Preparation method of a polypropylene carbonate-based flexible composite material and application thereof

Abstract

The application specifically relates to a preparation method of a polypropylene carbonate-based flexible composite material and application thereof. The composite material is prepared by taking polypropylene carbonate copolymerized from carbon dioxide and propylene oxide as a matrix phase and taking attapulgite modified by a silane coupling agent as a nano-reinforcing phase. The composite material is further integrally hot-pressed into a flexible substrate with a gradually-changing topology structure of thin in the middle and thick at both ends by using a partition-gradually-changing-gap mold, low-temperature self-repairing conductive paste with a PPC-GBVE ternary copolymer as a bonding phase is coated in an induction zone, a pure polypropylene carbonate encapsulation layer is hot-pressed to be combined, and a functional partition self-repairing flexible sensor is prepared. The composite material prepared by the application has excellent mechanical strength and barrier performance, the obtained sensor has high thickness precision, good tear resistance, stable strain coefficient, bending resistance and self-repairing capacity, and realizes high-value utilization of carbon dioxide resources.

Description

Technical Field

[0001] This invention belongs to the field of green polymer functional materials and flexible electronic sensing technology, specifically relating to a method for preparing a polypropylene carbonate-based flexible composite material and its application. Background Technology

[0002] The iterative improvement of carbon dioxide resource utilization and carbon sequestration technologies, along with the rapid development of the flexible wearable smart electronics industry, has driven an increasingly urgent demand for green and biodegradable polymer materials in the fields of flexible electronic substrates, low-temperature conductive media, and smart sensor devices.

[0003] Carbon dioxide-based polypropylene carbonate (PPC), as a typical carbon-fixing biodegradable polymer material, possesses unique advantages such as excellent low-temperature processability, renewable raw materials, and biodegradability, and has great industrialization potential in the fields of flexible wearable devices, biocompatible electronics, and intelligent sensing devices.

[0004] However, despite the many advantages mentioned above, unmodified pure PPC materials also have certain drawbacks when directly applied to high-performance flexible electronic devices: First, pure PPC is essentially an amorphous polymer, and its mechanical strength, stiffness, and toughness at room temperature are significantly insufficient. In particular, under dynamic stress such as repeated bending, stretching, or torsion, it is prone to plastic deformation or even fracture, and has poor fatigue resistance, making it difficult to meet the requirements of long-term, high-intensity service for wearable devices.

[0005] Second, while a lower glass transition temperature is beneficial for low-temperature processing, it also means that the device will soften at slightly higher ambient temperatures, leading to device structural deformation and sensor signal drift, which seriously affects the reliability and accuracy of the equipment.

[0006] Third, PPC has a lower barrier function against gases such as water vapor and oxygen than traditional substrates such as PET. This makes the sensitive electronic components encapsulated inside more susceptible to corrosion from moisture and oxygen in the environment, which accelerates aging and shortens the lifespan of the devices.

[0007] Fourth, for situations where the material needs to return to its initial state after deformation, pure PPC exhibits low recovery stress and low recovery rate.

[0008] Besides the inherent problems with the PPC substrate material itself, the overall performance of flexible sensors is constrained by the structural design and compatibility of functional components. Traditional flexible sensor substrates typically employ a uniform-thickness thin-film structure. This uniform-thickness design exposes certain structural defects during actual assembly and use. The ends of the sensor are usually clamped or connected to external circuitry, and these fixed areas are prone to stress concentration. When the sensor is bent or stretched, the edges of the clamping areas are easily torn due to stress concentration, leading to structural damage. Simultaneously, during dynamic deformation, the thin substrate is prone to irreversible localized plastic deformation, preventing the sensor from fully returning to its initial state after the external force is removed. This directly causes baseline drift in the sensing signal, severely affecting measurement accuracy and repeatability. Furthermore, substrate deformation can also cause relative displacement or even desorption between the printed conductive electrodes and the substrate, thereby disrupting the conductive path and leading to signal interruption or distortion.

[0009] In summary, existing technologies for the application of carbon dioxide-based biodegradable polymers (PPCs) in high-performance flexible electronics have the following problems: (1) There is a lack of a modification method that can effectively and synergistically improve the mechanical toughness, thermal stability and barrier properties of PPC; (2) Traditional equal-thickness substrates cannot fundamentally solve the reliability problems of flexible devices caused by stress concentration in practical applications, such as edge tearing and signal drift.

[0010] Therefore, there is an urgent need to propose a method for preparing polypropylene carbonate-based flexible composite materials and their applications to solve the problems existing in the current technology. Summary of the Invention

[0011] Existing technologies for the application of carbon dioxide-based biodegradable polymers (PPCs) in high-performance flexible electronics suffer from several shortcomings. Firstly, there is a lack of effective modification methods to synergistically improve the mechanical toughness, thermal stability, and barrier properties of PPCs. Secondly, stress concentration caused by thickness uniformity leads to reliability issues such as edge tearing and signal drift. This application proposes a method for preparing and applying polypropylene carbonate-based flexible composite materials.

