Preparation process of polyethylene ultrafine fiber membrane

Abstract

The application discloses a preparation process of polyethylene ultrafine fiber membrane, which comprises the following steps: mixing polyethylene, styrene, a functional monomer, a crosslinking agent and an initiator according to a proportion, and dissolving the mixture in a solvent; casting the mixed solution into a film, reacting the film at a certain temperature, crushing the prepared solid polymer film to obtain granular polymer; soaking the granular polymer in an ethanol-acetic acid mixed solution, and preparing modified polyethylene granular material through ultrasonic treatment; mixing the modified polyethylene granular material, an additive and a solvent, stirring and heating under a closed condition, then introducing auxiliary dissolving gas and pressurizing, continuously heating to a certain temperature and then keeping the temperature; after the temperature keeping is completed, reducing the pressure to spray; accumulating the sprayed ultrafine fiber filaments into a net, and preparing the polyethylene ultrafine fiber membrane after bonding and solidification. The preparation process improves the solubility of polyethylene, and combines a flash evaporation spinning process to prepare the polyethylene ultrafine fiber membrane which is good in uniformity, excellent in mechanical performance and chemical stability.

Description

Technical Field

[0001] This invention relates to the field of spinning fiber technology, and in particular to a process for preparing a polyethylene microfiber membrane. Background Technology

[0002] Polyethylene (PE) is a thermoplastic polymer polymerized from ethylene monomers. It is classified into high-density polyethylene (HDPE), low-density polyethylene (LDPE), and linear low-density polyethylene (LLDPE). Its molecular chain structure (such as branching degree and crystallinity) can directly affect film-forming properties. Polyethylene has a low melting point (110-130℃), good melt flowability, and is suitable for melt processing. Its chemical inertness, corrosion resistance, and low cost make it an ideal fiber film-forming material.

[0003] Polyethylene solution spinning is a method of forming fibers by dissolving polyethylene in a specific solvent and using a specific process, including wet spinning, dry spinning, electrospinning, and flash phase separation. The flash phase separation method involves dissolving polyethylene under high temperature and pressure to prepare a homogeneous spinning solution of a certain concentration, which is then fed to the spinneret and enters the depressurization chamber through a pressure-reducing orifice. At this point, due to the pressure reduction, the polymer and solvent undergo phase separation, with one phase being rich in polymer and the other rich in solvent. When the spinning solution reaches a certain point, the pressure drops to atmospheric pressure, and the solvent undergoes a phase transition, changing from liquid to vapor. The solvent and polymer separate rapidly at the spinneret, causing the polymer to rupture and be stretched at high speed by the vapor flow due to the velocity gradient. Simultaneously with the phase transition, the fluid undergoes high-speed stretching, and because it is adiabatic expansion, the solvent absorbs a large amount of heat, causing a sharp drop in temperature, which allows the polymer to rapidly crystallize and cool into highly oriented ultrafine fibers.

[0004] Flash evaporation is a highly efficient process for producing polyethylene spun membranes. These membranes are composed of stacked, bonded microfibers with diameters ranging from 0.2 to 5.0 μm. This microfiber structure provides a large specific surface area, resulting in superior filtration and adsorption performance. Flash evaporation also imparts extremely small fiber diameters and excellent monofilament strength, leading to high material strength after consolidation. Flash-evaporated polyethylene microfiber membranes exhibit good air permeability, ensuring excellent ventilation and improved user comfort during application.

[0005] However, when using flash evaporation for polyethylene spinning, insufficient dissolution occurs with increasing concentration. The effects of insufficient polyethylene dissolution on spinning and film formation include: spinning difficulties, fiber structure defects, poor film uniformity, abnormal pore structure, reduced mechanical properties, and decreased chemical stability. Improving polyethylene solubility by adding co-solvents introduces unnecessary impurities. Therefore, improving the solubility of polyethylene during spinning is crucial for the production of polyethylene microfiber membranes. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide a preparation process for polyethylene ultrafine fiber membranes. This preparation process improves the solubility of polyethylene and reduces the difficulty of spinning by modifying polyethylene and using supercritical gas-assisted dissolution. Combined with flash spinning, a polyethylene ultrafine fiber membrane with good uniformity, excellent mechanical properties, and superior chemical stability is obtained.

