Composite material capable of improving heat-conducting property of LDPE and preparation method of composite material

Abstract

The invention discloses a composite material capable of improving the thermal conductivity of LDPE and a preparation method of the composite material. The composite material is prepared from MOFS particles, NiS2 particles and LDPE. The preparation work of the composite material is carried out by adopting a melt blending principle and utilizing a rheometer, and the whole preparation process is simple in principle, easy to understand and convenient to operate. An infrared spectrum characterization characteristic test is carried out on the prepared nano composite material, it is found that after LDPE is doped with MOFs particles, NiS2 particles and MOFs / NiS2 composite particles with different concentrations, the molecular chain structure of the whole composite material is not changed, it is found through a heat conduction performance test that the heat conduction performance of the NiS2 / MOFs / LDPE composite material is better than that of pure LDPE on the basis that the dielectric performance of the NiS2 / MOFs / LDPE composite material is not affected, and the heat conduction performance of the NiS2 / MOFs / LDPE composite material is better than that of the pure LDPE. The thermal aging rate of the insulating material is slower, the service life is longer, and the loss of LDPE can be reduced to a certain extent.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrical insulation, and relates to a composite material capable of improving the thermal conductivity of low-density polyethylene (LDPE) and a preparation method thereof, in particular to a MOFS / NiS2 / LDPE composite material capable of improving the thermal conductivity and dielectric property of LDPE and a preparation method thereof. BACKGROUND

[0002] LDPE is a general-purpose thermoplastic polymer material widely used in food, packaging, household appliances, daily necessities and other fields, and has good physical and mechanical properties. However, its thermal conductivity is poor, which limits its application in some high-end fields with requirements for heat conduction. In some special application scenarios, such as electronic device heat dissipation, thermal management and the like, higher requirements are put forward for the thermal conductivity of the material.

[0003] At present, the common method to improve the thermal conductivity of LDPE is to add thermal conductive fillers such as graphene, boron nitride and the like. These fillers build a thermal conductive network in the polymer matrix, thereby improving the thermal conductivity of the composite material. For example, there is a study that uses graphene intercalated boron nitride as a thermal conductive filler to add to the LDPE matrix, and an LDPE-based thermal conductive composite material is prepared by a mechanical ball milling method. With the increase of the amount of the thermal conductive filler, the thermal conductivity of the composite system gradually increases, and when the mass fraction of the thermal conductive filler is 30%, the thermal conductivity of the composite material reaches a maximum value of 0.84 W·m -1 ·K -1 , which is 3.36 times that of pure LDPE. However, these traditional thermal conductive fillers still have some problems in application, such as poor dispersibility and weak interface combination, which limits the further improvement of their thermal conductivity.

[0004] Metal-organic frameworks (MOFs) are a kind of porous materials with high specific surface area, controllable pore structure and chemical stability. In recent years, MOFs have received extensive attention in the field of composite materials, and their unique structural characteristics make them have great potential in improving the performance of materials.

[0005] Nickel sulfide (NiS2) has a relative molecular mass of 90.77 and is a black, powdery particle with a melting point of approximately 797°C at standard atmospheric pressure. Nickel sulfide has important applications in polymer modification, mainly involving enhancing the performance of polymers, improving their electrical conductivity, heat resistance, and mechanical properties, etc. Adding nickel sulfide particles or nanoparticles to the polymer matrix can significantly improve the electrical conductivity of the polymer. This composite material has a wide range of applications in electronic devices, conductive coatings, flexible circuits, and sensors, etc. The electrical conductivity of nickel sulfide makes it an ideal additive for manufacturing flexible electronic devices and conductive plastics. In addition, adding nickel sulfide particles to polymers can also improve their mechanical properties, such as strength, stiffness, and wear resistance, which is very useful in the preparation of tough polymer composites. This composite material can be used to manufacture lightweight structural materials, aircraft parts, automotive parts, and sports equipment, etc. The high melting point and thermal conductivity of nickel sulfide make it an effective additive for improving the heat resistance of polymers, which can be used to prepare high-temperature-resistant polymer materials suitable for high-temperature applications, such as engine parts, spacecraft components, and thermoelectric devices. At the same time, polymer composites containing nickel sulfide have flame retardant properties, which can be used to prepare materials with fireproof performance, which is very important in the fields of construction, electronic devices, and transportation, etc. However, when applying nickel sulfide for polymer modification, it is necessary to carefully control the content, particle size, and dispersibility of nickel sulfide to ensure that the resulting composite material has the desired properties. In addition, the compatibility between nickel sulfide and the polymer matrix needs to be considered to ensure stable performance and long-term durability.

