Mofs / p-aramid pulp composite material, preparation method and application thereof

Abstract

The application belongs to the technical field of composites, and particularly relates to a MOFs / p-aramid pulp composite material and a preparation method and application thereof. The preparation method comprises the following steps: modifying the surface of p-aramid pulp by a dopamine self-polymerization method under room temperature conditions to obtain modified p-aramid pulp; soaking the modified p-aramid pulp in a zinc ion solution to obtain a mixed solution; and adding the mixed solution to an organic ligand solution to obtain a MOFs / p-aramid pulp composite material. The preparation method has the advantages of mild reaction conditions and simple operation. The MOFs / p-aramid pulp composite material has excellent thermal stability, excellent ultraviolet resistance and a high specific surface area, and has important application value in the fields of friction sealing, aerospace thermal insulation systems or the manufacturing of lightweight and heat-resistant parts.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of composite materials, and particularly relates to a MOFs / p-aramid pulp composite material and a preparation method and application thereof. BACKGROUND

[0002] The p-aramid pulp is a new type of synthetic fiber prepared by surface micro-fibrillation of p-aramid fibers, and contains a large number of super-fine fibers in a velvetized form on the surface. The p-aramid pulp has the advantages of large specific surface area, high strength, high temperature resistance and corrosion resistance, and is widely used in the fields of friction, sealing and reinforcing materials. However, the p-aramid pulp has poor ultraviolet resistance, is easily degraded, aged and yellowed under light, and causes irreversible attenuation of the mechanical properties of the material, which seriously restricts the application of the p-aramid pulp in the fields of aerospace, marine equipment, photovoltaic backboard and other fields with high weather resistance. The application proportion of the p-aramid pulp is less than 5%, which is much lower than that of carbon fiber or glass fiber. Therefore, it is an urgent need to develop a new p-aramid pulp with long-term ultraviolet resistance and high retention rate of intrinsic properties.

[0003] Currently, the industry often uses passive protection methods such as organic coating and blending of ultraviolet absorbers. However, the traditional modification methods generally have problems such as insufficient adhesion of the coating and migration and inactivation of the additives, and often sacrifice the lightweight characteristics or heat resistance of the material. The patent with publication number CN108276588B discloses a water-dispersible aramid nanofiber / nanocellulose composite system and a preparation method of an ultraviolet shielding transparent film. The film is prepared by uniformly mixing and dispersing natural plant fibers as basic raw materials and aramid nanofibers as an ultraviolet absorber through high shear and redispersion, and then performing ultrasonic degassing, vacuum filtration and low-temperature drying. The adhesion of the aramid nanofibers in the film prepared by the method is insufficient, and the aramid nanofibers are easily detached during use, which can cause aging and degradation of the material.

[0004] Metal-organic framework (hereinafter referred to as “MOFs”) material is a new type of nano-porous material with a three-dimensional network structure formed by self-assembly of metal ions and organic ligands. The nano-porous structure can attenuate ultraviolet rays through multiple light scattering / reflection, and the metal nodes can capture free radicals to block the photo-oxidation chain reaction of aramid.

[0005] However, the MOFs coating is greatly affected by the synthesis conditions during synthesis, which can easily cause aggregation or uneven crystallization of the MOFs.

[0006] In summary, the defect of the UV resistance of the p-aramid pulp has become a key bottleneck restricting its expansion to high-end outdoor fields, and there are certain technical difficulties in preparing high-performance composite materials by modifying the aramid pulp with MOFs materials, therefore, it is of great significance to develop a preparation method capable of retaining the excellent performance of p-aramid while making the composite material have excellent UV resistance, solving the stability problem of the material during transportation, storage and use, and breaking through the limitation of the application field of the material. SUMMARY

[0007] The present application provides a MOFs / p-aramid pulp composite material and a preparation method thereof, which has the advantages of mild reaction conditions and simple operation; the MOFs / p-aramid pulp composite material has excellent thermal stability, excellent UV resistance and high specific surface area, and can be used in the fields of new energy vehicles, aerospace, reinforcing materials and friction sealing, and has important application value.

[0008] The technical scheme for solving the above technical problems is as follows: a preparation method of a MOFs / p-aramid pulp composite material, the preparation method comprising the following steps:

[0009] S1, modifying the surface of the p-aramid pulp by dopamine self-polymerization at room temperature to obtain modified p-aramid pulp;

[0010] S2, soaking the modified p-aramid pulp in a zinc ion solution to obtain a mixed solution;

[0011] S3, adding the mixed solution to an organic ligand solution to obtain a MOFs / p-aramid pulp composite material.

[0012] Further, the operation in step S1 includes: immersing the p-aramid pulp in a dopamine salt solution, stirring, washing and drying;

[0013] The operation in step S3 includes: adding the mixed solution to an organic ligand solution, stirring, washing and drying.

[0014] Further, in step S1, the mass of the p-aramid pulp and the volume of the dopamine salt solution are in a ratio of 1g:(250-550)mL; wherein the concentration of the dopamine salt solution is 1.8-2.2g / L, preferably 2g / L.

[0015] Further, the dopamine salt solution is prepared from hydrochloric acid dopamine and tris-hydroxymethyl aminomethane hydrochloride buffer solution, wherein the concentration of the tris-hydroxymethyl aminomethane hydrochloride buffer solution used in the present application is 0.1mol / L, and the pH is 8.5.

[0016] Further, in step S1, the length of the para-aramid pulp is 0.5-2.0 mm.

[0017] Further, the zinc ion solution is a methanol solution of zinc nitrate hexahydrate, and the concentration is 0.05-0.2 mol / L; the organic ligand solution is a methanol solution of 2-methylimidazole, and the concentration is 0.3-0.6 mol / L.

[0018] Further, in step S2, the soaking time is 12-48 h.

[0019] Further, the mass of the modified para-aramid pulp, the volume of the zinc ion solution and the volume of the organic ligand solution are in a ratio of 1g:(300-600)mL:(300-600)mL.

[0020] Further, the concentration ratio of the zinc ion solution to the organic ligand solution is 1:(3-6).

[0021] Further, in step S1, the stirring rate is 500 rpm, the stirring time is 24-48 h; the drying temperature is 80-105 DEG C, and the drying time is 4-12 h.

[0022] In step S3, the stirring rate is 400-500 rpm, the stirring time is 12-24 h; the drying temperature is 80-105 DEG C, and the drying time is 12-24 h.