[0007] To achieve the above-mentioned technical objectives and effects, the present invention is implemented through the following technical solution:

[0008] A process for preparing a polyethylene microfiber membrane includes the following steps:

[0009] (1) Mix polyethylene, styrene, functional monomers, crosslinking agents and initiators in proportion and dissolve them in a solvent to form a uniform mixed solution; cast the mixed solution into a film, react the film at a certain temperature, crush the solid polymer film obtained after the reaction, and sieve it to obtain particulate polymer; immerse the particulate polymer in an ethanol-acetic acid mixture and sonicate it for a certain time to obtain modified polyethylene particulates.

[0010] (2) Mix the modified polyethylene particles, additives and solvent, stir and heat to a certain temperature under closed conditions, introduce auxiliary dissolving gas and pressurize, continue to heat to a certain temperature and keep it at that temperature; after the heat preservation is completed, reduce the pressure and spin the filaments.

[0011] (3) The sprayed ultrafine fiber filaments are piled into a net, and after bonding and curing, a polyethylene ultrafine fiber membrane is obtained.

[0012] Further, in step (1), the mixing ratio of polyethylene, styrene, functional monomer, crosslinking agent and initiator is: polyethylene 55%-70%, styrene 1%-8%, functional monomer 10%-25%, crosslinking agent 5%-10% and initiator 0.1%-5%.

[0013] Preferably, the functional monomer is selected from at least one of acrylic acid, methacrylic acid, and maleic anhydride.

[0014] Furthermore, in step (1), the reaction temperature is 60-80℃ and the reaction time is 10-18 hours.

[0015] Furthermore, in step (1), the volume ratio of ethanol to acetic acid in the ethanol-acetic acid mixture is 9:1.

[0016] Further, in step (1), the initiator is selected from at least one of benzoyl peroxide, tert-butyl hydroperoxide, di-tert-butyl peroxide, and azobisisobutyronitrile; the crosslinking agent is selected from divinylbenzene or ethylene glycol dimethacrylate.

[0017] Preferably, the adjuvant is an antioxidant, which is at least one of tris[2,4-di-tert-butylphenyl] phosphite, bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite, tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] pentaerythritol ester, and β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate n-octadecyl alcohol ester.

[0018] Further, in step (2), the mixing ratio of modified polyethylene particles, additives and solvent is: 5-20% modified polyethylene particles, 0.1-1% additives, and the remainder is solvent.

[0019] Further, in step (2), the temperature is heated to 30-80°C under sealed conditions, supercritical gas is introduced and pressurized to 6-10 MPa, and the temperature is further increased to 100-190°C.

[0020] Furthermore, the auxiliary dissolving gas is carbon dioxide or nitrogen.

[0021] The beneficial effects of this invention are:

[0022] This invention first modifies polyethylene. Specifically, styrene interacts with functional monomers to form a stable complex. Under the action of an initiator, a mixture of polyethylene, styrene, functional monomers, crosslinking agents, and the initiator undergoes a polymerization reaction. The functional monomers and crosslinking agents form a three-dimensional network structure, encapsulating the styrene within. The styrene forms specific binding sites within the polyethylene matrix. After immersing the resulting polymer in an ethanol-acetic acid mixture and ultrasonically treating it for a period of time, the styrene is dissolved and removed, thereby forming molecular channels or voids within the polymer. This effectively disrupts the crystalline structure of polyethylene, increases amorphous regions, and allows solvent molecules to penetrate more easily into the polymer interior. It also enhances the mobility of molecular chains, making them easier to disperse and dissolve in solvents, thus significantly improving the solubility of polyethylene. The functional monomers and crosslinking agents form a three-dimensional network structure with polyethylene, enhancing the polymer's stability and mechanical strength.

[0023] This invention also employs an auxiliary dissolving gas (supercritical gas) for assisted dissolution. The supercritical gas can penetrate between the polyethylene molecular chains, lower its glass transition temperature, increase the free volume of the amorphous region, thereby improving the mobility of the molecular chains and making them easier to disperse and dissolve in the solvent.

