Polymer alloy and preparation method and application thereof

Abstract

The invention discloses a polymer alloy and a preparation method and application thereof. The preparation method of the polymer alloy comprises the following steps: S1, premixing polyethylene resin, polypropylene resin and a compatibilizer to obtain a premix; and S2, adding the premix into a differential asymmetric twin-screw extruder, melting, mixing, extruding and pelletizing to obtain the composite material. According to the invention, the polyethylene resin and the polypropylene resin are blended, and melt extrusion is carried out by adopting a differential asymmetric twin-screw machine, so that the obtained polymer alloy has excellent mechanical properties. When the polymer alloy is used for preparing the cast film, the optical performance of the cast film can be greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, in particular to a polymer alloy and a preparation method and application thereof. Background Art

[0002] Polyethylene (PE) resin and polypropylene (PP) resin, as the two most widely used general-purpose resins, play an important role in the industrial field. However, with the rapid development of industrial technology, the performance limitations of single polymer materials have become increasingly prominent, making it difficult to meet the stringent requirements of complex application scenarios for the comprehensive performance of materials. Therefore, polyethylene / polypropylene alloy materials have become a research hotspot in the field of polymer materials due to their excellent performance. Polyethylene / polypropylene alloy is a multiphase composite material formed by organically combining two polymers through physical blending or chemical modification. It not only retains the inherent flexibility characteristics of polyethylene and the rigidity characteristics of polypropylene, but also effectively improves the performance defects of single materials, such as the low rigidity of polyethylene and the insufficient impact resistance of polypropylene.

[0003] In the preparation process of polyethylene / polypropylene alloy, melt blending is the most commonly used method. This method mainly uses a traditional twin-screw extruder to achieve melt blending and extrusion of two polymers, and obtains the final product through mold forming. However, the traditional twin-screw extruder has poor dispersion and distribution effects. In order to improve the dispersion and mixing efficiency, components such as kneading blocks with strong shearing effects are often used, but this will lead to a decrease in material degradation performance, especially in the case of recycling and reuse. In addition, polyethylene resin and polypropylene resin themselves have poor compatibility. These factors together lead to poor uniformity of dispersion and distribution of the dispersed phase in the matrix phase, which is manifested as a larger dispersed phase particle size and a wider particle size distribution. This microstructural defect will inevitably have a significant negative impact on the macroscopic mechanical properties of polyethylene / polypropylene alloy, making it difficult to meet the requirements of material properties for practical applications.

[0004] Therefore, it is necessary to provide a method for preparing a polymer alloy with good mechanical properties. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a method for preparing a polymer alloy in a first aspect. The polymer alloy prepared by this method has excellent mechanical properties.

[0006] The second aspect of the present invention also provides a polymer alloy.

[0007] The third aspect of the present invention also provides an application of the polymer alloy.

[0008] According to a first aspect of the present invention, a method for preparing a polymer alloy is provided, comprising the following steps:

[0009] S1, premixing polyethylene resin, polypropylene resin and compatibilizer to obtain a premix;

[0010] S2, adding the premix into a differential speed asymmetric twin-screw extruder, melting and mixing, extruding, and pelletizing;

[0011] The differential-speed asymmetric twin-screw extruder is equipped with a twin-screw consisting of a single-head screw and a twin-head screw; the twin-screw is composed of multiple sections, namely a feeding section, a conveying section, a melt mixing section, and a metering section; the melt mixing section of the single-head screw includes a reverse single-head screw element and at least 6 single-head perturbation rings; every three consecutive single-head perturbation rings form a group, and a reverse single-head screw element is provided between two adjacent groups;

[0012] The melt mixing section of the double-headed screw includes reverse double-headed thread elements and at least 6 double-headed perturbation rings; each three consecutive double-headed perturbation rings form a group, and reverse double-headed thread elements are provided between two adjacent groups.

[0013] The method for preparing a polymer alloy according to an embodiment of the present invention has at least the following beneficial effects:

[0014] The present invention blends polyethylene resin and polypropylene resin and melt-extrudes them using a differential asymmetric twin-screw extruder. The resulting polymer alloy exhibits excellent mechanical properties. This is because perturbation rings are installed in the melt mixing section. Three consecutive single-end perturbation rings form a group, with each group separated by a reverse-threaded element, allowing material backflow. This is intended to induce the formation of a chaotic flow field and a strong tensile force field, significantly improving the uniformity and distribution of the dispersed phase in the matrix, making the polypropylene dispersed phase particles more uniform and fine, and enhancing the overall mechanical properties of the polymer alloy.

