A composite film based on modified carbon nanotubes and thermoplastic polyurethane and a preparation method and application thereof

Abstract

The application provides a composite film based on modified carbon nanotubes and thermoplastic polyurethane and a preparation method and application thereof, wherein multi-walled carbon nanotubes, tannic acid and a coupling agent are dispersed in a solvent, nitrogen is introduced for protection, and amine treatment is carried out under stirring and heating; an epoxy-terminated polyether is added, and reaction is carried out under heating to obtain covalently bonded tannic acid-carbon nanotube powder; the powder is dispersed in a solvent, a dispersing agent is added thereto, and a solution I is obtained after ultrasonic treatment; polyurethane and a crosslinking agent are dissolved in a solvent, stirring is carried out under heating, and a solution II is obtained after activation; the solution I and the solution II are mixed, nano-hydroxyapatite is added thereto, and a dispersion liquid is obtained after mixing; the dispersion liquid is poured into a mold, and the composite film is obtained after crosslinking and solidification. The composite film realizes stable combination of tannic acid and carbon nanotubes through multi-step reaction, and simultaneously constructs a three-dimensional crosslinking network between a matrix and fillers.

Description

Technical Field

[0001] This invention belongs to the field of flexible electronic materials, and in particular relates to a composite film based on modified carbon nanotubes and thermoplastic polyurethane, its preparation method and application. Background Technology

[0002] With the rapid development of wearable smart devices, electronic skin, and precision medicine technologies, the demand for flexible strain sensors that combine high sensitivity, excellent tensile strength, and long-term stability is becoming increasingly urgent. Flexible strain sensors, with their advantages of low cost, easy integration, and simple signal conversion, show broad application prospects in human motion monitoring, rehabilitation assessment, and human-computer interaction systems.

[0003] Multi-walled carbon nanotubes (MWCNTs) are ideal conductive fillers for flexible composite sensors due to their excellent conductivity, ultra-high aspect ratio, and superior mechanical properties. However, virgin MWCNTs are prone to aggregation due to strong van der Waals forces between the tubes, resulting in poor dispersion and insufficient interfacial compatibility in the polymer matrix. This, in turn, affects the mechanical flexibility, conductive stability, and sensing reversibility of the composite material. Thermoplastic polyurethane (TPU), as an elastic matrix, possesses excellent tensile strength, biocompatibility, and processability. However, unmodified dispersion defects of MWCNTs in TPU typically lead to high percolation thresholds and poor sensing cycle stability in the composite material, severely limiting its practical application in wearable electronics.

[0004] Existing methods for surface modification of MWCNTs include silane coupling agent functionalization, surfactant-mediated dispersion, and polymer grafting modification. However, these methods often involve toxic chemical reagents, complex synthesis processes, or high energy consumption. Even existing green modification strategies suffer from insufficient performance synergy: for example, the gauge factor (GF) of chitosan-modified MWCNTs / TPU composites is only 11.5, the elongation at break is only 250%, and it lacks electrothermal functionality; the polydopamine-modified MWCNTs / TPU sensor has a maximum operating temperature of 112 °C at 10 V, but its GF is as low as 9.8, which cannot meet the requirements for high-sensitivity motion detection.

[0005] Tannic acid (TA), as a natural polyphenol compound, possesses biodegradability, excellent biocompatibility, and abundant functional groups, making it a highly promising green modifier. However, its traditional non-covalent modification methods rely solely on hydrogen bonds and π-π stacking interactions, resulting in insufficient durability of the modification effect. Summary of the Invention

[0006] In view of this, the present invention aims to overcome the defects in the prior art and proposes a composite film based on modified carbon nanotubes and thermoplastic polyurethane, its preparation method and application.

