Wet composite preparation process of graphene modified conductive thermoplastic polyurethane

Abstract

The invention relates to the technical field of preparation of advanced inorganic non-metallic materials, in particular to a wet-process composite preparation process of graphene modified conductive thermoplastic polyurethane. A solution is provided for solving the problems that in the prior art, graphene filler is prone to agglomeration, mechanical performance is reduced due to the fact that the filler adding amount is increased, heat conduction / electric conduction anisotropy regulation and control are insufficient, the organic solvent dosage is large, the recovery cost is high, and the process is complex and difficult to be continuous; graphene oxide and TPU emulsion are subjected to microfluidic laminar flow shearing in a low-boiling-point azeotropic solvent to achieve GO efficient dispersion oriented arrangement; then constructing a vertical ice crystal template by adopting a directional-bidirectional freezing technology, carrying out selective photo-thermal reduction on a freeze-dried substance by utilizing 808nm laser pulse, introducing polydopamine on the surface of GO, and adsorbing and filling silver nanowires in gaps of graphene lamellas to realize a multi-scale conductive network. And finally, performance improvement and process optimization of the composite material are realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of advanced inorganic non-metallic material preparation, and particularly relates to a wet compounding preparation process of graphene modified conductive thermoplastic polyurethane. BACKGROUND

[0002] Graphene is widely used as a functional filler of high polymer conductive composite material due to its super-high conductive and thermal conductive performance and mechanical strength. However, some key technical bottlenecks of the existing graphene / polymer composite material need to be broken through. One of them is the dispersion problem of graphene in the matrix: the specific surface area of graphene sheet is large, and the van der Waals force is strong, so it is easy to agglomerate in the matrix, especially when the filler content is high, it is difficult to uniformly disperse. Serious agglomeration not only reduces the formation of effective conductive path of graphene, but also weakens the stress transmission of the interface between graphene and the polymer matrix, resulting in the deterioration of the mechanical properties of the composite material. The traditional method often disperses graphene by means of long-time ultrasonic stripping or high-speed shearing, but excessive ultrasonic may cause the graphene sheet to be broken and the size to be small, and the high-strength mechanical dispersion consumes a lot of energy and is difficult to scale up.

[0003] Secondly, there is a contradiction between the filler addition amount and the mechanical properties of the composite material: in order to improve the conductive or thermal conductive performance, the content of graphene is often increased, but the agglomeration of graphene at high content and the poor combination with the matrix make the material brittle and the strength decrease. This makes it difficult for traditional composite materials to achieve both high filler content and good mechanical properties, limiting the performance improvement.

[0004] Thirdly, the problem of insufficient anisotropic regulation of conductive and thermal conductivity: graphene has a strong anisotropy of in-plane and vertical properties due to its two-dimensional sheet structure. However, the orientation of graphene in the conventional preparation method is random, and the conductive and thermal conductive path is uncontrollable, which leads to the fact that the anisotropy of the material as a whole is not obvious, and the advantages of the conductive or thermal conductive performance of graphene in a specific direction cannot be fully utilized. Some studies try to make graphene orient and arrange by magnetic field orientation, 3D printing, template guidance and other methods, but there are problems such as complex equipment, limited applicable materials, etc., and it is still difficult to realize simple and efficient anisotropic structure construction.

[0005] In addition, the existing graphene / TPU conductive composite material preparation mostly adopts solution method, which needs a large amount of organic solvent to dissolve TPU, and then mixes graphene dispersion liquid to cast into a film. DMF, THF and the like have high boiling points and are difficult to recover. When used in large quantities, not only the production cost and environmental pressure are increased, but also the preparation period is long due to slow volatilization. At the same time, such solution method is usually batch operation, and the process is complicated, which is difficult to realize continuous large-scale production, and is not conducive to industrial application. For example, the existing technology patent CN118620140A discloses a conductive polyurethane emulsion, a preparation method thereof and a flexible conductive polyurethane synthetic leather, and the preparation method thereof comprises: a shell monomer pre-emulsion preparation step, a core monomer pre-emulsion preparation step and a semi-continuous polymerization step; in the shell monomer pre-emulsion preparation step, the pre-polymer monomer, the acrylate and the reduced graphene oxide are added into the polymerizable emulsifier, and the shell monomer pre-emulsion is obtained by pre-emulsification. The preparation process is relatively complicated, and the above problems exist.