[0023] Further, the composite material is applied to the fields of new energy vehicles, aerospace, reinforced materials and friction sealing.

[0024] The beneficial effects of the present application are:

[0025] (1) The MOFs / para-aramid pulp composite material provided by the present application, under the condition that the concentration of the dopamine salt solution is determined, the mass of the para-aramid pulp and the volume of the dopamine salt solution are controlled to realize the thermal stability performance matching of the polydopamine film layer and the aramid matrix; the amount of metal ions and organic ligands is controlled, the modified para-aramid, metal ions and organic ligands jointly act, the metal ions are anchored on the surface of the modified para-aramid and a reasonable number of coordination anchor points are generated, the organic ligands are coordinated with the metal ions, and then the MOFs crystals can stably grow to form a nano-porous structure, and finally the structure matching of the polydopamine layer and the MOFs crystals is realized; the preparation method of the present application makes the composite material not only retain the thermal stability performance and the high specific surface area of the para-aramid, but also further improve the thermal stability performance and the specific surface area of the composite material due to the existence of the MOFs crystals on the surface of the composite material, and the specific surface area can reach more than 15 m 2 / g, and the composite material has excellent ultraviolet resistance performance.

[0026] (2) The application provides a preparation method of the MOFs / p-aramid pulp composite material, which is an in-situ synthesis method, first, dopamine self-polymerization surface modification is performed on the aramid pulp, then the obtained modified aramid pulp is immersed into a precursor solution for synthesizing MOFs, and thus the p-aramid pulp composite material with excellent ultraviolet resistance and thermal stability and high specific surface area is obtained; the in-situ synthesis method is that the MOFs are in-situ grown on the fiber surface of the aramid pulp through cross-linking action. The preparation method has the advantages of low pollution, low energy consumption and easy operation.

[0027] (3) The MOFs / p-aramid pulp composite material provided by the application forms a strong chemical bond with the aramid surface amide group through metal-nitrogen / oxygen coordination bond, and the nanoscale MOFs coating formed can realize molecular-level interface bonding. The aramid pulp is modified by the MOFs material to prepare a high-performance composite material, the weather resistance and environmental adaptability are improved, the stability problem of the traditional p-aramid pulp in the transportation and storage process can be solved, the limitation of the application scene is broken through, the p-aramid pulp can be used not only as a sealing material and a reinforcing material, but also as a structure reinforcing, safety protecting and functional composite material under extreme working conditions, the composite material can be applied to the manufacturing of a friction sealing field, an aerospace heat insulation system or a light-weight and heat-resistant part, and has a wide application prospect in the fields of new energy vehicles and aerospace. In addition, the composite material is environmentally friendly and low in cost. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 A synthesis mechanism diagram of the MOFs / p-aramid pulp composite material;

[0029] Figure 2 A scanning electron microscope diagram of the pure p-aramid pulp obtained in Comparative Example 1;

[0030] Figure 3 A scanning electron microscope diagram of the modified p-aramid pulp obtained in Comparative Example 2;

[0031] Figure 4 A scanning electron microscope diagram of the MOFs / p-aramid pulp composite material obtained in Embodiment 4. DETAILED DESCRIPTION

[0032] The specific embodiments of the application are described in detail below. The application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the application, therefore the application is not limited by the disclosed specific embodiments.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used only for describing particular embodiments is not intended to be limiting with respect to the application.

[0034] A preparation method of MOFs / p-aramid pulp composite material, the preparation method comprising the following steps:

[0035] S1, under room temperature conditions, the surface of the p-aramid pulp is modified by dopamine self-polymerization method to obtain modified p-aramid pulp, that is, phenolic hydroxyl groups are formed on the surface of the p-aramid pulp;

[0036] S2, the modified p-aramid pulp is soaked in a zinc ion solution to obtain a mixed solution, that is, zinc ions are anchored to the surface of the modified p-aramid pulp through phenolic hydroxyl groups, and the material in the solution at this time is a MOFs precursor;

[0037] S3, the mixed solution is added to an organic ligand solution, and the zinc ions on the surface of the MOFs precursor and the organic ligand synthesize MOFs crystals to obtain a MOFs / p-aramid pulp composite material.

[0038] Wherein, the synthesis mechanism of the MOFs / p-aramid pulp composite material of the application is as shown in Figure 1 .

[0039] Specifically, in step S1, the length of the p-aramid pulp is (0.5-2.0) mm.

[0040] Specifically, in step S1, the mass of the p-aramid pulp and the volume of the dopamine salt solution are in a ratio of 1g:(250-550)mL; wherein the concentration of the dopamine salt solution is 1.8-2.2g / L, and preferably 2g / L.

[0041] Specifically, the dopamine salt solution is prepared from hydrochloric acid dopamine and tris-hydroxymethyl aminomethane hydrochloride buffer solution.

[0042] More specifically, the concentration of the tris-hydroxymethyl aminomethane hydrochloride buffer solution used in the application is 0.1mol / L, and the pH is 8.5, but this does not limit the technology of the application, as long as the dopamine salt solution described in the application can be prepared.

[0043] Specifically, the operation in step S1 includes immersing the p-aramid pulp in the dopamine salt solution, stirring, washing and drying.

[0044] More specifically, in step S1, the preparation steps of the modified p-aramid pulp are:

[0045] The para-aramid pulp is immersed into the dopamine salt solution under room temperature, and stirred at a speed of 500 rpm for 24-48 h; after the stirring is completed, sample 1 is obtained by filtration, sample 1 is washed with deionized water for 3 times, and then dried at 80-105 ℃ for 4-12 h to obtain the modified para-aramid pulp.

[0046] Specifically, in step S2, the soaking time is 12-48 h.

[0047] More specifically, the zinc ion solution is a methanol solution of zinc nitrate hexahydrate, and the concentration is (0.05-0.2) mol / L.

[0048] More specifically, the organic ligand solution is a methanol solution of 2-methylimidazole, and the concentration is 0.3-0.6 mol / L.

[0049] Specifically, the operation in step S3 includes: adding the mixed solution into the organic ligand solution, stirring, washing and drying.

