Melt-blown polypropylene material, method of manufacture and use

Abstract

The application relates to the field of melt-blowing technology, in particular to a melt-blowing polypropylene material, a preparation method and application, which comprises polypropylene fibers, the polypropylene fibers are covalently connected with quaternary ammonium salt side groups on the molecular chains, the quaternary ammonium salt side groups have the following structure: wherein n is 2 or 3; the grafting rate of the quaternary ammonium salt side groups is 0.05%-1.5%. The quaternary ammonium salt side groups containing permanent ion pairs are covalently connected to the polypropylene molecular chains, the polarization structure is chemically fixed at the molecular level, the charge attenuation problem caused by the fact that the charges are only stored in physical traps in the traditional post-processing electret process is solved, and the surface potential retention rate of the obtained melt-blowing polypropylene material is greater than 80% after aging for 24 hours under the condition of a temperature of 80 DEG C and a relative humidity of 85%.

Description

Technical Field

[0001] This invention relates to the field of meltblown technology, specifically to meltblown polypropylene materials, methods for preparing meltblown polypropylene materials, and the application of meltblown polypropylene materials in oily aerosol filter products. Background Technology

[0002] Meltblown polypropylene nonwoven fabric is the core material of air filters. Its filtration mechanism relies on the physical interception and electrostatic adsorption effect between fibers, thus requiring the polypropylene fibers to store space charge.

[0003] Currently, the method for storing space charge in polypropylene fibers is the post-treatment electret process, which involves corona charging or water electret treatment of the formed meltblown fabric to inject the charge into physical traps on the fiber surface. This physical injection mode has the following drawbacks: the injected charge is only stored in the physical traps and will quickly dissipate in high temperature, high humidity or oily particulate environments, resulting in a significant decrease in filtration efficiency. Especially for oily aerosols, which spread on the fiber surface to form a conductive liquid film, they will quickly shield and dissipate the stored charge, causing the electrostatic adsorption effect to completely fail in a short time. In addition, the post-treatment electret process requires a separate electret section, which requires large equipment investment and high operating energy consumption. Summary of the Invention

[0004] This invention addresses the problems in the prior art by providing meltblown polypropylene materials, preparation methods, and applications. The specific technical solutions are as follows: In a first aspect, the present invention provides a meltblown polypropylene material, comprising polypropylene fibers, wherein quaternary ammonium salt side groups are covalently bonded to the molecular chains of the polypropylene fibers, and the quaternary ammonium salt side groups have the following structure: ; Where n is 2 or 3; The grafting rate of the quaternary ammonium salt side group is 0.05%-1.5%.

[0005] According to GB / T6165-2021 standard, when 200 mg of 0.3 μm diisooctyl sebacate oily aerosol is loaded at a flow rate of 32 L / min, the filtration efficiency of the meltblown polypropylene material decreases by no more than 2 percentage points.

[0006] As a further technical solution of the present invention, the average diameter of the polypropylene fiber is 0.5μm-10μm.

[0007] As a further technical solution of the present invention, the initial surface potential absolute value of the meltblown polypropylene material is greater than 1.5kV, and the surface potential retention rate is greater than 80% after aging for 24 hours at a temperature of 80℃ and a relative humidity of 85%.

[0008] Secondly, the present invention also provides a method for preparing meltblown polypropylene material, comprising the following steps: Step 1: Melt the polypropylene resin by heating; Step 2: Add unsaturated quaternary ammonium salt monomer and free radical initiator to molten polypropylene, mix, and allow the unsaturated quaternary ammonium salt monomer to undergo a grafting reaction with polypropylene under the action of the initiator to obtain modified polypropylene melt. Step 3: The modified polypropylene melt is extruded through a meltblown die, stretched by hot air to form fibers and a web, thus obtaining meltblown polypropylene material.

[0009] As a further technical solution of the present invention, in step two, the unsaturated quaternary ammonium salt monomer is selected from at least one of methacryloyloxyethyltrimethylammonium chloride, acryloyloxyethyltrimethylammonium chloride, and methacryloyloxypropyltrimethylammonium chloride.

