High-strength antibacterial polypropylene staple fiber and preparation method thereof

Abstract

The invention discloses a high-strength antibacterial polypropylene staple fiber and a preparation method thereof. The polypropylene staple fiber comprises the following raw materials in parts by mass: 100 parts of polypropylene and 1-3.5 parts of modified nano titanium dioxide, the modified nano titanium dioxide comprises the following raw materials: nano titanium dioxide, a vinyl silane compound, double-end hydrogen-containing silicone oil and styrene in a mass ratio of 100: (3-5): (10-30): (2-5), and the double-end hydrogen-containing silicone oil has two silicon hydrogen end-capping groups; the nano titanium dioxide is subjected to surface treatment by a vinyl silane compound, and then is subjected to hydrosilylation reaction with double-end hydrogen-containing silicone oil and styrene under the action of a platinum catalyst. According to the invention, the polysiloxane chain segment with enhancing, plastifying and broad-spectrum antibacterial effects is introduced to graft the nano titanium dioxide, so that the balance of various properties such as mechanical strength, antibacterial efficiency and softness of the polypropylene staple fiber is realized.

Description

Technical Field

[0001] The present application relates to the field of polypropylene materials, and particularly to a high-strength antibacterial polypropylene staple fiber and a preparation method thereof. Background Art

[0002] As a synthetic fiber with light weight, corrosion resistance, excellent chemical stability and low cost, polypropylene staple fiber is widely used in fields such as packaging, building materials, household and medical. Especially in the medical field, its non-hygroscopic, low-sensitizing and easy-to-disinfect characteristics make it a key material for products such as medical masks, surgical protective clothing, disposable sheets, bandages, etc. With the improvement of medical and health standards, the market's performance requirements for polypropylene staple fiber are becoming increasingly stringent: on the one hand, medical protective products need to withstand frequent mechanical stresses (such as stretching and friction during the wearing of surgical gowns), requiring the fiber to have higher breaking strength and fatigue resistance; on the other hand, medical textiles in close contact with the human body must effectively inhibit bacterial growth to avoid the risk of cross-infection.

[0003] Traditional methods for improving fiber strength are mostly achieved by introducing rigid inorganic fillers (such as glass fiber, calcium carbonate). For example, the patent application with the publication number CN116356444A realizes the improvement of both strength and antibacterial performance by introducing graphene, and the prepared polypropylene fiber shows excellent mechanical properties and broad-spectrum antibacterial effect.

[0004] However, although the introduction of such inorganic fillers can improve functionality, it significantly increases the fiber rigidity, resulting in a hard and stiff material feel, and is prone to frictional discomfort when in contact with the skin. This problem is particularly prominent in scenarios that require both softness and functionality, such as medical dressings, the surface layer of sanitary napkins, and baby diapers. The overly hard material not only reduces wearing comfort, but may also cause skin sensitivity or even damage after long-term use. In the prior art, how to balance the mechanical strength, antibacterial efficacy and softness of the fiber has become a key bottleneck restricting the development of high-end medical polypropylene staple fiber. Summary of the Invention

[0005] In order to achieve the balance of the mechanical strength, antibacterial efficacy and softness of polypropylene fiber, the present application provides a high-strength antibacterial polypropylene staple fiber and a preparation method thereof. By introducing polydimethylsiloxane chain grafted nano-titanium dioxide with enhancing, plasticizing and broad-spectrum antibacterial effects into the polypropylene matrix, the balance of various properties is significantly achieved.

[0006] In a first aspect, the present application provides a high-strength antibacterial polypropylene staple fiber, comprising the following raw materials in parts by mass: 100 parts of polypropylene, and 1 to 3.5 parts of modified nano-titanium dioxide; the raw materials of the modified nano-titanium dioxide comprise nano-titanium dioxide, vinyl silane compound, hydrogen-containing silicone oil with two ends and styrene in a mass ratio of 100:3 to 5:10 to 30:2 to 5, and the hydrogen-containing silicone oil with two ends has 2 silicon-hydrogen end groups; the nano-titanium dioxide is surface-treated with a vinyl silane compound, and then undergoes a hydrosilylation reaction with the hydrogen-containing silicone oil with two ends and styrene under a platinum catalyst.

[0007] The present application realizes the synergistic effects of antibacterial, strengthening and toughening by using modified nano-titanium dioxide. Specifically, nano-titanium dioxide itself has photocatalytic broad-spectrum antibacterial properties, which can improve the antibacterial efficiency. As rigid nano-particles, after surface modification, nano-titanium dioxide is uniformly dispersed in the polypropylene matrix. When the material is stressed, these particles can hinder crack propagation, absorb and disperse stress, delay fracture and hinder crack propagation to absorb stress, thus playing a role in enhancing the tensile strength of the fiber.

[0008] More importantly, a flexible polysiloxane chain segment is formed by introducing hydrogen-containing silicone oil with two ends onto the surface of nano-titanium dioxide particles for hydrosilylation grafting. On the one hand, the nano-titanium dioxide particles grafted with polysiloxane chain segments play an internal lubrication role in the PP matrix, reducing the frictional resistance between the filler and the matrix, making the PP molecular chains more likely to slip, thereby reducing rigidity and improving softness. On the other hand, these polysiloxane long chains are inserted between the polypropylene molecular chains, weakening the intermolecular van der Waals forces and entanglement density, increasing the free volume, and enhancing the chain segment mobility, thus significantly improving the flexibility of the material. In contrast, traditional silane coupling agents only improve the interfacial bonding through chemical bonding and cannot introduce flexible chain segments. In addition, the role of styrene is not only to consume the active hydrogen at the other end and improve the system stability, but also to improve the compatibility between the modified nano-titanium dioxide and the polypropylene matrix.

