Foaming type polypropylene wave-absorbing material and preparation method thereof

Abstract

The invention discloses a foamed polypropylene wave-absorbing material and a preparation method thereof. The preparation method comprises the following steps: mixing and grinding carbon nanotubes and ferric salt into powder, adding the powder into trimesic acid and N, N-dimethylformamide DMF, uniformly stirring, sealing, heating and reacting at 135-150 DEG C for 3-5 hours, and purifying a reaction product to obtain a powdery precursor; calcining the precursor in an air atmosphere at the temperature of 300 to 380 DEG C to obtain a Fe3O4-CNTs composite material; polypropylene resin, the composite material and an auxiliary agent are mixed, and extrusion granulation is performed through a double-screw extruder; and keeping the obtained particles for 3-10 minutes under the conditions that the pressure is 1.8-2.5 MPa and the temperature is 165-180 DEG C in a nitrogen atmosphere, and releasing the pressure to obtain the foaming type polypropylene wave-absorbing material. The foaming type polypropylene wave-absorbing material is low in internal stress, light in weight, high in straightness, low in sink mark and high in strength, good impedance matching is formed between foam material layers on the basis of the original magnetoelectric coupling effect of a composite material, the wave-absorbing capacity is high, and the manufacturing cost is low.

Description

Technical Field

[0001] The invention belongs to the technical field of new material development, and in particular relates to a foamed polypropylene absorbing material and a preparation method thereof. Background Art

[0002] Lightweight, energy-saving and environmentally friendly, and efficient and low-cost production have always been the goals that the automotive industry continues to pursue. Since polypropylene material is a material with a very high cost-effectiveness (low specific gravity, good mechanical properties and recyclability, excellent molding characteristics and low price), its application in automotive plastic parts has been continuously expanded. It has been widely used in major automotive plastic parts such as bumpers, car dashboards, door panels, central channels, decorative pillars, and luggage compartments. In addition, with the rapid development of electrification and intelligence of automobiles, accidents such as car loss of control caused by electromagnetic wave pollution and interference problems occur from time to time. Therefore, automotive plastic parts must not only consider lightweight and high efficiency, but also have the characteristics of preventing or eliminating electromagnetic wave pollution sources.

[0003] Expanded polypropyene is a high-performance foamed resin with the characteristics of light weight, impact resistance, drug resistance, heat resistance, light weight, green environmental protection, excellent acid and alkali resistance and high cost performance. In addition, the microporous structure in the expanded polypropyene resin also has a certain effect of broadband absorption of electromagnetic waves. In addition, composite materials prepared from expanded polypropyene resin and functional fillers with specific electromagnetic properties have become a hot topic of research today. There are many materials with specific electromagnetic properties, such as carbon nanotubes, graphene, ferrites, hard magnetic materials, metal powders, etc., but most of the functional fillers that can match well with expanded polypropyene resin are complicated to prepare or relatively expensive, such as graphene, which has high cost and large dosage, and is not suitable for the application of a wide range of automotive plastic parts. Summary of the invention

[0004] In order to overcome the shortcomings and deficiencies of the prior art, an object of the present invention is to provide a foamed polypropylene absorbing material and a preparation method thereof.

[0005] The present invention is achieved by a method for preparing a foamed polypropylene absorbing material, the method comprising the following steps:

[0006] (1) 3-9 mmol carbon nanotubes and 15-20 mmol iron salt are mixed and ground into powder, added into 20-30 mL trimesic acid and 60-150 mL N,N-dimethylformamide (DMF), stirred evenly, sealed, heated at 135-150° C. for reaction for 3-5 h, and the reaction product is purified to obtain a powdery precursor;

[0007] (2) calcining the precursor at 300-380°C in an air atmosphere to obtain Fe 3 O 4 -CNTs composites;

[0008] (3) mixing 20 to 30 parts by weight of polypropylene resin, 2 to 3 parts by weight of composite material and 0.5 to 2.5 parts by weight of additives, and extruding and granulating the mixture through a twin-screw extruder;

[0009] (4) Under a nitrogen atmosphere, the particles obtained in step (3) are maintained at 1.8 MPa to 2.5 MPa and 165° C. to 180° C. for 3 to 10 min, and the pressure is released to obtain a foamed polypropylene absorbing material.