[0006] In view of the above problems, it is urgent to develop a novel graphene / TPU composite material preparation process to realize uniform dispersion of graphene, construction of conductive and thermal anisotropic network, reduction of organic solvent dosage and simplification of process flow, so as to prepare a conductive composite material with high performance and flexibility, and meet the application requirements in the field of flexible electronic devices and the like. SUMMARY

[0007] The purpose of the present application is to provide a wet composite preparation process of graphene modified conductive thermoplastic polyurethane, which constructs a three-dimensional oriented graphene / silver nanowire conductive network structure in the TPU matrix through microfluidic dispersion orientation, directional-bidirectional freeze forming and in-situ photo-thermal reduction, and the obtained composite material is suitable for the field requiring high conductive and thermal performance and flexibility such as flexible electronic devices.

[0008] The specific technical scheme is as follows:

[0009] The wet composite preparation process of graphene modified conductive thermoplastic polyurethane comprises the following steps:

[0010] S1: functionalizing graphene oxide and preparing a water dispersion liquid, and preparing a thermoplastic polyurethane granule into an emulsion;

[0011] S2: the graphene oxide water dispersion liquid and the thermoplastic polyurethane emulsion prepared in S1 are respectively loaded into a syringe pump, and then injected into a microfluidic channel, and the two liquid streams keep laminar parallel flow state after converging in the main channel, and the uniform emulsion flows out at the outlet of the main channel;

[0012] S3: Pour the uniform emulsion obtained in S2 into a mold, with the bottom of the mold closely above a cold table, and at the same time insert a pre-cooled copper rod into the center of the emulsion as a second cold source to achieve synchronous freezing from the center to the periphery, and after the freezing is completed, move the mold into a freeze dryer for drying, and after the ice crystals sublimate, obtain a composite A;

[0013] S4: Perform photothermal reduction treatment on the composite A using a semiconductor laser, and after the reduction treatment, obtain a graphene modified conductive thermoplastic polyurethane.

[0014] Further, the functionalization treatment in S1 is polydopamine functionalization and silver nanowire dispersion functionalization; before the functionalization treatment, the graphene oxide needs to be dispersed in a basic buffer solution containing tris(hydroxymethyl) aminomethane; the solvent used in the preparation of the thermoplastic polyurethane emulsion in S1 is a mixed solvent of ethyl acetate / water with a mass ratio of 7:3.

[0015] Further, the graphene oxide accounts for 4% to 6% of the total dry weight of the materials excluding the ethyl acetate, the silver nanowire accounts for 2% to 4% of the total dry weight of the materials excluding the ethyl acetate, and the input mass ratio of the tris(hydroxymethyl) aminomethane, the polydopamine, and the graphene oxide is 1:1:2.

[0016] Further, the polydopamine functionalization specifically includes: adding dopamine hydrochloride, and magnetically stirring at room temperature for 6h to allow the dopamine to self-polymerize and deposit on the surface of the graphene oxide; and the silver nanowire dispersion functionalization specifically includes: adding a silver nanowire aqueous dispersion, and magnetically stirring at room temperature for 2h for dispersion.

[0017] Further, the injection speed of the microfluidic channel in S2 is 4 to 6mL / min; and the main channel of the microfluidic channel in S2 has a width of 1mm, a height of 300μm, and a length of 100mm.

[0018] Further, the mold in S3 needs to be pre-cooled to 0℃; the cold table in S3 is set to a temperature of -25℃ to -35℃; and the pre-cooled copper rod in S3 needs to be pre-cooled to -25℃ to -35℃.

[0019] Further, after the freezing in S3 is completed, the mold is moved into a freeze dryer for drying, and the specific process is: after freezing for 2h, drying is performed at -50℃ and under a vacuum of 10Pa for 48h.