[0009] It should be noted that if hydrogen-containing silicone oil with both ends and sides (both the two ends and the side chains have active hydrogen) is introduced for modification, it is easy to cause particle cross-linking and agglomeration, and the strengthening and toughening effects are poor; while if hydrogen-containing silicone oil with sides (only the side chains contain active hydrogen) is introduced for modification, the steric hindrance is large, the chain segment extensibility is poor, and the plasticizing effect is poor.

[0010] The molecular structure of the above-mentioned hydrogen-containing silicone oil with two ends is shown as follows, where Me is methyl.

[0011]

[0012] The molecular structure of the above-mentioned hydrogen-containing silicone oil with both ends and sides is shown as follows, where Me is methyl.

[0013]

[0014] The molecular structure of the above-mentioned side hydrogen-containing silicone oil is as follows, where Me is methyl.

[0015]

[0016] In one embodiment, the hydrogen content of the hydrogen-containing silicone oil is 0.04 - 0.19%.

[0017] In one embodiment, the viscosity of the hydrogen-containing silicone oil is 5 - 100 mm 2 / s.

[0018] The viscosity should be controlled within the above-mentioned value range so that the hydrogen-containing silicone oil has an appropriate molecular chain segment length, and has a good toughening effect after grafting on the surface of nano-titanium dioxide particles, which is beneficial to improving the flexibility of polypropylene fibers, and the increase in its viscosity has a positive effect on the improvement of flexibility.

[0019] This hydrogen content ensures sufficient chain segment flexibility. When the hydrogen content is too low (<0.04%), the silicon-hydrogen active sites are insufficient, resulting in low efficiency of the addition reaction with vinyl nano-titanium dioxide, poor toughening effect, and easy precipitation of unreacted silicone oil residues, affecting the material stability; double-ended hydrogen-containing silicone oil products with higher hydrogen content cannot be obtained.

[0020] In one embodiment, the vinyl silane compound is selected from one or more of vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(2-methoxyethoxy)silane, and vinylmethyldimethoxysilane.

[0021] In one embodiment, the median particle size of the nano-titanium dioxide is 20 - 200 nm.

[0022] The selection of the particle size of nano-titanium dioxide directly affects its plasticizing and modifying effect. When the particle size is less than 20 nm, the specific surface area of the particles surges, resulting in too high surface energy, and it is easy to agglomerate due to intermolecular forces during the grafting modification process, reducing the grafting efficiency of vinyl silane and double-ended hydrogen-containing silicone oil, and unable to form continuous flexible chain segments, significantly weakening the plasticizing and lubricating effect. When the particle size exceeds 200 nm, the particle size is close to or larger than the entanglement spacing of polypropylene molecular chains, and it is difficult to effectively embed in the polymer network, resulting in the inability of flexible polysiloxane chains to fully stretch to weaken the intermolecular forces, and the plasticizing ability is limited. In this application, by precisely controlling the particle size of nano-titanium dioxide within the range of 20 - 200 nm, it not only ensures that the particles have sufficient specific surface area to efficiently graft flexible chain segments, but also makes its size adapt to the polypropylene molecular chain spacing, thereby synergistically reducing the material rigidity through the lubrication effect and free volume effect of polysiloxane chains, and achieving an excellent balance of reinforcement and toughening. It should be noted that titanium dioxide with a size greater than 1 micron can hardly achieve a plasticizing effect.

[0023] In one embodiment, the melt flow index (MFI) of the polypropylene is 15 to 35 g / 10 min (230 °C / 2.16 kg).

[0024] In one embodiment, the raw material of the polypropylene staple fiber contains 10 to 20 parts of nitrogen-containing heterocyclic grafted polypropylene, and the finishing oil used for the polypropylene staple fiber contains 1 to 5 wt% of copper salt.

[0025] In one embodiment, the nitrogen-containing heterocyclic grafted polypropylene is prepared by a melt grafting reaction from a component containing the following parts by mass of raw materials: 100 parts of polypropylene, 1 to 5 parts of vinyl nitrogen-containing heterocycle, 0.5 to 1.5 parts of initiator, and 0.1 to 0.5 parts of antioxidant.

[0026] In one embodiment, the vinyl nitrogen-containing heterocycle is selected from one or more of vinyl imidazole, vinyl pyridine, and vinyl pyrrolidone.

[0027] In one embodiment, the preparation method of the nitrogen-containing heterocyclic grafted polypropylene is: mixing the vinyl nitrogen-containing heterocycle, initiator, antioxidant with polypropylene evenly, adding into a screw extruder, melt extruding at 170 - 185 °C, cutting the extrudate into pellets, extracting the homopolymer with boiling acetone, and drying to obtain the grafted product.

[0028] In one embodiment, the screw speed of the screw extruder is 50 - 100 rpm, and the residence time is 2 - 5 minutes.

[0029] In one embodiment, the initiator is dicumyl peroxide.

[0030] In one embodiment, the finishing oil is a diluted oil emulsion, and the diluted oil emulsion contains 40 - 60 wt% of spinning oil, 1 - 5 wt% of copper salt, and the balance is water.

[0031] In one embodiment, the copper salt is a water-soluble copper salt.

[0032] In one embodiment, the copper salt is selected from at least one of copper chloride, copper nitrate, copper sulfate, and copper acetate.