[0050] More specifically, in step S3, the preparation step of the MOFs / para-aramid pulp composite material is:

[0051] The mixed solution in S2 is added into the organic ligand solution, and stirred at a speed of 400-500 rpm for 12-24 h; after the stirring is completed, sample 2 is obtained by filtration, sample 2 is washed with deionized water for 3 times, and then dried at 80-105 ℃ for 12-24 h to obtain the MOFs / para-aramid pulp composite material.

[0052] Specifically, the ratio of the mass of the modified para-aramid pulp, the volume of the zinc ion solution and the volume of the organic ligand solution is 1 g:(300-600) mL:(300-600) mL.

[0053] More specifically, the ratio of the concentration of the zinc ion solution to the concentration of the organic ligand solution is 1:(3-6).

[0054] Example 1

[0055] A preparation of a MOFs / para-aramid pulp composite material includes the following steps:

[0056] S1, preparation of a modified para-aramid pulp

[0057] 2 g of para-aramid pulp is immersed into 1100 mL of a dopamine salt solution with a concentration of 2 g / L under room temperature, and stirred at a speed of 500 rpm for 24 h; after the stirring is completed, sample 1 is obtained by filtration, sample 1 is washed with deionized water for 3 times, and then dried at 105 ℃ for 4 h to obtain the modified para-aramid pulp.

[0058] S2, 1 g of modified para-aramid pulp was immersed in 300 mL of zinc ion solution with a concentration of 0.05 mol / L, and was placed at room temperature for 12 h to obtain a mixed solution.

[0059] S3, Preparation of MOFs / para-aramid pulp composite material

[0060] The mixed solution in S2 was added to 300 mL of 2-methylimidazole solution with a concentration of 0.3 mol / L, and was stirred at a rate of 400 rpm for 12 h; after stirring, sample 2 was obtained by filtration, sample 2 was washed with deionized water for 3 times, and then was dried at 80°C for 12 h to obtain the MOFs / para-aramid pulp composite material.

[0061] Example 2

[0062] A preparation method of a MOFs / para-aramid pulp composite material comprises the following steps:

[0063] S1, Preparation of modified para-aramid pulp

[0064] 5 g of para-aramid pulp was immersed in 1250 mL of dopamine salt solution with a concentration of 2 g / L at room temperature, and was stirred at a rate of 500 rpm for 48 h; after stirring, sample 1 was obtained by filtration, sample 1 was washed with deionized water for 3 times, and then was dried at 105°C for 12 h to obtain the modified para-aramid pulp.

[0065] S2, 4 g of modified para-aramid pulp was immersed in 2400 mL of zinc ion solution with a concentration of 0.1 mol / L, and was placed at room temperature for 24 h to obtain a mixed solution.

[0066] S3, Preparation of MOFs / para-aramid pulp composite material

[0067] The mixed solution in S2 was added to 2400 mL of 2-methylimidazole solution with a concentration of 0.4 mol / L, and was stirred at a rate of 500 rpm for 24 h; after stirring, sample 2 was obtained by filtration, sample 2 was washed with deionized water for 3 times, and then was dried at 105°C for 24 h to obtain the MOFs / para-aramid pulp composite material.

[0068] Example 3

[0069] A preparation method of a MOFs / para-aramid pulp composite material comprises the following steps:

[0070] S1, Preparation of modified para-aramid pulp

[0071] In the room temperature, 2 g of para-aramid pulp was immersed in 1100 mL of dopamine salt solution with a concentration of 2 g / L, and stirred at a speed of 500 rpm for 24 h; after stirring, sample 1 was obtained by filtration, and then sample 1 was washed with deionized water for 3 times, and then dried at 105 DEG C for 12 h to obtain modified para-aramid pulp.

[0072] S2, 1 g of modified para-aramid pulp was immersed in 500 mL of zinc ion solution with a concentration of 0.08 mol / L, and placed at room temperature for 24 h to obtain a mixed solution.

[0073] S3, preparation of MOFs / para-aramid pulp composite material

[0074] The mixed solution in S2 was added to 500 mL of 2-methylimidazole solution with a concentration of 0.4 mol / L, and stirred at a speed of 500 rpm for 12 h; after stirring, sample 2 was obtained by filtration, and then sample 2 was washed with deionized water for 3 times, and then dried at 105 DEG C for 24 h to obtain MOFs / para-aramid pulp composite material.

[0075] Example 4

[0076] A preparation of MOFs / para-aramid pulp composite material, comprising the following steps:

[0077] S1, preparation of modified para-aramid pulp

[0078] In the room temperature, 2 g of para-aramid pulp was immersed in 800 mL of dopamine salt solution with a concentration of 2 g / L, and stirred at a speed of 500 rpm for 24 h; after stirring, sample 1 was obtained by filtration, and then sample 1 was washed with deionized water for 3 times, and then dried at 105 DEG C for 12 h to obtain modified para-aramid pulp.

[0079] S2, 2 g of modified para-aramid pulp was immersed in 600 mL of zinc ion solution with a concentration of 0.2 mol / L, and placed at room temperature for 24 h to obtain a mixed solution.

[0080] S3, preparation of MOFs / para-aramid pulp composite material

[0081] The mixed solution in S2 was added to 600 mL of 2-methylimidazole solution with a concentration of 0.6 mol / L, and stirred at a speed of 500 rpm for 24 h; after stirring, sample 2 was obtained by filtration, and then sample 2 was washed with deionized water for 3 times, and then dried at 105 DEG C for 24 h to obtain MOFs / para-aramid pulp composite material.

[0082] Example 5

[0083] Example 5

[0084] S1, Preparation of modified para-aramid pulp

[0085] At room temperature, 2 g of para-aramid pulp was immersed in 1100 mL of dopamine salt solution with a concentration of 1.8 g / L, and stirred at a rate of 500 rpm for 24 h; after stirring, sample 1 was obtained by filtration, sample 1 was washed with deionized water for 3 times, and then dried at 105°C for 4 h to obtain modified para-aramid pulp.

[0086] S2, 1 g of modified para-aramid pulp was immersed in 300 mL of zinc ion solution with a concentration of 0.05 mol / L, and stood at room temperature for 12 h to obtain a mixed solution.

[0087] S3, Preparation of MOFs / para-aramid pulp composite material

[0088] The mixed solution in S2 was added to 300 mL of 2-methylimidazole solution with a concentration of 0.3 mol / L, and stirred at a rate of 400 rpm for 12 h; after stirring, sample 2 was obtained by filtration, sample 2 was washed with deionized water for 3 times, and then dried at 80°C for 12 h to obtain MOFs / para-aramid pulp composite material.

