Preparation process of polyethylene superfine fiber membrane

Abstract

The invention discloses a preparation process of a polyethylene superfine fiber membrane, which comprises the following steps: mixing polyethylene, styrene, a functional monomer, a cross-linking agent and an initiator in proportion, and dissolving in a solvent; casting the mixed solution into a thin film, reacting the thin film at a certain temperature, and crushing the prepared solid polymer film to obtain a particle polymer; soaking the particle polymer in an ethanol-acetic acid mixed solution, and performing ultrasonic treatment to obtain modified polyethylene particles; mixing the modified polyethylene particles, an auxiliary agent and a solvent, stirring and heating under a closed condition, introducing auxiliary dissolving gas, pressurizing, continuously heating to a certain temperature, and preserving heat; after heat preservation is finished, spinning under reduced pressure; stacking the sprayed superfine fiber yarns into a net, and bonding and curing to obtain the polyethylene superfine fiber membrane. According to the preparation process, the solubility of polyethylene is improved, and the polyethylene superfine fiber membrane which is good in uniformity and excellent in mechanical property and chemical stability is prepared in combination with a flash spinning process.

Description

Technical Field

[0001] The present invention relates to the technical field of spinning fibers, and particularly relates to a preparation process of a polyethylene ultrafine fiber membrane. Background Art

[0002] Polyethylene (PE) is a thermoplastic polymer polymerized from ethylene monomers, which is divided into high-density polyethylene (HDPE), low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE). Its molecular chain structure (such as degree of branching, crystallinity) can directly affect the film-forming performance; polyethylene has a relatively low melting point (110 - 130 °C), good melt fluidity, is suitable for melt processing, and its chemical inertness, corrosion resistance and low cost characteristics make it an ideal fiber film-forming material.

[0003] The polyethylene solution spinning technology is a method of forming fibers by dissolving polyethylene in a specific solvent through a specific process, including wet spinning, dry spinning, electrospinning, flash phase separation method, etc. Among them, the flash phase separation method is as follows: under high temperature and high pressure conditions, polyethylene is dissolved to prepare a homogeneous spinning solution with a certain concentration, which is sent to the spinneret, and enters the decompression chamber through a decompression throttle hole; at this time, due to the pressure reduction, phase separation occurs between the polymer and the solvent, one phase is a polymer-rich phase, and the other phase is a solvent-rich phase; when the spinning solution reaches a certain point, the pressure drops to atmospheric pressure, the solvent undergoes a phase transformation, changes from a liquid state to a vapor state, phase separation occurs between the solvent and the polymer, and it expands rapidly at the spinneret, and the polymer is broken and stretched at high speed by the vapor flow depending on the velocity gradient; at the same time as the phase conversion, the fluid undergoes high-speed stretching, and because it is an adiabatic expansion, the solvent needs to absorb a large amount of heat, and the temperature drops sharply, so that the polymer rapidly crystallizes and cools into highly oriented ultrafine fibers.

[0004] The flash method has high production efficiency. The polyethylene spun film produced by it is composed of ultrafine fibers adhered and stacked, and the fiber diameter is 0.2 - 5.0 μm; this ultrafine fiber structure gives it a large specific surface area, which can provide better filtration performance and adsorption performance. The flash method can also endow the fibers with ultra-small diameters and excellent monofilament strength, and the material has high strength after consolidation molding. The polyethylene ultrafine fiber membrane produced by the flash method has good air permeability, which enables it to maintain good ventilation performance during application and improve the use comfort.

[0005] However, when using the flash method for polyethylene spinning, with the increase of concentration, the problem of insufficient dissolution will occur. The insufficient dissolution of polyethylene has the following effects on spinning and film formation: difficult spinning, fiber structure defects, poor film uniformity, abnormal pore structure, reduced mechanical properties, reduced chemical stability, etc. And improving the solubility of polyethylene by adding a co-solvent will introduce unnecessary impurities. Therefore, improving the solubility during polyethylene spinning is crucial for the production of polyethylene ultrafine fiber membranes. Summary of the Invention

[0006] To solve the above technical problems, the object of the present invention is to provide a preparation process of a polyethylene ultrafine fiber membrane. By modifying polyethylene and using supercritical gas-assisted dissolution, the solubility of polyethylene is improved, the spinning difficulty is reduced, and combined with the flash spinning process, a polyethylene ultrafine fiber membrane with good uniformity, excellent mechanical properties and chemical stability is prepared.