[0020] Further, the wavelength of the semiconductor laser in S4 is set to 808nm, the laser power is set to 1W / cm 2 , and the spot coverage diameter is 10mm.

[0021] Further, the photothermal reduction treatment of S4 is specifically a process of scanning the upper surface of the complex A in a spiral trajectory, irradiating each place for 1.5-2.5 seconds, and scanning twice.

[0022] The application also provides an application of the graphene modified conductive thermoplastic polyurethane.

[0023] Compared with the prior art, the application has the following beneficial effects:

[0024] (1) The process scheme provided by the application combines microfluidic dispersion orientation modules, bidirectional freezing-in-situ photothermal reduction modules and multifunctional interface synergistic design, solves the problems of uniform dispersion and orientation assembly of graphene under high load, and constructs a through three-dimensional anisotropic conductive and thermal network.

[0025] (2) The application reduces the use of organic solvents by using a low-boiling-point ethyl acetate-water mixed solvent system and is conducive to recycling, and the process can be continuously controlled and is suitable for large-scale production. Compared with the traditional method, the graphene modified conductive TPU composite material prepared by the process of the application has a large improvement in electrical and thermal properties.

[0026] (3) The composite material prepared by the application maintains the inherent flexibility and good mechanical strength of TPU while improving the conductivity and thermal conductivity, thereby widening the application range. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 It is a flow chart of the wet composite preparation process of the graphene modified conductive thermoplastic polyurethane of the application;

[0028] Figure 2 It is a microfluidic specific structure and process schematic diagram of the application;

[0029] Figure 3 It is a schematic diagram of the bidirectional freezing process of the application;

[0030] Figure 4 It is a scanning electron microscope (SEM) result graph in experimental example 1 of the application;

[0031] Figure 5 It is an X-ray photoelectron spectroscopy (XPS) result graph in experimental example 2 of the application. DETAILED DESCRIPTION

[0032] The following examples further explain and illustrate the technical solutions of the present application. It is particularly pointed out that each specific embodiment is a specific embodiment and explanation of the technical solutions, and should not be regarded as a limitation on the protection scope of the present application. Those skilled in the art still have the right to modify the technical solutions of these examples, to make equivalent replacements to some or all of the technical features, and these modifications or replacements do not change the essence of the corresponding technical solutions, and do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions described in the present application.

[0033] The present application proposes a wet compounding preparation process of graphene modified conductive thermoplastic polyurethane, as shown in the attached Figure 1 The flow chart of the preparation process of the present application is shown in the attached

[0034] 1. Surface bifunctionalization treatment of graphene oxide (GO)

[0035] In order to improve the interface synergy between graphene and thermoplastic polyurethane (TPU) matrix and other conductive fillers, the present application performs multifunctional molecular modification on the surface of GO; preferably, a polydopamine (PDA) coating is introduced: taking advantage of the characteristic of dopamine monomer self-polymerization into a film in weak alkali solution, GO is dispersed in an alkaline buffer solution containing tris(hydroxymethyl) aminomethane (Tris), dopamine monomer is added and stirred, so that it is oxidized and polymerized on the surface of GO, forming a PDA coating layer with a thickness of 5-10 nm; the PDA coating layer contains a large number of functional groups such as catechol and amine groups, which on the one hand endows GO with good hydrophilicity and biological adhesion ability, and on the other hand these functional groups can form hydrogen bonds or covalent bonds with carbonyl groups and amino groups on the polyurethane segment, thereby firmly anchoring the GO platelets in the TPU matrix and greatly improving the interface bonding strength; the present application utilizes the interaction between polydopamine and graphene and TPU at the same time to play a bifunctional coupling role. In addition, the polydopamine layer also provides a platform for introducing other functional components; polydopamine has a reduction and adhesion effect on metal nanomaterials, and can introduce silver nanowire (AgNW) one-dimensional conductive material into the graphene network; based on this function, AgNW dispersion is added to the PDA functionalized GO dispersion, and the adhesion effect of PDA is used to make AgNW adsorbed and fixed on the surface and gap of GO platelets. AgNW has high aspect ratio and excellent conductivity, and can act as an electrical conduction bridge in the composite material to connect adjacent graphene platelets to form a conductive path; compared with a single filler, the hybrid filler formed by AgNW and graphene can significantly reduce the percolation threshold of the composite material, i.e. the conductive network is connected through with less total filler content. In addition, GO can also prevent AgNW from agglomerating and settling, and plays a role as a dispersant; at the same time, AgNW is embedded between graphene sheets to play a "support skeleton" role, avoiding the re-stacking of the platelets; the above-mentioned GO accounts for 4%-6% of the total mixture dry weight, AgNW accounts for 2%-4% of the total mixture dry weight, and the mass ratio of Tris, PDA and GO is 1:1:2.

