Fiber reinforced polypropylene composition and microcellular foamed material and method for making the same

Abstract

The application discloses a kind of fiber reinforced polypropylene composition and microcellular foaming material and preparation method thereof, the fiber reinforced polypropylene composition, by weight percentage, including 70~89% polypropylene, 5~15% polypropylene modifier, 1~3% compatilizer, 5~25% inorganic material fiber;The polypropylene modifier is prepared by polar monomer grafted polypropylene and amino-containing compound are reacted and extruded granulation, the amino-containing compound is compound A or compound B or mixture of the two, the compound A is organic matter containing amine group, ether bond and aryl group, the compound B is polyamine.The foaming ratio of the fiber reinforced polypropylene microcellular foaming material prepared by the application is 5-40 times, the average pore size is 5-50 μm, and the tensile strength and bending modulus are significantly improved.

Description

Technical Field

[0001] This invention relates to the field of new polypropylene microporous foam materials, specifically to a fiber-reinforced polypropylene composition and a microporous foam material and its preparation method. Background Technology

[0002] Microcellular polypropylene foam (MPP) is a novel porous polypropylene foam material with a cell size of less than 100 micrometers. The advantages of micron-scale cells include: at the same expansion ratio (or apparent density), the mechanical property loss of microcellular foam is less due to the smaller cell size. This means that using MPP can save material and further reduce the weight and volume of products; because the cell size is controllable between 1-100 μm, MPP can be slit into ultra-thin sheets with a thickness of less than 0.1 mm without surface perforation; micron-scale cells effectively reduce gas convection within the cells, thereby effectively reducing heat transfer caused by air convection. Therefore, high-expansion microcellular foam materials have a low thermal conductivity that is stable over the long term due to the cell structure; also, due to its micron-scale cells, MPP has excellent surface protection properties and can be used in packaging applications with high protective requirements, such as LCD panels. The unique structure and properties of MPP due to its micron-scale cells make it promising for applications in precision packaging, optoelectronic technology, and other fields. However, as a foamed material, the pores can become the source of cracks in the foam when subjected to external forces, reducing the material's mechanical properties. Therefore, the mechanical strength of foamed plastics generally decreases with increasing expansion ratio, thus limiting its applications.

[0003] Existing technologies generally improve the mechanical properties of composite foamed materials through blending modification and inorganic particle filling. The method of improving the properties of microfoamed polymer materials through blending typically involves adding rubber particles, elastomers, or similar polymers with different structures to a certain polymer. Rubber particles or elastomers can effectively hinder the slippage of the matrix material's molecular chains; similar polymers with different structures can form physical cross-linking to inhibit excessive cell growth, thereby improving certain foaming defects in the matrix material, such as cell coalescence and collapse. Inorganic powders used in blending with the matrix material mainly include mica powder, attapulgite, CaCO3, montmorillonite, talc, and silica. Because inorganic particles can significantly improve the cell structure of composite foamed materials to a certain extent, improve the foaming quality of the composite material, enhance its overall mechanical properties, and reduce production costs.

[0004] For example, CN201811216626.0 discloses a method for preparing lightweight high-strength polypropylene foam material and its application. The method disclosed in this patent is to obtain a PP-based composite by blending PP, TPU and a nucleating agent. Lightweight high-strength polypropylene foam products are prepared based on the coupling modification between thermoplastic polyurethane and nucleating agent. The density, mechanical properties and thermal insulation properties of PP foam products can be controlled within a wide range.

[0005] CN109501107A discloses a method for preparing a low-density, high-expansion-ratio polymer foam material. The method is characterized by using a core-receding microporous injection molding technique. The process involves mixing a polymer and filler, feeding the mixture into a twin-screw extruder, and then extruding and underwater pelletizing to obtain a modified polymer composite material. The prepared polymer foam material exhibits highly controllable density and expansion ratio, specifically a density of 0.1-0.5 g / cm³. 3 The foaming ratio is 2-10 times.

[0006] CN108276663A discloses a high melt strength chemically microporous foamed long glass fiber reinforced polypropylene composite material and its preparation method. The main components include: 20-30% long glass fiber by weight, 60-70% modified polypropylene resin, 1-6% maleic anhydride graft PP-g-MAH, 0.5-5% antioxidant, and 1-3% chemical foaming agent. This invention achieves microporous foaming under the action of a chemical foaming agent, ensuring a certain mechanical strength while reducing density.

