm and the average pore size is 1~5nm; the average flake size of the montmorillonite is 200~500nm and the average thickness is 1~3nm.

[0040] In some of the above-mentioned embodiments, by designing a composite filler of mesoporous silica and montmorillonite and combining their respective structural advantages, a composite microstructure having dense support, polar hydrophilicity and interface expansion capabilities can be formed in the hydrophilic layer, thereby further improving the structural stability of the hydrophilic layer, the hydration retention ability and the bonding efficiency with the matrix in the wet system.

[0041] Specifically, mesoporous silica has a mesoporous structure and high specific surface area, which not only provides a large number of distribution sites for functional groups such as amino and imidazole groups, helping to form high-density cross-linking points, but its internal pores can also adsorb some water molecules, constructing flexible hydration channels, and enhancing the water content and flexibility of the hydrophilic layer. Controlling the particle size between 100 and 200 nm facilitates uniform dispersion of particles, while forming a strong supporting skeleton, improving the density and shear resistance of the hydrophilic layer. Montmorillonite has a flaky structure and can be distributed in the hydrophilic layer in a transversely expanded or locally protruding manner. Its nanometer-scale thickness and large flake diameter enable it to form a rough microstructure on the fiber surface, enhancing the physical embedding force between the short fibers and the slurry. At the same time, the arranged gaps formed between the montmorillonite flakes can construct multi-directional migration paths for water and ions, promoting interfacial reactions and adsorption rearrangements in the wet system. The particle size is controlled at 200~500nm and the thickness is 1~3nm to take into account both dispersibility and structural stability.

[0042] The inventors found that if only mesoporous SiO2 is used as a filler, although it can provide good dispersibility and cross-linking properties, the roughness of the fiber surface is relatively low, and it is not easy to form a three-dimensional contact structure with the matrix material in the wet system, and there are local gaps in the interface bonding; and if montmorillonite is used alone, it is easy to form uneven dispersion or overlapping layers, resulting in discontinuous hydrophilic layer structure, stress concentration, and reduced stability.

[0043] Therefore, compounding mesoporous silica and montmorillonite in a mass ratio of 1 to 3:1 can not only construct a cross-linked main skeleton through mesoporous silica, but also utilize flaky montmorillonite to improve the surface roughness and permeation channel structure, thereby improving the density and consistency of the hydrophilic layer on a macro scale, and improving the adhesion and adsorption stability of the interface between the fiber and the matrix material in the wet system on a micro scale, thereby improving the reinforcement effect of the modified polypropylene staple fiber in the wet system.

[0044] As an example, in one embodiment of the present application, the mesoporous silica is SBA-15 with an average particle size of 150 nm and an average pore size of 3 nm; the montmorillonite is sodium-montmorillonite with an average sheet size of 400 nm and an average thickness of 2 nm.

[0045] In a second aspect, the present application provides a method for preparing modified polypropylene staple fibers suitable for wet use environments, comprising the following steps: The maleic anhydride grafted polypropylene staple fiber is immersed in a mixed solution in which a hydrophilic polymer and a hydrophilic filler are dispersed, so that the maleic anhydride grafted polypropylene staple fiber adsorbs the hydrophilic polymer and the hydrophilic filler through hydrogen bonding and / or electrostatic interaction; The maleic anhydride polypropylene staple fiber with hydrophilic polymer and hydrophilic filler adsorbed on the surface is cross-linked using a cross-linking agent, so that the hydrophilic polymer and hydrophilic particles adsorbed on the surface of the maleic anhydride polypropylene staple fiber are cross-linked to form a hydrophilic layer, thereby obtaining modified polypropylene staple fibers.

[0046] According to the present application, through the above-mentioned adsorption-cross-linking step-by-step treatment method, a structurally stable and evenly distributed hydrophilic layer can be constructed on its surface without changing the main structure of the polypropylene staple fiber, thereby significantly improving the fiber's dispersibility, suspension stability and interface adsorption capacity in the wet system.

[0047] Specifically, the polar groups on the surface of polypropylene fibers grafted with maleic anhydride can generate preliminary hydrogen bonds and electrostatic adsorption effects between the hydrophilic polymer and the hydrophilic filler during the immersion process, so that the hydrophilic components are directionally enriched and evenly distributed on the fiber surface, thereby improving the coating uniformity and construction efficiency; in the subsequent cross-linking step, the functional groups in the adsorption layer react and solidify under the action of the cross-linking agent to form a dense and stable cross-linked network structure, which not only enhances the structural integrity of the hydrophilic layer, but also improves its interfacial adhesion and adaptability to the matrix environment.