[0006] Combining NiS2 with MOFs to form a composite material not only takes advantage of the electrical and thermal conductivity of NiS2, but also utilizes the high specific surface area and porous structure of MOFs to further improve the performance of the composite material. SUMMARY

[0007] The present application provides a composite material that can improve the thermal conductivity of LDPE and a preparation method thereof, aiming to further explore the effect of MoFs / NiS2 on the thermal conductivity of LDPE and systematically test and compare its effect on dielectric properties, breakdown performance, and electrical conductivity.

[0008] The purpose of the present application is achieved by the following technical solutions:

[0009] A composite material that can improve the thermal conductivity of LDPE is prepared from MOFs particles, NiS2 particles, and LDPE, wherein: the addition amount of MOFs particles is 0.25-2wt%, the addition amount of NiS2 particles is 0.25-2wt%, and the mass ratio of MOFs to NiS2 is 1-2:1; when the addition amount of MOFs particles is 0.25wt% and the mass ratio of MOFs to NiS2 is 1:1, the thermal conductivity is optimal.

[0010] A preparation method of the composite material capable of improving the heat conduction performance of LDPE, comprising the following steps:

[0011] Step one, preparing nano MOFs and NiS2 particles by using a hot method;

[0012] Step two, using a torque rheometer, LDPE and nano MOFs particles and nano NiS2 particles are compounded at 100-200 DEG C by using a melt blending method, so as to obtain a NiS2 / MOFs / LDPE composite material.

[0013] Compared with the prior art, the present application has the following advantages:

[0014] 1. The present application uses a hydrothermal method to prepare nano MOFs particles and nano NiS2 particles, and carries out scanning electron microscope and XRD tests on the nano materials. It can be found that the hydrothermal method is an effective means for preparing insoluble nano materials, and the prepared nano particles have high purity.

[0015] 2. The present application uses a melt blending principle to prepare a composite material by using a rheometer, and the whole preparation process is simple, easy to understand and convenient to operate. After the prepared nano composite material is subjected to infrared spectrum characterization test, it is found that the molecular chain structure of the whole composite material does not change after LDPE is doped with different concentrations of MOFs particles, NiS2 particles and MOFs / NiS2 composite particles, and the subsequent heat conduction performance test can be carried out.

[0016] 3. The present application finds that, in the heat conduction performance test, the NiS2 / MOFs / LDPE composite material has better heat conduction performance than pure LDPE without affecting its dielectric performance, so that the heat aging rate of the insulating material is slower, the service life is stronger, and the loss of LDPE can be reduced to a certain extent. DETAILED DESCRIPTION

[0017] Figure 1 It is a scanning electron microscope graph of MoFs nanoparticles;

[0018] Figure 2 It is a scanning electron microscope graph of NiS2 nanoparticles;

[0019] Figure 3 It is a scanning electron microscope graph of NiS2 / MoFs;

[0020] Figure 4 It is an XRD graph of MOFs nanoparticles;

[0021] Figure 5 It is an XRD graph of NiS2 nanoparticles;

[0022] Figure 6For the infrared spectrum of the nanoparticles and composite materials;

[0023] Figure 7 For the dielectric performance test diagram of the NiS2 / MoFs / LDPE composite material;

[0024] Figure 8 For the thermal conductivity performance test diagram of the NiS2 / MoFs / LDPE composite material;

[0025] Figure 9 For the breakdown field strength (DC) distribution of the MOFs / LDPE composite medium;

[0026] Figure 10 For the breakdown field strength (DC) distribution of the NiS2 / LDPE composite medium;

[0027] Figure 11 For the breakdown field strength (DC) distribution of the MOFs / NiS2 / LDPE composite medium;

[0028] Figure 12 For the electric conduction current characteristic curve of the MOFs / LDPE composite material;

[0029] Figure 13 For the electric conduction current characteristic curve of the NiS2 / LDPE composite material;

[0030] Figure 14 For the electric conduction characteristic curve of the MOFs / NiS2 / LDPE composite medium. DETAILED DESCRIPTION

[0031] The technical solutions of the present application will be further described below in conjunction with the drawings, but are not limited thereto, and any modification or equivalent replacement of the technical solutions of the present application without departing from the spirit and scope of the technical solutions of the present application shall be covered in the protection scope of the present application.