[0007] To achieve the above technical object and reach the above technical effect, the present invention is realized through the following technical solutions:

[0008] A preparation process of a polyethylene ultrafine fiber membrane includes the following steps:

[0009] (1) Mix polyethylene, styrene, functional monomer, crosslinking agent and initiator in proportion, 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 after screening, obtain granular polymer; soak the granular polymer in an ethanol-acetic acid mixed solution and perform ultrasonic treatment for a certain time to obtain modified polyethylene particles.

[0010] (2) Mix the modified polyethylene particles, additives and solvent, stir and heat to a certain temperature under closed conditions, then introduce auxiliary dissolution gas and pressurize, continue to heat to a certain temperature and keep warm; after the heat preservation ends, depressurize and spin.

[0011] (3) Stack the ejected ultrafine fiber filaments into a web, and after bonding and curing, obtain a polyethylene ultrafine fiber membrane.

[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] Further, in step (1), the reaction temperature is 60-80°C and the reaction time is 10-18 hours.

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

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

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

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

[0019] Further, in step (2), it is heated to 30-80 °C under a closed condition, pressurized to 6-10 MPa by introducing a supercritical gas, and then continuously heated to 100-190 °C.

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

[0021] The beneficial effects of the present invention are as follows:

[0022] The present invention first modifies polyethylene. Specifically, styrene and the functional monomer interact to form a stable complex. Under the action of an initiator, a mixture of polyethylene, styrene, the functional monomer, the crosslinking agent, and the initiator undergoes a polymerization reaction. The functional monomer and the crosslinking agent form a three-dimensional network structure that wraps styrene inside, and specific binding sites of styrene are formed in the polyethylene matrix. After the formed polymer is soaked in an ethanol-acetic acid mixture and ultrasonically treated for a period of time, styrene is dissolved and removed, thereby forming molecular channels or cavity structures in the polymer, which can effectively destroy the crystalline structure of polyethylene, increase the amorphous region, make it easier for solvent molecules to penetrate into the interior of the polymer, and also improve the movement ability of molecular chains, making the molecular chains more easily dispersed and dissolved in the solvent, thus greatly improving the solubility of polyethylene. The functional monomer and the crosslinking agent therein form a three-dimensional network structure with polyethylene, enhancing the stability and mechanical strength of the polymer.

[0023] The present invention also uses an auxiliary dissolving gas (supercritical gas) for auxiliary dissolution. The supercritical gas can penetrate between the polyethylene molecular chains, lower its glass transition temperature, and increase the free volume of the amorphous region, thereby improving the movement ability of molecular chains and making it more easily dispersed and dissolved in the solvent.

[0024] By combining the modification of polyethylene and the auxiliary dissolution of supercritical gas, the present invention can greatly improve the solubility of polyethylene in the solvent, thereby improving the spinnability and enhancing the uniformity, mechanical properties, and chemical stability of the prepared polyethylene ultrafine fiber membrane. Specific embodiments

[0025] The technical solutions in the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0026] The present invention provides a preparation process for a polyethylene ultrafine fiber membrane, comprising the following steps:

[0027] (1) Mix polyethylene, styrene, a functional monomer, a crosslinking agent, and an initiator in proportion, dissolve them in a solvent to form a homogeneous mixed solution; cast the mixed solution into a film, place the film in an oven preheated to 65°C - 80°C, and carry out a polymerization reaction for 10 - 18 hours; after the reaction is completed, it can be kept in the oven for a period of time to gradually volatilize the solvent to form a solid polymer film; crush the solid polymer film obtained after the reaction, and after screening, obtain granular polymer; soak the granular polymer in an ethanol - acetic acid mixed solution, perform ultrasonic treatment for 2.5 - 3 hours, and then filter and dry to obtain modified polyethylene particles.

[0028] (2) Mix the modified polyethylene particles, an auxiliary agent, and a solvent, put the mixture into a reaction kettle, stir and heat it to 30 - 80°C under closed conditions, introduce an auxiliary dissolution gas, and pressurize it to 6 - 10 MPa, then continue to heat up to 100 - 190°C and keep it warm; after the heat preservation is completed, carry out pressure - reducing spinning.

[0029] (3) Stack the ejected ultrafine fiber filaments into a web, and after bonding and curing, obtain a polyethylene ultrafine fiber membrane.

[0030] In this step (1), the mixing ratio of polyethylene, styrene, the functional monomer, the crosslinking agent, and the initiator is: polyethylene 55% - 70%, styrene 1% - 8%, the functional monomer 10% - 25%, the crosslinking agent 5% - 10%, and the initiator 0.1% - 5%. The polyethylene therein 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 mixed solution, the volume ratio of ethanol to acetic acid is 9:1.