[0033] Nano-titanium dioxide generates reactive oxygen through photocatalysis, with broad-spectrum antibacterial properties and long-term effectiveness. However, its light response depends on ultraviolet excitation and its activity in the dark environment is insufficient, which limits its application efficiency in medical scenarios. In this application, by introducing nitrogen-containing heterocycles into the polypropylene chain segment, rich coordination sites are given on the fiber surface. In the finishing process, Cu in the finishing oil 2+ forms a complex with the nitrogen-containing heterocycles on the fiber surface through coordination bonds to achieve immediate antibacterial effects. More importantly, in the high-temperature stage of the subsequent stretching process, the molecular chain movement ability of the amorphous region of polypropylene is enhanced, and Cu 2+Diffuse into the interior of the fiber along the gaps between molecular chains and form a stable chelate structure with the inner-layer nitrogen-containing heterocycles. This gradient-distributed copper complex system not only achieves a short-term high antibacterial rate by releasing and killing Cu 2+ but also provides long-term antibacterial protection through the sustained release of the inner-layer complex, enabling the material to maintain excellent antibacterial activity even under limited light conditions.

[0034] In one embodiment, the preparation method of the modified nano-titanium dioxide is as follows: Vinylation: Mix a vinyl silane coupling agent with ethanol and deionized water, adjust the pH to 4 - 5, stir and hydrolyze at room temperature, add nano-titanium dioxide, reflux and react, then centrifuge, separate, wash and dry to obtain vinylated TiO2; Grafting reaction: Disperse the vinylated TiO2 in a solvent, add a hydrogen-containing silicone oil with two terminal groups and a platinum catalyst, heat up to 90 - 120 °C under nitrogen protection, stir and react for 4 - 6 hours; add a vinyl nitrogen-containing heterocycle and continue to react for 2 - 3 hours; after cooling, centrifuge, separate, wash and dry to obtain the product.

[0035] In one embodiment, the dosage of the platinum catalyst is 0.005 - 0.01 wt% of the dosage of the raw material hydrogen-containing silicone oil with two terminal groups.

[0036] In a second aspect, the present application provides a preparation method of high-strength antibacterial polypropylene staple fibers, including: according to the raw material ratio of any one of the above-mentioned polypropylene staple fibers, melt-blend the raw materials to obtain a melt, and then obtain the product through spinning, cooling, oiling, stretching, crimping, heat setting, and cutting.

[0037] In one embodiment, the cooling includes: First-stage cooling: The distance from the spinneret is 10 - 50 cm, and the wind speed is 1.1 - 1.6 m / s; Second-stage cooling: The distance from the spinneret is 50 - 100 cm, and the wind speed is 0.5 - 0.9 m / s.

[0038] In one embodiment, the cooling is annular air cooling, the cooling temperature is 15 - 20 °C, and the relative humidity is 40% - 60%.

[0039] In the present application, by setting a segmented cooling process, during the first-stage cooling, the polypropylene fibers are rapidly cooled at a high wind speed, which can form a temperature gradient between the interior and the surface layer of the fibers. The condensation speed of the fiber surface layer is fast, and the orientation degree is higher than that of the fiber interior, resulting in crystal region defects and stress concentration phenomena on the surface layer, and then forming microcracks. These crystal region defects and microcracks contribute to the diffusion of copper ions into the interior of the fibers during the oiling process, thereby coordinating with the nitrogen-containing heterocycles in the polypropylene chain segments to form stable complexes, playing a more uniform and efficient antibacterial role.

[0040] To implement the above-mentioned segmented cooling process, the original annular static pressure chamber can be divided into three independent annular air zones along the fiber extrusion direction, corresponding to the first-stage and second-stage static pressure chambers respectively. Each static pressure chamber is equipped with an independent air valve, and the air intake of each stage is controlled by adjusting the valve opening to achieve wind speed grading. The main air duct is divided into two groups of independent air ducts, which are respectively connected to different static pressure chambers. Pressure sensor interfaces are set in each static pressure chamber to monitor and feedback pressure data to the control system in real time, and dynamically adjust the air valve opening. The cooling air is centrally processed by the central air conditioning system to ensure that the air temperature and humidity in each static pressure chamber are constant within the preset range.

[0041] In one embodiment, the draw ratio is 3.5 to 4.5 times, and it is carried out in two stages: the primary drawing temperature is 60 to 80 °C, and the draw ratio is 1.5 to 2.0 times to achieve the preliminary orientation of molecular chains; the secondary drawing temperature is 120 to 140 °C, and the draw ratio is 2.0 to 2.5 times to complete high-ratio hot drawing and crystallization structure stabilization.

[0042] In one embodiment, in the oiling process, the oiling rate is controlled to be 0.3% to 0.8%.

[0043] In one embodiment, the heat setting temperature is 110 to 130 °C.

[0044] In one embodiment, the cut length is 38 to 65 mm.

[0045] In summary, the present application has the following beneficial effects: The present application constructs a core-shell structure with nano-titanium dioxide as the core. The rigid TiO2 inner core improves the fiber strength through heterogeneous nucleation and crack pinning effects; the flexible polysiloxane chain segments grafted on the surface are inserted between the polypropylene molecular chains, and the material is given a soft touch by reducing the entanglement density and interfacial friction. At the same time, the nitrogen-containing heterocycles introduced on the polypropylene molecular chains and Cu in the oil agent 2+ form a gradient coordination system, that is, the surface layer Cu 2+ quickly kills the contacting germs, and the internal amorphous region complex continuously releases antibacterial components, combined with the photocatalytic activity of TiO2 to construct a multiple antibacterial mechanism. The staple fiber of the present application has high breaking strength, the antibacterial rate against Escherichia coli / Staphylococcus aureus for 24 hours is > 99.9%, and the flexural rigidity is reduced by 40 to 60%, meeting the strict requirements of medical materials for mechanical strength, antibacterial performance and wearing comfort, and is particularly suitable for medical fields such as high-sensitivity skin dressings. Detailed implementation manners

[0046] Preparation examples

[0047] Preparation example 1, a modified nano-titanium dioxide, with the following raw material ratios: 100 g of nano-titanium dioxide (median particle size 50 nm), 4 g of vinyltrimethoxysilane, 20 g of hydrogen-containing silicone oil at both ends (model RH-H45, hydrogen content 0.12%, viscosity 17-22 mm 2 / s), 3.5 g of styrene, 0.1 g of platinum catalyst (isopropyl alcohol solution of chloroplatinic acid, Pt content 0.5 wt%), 200 mL of absolute ethanol, and 50 mL of deionized water.