[0015] Furthermore, when the polymer alloy of the present invention is used to prepare a cast film, the optical properties of the cast film can be greatly improved.

[0016] According to a preferred embodiment of the present invention, 1 to 3 single-head kneading blocks are further provided in the melt mixing section of the single-head screw. The high shearing effect provided by the single-head kneading blocks can fully break up the polymer melt droplets.

[0017] According to a preferred embodiment of the present invention, 1 to 3 double-headed kneading blocks are further provided in the melt mixing section of the double-headed screw. The high shearing effect provided by the double-headed kneading blocks can fully break up the polymer melt droplets.

[0018] According to a preferred embodiment of the present invention, the single-head screw and the double-head screw are engaged and rotated with each other.

[0019] According to a preferred embodiment of the present invention, the stagger angle of the single-head kneading block is set to 90 degrees to 180 degrees.

[0020] According to a preferred embodiment of the present invention, the stagger angle of the double-headed kneading block is set to 45 degrees to 90 degrees.

[0021] According to a preferred embodiment of the present invention, the melt-kneading section of the single-head screw further includes a single-head transition section.

[0022] According to a preferred embodiment of the present invention, the melt-kneading section of the twin-head screw further includes a twin-head transition section.

[0023] According to a preferred embodiment of the present invention, the conveying section consists of a kneading block and a screw element.

[0024] According to a preferred embodiment of the present invention, the metering section is composed of a threaded element.

[0025] According to a preferred embodiment of the present invention, the end surface of the single-ended kneading block is the same as that of the single-ended threaded element.

[0026] According to a preferred embodiment of the present invention, the end faces of the double-ended kneading block and the double-ended threaded element are the same.

[0027] According to a preferred embodiment of the present invention, the end faces of the single-end perturbation ring and the single-end kneading block are different.

[0028] According to a preferred embodiment of the present invention, the end faces of the double-ended perturbation ring and the double-ended kneading block are different.

[0029] According to a preferred embodiment of the present invention, one end face of the single-ended transition section is identical to the end face of the single-ended kneading block; and the other end face is identical to the end face of the single-ended perturbation ring.

[0030] According to a preferred embodiment of the present invention, one end face of the double-ended transition section is the same as the end face of the double-ended kneading block; and the other end face is the same as the end face of the double-ended perturbation ring.

[0031] According to a preferred embodiment of the present invention, the content of the polyethylene resin is 80 wt.% to 90 wt.% calculated based on the total mass of the polyethylene resin and the polypropylene resin.

[0032] According to a preferred embodiment of the present invention, the amount of the compatibilizer is 1% to 10% based on the total mass of the polyethylene resin and the polypropylene resin.

[0033] According to a preferred embodiment of the present invention, the amount of the compatibilizer is 1% to 5% based on the total mass of the polyethylene resin and the polypropylene resin.

[0034] According to a preferred embodiment of the present invention, the polyethylene resin is at least one of linear low-density polyethylene resin (LLDPE), low-density polyethylene resin (LDPE) and high-density polyethylene resin (HDPE).

[0035] According to a preferred embodiment of the present invention, the polypropylene resin is at least one of isotactic polypropylene resin (iPP), syndiotactic polypropylene resin (sPP) and atactic polypropylene resin (aPP).

[0036] According to a preferred embodiment of the present invention, the compatibilizer includes at least one of Weimei Da 3000, Weimei Da 6102, Weimei Da 6202, Weimei Da 6502, Weimei Da 6902, Weimei Da 8380 and Weimei Da 8880.

[0037] According to a preferred embodiment of the present invention, the polyethylene resin and the polypropylene resin are further dried before use.

[0038] According to a preferred embodiment of the present invention, the drying temperature is 60-90°C.

[0039] According to a preferred embodiment of the present invention, the drying time is 6 to 8 hours.

[0040] The second aspect of the present invention provides a polymer alloy prepared by the method for preparing the polymer alloy described in the first aspect of the present invention.