[0048] This method is easy to operate and suitable for normal temperature aqueous conditions. It is particularly suitable for post-processing of polypropylene staple fibers after melt spinning. It has good process compatibility and industrial scale-up potential, and can be widely used in various wet-process application scenarios such as pulp reinforcement, cement reinforcement, and wet non-wovens.

[0049] In some embodiments, the selection of maleic anhydride grafted polypropylene staple fibers, hydrophilic polymers, hydrophilic fillers, and corresponding crosslinking agents in the method can be selected according to any embodiment of the first aspect to achieve corresponding beneficial effects, which will not be further described in this section.

[0050] In some embodiments, in the mixed solution, the mass percentage of the hydrophilic polymer is 0.5% to 2%, and the mass percentage of the hydrophilic filler is 0.1% to 0.5%.

[0051] In some embodiments, the cross-linking conditions include: soaking the maleic anhydride polypropylene staple fibers having the hydrophilic polymer and the hydrophilic filler adsorbed on the surface in a 1 wt % to 5 wt % glutaraldehyde aqueous solution for cross-linking for 0.5 to 1 hour.

[0052] In a third aspect, the present application provides a paper product comprising: coniferous wood fiber, and modified polypropylene staple fiber according to any embodiment of the first aspect or modified polypropylene staple fiber prepared by the method according to any embodiment of the second aspect.

[0053] According to the present application, modified polypropylene staple fibers according to any embodiment of the first aspect or modified polypropylene staple fibers prepared by the method according to any embodiment of the second aspect are added to paper products. The modified polypropylene staple fibers have a hydrophilic layer coated on the surface and can form stable interface adsorption with coniferous wood fibers during the entire wet pulping-papermaking process, effectively overcoming the problems of "floating, agglomeration, delamination" caused by the hydrophobicity of traditional polypropylene fibers, so that the staple fibers have excellent dispersibility and enhanced durability in the pulp system. Therefore, the paper product has higher tensile strength while maintaining the original light paper base structure and strong papermaking ability, and is suitable for application scenarios such as packaging paper, tear-resistant paper, waterproof paper and industrial filter paper with high requirements on mechanical properties.

[0054] Specifically, by introducing modified polypropylene staple fibers with a hydrophilic coating layer on the surface into the paper product structure, a three-dimensional embedded network structure can be formed inside the paper sheet, and a stable interface bond can be constructed in the fiber cross-linking area. This structure is not easy to break or delaminate after drying and shaping, and can significantly improve the dry tensile strength, elongation at break and peel strength of the paper sheet. At the same time, since the modified staple fibers have good dispersibility and are not easy to agglomerate during the papermaking process, they are evenly distributed among the coniferous wood fibers, which helps to improve the overall density and structural uniformity of the paper sheet, and still maintains excellent thickness stability and dimensional stability after pressing and drying. Therefore, the paper product provided by this application is superior to traditional unreinforced paper products or paper sheet structures reinforced with conventional staple fibers in terms of strength, stability, functionality, etc., and is suitable for fields with higher requirements for paper performance, such as industrial packaging, building materials and auxiliary materials, and wet filtration materials.

[0055] Compared with the prior art, the present invention has the following advantages: 1. A structural modification method for constructing a hydrophilic coating on the surface of polypropylene staple fibers is provided, significantly improving their dispersibility and interfacial bonding ability in wet-process systems; 2. By compounding chitosan and polylysine, a flexible and stable positively charged hydrophilic layer is synergistically constructed, thereby enhancing the adsorption stability of the fiber to the matrix material in the wet process; 3. Use imidazole and amino bifunctional modified fillers, combined with mesoporous silica and montmorillonite compound design to improve the structural density and durability of the hydrophilic layer; 4. It has the comprehensive advantages of uniform coating, simple preparation and stable reinforcement effect, and is suitable for various reinforcement applications such as wet papermaking and cement-based materials. DETAILED DESCRIPTION

[0056] The various embodiments or implementation schemes in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments.