[0048] The preparation steps are as follows: Vinylation treatment: Mix vinyltrimethoxysilane with 40 mL of ethanol and 10 mL of water, adjust the pH to 4.5 with acetic acid, and stir and hydrolyze at room temperature for 30 minutes. Add nano-titanium dioxide, reflux and react at 80 °C for 6 hours, centrifuge and separate, wash with ethanol 3 times, and vacuum dry at 80 °C for 12 hours to obtain vinylated TiO2.

[0049] Hydrosilylation grafting: Disperse vinylated TiO2 in toluene (solid-liquid ratio 1:5), add hydrogen-containing silicone oil at both ends and platinum catalyst, heat up to 100 °C under nitrogen protection, and stir and react for 5 hours (rotation speed 200 rpm). Add styrene and continue to react for 2.5 hours. Cool to room temperature, centrifuge and separate, wash with toluene 3 times, and dry at 80 °C to obtain modified TiO2.

[0050] Preparation Example 2, a modified nano-titanium dioxide, with the following raw material ratios: 100 g of nano-titanium dioxide (median particle size 20 nm), 5 g of vinyltrimethoxysilane, 30 g of hydrogen-containing silicone oil at both ends (model RH-H518, hydrogen content 0.18%, viscosity 8-12 mm 2 / s), 5 g of styrene, 0.1 g of platinum catalyst (isopropyl alcohol solution of chloroplatinic acid, Pt content 0.5 wt%), 200 mL of absolute ethanol, and 50 mL of deionized water.

[0051] The preparation steps are as follows: Vinylation treatment: Mix vinyltrimethoxysilane with 50 mL of ethanol and 10 mL of water, adjust the pH to 4 with acetic acid, and stir and hydrolyze at room temperature for 30 minutes. Add nano-titanium dioxide, reflux and react at 80 °C for 6 hours, centrifuge and separate, wash with ethanol 3 times, and vacuum dry at 80 °C for 12 hours to obtain vinylated TiO2.

[0052] Hydrosilylation grafting: Disperse vinylated TiO2 in toluene (solid-liquid ratio 1:5), add hydrogen-containing silicone oil at both ends and platinum catalyst, heat up to 110 °C under nitrogen protection, and stir and react for 4 hours (rotation speed 200 rpm). Add styrene and continue to react for 3 hours. Cool to room temperature, centrifuge and separate, wash with toluene 3 times, and dry at 80 °C to obtain modified TiO2.

[0053] Preparation Example 3, a modified nano-titanium dioxide, with the following raw material ratios: Nano-titanium dioxide (median particle size 200 nm) 100 g, vinyltrimethoxysilane 3 g, hydrogen-containing silicone oil at both ends (model RH-DH04, hydrogen content 0.05%, viscosity 60 - 70 mm 2 / s) 10 g, styrene 2.2 g, platinum catalyst (isopropyl alcohol solution of chloroplatinic acid, Pt content 0.5 wt%) 0.1 g, absolute ethanol 200 mL, deionized water 50 mL.

[0054] The preparation steps are as follows: Vinylation treatment: Mix vinyltrimethoxysilane with 40 mL of ethanol and 10 mL of water, adjust the pH to 4.5 with acetic acid, and stir and hydrolyze at room temperature for 30 minutes. Add nano-titanium dioxide, reflux and react at 90°C for 6 hours, centrifuge and separate, wash with ethanol 3 times, and dry in vacuum at 80°C for 12 hours to obtain vinylated TiO2.

[0055] Hydrosilylation grafting: Disperse vinylated TiO2 in toluene (solid-liquid ratio 1:4), add hydrogen-containing silicone oil at both ends and platinum catalyst, heat up to 90°C under nitrogen protection, and stir and react for 6 hours (rotation speed 200 rpm). Add styrene and continue to react for 2 hours. Cool to room temperature, centrifuge and separate, wash with toluene 3 times, and dry at 80°C to obtain modified TiO2.

[0056] Preparation Example 4, a modified nano-titanium dioxide, which is different from Preparation Example 1 in that the hydrogen-containing silicone oil at both ends with a hydrogen content of 0.032% is replaced with the hydrogen-containing silicone oil at both ends with a hydrogen content of 0.11% in equal mass.

[0057] Preparation Example 5, a modified nano-titanium dioxide, which is different from Preparation Example 1 in that the nano-titanium dioxide with a median particle size of 300 nm is replaced with the nano-titanium dioxide with a median particle size of 50 nm in equal mass.

[0058] Preparation Example 6, a modified nano-titanium dioxide, which is different from Preparation Example 1 in that the nano-titanium dioxide with a median particle size of 10 nm is replaced with the nano-titanium dioxide with a median particle size of 50 nm in equal mass.