[0033] Among them, 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 the modified polyethylene particles, the additive and the solvent is as follows: 5-20% of the modified polyethylene particles, 0.1-1% of the additive, and the rest is the solvent. The solvent is one or more of dimethyl sulfoxide, N,N-dimethylformamide, acetone, benzene, xylene, dichloromethane, dichloroethane, and carbon tetrachloride.

[0035] Among them, the additive is an antioxidant, and the antioxidant is preferably at least one of tris[2,4-di-tert-butylphenyl]phosphite (antioxidant 168), bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite (antioxidant 626), pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1010), and n-octadecyl 3,5-di-tert-butyl-4-hydroxyphenylpropionate (antioxidant 1076).

[0036] Among them, the auxiliary dissolving gas is carbon dioxide or nitrogen

[0037] Example 1

[0038] (1) Mix polyethylene, styrene, functional monomer, crosslinking agent and initiator in proportion and dissolve them in an appropriate amount of solvent (dichloromethane) to form a uniform mixed solution (solid content is 30%); among them, polyethylene (a mixture of polyethylene with a molecular weight of 150,000 and polyethylene with a molecular weight of 500,000, and the mixing ratio is 30:1) 65%, styrene 5%, acrylic acid 20%, ethylene glycol dimethacrylate 8%, initiator 2%; Cast the mixed solution into a film, put the film into an oven preheated to 70 °C, and carry out a polymerization reaction for 15 hours; after the reaction is completed, it can be kept in the oven for a period of time to gradually volatilize the solvent to form a solid polymer film; Crush the solid polymer film obtained after the reaction, and after screening, obtain granular polymer; Immerse the granular polymer in an ethanol-acetic acid mixture (the volume ratio of ethanol to acetic acid is 9:1), ultrasonically treat for 3 hours, then filter and dry to obtain modified polyethylene particles;

[0039] (2) Mix the modified polyethylene particles, antioxidant (antioxidant 168) and dichloromethane solvent. Among them, 15% of the modified polyethylene particles, 1% of the antioxidant, and the rest is the solvent. Put the mixture into a reaction kettle, stir and heat it to 60 °C under closed conditions, then introduce the auxiliary dissolving gas carbon dioxide and pressurize it to 6 MPa, and continue to heat up to 160 °C and then keep warm; After the heat preservation is over, carry out pressure-reducing spinning;

[0040] (3) Stack the ejected ultrafine fiber filaments into a net, and after bonding and curing, obtain a polyethylene ultrafine fiber membrane.

[0041] Example 2

[0042] (1) Mix polyethylene, styrene, functional monomer, crosslinking agent and initiator in proportion, and dissolve them in an appropriate amount of solvent (dichloromethane) to form a uniform mixed solution (solid content is 30%); among them, polyethylene (a mixture of polyethylene with a molecular weight of 150,000 and polyethylene with a molecular weight of 500,000, the mixing ratio is 40:1) 60%, styrene 5%, acrylic acid 25%, ethylene glycol dimethacrylate 8%, initiator 2%; Cast the mixed solution into a film, put the film into an oven preheated to 70 °C, and carry out a polymerization reaction for 15 hours; after the reaction is completed, it can be kept in the oven for a period of time to gradually volatilize the solvent and form a solid polymer film; crush the solid polymer film obtained after the reaction, and after screening, obtain granular polymer; soak the granular polymer in an ethanol-acetic acid mixed solution (the volume ratio of ethanol to acetic acid is 9:1), ultrasonically treat for 3 hours, and then filter and dry to obtain modified polyethylene particles;

[0043] (2) Mix the modified polyethylene particles, antioxidant (antioxidant 168) and the solvent dichloromethane, among which, the modified polyethylene particles are 18%, the antioxidant is 1%, and the rest is the solvent. Put the mixture into a reaction kettle, stir and heat to 60 °C under closed conditions, then introduce the auxiliary dissolution gas carbon dioxide, and pressurize to 6 MPa, continue to heat up to 160 °C and then keep warm; after the heat preservation is over, carry out pressure-reducing spinning;

[0044] (3) Stack the ejected ultrafine fiber filaments into a web, and obtain a polyethylene ultrafine fiber membrane after bonding and curing.

