Preparation method of high-strength polypropylene foam board

Abstract

The invention provides a preparation method of a high-strength polypropylene foam board, which comprises the following steps: S1, mixing silicon dioxide nanoparticles and PP particles in proportion, and carrying out intermittent ball milling to obtain silicon dioxide coated PP particles with a core-shell structure; s2, crushing the skin-core structure PS / PVDF electrostatic spinning membrane, adding the crushed electrostatic spinning membrane into an ethanol solution, then adding the crushed PS powder, uniformly stirring, then carrying out ball milling, and finally taking out and drying to obtain PS mixed powder; s3, carrying out melt extrusion granulation on the silicon dioxide coated PP particles with the core-shell structure and the PS mixed powder to prepare granules of a PP / PS blend; and S4, hot-pressing the granules of the PP / PS blend into a plate, and foaming by adopting a supercritical carbon dioxide batch foaming method to obtain the high-strength polypropylene foam plate. According to the invention, PS and PP are compounded, foaming is carried out through a supercritical carbon dioxide technology, the foam board with a hierarchical pore structure is prepared, and the board with excellent mechanical properties is obtained and can be applied to various different fields.

Description

Technical Field

[0001] The invention relates to the field of polymer foam materials, and in particular to a method for preparing a high-strength polypropylene foam board. Background Art

[0002] PP is a thermoplastic polymer made by polymerizing propylene. PP boasts low cost, excellent overall performance, and ease of processing and molding. In recent years, PP-based copolymerization, blending, filling reinforcement, stretching, foaming, cross-linking, and additive modification technologies have developed rapidly. Blending modifications based on PP primarily improve low-temperature impact resistance, transparency, colorability, and antistatic properties. Polymers that can be used for PP blending modifications include PE, PS, ethylene propylene rubber, polybutadiene, butyl rubber, polyisobutylene, and EVA copolymers. PP-based reinforcement modification can improve the hardness, thermal stability, and flexural strength of PP. For example, filling PP with calcium carbonate or talc improves heat resistance and shrinkage. Polypropylene foam board is a lightweight, high-strength engineering plastic sheet made of polypropylene as the main raw material through an extrusion molding process. Its core feature is the unique internal pore structure, which forms evenly distributed hollow channels through multiple layers of parallel ribs. This design significantly reduces the material density while ensuring mechanical properties. Although the hollow structure reduces weight, the lack of uniformity in pore distribution and precise control of rib thickness may lead to local stress concentration and reduce the stability of the overall structure, especially under dynamic loads (such as transportation vibration), fatigue cracking is prone to occur. To address these deficiencies, there are currently methods to enhance interfacial compatibility by introducing maleic anhydride grafted polypropylene (MAH-g-PP) and epoxy resin, or to use branched epoxy resin to increase the molecular chain entanglement density to improve the stability of mechanical properties. Despite this, how to achieve a balance between lightweight, functional and high strength remains the core challenge of current technological research and development. Summary of the Invention

[0003] Technical problem to be solved: The purpose of the present invention is to provide a method for preparing a high-strength polypropylene foam board. After PS and PP are compounded, they are foamed by supercritical carbon dioxide technology to prepare a foam board with a multi-level pore structure, thereby obtaining a board with excellent mechanical properties for application in various fields.