[0059] Preparation Example 7, a modified nano-titanium dioxide, which is different from Preparation Example 1 in that styrene is not added in the raw materials. In the hydrosilylation grafting step, disperse vinylated TiO2 in toluene (solid-liquid ratio 1:5), add hydrogen-containing silicone oil at both ends and platinum catalyst, heat up to 100°C under nitrogen protection, and stir and react for 5 hours (rotation speed 200 rpm). Cool to room temperature, centrifuge and separate, wash with toluene 3 times, and dry at 80°C to obtain modified TiO2.

[0060] Preparation Example 8, a modified nano-titanium dioxide, which is different from Preparation Example 1 in that an equal mass of hydrogen-terminated silicone oil (model RH-H518, hydrogen content 0.18%, viscosity 8-12 mm 2 / s) is used to replace the hydrogen-terminated silicone oil (hydrogen content 0.12%, viscosity 17-22 mm 2 / s).

[0061] Preparation Example 9, a modified nano-titanium dioxide, which is different from Preparation Example 1 in that an equal mass of hydrogen-terminated silicone oil (model RH-H6, hydrogen content 0.11%, viscosity 20-25 mm 2 / s) is used to replace the hydrogen-terminated silicone oil (model RH-H45, hydrogen content 0.12%, viscosity 17-22 mm 2 / s).

[0062] Preparation Example 10, a modified nano-titanium dioxide, which is different from Preparation Example 1 in that an equal mass of hydrogen-terminated silicone oil on the end and side (model RH-LHC-3, hydrogen content 0.8%, viscosity 30-40 mm 2 / s) is used to replace the hydrogen-terminated silicone oil (model RH-H45, hydrogen content 0.12%, viscosity 17-22 mm 2 / s).

[0063] Preparation Example 11, a modified nano-titanium dioxide, which is different from Preparation Example 1 in that an equal mass of side hydrogen-terminated silicone oil (model RH-H57, hydrogen content 0.13%, viscosity 30-40 mm 2 / s) is used to replace the hydrogen-terminated silicone oil (model RH-H45, hydrogen content 0.12%, viscosity 17-22 mm 2 / s).

[0064] Preparation Example 12, a modified nano-titanium dioxide, which is different from Preparation Example 1 in that only vinylation treatment is carried out, without subsequent hydrosilylation and styrene grafting. The specific preparation steps are as follows: Vinylation treatment: Mix 4 g of vinyltrimethoxysilane with 40 mL of ethanol and 10 mL of water, adjust the pH to 4.5 with acetic acid, and stir and hydrolyze at room temperature for 30 minutes. Add 100 g of nano-titanium dioxide (median particle size 3 μm), reflux and react at 80°C for 6 hours, centrifuge and separate, wash with ethanol 3 times, and dry in vacuum at 80°C for 12 hours to obtain modified TiO2.

[0065] Preparation Example a, a nitrogen-containing heterocyclic grafted polypropylene, was prepared as follows: 30 g of 1-vinylimidazole, 10 g of diisopropylbenzene peroxide, 4 g of antioxidant 1010 and 1000 g of polypropylene (copolymerized PP, grade ExxonMobil Achieve3854) were mixed evenly, added to a twin-screw extruder, and melt-extruded at 170 - 185 °C. After the extrudate was pelletized, it was extracted with boiling acetone for 24 hours to remove the homopolymer, and the grafted product was obtained after drying.

[0066] Preparation Example b, a nitrogen-containing heterocyclic grafted polypropylene, was prepared as follows: 10 g of vinylpyridine, 5 g of diisopropylbenzene peroxide, 3 g of antioxidant BHT and 1000 g of polypropylene (homopolymerized PP, grade Basell Pro-fax 6301) were mixed evenly, added to a twin-screw extruder, and melt-extruded at 170 - 185 °C. After the extrudate was pelletized, it was extracted with boiling acetone for 24 hours to remove the homopolymer, and the grafted product was obtained after drying.

[0067] Preparation Example c, a nitrogen-containing heterocyclic grafted polypropylene, was prepared as follows: 50 g of vinylpyrrolidone, 15 g of diisopropylbenzene peroxide, 5 g of antioxidant 1010 and 1000 g of polypropylene (copolymerized PP, grade ExxonMobil Achieve3854) were mixed evenly, added to a twin-screw extruder, and melt-extruded at 170 - 185 °C. After the extrudate was pelletized, it was extracted with boiling acetone for 24 hours to remove the homopolymer, and the grafted product was obtained after drying.

[0068] Examples Example 1, a high-strength antibacterial polypropylene staple fiber, was prepared as follows: Blending and melting: 5 kg of polypropylene (Maoming Petrochemical Z30S0, MFI = 25 g / 10 min), 0.75 kg of nitrogen-containing heterocyclic grafted polypropylene (Preparation Example a), and 0.15 kg of modified nano-titanium dioxide (Preparation Example 1) were premixed and then added to a twin-screw extruder (L / D = 40). The temperature of each zone was set as follows: Zone 1 at 180 °C, Zone 2 at 200 °C, Zone 3 at 210 °C, Zone 4 at 205 °C, the screw speed was 200 rpm, and the melt pressure was 12 MPa.

[0069] Melt spinning: The melt was transported to a spinneret (hole diameter 0.25 mm × 108 holes) by a metering pump, and the melt temperature was 205 °C.

[0070] Cooling and forming: Ring blowing cooling was used (temperature 18 ± 2 °C, humidity 50%); First-stage cooling: The distance from the spinneret was 10 - 50 cm, and the wind speed was 1.4 m / s; Second-stage cooling: The distance from the spinneret was 50 - 100 cm, and the wind speed was 0.7 m / s.

[0071] Oil application: The oil application rate is 0.5%. The oil agent contains 50 wt% Hengrun TAB-314, 3 wt% copper sulfate, and 47 wt% deionized water.