[0024] This invention combines polyethylene modification with supercritical gas-assisted dissolution, which can greatly improve the solubility of polyethylene in solvents, thereby improving spinnability and enhancing the uniformity, mechanical properties, and chemical stability of the resulting polyethylene microfiber membrane. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] This invention provides a process for preparing a polyethylene microfiber membrane, comprising the following steps:

[0027] (1) Mix polyethylene, styrene, functional monomers, crosslinking agents and initiators in proportion and dissolve them in solvent to form a uniform mixed solution; cast the mixed solution into a film and place the film in an oven preheated to 65℃-80℃ for polymerization reaction for 10-18 hours; after the reaction is completed, the film can continue to be kept in the oven for a period of time to allow the solvent to gradually evaporate and form a solid polymer film; crush the solid polymer film obtained after the reaction, sieve it to obtain granular polymer; soak the granular polymer in an ethanol-acetic acid mixture, sonicate it for 2.5-3 hours, and then filter and dry it to obtain modified polyethylene granules.

[0028] (2) Mix the modified polyethylene particles, additives and solvent, put the mixture into the reactor, stir and heat it to 30-80°C under closed conditions, then introduce auxiliary dissolving gas and pressurize it to 6-10MPa, continue to heat it to 100-190°C and keep it at that temperature; after the heat preservation is completed, reduce the pressure and spin the filaments.

[0029] (3) The sprayed ultrafine fiber filaments are piled into a net, and after bonding and curing, a polyethylene ultrafine fiber membrane is obtained.

[0030] In step (1), the mixing ratio of polyethylene, styrene, functional monomers, crosslinking agent, and initiator is: polyethylene 55%-70%, styrene 1%-8%, functional monomers 10%-25%, crosslinking agent 5%-10%, and initiator 0.1%-5%. The polyethylene can be a mixture of polyethylenes with different molecular weights.

[0031] In step (1), the functional monomer is selected from at least one of acrylic acid, methacrylic acid, and maleic anhydride.

[0032] In the ethanol-acetic acid mixture, the volume ratio of ethanol to acetic acid is 9:1.

[0033] The initiator is selected from at least one of benzoyl peroxide, tert-butyl hydroperoxide, di-tert-butyl peroxide, and azobisisobutyronitrile; the crosslinking agent is selected from divinylbenzene or ethylene glycol dimethacrylate.

[0034] In step (2), the mixing ratio of modified polyethylene particles, additives, and solvent is: 5-20% modified polyethylene particles, 0.1-1% additives, and the remainder is solvent. The solvent is one or more of dimethyl sulfoxide, N,N-dimethylformamide, acetone, benzene, xylene, dichloromethane, dichloroethane, and carbon tetrachloride.

[0035] The adjuvant is an antioxidant, preferably at least one of the following: tris[2,4-di-tert-butylphenyl] phosphite (antioxidant 168), bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite (antioxidant 626), tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] pentaerythritol ester (antioxidant 1010), and β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate n-octadecyl alcohol ester (antioxidant 1076).

[0036] The auxiliary dissolving gas is carbon dioxide or nitrogen.

[0037] Example 1

[0038] (1) Polyethylene, styrene, functional monomers, crosslinking agents and initiators are mixed in proportion and dissolved in an appropriate amount of solvent (dichloromethane) to form a uniform mixed solution (solid content of 30%). Among them, polyethylene (a mixture of 150,000 molecular weight polyethylene and 500,000 molecular weight polyethylene in a mixing ratio of 30:1) 65%, styrene 5%, acrylic acid 20%, ethylene glycol dimethacrylate 8%, and initiator 2% are used. The mixed solution is cast into a film and placed in an oven preheated to 70°C for polymerization reaction for 15 hours. After the reaction is completed, the film can be kept in the oven for a period of time to allow the solvent to gradually evaporate and form a solid polymer film. The solid polymer film obtained after the reaction is crushed, sieved and granular polymer is obtained. The granular polymer is soaked in an ethanol-acetic acid mixture (volume ratio of ethanol to acetic acid is 9:1), ultrasonically treated for 3 hours, filtered and dried to obtain modified polyethylene granules.