[0057] Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" means that a specific feature, structure, material, or characteristic described in conjunction with an embodiment or example is included in at least one embodiment or example of the present application. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0058] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of such features. Throughout the description of this application, "plurality" means at least two, for example, two, three, etc., unless otherwise specifically defined.

[0059] In the description of this specification, unless otherwise specified, "parts" refer to "parts by mass".

[0060] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0061] Maleic anhydride grafted polypropylene: maleic anhydride grafting rate is 1wt%, weight average molecular weight is 80,000; Isotactic polypropylene: weight average molecular weight is 200,000; Chitosan: Deacetylation degree is 90%, weight average molecular weight is 150,000; Polylysine: weight average molecular weight is 6000; Mesoporous silica: SBA-15 with an average particle size of 150 nm and an average pore size of 3 nm; The montmorillonite is sodium-based montmorillonite having an average flake diameter of 400 nm and an average thickness of 2 nm.

[0062] Preparation Example 1 Preparation of maleic anhydride grafted polypropylene staple fiber: Maleic anhydride-grafted polypropylene and isotactic polypropylene were mixed in a mass ratio of 0.25:1 and melt-kneaded in a twin-screw extruder at 210°C, with a screw speed of 150 rpm and a kneading time of 8 minutes to produce a blended masterbatch. The resulting masterbatch was dried and fed into a melt spinning machine with a spinning head temperature of 235°C, a spinning speed of 500 m / min, and a draw ratio of 4. After cooling and shaping, the filaments were collected. The fiber tows were chopped to a cut length of 6 mm to produce maleic anhydride-grafted polypropylene staple fibers.

[0063] The obtained maleic anhydride grafted polypropylene staple fibers had a uniform appearance, no adhesion, and a fiber diameter of about 20 μm.

[0064] Preparation Example 2 Preparation of hydrophilic filler: 5 parts of mesoporous silica and 2.5 parts of montmorillonite were mixed and dispersed in 100 parts of an 80:20 (volume ratio) mixture of anhydrous ethanol and water. Ultrasonic dispersion was performed for 30 minutes. Under magnetic stirring, 1 part of 3-aminopropyltrimethoxysilane and 0.5 parts of N-(trimethoxysilylpropyl)imidazole were added sequentially. The reaction temperature was controlled at 60°C and stirred for 4 hours to graft the silane coupling agent onto the filler surface. After the reaction, the solid was centrifuged, washed three times with anhydrous ethanol, and dried under vacuum to obtain hydrophilic filler A.

[0065] Preparation Example 3 Preparation of hydrophilic filler: The hydrophilic filler B was obtained by using the same method as in Preparation Example 2, except that an equal amount of mesoporous silica was used instead of montmorillonite, that is, 7.5 parts by mass of mesoporous silica was used.

[0066] Preparation Example 4 Preparation of hydrophilic filler: The hydrophilic filler C was obtained by using the same method as in Preparation Example 2, except that an equal amount of montmorillonite was used instead of the mesoporous silica, that is, 7.5 parts by mass of montmorillonite was used.

[0067] Preparation Example 5 The hydrophilic filler D was obtained by using the same method as in Preparation Example 2, except that 3-aminopropyltrimethoxysilane was used in place of N-(trimethoxysilylpropyl)imidazole in equal parts by mass, i.e., 1.5 parts of 3-aminopropyltrimethoxysilane was used.

[0068] Preparation Example 6 The method is similar to Preparation Example 2, except that 0.5 parts of 3-aminopropyltrimethoxysilane and 1 part of N-(trimethoxysilylpropyl)imidazole are used as silane coupling agents to obtain hydrophilic filler E.

[0069] Preparation Example 7 The method is similar to Preparation Example 2, except that an equal amount of N-(trimethoxysilylpropyl)imidazole is used instead of 3-aminopropyltrimethoxysilane, that is, 1.5 parts of N-(trimethoxysilylpropyl)imidazole is used to obtain hydrophilic filler F.