[0010] As a further technical solution of the present invention, in step two, the free radical initiator is dicumyl peroxide, benzoyl peroxide, or 2,5-dimethyl-2,5-di-tert-butylperoxyhexane.

[0011] As a further technical solution of the present invention, the components in the meltblown polypropylene material, by weight, are: 95-99.8 parts of polypropylene resin, 0.1-3 parts of unsaturated quaternary ammonium salt monomer, and 0.01-0.5 parts of free radical initiator.

[0012] As a further technical solution of the present invention, in step two, the melt temperature of the grafting reaction stage is controlled within the range of 180℃-280℃, and the residence time is controlled within the range of 10s-120s.

[0013] As a further technical solution of the present invention, in step three, the temperature of the hot air stretching is 220℃-320℃, and the pressure is 0.1MPa-0.8MPa.

[0014] Thirdly, the present invention also provides the application of meltblown polypropylene materials in oily aerosol filtration products.

[0015] The beneficial effects of this invention are as follows: (1) The meltblown polypropylene material provided by the present invention achieves “chemical fixation” of polarization structure at the molecular level by connecting the quaternary ammonium salt side group containing permanent ion pairs to the polypropylene molecular chain in the form of covalent bonds. This solves the problem of charge decay caused by the charge being stored only in physical traps in the traditional post-processing electret process, and no longer relies on external charging treatment. The surface potential retention rate of the obtained meltblown polypropylene material is greater than 80% after aging for 24 hours at a temperature of 80°C and a relative humidity of 85%.

[0016] (2) The method for preparing meltblown polypropylene material provided by the present invention completes the grafting reaction before meltblown extrusion molding, so that the quaternary ammonium salt ion pairs are constructed in situ during the fiber forming process, thereby achieving permanent polarization characteristics without any subsequent electrostatic electret treatment. This solves the problem of dependence on post-treatment electret process for traditional meltblown polypropylene filter materials, eliminates the corona charging or water electret process, and achieves "self-electret effect".

[0017] (3) The meltblown polypropylene material provided by the present invention anchors quaternary ammonium salt ion pairs to the polypropylene molecular chain through covalent bonds, so that they are not dissolved or migrated by the oily liquid film, thereby maintaining the electrostatic adsorption efficiency after loading with oily aerosol. This solves the problem of charge shielding failure of traditional electret meltblown cloth in the oily aerosol environment. After loading with 200mg of oily aerosol, the filtration efficiency decreases by less than 2 percentage points. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments.

[0019] The meltblown polypropylene material provided by this invention aims to fundamentally replace the traditional post-processing electret step by fixing the polarized structure onto the polypropylene molecular chain in the form of chemical bonds, thereby achieving the intrinsic permanent polarization characteristics of the material; specifically as follows: First, the free radical initiator undergoes homolytic cleavage under heating conditions, generating a pair of primary free radicals. Second, the primary free radicals abstract hydrogen atoms from the tertiary carbon atoms on the polypropylene molecular chain, creating macromolecular free radical active centers on the polypropylene backbone. Subsequently, these macromolecular free radicals undergo an addition reaction with the carbon-carbon double bonds of the unsaturated quaternary ammonium salt monomer molecules, causing the monomer molecules to be covalently linked to the polypropylene backbone, forming grafted side groups. Since the unsaturated quaternary ammonium salt monomers themselves already contain ion pairs consisting of quaternary ammonium cations and chloride ions, these ion pairs are introduced onto the polypropylene molecular chain intact after grafting.

[0020] In this invention, the method for determining the grafting rate of quaternary ammonium salt side groups is as follows: Elemental analysis is used to determine the mass fraction of nitrogen in the grafted product, and the grafting rate is calculated using the following formula: Grafting rate (%) = (Nitrogen mass fraction / 14) × monomer molecular weight / polypropylene repeating unit molecular weight × 100%. The monomer molecular weight is calculated based on the unsaturated quaternary ammonium salt monomer used. To ensure accuracy, the sample must be extracted with xylene using a Soxhlet extractor for 48 hours to remove unreacted monomers and homopolymers, and then dried before elemental analysis.