[0004] Technical solution: A method for preparing a high-strength polypropylene foam board, comprising the following steps: S1. After washing and drying the silica nanoparticles with ethanol, they were mixed with PP particles in proportion and intermittently ball-milled to obtain silica-coated PP particles with a core-shell structure; S2. The skin-core structure PS / PVDF electrospun membrane was crushed, the crushed electrospun membrane was added to an ethanol solution, and then the crushed PS powder was added, stirred and then ball-milled, and finally removed and dried to obtain a PS mixed powder; S3. The core-shell silica-coated PP particles prepared in step S1 and the PS mixed powder prepared in step S2 were melt-blended and extruded using a twin-screw extruder, and granulated to obtain PP / PS blend pellets; S4. The PP / PS blend pellets are hot-pressed into sheets on a flat vulcanizer, and then foamed using a supercritical carbon dioxide intermittent foaming method to obtain a high-strength polypropylene foam sheet. Preferably, the mass ratio of the PP particles to the silicon dioxide nanoparticles is 10:1-2; and / or, The intermittent ball milling adopts a two-step ball milling method. First, a grinding ball with a diameter of 3 to 5 mm is selected and the ball milling time is 1 to 3 hours at a rotation speed of 300 to 500 r / min. Then, a grinding ball with a diameter of 8 to 10 mm is selected and the ball milling time is 30 to 60 minutes at a rotation speed of 600 to 800 r / min. Preferably, the preparation method of the skin-core structure PS / PVDF electrospinning membrane comprises the following steps: The polyvinylidene fluoride was mixed with a mixed solvent of DMF and acetone in a volume ratio of 1:0.8 to 1, and the mixture was stirred thoroughly to prepare a PVDF / DMF / acetone solution with a concentration of 12 to 16 wt %; After mixing PS and THF, stir thoroughly to prepare a PS / THF solution with a concentration of 15-18 wt%; PS / PVDF electrospinning membranes were prepared by coaxial electrospinning using PVDF / DMF / acetone solution as the core layer solution and PS / THF solution as the shell layer solution. Preferably, the coaxial electrospinning parameters are set as follows: core layer injection rate 0.8-1 mL / h, shell layer injection rate 1.4-1.6 mL / h, and voltage 16-18 kV. Preferably, the area of ​​the skin-core structure PS / PVDF electrospinning membrane in step S2 is 0.5 to 8 mm 2 ; and / or, the diameter of the ball mill is 3 to 5 mm, the rotation speed is 500 to 700 r / min, and the ball milling time is 30 to 90 min; and / or, the content of PS / PVDF electrospinning membrane in the PS mixed powder is 2 to 3:8. Preferably, in step S3, the mass ratio of the core-shell silica-coated PP particles to the PS mixed powder is 10:2-3; and / or, The temperature of the twin-screw extruder is set in sequence as follows: 160° C., 180° C., 220° C., 230° C., 230° C., and 220° C. Preferably, the temperature of the hot pressing in step S4 is 170-185° C., the pressure of the hot pressing is 8-10 MPa, and the time of the hot pressing is 6-10 min. Preferably, during the foaming reaction process using the supercritical carbon dioxide intermittent foaming method in step S4, the saturation temperature is controlled to be 85-95°C, the saturation pressure is 10.2-12.5 MPa, and the saturation time is 30-90 min. The pressure relief includes two steps, firstly quickly releasing the pressure to 8 MPa and then slowly reducing it to normal pressure. Beneficial effects: The high-strength polypropylene foam board prepared by the present invention has the following advantages: 1. The present invention uses two materials with different foaming ratios to composite. After foaming, the pores of PP are relatively small, while the pores of PS are relatively large. The large-pore PS can preferentially undergo elastic deformation to absorb impact energy, while the small-pore PP delays crack propagation through local compression and shear deformation. The two synergistically improve mechanical properties. 2. In the present invention, silica nanoparticles are first uniformly coated on the surface of PP particles through a two-step ball milling method to form a core-shell structure. The PS / PVDF electrospun membrane with a skin-core structure is then evenly mixed with PS powder by ball milling to ensure that the PS / PVDF electrospun membrane is evenly distributed in the PS. The silica and electrospun membrane are then blended to synergistically enhance the mechanical properties of the foam board. 3. The PS / PVDF sheath-core electrospun membrane of the present invention forms a sheet-like material after pulverization, which can be used as a "whisker-like" reinforcement. The electrospun fiber membrane is embedded in the bubble wall, imitating the "brick-and-mud" structure of the shell, thereby improving the impact resistance of the material. In addition, the skin of the electrospun layer uses PS as the skin layer, which can better blend and be compatible with the PS powder, thereby improving the compatibility of the electrospun membrane with the substrate. 4. The present invention adopts a two-step pressure relief method. The first pressure relief is quickly released to 8MPa to trigger the nucleation of micropores in the PP phase; the second pressure relief is slowly reduced to normal pressure to promote the growth of macropores in the PS phase, thereby obtaining a foaming material with a multi-level pore distribution. DETAILED DESCRIPTION The present invention will be further described below in conjunction with examples, which are provided to explain the present invention and are not limited to the following examples: Example 1 A method for preparing a high-strength polypropylene foam board comprises the following steps: S1. After washing and drying silica nanoparticles with ethanol, they were mixed with PP particles at a mass ratio of 1:10 and intermittently ball-milled. The milling process was initially performed using 3 mm diameter balls at 300 r / min for 3 h, followed by 60 min using 10 mm diameter balls at 600 r / min to obtain core-shell silica-coated PP particles. S2. Crushing the skin-core structure PS / PVDF electrospinning membrane into a size of 0.5-8 mm 2 The crushed electrospun membrane was added to an ethanol solution, and then the crushed PS powder was added. After stirring evenly, the mixture was ball-milled with a grinding ball diameter of 5 mm, a rotation speed of 500 r / min, and a ball-milling