[0070] Example 1

[0071] Preparation of modified polypropylene staple fiber: Chitosan was dissolved in a 1 wt % acetic acid aqueous solution, polylysine and hydrophilic filler A were added, and ultrasonic dispersion was performed for 15 minutes. Water was added to obtain a mixed solution; wherein the weight percentage of the hydrophilic polymer was 1%, which was a mixture of chitosan and polylysine in a mass ratio of 5:1, and the weight percentage of the hydrophilic filler A was 0.2%; The maleic anhydride grafted polypropylene staple fiber was immersed in the above-mentioned mixed solution, stirred and adsorbed at room temperature for 1 hour, and filtered after the adsorption to obtain the maleic anhydride polypropylene staple fiber with hydrophilic polymer and hydrophilic filler adsorbed on the surface. The maleic anhydride grafted polypropylene staple fiber was transferred and immersed in a 3wt% glutaraldehyde aqueous solution, stirred and cross-linked at room temperature for 1 hour, and taken out after the cross-linking was completed, washed three times with deionized water, and dried at 55°C for 12 hours to obtain the modified polypropylene staple fiber.

[0072] Example 2

[0073] Preparation of modified polypropylene staple fiber: Chitosan was dissolved in a 1 wt% acetic acid aqueous solution, and hydrophilic filler A was added, and ultrasonic dispersion was performed for 15 minutes. Water was added to obtain a mixed solution; wherein the mass percentage of the hydrophilic polymer was 1%, the hydrophilic polymer was chitosan, and the mass percentage of the hydrophilic filler A was 0.2%; The maleic anhydride grafted polypropylene staple fiber was immersed in the above-mentioned mixed solution, stirred and adsorbed at room temperature for 1 hour, and filtered after the adsorption to obtain the maleic anhydride polypropylene staple fiber with hydrophilic polymer and hydrophilic filler adsorbed on the surface. The maleic anhydride grafted polypropylene staple fiber was transferred and immersed in a 3wt% glutaraldehyde aqueous solution, stirred and cross-linked at room temperature for 1 hour, and taken out after the cross-linking was completed, washed three times with deionized water, and dried at 55°C for 12 hours to obtain the modified polypropylene staple fiber.

[0074] Example 3

[0075] Preparation of modified polypropylene staple fiber: The method is substantially the same as Example 1, except that the hydrophilic polymer is chitosan and polylysine in a mass ratio of 3:1.

[0076] Example 4

[0077] Preparation of modified polypropylene staple fiber: The method is substantially the same as Example 1, except that the hydrophilic polymer is chitosan and polylysine in a mass ratio of 9:1.

[0078] Example 5

[0079] Preparation of modified polypropylene staple fiber: The process is substantially the same as Example 1, with the only difference being that hydrophilic filler B is used instead of hydrophilic filler A.

[0080] Example 6

[0081] Preparation of modified polypropylene staple fiber: The process is substantially the same as Example 1, with the only difference being that hydrophilic filler C is used instead of hydrophilic filler A.

[0082] Example 7

[0083] Preparation of modified polypropylene staple fiber: The process is substantially the same as Example 1, with the only difference being that hydrophilic filler D is used instead of hydrophilic filler A.

[0084] Example 8

[0085] Preparation of modified polypropylene staple fiber: The process is substantially the same as Example 1, with the only difference being that hydrophilic filler E is used instead of hydrophilic filler A.

[0086] Example 9

[0087] Preparation of modified polypropylene staple fiber: The process is substantially the same as Example 1, with the only difference being that hydrophilic filler F is used instead of hydrophilic filler A.

[0088] Comparative Example 1 Preparation of modified polypropylene staple fiber: Chitosan was dissolved in a 1 wt % acetic acid aqueous solution, polylysine was added, and ultrasonic dispersion was performed for 15 minutes. Water was added to obtain a mixed solution; wherein the mass percentage of the hydrophilic polymer was 1%, and the hydrophilic polymer was a mixture of chitosan and polylysine in a mass ratio of 5:1; The maleic anhydride grafted polypropylene staple fiber was immersed in the above-mentioned mixed solution, stirred and adsorbed at room temperature for 1 hour, and filtered after the adsorption to obtain the maleic anhydride polypropylene staple fiber with the hydrophilic polymer adsorbed on the surface. The maleic anhydride polypropylene staple fiber was transferred and immersed in a 3wt% glutaraldehyde aqueous solution, stirred and cross-linked at room temperature for 1 hour, and taken out after the cross-linking was completed, washed three times with deionized water, and dried at 55°C for 12 hours to obtain the modified polypropylene staple fiber.

