A low bulk density ultra-high molecular weight polyethylene and a method for its preparation

Abstract

The application discloses a preparation method of low bulk density ultrahigh molecular weight polyethylene, which comprises the following steps: uniformly mixing a catalyst with metal organic framework (MOF) particles, then adding the mixture into an inert alkane solvent, and introducing ethylene and a small amount of hydrogen to carry out a polymerization reaction, so as to obtain ultrahigh molecular weight polyethylene. The obtained material has the following characteristics: (a) a viscosity average molecular weight in the range of 4-9 million; (b) a particle size (D50) of 60 microns <= D50 <= 130 microns; (c) a bulk density in the range of 0.2-0.35 g / cm 3 The obtained ultrahigh molecular weight polyethylene material is suitable for producing microporous filter materials.

Description

Technical Field

[0001] This invention belongs to the field of polymer preparation technology, and more specifically, relates to a low bulk density ultra-high molecular weight polyethylene material and its preparation method. Background Technology

[0002] Ultra-high molecular weight polyethylene (UHMWPE) generally refers to linear polyethylene with a relative molecular mass of 1.5 million g / mol or higher. Compared to ordinary polyethylene, it has significant advantages such as high impact resistance, extremely high abrasion resistance, high corrosion resistance, self-lubrication, resistance to environmental stress cracking, chemical resistance, low-temperature performance, and safety and hygiene. It is widely used in textiles, papermaking, food, chemicals, packaging, agriculture, construction, medical, water purification, sports, entertainment, and military industries.

[0003] Currently, the bulk density of general-purpose ultra-high molecular weight polyethylene (UHMWPE) materials on the market is generally between 0.40 and 0.50 g / cm³. 3 The development of low bulk density ultra-high molecular weight polyethylene resin microparticles suitable for microporous filtration materials remains limited.

[0004] Patent CN200580039390.2 discloses ethylene-based polymer microparticles and catalysts for their manufacture. At least 95% of the polymer microparticles by weight pass through a 37-micron mesh sieve, and the median diameter (d50) measured by laser diffraction scattering is 3μm ≤ d50 ≤ 25μm. However, the bulk density of the particles prepared by this technique is not listed, and the polymer requires a cumbersome process of removing inorganic impurities. Patent 202211153833.2 discloses a type of ultra-high molecular weight polyethylene microparticles with small particle size and low bulk density. The viscosity-average molecular weight ranges from 1 million to 5 million, the median diameter (d50) is 40μm < d50 < 80μm, and the powder bulk density is 0.25-0.33 g / cm³. 3 This invention produces low bulk density products simply by adjusting the Zigeler-Natta catalyst preparation process. There is a lack of methods for producing low bulk density ultra-high molecular weight polyethylene products using both metallocene and non-metallocene catalysts.

[0005] Therefore, to address the problems existing in the current technology, it is necessary to develop a low bulk density ultra-high molecular weight polyethylene material suitable for microporous filter media, based on existing multi-polyethylene catalyst systems. Summary of the Invention

[0006] This invention addresses the aforementioned problems by proposing a method for preparing low bulk density ultra-high molecular weight polyethylene (UHMWPE) materials. This method achieves rapid growth of UHMWPE chains, ultimately resulting in a popcorn-like morphology, and the product exhibits low bulk density. The production process is simple and easy to implement, and does not affect the product's ash content, thus possessing high practical value.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a low bulk density ultra-high molecular weight polyethylene material includes the following steps:

[0009] S1: Mix catalyst A with metal-organic framework (MOF) particles evenly, and then add the mixture to a reactor containing an inert solvent and co-catalyst B and disperse it evenly.

[0010] S2: Ethylene and hydrogen are introduced into the reactor to carry out a polymerization reaction, resulting in a polymer slurry, which is then separated to obtain ultra-high molecular weight polyethylene.

[0011] Metal-organic frameworks (MOFs), due to their suitable pore size, can effectively capture ethylene, achieving ethylene enrichment in inert solvents. In the early stages of ethylene polymerization, the catalyst can come into contact with a large amount of ethylene, enabling rapid growth of ultra-high molecular weight polyethylene chains. The resulting product exhibits low bulk density, making it suitable for further preparation of microporous filtration materials.

[0012] Further, catalyst A in S1 is selected from one of the following: a Ti-containing Zigeler-Natta catalyst, a metallocene catalyst, and a non-metallocene catalyst, preferably a Zigeler-Natta catalyst. Common ZN catalysts include titanium tetrachloride and chromium oxide; metallocene catalysts use transition metal element complexes such as Ti, Zr, and Hf as the main catalyst and alkylaluminoxane MAO as the co-catalyst; the metal center of the non-metallocene catalyst is also an organometallic complex of a transition metal element or some main group metal elements.