[0039] (2) Mix modified polyethylene particles, antioxidant (antioxidant 168) and solvent dichloromethane, wherein the modified polyethylene particles are 15%, the antioxidant is 1%, and the remainder is solvent. Put the mixture into a reaction vessel, stir and heat it to 60°C under closed conditions, then introduce carbon dioxide as an auxiliary dissolving gas and pressurize it to 6MPa. Continue to raise the temperature to 160°C and hold it at that temperature. After holding at that temperature, reduce the pressure and spin the filaments.

[0040] (3) The sprayed ultrafine fiber filaments are piled into a net, and after bonding and curing, a polyethylene ultrafine fiber membrane is obtained.

[0041] Example 2

[0042] (1) Polyethylene, styrene, functional monomers, crosslinking agents and initiators are mixed in proportion and dissolved in an appropriate amount of solvent (dichloromethane) to form a uniform mixed solution (solid content of 30%). Among them, polyethylene (a mixture of 150,000 molecular weight polyethylene and 500,000 molecular weight polyethylene in a mixing ratio of 40:1) 60%, styrene 5%, acrylic acid 25%, ethylene glycol dimethacrylate 8%, and initiator 2% are used. The mixed solution is cast into a film and placed in an oven preheated to 70°C for polymerization reaction for 15 hours. After the reaction is completed, the film can be kept in the oven for a period of time to allow the solvent to gradually evaporate and form a solid polymer film. The solid polymer film obtained after the reaction is crushed, sieved and granular polymer is obtained. The granular polymer is soaked in an ethanol-acetic acid mixture (volume ratio of ethanol to acetic acid is 9:1), ultrasonically treated for 3 hours, filtered and dried to obtain modified polyethylene granules.

[0043] (2) Mix modified polyethylene particles, antioxidant (antioxidant 168) and solvent dichloromethane, wherein the modified polyethylene particles are 18%, the antioxidant is 1%, and the remainder is solvent. Put the mixture into a reaction vessel, stir and heat it to 60°C under closed conditions, then introduce carbon dioxide as an auxiliary dissolving gas and pressurize it to 6MPa. Continue to heat it to 160°C and then keep it at that temperature. After the heat preservation is completed, depressurize and spin the fibers.

[0044] (3) The sprayed ultrafine fiber filaments are piled into a net, and after bonding and curing, a polyethylene ultrafine fiber membrane is obtained.

[0045] Example 3

[0046] (1) Polyethylene, styrene, functional monomers, crosslinking agents and initiators are mixed in proportion and dissolved in an appropriate amount of solvent (dichloromethane) to form a uniform mixed solution (solid content of 30%). Among them, polyethylene (a mixture of 150,000 molecular weight polyethylene and 500,000 molecular weight polyethylene in a mixing ratio of 35:1) 70%, styrene 8%, acrylic acid 15%, ethylene glycol dimethacrylate 5%, and initiator 2% are used. The mixed solution is cast into a film and placed in an oven preheated to 70°C for polymerization reaction for 15 hours. After the reaction is completed, the film can be kept in the oven for a period of time to allow the solvent to gradually evaporate and form a solid polymer film. The solid polymer film obtained after the reaction is crushed, sieved and granular polymer is obtained. The granular polymer is soaked in an ethanol-acetic acid mixture (volume ratio of ethanol to acetic acid is 9:1), ultrasonically treated for 3 hours, filtered and dried to obtain modified polyethylene granules.

[0047] (2) Mix modified polyethylene particles, antioxidant (antioxidant 168) and solvent dichloromethane, wherein the modified polyethylene particles are 15%, the antioxidant is 1%, and the remainder is solvent. Put the mixture into a reaction vessel, stir and heat it to 60°C under closed conditions, then introduce carbon dioxide as an auxiliary dissolving gas and pressurize it to 6MPa. Continue to raise the temperature to 160°C and hold it at that temperature. After holding at that temperature, reduce the pressure and spin the filaments.

[0048] (3) The sprayed ultrafine fiber filaments are piled into a net, and after bonding and curing, a polyethylene ultrafine fiber membrane is obtained.

[0049] There was no residue in the reactor and no blockage in the spinneret in Examples 1-3; this indicates that the polyethylene was fully dissolved and had excellent spinning processability.

