Polyethylene rich in shish-kebab structure and preparation method and application thereof

Abstract

The invention discloses polyethylene rich in shish-kebab structures, the polyethylene is granular, the shish-kebab structures in the polyethylene granules are pure polyethylene components or a mixture of polyethylene components and high-molecular polymers, and the shish-kebab structures are obtained through an ethylene polymerization reaction process without additional physical or chemical processing. In preparation of the polyethylene particles, a polymerization solvent component is a pure high-molecular polymer or a mixture of the high-molecular polymer and a solvent A, the polymerization temperature ranges from Tm-50 DEG C to Tm-10 DEG C, and the stirring rotating speed ranges from 10 rpm to 1000 rpm. The shish-kebab structure in the polyethylene not only exists on the surfaces of polyethylene particles, but also widely exists in the polyethylene particles. The polyethylene can be applied to the fields of microporous membrane materials, self-reinforced high-performance materials, fibers, films, wear-resistant materials and the like.

Description

Technical Field

[0001] The invention relates to a polyolefin material, in particular to a polyethylene rich in shish-kebab structure and a preparation method and application thereof. Background Art

[0002] The formation of a regularly arranged shish-kebab shredded crystal structure in polyolefin materials is the key to preparing high-strength, high-hardness, high-impact and high-wear-resistant materials. Existing studies have shown that shish-kebab shredded crystal structures can be prepared by methods such as solution crystallization, stress-induced crystallization and melt extrusion. The solution crystallization method can accurately control the size and period of the lamellae by adjusting the solution concentration, temperature and crystallization time, but this method requires precise control of the solvent evaporation rate and crystallization kinetics, and the operation is difficult, especially in large-scale production. The efficiency is low, organic solvent pollution may be introduced, and additional post-processing steps are required, which increases costs and takes a long time. The stress-induced crystallization method uses a strong shear or stretching flow field to quickly induce the orientation of polymer chains to form a high-density shish-kebab structure. However, this method has high requirements for equipment, requires precise control of the flow field intensity and distribution, has large equipment investment and energy consumption, and is sensitive to process parameters, and has high requirements and limitations on materials. The melt extrusion method has the advantages of high production efficiency, no need for solvents, and can be reinforced with other polymers or inorganic materials, but there are problems such as high temperature degradation and poor structural uniformity. It can be seen that the post-processing method to obtain the shish-kebab shredded structure generally has the disadvantages of complex process and high energy consumption.

[0003] Therefore, obtaining primary polyethylene particles rich in shish-kebab shredded crystal structure during the preparation stage of polyethylene materials is a more excellent preparation method, but also a difficult problem. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a polyethylene rich in shish-kebab structures and a preparation method and application thereof. The polyethylene preparation method provided by the present invention has the advantages of simple process and high content of shish-kebab structures in the prepared polyethylene.

[0005] According to one object of the present invention, the present invention provides a polyethylene rich in shish-kebab structures, wherein the polyethylene is in granular form, the shish-kebab structures in the polyethylene particles are pure polyethylene components or a mixture of polyethylene components and high molecular weight polymers, and the shish-kebab structures are obtained through an ethylene polymerization reaction process without the need for additional physical or chemical processing.

[0006] According to a preferred embodiment of the present invention, the molecular weight of the high molecular polymer is between 200-20000 g / mol and is selected from one or more of polyethylene wax, oxidized polyethylene wax, polypropylene wax, oxidized polypropylene wax, low-density polyethylene LDPE, linear low-density polyethylene LLDPE and polyethylene elastomer POE.

[0007] According to a preferred embodiment of the present invention, the shish kebab structure in the polyethylene not only exists on the surface of the polyethylene particles, but also widely exists inside the polyethylene particles. The molecular weight distribution of the polyethylene particles is 2-600, the branching degree is 0.1-100C / 1000C, the melting point is 130-144°C, and the crystallinity is 40-99%.