[0007] To achieve the above objectives, the technical solution of the present invention is implemented as follows: This invention provides a method for preparing a composite film based on modified carbon nanotubes and thermoplastic polyurethane, comprising the following steps: Step 1 involves dispersing multi-walled carbon nanotubes, tannic acid, and a coupling agent in a solvent, purging with nitrogen for protection, and stirring under heating conditions to perform an amination pretreatment. Step 2 involves adding epoxy-terminated polyether (EPE) to the reaction system obtained in Step 1, reacting under heating conditions, and then filtering, washing, and drying to obtain covalently bonded tannic acid-carbon nanotube powder (c-TA-MWCNTs). Step 3 involves dispersing the covalently bonded tannic acid-carbon nanotube powder in a solvent, adding a dispersant, and then sonicating it to obtain solution I. Step 4 involves dissolving polyurethane and crosslinking agent in a solvent, stirring under heating conditions, and activating the solution to obtain solution II. Step 5 involves mixing solution I and solution II, adding nano-hydroxyapatite (n-HA) to the mixture, and then pouring the dispersion into a mold. After drying and cross-linking curing, the composite film (c-TA-MWCNTs / TPU) based on modified carbon nanotubes and thermoplastic polyurethane is obtained.

[0008] Furthermore, in step 1, the mass ratio of multi-walled carbon nanotubes, tannic acid, and coupling agent is (2-3):(0.5-1):(0.25-0.5); the heating temperature in step 1 is 60-80 ℃; the amination pretreatment time in step 1 is 10-12 h; and the nitrogen flow rate in step 1 is 50-80 mL / min. Tannic acid is a polyphenol compound with chromatographic purity.

[0009] Furthermore, the coupling agent in step 1 is an aminosilane coupling agent; the coupling agent in step 1 is KH-550; the purity of the multi-walled carbon nanotubes in step 1 is ≥99 wt%, the length is 1-3 μm, and the outer diameter is 8-15 nm. The amino content of the coupling agent needs to be ≥30 wt%. The aminosilane coupling agent (KH-550) is a core molecular bridge and active site introducer, introducing active amino groups that can undergo epoxy ring-opening reactions onto the surface of inert MWCNTs, establishing the basis for the covalent connection between TA and MWCNTs, while improving the dispersibility of MWCNTs in the reaction solvent and pre-embedding interfacial binding sites to enhance its interfacial compatibility with the subsequent composite system. It is a key reagent for achieving stable covalent bonding between TA and MWCNTs.

[0010] Furthermore, the mass ratio of the epoxy-terminated polyether in step 2 to the tannic acid in step 1 is (3-4):(2-3); the epoxy value of the epoxy-terminated polyether in step 2 is 0.5-0.8 eq / 100g; the heating temperature in step 2 is 90-100 ℃; the reaction time in step 2 is 7-8 h; and the drying temperature in step 2 is 60-80 ℃, and the time is 9-10 h.

[0011] Furthermore, in step 3, the amount of dispersant added is 1-2 wt% of the mass of the covalently bonded tannic acid-carbon nanotube powder; the dispersant in step 3 is polyethylene glycol stearate; the solvent in step 3 is N,N-dimethylformamide (DMF); the ultrasonication step in step 3 has a power of 250-350 W and a time of 40-70 min, with stirring performed simultaneously at a speed of 1500-2000 rpm. This achieves single-tube dispersion of c-TA-MWCNTs in DMF.

[0012] Furthermore, in step 4, the mass ratio of polyurethane to crosslinking agent is 1:(0.01-0.015); the activation temperature in step 4 is 70-80 ℃, and the time is 30-40 min; the crosslinking agent in step 4 is an isocyanate crosslinking agent (MDI); and the solvent in step 4 is N,N-dimethylformamide.

[0013] Furthermore, the amount of covalently bonded tannic acid-carbon nanotube powder added in step 3 is 1-5 wt% of the mass of polyurethane in step 4; the amount of nano-hydroxyapatite added in step 5 is 0.57-0.67 wt% of the mass of polyurethane in step 4; the particle size of the nano-hydroxyapatite in step 5 is 20-50 nm, and the surface hydroxyl density is ≥5 mmol / g. n-HA can form a multiple hydrogen bond network with the ester groups of the TPU matrix and the phenolic hydroxyl groups of c-TA-MWCNTs.