[0007] However, existing technologies have limited effectiveness in improving the mechanical properties of composite foam materials through blending modification and inorganic particle filling. Fibers can significantly improve the mechanical properties of composite foam materials, but currently they are mostly used in low-ratio (≤2x) microfoam materials. Summary of the Invention

[0008] In view of this, the main objective of the present invention is to provide a fiber-reinforced polypropylene composition and a microporous foam material and a method for preparing the same. The obtained fiber-reinforced polypropylene microporous foam material has a foaming ratio of 5-40 times and an average pore size of 5-50 μm. The tensile strength and flexural modulus are significantly improved.

[0009] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: a fiber-reinforced polypropylene composition, comprising, by weight percentage, 70-89% polypropylene, 5-15% polypropylene modifier, 1-3% compatibilizer, and 5-19% inorganic fiber.

[0010] The polypropylene modifier is prepared by reacting polar monomer-grafted polypropylene with an amino-containing compound and then extruding and granulating. The amino-containing compound is compound A or compound B or a mixture of the two. Compound A is an organic compound containing amino groups, ether bonds and aryl groups, and compound B is a polyamine.

[0011] According to the composition of the present invention, compound A has a different structure from compound B.

[0012] Compound A that meets the aforementioned requirements can achieve the purpose of this invention. In a specific embodiment of this invention, compound A is preferably one or more of phenoxyaniline, 3,3',4,4'-tetraaminodiphenyl ether, 3,4'-diaminodiphenyl ether and 4,4'-diaminodiphenyl ether.

[0013] Compound B that meets the foregoing requirements can achieve the purpose of this invention. In specific embodiments of this invention, compound B is preferably one or more of alkyl diamine, alkylene diamine, alkylene triamine, alkylene tetraamine, alkylene pentaamine, aryl diamine, aryl triamine, and aryl tetraamine. More preferably, compound B is one or more of C2-12 alkyl diamine, C2-12 alkylene diamine, C2-C12 alkylene triamine, C2-C12 alkylene tetraamine, C2-C12 alkylene pentaamine, C6-C18 aryl diamine, C6-C18 aryl triamine, and C6-C18 aryl tetraamine.

[0014] The composition according to the present invention preferably comprises 71-80% polypropylene, 5-12% polypropylene modifier, 1-2% compatibilizer, and 10-19% inorganic material fiber; more preferably, it comprises 71-75% polypropylene, 10-12% polypropylene modifier, 1-2% compatibilizer, and 10-16% inorganic material fiber.

[0015] The content of the polar monomer grafted polypropylene is 98-99.8% by weight, the content of compound A is ≤2%, and the content of compound B is ≤2%.

[0016] According to the composition of the present invention, in a specific embodiment of the present invention, the polar monomer grafted polypropylene is one of acrylic acid, methacrylic acid, maleic anhydride, methyl methacrylate, ethylene tert-carbonate, butyl acrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, ethyl 2-methacrylate, allyl methacrylate, hydroxyethyl methacrylate, glycidyl methacrylate, and isooctyl acrylate; preferably one of acrylic acid, methacrylic acid, methyl acrylate, and methyl methacrylate.

[0017] According to the composition of the present invention, in a specific embodiment of the present invention, the preparation method of the polypropylene modifier includes: reacting polypropylene grafted with a polar monomer and an amino-containing compound at a reaction extrusion temperature of 150-220°C and extruding and granulating, and drying at 80-95°C for 30-120 min to obtain the polypropylene modifier.

[0018] According to the composition of the present invention, the polypropylene may be selected from homopolymer polypropylene, block copolymer polypropylene, random copolymer polypropylene, etc., obtained by various polymerization methods.

[0019] According to the composition of the present invention, the inorganic material fiber is at least one of glass fiber and carbon fiber; the glass fiber is one of continuous long glass fiber and short glass fiber, preferably long glass fiber; the carbon fiber may be one of polyacrylonitrile-based carbon fiber, viscose-based carbon fiber and pitch-based carbon fiber, preferably carbon fiber with polyacrylonitrile matrix.

[0020] According to the composition of the present invention, the compatibilizer is a polar monomer-grafted polymer. In specific embodiments of the present invention, the polymer may be polypropylene or polyethylene, and the polar monomer is one of acrylic acid, methacrylic acid, maleic anhydride, methyl methacrylate, ethylene tert-carbonate, butyl acrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, ethyl 2-methacrylate, allyl methacrylate, hydroxyethyl methacrylate, glycidyl methacrylate, and isooctyl acrylate, preferably one of acrylic acid, methacrylic acid, methyl acrylate, and methyl methacrylate. The compatibilizer may be the same polar monomer-grafted polypropylene used in the preparation of the polypropylene modifier.