[0089] Example 6

[0090] Example 6

[0091] S1, Preparation of modified para-aramid pulp

[0092] At room temperature, 2 g of para-aramid pulp was immersed in 1100 mL of dopamine salt solution with a concentration of 1.8 g / L, and stirred at a rate of 500 rpm for 24 h; after stirring, sample 1 was obtained by filtration, sample 1 was washed with deionized water for 3 times, and then dried at 105°C for 4 h to obtain modified para-aramid pulp.

[0093] S2, 1 g of modified para-aramid pulp was immersed in 300 mL of zinc ion solution with a concentration of 0.05 mol / L, and stood at room temperature for 12 h to obtain a mixed solution.

[0094] S3, Preparation of MOFs / para-aramid pulp composite material

[0095] The mixed solution in S2 was added to a 300 mL 2-methylimidazole solution with a concentration of 0.3 mol / L, and stirred at a rate of 400 rpm for 12 h; after stirring, sample 2 was obtained by filtration, sample 2 was washed with deionized water for 3 times, and then dried at 80°C for 12 h to obtain the MOFs / p-aramid pulp composite material.

[0096] Comparative Example 1

[0097] The p-aramid pulp was completely immersed in acetone, ultrasonically treated at room temperature for 0.5 h, and finally dried at 60°C for 4 h to obtain the pure p-aramid pulp of Comparative Example 1.

[0098] Comparative Example 2

[0099] 2 g of p-aramid pulp was immersed in 1100 mL of a dopamine salt solution with a concentration of 2 g / L, stirred at 500 rpm for 24 h, washed with deionized water for 3 times after stirring, and dried at 105°C for 12 h to obtain the modified p-aramid pulp.

[0100] Comparative Example 3

[0101] Comparative Example 3 was prepared by the same method as Example 1, except that the dopamine salt concentration in step S1 of Comparative Example 3 was lower than that of Example 1, and the dopamine salt concentration was 1 g / L. The specific preparation process included the following steps:

[0102] S1, Preparation of modified p-aramid pulp

[0103] 2 g of p-aramid pulp was immersed in 1100 mL of a dopamine salt solution with a concentration of 1 g / L at room temperature, and stirred at a rate of 500 rpm for 24 h; after stirring, sample 1 was obtained by filtration, sample 1 was washed with deionized water for 3 times, and then dried at 105°C for 4 h to obtain the modified p-aramid pulp.

[0104] S2, 1 g of the modified p-aramid pulp was immersed in a 300 mL zinc ion solution with a concentration of 0.05 mol / L, and left to stand at room temperature for 12 h to obtain a mixed solution.

[0105] S3, Preparation of MOFs / p-aramid pulp composite material

[0106] The mixed solution in S2 was added to a 300 mL 2-methylimidazole solution with a concentration of 0.3 mol / L, and stirred at a rate of 400 rpm for 12 h; after stirring, sample 2 was obtained by filtration, sample 2 was washed with deionized water for 3 times, and then dried at 80°C for 12 h to obtain the MOFs / p-aramid pulp composite material.

[0107] Comparative Example 4

[0108] Comparative Example 4 was prepared by the same method as Example 1, except that the dopamine salt concentration in step S1 was higher than that of Example 1, and the dopamine salt concentration was 3 g / L. The specific preparation process included the following steps:

[0109] S1, Preparation of modified para-aramid pulp

[0110] At room temperature, 2 g of para-aramid pulp was immersed in 1100 mL of dopamine salt solution with a concentration of 3 g / L, and stirred at a rate of 500 rpm for 24 h; after stirring, sample 1 was obtained by filtration, sample 1 was washed with deionized water for 3 times, and then dried at 105°C for 4 h to obtain modified para-aramid pulp.

[0111] S2, 1 g of modified para-aramid pulp was immersed in 300 mL of zinc ion solution with a concentration of 0.05 mol / L, and was placed at room temperature for 12 h to obtain a mixed solution.

[0112] S3, Preparation of MOFs / para-aramid pulp composite material

[0113] The mixed solution in S2 was added to 300 mL of 2-methylimidazole solution with a concentration of 0.3 mol / L, and stirred at a rate of 400 rpm for 12 h; after stirring, sample 2 was obtained by filtration, sample 2 was washed with deionized water for 3 times, and then dried at 80°C for 12 h to obtain a MOFs / para-aramid pulp composite material.

[0114] Comparative Example 5

[0115] Comparative Example 5 was prepared by the same method as Example 3, except that the zinc ion concentration in step S2 was 0.08 mol / L, and the concentration of 2-methylimidazole solution in step S3 was 1.04 mol / L; at this time, the concentration ratio of zinc ion solution to 2-methylimidazole solution was 1:13. The specific preparation process included the following steps:

[0116] S1, Preparation of modified para-aramid pulp

[0117] At room temperature, 2 g of para-aramid pulp was immersed in 1100 mL of dopamine salt solution with a concentration of 3 g / L, and stirred at a rate of 500 rpm for 24 h; after stirring, sample 1 was obtained by filtration, sample 1 was washed with deionized water for 3 times, and then dried at 105°C for 4 h to obtain modified para-aramid pulp.

[0118] S2, 1 g of the modified para-aramid pulp was immersed in a 500 mL zinc ion solution with a concentration of 0.08 mol / L, and was left to stand at room temperature for 24 h to obtain a mixed solution.

[0119] S3, Preparation of the MOFs / para-aramid pulp composite material

[0120] The mixed solution in S2 was added to a 500 mL 2-methylimidazole solution with a concentration of 1.04 mol / L, and was stirred at a rate of 500 rpm for 12 h; after stirring, sample 2 was obtained by filtration, sample 2 was washed with deionized water for 3 times, and then was dried at 105°C for 24 h to obtain the MOFs / para-aramid pulp composite material.

[0121] Comparative Example 6

[0122] Comparative Example 6 was prepared by the same method as Example 3, except that the zinc ion concentration in step S2 was 0.08 mol / L, and the concentration of the 2-methylimidazole solution in step S3 was 0.08 mol / L; at this time, the concentration ratio of the zinc ion solution to the 2-methylimidazole solution was 1:1. The specific preparation process included the following steps:

[0123] S1, Preparation of the modified para-aramid pulp

[0124] At room temperature, 2 g of para-aramid pulp was immersed in a 1100 mL dopamine salt solution with a concentration of 2 g / L, and was stirred at a rate of 500 rpm for 24 h; after stirring, sample 1 was obtained by filtration, sample 1 was washed with deionized water for 3 times, and then was dried at 105°C for 12 h to obtain the modified para-aramid pulp.