[0014] The sensor exhibits optimal overall performance when the c-TA-MWCNTs filling amount is 5.0 wt%. The addition amount of MDI is 1-1.5 wt% of the TPU mass to ensure the formation of a three-dimensional cross-linked network structure, thereby improving the mechanical stability and electrical continuity of the composite material.

[0015] Furthermore, the drying step in step 5 is performed at a temperature of 60-80 ℃ for 8-24 h; the cross-linking curing step in step 5 is performed at a temperature of 80-90 ℃ for 10-14 h.

[0016] This invention achieves covalent functionalization of MWCNTs by TA through a three-step reaction of "amineation-grafting-crosslinking", avoiding nanoparticle aggregation during the modification process.

[0017] The present invention also provides a composite film based on modified carbon nanotubes and thermoplastic polyurethane prepared by the preparation method described above.

[0018] The composite membrane has an elongation at break of ≥300%, a tensile strength of 16-17 MPa, a gauge factor (GF) of 15.35 in the strain range of 100-300%, and voltage-controllable electrothermal properties, with a steady-state temperature of 148 ℃ at 9 V.

[0019] The composite membrane exhibits a stable resistive response within a strain range of 20-300% and a tensile rate of 2-40 mm / min, and its performance shows no significant degradation after 1200 cycles of bending testing. It can accurately detect mechanical behaviors such as extrusion, bending, and torsion.

[0020] The present invention also provides an application of a composite film based on modified carbon nanotubes and thermoplastic polyurethane, wherein the composite film is used in the preparation of wearable electronic devices, health monitoring devices or sports function assessment devices; and in the preparation of flexible strain sensors.

[0021] Therefore, developing a green modification strategy based on covalent bonding to achieve stable bonding between tannic acid and carbon nanotubes through multi-step reactions, while simultaneously constructing a three-dimensional cross-linked network between the matrix and the filler, can realize the synergistic integration of high sensitivity, high tensile strength, long cycle stability and efficient electrothermal performance of flexible strain sensors. This has significant theoretical and practical application value.

[0022] This invention replaces the traditional simple hydrogen bonding / π-π non-covalent modification with a multi-step covalent bonding and multiple non-covalent interactions. It achieves stable bonding of tannic acid and MWCNTs through two core reactions: amination pretreatment and epoxy ring-opening covalent grafting. Amination pretreatment introduces active amino reaction sites into MWCNTs. Using an aminosilane coupling agent as a bridge, the alkoxy groups in the agent's molecular structure undergo hydrolytic condensation reactions with a small number of oxygen-containing functional groups (hydroxyl and carboxyl groups) on the MWCNTs surface. Simultaneously, the aminosilane coupling agent molecules adsorb onto the MWCNTs surface through van der Waals forces and hydrophobic interactions, ultimately successfully grafting a large number of active amino groups (-NH2) onto the MWCNTs surface. Epoxy ring-opening covalent grafting achieves stable covalent bonding between tannic acid and MWCNTs by adding […]. Epoxy-terminated polyethers utilize the epoxy groups (-CH-CH2-O-) at both ends of the epoxy-terminated polyether molecule to undergo an epoxy ring-opening addition reaction with the active amino groups on the surface of MWCNTs, generating stable CN covalent bonds. At the same time, the epoxy group at the other end of the epoxy-terminated polyether has low steric hindrance and can undergo further ring-opening reactions with the phenolic hydroxyl and carboxyl groups in the tannic acid molecule. Finally, the epoxy-terminated polyether acts as a "molecular bridge" to stably graft tannic acid molecules onto the surface of MWCNTs in the form of covalent bonds, forming a c-TA-MWCNTs covalent bonding system.