[0021] Another aspect of the present invention provides a method for preparing a fiber-reinforced polypropylene microporous foam material, comprising foaming and molding the aforementioned fiber-reinforced polypropylene composition. Specifically, it includes the following steps:

[0022] 1) Mix polypropylene, polypropylene modifier, and compatibilizer evenly, add inorganic fiber, melt extrude, cool and pelletize, and dry to obtain fiber-reinforced polypropylene particles.

[0023] 2) The fiber-reinforced polypropylene particles are extruded to obtain fiber-reinforced polypropylene sheets;

[0024] 3) Supercritical gas is introduced into the fiber-reinforced polypropylene sheet for compression molding to obtain the fiber-reinforced polypropylene microporous foam material.

[0025] According to the method of the present invention, in one specific embodiment, the supercritical gas is one of nitrogen, carbon dioxide and butane.

[0026] According to the method of the present invention, in step 1), the extrusion temperature is 170°C to 220°C.

[0027] According to the method of the present invention, in step 2), the extrusion temperature is 180°C to 220°C.

[0028] According to the method of the present invention, in step 3), supercritical gas is introduced into the fiber-reinforced polypropylene sheet at a temperature of 180℃~230℃ and a pressure of 0.1~10MPa to form a polypropylene / supercritical fluid single-phase solution. The temperature is then lowered to 130℃~170℃, the pressure is released, the mold is opened, and the fiber-reinforced polypropylene microporous foam material is obtained.

[0029] In another aspect, the present invention provides a fiber-reinforced polypropylene microporous foam material prepared by the above-described preparation method.

[0030] The fiber-reinforced polypropylene microporous foam material has a foaming ratio of 5-40 times, an average pore size of 5-50 μm, a flexural modulus greater than 12 MPa, and a tensile strength greater than 1.2 MPa.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] (1) In a twin-screw extruder, polar monomer-grafted polypropylene reacts with amino-containing compounds in the molten state to generate imide groups, thereby forming intermolecular crosslinks. This invention prepares polypropylene with a long-branched and micro-crosslinked structure. This product, with its special long-branched and micro-crosslinked structure, can be added to polypropylene as a modifier to improve its melt strength. When used as a raw material in the processing of foamed materials, processing at temperatures above the melting point can increase the melt viscosity and melt strength of polypropylene, overcoming the problem of cell rupture, thereby increasing the foaming ratio and improving the tensile strength and flexural modulus of the foamed products.

[0033] (2) This invention optimizes the raw material system, such as improving melt strength, and optimizes the foaming process (using supercritical fluid as a foaming agent), resulting in foamed products with small pore sizes, less than 50 μm. The advantages of small pore size are good mechanical properties, high tensile strength, and high flexural modulus.

[0034] It has been confirmed that the fiber-reinforced polypropylene microporous foam material prepared by this invention has a foaming ratio of 5-40 times, an average pore size of 5-50 μm, and significantly improved tensile strength and flexural modulus. The flexural modulus is greater than 12 MPa and the tensile strength is greater than 1.2 MPa. It has the advantages of being lightweight and having high mechanical strength. Detailed Implementation

[0035] The present invention will be further described below with reference to the embodiments. However, the present invention is not limited to the listed embodiments, but should also include equivalent improvements and modifications of the technical solutions defined in the appended claims of the present invention.

[0036] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0037] In the following examples and comparative examples:

[0038] (1) Main raw materials

[0039] Polypropylene L5E89 is ordinary linear polypropylene, purchased from Baotou Coal Chemical Branch of Shenhua Coal-to-Oil Chemical Co., Ltd.

[0040] The short glass fiber was purchased from Chongqing International Composite Materials Co., Ltd., and its grade was ECS303.

[0041] The continuous long glass fiber was purchased from Owens Corning, grade 4849;

[0042] The carbon fiber was purchased from Toray Industries, Inc. of Japan, grade T700.

[0043] Polar monomer-grafted polypropylene can be commercially available or prepared by methods well known in the art, such as solution grafting, melt grafting, solid-phase grafting, and radiation grafting.

[0044] (2) Characterization and testing

[0045] The tensile strength of the fiber-reinforced polypropylene microporous foam material was determined according to ISO 1929:2009, and the flexural modulus was determined according to ISO 1209-2:2007.

[0046] All portions mentioned refer to parts by weight.

[0047] The following examples illustrate the fiber-reinforced polypropylene microporous foam material and its preparation method of the present invention.