[0012] The technical solution of this application is as follows: On the one hand, this application provides a method for preparing a polypropylene carbonate-based flexible composite material, wherein the flexible composite material is prepared by using carbon dioxide-based polypropylene carbonate, which is copolymerized from carbon dioxide and propylene oxide, as the matrix phase and attapulgite modified with silane coupling agent as the nano-reinforcing phase.

[0013] The amount of silane coupling agent modified attapulgite added is 0.5 to 2.5 wt% of the mass of propylene oxide.

[0014] Preferably, the amount of silane coupling agent modified attapulgite added is 1.3 wt% of the mass of propylene oxide.

[0015] Preferably, the method for preparing the flexible composite material includes the following steps: S1. Mix propylene oxide and calcium hydride and reflux, then purify by vacuum distillation for later use; S2. The silane coupling agent modified attapulgite is mixed and stirred with deionized water, ultrasonically dispersed, washed with ethanol, centrifuged, and vacuum dried to obtain a single-stranded, uniformly dispersed modified attapulgite. S3. After drying and purifying the high-pressure reactor with nitrogen, add the modified attapulgite prepared in step S2 and the coordination polymerization catalyst; then replace the air with CO2 and pressurize to 3.3~4.1 MPa, stir at 150~200 r / min, and react at a constant temperature of 59~65℃ for 42~50 h. The pressure is controlled to be 4.8~5.4 MPa throughout the reaction by adding CO2. S4. After the reaction is completed, the temperature is reduced and the pressure is released. The crude product is dissolved in dichloromethane, purified by precipitation with deionized water, and dried under vacuum to obtain a polypropylene carbonate-based flexible composite material.

[0016] Preferably, in step S1, the mass ratio of propylene oxide to calcium hydride is 4.2~5.8:1, the mixing and reflux time is 48h, the temperature of vacuum distillation is 43~47℃, and the pressure of vacuum distillation is -0.1~-0.09MPa.

[0017] Preferably, the silane coupling agent used in step S2 for modifying attapulgite is KH550 or KH570.

[0018] Preferably, in step S2, the mass-to-volume ratio of silane coupling agent-modified attapulgite to deionized water is 1g:25mL, the stirring temperature is 72~82℃, the stirring time is 10~15min, the ultrasonic time is 20~30min, the material is washed with ethanol at least twice, the vacuum drying temperature is 60~80℃, the drying time is 12~24h, and the vacuum degree is -0.08~-0.095MPa.

[0019] Preferably, the coordination polymerization catalyst in step S3 is a zinc-cobalt bimetallic cyanide coordination polymerization catalyst, and the molar ratio of the coordination polymerization catalyst to the purified propylene oxide is 1:280~310.

[0020] Preferably, in step S4, the solid-liquid ratio of crude product to dichloromethane is 1g:10mL, the amount of deionized water added is 5 times the volume of the solution, the vacuum drying temperature is 60~80℃, the drying time is 12~24h, and the vacuum degree is -0.08~-0.095MPa.

[0021] On the other hand, this application proposes an application of a polypropylene carbonate-based flexible composite material for a functionally partitioned self-healing flexible sensor, as detailed below: A flexible substrate is integrally hot-pressed using a customized partitioned gradient gap mold to form a polypropylene carbonate-based flexible composite material. Low-temperature self-healing conductive paste is coated in the central sensing area of ​​the flexible substrate using screen printing process, and then cured at a low temperature of 73~92℃ for 25~45 min to form a conductive functional circuit layer. A flexible polypropylene carbonate composite material without added attapulgite was used as the encapsulation layer. The thickness ratio of the encapsulation layer to the thick area of ​​the substrate was 0.4~0.6. The encapsulation was completed by hot pressing at 80℃ and 0.5 MPa for 10 minutes, thus obtaining a self-healing flexible sensor with functional partitions.

[0022] Preferably, the substrate has a smooth, gradually changing topology that is thinner in the middle and thicker at both ends, without any abrupt changes in thickness. The thickness of the central strain sensing region is 0.10~0.15 mm, and the thickness of the symmetrical fixing and clamping regions on both sides is 0.20~0.28 mm. The hot pressing process parameters are: hot pressing temperature 115~130℃, pressure 0.6~1.0 MPa, constant temperature hot pressing for 10~15 min, and uniform slow cooling demolding.