[0032] The present application provides a MOFS / NiS2 / LDPE composite material which can improve the thermal conductivity and dielectric properties of LDPE. The method uses nickel sulfate, urea, trimesic acid, dimethylformamide and ethylene glycol as raw materials, and prepares nano NiS2 and MoFs particles in a high-temperature reaction kettle by a hydrothermal method, and performs X-ray diffraction (XRD) and scanning electron microscope (SEM) tests to observe the characterization morphology, and then uses the principle of melt blending to modify LDPE with MOFs particles, NiS2 particles and MOFs / NiS2 particles to prepare a nano composite material, and performs infrared spectrum test on the prepared material to observe the quality of the sample. Finally, the prepared sample is measured for thermal conductivity, dielectric spectrum, breakdown and electric conduction, and computer software is used for experimental data analysis and comparison. Specifically, the following steps are completed:

[0033] Step 1: Mix Co(NO3)2·6H2O and BTC (tricresyl ether) and add them into a beaker, add N,N-dimethylformamide (DMF), and use an ultrasonic stirrer to heat and stir until the reactants are completely dissolved. The mass ratio of Co(NO3)2·6H2O to BTC is 1:1, and the added N,N-dimethylformamide (DMF) should not exceed 2 / 3 of the reactor capacity.

[0034] Step 2: Transfer the stirred solution to a hydrothermal reactor, seal the reactor lid tightly, and place in an oven for reaction at 140°C for 24 hours. After the reaction is complete, remove the reactor and allow it to cool naturally to room temperature.

[0035] Step 3: Centrifuge at a speed of 5000-10000 r / min for 5-20 min, collect the solid matter at the bottom layer of the reaction solution, and obtain nano-MOFs particles, wherein: the particle size of the nano-MOFs particles is about 5 µm. This step should be repeated 3-4 times to ensure the purity of the sample.

[0036] Step 4: Place 0.52 g of nickel sulfate hexahydrate, 0.6 g of urea, and 0.6 g of trimesic acid (BTC) in a beaker, and pour a mixed solution of 30 ml of dimethylformamide and 40 ml of ethylene glycol into the beaker.

[0037] Step 5: The mixed solution from step 4 was magnetically stirred at room temperature for one hour. The stirred solution was then poured into a reaction kettle and placed in an oven at 180° C. for 14 hours.

[0038] Step 6: After the reaction is completed, the obtained off-white solution is centrifuged and washed with a centrifuge, and then placed in an oven for drying for 6 hours to obtain NiS2 nanoparticles, wherein: the particle size of the NiS2 nanoparticles is about 50nm, and the washing conditions are the same as in step 3.

[0039] from Figure 1 The scanning electron microscope image of MoFs nanoparticles shows that the surface of MoFs nanoparticles has a porous structure, a particle size of about 5µm, and a large specific surface area, which is consistent with its characteristics. It has a rich topological structure and can be loaded with NiS2 in a fault-like structure, so that the two can be fused to modify LDPE. Figure 2 From the scanning electron microscope image of NiS2 nanoparticles shown, it can be seen that the surface of NiS2 is smooth and the NiS2 particles have many spherical structures. A large number of particles with a diameter of 50nm are aggregated into spherical particles with a diameter of about 700nm. Figure 3SEM images of NiS2 / Co-BTC at 20 µm and 5 µm are shown, in which the spherical particles are NiS2 particles and the cuboid-shaped particles are Co-BTC materials. It can be seen from the images that the NiS2 particles are tightly attached to the Co-BTC materials. This is because the positively charged cobalt ions in the Co-BTC materials will attract the negatively charged sulfur ions in the NiS2 materials due to the mutual attraction of charges during the reaction, thereby forming a NiS2 / Co-BTC composite material. It can also be seen from the images that the NiS2 particles are relatively uniformly distributed on the Co-BTC materials, indicating that the two materials are well combined. Figure 4 The MOFs nanoparticle XRD image shows that the peak changes are relatively complex, which is consistent with the SEM test image. The material can be used normally. Figure 5 The NiS2 nanoparticle XRD image shows that NiS2 has obvious diffraction peak characteristics at diffraction angles 2θ of 20.36°, 23.03°, 27.36°, 30.22°, 31.72°, 35.46°, 38.99°, 45.93°, 53.62°, 58.98°, 61.29° and 72.96°. After comparison, it is found to be consistent with the NiS2 standard sample card. This indicates that the sample prepared in this embodiment has high purity and can be applied to later experiments.

[0040] Step seven, using a torque rheometer, low-density polyethylene (LDPE) and nano MOFs particles and NiS2 are compounded at 130°C by melt blending method to obtain a NiS2 / MOFs / LDPE composite material with good compatibility.

[0041] From Figure 6 The infrared spectrum of the composite material after doping LDPE with different particle mass fractions shows that the addition of nanoparticles does not change the position of the characteristic peaks, indicating that the LDPE molecular chain has not changed and its chemical properties have not changed.

[0042] Step eight, the thermal conductivity of the NiS2 / MOFs / LDPE composite material is tested using a laser thermal conductivity instrument.