[0013] Furthermore, the co-catalyst B comprises an alkyl aluminum compound, preferably one or more of methylaluminoxane, triethylaluminum, and triisobutylaluminoxane.

[0014] Furthermore, the molar ratio of the main catalyst A (calculated as Ti) to the co-catalyst B (calculated as aluminum) is 1:(10-5000), preferably 1:(25-2000).

[0015] Further, the inert solvent is a straight-chain alkane with 5 to 10 carbon atoms, preferably one or more selected from n-pentane, n-hexane, cyclohexane, n-heptane, n-octane, and n-decane. Preferably, the mass ratio of catalyst A to the inert solvent is 1:(3*10) 5 -15*10 5 ), more preferably 1:(5*10 5 -10*10 5 ).

[0016] Furthermore, the metal center selected for the MOF particles in S1 includes, but is not limited to, Cu, Zn, Ti, and Cr, with Cu being preferred; the organic ligands include, but are not limited to, phenyl-1,3,5-tricarboxylic acid, terephthalic acid, 2-aminoterephthalic acid, and 2,5-dioxo-1,4-benzenediacarboxylic acid, with phenyl-1,3,5-tricarboxylic acid being preferred.

[0017] Furthermore, the mass ratio of catalyst A to MOF is 1:(0.1-10), preferably 1:(0.8-5).

[0018] Furthermore, the synthesis temperature of the ultra-high molecular weight polyethylene described in S2 is 40℃~60℃, preferably 45℃~55℃; the pressure is 0.6~2MPa, preferably 0.8~1.5MPa; and the polymerization reaction time is 2-6h, preferably 2.5~5h.

[0019] A second aspect of the present invention provides a low-bulk-density ultra-high molecular weight polyethylene material prepared by the method described above:

[0020] (a) Viscosity-average molecular weight in the range of 3 million to 10 million.

[0021] (b) Particle size (D50) is 50μm≤D50≤150μm;

[0022] (c) Bulk density is 0.2-0.35 g / cm³ 3 .

[0023] Furthermore, the viscosity-average molecular weight of the material is in the range of 4 million to 8 million.

[0024] Furthermore, the particle size of the material is 60μm≤D50≤130μm.

[0025] Furthermore, the bulk density of the material is 0.2-0.30 g / cm³. 3 .

[0026] Through the above technical solutions, the preparation method of ultra-high molecular weight polyethylene and the ultra-high molecular weight polyethylene provided by the present invention achieve the following beneficial effects: The present invention utilizes the porous structure of MOF material to enrich ethylene, effectively improves catalyst efficiency, realizes rapid growth of ultra-high molecular weight polyethylene chains, and the product has the characteristics of low bulk density. The operation is simple and easy, and it has high practical value. Detailed Implementation

[0027] The technical solution of the present invention will be further described in detail below through specific embodiments. However, it should be noted that the following embodiments are only used to describe the content of the invention and do not constitute a limitation on the scope of protection of the present invention.

[0028] To better describe the preparation method of the low bulk density ultra-high molecular weight polyethylene material provided by the present invention, the following embodiments may differ in the order of description from the description in the specification, but this will not affect the understanding of the invention by those skilled in the art.

[0029] The molecular weight of the polymer was measured using a viscosity method with decahydronaphthalene as the solvent at 135°C. The outflow time of the polymer solution was measured using an Ubbelohde viscometer, and the intrinsic viscosity η of the polymer was then calculated. The formula was used to determine the molecular weight.

[0030] M = 5.37 × 10 4 ×(η) 1.37

[0031] The resulting M is the molecular weight of the polymer.

[0032] Polymer particle size distribution: determined using a Malvern S-type particle size analyzer.

[0033] The bulk density of the polymer is determined according to GB / T16913.1-1997: The funnel outlet is plugged with a stopper rod. A certain amount of polymer powder is loaded into the specific gravity cup of a powder natural bulk density meter. After leveling with a scraper, the powder is poured into the funnel. The stopper rod is removed, allowing the powder to fall freely into the bottom specific gravity cup. After all the powder has flowed out, the powder accumulated on the top of this specific gravity cup is scraped off with a scraper. The specific gravity cup containing the powder is weighed, and the tare weight is calculated to obtain the weight of the polymer powder. The bulk density value = measured weight / measured volume. The unit is g / cm³. 3 The arithmetic mean of the two measurements is recorded as the measurement result.

[0034] The MOF materials used in the examples were purchased from Beijing Innocare Technology Co., Ltd., and the grades were HKUST-1, MIL-53, MIL-101, and MOF-74.