[0041] A third aspect of the present invention provides a use of a polymer alloy prepared by the above-mentioned method for preparing a polymer alloy in preparing a cast film.

[0042] Other features and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0044] Figure 1 1 is a flow chart of the preparation of the polymer alloy according to an embodiment of the present invention.

[0045] Figure 2 Schematic diagram of components of a differential-speed asymmetric twin-screw extruder according to an embodiment of the present invention.

[0046] Figure 3 1. It is a diagram of the screw element assembly of the melt mixing section of the differential speed asymmetric twin-screw extruder according to an embodiment of the present invention.

[0047] Figure 4 It is an end view of a single-start threaded element and a double-start threaded element in an engaged state according to an embodiment of the present invention.

[0048] Figure 5 It is an end view of a single-head perturbation ring and a double-head perturbation ring in an engaged state according to an embodiment of the present invention.

[0049] Figure 6 This is a scanning electron microscope image of the polymer alloy prepared in Example 2.

[0050] Figure 7 This is a scanning electron microscope image of the polymer alloy prepared in Comparative Example 2. DETAILED DESCRIPTION

[0051] The following are specific embodiments of the present invention, and the technical solutions of the present invention are further described in conjunction with the embodiments, but the present invention is not limited to these embodiments.

[0052] Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0053] The embodiments of the present invention are further described below with reference to the accompanying drawings.

[0054] An embodiment of the present invention provides a method for preparing a polymer alloy.

[0055] Reference Figure 1 , a method for preparing a polymer alloy comprises the following steps:

[0056] drying the polyethylene resin and the polypropylene resin;

[0057] S1, premixing dried polyethylene resin, polypropylene resin and compatibilizer to obtain a premix;

[0058] S2, adding the premix into a differential-speed asymmetric twin-screw extruder for melt mixing, extrusion, and pelletizing.

[0059] In this embodiment, the present invention blends polyethylene resin and polypropylene resin and uses a differential asymmetric twin-screw extruder for melt extrusion, resulting in a polymer alloy with excellent mechanical properties. This is because the present invention provides a perturbation ring in the melt mixing section, with three consecutive single-head perturbation rings forming a group, and each two groups are separated by a reverse-threaded element, which allows the material to reflux. This is intended to induce the formation of a chaotic flow field and a strong tensile force field, thereby significantly improving the dispersion uniformity and distribution state of the dispersed phase in the matrix, making the polypropylene dispersed phase particles more uniform and fine, and improving the overall mechanical properties of the polymer alloy.

[0060] In an embodiment of the present invention, the polyethylene resin is at least one of linear low-density polyethylene resin (LLDPE), low-density polyethylene resin (LDPE) and high-density polyethylene resin (HDPE).

[0061] In an embodiment of the present invention, the polypropylene resin is at least one of isotactic polypropylene resin (iPP), syndiotactic polypropylene resin (sPP) and atactic polypropylene resin (aPP).

[0062] In an embodiment of the present invention, the drying temperature is 60-90°C.

[0063] In an embodiment of the present invention, the drying time is 6 to 8 hours.

[0064] In an embodiment of the present invention, the compatibilizer includes at least one of VIMEDA 3000, VIMEDA 6102, VIMEDA 6202, VIMEDA 6502, VIMEDA 6902, VIMEDA 8380 and VIMEDA 8880.

[0065] According to some embodiments of the present invention, Figure 2 ;For the differential asymmetric twin-screw extruder, it mainly includes eight parts: motor 100, gearbox 200, feed port 300, barrel 400, exhaust port 500, twin screw 600, water tank 700 and pelletizer 800.

[0066] In the embodiment of the present invention, referring to Figure 3 The differential asymmetric twin-screw extruder is provided with a single-head screw 610 and a double-head screw 620. The single-head screw 610 is composed of a single-head kneading block 611, a single-head kneading block 612, a single-head threaded element 613, a single-head transition section 614 and a single-head perturbation ring 615. The double-head screw 620 is composed of a double-head kneading block 621, a double-head kneading block 622, a double-head threaded element 623, a double-head transition section 624 and a double-head perturbation ring 625.

