A method of exfoliating graphene and its honeycomb carbon cage structure in a PVC in-situ polymerization process

Abstract

The application discloses a method for stripping graphene and honeycomb carbon cage structure in a PVC in-situ polymerization process, and belongs to the field of composite new materials.The surfactant and nano calcium carbonate are made to enter between flake graphite layers through ultrasonic intercalation treatment, and a graphene polymerization precursor is obtained; then, in-situ polymerization reaction is carried out in a reaction kettle, the polymerization reaction can be synchronously carried out between graphene layers, through the thermal expansion stress effect in the polymerization reaction process and the increase of coulomb repulsion force between flake graphite layers caused by the accumulation of electrostatic charges induced by polymerization free radicals, when the van der waals force between flake graphite layers cannot bind the structure, the coulomb explosion type disintegration occurs, and the graphene honeycomb carbon cage structure PVC composite material is formed in-situ. The thermal aging stability of the composite material is overturnedly improved, the special graphene carbon cage structure also has the functions of EMI shielding, wave absorption, heat management and heat storage, and can be used in the fields of unmanned aerial vehicle stealth coating, unmanned vehicle and electronic equipment electromagnetic protection.

Description

Technical Field

[0001] This disclosure relates to a method for preparing polymer nanocomposites and graphene structures, and more specifically, to the in-situ exfoliation of flake graphite into graphene structures during the suspension polymerization of vinyl chloride, and the resulting polyvinyl chloride composite material with enhanced mechanical strength and thermal stability. Background Technology

[0002] The high manufacturing cost of graphene materials has hindered the large-scale expansion of its applications. It is necessary to find a low-cost mass production technology. In the research on in-situ polymerization of nano-calcium carbonate, the inventors discovered that 100-nanometer calcium carbonate particles underwent coulombic micro-explosions during PVC polymerization, disintegrating into 5-nanometer small particles. Therefore, they also conducted research on the in-situ polymerization and exfoliation of flake graphite. As a result, an onion-ring-shaped carbon cage structure graphene was obtained in the polymerization system with added ammonium bicarbonate.

[0003] Meanwhile, the onion-ring-shaped carbon cage structure also possesses advantages that graphene's two-dimensional sheet structure lacks. With the development of drones, electric vehicles, 5G communications, and high-power electronic devices, electromagnetic pollution, electromagnetic leakage, and high-frequency electromagnetic interference are becoming increasingly serious problems. While traditional metal shielding materials have high conductivity, they suffer from high density, poor corrosion resistance, poor impedance matching performance, and severe secondary reflections.

[0004] Graphene, due to its excellent electrical and thermal conductivity and two-dimensional layered structure, is widely used in electromagnetic interference (EMI) shielding and microwave absorbing materials research. However, traditional graphene materials still have the following problems: 1. Graphene sheets are prone to aggregation; 2. Narrow absorption bandwidth; 3. Poor impedance matching; 4. Insufficient structural defects result in limited polarization loss; 5. Layered structures are prone to specular reflection; 6. Insufficient thermal stability and heat storage performance.

[0005] Existing technologies typically employ methods such as oxidation-reduction, strong acid intercalation, and high-temperature expansion to prepare porous graphene, but these methods suffer from problems such as complex processes, severe environmental pollution, uncontrollable structure, and difficulty in forming honeycomb carbon cage structures.

[0006] Therefore, it is of great significance to develop a novel method for preparing graphene composite materials that can form a honeycomb, multi-layered anchored, N-doped carbon cage structure in situ during the polymerization process. Summary of the Invention

[0007] The purpose of this invention is to prepare a new graphene material using the in-situ polymerization process of PVC, and to solve the problems of existing graphene microwave absorbing materials such as simple structure, insufficient absorption loss, poor impedance matching and easy agglomeration. Specifically, it provides a method for preparing N-doped honeycomb graphene carbon cage composite material by in-situ polymerization-induced electrostatic Coulomb micro-explosion.