[0048] Example 1

[0049] Weigh 99 parts of maleic anhydride-grafted polypropylene (grafting rate 1.0%) and 1 part of tetraethylenepentamine, and mix thoroughly. Add the completely mixed raw materials to an AK26 twin-screw extruder. Set the twin-screw extruder temperature to 220℃. Set the extruder speed to 150 r / min and the feed rate to 8 Hz. Extrude and granulate, and dry the resulting product at 90℃ for 60 min to obtain the polypropylene modifier.

[0050] Ten parts of the prepared polypropylene modifier, 77 parts of Shenhua polypropylene product (brand name L5E89), and 3 parts of maleic anhydride-grafted polypropylene were weighed and mixed evenly, then added to an AK26 twin-screw extruder for co-extrusion. Ten parts of short glass fibers were added through the side feed port. The extrusion temperature was set to 220℃. The extruder speed was 200 r / min, and the feed speed was 10 Hz. After extrusion granulation, the product was dried at 100℃ for 30 min to obtain fiber-reinforced polypropylene particles. The fiber-reinforced polypropylene particles were added to the twin-screw extruder, and fiber-reinforced polypropylene sheets with a thickness of 10 mm were extruded at 200℃.

[0051] Fiber-reinforced polypropylene sheets were cut into 1000mm long and 800mm wide pieces. These pieces were then placed in a molding compound foaming device. At 200℃ and 9MPa, supercritical CO2 was introduced, and the mixture was heated and held under pressure for 60 minutes. After cooling to 160℃, the pressure was released, and the mold was opened to obtain glass fiber reinforced polypropylene microporous foam material. The apparent density was measured, and the foaming ratio was calculated. The flexural and tensile properties were tested. The test data are shown in Table 1.

[0052] Example 2

[0053] Weigh 99.5 parts of methyl methacrylate-grafted polypropylene (grafting rate 1.2%) and mix thoroughly with 0.5 parts of diethylenetriamine. Add the fully mixed raw material to an AK26 twin-screw extruder at a temperature of 210℃. The extruder speed is 250 r / min, and the feed rate is 15 Hz. Extrusion granulation is performed, and the resulting product is dried at 95℃ for 30 min to obtain the polypropylene modifier.

[0054] Eight parts of the prepared polypropylene modifier, 75 parts of Shenhua polypropylene product (brand name L5E89), and 2 parts of methyl methacrylate-grafted polypropylene were weighed and mixed evenly before being added to an AK26 twin-screw extruder. Fifteen parts of short glass fibers were added through the side feed port, and the mixture was co-extruded. The extrusion temperature was set to 200℃. The extruder speed was 210 r / min, and the feed speed was 7 Hz. After granulation, the mixture was dried at 100℃ for 30 min to obtain fiber-reinforced polypropylene particles. The fiber-reinforced polypropylene particles were added to the twin-screw extruder, and fiber-reinforced polypropylene sheets with a thickness of 10 mm were extruded at 220℃.

[0055] Fiber-reinforced polypropylene sheets were cut into 1000mm long and 800mm wide pieces. These pieces were then placed in a molding compound foaming device. At 210℃ and 8MPa, supercritical CO2 was introduced, and the mixture was heated and held under pressure for 50 minutes. After cooling to 164℃, the pressure was released, and the mold was opened to obtain glass fiber reinforced polypropylene microporous foam material. The apparent density was measured, and the foaming ratio was calculated. The flexural and tensile properties were tested. The test data are shown in Table 1.

[0056] Example 3

[0057] Weigh 98 parts of isooctyl acrylate-grafted polypropylene (grafting rate 0.9%) and mix thoroughly with 2 parts of 1,8-diaminooctane. Add the fully mixed raw material to an AK26 twin-screw extruder at a temperature of 190℃. The extruder speed is 250 r / min, and the feed rate is 11 Hz. Extrusion granulation is performed, and the resulting product is dried at 90℃ for 40 min to obtain the polypropylene modifier.

[0058] Nine parts of the prepared polypropylene modifier, 78 parts of Shenhua polypropylene product (brand name L5E89), and 3 parts of acrylic acid-grafted polypropylene were weighed and mixed evenly before being added to an AK26 twin-screw extruder. Ten parts of carbon fiber were added through the fiber feeding port for co-extrusion. The extrusion temperature was set to 198℃. The extruder speed was 220 r / min, and the feed speed was 10 Hz. After granulation, the product was dried at 100℃ for 30 min to obtain fiber-reinforced polypropylene particles. The fiber-reinforced polypropylene particles were added to the twin-screw extruder, and fiber-reinforced polypropylene sheets with a thickness of 10 mm were extruded at 210℃.