[0045] Example 3

[0046] (1) Mix polyethylene, styrene, functional monomer, crosslinking agent and initiator in proportion, and dissolve them in an appropriate amount of solvent (dichloromethane) to form a uniform mixed solution (solid content is 30%); among them, polyethylene (a mixture of polyethylene with a molecular weight of 150,000 and polyethylene with a molecular weight of 500,000, the mixing ratio is 35:1) 70%, styrene 8%, acrylic acid 15%, ethylene glycol dimethacrylate 5%, initiator 2%; Cast the mixed solution into a film, put the film into an oven preheated to 70 °C, and carry out a polymerization reaction for 15 hours; after the reaction is completed, it can be kept in the oven for a period of time to gradually volatilize the solvent and form a solid polymer film; crush the solid polymer film obtained after the reaction, and after screening, obtain granular polymer; soak the granular polymer in an ethanol-acetic acid mixed solution (the volume ratio of ethanol to acetic acid is 9:1), ultrasonically treat for 3 hours, and then filter and dry to obtain modified polyethylene particles;

[0047] (2) Mix the modified polyethylene particles, antioxidant (antioxidant 168), and the solvent dichloromethane, where the modified polyethylene particles account for 15%, the antioxidant accounts for 1%, and the rest is the solvent. Put the mixture into a reaction kettle, stir and heat it to 60°C under closed conditions, then introduce the auxiliary dissolution gas carbon dioxide, and pressurize it to 6 MPa. Continue to heat up to 160°C and then keep it warm; after the heat preservation is over, carry out pressure-reducing spinning;

[0048] (3) Stack the ejected ultrafine fiber filaments into a web, and obtain a polyethylene ultrafine fiber membrane after bonding and curing.

[0049] There is no residue in the reaction kettles in Examples 1-3 and the spinneret is not blocked; this indicates that the polyethylene is fully dissolved and the spinning processability is excellent.

[0050] Comparative Example

[0051] (1) Mix the polyethylene particles (a mixture of polyethylene with a molecular weight of 150,000 and polyethylene with a molecular weight of 500,000, and the mixing ratio is 30:1), antioxidant (antioxidant 168), and the solvent dichloromethane, where the polyethylene particles account for 15%, the antioxidant accounts for 1%, and the rest is the solvent. Put the mixture into a reaction kettle, stir and heat it to 60°C under closed conditions, then introduce the auxiliary dissolution gas carbon dioxide, and pressurize it to 6 MPa. Continue to heat up to 160°C and then keep it warm; after the heat preservation is over, carry out pressure-reducing spinning;

[0052] (2) Stack the ejected ultrafine fiber filaments into a web, and obtain a polyethylene ultrafine fiber membrane after bonding and curing.

[0053] There is a lot of residue in the reaction kettle in the comparative example and the spinneret is blocked; this indicates that the polyethylene is not fully dissolved and the spinning processability is relatively poor.

[0054] Conduct mechanical property tests on the polyethylene ultrafine fiber membranes of Examples 1-3 and the comparative example respectively. Among them, the tensile strength of the polyethylene ultrafine fiber membranes of Examples 1-3 is greater than 18 MPa, and the tensile strength of the polyethylene ultrafine fiber membrane of the comparative example is 8.6 MPa.

[0055] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended to include all changes falling within the meaning and scope of the equivalent elements of the claims in the present invention.

[0056] In addition, it should be understood that although this specification is described in terms of embodiments, not every embodiment contains only one independent technical solution. This narrative manner of the specification is only for clarity. Those skilled in the art should regard 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 preparation process of a polyethylene ultra-fine fiber membrane, characterized in that, It includes the following steps: (1) Mix polyethylene, styrene, functional monomer, crosslinking agent and initiator in proportion, 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 granular polymer; soak the granular polymer in an ethanol-acetic acid mixture and perform ultrasonic treatment for a certain time to obtain modified polyethylene particles; (2) Mix the modified polyethylene particles, additives and solvent, stir and heat to a certain temperature under closed conditions, introduce auxiliary dissolution gas, pressurize, and continue to heat to a certain temperature and then keep warm; after the heat preservation is completed, carry out pressure-reducing spinning; (3) Stack the ejected ultrafine fiber filaments into a net, and obtain a polyethylene ultrafine fiber membrane after bonding and curing.

2. The preparation process of a polyethylene ultra-fine fiber 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 ultra-fine fiber membrane according to claim 1, characterized in that, The functional monomer is selected from at least one of acrylic acid, methacrylic acid, maleic anhydride.

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

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

1.

6. The preparation process of a polyethylene ultra-fine fiber 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, azobisisobutyronitrile; the crosslinking agent is selected from divinylbenzene or ethylene glycol dimethacrylate.

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

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

9. The preparation process of a polyethylene ultra-fine fiber membrane according to claim 1, characterized in that, In step (2), heat to 30-80°C under closed conditions, introduce auxiliary dissolution gas and pressurize to 6-10 MPa, and continue to heat to 100-190°C.

10. The preparation process of a polyethylene ultra-fine fiber membrane according to claim 1, characterized in that, The auxiliary dissolution gas is carbon dioxide or nitrogen.