Polypropylene dissolving agent and application thereof

Abstract

The invention provides a polypropylene dissolving agent and application thereof, and belongs to the technical field of olefin dissolving agents. The polypropylene dissolving agent is prepared from the following raw materials in parts by mass: 10 to 25 parts of dinitrile amine salt ionic liquid, 5 to 15 parts of betaine salt, 5 to 15 parts of tetrafluoroborate ionic liquid, 5 to 15 parts of ethyl sulfate salt ionic liquid, 10 to 20 parts of acetate ionic liquid, 10 to 40 parts of long carbon chain anion ionic liquid, 2 to 18 parts of dispersing agent and 2 to 20 parts of auxiliary agent. Under the condition of 180-280 DEG C, the mass fraction of polypropylene with the molecular weight of 500,000-10,000,000 dissolved by the polypropylene dissolving agent reaches 15% or above, the ultra-high molecular weight polypropylene wet processing casting piece film forming can be achieved, and a polypropylene diaphragm or polypropylene fiber obtained through processing has the advantages of being resistant to high temperature, high in strength (including tensile strength and puncture strength), high in porosity / high in breathability and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of olefin dissolving agent, and particularly relates to a polypropylene dissolving agent and application thereof. BACKGROUND

[0002] The existing wet-process lithium battery diaphragm uses polyethylene resin as raw material, is made into thick film through co-extrusion technology, is stretched longitudinally (MD) first, and then is stretched transversely (TD), and the porosity of the diaphragm is poor in uniformity relative to the wet-process polyethylene diaphragm; the dry-process PP diaphragm has low porosity (30-40%) and uniform pore size distribution, and is suitable for the scene with low requirement on electrolyte permeability. The wet-process diaphragm has high porosity and mechanical strength, and is suitable for the high energy density requirement of ternary lithium batteries, and occupies the dominant position in the high-end market. So far, there is no report on the suitable solvent for dissolving PP and then melting to produce the PP diaphragm and PP fiber through wet-process production.

[0003] Therefore, it is of great value to provide a polypropylene dissolving agent which has good solubility to PP and improves the strength and porosity of the polypropylene diaphragm or fiber. SUMMARY

[0004] The present application aims at providing a polypropylene dissolving agent and application thereof to overcome the shortcomings of the prior art.

[0005] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions.

[0006] The present application provides a polypropylene dissolving agent, which comprises the following raw materials in mass fraction:

[0007] 10-25 parts of dicyanamide salt ionic liquid, 5-15 parts of betaine salt, 5-15 parts of tetrafluoroborate ionic liquid, 5-15 parts of ethyl sulfate ionic liquid, 10-20 parts of acetate ionic liquid, 10-40 parts of long carbon chain anion ionic liquid, 2-18 parts of dispersant, and 2-20 parts of auxiliary agent.

[0008] Preferably, the dicyanamide salt ionic liquid comprises one or more of 1-butyl-3-methylimidazole dicyanamide salt, 1-ethyl-3-methylimidazole dicyanamide salt, 1-hexyl-3-methylimidazole dicyanamide salt, N-ethylimidazole dicyanamide salt and 1,2-dimethylimidazole dicyanamide salt.

[0009] Preferably, the betaine salt comprises betaine citrate and / or betaine salicylate.

[0010] As preferred, the tetrafluoroborate ionic liquid comprises one or more of 1-butyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-decyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium tetrafluoroborate, 1-octyl-3-methylimidazolium tetrafluoroborate, N-ethylimidazolium tetrafluoroborate and 1,2-dimethylimidazolium tetrafluoroborate.

[0011] As preferred, the ethyl sulfate ionic liquid comprises one or more of 1-butyl-3-methylimidazolium ethyl sulfate, 1-ethyl-3-methylimidazolium ethyl sulfate, 1-octyl-3-methylimidazolium ethyl sulfate, 1-hexyl-3-methylimidazolium ethyl sulfate, N-ethylimidazolium ethyl sulfate and 1,2-dimethylimidazolium ethyl sulfate.

[0012] As preferred, the acetate ionic liquid comprises one or more of 1-butyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium acetate, 1-hexyl-3-methylimidazolium acetate, N-ethylimidazolium acetate and 1,2-dimethylimidazolium acetate.