[0059] Fiber-reinforced polypropylene sheets were cut into 1000mm long and 800mm wide pieces. These pieces were then placed in a molding compound foaming device. At 195℃ and 7MPa, supercritical nitrogen was introduced, and the mixture was heated and held under pressure for 80 minutes. After cooling to 162℃, the pressure was released, and the mold was opened to obtain carbon fiber-reinforced polypropylene microporous foam material. The apparent density was measured, and the foaming ratio was calculated. The flexural and tensile properties were tested. The test data are shown in Table 1.

[0060] Example 4

[0061] Weigh 98.5 parts of ethylene tert-carbonate grafted polypropylene (grafting rate 1%) and mix thoroughly with 1.5 parts of 1,9-diaminononane. Add the fully mixed raw material to an AK26 twin-screw extruder at a temperature of 198℃. The extruder speed is 205 r / min, and the feed rate is 15 Hz. Extrusion granulation is performed, and the resulting product is dried at 95℃ for 30 min to obtain the polypropylene modifier.

[0062] Five parts of the prepared polypropylene modifier, 80 parts of Shenhua polypropylene product (brand name L5E89), and 1 part of acrylic acid-grafted polypropylene were weighed and mixed evenly, then added to an AK26 twin-screw extruder. Fourteen parts of continuous long glass fibers were added through the fiber feeding port, and the mixture was co-extruded. The extrusion temperature was set to 220℃. The extruder speed was 280 r / min, and the feed speed was 10 Hz. After granulation, the mixture was dried at 90℃ for 60 min to obtain fiber-reinforced polypropylene particles. The fiber-reinforced polypropylene particles were added to the twin-screw extruder, and fiber-reinforced polypropylene sheets with a thickness of 10 mm were extruded at 220℃.

[0063] Fiber-reinforced polypropylene sheets were cut into 1000mm long and 800mm wide pieces. These pieces were then placed in a molding compound foaming device. At 190℃ and 8MPa, supercritical nitrogen was introduced, and the mixture was heated and held under pressure for 60 minutes. After cooling to 150℃, the pressure was released, and the mold was opened to obtain glass fiber reinforced polypropylene microporous foam material. The apparent density was measured, and the foaming ratio was calculated. The flexural and tensile properties were tested. The test data are shown in Table 1.

[0064] Example 5

[0065] Weigh 99.2 parts of glycidyl methacrylate-grafted polypropylene (grafting rate 1.5%) and mix thoroughly with 0.8 parts of phenoxyaniline. Add the fully mixed raw material to an AK26 twin-screw extruder at a temperature of 195℃. The extruder speed is 300 r / min, and the feed rate is 17 Hz. Extrusion granulation is performed, and the resulting product is dried at 95℃ for 30 min to obtain the polypropylene modifier.

[0066] Weigh 12 parts of the prepared polypropylene modifier, 80 parts of Shenhua polypropylene product (brand name L5E89), and 3 parts of glycidyl methacrylate-grafted polypropylene, mix them evenly, and add them to an AK26 twin-screw extruder. Add 5 parts of continuous long glass fiber through the fiber feeding port and co-extrude. The extrusion temperature is set to 210℃. The extruder speed is 200 r / min, and the feed speed is 10 Hz. After granulation, dry at 95℃ for 40 min to obtain fiber-reinforced polypropylene particles. Add the fiber-reinforced polypropylene particles to the twin-screw extruder and extrude fiber-reinforced polypropylene sheets with a thickness of 10 mm at 210℃.

[0067] Fiber-reinforced polypropylene sheets were cut into 1000mm long and 800mm wide pieces. These pieces were then placed in a molding compound foaming device. At 195℃ and 9MPa, supercritical nitrogen was introduced, and the mixture was heated and pressure-held for 40 minutes. After cooling to 160℃, the pressure was released, and the mold was opened to obtain glass fiber reinforced polypropylene microporous foam material. The apparent density was measured, and the foaming ratio was calculated. The flexural and tensile properties were tested. The test data are shown in Table 1.

[0068] Example 6

[0069] Weigh 99.2 parts of glycidyl methacrylate-grafted polypropylene (grafting rate 1.5%) and mix thoroughly with 0.8 parts of phenoxyaniline. Add the fully mixed raw material to an AK26 twin-screw extruder at a temperature of 195℃. The extruder speed is 300 r / min, and the feed rate is 17 Hz. Extrusion granulation is performed, and the resulting product is dried at 95℃ for 30 min to obtain the polypropylene modifier.