[0036] 2. Microfluidic laminar high-efficiency dispersion and induced orientation arrangement

[0037] The functionalized GO is dispersed in an aqueous phase to prepare a stable GO aqueous dispersion; meanwhile, the TPU elastomer is dissolved in an ethyl acetate organic phase, and water is added to form a TPU ethyl acetate / water emulsion by stirring; then the GO aqueous dispersion and the TPU emulsion are respectively injected through the microchannel by using a specific microfluidic laminar shear channel, and are converged in the main channel to form a laminar co-flow, and the specific structure and process are shown in FIG. 1. Figure 2 The Reynolds number of the microfluidic channel is very low under the scale, and the flow is in a laminar state without turbulent mixing, so that the two liquid flows can flow in parallel for a long distance in the microchannel, and the GO nanosheet is oriented and highly uniformly dispersed in the TPU emulsion matrix along the flow direction under the shear action of the laminar flow, without ultrasonic, so as to achieve ideal peeling and dispersion effect. The orientation assembly induced by the microfluidic laminar flow can realize the ordered arrangement and high dispersion of the monolayer GO in the in-plane direction in a short time, and effectively avoids the agglomeration of the sheet layer.

[0038] 3. Bidirectional freezing process

[0039] The GO / TPU emulsion oriented by microfluidic blending is rapidly placed in a freezing device for directional freezing. Preferably, the present application adopts a vertical gradient cooling method combined with bidirectional freezing: the bottom of the mold containing the emulsion is placed above the cold source, so that the freezing interface advances from bottom to top, realizing vertical directional solidification; meanwhile, a second cold source is inserted into the center of the emulsion, and the two freezing interfaces advance towards each other in the system, so as to induce the growth of ice crystals in the vertical and horizontal directions at the same time, and the specific setting is shown in FIG. 2. Figure 3 By controlling the temperature gradient and rate of bidirectional freezing, the ice crystals generate ordered crystal templates arranged in two orthogonal directions in the system, the GO sheet layer is gradually squeezed and assembled at the ice crystal grain boundary, and is arranged in the direction of ice crystal growth to form a network structure; especially under the condition of bidirectional freezing, the ice crystals no longer grow vertically, but present a pattern of simultaneous vertical and radial development, so that the GO constructs a three-dimensional anisotropic ordered skeleton structure, which is not only vertically oriented in the thickness direction, but also radially or layer-oriented in the plane. After freezing, freeze-drying is performed to remove the ice crystals, and the porous framework composed of GO and TPU is retained.

[0040] 4. Photothermal reduction process

[0041] After obtaining the dried GO / TPU porous structure, in-situ reduction of GO in it is performed to improve the electrical conductivity. The present application uses a photothermal reduction process instead of the traditional high-temperature thermal reduction: the composite porous framework is scanned and irradiated by a near-infrared laser with a wavelength of 808 nm. Due to the strong absorption and photothermal conversion capability of graphene-based materials to near-infrared light, the light energy can be rapidly converted into heat energy; in the laser irradiation area, the local temperature of GO rises sharply, and its oxygen-containing functional groups are pyrolyzed and removed, so that the GO is reduced to conductive reduced graphene (rGO) within a few seconds; in contrast, the absorption of the TPU matrix to the 808 nm laser is weak, and the laser irradiation time is short, so that the TPU is basically not damaged by heat and the mechanical properties are maintained. By adjusting the laser power and scanning speed, the graphene can be selectively reduced without damaging the integrity of the polymer matrix; the photothermal reduction process is carried out at room temperature, without the need to heat the entire composite material to a high temperature, avoiding the problem of thermal aging of TPU at a high temperature of >200℃ required by traditional thermal reduction.