[0043] From Figure 8 The thermal conductivity test image of the NiS2 / MOFs / LDPE composite material shows that the doping of nanoparticles can significantly improve the thermal conductivity of LDPE, making the thermal aging rate of the insulating material slower and the service life stronger. From the test results, when the doping mass fraction of MOFs / NiS2 / LDPE is 0.25% and the ratio of MOFs to NiS2 is 1:1, the thermal conductivity is best.

[0044] Step nine, the dielectric properties of NiS2 / MOFs / LDPE composite material are tested by using broadband dielectric tester.

[0045] From Figure 7 It can be found from the dielectric property test diagram of NiS2 / MOFs / LDPE composite material that the dielectric constant is continuously improved with the increase of doping concentration when MOF particles improve the dielectric property, the NiS2 particles show a parabolic rule change, and moderate doping of NiS2 particles is conducive to improving the relative dielectric constant. The effect of 1:1 composite of the two is the best. The change of nanomaterial in improving the loss is relatively complex, only a part of the sample reduces the loss of LDP matrix to a certain extent. From the test results, the dielectric property of MOFs / NiS2 / LDPE composite medium with 1% doping mass fraction is the best when the ratio of MOFs to NiS2 is 1:1.

[0046] Step ten, the breakdown property of NiS2 / MOFs / LDPE composite material is tested by using KZT series power frequency high voltage console.

[0047] From Figure 9~Figure 11 It can be concluded from the breakdown property test diagram of NiS2 / MOFs / LDPE composite material that when the MOFs addition amount is 0.25%, 0.5% and 2%, the breakdown strength (direct current) is slightly improved, and when the doping amount of NiS2 accounts for 0.25% of NiS2 / LDPE composite medium, the direct current breakdown strength is improved. When the doping amount of NiS2 accounts for 0.25% of MOFs / NiS2 / LDPE composite medium, and the ratio of MOFs to NiS2 is 1:1, the field strength of MOFs / NiS2 / LDPE composite medium will decrease. From the test results, the best ratio of NiS2 / MOFs / LDPE composite material is that the mass ratio of NiS2 to MOFs is 1:1, and the total mass fraction is 0.25%, at this time, the breakdown property of the composite material is the best.

[0048] Step eleven, the conductivity of NiS2 / MOFs / LDPE composite material is tested by using conductivity instrument.

[0049] From Figure 12~Figure 14The conductivity performance test chart of the shown NiS2 / MOFs / LDPE composite material can draw the following conclusions: with the increase of the mass fraction of MOFs / LDPE, the conductivity of the composite material is more and more large; when the mass fraction of NiS2 is 2%, the conductivity of NiS2 / LDPE is the highest; when the ratio of MOFs and NiS2 is 1:1, the conductivity of MOFs / NiS2 / LDPE is higher than that of MOFs / NiS2 / LDPE when the ratio of MOFs and NiS2 is 2:1. From the test results, the best ratio of NiS2 / MOFs / LDPE composite material is that the mass ratio of NiS2 and MOFs is 1:1, and the total mass fraction is 0.25%, at this time, the conductivity performance of the composite material is the best.

Claims

1. A composite material that can improve the thermal conductivity of LDPE, characterized in that The composite material is prepared from MOFs particles, NiS2 particles and LDPE, wherein the addition amount of MOFs particles is 0.25-2wt%, and the addition amount of NiS2 particles is 0.25-2wt%.

2. The composite material capable of improving the thermal conductivity of LDPE according to claim 1, characterized in that The addition amount of the MOFs particles is 0.25 wt%, 0.5 wt% or 2 wt%.

3. The composite material capable of improving the thermal conductivity of LDPE according to claim 1 or 2, characterized in that The mass ratio of the MOFs to NiS2 is 1-2:

1.

4. The composite material capable of improving the thermal conductivity of LDPE according to claim 3, characterized in that The mass ratio of the MOFs to NiS2 is 1:1 or 2:

1.

5. The composite material capable of improving the thermal conductivity of LDPE according to claim 1, characterized in that When the addition amount of the MOFs particles is 0.25 wt% and the mass ratio of MOFs to NiS2 is 1:1, the thermal conductivity is optimal.

6. A method for preparing a composite material capable of improving the thermal conductivity of LDPE according to any one of claims 1 to 5, characterized in that The method comprises the following steps: Using a torque rheometer, LDPE and nano-MOFs particles were compounded with nano-NiS2 particles at 100~200℃ by melt blending method to obtain NiS2 / MOFs / LDPE composite materials.

7. The method for preparing a composite material capable of improving the thermal conductivity of LDPE according to claim 6, characterized in that The nano-MOFs and NiS2 particles are prepared by a hydrothermal method.

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