[0013] As preferred, the dispersant comprises one or more of sodium polyacrylate, sodium polycarboxylate, stearyl erucamide, erucamide, methylene bis-naphthalene sulfonic acid sodium, methylene bis-methyl naphthalene sulfonic acid sodium, sodium lignosulfonate, sodium polyphosphate, 2-(2-hydroxy-5-tert-octylphenyl) benzotriazole, acrylic acid-2-acrylamide-2-methylpropane sulfonic acid copolymer, oleic acid amide and polyethylene oxide.

[0014] As preferred, the adjuvant comprises one or more of isooctanol polyoxyethylene ether phosphate, lauryl alcohol ether phosphate, sorbitan monooleate polyoxyethylene ether, polyoxyethylene sorbitan monolaurate, trimethylolpropane trimethylacrylate, acetyl tri-butyl citrate, polyethylene glycol 6000 bis-stearate, glycerol tri(ethylhexanoate), cetearyl phosphate, trimethylolpropane tris(3-mercaptopropionate), trimethylolpropane stearyl octenylate, calcium stearate, dioctyl phthalate, dibutyl phthalate, diisononyl cyclohexane 1,2-dicarboxylate, diisononyl phthalate, dimethyl phthalate, isodioctyl sebacate, di(2-ethylhexyl) adipate, dioctyl sebacate, castor oil polyoxyethylene ether, cardanol polyoxyethylene ether and trioctyl trimellitate.

[0015] The present application also provides the use of the polypropylene dissolving agent in the preparation of polypropylene membrane or polypropylene fiber.

[0016] In the present application, polypropylene powder is dissolved in the polypropylene dissolving agent, and the solution is extruded and plasticized to obtain polypropylene membrane or polypropylene fiber.

[0017] The beneficial effects of the present application are as follows:

[0018] 1) The polypropylene dissolving agent of the present application can dissolve 50-1000 million molecular weight polypropylene to more than 15% of mass fraction under the condition of 180-280℃, and the double screw extruder can be effectively extruded; the polypropylene dissolving agent of the present application can realize wet processing of ultra-high molecular weight polypropylene into film (molecular weight of 50-1000 million), and the processed polypropylene membrane or polypropylene fiber has the characteristics of high temperature resistance, high strength (including tensile and puncture strength), high porosity / high permeability, etc.

[0019] 2) The PP powder is dissolved and then cast or spun, and the cast or PP fiber is washed with ethanol / dichloromethane / tetrachloroethylene / ionic liquid extractant to remove the ionic liquid, to prepare a polypropylene membrane or polypropylene fiber; the washed ionic liquid is concentrated and purified to effectively recover the ionic liquid, realizing the recycling of the ionic liquid. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 Picture of complete dissolution of polypropylene powder in application example 1;

[0021] Figure 2 Picture of complete dissolution of polypropylene powder in application example 2;

[0022] Figure 3 Picture of complete dissolution of polypropylene powder in application example 3;

[0023] Figure 4 Picture of complete dissolution of polypropylene powder in application example 4;

[0024] Figure 5 Picture of complete dissolution of polypropylene powder in application example 5;

[0025] Figure 6 Picture of the finished product membrane after stretching, extraction and drying of the polypropylene powder dissolved in application example 2;

[0026] Figure 7 Picture of the pre-oriented fiber after stretching of the polypropylene powder dissolved in application example 5. DETAILED DESCRIPTION

[0027] The present application provides a polypropylene dissolving agent, which comprises the following raw materials in mass fraction:

[0028] 10-25 parts of dicyanamide salt ionic liquid, 5-15 parts of betaine salt, 5-15 parts of tetrafluoroborate salt ionic liquid, 5-15 parts of ethyl sulfate salt ionic liquid, 10-20 parts of acetate salt ionic liquid, 10-40 parts of long carbon chain anion ionic liquid, 2-18 parts of dispersing agent, and 2-20 parts of auxiliary agent.

[0029] The mass fraction of the dicyanamide salt ionic liquid in the polypropylene dissolving agent is preferably 13-21 parts, further preferably 15-20 parts, and more preferably 17-18 parts; the mass fraction of the betaine salt is preferably 7-12 parts, further preferably 8-10 parts, and more preferably 9 parts; the mass fraction of the tetrafluoroborate ionic liquid is preferably 7-12 parts, further preferably 8-10 parts, and more preferably 9 parts; the mass fraction of the ethyl sulfate ionic liquid is preferably 7-12 parts, further preferably 8-10 parts, and more preferably 9 parts; the mass fraction of the acetate ionic liquid is preferably 12-18 parts, further preferably 14-16 parts, and more preferably 15 parts; the mass fraction of the long carbon chain anion ionic liquid is preferably 20-30 parts, further preferably 25 parts; the mass fraction of the dispersant is preferably 5-12 parts, further preferably 8-10 parts; and the mass fraction of the auxiliary agent is preferably 4-15 parts, further preferably 6-10 parts.