time of 30 min. Finally, the mixture was taken out and dried to obtain a PS mixed powder. The content of PS / PVDF electrospun membrane in the PS mixed powder was 3:8. S3. The core-shell silica-coated PP particles prepared in step S1 and the PS mixed powder prepared in step S2 were melt-blended and extruded in a twin-screw extruder at a mass ratio of 10:2. The temperatures of the twin-screw extruder were set in the following order: 160°C, 180°C, 220°C, 230°C, 230°C, and 220°C to obtain PP / PS blend pellets. S4. The PP / PS blend pellets were hot-pressed into sheets on a flat vulcanizer at a temperature of 170°C, a pressure of 10 MPa, and a time of 6 min. The sheets were then foamed using a supercritical carbon dioxide intermittent foaming method. During the foaming reaction, the saturation temperature was controlled at 95°C, the saturation pressure was 10.2 MPa, and the saturation time was 90 min. After foaming, the pressure was released in two steps: first, quickly to 8 MPa, and then slowly reduced to atmospheric pressure, to obtain a high-strength polypropylene foam sheet. The preparation method of the skin-core structure PS / PVDF electrospinning membrane comprises the following steps: PVDF was mixed with a mixed solvent of DMF and acetone in a volume ratio of 1:0.8 and stirred thoroughly to prepare a PVDF / DMF / acetone solution with a concentration of 16 wt %; PS and THF were mixed and stirred thoroughly to prepare a PS / THF solution with a concentration of 15 wt%; Coaxial electrospinning was carried out using PVDF / DMF / acetone solution as the core layer solution and PS / THF solution as the shell layer solution. The coaxial electrospinning parameters were set as: core layer injection rate 0.8 mL / h, shell layer injection rate 1.4 mL / h, and voltage 16 kV to prepare PS / PVDF electrospinning membrane. Example 2 A method for preparing a high-strength polypropylene foam board comprises the following steps: S1. After washing and drying silica nanoparticles with ethanol, they were mixed with PP particles at a mass ratio of 1:5 and intermittently ball-milled. The milling time was first 1 hour using 5 mm diameter balls at 500 r / min, followed by 30 minutes using 8 mm diameter balls at 800 r / min to obtain core-shell silica-coated PP particles. S2. Crushing the skin-core structure PS / PVDF electrospinning membrane into a size of 0.5-8 mm 2 The crushed electrospun membrane was added to an ethanol solution, and then the crushed PS powder was added. After stirring evenly, the mixture was ball-milled with a grinding ball diameter of 3 mm, a rotation speed of 700 r / min, and a ball-milling time of 90 min. Finally, the mixture was taken out and dried to obtain a PS mixed powder. The content of PS / PVDF electrospun membrane in the PS mixed powder was 2:8; S3. The core-shell silica-coated PP particles prepared in step S1 and the PS mixed powder prepared in step S2 were melt-blended and extruded in a twin-screw extruder at a mass ratio of 10:3. The temperatures of the twin-screw extruder were set in the following order: 160°C, 180°C, 220°C, 230°C, 230°C, and 220°C to obtain PP / PS blend pellets. S4. The PP / PS blend pellets were hot-pressed into sheets on a flat vulcanizer at a temperature of 185°C, a pressure of 8 MPa, and a time of 10 min. The sheets were then foamed using a supercritical carbon dioxide intermittent foaming method. During the foaming reaction, the saturation temperature was controlled at 85°C, the saturation pressure was 12.5 MPa, and the saturation time was 30 min. After foaming, the pressure was released in two steps: first, quickly to 8 MPa, and then slowly reduced to atmospheric pressure, to obtain a high-strength polypropylene foam sheet. The preparation method of the skin-core structure PS / PVDF electrospinning membrane comprises the following steps: PVDF was mixed with a 1:1 volume ratio DMF and acetone mixed solvent, and stirred thoroughly to prepare a 12 wt% PVDF / DMF / acetone solution; PS and THF were mixed and stirred thoroughly to prepare a PS / THF solution with a concentration of 18 wt%; Coaxial electrospinning was carried out using PVDF / DMF / acetone solution as the core layer solution and PS / THF solution as the shell layer solution. The coaxial electrospinning parameters were set as: core layer injection rate 1 mL / h, shell layer injection rate 1.6 mL / h, and voltage 18 kV to prepare PS / PVDF electrospinning membrane. Example 3 A method for preparing a high-strength polypropylene foam board comprises the following steps: S1. After washing and drying silica nanoparticles with ethanol, they were mixed with PP particles at a mass ratio of 1.2:10 and intermittently ball-milled. The milling process was initially performed using 3 mm diameter balls at 450 rpm for 1.5 h, followed by 8 mm diameter balls at 650 rpm for 50 min to obtain core-shell silica-coated PP particles. S2. Crushing the skin-core structure PS / PVDF electrospinning membrane into a size of 0.5-8 mm 2 The crushed electrospun membrane was added to an ethanol solution, and then the crushed PS powder was added. After stirring evenly, the mixture was ball-milled with a grinding ball diameter of 3 mm, a rotation speed of 550 r / min, and a ball-milling time of 50 min. Finally, the mixture was taken out and dried to obtain a PS mixed powder. The content of PS / PVDF electrospun membrane in the PS mixed powder was 2.2:8; S3. The core-shell silica-coated PP particles prepared in step S1 and the PS mixed powder prepared in step S2 were melt-blended and extruded using a twin-screw extruder at a mass ratio of 10:2.3. The temperatures of the twin-screw extruder were set in the following order: 160°C, 180°C, 220°C, 230°C, 230°C, and 220°C to obtain PP / PS blend pellets. S4. The PP / PS blend pellets were hot-pressed into sheets on a flat vulcanizer at a temperature of 180°C, a pressure of 8 MPa, and a time of 9 min. The sheets were then foamed using a supercritical carbon dioxide intermittent foaming method. During the foaming reaction, the saturation temperature was controlled at 85°C, the saturation pressure was 12 MPa, and the saturation time was 70 min. After foaming, the pressure was released in two steps: first, quickly to 8 MPa, and then slowly reduced to atmospheric pressure, to obtain a high-strength polypropylene foam sheet. The preparation method of the skin-core structure PS / PVDF electrospinning membrane comprises the following steps: PVDF was mixed with a mixed solvent of DMF and acetone in a