[0023] Preferably, the preparation method of the low-temperature self-healing conductive paste is as follows: (1) Using CO2, propylene oxide (PO), and 4-glycidyl butyl vinyl ether (GBVE) as comonomers, the mass ratio of PO to GBVE was controlled at 26~33:1. The reaction was carried out for 43~51 h at a reaction temperature of 59~65℃ and a constant pressure of 4.8~5.4 MPa. The reaction product was dissolved in dichloromethane, purified by precipitation with anhydrous ethanol, and vacuum dried to obtain PPC-GBVE ternary copolymer. (2) Using the PPC-GBVE terpolymer from step (1) as the bonding matrix, the flake silver-coated copper micro powder as the conductive functional phase, the GBVE monomer as the active diluent, and the modified carboxylic anhydride as the low-temperature curing initiator to prepare a low-temperature self-healing conductive slurry. The PPC-GBVE terpolymer needs to be dissolved in a dispersing solvent to form a binder phase solution before use. The dispersing solvent is a mixture of dipropylene glycol methyl ether acetate and propylene glycol methyl ether acetate in a mass ratio of 7.2:2.8. The PPC-GBVE terpolymer and the dispersing solvent are mixed in a ratio of 1g:5mL. (3) Mix the silver-coated copper micro powder, binder solution, diluent and curing agent in a mass ratio of 70~77:16~23:2.4~3.6:0.4~0.8 until uniform; then disperse by high-speed shearing at 2500~3000 r / min and grind by gradient grinding with a three-roll mill to obtain a uniform and stable low-temperature self-healing conductive slurry.

[0024] The beneficial effects of this application are as follows: This invention employs low-dosage one-dimensional silane-modified ATP in-situ coupled reinforcement of a modified PPC matrix, achieving single-level uniform dispersion of nanofillers and high-strength interfacial bonding. While fully preserving the biodegradable properties of the substrate, it synergistically enhances the mechanical toughness, shape memory recovery, thermal stability, and gas barrier performance of the PPC matrix. The tensile strength, elongation at break, and shape recovery rate of the composite material are significantly improved compared to pure PPC substrates, with the shape recovery rate increasing from less than 20% in pure PPC to over 60%. Oxygen and water vapor barrier properties are optimized by 30%–50%, respectively, and the glass transition temperature and thermal decomposition temperature are also improved.

[0025] This invention designs an integrated gradient substrate structure with functional partitions. Through integrated hot pressing with a partitioned gradient gap mold, a smooth gradient topology substrate with a thinner middle and thicker ends is fabricated, achieving a functional differentiation match between high-sensitivity sensing in the sensing area and high-stability clamping in the fixing area. Example data shows that this substrate possesses a high strain coefficient within the 5%~50% strain range, and its thickness change rate after repeated bending is less than 2%, effectively avoiding the stress concentration and edge tearing problems of traditional uniform-thickness substrates in the fixing and clamping area.

[0026] The PPC-GBVE ternary copolymer functional binder prepared in this invention, combined with flake-like silver-coated copper micropowder and a low-temperature curing system, yields a low-temperature self-healing conductive slurry suitable for PPC composite substrates. This slurry achieves over 90% curing degree at temperatures ranging from 73 to 92°C, and the resistivity after curing reaches 10⁻⁶. -4 With a resistivity on the order of Ω·cm, it exhibits excellent adhesion to PPC substrates. After repeated bending, the resistivity decay rate can be controlled within 30%, and it also has room temperature self-healing capability, which improves the stability of conductive networks and the service life of devices. It can be adapted to the harsh service scenarios of flexible and biodegradable electronic devices with repeated deformation.

[0027] This invention, based on the aforementioned composite material, substrate structure, and conductive paste, produces a fully PPC-based homologous interface flexible sensor. The substrate, conductive layer, and encapsulation layer achieve excellent interfacial bonding without delamination defects. Example data shows that this sensor possesses a wide strain response range, millisecond-level response / recovery time, high linearity (R²≥0.99), low resistivity change rate after long-term tensile cycling, high sensing performance recovery rate after room temperature crack repair, and stable performance over a wide temperature range. Its overall performance meets the requirements for wearable flexible sensing applications.

[0028] This invention enables the innovative development of modified and reinforced composite materials, self-healing functional binder phases, low-temperature conductive pastes, and functionally partitioned sensor devices. The process parameters are precisely controllable and the preparation conditions are mild, providing a technical route for the high-value application of CO2-based biodegradable polymers and their composite materials in the field of high-end flexible electronics. Attached Figure Description

[0029] Figure 1 This is a multi-cycle tensile curve of pure PPC at 50% maximum strain; Figure 2 The multi-cycle tensile curve of PPC-ATP-13 at 50% maximum strain; Figure 3 DSC plots of pure PPC and PPC-ATP-13; Figure 4 TG curves for pure PPC and PPC-ATP-13; Figure 5 The diagram shows the alkaline degradation performance of pure PPC and PPC-ATP-13. Figure 6 This is a schematic diagram of the self-healing functional partition flexible sensor structure of this application; Figure 7 This is a diagram illustrating the repair mechanism of the self-healing functional partition flexible sensor of this application. Detailed Implementation

[0030] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the specific embodiments, structures, features, and effects of the present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. This application provides a method for preparing a PPC ATP flexible composite material, the specific steps of which are as follows: S1. Mix propylene oxide and calcium hydride under reflux, then purify by vacuum distillation for later use; the mass ratio of propylene oxide to calcium hydride is 4.2~5.8:1, the mixing and reflux time is 48h, the vacuum distillation temperature is 43~47℃, and the vacuum distillation pressure is -0.1~-0.09MPa.