[0030] In the present application, the dicyanamide salt ionic liquid preferably comprises one or more of 1-butyl-3-methylimidazolium dicyanamide, 1-ethyl-3-methylimidazolium dicyanamide, 1-hexyl-3-methylimidazolium dicyanamide, N-ethylimidazolium dicyanamide, and 1,2-dimethylimidazolium dicyanamide.

[0031] In the present application, the betaine salt preferably comprises betaine citrate and / or betaine salicylate.

[0032] In the present application, the tetrafluoroborate ionic liquid preferably comprises one or more of 1-butyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-decyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium tetrafluoroborate, 1-octyl-3-methylimidazolium tetrafluoroborate, N-ethylimidazolium tetrafluoroborate, and 1,2-dimethylimidazolium tetrafluoroborate.

[0033] In the present application, the ethyl sulfate ionic liquid preferably comprises one or more of 1-butyl-3-methylimidazolium ethyl sulfate, 1-ethyl-3-methylimidazolium ethyl sulfate, 1-octyl-3-methylimidazolium ethyl sulfate, 1-hexyl-3-methylimidazolium ethyl sulfate, N-ethylimidazolium ethyl sulfate, and 1,2-dimethylimidazolium ethyl sulfate.

[0034] In the present application, the acetate ionic liquid preferably comprises one or more of 1-butyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium acetate, 1-hexyl-3-methylimidazolium acetate, N-ethylimidazolium acetate, and 1,2-dimethylimidazolium acetate.

[0035] In the present application, the long carbon chain anion in the long carbon chain anion ionic liquid is preferably one or more of dodecyl sulfonate, dodecyl benzene sulfonate, dodecanoate, tetradecanoate, hexadecanoate, octadecanoate, octadecenoate, hexadecenoate, 12-hydroxy, cis-9-octadecenoate, cis, cis-9, 12-octadecadienoate, docosahexaenoic acid and docosahexaenoic acid, and the corresponding cation is preferably 1-butyl-3-methyl imidazole.

[0036] In the present application, the dispersant preferably comprises one or more of sodium polyacrylate, sodium polycarboxylate, stearyl erucamide, erucamide, methylene bis naphthalene sulfonic acid sodium, methylene bis naphthalene sulfonic acid sodium, sodium lignosulfonate, sodium polyphosphate, 2-(2-hydroxy-5-tert-octyl phenyl) benzotriazole, acrylic acid-2-acrylamide-2-methylpropane sulfonic acid copolymer, oleic acid amide and polyethylene oxide.

[0037] In the present application, the auxiliary agent preferably comprises one or more of isooctanol polyoxyethylene ether phosphate, lauryl alcohol ether phosphate, sorbitan monooleate polyoxyethylene ether, polyoxyethylene sorbitan monolaurate, trimethylolpropane trimethacrylate, acetyl tri-butyl citrate, polyethylene glycol 6000 distearate, glycerol tri(ethylhexanoate), cetearyl phosphate, trimethylolpropane tris(3-mercaptopropionate), trimethylolpropane octadecenoate, calcium stearate, dioctyl phthalate, dibutyl phthalate, diisononyl cyclohexane 1,2-dicarboxylate, diisononyl phthalate, dimethyl phthalate, isodioctyl sebacate, di(2-ethylhexyl) adipate, dioctyl sebacate, castor oil polyoxyethylene ether, cardanol polyoxyethylene ether and trioctyl trimellitate.

[0038] The present application also provides the use of the polypropylene dissolving agent in the preparation of polypropylene membranes or polypropylene fibers. The polypropylene powder is dissolved in the polypropylene dissolving agent, and the solution is extruded and plasticized to obtain polypropylene membranes or polypropylene fibers.

[0039] In the present application, the polypropylene powder is dissolved in the polypropylene dissolving agent to obtain a solution, the mass fraction of the polypropylene powder is preferably 15-35%, and the molecular weight of the polypropylene is preferably 500-1000 million; when the molecular weight of the polypropylene is 100-300 million, the mass fraction of the polypropylene powder in the solution is preferably 20-35%, and further preferably 25-30%; when the molecular weight of the polypropylene is 300-500 million, the mass fraction of the polypropylene powder in the solution is preferably 15-22%, and further preferably 18-20%; when the molecular weight of the polypropylene is 800-1000 million, the mass fraction of the polypropylene powder in the solution is preferably 15-20%, and further preferably 16-18%; and the polypropylene is preferably isotactic polypropylene, syndiotactic polypropylene or atactic polypropylene.