volume ratio of 1:0.8 and stirred thoroughly to prepare a PVDF / DMF / acetone solution with a concentration of 13 wt %; PS and THF were mixed and stirred thoroughly to prepare a PS / THF solution with a concentration of 18 wt%; Coaxial electrospinning was carried out using PVDF / DMF / acetone solution as the core layer solution and PS / THF solution as the shell layer solution. The coaxial electrospinning parameters were set as: core layer injection rate 0.8 mL / h, shell layer injection rate 1.6 mL / h, and voltage 18 kV to prepare PS / PVDF electrospinning membrane. Example 4 A method for preparing a high-strength polypropylene foam board comprises the following steps: S1. After washing and drying silica nanoparticles with ethanol, they were mixed with PP particles at a mass ratio of 1.7:10 and intermittently ball-milled. The milling process was initially performed using 5 mm diameter balls at a speed of 350 r / min for 2.5 h, followed by 40 min of ball milling using 10 mm diameter balls at a speed of 750 r / min to obtain core-shell silica-coated PP particles. S2. Crushing the skin-core structure PS / PVDF electrospinning membrane into a size of 0.5-8 mm 2 The crushed electrospun membrane was added to an ethanol solution, and then the crushed PS powder was added. After stirring evenly, the mixture was ball-milled with a grinding ball diameter of 5 mm, a rotation speed of 650 r / min, and a ball-milling time of 70 min. Finally, the mixture was taken out and dried to obtain a PS mixed powder. The content of PS / PVDF electrospun membrane in the PS mixed powder was 2.6:8; S3. The core-shell silica-coated PP particles prepared in step S1 and the PS mixed powder prepared in step S2 were melt-blended and extruded using a twin-screw extruder at a mass ratio of 10:2.7. The temperatures of the twin-screw extruder were set in the following order: 160°C, 180°C, 220°C, 230°C, 230°C, and 220°C to obtain PP / PS blend pellets. S4. The PP / PS blend pellets were hot-pressed into sheets on a flat vulcanizer at a temperature of 175°C, a pressure of 10 MPa, and a time of 7 min. The sheets were then foamed using a supercritical carbon dioxide intermittent foaming method. During the foaming reaction, the saturation temperature was controlled at 95°C, the saturation pressure was 10.8 MPa, and the saturation time was 50 min. After foaming, the pressure was released in two steps: first, quickly to 8 MPa, and then slowly reduced to atmospheric pressure, to obtain a high-strength polypropylene foam sheet. The preparation method of the skin-core structure PS / PVDF electrospinning membrane comprises the following steps: PVDF was mixed with a 1:1 volume ratio DMF and acetone mixed solvent, and stirred thoroughly to prepare a 15 wt% PVDF / DMF / acetone solution; PS and THF were mixed and stirred thoroughly to prepare a PS / THF solution with a concentration of 16 wt%; Coaxial electrospinning was carried out using PVDF / DMF / acetone solution as the core layer solution and PS / THF solution as the shell layer solution. The coaxial electrospinning parameters were set as: core layer injection rate 0.8 mL / h, shell layer injection rate 1.4 mL / h, and voltage 16 kV to prepare PS / PVDF electrospinning membrane. Example 5 A method for preparing a high-strength polypropylene foam board comprises the following steps: S1. After washing and drying silica nanoparticles with ethanol, they were mixed with PP particles at a mass ratio of 1.4:10 and intermittently ball-milled. The mixture was first milled at 400 rpm for 2 h using 3 mm diameter balls, and then at 700 rpm for 45 min using 8 mm diameter balls to obtain core-shell silica-coated PP particles. S2. Crushing the skin-core structure PS / PVDF electrospinning membrane into a size of 0.5-8 mm 2 The crushed electrospun membrane was added to an ethanol solution, and then the crushed PS powder was added. After stirring evenly, the mixture was ball-milled with a grinding ball diameter of 5 mm, a rotation speed of 600 r / min, and a ball-milling time of 60 min. Finally, the mixture was taken out and dried to obtain a PS mixed powder. The content of PS / PVDF electrospun membrane in the PS mixed powder was 2.4:8; S3. The core-shell silica-coated PP particles prepared in step S1 and the PS mixed powder prepared in step S2 were melt-blended and extruded using a twin-screw extruder at a mass ratio of 10:2.5. The temperatures of the twin-screw extruder were set in the following order: 160°C, 180°C, 220°C, 230°C, 230°C, and 220°C to obtain PP / PS blend pellets. S4. The PP / PS blend pellets were hot-pressed into sheets on a flat vulcanizer at a temperature of 180°C, a pressure of 9 MPa, and a time of 8 min. The sheets were then foamed using a supercritical carbon dioxide intermittent foaming method. During the foaming reaction, the saturation temperature was controlled at 90°C, the saturation pressure was 11.5 MPa, and the saturation time was 60 min. After foaming, the pressure was released in two steps: first, quickly to 8 MPa, and then slowly reduced to atmospheric pressure, to obtain a high-strength polypropylene foam sheet. The preparation method of the skin-core structure PS / PVDF electrospinning membrane comprises the following steps: PVDF was mixed with a mixed solvent of DMF and acetone in a volume ratio of 1:0.9 and stirred thoroughly to prepare a PVDF / DMF / acetone solution with a concentration of 14 wt %; PS and THF were mixed and stirred thoroughly to prepare a PS / THF solution with a concentration of 17 wt %; Coaxial electrospinning was carried out using PVDF / DMF / acetone solution as the core layer solution and PS / THF solution as the shell layer solution. The coaxial electrospinning parameters were set as: core layer injection rate 0.9 mL / h, shell layer injection rate 1.2 mL / h, and voltage 16 kV to prepare PS / PVDF electrospinning membrane. Comparative Example 1 The difference between Comparative Example 1 and Example 5 is that: instead of using electrospinning with a skin-core structure, a PVDF electrospinning membrane is used directly; A method for preparing a high-strength polypropylene foam board comprises the following steps: S1. After washing and drying silica nanoparticles with ethanol, they were mixed with PP particles at a mass ratio of 1.4:10 and intermittently ball-milled. The mixture was first milled at 400 rpm for 2 h using 3 mm diameter balls, and then at 700 rpm for 45 min using 8 mm diameter balls to obtain core-shell silica-coated PP particles. S2. Crushing