[0125] S2, 1 g of the modified para-aramid pulp was immersed in a 500 mL zinc ion solution with a concentration of 0.08 mol / L, and was left to stand at room temperature for 24 h to obtain a mixed solution.

[0126] S3, Preparation of the MOFs / para-aramid pulp composite material

[0127] The mixed solution in S2 was added to a 500 mL 2-methylimidazole solution with a concentration of 0.08 mol / L, and was stirred at a rate of 500 rpm for 12 h; after stirring, sample 2 was obtained by filtration, sample 2 was washed with deionized water for 3 times, and then was dried at 105°C for 24 h to obtain the MOFs / para-aramid pulp composite material.

[0128] Comparative Example 7

[0129] Example 3 was prepared by the same method as Example 1, except that in step S2, 2 g of modified para-aramid pulp was added, and the ratio of the mass of the modified para-aramid pulp, the volume of the zinc ion solution, and the volume of the 2-methylimidazole solution was 1 g: 150 mL: 150 mL. The specific preparation process included the following steps:

[0130] S1, Preparation of modified para-aramid pulp

[0131] At room temperature, 2 g of para-aramid pulp was immersed in 1100 mL of a dopamine salt solution with a concentration of 2 g / L, and stirred at a rate of 500 rpm for 24 h; after stirring, sample 1 was obtained by filtration, sample 1 was washed with deionized water for 3 times, and then dried at 105°C for 12 h to obtain modified para-aramid pulp.

[0132] S2, 1 g of modified para-aramid pulp was immersed in 500 mL of a zinc ion solution with a concentration of 0.08 mol / L, and left to stand at room temperature for 24 h to obtain a mixed solution.

[0133] S3, Preparation of MOFs / para-aramid pulp composite material

[0134] The mixed solution in S2 was added to 500 mL of a 2-methylimidazole solution with a concentration of 0.04 mol / L, and stirred at a rate of 500 rpm for 12 h; after stirring, sample 2 was obtained by filtration, sample 2 was washed with deionized water for 3 times, and then dried at 105°C for 24 h to obtain a MOFs / para-aramid pulp composite material.

[0135] Comparative Example 8

[0136] Example 3 was prepared by the same method as Example 1, except that in step S2, 2 g of modified para-aramid pulp was added, and the ratio of the mass of the modified para-aramid pulp, the volume of the zinc ion solution, and the volume of the 2-methylimidazole solution was 1 g: 150 mL: 150 mL. The specific preparation process included the following steps:

[0137] S1, Preparation of modified para-aramid pulp

[0138] At room temperature, 2 g of para-aramid pulp was immersed in 1100 mL of a dopamine salt solution with a concentration of 2 g / L, and stirred at a rate of 500 rpm for 24 h; after stirring, sample 1 was obtained by filtration, sample 1 was washed with deionized water for 3 times, and then dried at 105°C for 12 h to obtain modified para-aramid pulp.

[0139] S2, 2 g of modified para-aramid pulp was immersed in 300 mL of zinc ion solution with a concentration of 0.05 mol / L, and was placed at room temperature for 12 h to obtain a mixed solution.

[0140] S3, Preparation of MOFs / para-aramid pulp composite material

[0141] The mixed solution in S2 was added to 300 mL of 2-methylimidazole solution with a concentration of 0.3 mol / L, and was stirred at a speed of 400 rpm for 12 h; after stirring, sample 2 was obtained by filtration, sample 2 was washed with deionized water for 3 times, and then was dried at 80°C for 12 h to obtain the MOFs / para-aramid pulp composite material.

[0142] Comparative Example 9

[0143] Comparative Example 9 was prepared by the same method as Example 1, except that the volume of zinc ion solution in step S2 was 700 mL, and the volume of 2-methylimidazole solution in step S3 was 700 mL, and the ratio of the mass of modified para-aramid pulp, the volume of zinc ion solution and the volume of 2-methylimidazole solution was 1 g:700 mL:700 mL. The specific preparation process included the following steps:

[0144] S1, Preparation of modified para-aramid pulp

[0145] 2 g of para-aramid pulp was immersed in 1100 mL of dopamine salt solution with a concentration of 2 g / L at room temperature, and was stirred at a speed of 500 rpm for 24 h; after stirring, sample 1 was obtained by filtration, sample 1 was washed with deionized water for 3 times, and then was dried at 105°C for 4 h to obtain the modified para-aramid pulp.

[0146] S2, 1 g of modified para-aramid pulp was immersed in 700 mL of zinc ion solution with a concentration of 0.05 mol / L, and was placed at room temperature for 12 h to obtain a mixed solution.

[0147] S3, Preparation of MOFs / para-aramid pulp composite material

[0148] The mixed solution in S2 was added to 700 mL of 2-methylimidazole with a concentration of 0.3 mol / L, and was stirred at a speed of 400 rpm for 12 h; after stirring, sample 2 was obtained by filtration, sample 2 was washed with deionized water for 3 times, and then was dried at 80°C for 12 h to obtain the MOFs / para-aramid pulp composite material.

[0149] Comparative Example 10

[0150] Example 1 was prepared by the same method as Example 1, except that in step S1, 5 g of para-aramid pulp was added, and the mass and volume ratio of para-aramid pulp to dopamine salt solution was 1 g: 220 mL. The specific preparation process included the following steps:

[0151] S1, preparation of modified para-aramid pulp

[0152] At room temperature, 5 g of para-aramid pulp was immersed in 1100 mL of dopamine salt solution with a concentration of 2 g / L, and stirred at a rate of 500 rpm for 24 h; after stirring, sample 1 was obtained by filtration, sample 1 was washed with deionized water for 3 times, and then dried at 105°C for 4 h to obtain modified para-aramid pulp.

[0153] S2, 1 g of modified para-aramid pulp was immersed in 300 mL of zinc ion solution with a concentration of 0.05 mol / L, and was placed at room temperature for 12 h to obtain a mixed solution.