[0089] Test section Determination of strength of paper reinforced with modified polypropylene staple fibers: Bleached softwood kraft pulp was used as the primary pulp and thoroughly dispersed before beating. The pulp was beaten in a pulper until the Canadian freeness reached 330 mL and the pulp consistency reached 2 wt%. The beating time was approximately 20 minutes. The resulting pulp had fibers approximately 1.5–2.0 mm in length, with uniform fiber thickness and no flocculent lumps.

[0090] Weigh 9.80g of the dry weight of the softwood pulp after beating, add water to dilute it to 1000mL, and stir evenly. Pre-disperse the modified polypropylene staple fibers (length 6mm, dry weight 0.20g) prepared in each embodiment of the present application and the comparison in a small amount of water, ultrasonicate for 2 minutes, and stir to form a uniform dispersion. Add the staple fiber dispersion to the pulp system and continue stirring for 5 minutes to form a composite slurry with a dry matter weight of 10g (the dry weight of the polypropylene staple fibers accounts for 2wt%). Use a cylindrical papermaking machine with a diameter of 200mm, pour the slurry into the papermaking barrel, stir evenly, let it stand for 30s, filter it into paper sheets, and control the paper quantity at 80g / m 2 The paper was pressed through filter cloth to a moisture content of approximately 60%, and then dried in a forced air drying oven at 105°C for 10 minutes. After drying, the paper was placed in a constant temperature and humidity chamber (23±1°C, relative humidity 50±2%) for 24 hours.

[0091] It should be noted that in order to eliminate chemical additives and process interference, in the test part of this application, no retaining agents, dry strength agents, sizing agents and other additives were added during the papermaking process. The pulp and modified polypropylene staple fibers were directly papered by physical mixing, and no corresponding calendering or other treatments were performed to test the reinforcing effect of the modified polypropylene staple fibers on the paper.

[0092] At the same time, paper obtained by using the maleic anhydride grafted polypropylene staple fibers obtained in Preparation Example 1 with the same doping amount was used as a blank example.

[0093] Subsequently, the tensile strength of the papers to be tested was tested in accordance with GB / T 12914-2018, and the results are shown in Table 1.

[0094] Table 1

[0095] According to Table 1, each embodiment has a higher tensile strength than the blank example and comparative example 1, indicating that the present application can significantly enhance the interfacial bonding ability between the staple fibers and the pulp matrix and improve the overall strength of the paper sheet structure by constructing a hydrophilic coating layer formed by cross-linking a hydrophilic polymer and a modified filler on the surface of the polypropylene staple fibers. Among them, the blank example only uses uncoated maleic anhydride grafted polypropylene staple fibers. Since its surface is still hydrophobic, the staple fibers are prone to aggregation, floating or delamination in the slurry, making it difficult to establish an effective bond with the hydrophilic pulp fibers, resulting in a weak reinforcement effect. Although comparative example 1 introduces a hydrophilic polymer to form a hydrophilic layer, due to the lack of filler support and a cross-linked network, the hydrophilic layer structure is unstable and the fiber reinforcement effect is limited.

[0096] Examples 1-4 demonstrate that the use of different hydrophilic polymers significantly impacts the effectiveness of modified polypropylene staple fiber-reinforced paper. In Example 2, chitosan alone exhibited significantly weaker reinforcement than the combined system, demonstrating that while chitosan possesses hydrophilicity and flexibility, it lacks sufficient crosslinking capacity, resulting in a lack of structural stability in the hydrophilic layer. In contrast, the introduction of polylysine in Examples 3 and 4, by adjusting the combined ratio, enhanced crosslinking density and improved structural compactness and interfacial compatibility in the hydrophilic layer. This demonstrates that using a certain ratio of chitosan and polylysine as hydrophilic polymers yields superior paper reinforcement, making modified polypropylene staple fibers more suitable for wet-process applications.

[0097] Examples 1, 5, and 6 show that using different filler structures significantly impacts the effectiveness of modified polypropylene staple fiber-reinforced paper. The composite structure employed in Example 1 is more conducive to forming a dense, hierarchical hydrophilic layer network, balancing adsorption stability and interfacial roughness, and facilitating uniform embedding of the staple fibers within the slurry. The resulting modified polypropylene staple fibers exhibit a superior paper reinforcement effect and are more suitable for wet-process applications.