[0008] The specific technical solution adopted in this invention is as follows: In a first aspect, the present invention provides a method for exfoliating graphene and its honeycomb carbon cage structure during the in-situ polymerization process of PVC, comprising: Flake graphite is dispersed in a surfactant to form a dispersion system. Then, nano-calcium carbonate and an emulsifier are added. The surfactant and nano-calcium carbonate are then injected into the spaces between the flake graphite layers by high-power ultrasonic treatment to obtain an in-situ polymerization precursor dispersion. Deionized water, the precursor dispersion, and a polymerization formulation containing a dispersant, an N-doped nitrogen atom source, and an initiator are added to a reaction vessel. The N-doped nitrogen atom source is ammonium bicarbonate and / or ammonia. After mixing, vinyl chloride monomer is added under vacuum or nitrogen protection. The polymerization reaction is then carried out at a pressure and temperature sufficient to initiate the polymerization reaction. The graphene honeycomb carbon cage structure is obtained by in-situ exfoliation of flake graphite through the residual heat of the polymerization reaction and the electron-induced coulombic repulsion force at the free radical trapping interface. After the reaction is terminated, a PVC composite material containing graphene and its honeycomb carbon cage structure is obtained.

[0009] As a preferred embodiment of the first aspect above, the mass ratio of flake graphite to nano-calcium carbonate in the precursor dispersion is 1:8~12, and the amount of precursor dispersion added to the reactor during the polymerization reaction is 0.2 wt%~30 wt% of the mass of the added vinyl chloride monomer.

[0010] As a preferred embodiment of the first aspect, the ultrasonic power density of the high-power ultrasonic treatment is configured to be 500-1000 W / L, the ultrasonic frequency is two frequencies in the range of 10-40 kHz, and the ultrasonic treatment time is 4-6 hours.

[0011] As a preferred embodiment of the first aspect above, the surfactant is sodium dodecylbenzenesulfonate (SDBS) or sodium dodecyl sulfate (SDS).

[0012] As a preferred embodiment of the first aspect described above, the diameter of the flake graphite is 2~10 μm. More preferably, the flake graphite is pre-treated mechanically to present an arched structure.

[0013] As a preferred embodiment of the first aspect above, the particle size of the nano-calcium carbonate particles is 30~100 nm.

[0014] As a preferred embodiment of the first aspect above, the emulsifier is one or more of Tween, n-hexadecyl alcohol, n-heptadecyl alcohol, or n-octadecyl alcohol.

[0015] As a preferred embodiment of the first aspect above, the dispersant is one or more of polyvinyl alcohol or hydroxypropyl methylcellulose.

[0016] As a preferred embodiment of the first aspect above, the initiator is one or more of bis(2-ethylhexyl) peroxide dicarbonate (EHP), benzoyl peroxide, or diisobutyronitrile peroxide.

[0017] As a preferred embodiment of the first aspect above, the following should be added to the reactor relative to every 100 parts by mass of vinyl chloride monomer: 100-300 parts by weight of deionized water; 0.1~0.5 parts by weight of dispersant; 0.05~0.3 parts by mass of N-doped nitrogen atom source; 1-30 parts by weight of precursor dispersion; 0.05~0.2 parts by weight of initiator.

[0018] As a preferred embodiment of the first aspect above, the temperature of the polymerization reaction is controlled at 50~60°C and the pressure is controlled at 6~10 bar.

[0019] As a preferred embodiment of the first aspect, the multilayer honeycomb graphene carbon cage composite material is further dissolved in an organic solvent to dissolve polyvinyl chloride, and then purified to obtain pure graphene carbon cage.

[0020] More preferably, the organic solvent is one or more of tetrahydrofuran, cyclohexanone, and DMF.

[0021] Secondly, the present invention provides a graphene-PVC composite material prepared according to any one of the methods described in the first aspect above. TEM results show that the composite material has a honeycomb-like multilayer carbon cage structure formed by N atoms doping between graphene layers to induce anchor points, and a plasma micro-area pore mark formed at the top of the carbon cage structure during the instantaneous release of electrostatic charge.

[0022] Thirdly, the present invention provides an application of the composite material as described in the second aspect above as an EMI shielding material and a microwave absorbing material.