[0023] Compared with the prior art, the present invention has the following advantages: The composite membrane based on modified carbon nanotubes and thermoplastic polyurethane described in this invention adopts a three-step covalent modification strategy of "amine-graft-crosslinking" to replace traditional non-covalent modification and single silane coupling agent modification. It achieves stable covalent bonding between TA and MWCNTs through the ring-opening reaction of amino and epoxy groups, which solves the technical pain points of easy molecule detachment and poor stability in traditional modification. All the modifiers used are green and environmentally friendly materials, and the preparation process does not involve toxic reagents, which is in line with the concept of sustainable development.

[0024] The present invention describes a composite film based on modified carbon nanotubes and thermoplastic polyurethane, which constructs a triple synergistic system of "conductive network (c-TA-MWCNTs) - three-dimensional cross-linked matrix (TPU-MDI) - surface-reinforcing particles (n-HA)". Through the synergistic effect of covalent bonds, multiple hydrogen bonds and cross-linked networks, it simultaneously solves the three core problems of poor dispersion of conductive fillers, insufficient interfacial compatibility and weak mechanical stability of the matrix, and achieves simultaneous improvement of dispersion, interfacial bonding force and mechanical properties.

[0025] The composite membrane based on modified carbon nanotubes and thermoplastic polyurethane described in this invention has high sensing sensitivity. Its GF values ​​in the strain ranges of 0-40%, 40-100%, and 100-300% are 6.37, 10.57, and 15.35, respectively, which are superior to most traditional modified MWCNTs / TPU sensors.

[0026] The composite membrane based on modified carbon nanotubes and thermoplastic polyurethane described in this invention, when used as a sensor, exhibits stable resistance response within a strain range of 20-300% and a tensile rate of 2-40 mm / min. Its performance shows no significant degradation after 1200 cycles of bending testing, enabling accurate detection of mechanical behaviors such as compression, bending, and torsion, as well as human joint movements (e.g., ...). Figures 5-6 As shown in the figure, it has a wide range of applications.

[0027] The composite film based on modified carbon nanotubes and thermoplastic polyurethane described in this invention integrates high-efficiency electrothermal performance. The steady-state temperature is positively correlated with voltage in the voltage range of 1-9 V, and the steady-state temperature can reach 148 ℃ at 9 V. Moreover, the electrothermal response is fast and reversible, and the cycle stability is excellent. Attached Figure Description

[0028] Figure 1 This is a SEM image of the unmodified MWCNTs / TPU composite material described in the embodiments of the present invention; Figure 2 This is a SEM image of the c-TA-MWCNTs / TPU composite membrane described in an embodiment of the present invention; Figure 3 These are the temperature response curves under different voltages described in the embodiments of the present invention; Figure 4 This is a schematic diagram illustrating the stability after 1200 cycles according to an embodiment of the present invention; Figure 5 This is a schematic diagram illustrating the human joint (finger) motion monitoring using the c-TA-MWCNTs / TPU sensor described in an embodiment of the present invention. Figure 6 This is a schematic diagram of human joint (wrist) motion monitoring using the c-TA-MWCNTs / TPU sensor described in an embodiment of the present invention. Detailed Implementation

[0029] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods described are conventional methods.

[0030] The abbreviations used in this invention are all fixed abbreviations in the art, and some of the letters are explained as follows: MWCNTs: Multi-walled carbon nanotubes; TA: Tannic acid; c-TA-MWCNTs: Covalently bonded tannic acid-carbon nanotubes; TPU: Thermoplastic polyurethane; KH-550: Aminosilane coupling agent; EPE: Epoxy-terminated polyether; n-HA: Nano-hydroxyapatite; MDI: Isocyanate crosslinking agent; DMF: N,N-dimethylformamide; PEG-4000: Polyethylene glycol stearate; GF: Gauge factor; SEM: Scanning electron microscope; FT-IR: Fourier transform infrared spectroscopy; XPS: X-ray photoelectron spectroscopy.