[0067] Reference Figure 4 and Figure 5 The end faces of the single-ended kneading block and the single-ended threaded element are identical, while the end faces of the double-ended kneading block and the double-ended threaded element are identical. The end faces of the single-ended perturbation ring, the single-ended kneading block and the single-ended threaded element are different, while the end faces of the double-ended perturbation ring are different. The end face of one end of the single-ended transition section is identical to the single-ended kneading block and the single-ended threaded element, while the end face of the other end is identical to the single-ended perturbation ring. The end face of one end of the double-ended transition section is identical to the double-ended kneading block and the double-ended threaded element, while the end face of the other end is identical to the double-ended perturbation ring. From the end face diagrams of the meshed state of the single-ended threaded element 613 and the double-ended threaded element 623 or the single-ended perturbation ring 615 and the double-ended perturbation ring 625, it can be seen that the end faces of the single-ended element and the double-ended element are different.

[0068] In an embodiment of the present invention, the single-head kneading block 611 and the single-head kneading block 612 are composed of different numbers of meshing discs stacked at different offset angles; the same applies to the double-head kneading blocks 621 and 622. Specifically, the single-head kneading block 611 is composed of five meshing discs stacked at an offset angle of 45 degrees or 90 degrees, while the single-head kneading block 612 is composed of four meshing discs stacked at an offset angle of 60 degrees. The double-head kneading block 621 is composed of five meshing discs stacked at an offset angle of 90 degrees or 180 degrees, while the double-head kneading block 622 is composed of four meshing discs stacked at an offset angle of 120 degrees.

[0069] In embodiments of the present invention, the transition section can connect a perturbation ring to a kneading block or a threaded element. For example, a single-ended transition section 614 can connect any one of the single-ended kneading blocks 611, 612 and the single-ended threaded element 613 to a single-ended perturbation ring 615, while a double-ended transition section 624 can connect any one of the double-ended kneading blocks 621, 622 and the double-ended threaded element 623 to a double-ended perturbation ring 625.

[0070] In an embodiment of the present invention, the speed ratio of the single-head screw to the double-head screw is 2: 1. Specifically, the speed of the single-head screw is set to 400 rpm, and the speed of the double-head screw is set to 200 rpm.

[0071] The barrel 400 houses a twin-screw 600, which is comprised of a single-headed screw 610 and a double-headed screw 620 meshing with each other. The gearbox 200 converts the speed of the motor 100 to that of the single-headed screw 610 and the double-headed screw 620. In a differential-speed asymmetric twin-screw extruder, resin enters the barrel 400 through the feed port 300, where the twin screw 600 melts, mixes, degasses, and homogenizes the material. The material then enters a water tank 700 for rapid cooling before being drawn into a pelletizer 800 for cutting into pellets. The exhaust port 500 is used to discharge exhaust gases generated during processing. The barrel 400 consists of six heating zones, each with its own temperature setting. The heating zones utilize both electrical heating and water cooling to precisely control the temperature of each zone. The kneading blocks primarily facilitate plasticization, mixing, and dispersion of the material.

[0072] The two screws in a traditional twin-screw extruder operate at the same speed when processing materials, and the screw structure is completely symmetrical, making it difficult to achieve uniform dispersion of the dispersed polyethylene resin in the matrix polypropylene resin, limiting the melting and plasticization of the material and resulting in poor mixing. However, the symmetry-breaking effect caused by the asymmetry in the geometry and speed of the single-head screw 610 and the double-head screw 620 of the differential asymmetric twin-screw extruder effectively induces the formation of a chaotic flow field and a strong tensile force field, significantly improving the uniformity of the dispersed phase distribution in the matrix and significantly enhancing the melt mixing effect of the material during processing.

[0073] Example 1

[0074] This example provides a method for preparing a polymer alloy, the steps are as follows:

[0075] Drying: Place the polyethylene resin and polypropylene resin in a constant temperature forced air drying oven at 80°C and dry for 6 to 8 hours;

[0076] S1. Pre-mix 900 g of polyethylene resin (model LL0220AA, Shanghai Secco Petrochemical Co., Ltd.), 100 g of polypropylene resin (model HP510M, LyondellBasell), and 10 g of compatibilizer (model Weimei Da 6102, Essenk Mobil).