[0070] Weigh out 11 parts of the prepared polypropylene modifier, 71 parts of Shenhua polypropylene product (brand name L5E89), and 2 parts of glycidyl methacrylate-grafted polypropylene, mix them evenly, and add them to an AK26 twin-screw extruder. Add 16 parts of continuous long glass fibers through the fiber feeding port, and co-extrude. The extrusion temperature is set to 210℃. The extruder speed is 200 r / min, and the feed speed is 10 Hz. After granulation, dry at 95℃ for 40 min to obtain fiber-reinforced polypropylene particles. Add the fiber-reinforced polypropylene particles to the twin-screw extruder, and extrude fiber-reinforced polypropylene sheets with a thickness of 10 mm at 210℃.

[0071] Fiber-reinforced polypropylene sheets were cut into 1000mm long and 800mm wide pieces. These pieces were then placed in a molding compound foaming device. At 195℃ and 9MPa, supercritical nitrogen was introduced, and the mixture was heated and pressure-held for 40 minutes. After cooling to 160℃, the pressure was released, and the mold was opened to obtain glass fiber reinforced polypropylene microporous foam material. The apparent density was measured, and the foaming ratio was calculated. The flexural and tensile properties were tested. The test data are shown in Table 1.

[0072] Comparative Example 1

[0073] The experiment was conducted without glass fiber, following the method described in Example 1.

[0074] Weigh 99 parts of maleic anhydride-grafted polypropylene (grafting rate 1.0%) and 1 part of tetraethylenepentamine, and mix thoroughly. Add the completely mixed raw materials to an AK26 twin-screw extruder. Set the twin-screw extruder temperature to 220℃. Set the extruder speed to 150 r / min and the feed rate to 8 Hz. Extrude and granulate, and dry the resulting product at 90℃ for 60 min to obtain the polypropylene modifier.

[0075] Weigh 10 parts of the prepared polypropylene modifier and 90 parts of Shenhua polypropylene product (brand name L5E89), mix them evenly, and then add them to an AK26 twin-screw extruder for co-extrusion. The extrusion temperature is set to 220℃. The extruder speed is 200 r / min, and the feed speed is 10 Hz. After extrusion granulation, dry at 100℃ for 30 min to obtain polypropylene particles. Add the polypropylene particles to the twin-screw extruder and extrude polypropylene sheets with a thickness of 10 mm at 200℃.

[0076] Polypropylene sheets were cut into 1000mm long and 800mm wide pieces. These pieces were then placed in a molding compound of a foaming equipment. At 200℃ and 9MPa, supercritical CO2 was introduced, and the mixture was heated and held under pressure for 60 minutes. After cooling to 160℃, the pressure was released, and the mold was opened to obtain microporous polypropylene foam material. The apparent density was measured, and the expansion ratio was calculated. The flexural and tensile properties were tested. The test data are shown in Table 1.

[0077] Comparative Example 2

[0078] The experiment was conducted according to the method of Example 1, without the addition of a modifier.

[0079] 87 parts of Shenhua polypropylene product (brand name L5E89) and 3 parts of maleic anhydride-grafted polypropylene were weighed, mixed evenly, and then added to an AK26 twin-screw extruder for co-extrusion. 10 parts of short glass fibers were added through the side feed port. The extrusion temperature was set to 220℃. The extruder speed was 200 r / min, and the feed speed was 10 Hz. After extrusion granulation, the product was dried at 100℃ for 30 min to obtain fiber-reinforced polypropylene particles. The fiber-reinforced polypropylene particles were added to the twin-screw extruder, and fiber-reinforced polypropylene sheets with a thickness of 10 mm were extruded at 200℃.

[0080] Fiber-reinforced polypropylene sheets were cut into 1000mm long and 800mm wide pieces. These pieces were then placed in a molding compound foaming device. At 200℃ and 9MPa, supercritical CO2 was introduced, and the mixture was heated and held under pressure for 60 minutes. After cooling to 160℃, the pressure was released, and the mold was opened to obtain glass fiber reinforced polypropylene microporous foam material. The apparent density was measured, and the foaming ratio was calculated. The flexural and tensile properties were tested. The test data are shown in Table 1.

[0081] Comparative Example 3

[0082] The test was conducted using air, following the method described in Example 1.

[0083] Weigh 99 parts of maleic anhydride-grafted polypropylene (grafting rate 1.0%) and 1 part of tetraethylenepentamine, and mix thoroughly. Add the completely mixed raw materials to an AK26 twin-screw extruder. Set the twin-screw extruder temperature to 220℃. Set the extruder speed to 150 r / min and the feed rate to 8 Hz. Extrude and granulate, and dry the resulting product at 90℃ for 60 min to obtain the polypropylene modifier.