[0031] S2. The silane coupling agent modified attapulgite is mixed with deionized water, stirred, and ultrasonically dispersed. After washing with ethanol, centrifugation, and vacuum drying, a single-strand, uniformly dispersed modified attapulgite is obtained. The silane coupling agent used in the silane coupling agent modified attapulgite is KH550 or KH570. The mass-to-volume ratio of silane coupling agent modified attapulgite to deionized water is 1g:25mL. The stirring temperature is 72~82℃, the stirring time is 10~15min, the ultrasonic time is 20~30min, the attapulgite is washed with ethanol at least twice, and the vacuum drying temperature is 60~80℃, the drying time is 12~24h, and the vacuum degree is -0.08~-0.095MPa.

[0032] S3. After drying and purifying the high-pressure reactor with nitrogen, add the modified attapulgite prepared in step S2, and add the coordination polymerization catalyst; then replace the air with CO2 and pressurize to 3.3~4.1 MPa, stir at 150~200 r / min, and react at a constant temperature of 59~65℃ for 42~50 h. The pressure is controlled at 4.8~5.4 MPa throughout the reaction by adding CO2; the amount of modified attapulgite added is 0.5~2.5 wt% of the mass of propylene oxide; the coordination polymerization catalyst is a zinc-cobalt bimetallic cyanide coordination polymerization catalyst, and the molar ratio of coordination polymerization catalyst to purified propylene oxide is 1:280~310; S4. After the reaction is complete, the temperature is lowered and the pressure is released. The crude product is dissolved in dichloromethane, purified by precipitation with deionized water, and then vacuum dried to obtain a polypropylene carbonate-based flexible composite material. The solid-liquid ratio of the crude product to dichloromethane is 1 g:10 mL, the amount of deionized water added is 5 times the volume of the solution, the vacuum drying temperature is 60~80℃, the drying time is 12~24 h, and the vacuum degree is -0.08~-0.095 MPa. Experiments revealed that the flexible composite material prepared using the parameter ratios described in Example 1 exhibited the best performance. Therefore, the flexible composite material prepared in Example 1 was used in subsequent experiments.

[0033] Example 1

[0034] This embodiment provides a method for preparing a PPC ATP flexible composite material, as detailed below: Step S1. Purification of propylene oxide: PO and calcium hydride were mixed at a mass ratio of 5:1 and refluxed for 2 days. The mixture was then purified by vacuum distillation at 45°C and a system pressure of -0.095 MPa. The purified propylene oxide was then added to a high-temperature activated molecular sieve and sealed for storage. Step S2. Pretreatment of filler: KH550 modified ATP: deionized water = 1g: 25mL was mixed, stirred at 75℃ for 12min, ultrasonically dispersed for 25min until uniformly dispersed, washed twice with ethanol, centrifuged, and vacuum dried at 70℃ and vacuum degree -0.09MPa to constant weight to obtain exfoliated modified ATP; Step S3. In-situ polymerization: After purification and drying in a 500mL high-pressure reactor, modified ATP was added, along with a zinc-cobalt bimetallic cyanide coordination polymerization catalyst. The molar ratio of catalyst to purified PO was controlled at 1:290, the mass of ATP added was 1.3wt%, and the amount of PO added was 150mL. After replacing the air with CO2 three times, the pressure was increased to 3.7MPa, stirred at 180r / min, and reacted at a constant temperature of 62℃ for 46h. The reaction pressure stabilized at 5.1MPa. Preparation of zinc-cobalt bimetallic cyanide: 2.0 g potassium hexacyanocobalaminate was dissolved in 30 mL of deionized water to obtain solution A. 7.0 g zinc chloride was dissolved in a mixed solvent of 30 mL of deionized water and 20 mL of tert-butanol to obtain solution B. Solution A was added dropwise to solution B and stirred at room temperature for 10 h. Then, solid-liquid separation was performed by washing with tert-butanol and deionized water. Finally, the solution was dried to obtain the zinc-cobalt bimetallic cyanide coordination polymerization catalyst.

[0035] Step S4. Post-processing: The crude product was dissolved in dichloromethane at a solid-liquid ratio of 1g:10mL, and precipitated and purified by adding 5 times the volume of deionized water. The product was then vacuum dried at 70℃ and a vacuum degree of -0.09MPa to obtain the PPC ATP composite material.