[0042] Example 1

[0043] The wet composite preparation process of graphene-modified conductive thermoplastic polyurethane is as follows:

[0044] Table 1: Detailed information of main raw materials

[0045]

[0046]

[0047] S1: Take 0.5 g of graphene oxide (GO) powder, disperse it in 100 mL of deionized water, add 0.25 g of tris(hydroxymethyl)aminomethane (Tris) to adjust the pH to 8.5, and ultrasonically disperse for 10 min to obtain a uniform GO slurry; then add 0.25 g of dopamine hydrochloride, and magnetically stir at room temperature for 6 h to allow the dopamine to self-polymerize and deposit on the surface of GO, obtaining a polydopamine functionalized GO dispersion; then add 1 mg / mL of silver nanowire (AgNW) water dispersion and magnetically stir at room temperature for 2 h, the dispersion contains 0.3 g of AgNW, the diameter of AgNW is 20-30 nm, and the length is 20-40 μm; take another 8.7 g of polytetrahydrofuran glycol-4,4'-diphenylmethane diisocyanate-based TPU granules, add them to 100 mL of ethyl acetate / water mixed solvent with a mass ratio of 7:3, and magnetically stir at 40℃ for 2 h to fully dissolve the TPU, forming a milky white TPU emulsion.

[0048] S2: A Y-shaped microfluidic device was designed and used, the main channel width was 1 mm, height was 300 μm, and length was 100 mm. Two injection pumps were connected to the inlet of the main channel through branch channels. The GO aqueous dispersion and the TPU ethyl acetate emulsion were loaded into the injection pumps and injected into the microfluidic channel at a flow rate of 5 mL / min. The two streams kept a laminar flow state after merging in the main channel, and the Reynolds number was less than 50. The uniform emulsion flowed out of the outlet of the main channel.

[0049] S3: The GO / TPU uniform emulsion was immediately poured into a pre-cooled stainless steel mold with an inner diameter of 50 mm and a height of 20 mm. The bottom of the mold was tightly attached to the top of a cold table, and the temperature of the cold table was set to -30°C. The emulsion began to solidify from bottom to top, and a pre-cooled copper rod was inserted into the center of the emulsion as a second cooling source to achieve simultaneous freezing from the center to the periphery. The entire freezing process lasted for 2 hours, and then the mold was moved into a freeze dryer and dried at -50°C under a vacuum of 10 Pa for 48 hours. After the sublimation of ice crystals, a complete porous aerogel-like GO / TPU composite was obtained.

[0050] S4: The freeze-dried GO / TPU composite was subjected to photothermal reduction treatment using an 808 nm semiconductor laser. The laser power was set to 1 W / cm 2 , the spot coverage diameter was 10 mm, and the sample surface was scanned in a spiral trajectory. Each irradiation lasted for 2 seconds, and the sample was scanned twice to ensure uniform irradiation. The color of the sample gradually changed from brown to black, indicating that the GO was reduced. After reduction, a graphene-modified conductive thermoplastic polyurethane was obtained.

[0051] Example 2

[0052] The preparation method of Example 1 was used, except that:

[0053] In S1, graphene oxide (GO) powder 0.4 g, 0.2 g of trimethylol aminomethane, 0.2 g of dopamine hydrochloride, 0.2 g of AgNW in AgNW water dispersion, and 9 g of polytetramethylene glycol-4,4'-diphenylmethane diisocyanate-based TPU granules were used.