the PVDF electrospun membrane into an area of ​​0.5-8 mm 2 The crushed electrospun membrane was added to an ethanol solution, and then the crushed PS powder was added. After stirring evenly, the mixture was ball-milled with a grinding ball diameter of 5 mm, a rotation speed of 600 r / min, and a ball-milling time of 60 min. Finally, the mixture was taken out and dried to obtain a PS mixed powder. The content of PS / PVDF electrospun membrane in the PS mixed powder was 2.4:8; S3. The core-shell silica-coated PP particles prepared in step S1 and the PS mixed powder prepared in step S2 were melt-blended and extruded using a twin-screw extruder at a mass ratio of 10:2.5. The temperatures of the twin-screw extruder were set in the following order: 160°C, 180°C, 220°C, 230°C, 230°C, and 220°C to obtain PP / PS blend pellets. S4. The PP / PS blend pellets were hot-pressed into sheets on a flat vulcanizer at a temperature of 180°C, a pressure of 9 MPa, and a time of 8 min. The sheets were then foamed using a supercritical carbon dioxide intermittent foaming method. During the foaming reaction, the saturation temperature was controlled at 90°C, the saturation pressure was 11.5 MPa, and the saturation time was 60 min. After foaming, the pressure was released in two steps: first, quickly to 8 MPa, and then slowly reduced to atmospheric pressure, to obtain a high-strength polypropylene foam sheet. Preferably, the preparation method of the PVDF electrospinning membrane comprises the following steps: After polyvinylidene fluoride was mixed with a mixed solvent of DMF and acetone in a volume ratio of 1:0.9 and stirred thoroughly, a PVDF / DMF / acetone solution with a concentration of 14 wt% was prepared for electrospinning. The electrospinning parameters were set as follows: injection rate 1.2 mL / h, voltage 16 kV, and PVDF electrospinning membrane was prepared. Comparative Example 2 The difference between Comparative Example 2 and Example 5 is that only PP foaming is used; A method for preparing a high-strength polypropylene foam board comprises the following steps: S1. After washing and drying silica nanoparticles with ethanol, they were mixed with PP particles at a mass ratio of 1.4:10 and intermittently ball-milled. The mixture was first milled at 400 rpm for 2 h using 3 mm diameter balls, and then at 700 rpm for 45 min using 8 mm diameter balls to obtain core-shell silica-coated PP particles. S2. The skin-core structure PS / PVDF electrospun membrane and the core-shell structure silica-coated PP particles prepared in step S1 were melt-blended and extruded using a twin-screw extruder at a mass ratio of 0.5:10. The temperatures of the twin-screw extruder were set in the following order: 160°C, 180°C, 220°C, 230°C, 230°C, and 220°C to produce pellets of the PP / PS blend. S4. The PP pellets were hot-pressed into sheets on a flat vulcanizer at a temperature of 180°C, a pressure of 9 MPa, and a time of 8 min. The sheets were then foamed using a supercritical carbon dioxide intermittent foaming method. During the foaming reaction, the saturation temperature was controlled at 90°C, the saturation pressure was 11.5 MPa, and the saturation time was 60 min. After foaming, the pressure was released in two steps: first, the pressure was quickly released to 8 MPa, and then slowly dropped to normal pressure to obtain a high-strength polypropylene foam sheet. Preferably, the preparation method of the skin-core structure PS / PVDF electrospinning membrane comprises the following steps: PVDF was mixed with a mixed solvent of DMF and acetone in a volume ratio of 1:0.9 and stirred thoroughly to prepare a PVDF / DMF / acetone solution with a concentration of 14 wt %; PS and THF were mixed and stirred thoroughly to prepare a PS / THF solution with a concentration of 17 wt %; Coaxial electrospinning was carried out using PVDF / DMF / acetone solution as the core layer solution and PS / THF solution as the shell layer solution. The coaxial electrospinning parameters were set as: core layer injection rate 0.9 mL / h, shell layer injection rate 1.2 mL / h, and voltage 16 kV to prepare PS / PVDF electrospinning membrane. Comparative Example 3 The difference between Comparative Example 3 and Example 5 is that: no PS / PVDF electrospinning membrane is added; A method for preparing a high-strength polypropylene foam board comprises the following steps: S1. After washing and drying silica nanoparticles with ethanol, they were mixed with PP particles at a mass ratio of 1.4:10 and intermittently ball-milled. The mixture was first milled at 400 rpm for 2 h using 3 mm diameter balls, and then at 700 rpm for 45 min using 8 mm diameter balls to obtain core-shell silica-coated PP particles. S2. The core-shell silica-coated PP particles prepared in step S1 were melt-blended with PS particles in a mass ratio of 10:2.5 using a twin-screw extruder, and then extruded. The temperatures of the twin-screw extruder were set in the following order: 160°C, 180°C, 220°C, 230°C, 230°C, and 220°C to obtain pellets of the PP / PS blend. S4. The PP / PS blend pellets were hot-pressed into sheets on a flat-plate vulcanizer at a temperature of 180°C, a pressure of 9 MPa, and a time of 8 min. The sheets were then foamed using a supercritical carbon dioxide intermittent foaming method. During the foaming reaction, the saturation temperature was controlled at 90°C, the saturation pressure was controlled at 11.5 MPa, and the saturation time was 60 min. After foaming, the pressure was released in two steps: first, the pressure was quickly released to 8 MPa, and then it was slowly reduced to normal pressure to obtain a high-strength polypropylene foam sheet. Comparative Example 4 The difference between Comparative Example 4 and Example 5 is that: one-step pressure relief is adopted; A method for preparing a high-strength polypropylene foam board comprises the following steps: S1. After washing and drying silica nanoparticles with ethanol, they were mixed with PP particles at a mass ratio of 1.4:10 and intermittently ball-milled. The mixture was first milled at 400 rpm for 2 h using 3 mm diameter balls, and then at 700 rpm for 45 min using 8 mm diameter balls to obtain core-shell silica-coated PP particles. S2. Crushing the skin-core structure PS / PVDF electrospinning membrane into a size of 0.5-8 mm 2 The crushed electrospun membrane was added to an ethanol solution, and then the crushed PS powder was added. After stirring evenly, the mixture was ball-milled with a grinding