[0036] This embodiment employs a low-dosage in-situ polymerization process using KH550 silane coupling agent-modified attapulgite, which synergistically imparts excellent mechanical toughness, tensile strength, shape recovery characteristics, and thermal stability to the PPC matrix, while fully preserving the biodegradable properties of the substrate. This effectively improves the mechanical, shape recovery, and water / gas barrier properties of pure PPC. Unlike existing amino-modified attapulgite blending processes, this application utilizes an in-situ polymerization coupled with in-situ composite technology. Under the mediation of a coordination catalytic system, it achieves in-situ alternating copolymerization of silane coupling agent-modified ATP with propylene oxide and carbon dioxide, followed by purification and drying to prepare a high-regularity PPC-ATP-13 composite flexible material. This achieves uniform dispersion and enhanced interfacial bonding, thereby improving overall performance.

[0037] The PPC ATP composite flexible material prepared in Example 1 and pure PPC were tested. Tensile properties were determined according to GB / T1040.1-2018. Figure 1 and Figure 2 Degradation performance was determined by alkaline degradation in 0.1 mol / L NaOH solution over 14 days; see [link to relevant documentation]. Figure 5 (The vertical axis value represents the mass loss rate; the larger the value, the greater the mass loss due to material degradation, and the higher the degree of degradation); Gas barrier performance is based on GB / T 1038-2022 and GB / T 1037-2023; Heat resistance performance, including the glass transition temperature, is as follows. Figure 3 Thermogravimetric curves can be found in [reference]. Figure 4 The specific test results are shown in Table 1.

[0038] Table 1 Properties of pure PPC and PPC-ATP composite flexible materials

[0039] Figure 1 as well as Figure 2The paper presents multi-cycle tensile curves of pure PPC and PPC-ATP-13 composite material at 50% maximum strain to evaluate the energy dissipation capacity, structural stability and cyclic recovery performance of the materials. Figure 1 Pure PPC exhibits a stress response of 0.55 MPa in the first tensile test, but the stress decreases significantly with the increase of the number of cycles, and the curve shrinks inward, indicating that obvious stress softening and irreversible plastic deformation occur. The deformation recovery rate Rf is 15%, indicating that pure PPC has large residual strain and poor recovery ability after cycling. Figure 2 The PPC-ATP-13 composite material exhibits significantly improved cyclic response. On one hand, the cyclic tensile stress is enhanced; the initial tensile stress is 0.72 MPa, and after 10 tensile cycles, the stress is 0.51 MPa, achieving a stress retention rate of 71%. On the other hand, the recovery rate (Rf) after 10 tensile cycles is 65%, demonstrating stable recovery during repeated deformation. Therefore, compared to PPC materials, the PPC-ATP-13 composite material exhibits higher stress strength, significantly enhanced tensile cyclic stress retention, and a significantly improved deformation recovery rate.

[0040] In summary, the PPC-ATP-13 composite material prepared using the method of this application has a tensile strength of 24.6 MPa, an elongation at break of 358%, a shape recovery rate of ≥65%, and an oxygen permeability coefficient of ≤254.87 cc・m. -2 ・day -1 ・0.1MPa -1 The water vapor permeability is 3.51 g·cm⁻¹. -2 ・day -1 It exhibits good barrier properties, with an alkali degradation rate of 84% after 14 days, maintaining good alkali degradation performance.

[0041] Example 2

[0042] This embodiment provides a method for fabricating a functionally partitioned flexible substrate, as detailed below: Using the PPC ATP composite flexible material prepared in Example 1 as raw material, the material was hot-pressed using a partitioned gradient gap mold with a middle gap of 0.12 mm and two side gaps of 0.24 mm. The material was hot-pressed for 12 min at 120°C and 0.8 MPa, and then slowly cooled and demolded to obtain a functional partitioned flexible substrate in one step.

[0043] The performance of the functional partitioned flexible substrate prepared in this embodiment was tested. The test standards were as follows: thickness uniformity was tested according to GB / T 6672-2001; strain response sensitivity was tested using a universal testing machine combined with a resistance tester. The test results are shown in Table 2.

[0044] Table 2

[0045] In summary, the thickness deviation of the sensing area of ​​the functional partitioned flexible substrate is ≤0.01 mm, the thickness deviation of the fixed area is ≤0.02 mm, the strain coefficient GF=10.8 within the strain range of 5%~50%, and the thickness change rate after 1000 180° bends is 1.2%, demonstrating good bending stability.