[0021] The reaction equation is shown below: Polypropylene backbone (containing tertiary hydrocarbons) + initiator → polypropylene macromolecular free radicals; Polypropylene macromolecular free radicals →Polypropylene main chain ; In the above equation, -g- represents grafting, and the grafting side group is methacryloyloxyethyltrimethylammonium chloride as an example.

[0022] Example 1

[0023] This embodiment provides meltblown polypropylene material, and the raw material formulation, by weight, is as follows: Polypropylene, melt index 1500 g / 10 min, dosage 99.2 parts; Methacryloxyethyltrimethylammonium chloride, dosage 0.5 parts; Dicumyl peroxide, 0.2 parts; White oil, used as a dispersant, is used in a dosage of 0.1 parts.

[0024] Preparation process: Polypropylene is fed into a screw extruder, with the temperatures of each zone set sequentially to 160℃, 200℃, 240℃, 260℃, and 270℃. Methacryloxyethyltrimethylammonium chloride, dicumyl peroxide, and white oil are pre-mixed and injected before the metering section of the screw extruder using a precision plunger pump, and then mixed in a static mixer. The residence time of the melt at 270℃ is controlled to approximately 60 seconds to complete the grafting reaction. The grafted and modified melt enters the die at 260℃ and is stretched into a web by hot air at 280℃ and 0.4MPa. After winding, the meltblown polypropylene material is obtained without any subsequent electret treatment.

[0025] Performance testing: The average fiber diameter is 2.1 μm; the quaternary ammonium salt side grafting rate is 0.21%; and the initial surface potential is 2.8 kV.

[0026] The initial filtration efficiency for 0.3μm sodium chloride aerosol at a flow rate of 32L / min was 99.2%; after aging at 80℃ and 85% relative humidity for 24h, the filtration efficiency retention rate was 97.5%.

[0027] The initial filtration efficiency of 0.3 μm diisooctyl sebacate oily aerosol at a flow rate of 32 L / min was 98.7%; after loading with 200 mg of oily aerosol, the filtration efficiency was 97.1%, with a decrease in filtration efficiency of 1.6 percentage points.

[0028] Example 2

[0029] This embodiment provides meltblown polypropylene material, and the raw material formulation, by weight, is as follows: Polypropylene, melt index 1500 g / 10 min, dosage 99.8 parts; Acryloyloxyethyltrimethylammonium chloride, dosage 0.15 parts; Benzoyl peroxide, 0.05 parts.

[0030] Preparation process: Polypropylene is fed into a screw extruder, with the temperatures of each zone set sequentially to 160℃, 200℃, 230℃, 250℃, and 260℃. Acryloyloxyethyltrimethylammonium chloride and benzoyl peroxide are premixed and injected before the metering section of the screw extruder via a precision plunger pump, and then mixed in a static mixer. The residence time of the melt at 260℃ is controlled to be approximately 30 seconds. The grafted and modified melt enters the die at 250℃ and is stretched into a web by hot air at 270℃ and 0.3MPa. After winding, the meltblown polypropylene material is obtained without any subsequent electret treatment.

[0031] Performance testing: The average fiber diameter is 3.5 μm; the quaternary ammonium salt side grafting rate is 0.06%; and the initial surface potential is 1.8 kV.

[0032] The initial filtration efficiency for 0.3μm sodium chloride aerosol at a flow rate of 32L / min was 97.8%; after aging at 80℃ and 85% relative humidity for 24h, the filtration efficiency retention rate was 95.1%.

[0033] The initial filtration efficiency of 0.3 μm diisooctyl sebacate oily aerosol at a flow rate of 32 L / min was 97.2%; after loading with 200 mg of oily aerosol, the filtration efficiency was 95.8%, with an efficiency decrease of 1.4 percentage points.