[0054] In S2, the above GO aqueous dispersion and TPU ethyl acetate emulsion were loaded into the injection pumps and injected into the microfluidic channel at a flow rate of 4 mL / min.

[0055] In S3, the temperature of the cold table was set to -25°C, and the copper rod was pre-cooled to -25°C.

[0056] In S4, the semiconductor laser irradiated each point for 1.5 seconds.

[0057] The other steps were the same.

[0058] Example 3

[0059] The preparation method of Example 1 is referred to, except that:

[0060] In S1, 0.6 g of graphene oxide (GO) powder is taken, 0.3 g of tris-hydroxymethyl aminomethane is added, 0.3 g of dopamine hydrochloride is added, 0.4 g of AgNW is taken in the AgNW water dispersion, and 8.4 g of polytetrahydrofuran glycol-4, 4'-diphenyl methane diisocyanate-based TPU granules are taken;

[0061] In S2, the above GO water dispersion and TPU ethyl acetate emulsion are respectively loaded into the syringe pump, and are simultaneously injected into the microfluidic channel at a flow rate of 6 mL / min each;

[0062] In S3, the cold table temperature is set to -35°C, and the copper rod is pre-cooled to -35°C;

[0063] In S4, the semiconductor laser irradiates for 2.5 seconds each time;

[0064] The other steps are the same.

[0065] Comparative Example 1

[0066] The preparation method of Example 1 is referred to, but instead of microfluidic laminar dispersion, traditional ultrasonic dispersion is used. The GO water dispersion and TPU ethyl acetate emulsion in S1 are directly mixed, an ultrasonic probe is used with a power setting of 300 W, and the mixed liquid is ultrasonically treated for 20 minutes. Then, pouring, freezing, freeze-drying and photothermal reduction are performed, and the other steps are the same.

[0067] Comparative Example 2

[0068] The preparation method of Example 1 is referred to, but instead of directional freezing, natural sedimentation drying is used; in S3, the GO / TPU emulsion is directly placed at room temperature to volatilize the solvent and form, and then the same photothermal reduction is performed, and the other steps are the same.

[0069] Comparative Example 3

[0070] The preparation method of Example 1 is referred to, but instead of 808 nm photothermal reduction, conventional thermal reduction is used; in S4, the freeze-dried product is placed in a 200°C vacuum oven for 2 hours to reduce the GO, and then the composite material is obtained after cooling. The other steps are the same.

[0071] Comparative Example 4

[0072] The preparation method of Example 1 is referred to, but instead of introducing polydopamine modification and AgNW, only unmodified pure GO is used as the filler. The pure GO is dispersed in N,N-dimethylformamide (DMF), and the same microfluidic-freezing-thermal reduction process as in Example 1 is used to prepare the composite material.

[0073] Experimental Example 1

[0074] The graphene-modified conductive thermoplastic polyurethane prepared in Example 1 was observed by scanning electron microscopy (SEM), and the specific process and settings refer to the standard GB / T 43196-2023 "Nanotechnology - Scanning electron microscopy for the measurement of particle size and shape distribution of nanoparticles". A sample of 5x5x2mm size was taken, and the surface was blown by a nitrogen spray gun with a blowing pressure of 0.2MPa and a blowing distance of 50mm. A 5nm gold-palladium alloy layer was sprayed on the surface of the sample, and then the sample was adhered to the sample stage using conductive adhesive. The electron microscope acceleration voltage was set to 5kV, and the working distance was 6mm. The test results are shown in FIG. 1, and it can be observed that the rGO is uniformly dispersed in the TPU, and the AgNWs are distributed through the vertical conductive path. Figure 4