[0031] The present invention will be described in detail below with reference to the embodiments.

[0032] Example 1

[0033] A method for fabricating a flexible strain sensor based on a composite film of modified carbon nanotubes and thermoplastic polyurethane includes the following steps: (1) Preparation of c-TA-MWCNTs: Weigh 0.3 g MWCNTs (purity 99 wt%, length 1-2 μm, outer diameter 8-12 nm), 0.1 g TA and 0.05 g KH-550, disperse them in 100 mL ethanol-deionized water mixed solvent (volume ratio 3:1), purge with nitrogen (flow rate 60 mL / min), and stir at 80 °C for 12 h for amination pretreatment; then add 0.15 g EPE (epoxy value 0.6 eq / 100 g), heat to 100 °C and react for 8 h; after the reaction is completed, filter under vacuum, wash three times with anhydrous ethanol, and dry under vacuum at 60 °C for 10 h to obtain (c-TA-MWCNTs) powder; (2) Preparation of c-TA-MWCNTs dispersion: Weigh 0.12 g of c-TA-MWCNTs powder (filling amount 4.0 wt%), add it to 100 mL of DMF, add 0.0018 g of PEG-4000 as a dispersant, sonicate at 300 W for 45 min, and stir at 1800 rpm for 30 min to obtain a uniform and stable c-TA-MWCNTs dispersion; (3) Preparation of TPU solution: Weigh 10 g of TPU particles and 0.1 g of isocyanate crosslinking agent, add them to 100 mL of DMF, stir at 70 °C for 30 min until the TPU is completely dissolved and a uniform TPU solution is formed; (4) Preparation of composite slurry: Take 20 mL of c-TA-MWCNTs dispersion and mix with 80 mL of cross-linked TPU solution, add 0.057 g n-HA (particle size 20-50 nm), stir at 2000 rpm for 60 min at 28℃ to ensure that each component is fully mixed and obtain a uniform c-TA-MWCNTs / TPU composite slurry; (5) Preparation of flexible strain sensor: Pour the composite slurry into a PTFE mold of 5 cm × 3 cm × 0.05 cm, dry it in an oven at 60 ℃ for 24 h, and crosslink and cure it at 90 ℃ for 12 h to obtain a flexible strain sensor (c-TA-MWCNTs / TPU).

[0034] Comparative Example 1 A method for fabricating a flexible strain sensor using a composite film of carbon nanotubes and thermoplastic polyurethane includes the following steps: (1) Preparation of MWCNTs dispersion: Weigh 0.5 g MWCNTs, add to 100 mL DMF, add 0.005 g SDBS, and sonicate at 200 W for 30 min to obtain MWCNTs dispersion; (2) Preparation of TPU solution: Weigh 10 g of TPU particles and 0.1 g of isocyanate crosslinking agent, add them to 100 mL of DMF, stir at 25 °C for 2 h until the TPU is completely dissolved and a uniform TPU solution is formed; (3) Preparation of composite slurry: Take 20 mL of MWCNTs dispersion and mix with 80 mL of TPU solution, and mix at 25℃ for 60 min to obtain a uniform MWCNTs / TPU composite slurry; (4) Preparation of flexible strain sensor: Pour the composite slurry into a PTFE mold of 5 cm × 3 cm × 0.05 cm and dry it in an oven at 60 ℃ for 24 h to obtain flexible strain sensor (MWCNTs / TPU).

[0035] Comparative Example 2 The only difference from Example 1 is that: Step (1) prepares chitosan modified MWCNTs / TPU powder: Weigh 0.5 g MWCNTs and 1.0 g chitosan at a mass ratio of 1:2, disperse in 100 mL deionized water, stir at 60 °C for 24 h, centrifuge, wash and dry to obtain chitosan modified MWCNTs powder.