[0034] Example 3

[0035] This embodiment provides meltblown polypropylene material, and the raw material formulation, by weight, is as follows: Polypropylene, melt index 800 g / 10 min, dosage 97.5 parts; Methacryloxypropyltrimethylammonium chloride, 2.0 parts; 2,5-Dimethyl-2,5-di-tert-butylperoxyhexane, 0.4 parts; White oil, used as a dispersant, is used in a dosage of 0.1 parts.

[0036] Preparation process: Polypropylene is fed into a screw extruder, with the temperatures of each zone set sequentially to 160℃, 200℃, 250℃, 270℃, and 280℃. Methacryloxypropyltrimethylammonium chloride, initiator, and white oil are pre-mixed uniformly and injected before the metering section of the screw extruder using a precision plunger pump, and then mixed in a static mixer. The residence time of the melt at 280℃ is controlled to approximately 100 seconds. The grafted and modified melt enters the die at 270℃ and is stretched into a web by hot air at 290℃ and 0.6MPa. After winding, the meltblown polypropylene material is obtained without any subsequent electret treatment.

[0037] Performance testing: The average fiber diameter is 1.5 μm; the quaternary ammonium salt side grafting rate is 1.2%; and the initial surface potential is 3.5 kV.

[0038] The initial filtration efficiency for 0.3μm sodium chloride aerosol at a flow rate of 32L / min was 99.7%; after aging at 80℃ and 85% relative humidity for 24h, the filtration efficiency retention rate was 98.8%.

[0039] The initial filtration efficiency of 0.3 μm diisooctyl sebacate oily aerosol at a flow rate of 32 L / min was 99.3%; after loading with 200 mg of oily aerosol, the filtration efficiency was 98.1%, with an efficiency decrease of 1.2 percentage points.

[0040] Example 4

[0041] This embodiment provides meltblown polypropylene material, with the following raw material formulation by weight: Polypropylene, melt index 1800 g / 10 min, dosage 99.5 parts; Methacryloxyethyltrimethylammonium chloride, dosage 0.3 parts; Dicumyl peroxide, 0.1 parts; White oil, used as a dispersant, is used in a dosage of 0.1 parts.

[0042] Preparation process: Polypropylene is fed into a screw extruder, with the temperatures of each zone set sequentially to 160℃, 200℃, 230℃, 250℃, and 260℃. Methacryloxyethyltrimethylammonium chloride, dicumyl peroxide, and white oil are pre-mixed and injected before the metering section of the screw extruder using a precision plunger pump, and then mixed in a static mixer. The residence time of the melt at 260℃ is controlled to approximately 40 seconds. The grafted and modified melt enters the die at 250℃ and is stretched into a web by hot air at 260℃ and 0.2MPa. After winding, the meltblown polypropylene material is obtained without any subsequent electret treatment.

[0043] Performance testing: The average fiber diameter is 4.8 μm; the quaternary ammonium salt side group grafting rate is 0.12%; and the initial surface potential is 2.1 kV.

[0044] The initial filtration efficiency for 0.3μm sodium chloride aerosol at a flow rate of 32L / min was 98.5%; after aging at 80℃ and 85% relative humidity for 24h, the filtration efficiency retention rate was 96.2%.

[0045] The initial filtration efficiency of 0.3 μm diisooctyl sebacate oily aerosol at a flow rate of 32 L / min was 98.0%; after loading with 200 mg of oily aerosol, the filtration efficiency was 96.9%, with an efficiency decrease of 1.1 percentage points.

[0046] Comparative Example 1 The same polypropylene raw materials and meltblown molding process as in Example 1 were used, but no quaternary ammonium salt monomers and initiators were added, and no online grafting was performed. After winding, the resulting meltblown fabric was subjected to corona charging treatment with a charging voltage of 15kV.

[0047] Performance testing: The initial surface potential is 2.6 kV.