[0075] Experimental Example 2

[0076] The freeze-dried GO / TPU composite before S4 laser irradiation and the graphene-modified conductive thermoplastic polyurethane prepared in Example 1 were subjected to X-ray photoelectron spectroscopy (XPS) experiments, and the specific process and settings refer to the standards GB / T 19500-2004 "General methods for X-ray photoelectron spectroscopy analysis" and GB / T 25184-2010 "X-ray photoelectron spectrometer verification method". The freeze-dried GO / TPU composite before S4 laser irradiation and the graphene-modified conductive thermoplastic polyurethane were taken as bulk samples, and the cross sections were obtained by liquid nitrogen brittle fracture, respectively. A 5x5mm area of each cross section was adhered to a conductive tape, and the surface was cleaned with Ar + sputtering; the X-ray source was monochromatic Al Kα, the analysis mode was high-resolution narrow scan, and the binding energy correction was based on C1s; the test results are shown in FIG. 2, and it can be seen from the results that the C / O atomic ratio increased from 2.45 before laser irradiation reduction to 4.84, which proves that the oxygen-containing functional groups of GO are largely removed and successfully converted into conductive rGO. Figure 5

[0077] Experimental Example 3

[0078] The final graphene-modified polyurethane composites obtained in Examples 1-3 and Comparative Examples 1-4 were subjected to performance test comparison, including electrical conductivity test, thermal conductivity test and mechanical property test, and the specific experimental process design is as follows:

[0079] 1. Electrical conductivity test

[0080] (1) Method: four-point probe method;

[0081] (2) Equipment: linear four-point probe tester;

[0082] ​​(3) Parameters: probe spacing, 1.0 mm; current range, 1 mA-100 mA; testing direction, in-plane (parallel to the hot-pressing surface) and vertical direction;

[0083] (4) Test sampling method: in-plane conductivity sampling, 5-point average of the sample surface; vertical conductivity test, polished sample cross-section for testing.

[0084] 2. Thermal conductivity test

[0085] (1) Method: laser flash method;

[0086] (2) Equipment: laser thermal conductivity instrument;

[0087] (3) Parameters: test temperature, 25℃; laser pulse energy, 15 J; direction, in-plane (radial) and vertical (axial);

[0088] (4) Test sampling method: repeated 3 times for average.

[0089] 3. Mechanical property test

[0090] (1) Method: tensile test;

[0091] (2) Equipment: universal mechanical testing machine;

[0092] (3) Parameters: tensile rate, 50 mm / min; gauge length, 25 mm; ambient temperature, 25℃;

[0093] (4) Measurement index: tensile strength (MPa), elongation at break (%).

[0094] The experimental results are shown in Tables 2 and 3.

[0095] Table 2 Comparison table of conductivity and thermal conductivity experimental results

[0096]

[0097] From the above results, it can be seen that the conductivity and thermal conductivity of Examples 1-3 are relatively high, and the conductivity and thermal conductivity of Example 3 are greater due to the larger amount of filler; the conductivity and thermal conductivity of Comparative Example 1 are greatly reduced due to uneven dispersion and poor orientation of the filler caused by ultrasonic dispersion; the conductivity and thermal conductivity of Comparative Example 2 are relatively low and the anisotropy is weak due to the natural drying without directional structure; the conductivity of Comparative Example 3 is slightly lower than that of Example 1 due to the possible partial degradation of TPU caused by thermal reduction; and the conductivity and thermal conductivity of Comparative Example 4 are extremely poor due to the absence of AgNW and polydopamine.

[0098] Table 3 Comparison table of mechanical property test results

[0099]

[0100] From the above results, it can be seen that the mechanical properties of Examples 1-3 are better, and although Example 3 has more fillers, the mechanical properties do not decrease much; Comparative Example 1 has a structure defect due to the ultrasonic dispersion process, and the mechanical properties decrease; Comparative Example 2 has a structure defect due to the natural drying process, and the mechanical properties decrease; in Comparative Example 3, thermal reduction causes the TPU to thermally degrade, and the elongation at break decreases significantly; and in Comparative Example 4, without interface modification, the fillers agglomerate, and the mechanical properties are the worst.