[0084] Ten parts of the prepared polypropylene modifier, 77 parts of Shenhua polypropylene product (brand name L5E89), and 3 parts of maleic anhydride-grafted polypropylene were weighed and mixed evenly, then added to an AK26 twin-screw extruder for co-extrusion. Ten parts of short glass fibers were added through the side feed port. The extrusion temperature was set to 220℃. The extruder speed was 200 r / min, and the feed speed was 10 Hz. After extrusion granulation, the product was dried at 100℃ for 30 min to obtain fiber-reinforced polypropylene particles. The fiber-reinforced polypropylene particles were added to the twin-screw extruder, and fiber-reinforced polypropylene sheets with a thickness of 10 mm were extruded at 200℃.

[0085] Fiber-reinforced polypropylene sheets were cut into 1000mm long and 800mm wide pieces. These pieces were then placed in a molding compound of a foaming equipment. Air was introduced at 200℃ and 9MPa, and the mixture was heated and pressure-held for 60 minutes. After cooling to 160℃, the pressure was released, and the mold was opened to obtain glass fiber reinforced polypropylene microporous foam material. The apparent density was measured, and the expansion ratio was calculated. The flexural and tensile properties were tested. The test data are shown in Table 1.

[0086] Table 1 lists the performance test data for each embodiment and comparative product.

[0087] Table 1

[0088] Example 1 26 20 1.81 28.76 Example 2 25 24 1.95 30.22 Example 3 26 21 2.26 35.12 Example 4 24 29 1.89 29.54 Example 5 29 15 2.08 32.26 Example 6 33 12 2.61 37.91 Comparative Example 1 24 22 0.98 10.9 Comparative Example 2 4 179 2.87 40.07 Comparative Example 3 2 227 2.96 41.91

[0089] As can be seen from the results of the examples, comparative examples, and Table 1, the fiber-reinforced polypropylene microporous foam materials prepared in Examples 1-6 of this invention have a foaming ratio greater than 20 times and an average pore size of about 20 μm, exhibiting high foaming ratio and small average pore size. Tensile strength and flexural modulus are significantly improved. They possess the advantages of being lightweight and having high mechanical strength. In Example 6, following the optimized scheme, the mass percentages of polypropylene modifier, compatibilizer, and inorganic fiber are all within the preferred range. The optimized raw material formulation results in high melt strength and high interfacial bonding strength between polypropylene resin and inorganic fiber, thus producing a foam material with a high foaming ratio, smaller average pore size, and optimal mechanical properties. Comparative Example 1, without the addition of glass fiber, produces a polypropylene microporous foam material with lower tensile strength and flexural modulus, exhibiting poorer mechanical properties. Comparative Example 2, without the addition of polypropylene modifier, produces a fiber-reinforced polypropylene foam material with a low foaming ratio of only 4 times and an average pore size greater than 100 μm, exhibiting poor foaming performance. Comparative Example 3 used air as a foaming agent, and the foaming ratio of the prepared fiber-reinforced polypropylene foam material was only 2 times, with an average pore size greater than 200 micrometers.

[0090] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is impossible to exhaustively list all embodiments here. All obvious variations or modifications derived from the technical solutions of the present invention are within the spirit and scope of the present invention.

Claims

1. A fiber-reinforced polypropylene microporous foam material, characterized in that: By weight percentage, it includes 70-89% polypropylene, 5-15% polypropylene modifier, 1-3% compatibilizer, and 5-19% inorganic fiber. The polypropylene modifier is prepared by grafting a polar monomer onto polypropylene and reacting it with an amino-containing compound, followed by extrusion granulation. The amino-containing compound is compound A or compound B, or a mixture of both. Compound A is an organic compound containing an amino group, an ether bond, and an aryl group. Compound B is one or more of alkyl diamine, alkylene diamine, alkylene triamine, alkylene tetraamine, alkylene pentaamine, aryl diamine, aryl triamine, and aryl tetraamine. The inorganic material fiber is at least one of glass fiber and carbon fiber. The polar monomer is one of acrylic acid, methacrylic acid, maleic anhydride, methyl methacrylate, vinyl tert-carbonate, butyl acrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, ethyl 2-methacrylate, allyl methacrylate, hydroxyethyl methacrylate, glycidyl methacrylate, and isooctyl acrylate. The preparation method of the fiber-reinforced polypropylene microporous foam material includes the following steps: 1) Mix polypropylene, polypropylene modifier, and compatibilizer evenly, add inorganic fiber, melt extrude, cool and pelletize, and dry to obtain fiber-reinforced polypropylene particles. 2) The fiber-reinforced polypropylene particles are extruded to obtain fiber-reinforced polypropylene sheets; 3) Supercritical gas is introduced into the fiber-reinforced polypropylene sheet for compression molding to obtain the fiber-reinforced polypropylene microporous foam material; By weight percentage, the content of the polar monomer grafted polypropylene in the polypropylene modifier is 98-99.8%, the content of compound A is ≤2%, and the content of compound B is ≤2%.