[0010] Preferably, in step (1), the iron salt is selected from at least one of ferric nitrate, ferric chloride and ferric acetate.

[0011] Preferably, in step (2), the temperature is raised to 360° C. at a rate of 5° C. / min and calcined for 2 hours.

[0012] Preferably, in step (3), the polypropylene resin has a density of 0.89 to 0.91 g / cm 3 , the melt index is 8 to 10 g / min.

[0013] Preferably, in step (3), the auxiliary agent is selected from at least one of a plasticizer, a lubricant, an antioxidant and a dispersant.

[0014] Preferably, the plasticizer is selected from at least one of diisononyl phthalate, di-n-butyl phthalate and dioctyl adipate;

[0015] Preferably, the lubricant is selected from at least one of oleic acid amide and low molecular weight paraffin;

[0016] Preferably, the antioxidant is selected from at least one of alkylphenol and organic phosphite;

[0017] Preferably, the dispersant is selected from at least one of AB dispersants and alkyl naphthalene sulfonates.

[0018] Preferably, in step (4), the pressure relief is carried out at a temperature of 70 to 80° C. and a rate of 0.5 to 0.6 MPa / min.

[0019] The invention further discloses a foamed polypropylene wave absorbing material prepared by the method.

[0020] The present invention overcomes the shortcomings of the prior art and provides a foamed polypropylene absorbing material and a preparation method thereof. The present invention uses trimesic acid as an organic ligand, trivalent iron as a skeleton metal, and introduces carbon nanotubes (CNTs) to first prepare a uniform spherical Fe-MOFs / CNTs composite material precursor; on this basis, the obtained Fe-MOFs / CNTs composite material precursor is calcined in an air atmosphere to obtain a uniform nanoscale hollow spherical Fe 3 O 4 -CNTs composite material, the composite material has good magnetic properties and electromagnetic wave absorption capacity, and due to the direct introduction of carbon nanotubes in the preparation process, the composite material can be better compounded with polypropylene resin and the like. On this basis, the present invention mixes polypropylene resin, composite material and additives, extrude and granulate through a twin-screw extruder, and in a nitrogen atmosphere, keeps the obtained particles at 1.8MPa-2.5Mpa and 165℃-180℃ for 3-10min, and releases the pressure to obtain a foamed polypropylene absorbing material.

[0021] Compared with the shortcomings and deficiencies of the prior art, the present invention has the following beneficial effects: the foamed polypropylene absorbing material of the present invention has micron-level closed micropores distributed inside, the foaming ratio reaches 3 to 5 times, the surface layer is a skin-core structure of a dense layer, low internal stress, light weight, high flatness, low shrinkage, and high strength. On the basis of the original magnetoelectric coupling effect of the composite material, good impedance matching is formed between the foam material layers, further enhancing the overall absorbing ability, and the manufacturing cost is low, which can well meet the plastic product needs of industries such as electric intelligent vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The Fe prepared in Example 1 of the present invention 3 O 4 -TEM images of CNTs composites;

[0023] Figure 2 This is the absorbing performance of the foamed polypropylene absorbing material 1 prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0025] Example 1

[0026] (1) 3 mmol of carbon nanotubes and 20 mmol of ferric nitrate were mixed and ground into powder, added into 20 mL of trimesic acid and 150 mL of N,N-dimethylformamide (DMF), stirred evenly, sealed, and heated at 150° C. for 3 h. The reaction product was purified to obtain a powdery precursor;

[0027] (2) The precursor was calcined in an air atmosphere at a temperature of 5°C / min to 380°C to obtain Fe 3 O 4 -CNTs composites;