[0035] The catalysts used in the examples were purchased from BCE-H100 and NTR-971 from Beijing Aoda Branch of Sinopec Catalyst Co., Ltd.; the metallocene catalyst MAO-CAT1 and the non-metallocene NMAO-CAT1 catalyst used were both from Wanhua Chemical Group Co., Ltd.

[0036] Example 1

[0037] A 5L polymerization reactor was evacuated and purged with nitrogen. 3L of cyclohexane and 2mL of triethylaluminum were added, and the stirring speed was controlled at 250rpm. 2mg of BCE-H100 catalyst (Ti element content 1.7wt%) from Beijing Aoda Branch of Sinopec Catalyst Co., Ltd. and 20mg of MOF HKUST-1 material were mixed thoroughly. Then, 10mL of cyclohexane was used to flush the mixture of BCE-H100 catalyst and HKUST-1 into the polymerization reactor. Ethylene gas was then introduced to bring the reactor pressure to 0.6MPa, and the reactor temperature was controlled at 60℃. After polymerization for 5 hours, the ethylene supply was stopped, the gas in the system was vented, and the product was discharged. After drying, granular polymer was obtained. The properties of the polymer particles are shown in Table 1.

[0038] Example 2

[0039] A 5L polymerization reactor was evacuated and purged with nitrogen. 1.5L of n-pentane and 1mL of triisobutylaluminoxane were added, and the stirring speed was controlled at 250rpm. 2mg of Wanhua Chemical MAO-CAT1 catalyst (Ti element content 8.3wt%) and 1.6mg of MOFMIL-53 were mixed thoroughly. Then, 10mL of n-pentane was used to flush the mixture of MAO-CAT1 catalyst and MOFMIL-53 into the polymerization reactor. Ethylene gas was then introduced to bring the reactor pressure to 2MPa, and the reactor temperature was controlled at 55℃. After polymerization for 6 hours, the ethylene supply was stopped, the gas in the system was vented, and the product was discharged. After drying, granular polymer was obtained. The properties of the polymer particles are shown in Table 1.

[0040] Example 3

[0041] A 5L polymerization reactor was evacuated and purged with nitrogen. 2L of n-hexane and 4mL of triethylaluminum were added, and the stirring speed was controlled at 250rpm. 2mg of BCE-H100 catalyst (Ti element content 1.7wt%) from Beijing Aoda Branch of Sinopec Catalyst Co., Ltd. and 2.4mg of MOF MIL-101 material were mixed thoroughly. Then, 10mL of n-hexane was used to flush the mixture of BCE-H100 catalyst and MIL-101 into the polymerization reactor. Ethylene gas was then introduced to bring the reactor pressure to 0.8MPa, and the reactor temperature was controlled at 55℃. After polymerization for 3 hours, the ethylene supply was stopped, the gas in the system was vented, and the product was discharged. After drying, granular polymer was obtained. The properties of the polymer particles are shown in Table 1.

[0042] Example 4

[0043] A 5L polymerization reactor was evacuated and purged with nitrogen. 1L of n-heptane and 10mL of methylaluminoxane were added, and the stirring speed was controlled at 250rpm. 2mg of Wanhua Chemical NMAO-CAT1 catalyst (Ti element content 6.1wt%) and 10mg of MOF MIL-101 material were mixed thoroughly. Then, the mixture of NMAO-CAT1 catalyst and MIL-101 was injected into the polymerization reactor using 10mL of n-heptane. Ethylene gas was then introduced to bring the pressure inside the reactor to 1.5MPa, and the temperature inside the reactor was controlled at 45℃. After polymerization for 2 hours, the ethylene supply was stopped, the gas in the system was vented, and the product was discharged. After drying, granular polymer was obtained. The properties of the polymer particles are shown in Table 1.

[0044] Example 5

[0045] A 5L polymerization reactor was evacuated and purged with nitrogen. 4L of n-octane and 6mL of triethylaluminum were added, and the stirring speed was controlled at 250rpm. 2mg of NTR-971 catalyst (Ti element content 1.48wt%) from Beijing Aoda Branch of Sinopec Catalyst Co., Ltd. and 0.2mg of MOF-74 material were mixed thoroughly. Then, 10mL of n-octane was used to flush the NTR-971 catalyst and MOF-74 mixture into the polymerization reactor. Ethylene gas was then introduced to bring the reactor pressure to 0.8MPa, and the reactor temperature was controlled at 40℃. After polymerization for 2.5h, the ethylene supply was stopped, the gas in the system was vented, and the product was discharged. After drying, granular polymer was obtained. The properties of the polymer particles are shown in Table 1.