[0050] Comparative Example

[0051] (1) Mix polyethylene granules (a mixture of 150,000 molecular weight polyethylene and 500,000 molecular weight polyethylene in a ratio of 30:1), antioxidant (antioxidant 168), and solvent dichloromethane. The mixture consists of 15% polyethylene granules, 1% antioxidant, and the remainder solvent. Add the mixture to a reaction vessel and heat it to 60°C under sealed conditions. Then, introduce carbon dioxide as an auxiliary dissolving gas and pressurize it to 6 MPa. Continue to heat the mixture to 160°C and hold it at that temperature. After holding the temperature, reduce the pressure and spin the filaments.

[0052] (2) The sprayed ultrafine fiber filaments are piled into a net, and after bonding and curing, a polyethylene ultrafine fiber membrane is obtained.

[0053] The comparative example showed significant residue in the reactor and blockage in the spinneret, indicating that the polyethylene was not fully dissolved and had relatively poor spinning processability.

[0054] Mechanical properties of the polyethylene microfiber membranes of Examples 1-3 and the comparative example were tested respectively. The tensile strength of the polyethylene microfiber membranes of Examples 1-3 was greater than 18 MPa, and the tensile strength of the polyethylene microfiber membrane of the comparative example was 8.6 MPa.

[0055] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0056] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A process for preparing a polyethylene microfiber membrane, characterized in that, Includes the following steps: (1) Mix polyethylene, styrene, functional monomers, crosslinking agents and initiators in proportion and dissolve them in a solvent to form a uniform mixed solution; cast the mixed solution into a film, react the film at a certain temperature, crush the solid polymer film obtained after the reaction, and sieve it to obtain particulate polymer; immerse the particulate polymer in an ethanol-acetic acid mixture and sonicate it for a certain time to obtain modified polyethylene particulates. (2) Mix the modified polyethylene particles, additives and solvent, stir and heat to a certain temperature under closed conditions, introduce auxiliary dissolving gas and pressurize, continue to heat to a certain temperature and keep it at that temperature; after the heat preservation is completed, reduce the pressure and spin the filaments. (3) The sprayed ultrafine fiber filaments are piled into a net, and after bonding and curing, a polyethylene ultrafine fiber membrane is obtained.

2. The preparation process of a polyethylene microfiber membrane according to claim 1, characterized in that, In step (1), the mixing ratio of polyethylene, styrene, functional monomer, crosslinking agent and initiator is: polyethylene 55%-70%, styrene 1%-8%, functional monomer 10%-25%, crosslinking agent 5%-10% and initiator 0.1%-5%.

3. The preparation process of a polyethylene microfiber membrane according to claim 1, characterized in that, The functional monomer is selected from at least one of acrylic acid, methacrylic acid, and maleic anhydride.

4. The preparation process of a polyethylene microfiber membrane according to claim 1, characterized in that, In step (1), the reaction temperature is 60-80℃ and the reaction time is 10-18 hours.

5. The preparation process of a polyethylene microfiber membrane according to claim 1, characterized in that, In step (1), the volume ratio of ethanol to acetic acid in the ethanol-acetic acid mixture is 9:

1.

6. The preparation process of a polyethylene microfiber membrane according to claim 1, characterized in that, In step (1), the initiator is selected from at least one of benzoyl peroxide, tert-butyl hydroperoxide, di-tert-butyl peroxide, and azobisisobutyronitrile; the crosslinking agent is selected from divinylbenzene or ethylene glycol dimethacrylate.

7. The preparation process of a polyethylene microfiber membrane according to claim 1, characterized in that, The adjuvant is an antioxidant, which is at least one of tris[2,4-di-tert-butylphenyl] phosphite, bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite, tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] pentaerythritol ester, and β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate n-octadecyl alcohol ester.

8. The preparation process of a polyethylene microfiber membrane according to claim 1, characterized in that, In step (2), the mixing ratio of modified polyethylene particles, additives and solvent is: 5-20% modified polyethylene particles, 0.1-1% additives, and the remainder is solvent.

9. The preparation process of a polyethylene microfiber membrane according to claim 1, characterized in that, In step (2), the temperature is heated to 30-80°C under sealed conditions, and an auxiliary dissolving gas is introduced to pressurize to 6-10 MPa, and the temperature is further increased to 100-190°C.

10. The preparation process of a polyethylene microfiber membrane according to claim 1, characterized in that, The auxiliary dissolving gas is carbon dioxide or nitrogen.