[0046] This application utilizes integrated hot pressing to fabricate a continuous, smooth, gradient substrate structure that is thin in the middle and thick at both ends, avoiding the step structure defects of traditional equal-thickness substrates. The thin sensing area of ​​the functionally partitioned flexible substrate fabricated in this application can effectively amplify the strain response signal and improve sensing sensitivity; the thickened fixing area can enhance the substrate's clamping stability and tear resistance, avoiding problems such as edge damage, local plastic deformation, and signal drift during device assembly and wear deformation, thus balancing high-precision sensing output and long-term structural stability.

[0047] Example 3

[0048] This embodiment provides a method for preparing a PPC-GBVE terpolymer, as detailed below: ①Pre-treatment of the apparatus: The 500mL high-pressure reactor is thoroughly purified and dried for later use; ② Feeding and Replacement: Feed the materials according to the mass ratio of purified PO:GBVE=30:1, replace the air in the reactor with CO2 3 times, and pressurize to 3.5MPa; ③ Copolymerization reaction: Stir at 160 r / min, react at 62℃ for 47 h, and maintain the pressure inside the reactor at 5.0 MPa. ④ Post-processing: The product was dissolved in dichloromethane at a solid-liquid ratio of 1g:10mL, and then purified by adding 5 times the volume of deionized water. The product was then vacuum dried at 70℃ and a vacuum degree of -0.09MPa to obtain the PPC-GBVE terpolymer.

[0049] The prepared PPC-GBVE terpolymer was subjected to performance tests. The test standards were as follows: molecular weight was determined by gel permeation chromatography; glass transition temperature was determined according to GB / T 11357-2019; and the repair rate was calculated by measuring the change in scratch width using SEM. The test results are shown in Table 3.

[0050] Table 3

[0051] This application is based on a ternary controllable copolymer system of CO2, propylene oxide, and 4-glycidyl butyl vinyl ether. The main chain has a regular PPC molecular structure, while the side chains retain highly active unsaturated double bond functional groups. This allows for low-temperature crosslinking and curing, as well as room-temperature dynamic self-healing and reconstruction. It also exhibits excellent interfacial compatibility with the PPC matrix and conductive fillers, making it a functional medium for achieving device interface self-healing and high interfacial bonding strength. Unlike conventional PPC copolymers without active side groups, the GBVE monomer of this invention possesses both epoxy polymerization active groups and side-chain vinyl functional groups. The epoxy groups participate in the regular copolymerization of the main chain, while the inert double bonds on the side chains are retained, which can subsequently trigger crosslinking rearrangement reactions, endowing the composite material with specific functional properties of low-temperature curing and room-temperature self-healing.

[0052] Example 4

[0053] This embodiment provides a method for preparing a low-temperature self-healing conductive paste, as detailed below: ① Pretreatment of silver-coated copper micro powder: Mix flake silver-coated copper micro powder with anhydrous ethanol at a ratio of 20g:200mL, stir at room temperature for 4 hours, let stand to precipitate, and then vacuum dry to remove surface impurities. ② Preparation of binder phase solution: A mixed solvent was prepared according to the ratio of dipropylene glycol methyl ether acetate: propylene glycol methyl ether acetate = 7.2: 2.8. The PPC-GBVE terpolymer prepared in Example 3 was mixed with the mixed solvent at a ratio of 1g: 5mL. The mixture was heated at 60°C for 3 hours to dissolve. After cooling, the mixture was degassed under vacuum to obtain a uniform binder phase solution. ③Slurry preparation: Mix and stir at a mass ratio of silver-coated copper micro powder: binder solution: GBVE diluent: curing agent = 74:20:3:0.6 for 60 min, disperse at high speed of 2800 r / min for 2 min, and then grind at multiple stages of 120 μm, 5 μm and 5 μm using a three-roll mill to obtain a low-temperature self-healing conductive slurry.

[0054] The performance of the low-temperature self-healing conductive paste prepared in this embodiment was tested. The test standards were as follows: the resistivity after curing was measured using a four-probe tester; the curing performance was determined by weighing after heating to a specified temperature and time in an oven; the adhesion was determined according to GB / T 9286-1998; and the self-healing performance was determined by resistivity or sensing performance recovery rate. The results are shown in Table 4.

[0055] Table 4

[0056] This application uses PPC-GBVE terpolymer as the bonding matrix and silver-coated copper microparticles as the conductive carrier phase, combined with a special reactive diluent and a low-temperature curing system, to prepare a low-temperature curing conductive system suitable for PPC substrates, avoiding thermal damage to the biodegradable substrate caused by high-temperature processing. The slurry exhibits excellent interfacial adhesion, strong bending resistance, and hierarchical synergistic self-healing properties: the PPC-GBVE conductive layer repairs the conductive circuitry through reversible covalent cross-linking of side-chain vinyl groups and hydrogen bonding of the main chain; the PPC-ATP substrate forms a reversible hydrogen bond network with the help of modified attapulgite clay, and rigid nanorods restrict chain slippage and provide high elastic recovery, autonomously closing microcracks in the substrate; interdiffusion of three homologous PPC molecules and reconstruction of interlayer hydrogen bonds resolve interfacial delamination, with multiple mechanisms synergistically achieving self-healing reconstruction and self-repair of the conductive network and device. It is highly adaptable to application scenarios involving flexible, biodegradable electronic reciprocating deformation.