[0036] Comparative Example 3 The only difference from Example 1 is that TA is replaced with caffeic acid.

[0037] Comparative Example 4 The only difference from Example 1 is: (1) Preparation of TA-MWCNTs: Weigh 0.3 g MWCNTs (purity 99wt%, length 1-2 μm, outer diameter 8-12 nm), 0.1 g TA and 0.05 g KH-550, disperse them in 100 mL ethanol-deionized water mixed solvent (volume ratio 3:1), purge with nitrogen (flow rate 60 mL / min), stir at 80 °C for 12 h for amination pretreatment, and then vacuum dry at 60 °C for 10 h to obtain (c-TA-MWCNTs) powder.

[0038] Performance testing and results analysis: 1. Dispersion and Microstructure: The c-TA-MWCNTs / TPU composite film prepared in Example 1 remained uniformly dispersed after standing in DMF for 24 hours. Figure 2 As shown, SEM characterization of Example 1 shows that c-TA-MWCNTs do not have obvious aggregation in the TPU matrix and the interface is tightly bound. Figure 1 In Comparative Example 1, the unmodified MWCNTs showed severe aggregation in the matrix, with gaps at the interface.

[0039] As shown in Table 1, the composite material of Example 1 has an elongation at break of 320% and a tensile strength of 16.8 MPa.

[0040] 2. Electrothermal performance: such as Figure 3 As shown, Example 1 achieved a steady-state temperature of 148 °C at 9 V; as shown in Table 1, Comparative Example 1 achieved a steady-state temperature of 87 °C at the same voltage; Comparative Example 2 showed no significant electrothermal response; Comparative Example 3 achieved a steady-state temperature of 95 °C at the same voltage; and Comparative Example 4 achieved a steady-state temperature of 67 °C at the same voltage.

[0041] 3. Sensing performance: As shown in Table 1, the sensor of Example 1 has a GF of 15.35 under 100-300% strain; the sensor of Comparative Example 1 has a GF of 8.2 (50% strain); the sensor of Comparative Example 2 has a GF of 11.5 (50% strain); the sensor of Comparative Example 3 has a GF of 12.28 (50% strain); and the sensor of Comparative Example 4 has a GF of 7.4 (50% strain).

[0042] 4. Cyclic Stability: After 1200 cycles of bending test, the resistance response fluctuation of Example 1 is <5%. Figure 4 As shown, R is the resistance at a certain moment, R0 is the initial resistance, and ΔR is the change in resistance (R-R0); the fluctuation range of Comparative Example 1 is >15%; the fluctuation range of Comparative Example 2 is >10%.