[0028] (3) 2 kg of polypropylene resin, 0.2 kg of composite material, 0.05 kg of diisononyl phthalate, 0.1 kg of oleic acid amide, and 0.1 kg of AB dispersant were mixed and extruded into granules by a twin-screw extruder; wherein the density of the polypropylene resin was 0.89 to 0.91 g / cm 3 , the melt index is 8-10g / min, the aspect ratio of the twin-screw extruder is 20:1, the speed is 100r / min, it is divided into seven zones from the feed end to the discharge end, and the extrusion temperature is set as follows: 180°C for the first zone, 200°C for the second zone, 210°C for the third zone, 220°C for the fourth zone, 235°C for the fifth zone, 220°C for the sixth zone, and 210°C for the seventh zone;

[0029] (4) Under a nitrogen atmosphere, the particles obtained in step (3) were maintained at 2.5 MPa and 165° C. for 10 min, and the pressure was released at 80° C. at a rate of 0.5 MPa / min to obtain a foamed polypropylene absorbing material 1.

[0030] Example 2

[0031] (1) 9 mmol of carbon nanotubes and 15 mmol of ferric chloride were mixed and ground into powder, added into 30 mL of trimesic acid and 60 mL of N,N-dimethylformamide (DMF), stirred evenly, sealed, and heated at 135° C. for 5 h. The reaction product was purified to obtain a powdery precursor;

[0032] (2) The precursor was calcined in an air atmosphere at a temperature of 5°C / min to 300°C to obtain Fe 3 O 4 -CNTs composites;

[0033] (3) 3 kg of polypropylene resin, 0.3 kg of composite material, 0.02 kg of di-n-butyl phthalate, 0.01 kg of low molecular weight paraffin, 0.01 kg of organic phosphite, and 0.01 kg of sodium alkylnaphthalene sulfonate are mixed and extruded into granules by a twin-screw extruder; wherein the density of the polypropylene resin is 0.89 to 0.91 g / cm 3, the melt index is 8-10g / min, the aspect ratio of the twin-screw extruder is 20:1, the speed is 100r / min, it is divided into seven zones from the feed end to the discharge end, and the extrusion temperature is set as follows: 180°C for the first zone, 200°C for the second zone, 210°C for the third zone, 220°C for the fourth zone, 235°C for the fifth zone, 220°C for the sixth zone, and 210°C for the seventh zone;

[0034] (4) Under a nitrogen atmosphere, the particles obtained in step (3) were maintained at 2.5 MPa and 180° C. for 3 min, and the pressure was released at 70° C. at a rate of 0.6 MPa / min to obtain a foamed polypropylene absorbing material 2.

[0035] Example 3

[0036] (1) 5 mmol of carbon nanotubes and 18 mmol of ferric acetate were mixed and ground into powder, added into 25 mL of trimesic acid and 100 mL of N,N-dimethylformamide (DMF), stirred evenly, sealed, and heated at 140° C. for 4 h. The reaction product was purified to obtain a powdery precursor;

[0037] (2) The precursor was calcined in an air atmosphere at a temperature of 5°C / min to 350°C to obtain Fe 3 O 4 -CNTs composites;

[0038] (3) 2.5 kg of polypropylene resin, 0.25 kg of composite material, 0.05 kg of dioctyl adipate, 0.05 kg of oleic acid amide, 0.05 kg of alkylphenol, and 0.05 kg of AB dispersant were mixed and extruded into granules by a twin-screw extruder; wherein the density of the polypropylene resin was 0.89 to 0.91 g / cm 3 , the melt index is 8-10g / min, the aspect ratio of the twin-screw extruder is 20:1, the speed is 100r / min, it is divided into seven zones from the feed end to the discharge end, and the extrusion temperature is set as follows: 180°C for the first zone, 200°C for the second zone, 210°C for the third zone, 220°C for the fourth zone, 235°C for the fifth zone, 220°C for the sixth zone, and 210°C for the seventh zone;

[0039] (4) Under a nitrogen atmosphere, the particles obtained in step (3) were maintained at 2.0 MPa and 175° C. for 5 min, and the pressure was released at 75° C. at a rate of 0.5 MPa / min to obtain a foamed polypropylene absorbing material 3.