[0098] According to Examples 1, 7 to 9, it can be seen that the configuration of the functional groups on the filler surface has a significant impact on the effect of the modified polypropylene staple fiber reinforced paper. In Example 7, the hydrophilic filler does not contain an imidazole structure, and the tensile strength is significantly reduced, indicating that after the lack of polar adsorption and metal coordination ability, the interfacial adsorption force between the hydrophilic layer of the modified polypropylene staple fiber and the fibers in the pulp decreases; and after increasing the imidazole ratio in Example 8, the tensile strength is improved to a certain extent, but because the proportion of imidazole groups is too high, the cross-linking point density is relatively insufficient, the overall density of the hydrophilic layer is limited, and the tensile strength is lower than that in Example 1; in Example 9, the hydrophilic filler is not grafted with amino groups, and the cross-linking density is significantly reduced, resulting in poor stability of the hydrophilic layer and a significant decrease in tensile strength; in Example 1, aminosilane and imidazole silane are compounded in a mass ratio of 2:1, which can make the hydrophilic filler take into account good cross-linking and curing ability and interfacial adsorption ability, achieve a balance between structural density and environmental adaptability of the hydrophilic layer, and have better tensile strength; It shows that in the process of filler modification, by regulating the appropriate ratio of amino and imidazole functional groups to form a synergistic structure, the modified polypropylene staple fiber can have a better reinforcing effect on paper, making it more suitable for wet use environment.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A modified polypropylene staple fiber suitable for wet use environment, characterized in that: include: Maleic anhydride grafted polypropylene staple fiber, and a hydrophilic layer coated on the surface of the maleic anhydride grafted polypropylene staple fiber, wherein the hydrophilic layer is obtained by cross-linking a hydrophilic polymer and a hydrophilic filler.

2. The modified polypropylene staple fiber according to claim 1, characterized in that The maleic anhydride grafted polypropylene staple fibers are obtained by melt spinning maleic anhydride grafted polypropylene and polypropylene.

3. The modified polypropylene staple fiber according to claim 1, characterized in that The hydrophilic polymer includes chitosan and polylysine, and the mass ratio of the chitosan to polylysine is 4-8:

1.

4. The modified polypropylene staple fiber according to claim 3, characterized in that The surface of the hydrophilic filler is grafted with amino groups.

5. The modified polypropylene staple fiber according to claim 4, characterized in that The hydrophilic layer is obtained by cross-linking the hydrophilic polymer and the hydrophilic filler with glutaraldehyde.

6. The modified polypropylene staple fiber according to claim 4, characterized in that Imidazole rings are also grafted onto the surface of the hydrophilic filler.

7. The modified polypropylene staple fiber according to claim 6, characterized in that The hydrophilic filler is obtained by modifying the filler with an aminosilane coupling agent and an imidazole silane coupling agent, wherein the mass ratio of the aminosilane coupling agent to the imidazole silane coupling agent is 1-3:

1.

8. The modified polypropylene staple fiber according to claim 7, characterized in that The filler comprises mesoporous silica and montmorillonite, and the mass ratio of the mesoporous silica to the montmorillonite is 1 to 3:1; Wherein, the average particle size of the mesoporous silica is 100-200 nm and the average pore size is 1-5 nm; The average flake diameter of the montmorillonite is 200-500 nm, and the average thickness is 1-3 nm.

9. A method for preparing modified polypropylene staple fibers suitable for wet use environments, characterized in that: The following steps are involved: The maleic anhydride grafted polypropylene staple fiber is immersed in a mixed solution in which a hydrophilic polymer and a hydrophilic filler are dispersed, so that the maleic anhydride grafted polypropylene staple fiber adsorbs the hydrophilic polymer and the hydrophilic filler through hydrogen bonding and / or electrostatic interaction; The maleic anhydride polypropylene staple fiber with hydrophilic polymer and hydrophilic filler adsorbed on the surface is cross-linked using a cross-linking agent, so that the hydrophilic polymer and hydrophilic particles adsorbed on the surface of the maleic anhydride polypropylene staple fiber are cross-linked to form a hydrophilic layer, thereby obtaining modified polypropylene staple fibers.

10. A paper product, characterized in that include: Coniferous wood fiber, and the modified polypropylene staple fiber according to any one of claims 1 to 8 or Modified polypropylene staple fiber prepared according to the method of claim 9.

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