[0046] Comparative Example 1

[0047] The difference between this comparative example and Example 1 is that the MOF material was not added to the reactor, and the same polymerization conditions were used. The polymer particle properties are shown in Table 1.

[0048] Comparative Example 2

[0049] The difference between this comparative example and Example 1 is that the catalyst was added to the reactor first, followed by the MOF material, and the same polymerization conditions were used. The polymer particle properties are shown in Table 1.

[0050] Table 1

[0051]

[0052] As can be seen from the above embodiments, the preparation method of ultra-high molecular weight polyethylene and the ultra-high molecular weight polyethylene provided by the present invention have the characteristics of low bulk density, are simple and easy to operate, have high practical value and good industrial application prospects.

Claims

1. A method for preparing a low bulk density ultra-high molecular weight polyethylene material, characterized in that, The preparation method includes the following steps: S1. Mix catalyst A with metal-organic framework (MOF) particles evenly, and then add the mixture to a reactor containing an inert solvent and co-catalyst B and disperse it evenly. S2. Ethylene and hydrogen are introduced into the reactor to carry out a polymerization reaction, and a polymer slurry is obtained. The slurry is then separated to obtain ultra-high molecular weight polyethylene. The catalyst A in S1 is selected from one of the following: a Ti-containing Zigeler-Natta catalyst, a metallocene catalyst, and a non-metallocene catalyst; the co-catalyst B includes an alkylaluminum compound.

2. The preparation method according to claim 1, characterized in that, The catalyst A mentioned in S1 is a Zigeler-Natta catalyst.

3. The preparation method according to claim 1, characterized in that, The cocatalyst B mentioned in S1 is one or more of methylaluminoxane, triethylaluminum, and triisobutylaluminoxane.

4. The preparation method according to claim 2, characterized in that, The molar ratio of the main catalyst A (calculated as Ti) to the co-catalyst B (calculated as aluminum) is 1:(10-5000).

5. The preparation method according to claim 4, characterized in that, The molar ratio of the main catalyst A (calculated as Ti) to the co-catalyst B (calculated as aluminum) is 1:(20-2000).

6. The preparation method according to any one of claims 1-5, characterized in that, The inert solvent is a straight-chain alkane with 5 to 10 carbon atoms.

7. The preparation method according to claim 6, characterized in that, The inert solvent is one or more of n-pentane, n-hexane, cyclohexane, n-heptane, n-octane, and n-decane.

8. The preparation method according to claim 6, characterized in that, The mass ratio of catalyst A to inert solvent is 1:(3×10). 5 -15 x 10 5 ).

9. The preparation method according to claim 8, characterized in that, The mass ratio of catalyst A to inert solvent is 1:(5×10). 5 -10✖10 5 ).

10. The preparation method according to any one of claims 1-5, characterized in that, The metal centers selected for the MOF particles in S1 include Cu, Zn, Ti, and Cr; the organic ligands include phenyl-1,3,5-tricarboxylic acid, terephthalic acid, and 2-aminoterephthalic acid.

11. The preparation method according to claim 10, characterized in that, The MOF particles described in S1 use Cu as the metal center and benzene-1,3,5-tricarboxylic acid as the organic ligand.

12. The preparation method according to any one of claims 1-5, characterized in that, The mass ratio of catalyst A to MOF is 1:(0.1-10).

13. The preparation method according to claim 12, characterized in that, The mass ratio of catalyst A to MOF is 1:(0.8-5).

14. The preparation method according to any one of claims 1-5, characterized in that, The synthesis temperature of ultra-high molecular weight polyethylene in S2 is 40℃~60℃; the pressure is 0.6~2MPa; and the polymerization reaction time is 2-6h.

15. The preparation method according to claim 14, characterized in that, The synthesis temperature of ultra-high molecular weight polyethylene in S2 is 45℃~55℃; the pressure is 0.8~1.5MPa; and the polymerization reaction time is 2.5~5h.

16. The ultra-high molecular weight polyethylene material prepared by the method according to any one of claims 1-15, characterized in that, The material has a viscosity-average molecular weight in the range of 3 million to 10 million; a particle size D50 of 50 μm ≤ D50 ≤ 150 μm; and a bulk density of 0.2-0.35 g / cm³. 3 .

17. The ultra-high molecular weight polyethylene material prepared by the method according to claim 16, characterized in that, The material has a viscosity-average molecular weight in the range of 4-8 million; a particle size D50 of 60μm ≤ D50 ≤ 130μm; and a bulk density of 0.2-0.30 g / cm³. 3 .

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