[0072] Drawing: First-stage drawing (70 °C, 1.8 times), second-stage drawing (130 °C, 2.3 times).

[0073] Crimping: The steam temperature is 100 °C.

[0074] Heat setting: Hot air treatment at 125 °C for 4 minutes.

[0075] Cutting: The fiber length is 65 mm.

[0076] Example 2. A high-strength antibacterial polypropylene staple fiber is prepared according to the following steps: Blending and melting: 5 kg of polypropylene (Zhongjing Petrochemical H30S, MFI = 20 g / 10 min), 0.5 kg of nitrogen-containing heterocyclic grafted polypropylene (Preparation Example b), and 0.175 kg of modified nano-titanium dioxide (Preparation Example 2) are premixed and then added to a twin-screw extruder (L / D = 40). The temperature of each zone is set as follows: Zone 1: 180 °C, Zone 2: 195 °C, Zone 3: 205 °C, Zone 4: 200 °C. The screw speed is 200 rpm, and the melt pressure is 12 MPa.

[0077] Melt spinning: The melt is transported to a spinneret (hole diameter 0.25 mm × 108 holes) by a metering pump, and the melt temperature is 200 °C.

[0078] Cooling and forming: Ring blowing cooling is used (temperature 18 ± 2 °C, humidity 60%); First-stage cooling: The distance from the spinneret is 10 - 50 cm, and the wind speed is 1.2 m / s; Second-stage cooling: The distance from the spinneret is 50 - 100 cm, and the wind speed is 0.5 m / s.

[0079] Oil application: The oil application rate is 0.7%. The oil agent contains 60 wt% Hengrun TAB-314, 1.5 wt% copper chloride, and 38.5 wt% deionized water.

[0080] Drawing: First-stage drawing (80 °C, 2.0 times), second-stage drawing (120 °C, 2.2 times).

[0081] Crimping: The steam temperature is 100 °C.

[0082] Heat setting: Hot air treatment at 130 °C for 3 minutes.

[0083] Cutting: The fiber length is 51 mm.

[0084] Example 3. A high-strength antibacterial polypropylene staple fiber is prepared according to the following steps: Blending and melting: 5 kg of polypropylene (Prime Polymer HP561S, MFI = 33 g / 10 min), 1 kg of nitrogen-containing heterocyclic grafted polypropylene (Preparation Example c), and 0.075 kg of modified nano-titanium dioxide (Preparation Example 3) were premixed and then added to a twin-screw extruder (L / D = 40). The temperature of each zone was set as follows: Zone 1: 190 °C, Zone 2: 205 °C, Zone 3: 210 °C, Zone 4: 205 °C. The screw speed was 200 rpm, and the melt pressure was 12 MPa.

[0085] Melt spinning: The melt was delivered to a spinneret (hole diameter 0.25 mm × 108 holes) through a metering pump, and the melt temperature was 205 °C.

[0086] Cooling and forming: Cooling was carried out using a ring blower (temperature 18 ± 2 °C, humidity 40%); Primary cooling: The distance from the spinneret was 10 - 50 cm, and the wind speed was 1.6 m / s; Secondary cooling: The distance from the spinneret was 50 - 100 cm, and the wind speed was 0.9 m / s.

[0087] Oil application: The oil application rate was 0.4%. The oil agent contained 40 wt% Hengrun TAB-314, 5 wt% copper sulfate, and 55 wt% deionized water.

[0088] Drawing: Primary drawing (70 °C, 1.5 times), secondary drawing (140 °C, 2.5 times).

[0089] Crimping: The steam temperature was 100 °C.

[0090] Heat setting: Heat treatment with hot air at 125 °C for 3 minutes.

[0091] Cutting: The fiber length was 45 mm.

[0092] Example 4, a high-strength antibacterial polypropylene staple fiber, different from Example 1 in that the modified nano-titanium dioxide of Preparation Example 4 with equal mass was used to replace the modified nano-titanium dioxide of Preparation Example 1.

[0093] Example 5, a high-strength antibacterial polypropylene staple fiber, different from Example 1 in that the modified nano-titanium dioxide of Preparation Example 5 with equal mass was used to replace the modified nano-titanium dioxide of Preparation Example 1.

[0094] Example 6, a high-strength antibacterial polypropylene staple fiber, different from Example 1 in that the modified nano-titanium dioxide of Preparation Example 6 with equal mass was used to replace the modified nano-titanium dioxide of Preparation Example 1.

[0095] Example 7, a high-strength antibacterial polypropylene staple fiber, different from Example 1 in that the modified nano-titanium dioxide of Preparation Example 7 with equal mass was used to replace the modified nano-titanium dioxide of Preparation Example 1.

[0096] Example 8. A high-strength antibacterial polypropylene staple fiber, which is different from Example 1 in that the modified nano-titanium dioxide of Preparation Example 8 is used to replace the modified nano-titanium dioxide of Preparation Example 1 in equal mass.

[0097] Example 9. A high-strength antibacterial polypropylene staple fiber, which is different from Example 1 in that the modified nano-titanium dioxide of Preparation Example 9 is used to replace the modified nano-titanium dioxide of Preparation Example 1 in equal mass.

[0098] Example 10. A high-strength antibacterial polypropylene staple fiber, which is different from Example 1 in that the nitrogen-containing heterocyclic grafted polypropylene of Preparation Example a is replaced with polypropylene (copolymerized PP, grade ExxonMobil Achieve 3854) in equal mass.

[0099] Example 11. A high-strength antibacterial polypropylene staple fiber, which is different from Example 1 in that the copper sulfate in the oil agent used for oiling is replaced with Hengrun TAB-314 in equal mass.