[0040] The polypropylene separator prepared by the present application has uniform pore size (±5% size deviation), is suitable for power batteries, and the residue of one or more substances of the dissolving agent described in the present application can be detected on the polypropylene separator, so that it can be proved that the dissolving agent of the present application can be used to produce and process polypropylene separators. The polypropylene separator produced by the dissolving agent of the present application has a puncture strength of 200-1000 gf, a transverse tensile strength of 1000-9000 kgf / cm 2 , a longitudinal tensile strength of 100-9000 kgf / cm 2 , a gas permeability (100 mL) of 30-500 s, and a porosity of 20-95%.

[0041] The polypropylene fiber prepared by the present application has high strength, is suitable for fiber weaving and textile processing fields, and the residue of one or more substances of the dissolving agent described in the present application can be detected on the polypropylene fiber, so that it can be proved that the dissolving agent of the present application can be used to produce and process polypropylene fibers. The polypropylene fiber produced by the dissolving agent of the present application has a fineness of 20-1500 D and a strength of 20-100 cN.

[0042] The technical solutions provided by the present application will be described in detail below in conjunction with the examples, but they should not be understood as limiting the scope of protection of the present application.

[0043] Example 1

[0044] The polypropylene dissolving agent of the present example is composed of the following raw materials in mass fraction: 1-butyl-3-methyl imidazole dicyanamide salt 18 parts, betaine citrate 10 parts, 1-butyl-3-methyl imidazole tetrafluoroborate salt 10 parts, 1-butyl-3-methyl imidazole ethyl sulfate salt 10 parts, 1-butyl-3-methyl imidazole acetate 15 parts, 1-butyl-3-methyl imidazole dodecyl sulfonate 25 parts, methylene bis naphthalene sulfonate sodium 8 parts, dioctyl sebacate 3 parts, and isooctanol polyoxyethylene ether phosphate 3 parts.

[0045] Example 2

[0046] The polypropylene dissolving agent of this example is composed of the following raw materials in mass parts: 1-ethyl-3-methylimidazole dicyanamide salt 15 parts, betaine citrate 12 parts, 1-ethyl-3-methylimidazole tetrafluoroborate 6 parts, 1-ethyl-3-methylimidazole ethyl sulfate salt 8 parts, 1-ethyl-3-methylimidazole acetate salt 18 parts, 1-butyl-3-methylimidazole dodecylsulfonic acid salt 20 parts, sodium lignosulfonate 4 parts, dioctyl phthalate 5 parts, trimethylolpropane trimethacrylate 5 parts.

[0047] Example 3

[0048] The polypropylene dissolving agent of this example is composed of the following raw materials in mass parts: 1-hexyl-3-methylimidazole dicyanamide salt 22 parts, betaine salicylate 8 parts, 1-hexyl-3-methylimidazole tetrafluoroborate 15 parts, 1-hexyl-3-methylimidazole ethyl sulfate salt 12 parts, 1-hexyl-3-methylimidazole acetate salt 12 parts, 1-butyl-3-methylimidazole dodecylbenzenesulfonic acid salt 30 parts, polyethylene oxide (molecular weight 120000) 12 parts, trimethylolpropane octadecenoate 2 parts, dioctyl phthalate 3 parts.

[0049] Example 4

[0050] The polypropylene dissolving agent of this example is composed of the following raw materials in mass parts: N-ethylimidazole dicyanamide salt 15 parts, betaine citrate 9 parts, 1,2-dimethylimidazole tetrafluoroborate 13 parts, 1-octyl-3-methylimidazole ethyl sulfate salt 14 parts, N-ethylimidazole acetate salt 10 parts, 1-butyl-3-methylimidazole hexadecanoate 25 parts, 2-(2-hydroxy-5-tert-octylphenyl)benzotriazole 10 parts, trimethylolpropane tris(3-mercaptopropionic acid) ester 6 parts, acetyl citric acid tributyl ester 4 parts.