[0077] S2. Add the premixed material through the feed port 300 of the differential-speed asymmetric twin-screw extruder. The feed frequency of the feed port is 6 Hz. The temperatures of the heating zones and die heads along the extrusion direction of the differential-speed asymmetric twin-screw extruder are 160°C, 165°C, 170°C, 170°C, 180°C, 180°C, and 170°C, respectively. The speeds of the single-head screw 610 and the double-head screw 620 are 400 rpm and 200 rpm, respectively. The premixed material is melt-mixed and stretched and sheared to produce extruded strands. The extruded strands are water-cooled and pelletized, and then dried in a constant-temperature forced air drying oven at 80°C for 7 hours.

[0078] The melt mixing section of the differential speed asymmetric twin-screw extruder is set as follows: Figure 3 As shown, the melt mixing section of the single-head screw is arranged from right to left in sequence: 3 single-head kneading blocks, 1 single-head transition section, 3 single-head perturbation rings, 1 single-head transition section, 1 reverse single-head screw element, 1 single-head transition section, and 3 single-head perturbation rings.

[0079] The melt mixing section of the double-headed screw is arranged from right to left with 3 double-headed kneading blocks, 1 double-headed transition section, 3 double-headed perturbation rings, 1 double-headed transition section, 1 reverse double-headed thread element, 1 double-headed transition section, and 3 double-headed perturbation rings.

[0080] Example 2

[0081] This example provides a method for preparing a polymer alloy, which is the same as that in Example 1, except that the amount of the compatibilizer in step S1 is 40 g.

[0082] Example 3

[0083] This example provides a method for preparing a polymer alloy, which is the same as that in Example 1, except that the amount of the compatibilizer in step S1 is 70 g.

[0084] Comparative Example 1

[0085] Comparative Example 1 provides a preparation method of a polymer alloy, which is the same as that of Example 1, except that a conventional twin-screw extruder (model HK26, Nanjing Keya; the two screws have the same speed of 300 rpm; the melt mixing section is composed of kneading blocks) is used for melt mixing.

[0086] Comparative Example 2

[0087] Comparative Example 2 provides a preparation method of a polymer alloy, which is the same as that of Comparative Example 1, except that the amount of the compatibilizer in step S1 is 40 g.

[0088] Comparative Example 3

[0089] Comparative Example 3 provides a preparation method of a polymer alloy, which is the same as that of Comparative Example 1, except that the amount of the compatibilizer in step S1 is 70 g.

[0090] Performance Testing

[0091] The polymer alloy pellets obtained in Examples 1-3 and Comparative Examples 1-3 were subjected to the following procedures: a portion was molded and then cut into standard tensile bars. Tensile properties were tested according to ISO 527-2 at a tensile rate of 50 mm / min. The tensile strength and elongation at break of the standard bars are shown in Table 1.

[0092] Table 1 Comparison of tensile strength and elongation at break of standard splines

[0093] Tensile strength (MPa) Elongation at break (%) Example 1 22.91 1502.21 Comparative Example 1 22.52 1492.84 Example 2 22.76 1625.91 Comparative Example 2 21.25 1498.35 Example 3 21.29 1611.90 Comparative Example 3 20.42 1523.46

[0094] Furthermore, the polymer alloy pellets obtained in Examples 1-3 of the present invention and Comparative Examples 1-3 were prepared into cast films; the steps were as follows: a portion was added to a casting machine to form a cast film. The casting process parameters were a screw speed of 70 rpm, a casting roll speed of approximately 5-6 m / min, and a pull-out speed of approximately 5-6 m / min. The resulting cast film had a thickness of approximately 0.12 mm. The cast film was then cut into rectangular strips 150 mm long and 15 mm wide to test tensile properties, circular discs 80 mm in diameter to test the maximum impact force the cast film could withstand, and square discs 50 mm long and 50 mm wide to test haze. The tensile properties of the cast films were tested according to ISO 527-3 at a tensile rate of 300 mm / min; the impact properties were tested according to ISO 7765-2-2022, with a drop height of 500 mm and a total drop weight of 1 kg; and the haze was measured according to GB / T 2410-2008. The test results of the mechanical properties and haze of the cast films are shown in Table 2.