[0008] According to a preferred embodiment of the present invention, in the shish-kebab structure of the polyethylene, the thickness of the kebab lamellae is 10-200 nm, and the distance between adjacent kebab lamellae is 10-1000 nm. 4 The molecular chain mass of g / mol accounts for 0.1-99.9wt% of the total mass of the polyethylene particles.

[0009] According to the second object of the present invention, the present invention also provides a method for preparing polyethylene rich in shish-kebab structure, wherein the polyethylene is obtained by slurry polymerization, and the polymerization solvent component is the pure polymer or a mixture of the polymer and solvent A; when the pure polymer is used as the polymerization solvent component, the polymer is added to the reaction kettle in advance to be heated and melted and dehydrated and deoxygenated; when the mixture of the polymer and solvent A is used as the polymerization solvent component, after the polymer is heated and melted and dehydrated and deoxygenated, solvent A is added, stirred evenly and the polymer is fully dissolved;

[0010] Then, a co-catalyst and a catalyst are added to the reactor, stirring is started, and after the temperature is raised to the polymerization temperature, ethylene monomer is introduced to the polymerization pressure to carry out polymerization reaction. After a certain reaction time, the introduction of ethylene is stopped, and the solid and liquid phases are separated to obtain the polyethylene.

[0011] According to a preferred embodiment of the present invention, the solvent A is selected from one or more of n-pentane, isopentane, n-hexane, cyclohexane, n-heptane, methylcyclohexane, n-octane, isoparaffin Isopar E, isoparaffin Isopar G, and toluene, and the solvent A component used in the polymerization accounts for 0.1-50wt% of the polymerization solvent composed of solvent A and high molecular polymer.

[0012] According to a preferred embodiment of the present invention, the polymerization temperature range is T m -50℃ to T m -10℃, where T mis the melting point of the polyethylene product.

[0013] According to a preferred embodiment of the present invention, the stirring speed during the polymerization process is 10-1000 rpm.

[0014] According to an optional solution of the present invention, a comonomer is further added during the polymerization process, and the comonomer is selected from one or more of propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, and 1-decene. The timing of adding the comonomer is conventionally selected according to needs, for example, it can be added before starting stirring.

[0015] According to a preferred embodiment of the present invention, the co-catalyst is selected from one or more of trimethylaluminum, triethylaluminum, triisobutylaluminum, trihexylaluminum, trioctylaluminum, diethylaluminum monochloride, ethylaluminum dichloride, methylaluminoxane, modified methylaluminoxane, triphenylborane, tri(4-fluorophenyl)borane, tri(pentafluorophenyl)borane, tri(3,5-difluorophenyl)borane and tri(2,4,6-trifluorophenyl)borane.

[0016] According to a preferred embodiment of the present invention, the catalyst is selected from one or more of a supported Ziegler-Natta catalyst, a supported metallocene catalyst, a supported late transition metal catalyst, a supported FI catalyst, and a supported non-metallocene catalyst.

[0017] According to a preferred embodiment of the present invention, the polymerization pressure is 5-50 bar and the polymerization time is 0.1-10 h.

[0018] According to another object of the present invention, the present invention also provides an application of the above polyethylene, which can be used to prepare microporous membrane materials, self-reinforced high-performance materials, fibers, films and wear-resistant materials.

[0019] Compared with the prior art, the present invention has the following outstanding beneficial effects:

[0020] (1) The shredded crystal structure in the polyethylene can be obtained in the process of preparing polyethylene particles without the need to adopt a solution crystallization method or a stress-induced crystallization method, which are complicated, energy-intensive, time-consuming, and sensitive to process parameters. The process is simple, convenient, and has high production efficiency.

[0021] (2) By optimizing the polymer and polymerization conditions, a shish-kebab shredded crystal structure composed of the polymer and polyethylene can be obtained, and there is no need to physically blend and melt-extrude the polymer and polyethylene in the physical post-processing process. Therefore, the polyethylene preparation method has the advantage of high compatibility with polyolefin materials.

[0022] (3) The shish-kebab shredded crystal structure in the polyethylene particles exists not only on the surface of the particles but also widely inside the particles, which can improve the structural uniformity of the surface and interior of the polyethylene particles.