[0100] Example 12. A high-strength antibacterial polypropylene staple fiber, which is different from Example 10 in that the copper sulfate in the oil agent used for oiling is replaced with Hengrun TAB-314 in equal mass.

[0101] Example 13. A high-strength antibacterial polypropylene staple fiber, which is different from Example 1 in that the cooling and forming process is different. Specifically: ring blowing cooling is adopted (temperature 18 ± 2°C, humidity 50%); the cooling wind speed is 1.4 m / s, and the cold zone is the interval with a distance of 10 - 100 cm from the spinneret plate.

[0102] Example 14. A high-strength antibacterial polypropylene staple fiber, which is different from Example 1 in that the cooling and forming process is different. Specifically: ring blowing cooling is adopted (temperature 18 ± 2°C, humidity 50%); the cooling wind speed is 0.7 m / s, and the cold zone is the interval with a distance of 10 - 100 cm from the spinneret plate.

[0103] Comparative Example

[0104] Comparative Example 1. A high-strength antibacterial polypropylene staple fiber, which is different from Example 1 in that the modified nano-titanium dioxide of Preparation Example 10 is used to replace the modified nano-titanium dioxide of Preparation Example 1 in equal mass.

[0105] Comparative Example 2. A high-strength antibacterial polypropylene staple fiber, which is different from Example 1 in that the modified nano-titanium dioxide of Preparation Example 11 is used to replace the modified nano-titanium dioxide of Preparation Example 1 in equal mass.

[0106] Comparative Example 3. A high-strength antibacterial polypropylene staple fiber, which is different from Example 1 in that the modified nano-titanium dioxide of Preparation Example 12 is used to replace the modified nano-titanium dioxide of Preparation Example 1 in equal mass.

[0107] Performance Detection Test

[0108] 1. Antibacterial property (short-term) test Test method: Refer to GB / T 20944.3-2008 "Evaluation of Antibacterial Properties of Textiles" for determination. The test bacteria are Escherichia coli (ATCC8739) and Staphylococcus aureus (ATCC6538).

[0109] Sample preparation: Take 1 g of the staple fibers obtained from the examples and comparative examples, cut them into 1-mm length segments, and disperse them in 10 mL of sterile physiological saline to prepare a suspension.

[0110] Test procedure: Take 0.2 mL of the bacterial suspension (concentration 1×106 CFU / mL) and mix it with the sample suspension. Incubate with shaking at 37°C for 24 hours. Dilute and spread on an agar plate, and incubate at 37°C for 24 hours. Calculate the number of colonies. Calculate the antibacterial rate (short-term) according to the following formula: Antibacterial rate (%) = (A - B) / A × 100% Where A is the number of colonies in the blank control group, and B is the number of colonies in the sample group.

[0111] 2. Long-term antibacterial property test Test method: Refer to ISO 20743:2021 "Determination of Antibacterial Activity of Textiles" for determination.

[0112] Sample preparation: Immerse the fiber sample (5 g) in 50 mL of simulated sweat (pH 5.5, the preparation of artificial sweat follows the regulations of ISO105 E04:2013 standard - Test method for color fastness to perspiration). Incubate with constant shaking at 37°C and take samples after 7 days.

[0113] Long-term antibacterial rate: Test the long-term antibacterial rate of the sample soaked in artificial sweat for 7 days according to the above short-term antibacterial rate test method, and calculate the antibacterial rate decrease value (%) = short-term antibacterial rate - long-term antibacterial rate.

[0114] 3. Tensile property test Test method: Refer to ASTM D3822 / D3822M-14 "Test Method for Tensile Properties of Textile Monofilaments" to determine the breaking strength (MPa) and elongation at break (%) of the staple fiber samples.

[0115] Sample preparation: Randomly select 50 polypropylene staple fibers and pre-condition them (temperature 20°C, humidity 65%RH, 24 hours).

[0116] Test conditions: Tensile speed 10 mm / min, grip distance 20 mm, and take the average value of 50 tests.

[0117] 4. Rigidity and flexibility test of polypropylene fabric Sample Preparation: Polypropylene staple fibers were made into non-woven fabrics (grammage 50 g / m²), with a thickness of 0.3 ± 0.05 mm. Five specimens (250 mm × 25 mm) were cut along the warp and weft directions and placed in an environment of 20°C ± 2°C and 65% ± 5% RH for 24 hours of equilibration.

[0118] Test Method: Referring to GB / T 18318.1-2009 "Textiles - Determination of bending properties - Part 1: Inclined plane method", the flexural rigidity (cN·cm) of the specimens was measured using a fabric stiffness tester (LLY-01B type electronic stiffness tester).

[0119] Table 1. Performance test results

[0120] Analysis of test results: 1. Antibacterial performance analysis The short-term antibacterial rate of Examples 1-3 > 99.9%, and the long-term antibacterial rate decreased only by 8.13 - 9.55%; while for Examples 10-12 (without grafting nitrogen heterocycles or without adding copper salts), the short-term antibacterial rate or long-term antibacterial rate decreased sharply, proving the stabilizing effect of nitrogen heterocyclic coordination anchoring on copper ions.

[0121] In addition, although too fast a cooling rate after fiber extrusion (Example 13) helps to form microcracks and crystal defects, it also causes a decrease in mechanical properties. At the same time, too fast a temperature drop results in insufficient fiber drawing, a decrease in orientation and crystallinity, a decrease in its breaking strength and elongation at break, and also a decrease in its overall softness. On the contrary, too slow a fiber cooling rate (Example 14) makes it difficult to form microcracks and crystal defects, resulting in a decrease in the amount of copper ions infiltrated and complexed, and a reduction in the long-term antibacterial performance.