[0057] Example 5

[0058] This embodiment provides the fabrication and application of a functionally partitioned self-healing flexible sensor, as detailed below: The functional partition flexible substrate prepared in Example 2 was cut into 20mm×50mm size, and the low-temperature self-healing conductive paste of Example 4 was printed on the middle sensing area of ​​the substrate using screen printing process. It was then cured at 85℃ for 30min to form conductive lines. Pure polypropylene carbonate without added attapulgite was used as the encapsulation layer. The encapsulation layer was hot-pressed to the substrate thickness at a ratio of 0.5:1, and the encapsulation was completed by holding the layers at 80℃ and 0.5MPa for 10 minutes. The target sensor was thus fabricated. A schematic diagram of its structure can be found in [reference needed]. Figure 6 .

[0059] The above sensors were subjected to performance testing. The testing standards were as follows: sensing performance was tested using a universal testing machine and a resistance meter, measuring resistance changes within a specified strain range; cyclic stability was tested using tensile and bending cycles; self-healing performance was tested using a self-developed method, the self-healing mechanism of which is described in [reference needed]. Figure 7(Hierarchical synergistic self-repair achieved by leveraging differences in molecular structure: The PPC-GBVE conductive layer repairs conductive pathways through reversible covalent cross-linking of side-chain vinyl groups and hydrogen bonding of the main chain; the PPC-ATP substrate constructs a reversible hydrogen bond network through silane-modified attapulgite, with rigid nanorods constraining molecular chain slippage, while simultaneously endowing the substrate with excellent elastic recovery, enabling it to autonomously close microcracks in the substrate; the substrate, conductive layer, and encapsulation layer are homologous PPC structures, with molecular chains diffusing into each other and rebuilding interlayer hydrogen bonds, eliminating interlayer delamination defects; pure PPC lacks active cross-linking sites and rigid filler constraints, resulting in irreversible molecular slippage and extremely poor deformation recovery ability, thus lacking self-healing properties. The three types of molecular repair mechanisms work synergistically, combined with the strong recovery effect of the substrate, to achieve multi-mechanism synergistic self-repair of the device's conductive pathways, substrate structure, and interlayer interfaces); the human motion monitoring performance was verified through actual wearable testing. The results are shown in Table 5.

[0060] Table 5

[0061] The device substrate, conductive functional layer, and encapsulation protective layer all adopt the same PPC base system, achieving a robust interface bond and eliminating interlayer delamination and delamination failure issues. The device possesses multiple advantages, including room temperature self-healing, easy degradation, considerable strain response sensitivity, and long-term stability, effectively optimizing sensing accuracy and device lifespan. Its stable conductivity allows for precise and continuous monitoring of flexion and extension movements of multiple joints in the human body, such as fingers, wrists, elbows, and knees, making it suitable for applications such as wearable motion monitoring and flexible electronic skin.

[0062] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a polypropylene carbonate-based flexible composite material, characterized in that, The flexible composite material is prepared using carbon dioxide-based polypropylene carbonate, which is copolymerized from carbon dioxide and propylene oxide, as the matrix phase and attapulgite modified with silane coupling agent as the nano-reinforcing phase. The amount of silane coupling agent modified attapulgite added is 0.5 to 2.5 wt% of the mass of propylene oxide.

2. The method for preparing a polypropylene carbonate-based flexible composite material according to claim 1, characterized in that, The preparation method of the flexible composite material includes the following steps: S1. Mix propylene oxide and calcium hydride and reflux, then purify by vacuum distillation for later use; S2. The silane coupling agent modified attapulgite is mixed and stirred with deionized water, ultrasonically dispersed, washed with ethanol, centrifuged, and vacuum dried to obtain a single-stranded, uniformly dispersed modified attapulgite. S3. After drying and purifying the high-pressure reactor with nitrogen, add the modified attapulgite prepared in step S2 and the coordination polymerization catalyst; then replace the air with CO2 and pressurize to 3.3~4.1 MPa, stir at 150~200 r / min, and react at a constant temperature of 59~65℃ for 42~50 h. The pressure is controlled to be 4.8~5.4 MPa throughout the reaction by adding CO2. S4. After the reaction is completed, the temperature is reduced and the pressure is released. The crude product is dissolved in dichloromethane, purified by precipitation with deionized water, and dried under vacuum to obtain a polypropylene carbonate-based flexible composite material.