[0023] (4) In the polyethylene preparation method, an appropriate amount of inorganic filler, such as carbon fiber, carbon nanotube, graphene, etc., can be introduced to obtain a polyethylene composite material reinforced with inorganic filler of a primary ecological structure. The inorganic filler in the polyethylene composite material has excellent dispersibility and can further optimize the mechanical properties of polyethylene. In addition, the shish-kebab shredded crystal structure parameters and orientation degree in the polyethylene particles can be regulated by adjusting the stirring speed during the polymerization process. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a scanning electron microscope image of the polyethylene particles obtained in Example 1.

[0025] Figure 2 This is a scanning electron microscope image of the polyethylene particles obtained in Comparative Example 1. DETAILED DESCRIPTION

[0026] The embodiments of the present invention will be described in detail below in conjunction with the examples, but those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be considered to limit the scope of the present invention. If no specific conditions are specified in the examples, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0027] The following methods are used to test the structure or performance of the polyethylene produced in the examples described:

[0028] High temperature gel permeation chromatography (GPC) is used to test the weight average molecular weight and molecular weight distribution of polyethylene.

[0029] Nuclear magnetic resonance spectrometer is used to test the short chain branch content or branching degree in polyethylene.

[0030] Differential scanning calorimetry (DSC) was used to measure the melting point and crystallinity of polyethylene.

[0031] The thickness of kebab lamellae and the distance between adjacent kebab lamellae were obtained by scanning electron microscopy and statistically analyzed using image J software.

[0032] Molecular weight less than 10 4 The ratio of the mass of polyethylene molecular chains in g / mol to the total mass of polyethylene particles is calculated based on the test results of high temperature gel permeation chromatography (GPC).

[0033] Taber abrasion tester is used to test the abrasion index of polyethylene.

[0034] Example 1

[0035] Add 1.5 kg polyethylene wax (M w =680g / mol), the reactor was heated to 100°C and vacuumed for 4h to remove water and oxygen, then 1.5L of n-hexane was added and stirred evenly for 2h, 10mL of triethylaluminum (1mol / L) and 100mg of supported Ziegler-Natta catalyst were added, stirring was started and the temperature in the reactor was raised to 110°C, ethylene was introduced until the polymerization pressure reached 10bar, the stirring speed was adjusted to 200rpm, and the introduction of ethylene was stopped after polymerization for 3h, and polyethylene wax and n-hexane were removed to obtain polyethylene A. The physical property characterization results of polyethylene A are shown in Table 1.

[0036] Example 2

[0037] Add 2.0 kg of oxidized polyethylene wax (M w =610g / mol), the reactor was heated to 100°C and vacuumed for 4h to remove water and oxygen, then 1.1L of n-hexane was added and stirred evenly for 2h, 20mL of 1-hexene, 12mL of triethylaluminum (1mol / L), and 100mg of supported metallocene catalyst were added, stirring was started and the temperature in the reactor was raised to 105°C, ethylene was introduced until the polymerization pressure reached 12bar, the stirring speed was adjusted to 500rpm, and the introduction of ethylene was stopped after 4h of polymerization, and the oxidized polyethylene wax and n-hexane were removed to obtain polyethylene B. The physical property characterization results of polyethylene B are shown in Table 1.

[0038] Example 3

[0039] Add 1.5 kg polyethylene wax (M w =800g / mol), the reactor was heated to 100°C and vacuumed for 4h to remove water and oxygen, then 1.2L of n-heptane was added and stirred evenly for 2h, 10mL of diethylaluminum chloride (1.5mol / L) and 100mg of supported Ziegler-Natta catalyst were added, stirring was started and the temperature in the reactor was raised to 110°C, ethylene was introduced until the polymerization pressure was 20bar, the stirring speed was adjusted to 700rpm, and the introduction of ethylene was stopped after polymerization for 2.5h, and polyethylene wax and n-heptane were removed to obtain polyethylene C. The physical property characterization results of polyethylene C are shown in Table 1.