[0043] Table 1 Test Results

[0044] As shown in Table 1, the overall performance (GF, elongation, and electrothermal temperature) of Example 1 is significantly better than that of Comparative Examples 1-4, demonstrating good application potential. Comparative Example 1, which uses unmodified MWCNTs combined with ordinary TPU, produced a flexible strain sensor whose performance indicators were far lower than those of Example 1. Because the surface of unmodified MWCNTs lacks active functional groups, its dispersibility in DMF solvent and TPU matrix is ​​extremely poor, easily leading to agglomeration and difficulty in forming a continuous and uniform conductive network. Under external stretching, the agglomerated MWCNTs are prone to debonding and breakage, resulting in poor sensing signal stability and a significant decrease in sensing performance (GF value). Simultaneously, the discontinuous conductive network limits the efficient conduction and conversion of Joule heat, significantly reducing electrothermal performance. Furthermore, the weak interfacial bonding between MWCNTs and the TPU matrix makes the interface prone to defects under external force, failing to effectively guarantee the material's flexibility (elongation at break), ultimately leading to inferior overall performance. Comparative Example 2 used chitosan-modified MWCNTs but did not introduce TA and EPE components. The resulting material exhibited low elongation at break, no electrothermal properties, and low sensing performance. Although chitosan can improve the dispersibility of MWCNTs through electrostatic interactions, it is itself an insulating polysaccharide. Excessive coating on the MWCNT surface forms an insulating layer, blocking electron transport paths and directly causing the material to lose its electrothermal properties. Furthermore, the lack of a polyphenolic structure mediated by TA and a flexible, toughening network of EPE prevents efficient interfacial compatibility between MWCNTs and the TPU matrix. The material is prone to brittle fracture under external forces, exhibiting extremely poor flexibility and ultimately demonstrating comprehensive performance shortcomings. Comparative Example 3 replaced TA with caffeic acid, resulting in the best overall performance among the comparative examples, but still significantly lower than Example 1. Caffeic acid and TA are both polyphenols that can assist in the dispersion of MWCNTs and enhance interfacial compatibility through π-π stacking and hydrogen bonding, thus outperforming Comparative Examples 1, 2, and 4. However, the two materials differ in structure: TA molecules contain more active functional groups, enabling them to form tighter intermolecular forces with the surface of MWCNTs and TPU / EPE, and their conjugated structure is more conducive to constructing a continuous and efficient conductive network; while caffeic acid has a weaker conjugated structure and intermolecular forces, making it difficult to form a synergistic toughening and conductivity enhancement effect comparable to TA. This results in the conductive network integrity, electrothermal conversion efficiency, and flexibility of the material being inferior to Example 1, showing a significant performance gap. Comparative Example 4, without the addition of EPE, exhibits comprehensively inferior material performance, with lower elongation at break, lower electrothermal temperature, and lower sensing performance.EPE, as a flexible elastomer component, is crucial for constructing a flexible and toughened network and assisting in conductive pathways in materials. Without EPE, the system relies solely on TPU for flexibility, failing to form an interpenetrating network, resulting in a significant increase in overall material rigidity and a substantial decrease in elongation at break. Simultaneously, EPE helps MWCNTs disperse uniformly within the TPU matrix; its absence exacerbates MWCNT aggregation, severely fragments the conductive network, and leads to extremely low electron transport efficiency. This not only minimizes electrothermal conversion efficiency but also hinders signal transmission during sensing, resulting in the worst sensing performance and ultimately limiting the material's comprehensive application potential. Example 1 demonstrates how TA-modified MWCNTs and EPE synergistically toughen the material, achieving three major advantages: TA's polyphenol structure stably disperses MWCNTs through π-π interactions and hydrogen bonds, constructing a highly efficient conductive network and improving electrothermal and sensing performance; EPE, as a flexible component, forms an interpenetrating network with TPU, significantly increasing the material's elongation at break; and the synergistic effect of TA and EPE ensures both interfacial bonding and continuity of conductive pathways, achieving comprehensive performance superiority.

[0045] Due to the lack of key modification or toughening components, each comparative example has significant shortcomings in conductive network integrity, interfacial bonding, or flexibility, ultimately resulting in overall performance that is inferior to Example 1.

[0046] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a composite film based on modified carbon nanotubes and thermoplastic polyurethane, characterized in that: Includes the following steps: Step 1 involves dispersing multi-walled carbon nanotubes, tannic acid, and a coupling agent in a solvent, purging with nitrogen for protection, and stirring under heating conditions to perform an amination pretreatment. Step 2 involves adding epoxy-terminated polyether to the reaction system obtained in Step 1, reacting under heating conditions, and then filtering, washing, and drying to obtain covalently bonded tannic acid-carbon nanotube powder. Step 3 involves dispersing the covalently bonded tannic acid-carbon nanotube powder in a solvent, adding a dispersant, and then sonicating it to obtain solution I. Step 4 involves dissolving polyurethane and crosslinking agent in a solvent, stirring under heating conditions, and activating the solution to obtain solution II. Step 5 involves mixing solution I and solution II, adding nano-hydroxyapatite, and mixing to obtain a dispersion. The dispersion is then poured into a mold, dried, and cross-linked to obtain the composite film based on modified carbon nanotubes and thermoplastic polyurethane. The coupling agent in step 1 is an aminosilane coupling agent; The solvent in step 3 is N,N-dimethylformamide; The solvent in step 4 is N,N-dimethylformamide; The crosslinking agent in step 4 is isocyanate MDI.