[0154] S3, preparation of MOFs / para-aramid pulp composite material

[0155] The mixed solution in S2 was added to 300 mL of 2-methylimidazole solution with a concentration of 0.3 mol / L, and stirred at a rate of 400 rpm for 12 h; after stirring, sample 2 was obtained by filtration, sample 2 was washed with deionized water for 3 times, and then dried at 80°C for 12 h to obtain a MOFs / para-aramid pulp composite material.

[0156] Comparative Example 11

[0157] Example 1 was prepared by the same method as Example 1, except that in step S1, the volume of dopamine salt solution was 1400 mL, and the mass and volume ratio of para-aramid pulp to dopamine salt solution was 1 g: 700 mL. The specific preparation process included the following steps:

[0158] S1, preparation of modified para-aramid pulp

[0159] At room temperature, 2 g of para-aramid pulp was immersed in 1400 mL of dopamine salt solution with a concentration of 2 g / L, and stirred at a rate of 500 rpm for 24 h; after stirring, sample 1 was obtained by filtration, sample 1 was washed with deionized water for 3 times, and then dried at 105°C for 4 h to obtain modified para-aramid pulp.

[0160] S2, 1g of modified para-aramid pulp was immersed into 300 mL of zinc ion solution with a concentration of 0.05 mol / L, and was placed at room temperature for 12h to obtain a mixed solution.

[0161] S3, preparation of MOFs / para-aramid pulp composite material

[0162] The mixed solution in S2 was added into 300 mL of 2-methylimidazole solution with a concentration of 0.3 mol / L, and was stirred at a speed of 400 rpm for 12h; after stirring, sample 2 was obtained by filtration, and sample 2 was washed with deionized water for 3 times, and then was dried at 80℃ for 12h to obtain a MOFs / para-aramid pulp composite material.

[0163] The MOFs / para-aramid pulp composite material, pure para-aramid pulp and modified para-aramid pulp prepared in the examples and comparative examples of the present application were subjected to performance tests, and the test data of ultraviolet transmittance and the test data of specific surface area of the materials after the test were shown in Table 1, and the test data of thermal decomposition temperature retention rate were shown in Table 2. The specific test methods were as follows:

[0164] (1) Scanning electron microscope test: the morphology of the sample was studied by field emission scanning electron microscope.

[0165] (2) Ultraviolet transmittance test: the ultraviolet transmittance of the surface of the sample was measured by ultraviolet spectrophotometer, and the wavelength range was 250nm~400nm.

[0166] (3) Ultraviolet resistance: the light resistance of pure para-aramid pulp, modified aramid pulp and MOFs / para-aramid pulp was tested in an ultraviolet lamp box (power 50 W, temperature 25~30℃, humidity 55~65%), and the thermal decomposition temperature of aramid pulp under different irradiation time was studied.

[0167] Table 1 test data of ultraviolet transmittance and specific surface area of the materials obtained in each test example

[0168]

[0169] Table 2 test data of thermal decomposition temperature retention rate of the materials obtained in each test example

[0170]

[0171] From Figure 2 , Figure 3 and Figure 4 , it can be seen that the morphology of the surface of the material at each stage, Figure 3 the surface of the fiber in Figure 2The pure para-aramid pulp fiber surface in the table is rough, which shows that the pure para-aramid pulp surface is deposited with a dopamine coating, proving that the para-aramid pulp is successfully modified on the surface by the dopamine self-polymerization method, and the modified para-aramid pulp is obtained. Figure 4 It can be seen from the table that a large number of MOFs crystals are uniformly distributed on the surface of the composite material, which shows that after the dopamine coating is deposited on the fiber surface of the aramid pulp, the phenolic hydroxyl group provided by the dopamine makes the zinc ions anchor to the surface of the para-aramid pulp, and then the zinc ions and the organic ligand 2-methyl imidazole are successfully synthesized into crystals, that is, the MOFs / para-aramid pulp composite material.

[0172] It can be seen from the data in Table 1 that compared with Comparative Examples 1 and 2, the UV transmittance of the MOFs / para-aramid pulp composite material obtained by the preparation method of the present application in Examples 1-6 is almost 0, which is significantly better than that of pure para-aramid pulp and modified para-aramid pulp, and exhibits excellent anti-UV effect. In addition, the specific surface area of the MOFs / para-aramid pulp composite material obtained by the preparation method of the present application in Examples 1-4 is all above 15 m 2 / g, which is significantly better than that of pure para-aramid pulp in Comparative Example 1 and modified para-aramid pulp in Comparative Example 2. This is because the MOFs crystals on the surface of the para-aramid pulp are formed by the in-situ growth process, which has a regular three-dimensional porous network structure. The MOFs crystals form a uniform coverage on the surface of the aramid fiber, effectively increasing the number of surface pores of the material, making the accessible surface area of the unit mass material increase by 2-3 times compared with pure aramid pulp, and finally achieving a significant increase in the specific surface area.

[0173] It can be seen from the data in Table 2 that after 10 days of UV irradiation, the thermal decomposition temperature retention rate of the MOFs / para-aramid pulp composite material obtained by the preparation method of the present application in Examples 1-6 is all ≥99%, which exhibits excellent thermal stability. This advantage of thermal decomposition temperature retention rate is realized by the synergistic effect of UV blocking effect and thermal stability. The MOFs crystals on the surface of the para-aramid pulp form a dense protective layer, which can reduce the damage of UV to the amide bond in the aramid molecular chain; at the same time, the thermal decomposition temperature of MOFs is high in matching degree with the aramid body, and the two are stably combined to synergistically enhance the thermal stability of the composite material. The result verifies the effectiveness of the MOFs modification strategy in improving the anti-UV and thermal stability of the aramid pulp.

[0174] According to the data in Table 1 and Table 2, it can be seen from the comparison of the data results of Comparative Example 3 and Example 1 that when the concentration of the dopamine solution used in Comparative Example 3 is lower than that of Example 1, the ultraviolet transmittance increases, the ultraviolet resistance effect decreases, the thermal decomposition temperature retention rate decreases, and the specific surface area decreases significantly. This is because when a lower concentration of dopamine solution is used for modification treatment of the aramid pulp, incomplete modification phenomenon occurs, thereby affecting the growth of MOFs crystals, resulting in a significant decrease in the ultraviolet resistance effect. When the concentration of the dopamine solution deviates from the optimal range, typical defects occur in the surface modification of the aramid pulp. At a low concentration, the concentration of dopamine monomers does not reach the critical polymerization threshold, resulting in insufficient coverage of the fiber surface active sites of the aramid pulp. In addition, when the concentration of the dopamine solution deviates from the optimal range, the specific surface area of the composite material decreases, and the core reason is the decrease in the MOFs loading amount caused by the reduction of the fiber surface active sites.