[0023] Fourthly, the present invention relates to the application of a composite material as described in the second aspect above in stealth skin for unmanned aerial vehicles, electromagnetic shielding for new energy vehicles, electromagnetic protection for electronic equipment, or battery thermal management.

[0024] Compared with the prior art, the present invention has the following advantages: 1. Significantly Improved PVC Thermal Stability: The graphene nano-calcium carbonate / PVC composite material provided by this invention can significantly improve the thermal stability of PVC. It leverages the dual effects of nano-calcium carbonate absorbing hydrogen chloride released from PVC decomposition and the π-π conjugation between the large π-bond electrons at the graphene interface and the residual double bonds in PVC, thus addressing the insufficient thermal stability of PVC polymers at the molecular level. Congo red test results show that the thermal aging decomposition time of the material is extended by 30 times.

[0025] 2. In-situ Construction of Honeycomb Carbon Cage Structure: This invention employs a conventional liquid-phase mechanical exfoliation method for graphene, and further utilizes the Coulomb repulsion effect induced by localized electrostatic accumulation between graphite layers in the polymerization environment to generate a large number of honeycomb-like channels and closed, curved graphene structures in situ within the material. During this process, the honeycomb exfoliation of flake graphite requires no external energy input, relying entirely on the excess heat and waste energy from the in-situ polymerization reaction. Through the synergistic effect of electron transfer, nitrogen doping, and interlayer anchoring, the three-dimensional honeycomb reconstruction of graphene is achieved, thereby significantly reducing the manufacturing cost of graphene material exfoliation.

[0026] 3. The graphene-carbon cage composite material prepared by this invention possesses a unique three-dimensional porous honeycomb structure, which enhances the material's ability to absorb electromagnetic waves, thereby effectively improving its wave absorption performance and impedance matching characteristics, while also providing heat storage and thermal management functions. The honeycomb and defect structures in the graphene-carbon cage composite material prepared by this invention reduce the reflection of electromagnetic waves from the material surface, improving the absorption and loss efficiency of electromagnetic waves entering the material's interior. Specific mechanisms include: multiple scattering, conductive loss, defect polarization, dipole polarization, and interface polarization. Simultaneously, the micro-nano cavities formed within the honeycomb carbon cage enable heat buffering and thermal management regulation.

[0027] 4. Good structural stability: The graphene carbon cage composite material prepared by this invention has an interlayer anchoring structure, which can effectively inhibit the re-agglomeration of graphene and improve the cycling stability and mechanical stability of the material. Attached Figure Description

[0028] Figure 1 The first transmission electron microscope image of the composite material in this embodiment of the invention.

[0029] Figure 2 The second transmission electron microscope image of the composite material in this embodiment of the invention.

[0030] Figure 3 The third transmission electron microscope image of the composite material in this embodiment of the invention. Detailed Implementation

[0031] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. Technical features in various embodiments of the present invention can be combined accordingly without mutual conflict.

[0032] This invention provides a method for exfoliating graphene and its honeycomb carbon cage structure during the in-situ polymerization process of PVC. The specific steps of this method are as follows: S1. Flake graphite is dispersed in a surfactant to form a dispersion system. Then, nano-calcium carbonate and emulsifier are added. The surfactant and nano-calcium carbonate are then introduced into the graphite flakes by high-power ultrasonic treatment to obtain an in-situ polymerization precursor dispersion.

[0033] S2. Deionized water, the precursor dispersion, and a polymerization formulation containing a dispersant, an N-doped nitrogen atom source, and an initiator are added to a reaction vessel. The N-doped nitrogen atom source is one or a combination of ammonium bicarbonate and ammonia water. After mixing, vinyl chloride monomer is added under vacuum or nitrogen protection. The polymerization reaction is then carried out at a pressure and temperature sufficient to initiate the polymerization reaction. Through the combined effects of residual heat from the polymerization reaction and electron-induced Coulombic repulsion at the free radical trapping interface, graphene honeycomb carbon cage structures are obtained by in-situ exfoliation of flake graphite. After the reaction is terminated, a composite material containing graphene and its honeycomb carbon cage structure is obtained. This composite material is a graphene-PVC composite material, in which the graphene structure contains a few two-dimensional graphene sheets exfoliated by pre-ultrasonic exfoliation, and the majority is graphene honeycomb carbon cage structure obtained by in-situ polymerization.