2. The method for preparing the composite film based on modified carbon nanotubes and thermoplastic polyurethane according to claim 1, characterized in that: The mass ratio of multi-walled carbon nanotubes, tannic acid and coupling agent in step 1 is (2-3):(0.5-1):(0.25-0.5); the heating temperature in step 1 is 60-80 ℃; the amination pretreatment time in step 1 is 10-12 h; and the nitrogen flow rate in step 1 is 50-80 mL / min.

3. The method for preparing the composite film based on modified carbon nanotubes and thermoplastic polyurethane according to claim 1, characterized in that: The coupling agent in step 1 is KH-550; the multi-walled carbon nanotubes in step 1 have a purity ≥99wt%, a length of 1-3 μm, and an outer diameter of 8-15 nm; the solvent in step 1 is a mixture of ethanol and deionized water in a volume ratio of 3:

1.

4. The method for preparing the composite film based on modified carbon nanotubes and thermoplastic polyurethane according to claim 1, characterized in that: The mass ratio of the epoxy-terminated polyether in step 2 to the tannic acid in step 1 is (3-4):(2-3); the epoxy value of the epoxy-terminated polyether in step 2 is 0.5-0.8 eq / 100g; the heating temperature in step 2 is 90-100 ℃; the reaction time in step 2 is 7-8 h; and the drying temperature in step 2 is 60-80 ℃, and the time is 9-10 h.

5. The method for preparing a composite film based on modified carbon nanotubes and thermoplastic polyurethane according to claim 1, characterized in that: The amount of dispersant added in step 3 is 1-2 wt% of the mass of the covalently bonded tannic acid-carbon nanotube powder; the dispersant in step 3 is polyethylene glycol stearate; the ultrasonic step in step 3 has a power of 250-350 W and a time of 40-70 min, and stirring is carried out simultaneously with ultrasonication at a speed of 1500-2000 rpm.

6. The method for preparing a composite film based on modified carbon nanotubes and thermoplastic polyurethane according to claim 1, characterized in that: In step 4, the mass ratio of polyurethane to crosslinking agent is 1:(0.01-0.015); the activation temperature in step 4 is 70-80 ℃, and the time is 30-40 min.

7. The method for preparing a composite film based on modified carbon nanotubes and thermoplastic polyurethane according to claim 1, characterized in that: The amount of covalently bonded tannic acid-carbon nanotube powder added in step 3 is 1-5 wt% of the mass of polyurethane in step 4; the amount of nano-hydroxyapatite added in step 5 is 0.57-0.67 wt% of the mass of polyurethane in step 4; the nano-hydroxyapatite in step 5 has a particle size of 20-50 nm and a surface hydroxyl density ≥5 mmol / g.

8. The method for preparing a composite film based on modified carbon nanotubes and thermoplastic polyurethane according to claim 1, characterized in that: The drying step in step 5 is performed at a temperature of 60-80 ℃ for 8-24 h; the cross-linking curing step in step 5 is performed at a temperature of 80-90 ℃ for 10-14 h.

9. A composite film based on modified carbon nanotubes and thermoplastic polyurethane prepared by the preparation method according to any one of claims 1-8.

10. The application of the composite film based on modified carbon nanotubes and thermoplastic polyurethane as described in claim 9, characterized in that: The composite membrane is used in the fabrication of wearable electronic devices, health monitoring devices, or motion function assessment devices; the composite membrane is also used in the fabrication of flexible strain sensors.

Images