[0095] Table 2 Comparison of mechanical properties and haze of cast films

[0096]

[0097] According to the comparative analysis of the experimental data in Table 1 and Table 2, the polymer alloy material prepared by the differential asymmetric twin-screw extruder showed a significant improvement in mechanical properties compared to the traditional twin-screw extruder. This result was verified in both the spline specimens and the cast film specimens. Among them, Example 2 with 4% of the compatibilizer added showed the best comprehensive mechanical properties. Figure 6 and Figure 7 From the microstructural characterization, it can be found that the polymer alloy material obtained in Example 2 has a smaller dispersed phase particle size and a more uniform particle size distribution than that in Comparative Example 2, and the interfacial compatibility is significantly improved, which corresponds well to the improvement in mechanical properties. This performance improvement can be attributed to the unique design of the differential asymmetric twin-screw extruder: the symmetry breaking effect produced by the speed difference and structural asymmetry of the twin screws induces the formation of a chaotic flow field and a strong tensile force field, thereby significantly improving the dispersion uniformity and distribution state of the dispersed phase in the matrix. In addition, the experimental results show that compared with the comparative example, the haze values of all examples have decreased to varying degrees, among which the decrease in Examples 2 and 3 is particularly significant, indicating that the transparency of the cast film is significantly improved. This improvement in optical properties is conducive to enhancing light transmittance, which has important practical significance for the application of cast film in the agricultural field.

[0098] In summary, the preparation method for this polyethylene resin / polypropylene resin polymer alloy relies on the chaotic flow field superimposed on the tensile force field triggered by the unique design of the differential asymmetric twin-screw extruder, achieving good dispersion and uniform distribution of the dispersed phase in the matrix, ultimately significantly improving the material's overall mechanical properties. This preparation method also significantly improves the material's optical properties, specifically by reducing haze and increasing transparency. This characteristic ensures that the resulting material fully meets the performance requirements of agricultural cast film.

[0099] The above is a detailed description of the embodiments of the present invention, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in the relevant technical field without departing from the scope of the present invention.

Claims

1. A method for preparing a polymer alloy, characterized in that: The steps include: S1, premixing polyethylene resin, polypropylene resin and compatibilizer to obtain a premix; S2, adding the premix into a differential speed asymmetric twin-screw extruder, melting and mixing, extruding, and pelletizing; The differential-speed asymmetric twin-screw extruder is equipped with a twin-screw consisting of a single-head screw and a twin-head screw; the twin-screw is composed of multiple sections, namely a feeding section, a conveying section, a melt mixing section, and a metering section; the melt mixing section of the single-head screw includes a reverse single-head screw element and at least 6 single-head perturbation rings; every three consecutive single-head perturbation rings form a group, and a reverse single-head screw element is provided between two adjacent groups; The melt mixing section of the double-headed screw includes reverse double-headed thread elements and at least 6 double-headed perturbation rings; each three consecutive double-headed perturbation rings form a group, and reverse double-headed thread elements are provided between two adjacent groups.

2. The method for preparing a polymer alloy according to claim 1, wherein: One to three single-head kneading blocks are also provided in the melt-kneading section of the single-head screw.

3. The method for preparing a polymer alloy according to claim 1, wherein: One to three double-headed kneading blocks are also provided in the melt-kneading section of the double-headed screw.

4. The method for preparing a polymer alloy according to claim 1, wherein: The single-head screw and the double-head screw are meshed and rotated with each other.

5. The method for preparing a polymer alloy according to claim 2, wherein: The stagger angle of the single-head kneading block is set to 90 degrees to 180 degrees.

6. The method for preparing a polymer alloy according to claim 3, wherein: The stagger angle of the double-headed kneading block is set to 45 degrees to 90 degrees.

7. The method for preparing a polymer alloy according to claim 1, wherein: Calculated based on the total mass of the polyethylene resin and the polypropylene resin, the content of the polyethylene resin is 80 wt.% to 90 wt.%.

8. The method for preparing a polymer alloy according to claim 1, wherein: Calculated based on the total mass of the polyethylene resin and the polypropylene resin, the amount of the compatibilizer is 1% to 10%.

9. A polymer alloy, characterized in that The polymer alloy is prepared by the preparation method of any one of claims 1 to 8.

10. Use of the polymer alloy prepared by the method for preparing a polymer alloy according to any one of claims 1 to 8 in preparing a cast film.

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