[0175] According to the data in Table 1 and Table 2, it can be seen from the comparison of the data results of Comparative Example 2 and Example 1 that when the concentration of the dopamine solution used in Comparative Example 2 is higher than that of Example 1, the ultraviolet transmittance increases, the ultraviolet resistance effect decreases, the thermal decomposition temperature retention rate decreases, and the specific surface area decreases significantly. This is because when a higher concentration of dopamine solution is used for modification treatment of the aramid pulp, a phenomenon of excessive thickness of the polydopamine film occurs, thereby affecting the growth of MOFs crystals, resulting in a significant decrease in the ultraviolet resistance effect. When the concentration of the dopamine solution deviates from the optimal range, typical defects occur in the surface modification of the aramid pulp. At a high concentration, the excessive generation of the polydopamine film layer has a self-decomposition initiation temperature (about 280°C) that is much lower than that of the aramid body (above 550°C), and the interface heat conduction destroys the regular arrangement of the rigid molecular chains of the aramid fiber. In addition, when the concentration of the dopamine solution deviates from the optimal range, the specific surface area of the composite material decreases, and the core reason is the decrease in the MOFs loading amount caused by the reduction of the fiber surface active sites. At a high concentration, the self-polymerization reaction of the dopamine layer is intensified, resulting in a decrease in the number of metal ion coordination anchors required for the growth of MOFs on the fiber surface of the aramid pulp, and finally weakening the functional characteristics of the composite material.

[0176] In summary, according to the result analysis of Example 1, Comparative Example 3 and Comparative Example 4, the concentration of dopamine needs to be strictly controlled within the optimal range to achieve the thermal performance matching of the polydopamine film layer and the aramid matrix, as well as the structure matching of the polydopamine layer and the MOFs crystals.

[0177] According to the data in Table 1 and Table 2, it can be seen from the comparison of the data results of Comparative Example 5 and Example 3 that when the concentration ratio of zinc ion solution to 2-methylimidazole solution is lower than the optimal range ratio of the present application, the UV transmittance increases, the anti-UV effect decreases, the thermal decomposition temperature retention decreases, and the specific surface area decreases significantly. This is because the amount of zinc ion supply is insufficient, resulting in that the 2-methylimidazole ligand cannot be fully coordinated, thereby causing the MOFs crystal growth kinetics to be limited, resulting in a decrease in the particle size of the MOFs crystal. The deterioration of the crystal structure directly causes the thermal stability of the material to decrease significantly, and the crystal lattice collapse and ligand detachment are more likely to occur under thermal stress, ultimately losing the thermal stability enhancement effect on the composite material. When the concentration ratio of zinc ion solution to 2-methylimidazole solution is lower than the optimal range, the amount of zinc ion supply is also insufficient, resulting in that the 2-methylimidazole ligand cannot be fully coordinated, thereby causing the MOFs crystal growth to be limited, directly causing the specific surface area of the material to decrease significantly. This illustrates the necessity of strictly controlling the concentration ratio of metal ions to ligand in the stoichiometric balance interval.

[0178] According to the data in Table 1 and Table 2, it can be seen from the comparison of the data results of Comparative Example 6, Comparative Example 7 and Example 3 that when the concentration ratio of zinc ion solution to 2-methylimidazole solution is increased to 1:1 and 2:1, the thermal stability of the prepared MOFs / aramid pulp presents a stepwise decreasing trend, and the specific surface area presents a decreasing trend. This is because when the concentration ratio of zinc ion solution to 2-methylimidazole solution is increased to 1:1 and 2:1, the excess Zn 2+ will destroy the coordination balance, resulting in free Zn 2+ ions that do not participate in coordination, forming a hydroxylated impurity phase on the surface of the MOFs crystal, which will decompose first and trigger the degradation of the skeleton chain; at the same time, high Zn 2+ concentration will accelerate the crystal growth rate, resulting in an increase in grain boundary defects, which become weak points for skeleton collapse at high temperatures; at the same time, this impurity phase covers the surface of the MOFs porous structure in the form of amorphous particles, not only blocking the crystal pores, but also reducing the effective specific surface area of the material through the physical shielding effect, ultimately resulting in the loss of the advantages of the porous structure of the composite material.

[0179] According to the data in Table 1 and Table 2, from the data result comparison of Comparative Example 8 and Example 1, it can be seen that when the amount of modified p-aramid is increased, while the volume of zinc ion solution and the volume of 2-methyl imidazole solution do not change, the ratio of the mass of modified p-aramid pulp, the volume of zinc ion solution and the volume of 2-methyl imidazole solution is 1 g: 150 mL: 150 mL. The performance test of the composite material shows that the ultraviolet transmittance increases, the ultraviolet resistance effect decreases, the thermal decomposition temperature retention rate decreases, and the specific surface area significantly decreases. This is because when the amount of modified p-aramid is increased, while the volume of zinc ion solution and the volume of 2-methyl imidazole solution do not change, the supply of zinc ions is insufficient, resulting in fewer zinc ions anchored on the surface of the modified p-aramid, so that the 2-methyl imidazole ligand can only coordinate on the limited zinc ions, thereby causing the MOFs crystal growth to be limited, resulting in a decrease in the number of MOFs crystals, and finally causing the thermal stability of the material to decrease significantly and the specific surface area to decrease significantly.

[0180] According to the data in Table 1 and Table 2, from the data result comparison of Comparative Example 9 and Example 1, it can be seen that when the volume of zinc ion solution and the volume of 2-methyl imidazole solution are increased, while the amount of modified p-aramid does not change, the ratio of the mass of modified p-aramid pulp, the volume of zinc ion solution and the volume of 2-methyl imidazole solution is 1 g: 700 mL: 700 mL. The performance test of the composite material shows that the ultraviolet transmittance increases, the ultraviolet resistance effect decreases, the thermal decomposition temperature retention rate decreases, and the specific surface area significantly decreases. This is because when the volume of zinc ion solution and the volume of 2-methyl imidazole solution are increased, while the amount of modified p-aramid does not change, the total amount of metal ions and ligands is excessive, which causes the MOFs to more easily nucleate and grow rapidly in the solution phase, rather than preferentially growing in situ on the active sites on the surface of the modified p-aramid. In addition, the excessive self-nucleation consumes a large amount of reactants, and the generated free MOFs crystals are difficult to be anchored on the surface of the aramid fiber through coordination or physical adsorption due to their large size or low surface energy, finally resulting in a decrease in the loading amount of MOFs in the composite material, causing the thermal stability of the material to decrease significantly and the specific surface area to decrease significantly.