ball diameter of 5 mm, a rotation speed of 600 r / min, and a ball-milling time of 60 min. Finally, the mixture was taken out and dried to obtain a PS mixed powder. The content of PS / PVDF electrospun membrane in the PS mixed powder was 2.4:8; S3. The core-shell silica-coated PP particles prepared in step S1 and the PS mixed powder prepared in step S2 were melt-blended and extruded using a twin-screw extruder at a mass ratio of 10:2.5. The temperatures of the twin-screw extruder were set in the following order: 160°C, 180°C, 220°C, 230°C, 230°C, and 220°C to obtain PP / PS blend pellets. S4. The PP / PS blend pellets were hot-pressed into sheets on a flat vulcanizer at a temperature of 180°C, a pressure of 9 MPa, and a time of 8 min. The sheets were then foamed using a supercritical carbon dioxide intermittent foaming method. During the foaming reaction, the saturation temperature was controlled at 90°C, the saturation pressure was 11.5 MPa, the saturation time was 60 min, and the pressure was rapidly released to atmospheric pressure to obtain a high-strength polypropylene foam sheet. The preparation method of the skin-core structure PS / PVDF electrospinning membrane comprises the following steps: PVDF was mixed with a mixed solvent of DMF and acetone in a volume ratio of 1:0.9 and stirred thoroughly to prepare a PVDF / DMF / acetone solution with a concentration of 14 wt %; PS and THF were mixed and stirred thoroughly to prepare a PS / THF solution with a concentration of 17 wt %; Coaxial electrospinning was carried out using PVDF / DMF / acetone solution as the core layer solution and PS / THF solution as the shell layer solution. The coaxial electrospinning parameters were set as: core layer injection rate 0.9 mL / h, shell layer injection rate 1.2 mL / h, and voltage 16 kV to prepare PS / PVDF electrospinning membrane. Comparative Example 5 The difference between Comparative Example 5 and Example 5 is that the silicon dioxide is not ball-milled intermittently; A method for preparing a high-strength polypropylene foam board comprises the following steps: S1. After washing and drying the silica nanoparticles with ethanol, they were mixed with PP particles at a mass ratio of 1.4:10 and ball-milled using 3 mm diameter balls at a speed of 400 r / min for 2 h to obtain core-shell silica-coated PP particles. S2. Crushing the skin-core structure PS / PVDF electrospinning membrane into a size of 0.5-8 mm 2 The crushed electrospun membrane was added to an ethanol solution, and then the crushed PS powder was added. After stirring evenly, the mixture was ball-milled with a grinding ball diameter of 5 mm, a rotation speed of 600 r / min, and a ball-milling time of 60 min. Finally, the mixture was taken out and dried to obtain a PS mixed powder. The content of PS / PVDF electrospun membrane in the PS mixed powder was 2.4:8; S3. The core-shell silica-coated PP particles prepared in step S1 and the PS mixed powder prepared in step S2 were melt-blended and extruded using a twin-screw extruder at a mass ratio of 10:2.5. The temperatures of the twin-screw extruder were set in the following order: 160°C, 180°C, 220°C, 230°C, 230°C, and 220°C to obtain PP / PS blend pellets. S4. The PP / PS blend pellets were hot-pressed into sheets on a flat vulcanizer at a temperature of 180°C, a pressure of 9 MPa, and a time of 8 min. The sheets were then foamed using a supercritical carbon dioxide intermittent foaming method. During the foaming reaction, the saturation temperature was controlled at 90°C, the saturation pressure was 11.5 MPa, and the saturation time was 60 min. After foaming, the pressure was released in two steps: first, quickly to 8 MPa, and then slowly reduced to atmospheric pressure, to obtain a high-strength polypropylene foam sheet. The preparation method of the skin-core structure PS / PVDF electrospinning membrane comprises the following steps: PVDF was mixed with a mixed solvent of DMF and acetone in a volume ratio of 1:0.9 and stirred thoroughly to prepare a PVDF / DMF / acetone solution with a concentration of 14 wt %; PS and THF were mixed and stirred thoroughly to prepare a PS / THF solution with a concentration of 17 wt %; Coaxial electrospinning was carried out using PVDF / DMF / acetone solution as the core layer solution and PS / THF solution as the shell layer solution. The coaxial electrospinning parameters were set as: core layer injection rate 0.9 mL / h, shell layer injection rate 1.2 mL / h, and voltage 16 kV to prepare PS / PVDF electrospinning membrane. Experimental method: Impact strength: The sample size is 80mm×15mm×4mm. After cutting, it is polished to the required size with sandpaper. The notch is located in the middle of the sample and is V-shaped with a depth of 2mm. Each set of experiments requires at least 5 samples; Tensile strength: The sample size is 22mm×4mm×2mm. The foamed specimen needs to be cut and polished to this size with sandpaper. The stretching rate is 50 mm / min. The raw materials in the samples prepared in the above examples and comparative examples are from the same source. <![CDATA[Impact strength kJ / m 2 > Tensile strength MPa Example 1 14.6 39.8 Example 2 13.5 38.8 Example 3 14.8 42.1 Example 4 14.5 41.5 Example 5 14.7 42.4 Comparative Example 1 11.6 32.5 Comparative Example 2 10.8 29.6 Comparative Example 3 11.2 31.9 Comparative Example 4 12.2 35.1 Comparative Example 5 13.1 36.3 Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing a high-strength polypropylene foam board, characterized in that: The following steps are involved: S1. After washing and drying the silica nanoparticles with ethanol, they were mixed with PP particles in proportion and intermittently ball-milled to obtain silica-coated PP particles with a core-shell structure; S2. The skin-core structure PS / PVDF electrospun membrane was crushed, the crushed electrospun membrane was added to an ethanol solution, and then the crushed PS powder was added, stirred and then ball-milled, and finally removed and dried to obtain a PS mixed powder; S3. The core-shell silica-coated PP particles prepared in step S1 and the PS mixed powder prepared in step S2 were melt-blended and extruded using a twin-screw extruder, and granulated to obtain PP / PS blend pellets; S4. The PP / PS blend pellets are hot-pressed into sheets on a flat vulcanizer, and then foamed using a supercritical carbon dioxide intermittent foaming method, and the pressure is released to obtain a high-strength polypropylene foam sheet.