[0034] In the polymerization process of this invention, the exfoliation of flake graphite is activated by capturing the waste energy dissipated during the in-situ polymerization process. Firstly, it fully utilizes the residual heat of the polymerization reaction; secondly, it leverages the Coulomb repulsion generated between the flake graphite layers by electron transfer during free radical reactions within the monomer droplets. In this invention, no energy is input from the outside during graphene exfoliation. On the contrary, because the heat from the polymerization reaction is absorbed by the graphene exfoliation process, the consumption of cooling water in the polymerization cycle is also reduced. Therefore, this invention represents a typical low-cost, green method for manufacturing graphene.

[0035] It should be noted that the flake graphite used as the carbon source in this invention undergoes preliminary mechanical treatment. Specifically, the flake graphite can be added to a rolling mill or ball mill for processing. The treated flake graphite has a certain arched structure, which is beneficial for the concentration of electrostatic charge at the top of the arch with the smallest radius of curvature. In the embodiments of this invention, the flake graphite sheet diameter is preferably 2~10μm, and its carbon purity is preferably greater than 99.5%.

[0036] In step S1 above, flake graphite is first dispersed in a surfactant solution to form a dispersion system. The specific surfactant can be sodium dodecylbenzenesulfonate (SDBS) or sodium dodecyl sulfate (SDS), with SDBS being preferred. SDBS can effectively disperse the flake graphite at the nanoscale, forming a well-dispersed pre-dispersed slurry. Additionally, nano-calcium carbonate and an emulsifier are added to the dispersion system. Then, high-power ultrasonic treatment is performed. Under the action of high-power ultrasound, certain gaps appear in the graphite flakes. The surfactant and nano-calcium carbonate perform molecular intercalation and interlayer mechanical isolation of the flake graphite. Combined with the emulsifying effect of the emulsifier, a stable and usable polymerization precursor dispersion is formed. The surfactant molecules intercalate between the graphite flakes to increase the interlayer spacing, while the nano-calcium carbonate can further embed itself between the graphite flakes to form interlayer physical isolation. Thus, the surfactant molecules and nano-calcium carbonate create physical channels for vinyl chloride monomer to enter the gaps between the graphite flakes. Each graphene flake will serve as a microreactor for the subsequent in-situ polymerization reaction. Under the combined effects of the thermal expansion stress of the polymerization reaction and the Coulomb repulsion force accumulated by the electrostatic charge at the free radical trapping interface, when the van der Waals forces between the graphene flakes acting as microreactors are insufficient to maintain the graphite structure, a Coulombic explosive disintegration will occur instantaneously. Due to the encapsulation and compression of the surrounding PVC precipitated during the in-situ polymerization process, the exfoliated graphene sheets will form a concentric onion ring structure. TEM shows that anchor points also appear between the graphene sheets, forming an ordered honeycomb-like three-dimensional network structure. The appearance of these anchor points is likely related to the interlayer chemical bonds induced by nitrogen atom doping. Without nitrogen atom doping to form the CNC structure between graphene layers, the Coulombic disintegration of graphene fragments would result in a scattered and disordered structure.

[0037] Furthermore, the molecular intercalation and interlayer mechanical isolation of flake graphite by the aforementioned surfactant molecules and nano-calcium carbonate require high-power ultrasound. Ultrasonic processing can prepare a stable microemulsion graphene polymerization precursor dispersion system, which is compatible with and optimized for classic vinyl chloride suspension polymerization formulations. Therefore, this precursor can be added to conventional suspension polymerization systems, and its impact on reaction kinetics or particle properties remains entirely predictable and controllable.

[0038] A stable microemulsion graphene polymerization precursor dispersion system can prevent the aggregation of nano-calcium carbonate and flake graphite, and the embedded interspersed nano-calcium carbonate particles can also be stably retained between graphite layers until the exfoliation step occurs during the polymerization reaction.