[0051] Example 5

[0052] The polypropylene dissolving agent of this example is composed of the following raw materials in mass parts: 1,2-dimethylimidazole dicyanamide salt 17 parts, betaine citrate 4 parts, betaine salicylate 4 parts, 1-octyl-3-methylimidazole tetrafluoroborate 10 parts, 1,2-dimethylimidazole ethyl sulfate salt 10 parts, 1,2-dimethylimidazole acetate salt 18 parts, 1-butyl-3-methylimidazole tetradecanoate 23 parts, erucic acid amide 17 parts, adipic acid di(2-ethylhexyl) ester 3 parts, cetearyl alcohol phosphate 7 parts.

[0053] Application Example 1

[0054] Isotactic polypropylene powder with a molecular weight of 1.5 million (average particle size 150 μm) was dissolved in the polypropylene dissolving agent of Example 1 at 200°C, and the mass fraction of polypropylene in the solution was 30%. The solution was sequentially subjected to extrusion plasticization (extrusion temperature 230°C), sheet cooling (5°C), biaxial stretching (transverse stretching temperature 70°C, longitudinal stretching temperature 130°C), extraction (30°C), drying (70°C), thickness measurement by edge stretching, post-treatment, and winding to obtain a polypropylene separator. The performance test results of the polypropylene separator are shown in Table 1.

[0055] Table 1 Performance of polypropylene separator prepared from polypropylene with a molecular weight of 1.5 million

[0056]

[0057] The picture of complete dissolution of the polypropylene powder of Application Example 1 is shown in Figure 1 .

[0058] Application Example 2

[0059] Isotactic polypropylene powder with a molecular weight of 3 million (average particle size 150 μm) was dissolved in the polypropylene dissolving agent of Example 2 at 210°C, and the mass fraction of polypropylene in the solution was 20%. The solution was sequentially subjected to extrusion plasticization (extrusion temperature 250°C), sheet cooling (10°C), biaxial stretching (transverse stretching temperature 90°C, longitudinal stretching temperature 140°C), extraction (30°C), drying (70°C), thickness measurement by edge stretching, post-treatment, and winding to obtain a polypropylene separator. The performance test results of the polypropylene separator are shown in Table 2.

[0060] Table 2 Performance of polypropylene separator prepared from polypropylene with a molecular weight of 3 million

[0061]

[0062] The picture of complete dissolution of the polypropylene powder of Application Example 2 is shown in Figure 2 .

[0063] Application Example 3

[0064] Isotactic polypropylene powder with a molecular weight of 10 million (average particle size 150 μm) was dissolved in the polypropylene dissolving agent of Example 3 at 250°C, and the mass fraction of polypropylene in the solution was 15%. The solution was sequentially subjected to extrusion plasticization (extrusion temperature 250°C), sheet cooling (5°C), biaxial stretching (transverse stretching temperature 100°C, longitudinal stretching temperature 150°C), extraction (30°C), drying (70°C), thickness measurement by edge stretching, post-treatment, and winding to obtain a polypropylene separator. The performance test results of the polypropylene separator are shown in Table 3.

[0065] Table 3 Performance of polypropylene separator prepared from polypropylene with a molecular weight of 10 million

[0066]

[0067] The picture of the polypropylene powder of application example 3 completely dissolved is shown in Figure 3

[0068] Application Example 4

[0069] The polypropylene powder with a molecular weight of 3 million was dissolved in the polypropylene dissolving agent of example 4 at 230°C, and the mass fraction of polypropylene in the solution was 22%; the solution was successively subjected to extrusion (230°C), cooling (20°C), equilibration, primary stretching (35°C), extraction (30°C), drying (70°C), draw cutting thickness (draw temperature 140°C), post-treatment, and winding to obtain polypropylene fibers. The test results of the properties of the polypropylene fibers are shown in table 4.

[0070] Table 4 Properties of polypropylene fibers prepared from polypropylene with a molecular weight of 3 million

[0071]

[0072] The picture of the polypropylene powder of application example 4 completely dissolved is shown in Figure 4

[0073] Application Example 5

[0074] The polypropylene powder with a molecular weight of 10 million was dissolved in the polypropylene dissolving agent of example 5 at 270°C, and the mass fraction of polypropylene in the solution was 15%; the solution was successively subjected to extrusion (270°C), cooling (20°C), equilibration, primary stretching (35°C), extraction (30°C), drying (70°C), draw cutting thickness (draw temperature 140°C), post-treatment, and winding to obtain polypropylene fibers. The test results of the properties of the polypropylene fibers are shown in table 5.