2. The method for preparing the high-strength polypropylene foam board according to claim 1, wherein: The mass ratio of the PP particles to the silicon dioxide nanoparticles is 10:1-2; and / or, The intermittent ball milling adopts a two-step ball milling method. First, a grinding ball with a diameter of 3 to 5 mm is selected and the ball milling time is 1 to 3 hours at a rotation speed of 300 to 500 r / min. Then, a grinding ball with a diameter of 8 to 10 mm is selected and the ball milling time is 30 to 60 minutes at a rotation speed of 600 to 800 r / min.

3. The method for preparing a high-strength polypropylene foam board according to claim 1, wherein: The preparation method of the skin-core structure PS / PVDF electrospinning membrane comprises the following steps: The polyvinylidene fluoride was mixed with a mixed solvent of DMF and acetone in a volume ratio of 1:0.8 to 1, and the mixture was stirred thoroughly to prepare a PVDF / DMF / acetone solution with a concentration of 12 to 16 wt %; After mixing PS and THF, stir thoroughly to prepare a PS / THF solution with a concentration of 15-18 wt%; PS / PVDF electrospinning membranes were prepared by coaxial electrospinning using PVDF / DMF / acetone solution as the core layer solution and PS / THF solution as the shell layer solution.

4. The method for preparing a high-strength polypropylene foam board according to claim 3, wherein: The coaxial electrospinning parameters are set as follows: core layer injection rate 0.8-1 mL / h, shell layer injection rate 1.4-1.6 mL / h, and voltage 16-18 kV.