Claims

1. A process for the preparation of graphene-modified conductive thermoplastic polyurethane by wet compounding, characterized in that, The method comprises the following steps: S1: functionalizing graphene oxide and preparing a water dispersion, and preparing thermoplastic polyurethane pellets into an emulsion; S2: loading the graphene oxide water dispersion and the thermoplastic polyurethane emulsion prepared in S1 into a syringe pump respectively, and injecting them into a microfluidic channel, and keeping the two liquid streams in a laminar parallel flow state after merging in the main channel, and discharging a uniform emulsion at the outlet of the main channel; S3: pouring the uniform emulsion obtained in S2 into a mold, tightly attaching the bottom of the mold to the top of a cold table, and inserting a pre-cooled copper rod into the center of the emulsion as a second cold source to realize synchronous freezing from the center to the periphery, and after freezing, moving the mold into a freeze dryer for drying, and obtaining a composite A after sublimation of ice crystals; S4: performing photothermal reduction treatment on the composite A by using a semiconductor laser, and obtaining a graphene-modified conductive thermoplastic polyurethane after reduction treatment.

2. The process for the preparation of graphene-modified conductive thermoplastic polyurethane by wet compounding as claimed in claim 1, wherein, The functionalization treatment in S1 is polydopamine functionalization and silver nanowire dispersion functionalization; the graphene oxide needs to be dispersed in a basic buffer solution containing tris(hydroxymethyl)aminomethane before the functionalization treatment; the solvent used in preparing the thermoplastic polyurethane emulsion in S1 is a mixed solvent of ethyl acetate and water with a mass ratio of 7:

3.

3. The process for the preparation of graphene-modified conductive thermoplastic polyurethane by wet compounding as claimed in claim 2, wherein, The graphene oxide accounts for 4-6% of the total dry weight of the materials excluding the ethyl acetate, the silver nanowires account for 2-4% of the total dry weight of the materials excluding the ethyl acetate, and the mass ratio of the tris(hydroxymethyl)aminomethane, the polydopamine and the graphene oxide is 1:1:

2.

4. The process for the preparation of graphene-modified conductive thermoplastic polyurethane by wet compounding as claimed in claim 2, wherein, The polydopamine functionalization specifically includes: adding dopamine hydrochloride, and magnetically stirring at room temperature for 6h to make the dopamine self-polymerize and deposit on the surface of the graphene oxide; the silver nanowire dispersion functionalization specifically includes: adding a silver nanowire water dispersion, and magnetically stirring at room temperature for 2h for dispersion.

5. The process for the preparation of graphene-modified conductive thermoplastic polyurethane by wet compounding as claimed in claim 1, wherein, The injection speed of the simultaneous injection into the microfluidic channel in S2 is 4-6mL / min; the main channel of the microfluidic channel in S2 has a width of 1mm, a height of 300μm and a length of 100mm.

6. The process for the preparation of graphene-modified conductive thermoplastic polyurethane by wet compounding as claimed in claim 1, wherein, The mold in S3 needs to be pre-cooled to 0℃; the cold table in S3 is set to a temperature of-25℃ to-35℃; and the pre-cooled copper rod in S3 needs to be pre-cooled to-25℃ to-35℃.

7. The process for the preparation of graphene-modified conductive thermoplastic polyurethane by wet compounding as claimed in claim 1, wherein, After the freezing in S3, the mold is moved into a freeze dryer for drying, and the specific process is: drying for 48h at-50℃ and under a vacuum of 10Pa after freezing for 2h.

8. The process for the preparation of graphene-modified conductive thermoplastic polyurethane by wet compounding as claimed in claim 1, wherein, The semiconductor laser of S4, wavelength is set to 808nm, laser power is set to 1W / cm 2 , spot coverage diameter is 10mm.

9. The process for the preparation of graphene-modified conductive thermoplastic polyurethane by wet compounding as claimed in claim 1, wherein, The photothermal reduction treatment in S4 specifically includes: scanning the upper surface of the composite A in a spiral trajectory, and irradiating each place for 1.5-2.5s, and scanning twice.

10. Use of the graphene-modified electrically conductive thermoplastic polyurethane according to any one of claims 1 to 9, characterized in that, The graphene-modified conductive thermoplastic polyurethane can be used for manufacturing flexible electronic devices.

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