3. The method for preparing a polypropylene carbonate-based flexible composite material according to claim 2, characterized in that, In step S1, the mass ratio of propylene oxide to calcium hydride is 4.2~5.8:1, the mixing and reflux time is 48h, the temperature of vacuum distillation is 43~47℃, and the pressure of vacuum distillation is -0.1~-0.09MPa.

4. The method for preparing a polypropylene carbonate-based flexible composite material according to claim 2, characterized in that, In step S2, the silane coupling agent used for modifying attapulgite is KH550 or KH570.

5. The method for preparing a polypropylene carbonate-based flexible composite material according to claim 2, characterized in that, In step S2, the mass-to-volume ratio of silane coupling agent-modified attapulgite to deionized water is 1g:25mL, the stirring temperature is 72~82℃, the stirring time is 10~15min, the ultrasonic time is 20~30min, the mixture is washed with ethanol at least twice, the vacuum drying temperature is 60~80℃, the drying time is 12~24h, and the vacuum degree is -0.08~-0.095MPa.

6. The method for preparing a polypropylene carbonate-based flexible composite material according to claim 2, characterized in that, In step S3, the coordination polymerization catalyst is a zinc-cobalt bimetallic cyanide coordination polymerization catalyst, and the molar ratio of the coordination polymerization catalyst to the purified propylene oxide is 1:280~310.

7. The method for preparing a polypropylene carbonate-based flexible composite material according to claim 2, characterized in that, In step S4, the solid-liquid ratio of crude product to dichloromethane is 1g:10mL, the amount of deionized water added is 5 times the volume of the solution, the vacuum drying temperature is 60~80℃, the drying time is 12~24h, and the vacuum degree is -0.08~-0.095MPa.

8. An application of a polypropylene carbonate-based flexible composite material, comprising the preparation method of a polypropylene carbonate-based flexible composite material according to any one of claims 1 to 7, characterized in that, For self-healing flexible sensors with functional zones, the details are as follows: A flexible substrate is integrally hot-pressed using a customized partitioned gradient gap mold to form a polypropylene carbonate-based flexible composite material. Low-temperature self-healing conductive paste is coated in the central sensing area of ​​the flexible substrate using screen printing process, and then cured at a low temperature of 73~92℃ for 25~45 min to form a conductive functional circuit layer. Pure polypropylene carbonate without added attapulgite was used as the encapsulation layer. The thickness ratio of the encapsulation layer to the thick area of ​​the substrate was 0.4~0.

6. The encapsulation was completed by hot pressing at 80℃ and 0.5 MPa for 10 minutes, thus obtaining a functional self-healing flexible sensor.

9. The application of the polypropylene carbonate-based flexible composite material according to claim 8, characterized in that, The substrate has a smooth, gradually changing topology that is thinner in the middle and thicker at both ends, without any abrupt changes in thickness. The thickness of the central strain sensing region is 0.10~0.15 mm, and the thickness of the symmetrical fixing and clamping regions on both sides is 0.20~0.28 mm. The hot pressing process parameters are: hot pressing temperature 115~130℃, pressure 0.6~1.0 MPa, constant temperature hot pressing for 10~15min, and uniform slow cooling demolding.

10. The application of the polypropylene carbonate-based flexible composite material according to claim 8, characterized in that, The preparation method of the low-temperature self-healing conductive paste is as follows: (1) Using CO2, propylene oxide (PO), and 4-glycidyl butyl vinyl ether (GBVE) as comonomers, the mass ratio of PO to GBVE was controlled at 26~33:

1. The reaction was carried out for 43~51 h at a reaction temperature of 59~65℃ and a constant pressure of 4.8~5.4 MPa. The reaction product was dissolved in dichloromethane, purified by precipitation with anhydrous ethanol, and vacuum dried to obtain PPC-GBVE ternary copolymer. (2) Using the PPC-GBVE terpolymer from step (1) as the bonding matrix, the flake silver-coated copper micro powder as the conductive functional phase, the GBVE monomer as the active diluent, and the modified carboxylic anhydride as the low-temperature curing initiator to prepare a low-temperature self-healing conductive slurry. Before use, the PPC-GBVE terpolymer needs to be dissolved in a dispersing solvent to form a binder phase solution. The dispersing solvent is composed of dipropylene glycol methyl ether acetate and propylene glycol methyl ether acetate in a mass ratio of 7.2:2.

8. The PPC-GBVE terpolymer and the dispersing solvent are mixed in a ratio of 1g:5mL. (3) The silver-coated copper micro powder, binder phase solution, diluent and curing agent are mixed and stirred evenly in a mass ratio of 70~77:16~23:2.4~3.6:0.4~0.

8. Then, the mixture is dispersed by high-speed shearing at 2500~3000 r / min and ground by gradient grinding in a three-roll mill to obtain a uniform and stable low-temperature self-healing conductive slurry.

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