[0040] Effect Example

[0041] 1. The Fe prepared in Example 1 3 O 4 -CNTs composites were observed, such as Figure 1As shown, the Fe 3 O 4 -CNTs composite material is spherical in shape, with the wall and the middle of the sphere having different brightness, showing a hollow frame structure, and small CNTs particles attached to the sphere wall.

[0042] 2. The performance of the foamed polypropylene absorbing material 1 was tested. The test results were as follows: Density: 0.61 g / cm 3 ;Tensile strength: 18MPa;Flexural modulus: 1380MPa;Notched impact strength: 30kJ / m 2 ; Light aging: Level 4; Scratch resistance (△L): 0.5; Odor: Level 6, Pore size: 10-100 microns.

[0043] The results show that the foamed polypropylene absorbing material 1 of the present invention meets the requirements of standards such as Q / 320.501SZRJ 07-2015 and Shanghai General GMW15549.

[0044] 3. Prepare a plate from the foamed polypropylene absorbing material 1, and use an engraving machine to carve a ring to obtain a coaxial ring for absorbing test. The absorbing performance is tested by the coaxial method. The test instrument is a vector network analyzer VNA. The test frequency range is 2 to 18 GHz. The test results are as follows: Figure 1 As shown. Figure 1 It can be seen that in the test frequency range of 2 to 18 GHz, the foamed polypropylene absorbing material 1 has good absorbing performance and can well meet the absorbing performance requirements for plastic components in the fields of smart cars and the like.

[0045] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a foamed polypropylene absorbing material, characterized in that: The method comprises the following steps: (1) 3-9 mmol carbon nanotubes and 15-20 mmol iron salt are mixed and ground into powder, added into 20-30 mL trimesic acid and 60-150 mL N,N-dimethylformamide (DMF), stirred evenly, sealed, heated at 135-150° C. for reaction for 3-5 h, and the reaction product is purified to obtain a powdery precursor; (2) calcining the precursor at 300-380° C. in an air atmosphere to obtain a Fe3O4-CNTs composite material; (3) mixing 20 to 30 parts by weight of polypropylene resin, 2 to 3 parts by weight of composite material and 0.5 to 2.5 parts by weight of additives, and extruding and granulating the mixture through a twin-screw extruder; (4) Under a nitrogen atmosphere, the particles obtained in step (3) are maintained at 1.8 MPa to 2.5 MPa and 165° C. to 180° C. for 3 to 10 min, and the pressure is released to obtain a foamed polypropylene absorbing material.

2. The method according to claim 1, characterized in that In step (1), the iron salt is selected from at least one of ferric nitrate, ferric chloride and ferric acetate.

3. The method according to claim 1, characterized in that In step (2), the temperature is raised to 360°C at a rate of 5°C / min and calcined for 2 hours.

4. The method according to claim 1, characterized in that In step (3), the polypropylene resin has a density of 0.89 to 0.91 g / cm 3 , the melt index is 8~10g / min.

5. The method according to claim 1, characterized in that In step (3), the auxiliary agent is selected from at least one of a plasticizer, a lubricant, an antioxidant, and a dispersant.

6. The method according to claim 5, characterized in that The plasticizer is selected from at least one of diisononyl phthalate, di-n-butyl phthalate and dioctyl adipate; The lubricant is selected from at least one of oleic acid amide and low molecular weight paraffin; The antioxidant is selected from at least one of alkylphenol and organic phosphite; The dispersant is selected from at least one of AB dispersants and alkylnaphthalene sulfonates.

7. The method according to claim 1, characterized in that In step (4), the pressure relief is carried out at a temperature of 70 to 80° C. at a rate of 0.5 to 0.6 MPa / min.

8. The foamed polypropylene absorbing material prepared by the method according to any one of claims 1 to 7.

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