[0040] Example 4

[0041] Add 2.1 kg of polyethylene wax (M w=1200g / mol), the reactor was heated to 110°C and vacuumed for 4h to remove water and oxygen, then 1.0L toluene was added and stirred evenly for 2h, 10mL triethylaluminum (1mol / L) and 100mg supported Ziegler-Natta catalyst were added, stirring was started and the temperature in the reactor was raised to 120°C, ethylene was introduced until the polymerization pressure was 40bar, the stirring speed was adjusted to 800rpm, and the introduction of ethylene was stopped after 9h of polymerization, and polyethylene wax and toluene were removed to obtain polyethylene D. The physical property characterization results of polyethylene D are shown in Table 1.

[0042] Example 5

[0043] Add 3.5 kg polyethylene wax (M w =1000g / mol), the reactor was heated to 110°C and vacuumed for 4h to remove water and oxygen, 10mL triethylaluminum (1mol / L) and 100mg supported Ziegler-Natta catalyst were added, stirring was started and the temperature in the reactor was raised to 120°C, ethylene was introduced until the polymerization pressure reached 20bar, the stirring speed was adjusted to 500rpm, and the introduction of ethylene was stopped after 5h of polymerization, and the liquid phase polyethylene wax was removed to obtain polyethylene E. The physical property characterization results of polyethylene E are shown in Table 1.

[0044] Comparative Example 1

[0045] 3L of n-heptane, 10mL of triethylaluminum (1mol / L), and 100mg of supported Ziegler-Natta catalyst were added to a 5L reactor, stirring was started, the temperature in the reactor was raised to 80°C, ethylene was introduced until the polymerization pressure reached 20bar, the stirring speed was adjusted to 500rpm, and the introduction of ethylene was stopped after polymerization for 3h, and n-heptane was removed to obtain polyethylene F. The physical property characterization results of polyethylene F are shown in Table 1.

[0046] Comparative Example 2

[0047] Add 1.5 kg polyethylene wax (M w =680g / mol), the reactor was heated to 120°C and vacuumed for 4h to remove water and oxygen, then 1.5L of n-hexane was added and stirred evenly for 2h, 10mL of triethylaluminum (1mol / L) and 100mg of supported Ziegler-Natta catalyst were added, stirring was started and the temperature in the reactor was raised to 140°C, ethylene was introduced until the polymerization pressure reached 10bar, the stirring speed was adjusted to 200rpm, and the introduction of ethylene was stopped after polymerization for 3h, and polyethylene wax and n-hexane were removed to obtain polyethylene G. The physical property characterization results of polyethylene G are shown in Table 1.

[0048] Table 1 Polyethylene AE characterization results

[0049]

[0050]

[0051] As can be seen from Table 1, the polyethylene AE prepared in Examples 1-5 are all in a granular state, and the granules contain a large amount of shish-kebab skewers, as shown in the attached figure. Figure 1 The figure shows a scanning electron microscope image of polyethylene A in Example 1. The shish-kebab shish-kebab crystal structure in polyethylene AE has a high degree of orientation and is oriented in a specific direction. However, the polyethylene particles F obtained without the preparation method of the present invention do not contain shish-kebab shish-kebab crystal structures in the particles, as shown in the attached figure. Figure 2 As shown. The polyethylene G obtained without the preparation method described in the present invention does not present a granular form and does not contain a shish-kebab shredded crystal structure. From the wear test results, it can be found that the polyethylene samples AE with a shish-kebab shredded crystal structure have lower wear, ranging from 0.5 to 0.92%, while the polyethylene F without a shish-kebab shredded crystal structure has a higher wear (1.067%), which is not only higher than the wear of hexene copolymer polyethylene B of 0.912%, but also much higher than the wear of polyethylene A with a similar molecular weight (0.608%). Similarly, the polyethylene G without a shish-kebab shredded crystal structure has a higher wear, up to 3.125%.