[0122] 2. Analysis of mechanical properties and softness properties Breaking strength: The strength of Examples 1-3 was 630 - 670 MPa, and the elongation at break was 35 - 40%; while for the sample using large particle sizes (Example 5), the strength decreased to 530 MPa and the elongation at break decreased to 28%, indicating that inorganic fillers with too large particle sizes have poor reinforcing and toughening effects. For the sample using small particle sizes (Example 6), the strength increased to 600 MPa, but the elongation at break decreased to 30%, indicating that too small nano-titanium dioxide has a promoting effect on the improvement of fiber rigidity strength, but has a negative impact on the toughening effect and softness. The flexibility of Example 8 (with reduced viscosity) decreased, and the flexibility of Example 9 (with increased viscosity) increased. Since there are only two terminal hydrogen groups in the bis-end hydrogen silicone oil, and the difference lies only in the increase or decrease of viscosity, it can be seen that when other conditions are the same, an increase in viscosity is beneficial to the improvement of the fiber toughening effect.

[0123] Furthermore, the strength and elongation at break of the sample using terminal hydrogen-containing silicone oil (Comparative Example 1) both decreased significantly. The reason may be that terminal hydrogen-containing silicone oil has more than three active hydrogens, which easily causes cross-linking and agglomeration of nano-titanium dioxide. It is difficult for nano-titanium dioxide to be effectively dispersed and play a good filling and plasticizing role, resulting in an increase in rigidity but a decrease in breaking strength instead. Using side hydrogen-containing silicone oil (Comparative Example 2) causes a decrease in elongation at break and softness. The reason may be that there are more active hydrogens in the molecular chain of side hydrogen-containing silicone oil, which has an obvious promoting effect on the product strength and deteriorates the plasticizing ability.

[0124] This specific embodiment is only an interpretation of the present application, and it does not limit the present application. After reading this specification, those skilled in the art can make modifications to this embodiment without creative contributions as needed, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A high-strength antibacterial polypropylene staple fiber, characterized in that, It comprises the following raw materials in parts by mass: 100 parts of polypropylene and 1 - 3.5 parts of modified nano - titanium dioxide; the raw materials of the modified nano - titanium dioxide comprise nano - titanium dioxide, vinyl silane compound, hydrogen - terminated silicone oil with two silicon - hydrogen end - groups, and styrene in a mass ratio of 100:3 - 5:10 - 30:2 - 5; the nano - titanium dioxide is surface - treated with vinyl silane compound and then subjected to a hydrosilylation reaction with hydrogen - terminated silicone oil and styrene under a platinum catalyst.

2. The polypropylene staple fiber according to claim 1, wherein The hydrogen content of the hydrogen - terminated silicone oil is 0.04 - 0.19%.

3. The polypropylene staple fiber according to claim 1, wherein, The median particle size of the nano - titanium dioxide is 20 - 200 nm.

4. The polypropylene staple fiber according to claim 1, characterized in that, The raw materials of the polypropylene staple fiber contain 10 - 20 parts of nitrogen - containing heterocyclic - grafted polypropylene, and the oiling agent used for the polypropylene staple fiber contains 1 - 5 wt% of copper salt.

5. The polypropylene staple fiber according to claim 4, characterized in that, The nitrogen - containing heterocyclic - grafted polypropylene is prepared by a melt - grafting reaction from a component comprising the following raw materials in parts by mass: 100 parts of polypropylene, 1 - 5 parts of vinyl - containing nitrogen - containing heterocycle, 0.5 - 1.5 parts of initiator, and 0.1 - 0.5 parts of antioxidant.

6. The polypropylene staple fiber according to claim 5, characterized in that, The vinyl - containing nitrogen - containing heterocycle is selected from one or more of vinyl imidazole, vinyl pyridine, and vinyl pyrrolidone.

7. The polypropylene staple fiber according to claim 5, characterized in that, The preparation method of the nitrogen - containing heterocyclic - grafted polypropylene is as follows: uniformly mix 1 - vinyl imidazole, initiator, antioxidant with polypropylene, add them into a screw extruder, melt - extrude at 170 - 185 °C, pelletize the extrudate, extract the homopolymer with boiling acetone, and obtain the grafted product after drying.

8. The polypropylene staple fiber according to claim 1, wherein, The preparation method of the modified nano - titanium dioxide is as follows: Vinylation: Mix vinyl silane coupling agent with ethanol and deionized water, adjust the pH to 4 - 5, stir and hydrolyze at room temperature, add nano - titanium dioxide, carry out a reflux reaction, centrifuge, separate, wash and dry to obtain vinylated TiO2; Grafting reaction: Disperse vinylated TiO2 in a solvent, add hydrogen - terminated silicone oil and platinum catalyst, heat up to 90 - 120 °C under nitrogen protection, stir and react for 4 - 6 hours; add styrene and continue to react for 2 - 3 hours; after cooling, centrifuge, separate, wash and dry to obtain the product.

9. A preparation method of high-strength antibacterial polypropylene staple fiber, characterized in that, It includes: According to the raw material ratio of the polypropylene staple fiber described in any one of claims 1 - 8, blend the raw materials and melt them to obtain a melt, and then obtain the product through spinning, cooling, oiling, stretching, crimping, heat - setting, and cutting.

10. The preparation method according to claim 9, characterized in that, The cooling includes: Primary cooling: The distance from the spinneret is 10 - 50 cm, and the wind speed is 1.1 - 1.6 m / s; Secondary cooling: The distance from the spinneret is 50 - 100 cm, and the wind speed is 0.5 - 0.9 m / s.

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