5. The method for preparing a high-strength polypropylene foam board according to claim 1, wherein: The area of ​​the skin-core structure PS / PVDF electrospinning membrane in step S2 is 0.5-8 mm 2 and / or, The diameter of the grinding balls of the ball mill is 3 to 5 mm, the rotation speed is 500 to 700 r / min, and the ball milling time is 30 to 90 min; and / or, The content of PS / PVDF electrospinning membrane in the PS mixed powder is 2-3:

8.

6. The method for preparing a high-strength polypropylene foam board according to claim 1, wherein: In step S3, the mass ratio of the core-shell silica-coated PP particles to the PS mixed powder is 10:2-3; and / or, The temperatures of the twin-screw extruder were set in sequence as follows: 160°C, 180°C, 220°C, 230°C, 230°C, and 220°C.

7. The method for preparing a high-strength polypropylene foam board according to claim 1, wherein: In step S4, the hot pressing temperature is 170-185° C., the hot pressing pressure is 8-10 MPa, and the hot pressing time is 6-10 minutes.

8. The method for preparing a high-strength polypropylene foam board according to claim 1, wherein: During the foaming reaction process of the intermittent supercritical carbon dioxide foaming method in step S4, the saturation temperature is controlled to be 85-95°C, the saturation pressure is controlled to be 10.2-12.5 MPa, and the saturation time is 30-90 min. The pressure relief includes two steps, firstly quickly releasing the pressure to 8 MPa and then slowly reducing it to normal pressure.