[0181] According to the data in Table 1 and Table 2, from the data result comparison of Comparative Example 10 and Example 1, it can be seen that when Comparative Example 10 adds 5 g of para-aramid pulp in step S1, the mass and volume ratio of para-aramid pulp and dopamine salt solution is 1 g:220 mL. The performance test of the composite material shows that the ultraviolet transmittance increases, the ultraviolet resistance effect decreases, the thermal decomposition temperature retention rate decreases, and the specific surface area decreases significantly. This is because the addition of too much para-aramid pulp causes incomplete modification, which affects the growth of MOFs crystals, resulting in a significant decrease in the ultraviolet resistance effect. The surface modification of aramid pulp produces typical defects, and the coverage rate of active sites on the fiber surface of aramid pulp is insufficient, which ultimately leads to a decrease in the specific surface area of the composite material. The core reason is that the reduction of active sites on the fiber surface reduces the number of metal ion coordination anchors required for the growth of MOFs on the fiber surface of aramid pulp, which reduces the MOFs loading and ultimately weakens the functional characteristics of the composite material.

[0182] According to the data in Table 1 and Table 2, from the data result comparison of Comparative Example 11 and Example 1, it can be seen that when Comparative Example 11 uses 1400 mL of dopamine salt solution in step S1, the mass and volume ratio of para-aramid pulp and dopamine salt solution is 1 g:700 mL. The performance test of the composite material shows that the ultraviolet transmittance increases, the ultraviolet resistance effect decreases, the thermal decomposition temperature retention rate decreases, and the specific surface area decreases significantly. This is because the addition of too much dopamine solution for modification of aramid pulp causes the polydopamine film to be too thick, which affects the growth of MOFs crystals, resulting in a significant decrease in the ultraviolet resistance effect. The thermal decomposition onset temperature of the excess polydopamine film layer is much lower than that of aramid (above 550°C), and the interface heat conduction destroys the regular arrangement of the rigid molecular chains of aramid fibers. In addition, when the dopamine solution is excessive, it also leads to a decrease in the specific surface area of the composite material. The reason is that the polydopamine formed during the modification process is excessively deposited on the surface of para-aramid fibers, forming a thick polymer film that covers the original active functional groups (amide bonds) and pore structure of aramid fibers, resulting in the inability of MOFs precursors (such as metal ions and ligands) to effectively bind to the surface of the carrier, and the reduction of directional nucleation sites. In addition, the catechol and amine groups in the polydopamine molecule compete with MOFs precursors (Zn 2+ ) for coordination—excessive PDA preferentially chelates metal ions, weakening their directional assembly ability with organic ligands (2-methylimidazole), ultimately leading to a significant decrease in the loading and specific surface area of MOFs in the composite material.

[0183] The technical features of the above-described embodiments can be combined in any manner. For the sake of brevity, not all possible combinations of the technical features in the above-described embodiments are listed, however, as long as the combinations of the technical features do not contradict each other, they should be considered to be within the scope of the present disclosure.

[0184] Those skilled in the art will appreciate that, without departing from the concept of the present disclosure, a number of variations and modifications can be made, and these should be considered to be within the scope of the present disclosure, which is defined by the appended claims.

Claims

1. A method for preparing MOFs / p-aramid pulp composite material, characterized in that, The preparation method comprises the following steps: S1, modifying the surface of para-aramid pulp by dopamine self-polymerization at room temperature to obtain modified para-aramid pulp; S2, soaking the modified para-aramid pulp in a zinc ion solution to obtain a mixed solution; S3, adding the mixed solution to an organic ligand solution to obtain a MOFs / para-aramid pulp composite material; In step S1, the operations include: immersing the para-aramid pulp in a dopamine salt solution, stirring, washing and drying; wherein the mass of the para-aramid pulp and the volume of the dopamine salt solution are in a ratio of 1g:(250-550)mL, and the concentration of the dopamine salt solution is 1.8-2.2g / L; In step S3, the organic ligand solution is a 2-methylimidazole methanol solution with a concentration of 0.3-0.6mol / L; The ratio of the mass of the modified para-aramid pulp, the volume of the zinc ion solution and the volume of the organic ligand solution is 1g:(300-600)mL:(300-600)mL; The ratio between the concentration of the zinc ion solution and the concentration of the organic ligand solution is 1:(3-6).

2. The method for preparing a MOFs / para-aramid pulp composite material according to claim 1, characterized in that, The operations in step S3 include: adding the mixed solution to the organic ligand solution, stirring, washing and drying.

3. The method for preparing a MOFs / para-aramid pulp composite material according to claim 1, characterized in that, In step S1, the length of the para-aramid pulp is 0.5-2.0mm.

4. The method for preparing a MOFs / para-aramid pulp composite material according to claim 3, characterized in that, The dopamine salt solution is prepared from dopamine hydrochloride and tris-hydroxymethyl aminomethane hydrochloride buffer.

5. The method for preparing a MOFs / para-aramid pulp composite material according to claim 1, characterized in that, In step S2, the zinc ion solution is a zinc nitrate hexahydrate methanol solution with a concentration of 0.05-0.2mol / L.

6. The method of claim 1, wherein the MOFs / p-aramid pulp composite is prepared by the steps of: (a) mixing the MOFs and the p-aramid pulp to form a mixture; (b) drying the mixture; and (c) heating the mixture to form the MOFs / p-aramid pulp composite. In step S2, the soaking time is 12-48h.

7. A MOFs / p-aramid pulp composite material, characterized in that, The MOFs / para-aramid pulp composite material is prepared by the preparation method according to any one of claims 1-6.

8. The use of the MOFs / p-aramid pulp composite material according to claim 7, characterized in that, The composite material is applied to the field of friction sealing, aerospace thermal insulation system or the manufacturing of lightweight and heat-resistant parts.

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