[0048] The initial filtration efficiency for 0.3μm sodium chloride aerosol at a flow rate of 32L / min was 99.1%; after aging at 80℃ and 85% relative humidity for 24h, the filtration efficiency retention rate was only 72.3%.

[0049] The initial filtration efficiency of 0.3 μm diisooctyl sebacate oily aerosol at a flow rate of 32 L / min was 98.5%; after loading with 200 mg of oily aerosol, the filtration efficiency plummeted to 61.2%, with an efficiency decrease of up to 37.3 percentage points.

[0050] Summary of Results Examples 1 to 4, within a grafting rate range of 0.06% to 1.2% and an average fiber diameter range of 1.5 to 4.8 μm, all achieved high filtration efficiency and excellent long-lasting performance without subsequent electret treatment. In the accelerated aging test with saline aerosols, the efficiency retention rate of each example was above 95%. In the oily aerosol loading test, the efficiency decline of each example was within 2 percentage points, while that of Comparative Example 1 was 37.3 percentage points. This significant difference demonstrates that the covalently fixed quaternary ammonium salt ions can effectively resist the charge shielding effect of oily liquid films, and this effect can be achieved within the grafting rate range defined in the claims.

[0051] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it.

Claims

1. A meltblown polypropylene material, including polypropylene fibers, characterized in that, The polypropylene fiber has quaternary ammonium salt side groups covalently bonded to its molecular chains, and these quaternary ammonium salt side groups have the following structure: ； Where n is 2 or 3; The grafting rate of the quaternary ammonium salt side group is 0.05%-1.5%.

2. The meltblown polypropylene material according to claim 1, characterized in that: The average diameter of the polypropylene fiber is 0.5 μm-10 μm.

3. The meltblown polypropylene material according to claim 1, characterized in that: The initial absolute value of the surface potential of the meltblown polypropylene material is greater than 1.5kV, and the surface potential retention rate is greater than 80% after aging for 24 hours at a temperature of 80℃ and a relative humidity of 85%.

4. A method for preparing meltblown polypropylene material, characterized in that, Includes the following steps: Step 1: Melt the polypropylene resin by heating; Step 2: Add unsaturated quaternary ammonium salt monomer and free radical initiator to molten polypropylene, mix, and allow the unsaturated quaternary ammonium salt monomer to undergo a grafting reaction with polypropylene under the action of the initiator to obtain modified polypropylene melt. Step 3: The modified polypropylene melt is extruded through a meltblown die, stretched by hot air to form fibers and a web, thus obtaining meltblown polypropylene material.

5. The method for preparing meltblown polypropylene material according to claim 4, characterized in that: In step two, the unsaturated quaternary ammonium salt monomer is selected from at least one of methacryloyloxyethyltrimethylammonium chloride, acryloyloxyethyltrimethylammonium chloride, and methacryloyloxypropyltrimethylammonium chloride.

6. The method for preparing meltblown polypropylene material according to claim 4, characterized in that: In step two, the free radical initiator is dicumyl peroxide, benzoyl peroxide, or 2,5-dimethyl-2,5-di-tert-butylperoxyhexane.

7. The method for preparing meltblown polypropylene material according to claim 4, characterized in that: The components of the meltblown polypropylene material, by weight, are as follows: polypropylene resin 95-99.8 parts, unsaturated quaternary ammonium salt monomer 0.1-3 parts, and free radical initiator 0.01-0.5 parts.

8. The method for preparing meltblown polypropylene material according to claim 4, characterized in that: In step two, the melt temperature during the grafting reaction stage is controlled within the range of 180℃-280℃, and the residence time is controlled within the range of 10s-120s.

9. The method for preparing meltblown polypropylene material according to claim 4, characterized in that: In step three, the temperature of the hot air stretching is 220℃-320℃, and the pressure is 0.1MPa-0.8MPa.

10. The use of the meltblown polypropylene material according to any one of claims 1-3 in oily aerosol filter products.

Images