2. The fiber-reinforced polypropylene microporous foam material according to claim 1, characterized in that: Compound A is one or more selected from phenoxyaniline, 3,3',4,4'-tetraaminodiphenyl ether, 3,4'-diaminodiphenyl ether, and 4,4'-diaminodiphenyl ether; and / or Compound B is one or more of the following: C2-12 alkyl diamine, C2-12 alkylene diamine, C2-C12 alkylene triamine, C2-C12 alkylene tetraamine, C12 alkylene pentamine, C6-C18 aryl diamine, C6-C18 aryl triamine, and C6-C18 aryl tetraamine.

3. The fiber-reinforced polypropylene microporous foam material according to claim 1, characterized in that: The composition comprises 71-80% polypropylene, 5-12% polypropylene modifier, 1-2% compatibilizer, and 10-19% inorganic fiber.

4. The fiber-reinforced polypropylene microporous foam material according to claim 1, characterized in that: In the polar monomer-grafted polypropylene, the polar monomer is one of acrylic acid, methacrylic acid, methyl acrylate, and methyl methacrylate.

5. The fiber-reinforced polypropylene microporous foam material according to any one of claims 1-4, characterized in that: The preparation method of the polypropylene modifier includes: reacting polypropylene grafted with a polar monomer and an amino-containing compound at a reaction extrusion temperature of 150~220℃ and extruding and granulating, and drying at 80~95 ºC for 30~120 min to obtain the polypropylene modifier.

6. The fiber-reinforced polypropylene microporous foam material according to claim 1, characterized in that: The polypropylene is homopolymer polypropylene, block copolymer polypropylene, or random copolymer polypropylene; and / or... The glass fiber is one of continuous long glass fiber and short glass fiber; the carbon fiber is one of polyacrylonitrile-based carbon fiber, viscose-based carbon fiber, and pitch-based carbon fiber; and / or, The compatibilizer is a polar monomer grafted polymer, which is polypropylene or polyethylene, and the polar monomer is one of acrylic acid, methacrylic acid, maleic anhydride, methyl methacrylate, ethylene tert-carbonate, butyl acrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, ethyl 2-methacrylate, allyl methacrylate, hydroxyethyl methacrylate, glycidyl methacrylate, and isooctyl acrylate.

7. The fiber-reinforced polypropylene microporous foam material according to claim 6, characterized in that: The glass fiber is a long glass fiber; the carbon fiber is a polyacrylonitrile-based carbon fiber; and / or, The polar monomer of the compatibilizer is one of acrylic acid, methacrylic acid, methyl acrylate, and methyl methacrylate.

8. A method for preparing the fiber-reinforced polypropylene microporous foam material according to any one of claims 1-7, characterized in that... The steps include the following: 1) Mix polypropylene, polypropylene modifier, and compatibilizer evenly, add inorganic fiber, melt extrude, cool and pelletize, and dry to obtain fiber-reinforced polypropylene particles. 2) The fiber-reinforced polypropylene particles are extruded to obtain fiber-reinforced polypropylene sheets; 3) Supercritical gas is introduced into the fiber-reinforced polypropylene sheet for compression molding to obtain the fiber-reinforced polypropylene microporous foam material; The supercritical gas is one of nitrogen, carbon dioxide, and butane; In step 1), the extrusion temperature is 170℃~220℃; and / or, In step 2), the extrusion temperature is 180℃~220℃; and / or, In step 3), supercritical gas is introduced into the fiber-reinforced polypropylene sheet at a temperature of 180℃~230℃ and a pressure of 7~10MPa to form a polypropylene / supercritical fluid single-phase solution. The temperature is then lowered to 130℃~170℃, the pressure is released, the mold is opened, and the fiber-reinforced polypropylene microporous foam material is obtained.

9. The method for preparing fiber-reinforced polypropylene microporous foam material according to claim 8, characterized in that, The fiber-reinforced polypropylene microporous foam material has a foaming ratio of 5-40 times, an average pore size of 5-50 μm, a flexural modulus greater than 12 MPa, and a tensile strength greater than 1.2 MPa.