[0075] Table 5 Properties of polypropylene fibers prepared from polypropylene with a molecular weight of 10 million

[0076]

[0077] The picture of the polypropylene powder of application example 5 completely dissolved is shown in Figure 5

[0078] ​​​The application provides a polypropylene dissolving agent, which can dissolve 500-1000 million molecular weight polypropylene with a mass fraction of 15% or more under the condition of 180-280 DEG C, and the double screw extruder can effectively extrude; the polypropylene dissolving agent can realize wet processing of ultra-high molecular weight polypropylene into a film (molecular weight of 50-1000 million), and the polypropylene diaphragm or polypropylene fiber obtained by processing has the characteristics of high temperature resistance, high strength (including tensile and puncture strength), high porosity / high permeability and the like.

[0079] The above only describes the preferred embodiments of the present application, and it should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A polypropylene dissolving agent, characterized by, The polypropylene dissolving agent comprises raw materials in the following mass fractions: The dicyanamide salt ionic liquid is one or more of 1-butyl-3-methylimidazolium dicyanamide, 1-ethyl-3-methylimidazolium dicyanamide, 1-hexyl-3-methylimidazolium dicyanamide, N-ethylimidazolium dicyanamide and 1,2-dimethylimidazolium dicyanamide.

2. The polypropylene dissolving agent according to claim 1, characterized in that, The betaine salt comprises betaine citrate and / or betaine salicylate.

3. The polypropylene dissolving agent according to claim 1 or 2, characterized in that, The tetrafluoroborate ionic liquid comprises one or more of 1-butyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-decyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium tetrafluoroborate, 1-octyl-3-methylimidazolium tetrafluoroborate, N-ethylimidazolium tetrafluoroborate and 1,2-dimethylimidazolium tetrafluoroborate.

4. The polypropylene dissolving agent according to claim 3, characterized in that, The ethyl sulfate ionic liquid comprises one or more of 1-butyl-3-methylimidazolium ethyl sulfate, 1-ethyl-3-methylimidazolium ethyl sulfate, 1-octyl-3-methylimidazolium ethyl sulfate, 1-hexyl-3-methylimidazolium ethyl sulfate, N-ethylimidazolium ethyl sulfate and 1,2-dimethylimidazolium ethyl sulfate.

5. The polypropylene dissolving agent according to claim 4, characterized in that, The acetic acid salt ionic liquid comprises one or more of 1-butyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium acetate, 1-hexyl-3-methylimidazolium acetate, N-ethylimidazolium acetate and 1,2-dimethylimidazolium acetate.

6. The polypropylene dissolving agent according to claim 5, characterized in that, The dispersant comprises one or more of sodium polyacrylate, sodium polycarboxylate, stearyl erucamide, erucamide, methylene bis-naphthalene sulfonic acid sodium, methylene bis-methyl naphthalene sulfonic acid sodium, sodium lignosulfonate, sodium polyphosphate, 2-(2-hydroxy-5-tert-octylphenyl) benzotriazole, acrylic acid-2-acrylamide-2-methylpropane sulfonic acid copolymer, oleic acid amide and polyethylene oxide.

7. The polypropylene dissolving agent according to any one of claims 4 to 6, characterized in that, The auxiliary agent comprises one or more of isooctanol polyoxyethylene ether phosphate, lauryl alcohol ether phosphate, sorbitan monooleate polyoxyethylene ether, polyoxyethylene sorbitan monolaurate, trimethylolpropane trimethylacrylate, acetyl tri-butyl citrate, polyethylene glycol 6000 distearate, glycerol tri(ethylhexanoate), cetearyl phosphate, trimethylolpropane tris(3-mercaptopropionate), trimethylolpropane octadecenoate, calcium stearate, dioctyl phthalate, dibutyl phthalate, diisononyl cyclohexane 1,2-dicarboxylate, diisononyl phthalate, dimethyl phthalate, isodioctyl sebacate, di(2-ethylhexyl) adipate, dioctyl sebacate, castor oil polyoxyethylene ether, cardanol polyoxyethylene ether and trioctyl trimellitate.

8. The polypropylene dissolving agent according to claim 7, characterized in that, 9. Use of the polypropylene dissolving agent of any one of claims 1-8 in the preparation of a polypropylene membrane or a polypropylene fiber. ​ 10. Use according to claim 9, characterized in that, Polypropylene powder is dissolved in a polypropylene dissolving agent, and the solution is extruded and plasticized to form a cast sheet or a fiber, thereby obtaining a polypropylene separator or a polypropylene fiber.

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