[0052] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A polyethylene rich in shish-kebab structure, characterized in that: The polyethylene is in granular form, and the shish-kebab structure in the polyethylene granules is a pure polyethylene component or a mixture of a polyethylene component and a high molecular polymer, and the shish-kebab structure is obtained through an ethylene polymerization process without additional physical or chemical processing; The shish-kebab structure in the polyethylene exists not only on the surface of the polyethylene particles, but also inside the polyethylene particles; the molecular weight distribution of the polyethylene particles is 2-600, the branching degree is 0.1-100C / 1000C, the melting point is 130-144°C, and the crystallinity is 40-99%; The shish-kebab structure is a shish-kebab structure. In the shish-kebab structure, the thickness of the kebab lamellae is 10-200nm, and the distance between adjacent kebab lamellae is 10-1000nm. The molecular weight of the polyethylene is less than 10 4 The molecular chain mass of g / mol accounts for 0.1-99.9wt% of the total mass of the polyethylene particles; The molecular weight of the high molecular polymer is between 200-20000 g / mol, and is selected from one or more of polyethylene wax, oxidized polyethylene wax, polypropylene wax, oxidized polypropylene wax, low-density polyethylene LDPE, linear low-density polyethylene LLDPE and polyethylene elastomer POE.

2. A method for preparing polyethylene according to claim 1, characterized in that: The polyethylene is obtained by slurry polymerization, and the polymerization solvent component is the pure high molecular polymer or a mixture of the high molecular polymer and solvent A. When the pure high molecular polymer is used as the polymerization solvent component, the high molecular polymer is added to the reaction kettle in advance to be heated and melted and dehydrated and deoxygenated. When the mixture of the high molecular polymer and solvent A is used as the polymerization solvent component, after the high molecular polymer is heated and melted and dehydrated and deoxygenated, solvent A is added, stirred evenly and the high molecular polymer is fully dissolved. Then, a co-catalyst and a catalyst are added to the reactor, stirring is started, and after the temperature is raised to the polymerization temperature, ethylene monomer is introduced to the polymerization pressure to carry out polymerization reaction. After a certain reaction time, the introduction of ethylene is stopped, and the solid and liquid phases are separated to obtain the polyethylene.

3. The preparation method according to claim 2, characterized in that: Solvent A is selected from one or more of n-pentane, isopentane, n-hexane, cyclohexane, n-heptane, methylcyclohexane, n-octane, isoparaffin Isopar E, isoparaffin Isopar G, and toluene, and the solvent A component used in the polymerization accounts for 0.1-50wt% of the polymerization solvent component composed of solvent A and high molecular polymer.

4. The preparation method according to claim 2, characterized in that: The polymerization temperature range is T m -50℃ to T m -10℃, where T m is the melting point of the polyethylene product; during polymerization, the stirring speed is 10-1000rpm.

5. The preparation method according to claim 2, characterized in that: Optionally, a comonomer is further added during the polymerization process, and the comonomer is selected from one or more of propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, and 1-decene.

6. The preparation method according to claim 2, characterized in that: The co-catalyst is selected from one or more of trimethylaluminum, triethylaluminum, triisobutylaluminum, trihexylaluminum, trioctylaluminum, diethylaluminum monochloride, ethylaluminum dichloride, methylaluminoxane, modified methylaluminoxane, triphenylborane, tri(4-fluorophenyl)borane, tri(pentafluorophenyl)borane, tri(3,5-difluorophenyl)borane, and tri(2,4,6-trifluorophenyl)borane.

7. The preparation method according to claim 2, characterized in that: The catalyst is selected from one or more of a supported Ziegler-Natta catalyst, a supported metallocene catalyst, a supported late transition metal catalyst, a supported FI catalyst, and a supported non-metallocene catalyst.

8. The preparation method according to claim 2, characterized in that: The polymerization pressure is 5-50 bar; the polymerization time is 0.1-10 h.

9. Use of the polyethylene according to claim 1 in the preparation of microporous membrane materials, self-reinforced high-performance materials, fibers, films or wear-resistant materials.

Images