[0039] In the process of preparing the precursor dispersion, the control parameters of the ultrasonic treatment used need to be reasonably adjusted based on the actual treatment effect.

[0040] In embodiments of the present invention, for the dispersion system after adding nano-calcium carbonate and emulsifier, the ultrasonic power density for ultrasonic treatment is recommended to be set to 500-1000 W / L.

[0041] In embodiments of the present invention, the ultrasonic frequency is recommended to be set to 10-40 kHz, preferably with a high frequency and a low frequency selected simultaneously within this range, combining the two to achieve dual-frequency synergy. The selection of the ultrasonic frequency can be adjusted according to the specific intercalating agent and graphite material characteristics used. The present invention employs multiple probe-type ultrasonic generators connected in series with a water bath-type ultrasonic generator, using a dual-frequency synergy configuration. This allows for adjustment of the amplitude and pulse mode to accommodate the more effective embedding of nano-calcium carbonate into the graphite layers through ultrasonic cavitation kinetic energy. In embodiments of the present invention, a dual-frequency synergy configuration of 40 kHz and 23 kHz is preferred.

[0042] In embodiments of the present invention, the recommended ultrasonic treatment time is 4 to 6 hours. The specific ultrasonic treatment time depends on the characteristics of the flake graphite raw material and the degree of monolayer exfoliation. The ultrasonic treatment endpoint is defined as the increase in material viscosity at the onset of hydrogelation. A longer ultrasonic treatment time can achieve more thorough intercalation and increase the monolayer exfoliation ratio. However, excessive ultrasonic treatment in the present invention will destroy the relatively closed in-situ polymerization microreactor structure between graphite layers, thus failing to achieve the expected effect of electrostatic charge accumulation in flake graphite, resulting in Coulomb microexplosions to form an onion ring carbon cage structure.

[0043] Furthermore, the nano-calcium carbonate particles added to the dispersion system in this invention primarily serve as physical spacers between graphite layers. Therefore, the particle size of these nano-calcium carbonate particles needs to be carefully controlled to ensure they can effectively penetrate between graphite layers. The preferred particle size is 30–100 nm, more preferably 50–70 nm, and even more preferably approximately 70 nm. Adding nano-CaCO3 to flake graphite can create VCM monomer entry channels by providing physical interlayer isolation, thereby facilitating in-situ polymerization within the graphite interlayer voids. The polymerization reaction heat generated by the relatively closed local environment and the Coulomb repulsion force from the accumulation of local static charge become the driving excitation energy source for the subsequent generation of graphene cage-like exfoliation.

[0044] Furthermore, the amount of flake graphite and nano-calcium carbonate added during the preparation of the precursor dispersion needs to be determined in conjunction with the amount of vinyl chloride monomer added in the in-situ polymerization in the subsequent S2 step. In the embodiments of the present invention, the preferred mass ratio of flake graphite to nano-calcium carbonate in the precursor dispersion is 1:(8~12), more preferably 1:10, and the amount of precursor dispersion added to the reactor during the polymerization reaction is 0.2 wt%~30 wt% of the mass of the added vinyl chloride monomer. If the target product is a graphene-modified PVC resin with high heat resistance, it can have a revolutionary effect even with a relatively low graphene content. It is recommended that the amount of flake graphite be 0.25% of the mass of the added vinyl chloride monomer, and the amount of nano-calcium carbonate be 3.5% of the mass of the added vinyl chloride monomer. However, if it is used in the EMI field, where the graphene carbon cage structure is mainly utilized and PVC is only used as a coating carrier material, the concentration of the absorbing component must be increased, and the polymerization formula also needs to be adjusted accordingly according to different user requirements.

[0045] Furthermore, the emulsifier added to the polymerization precursor dispersion system in this invention aims to ensure the stability and emulsifying properties of the precursor dispersion. In embodiments of this invention, the emulsifier is preferably one or more of Tween, n-hexadecyl alcohol, n-heptadecyl alcohol, or n-octadecyl alcohol. This emulsifier can stabilize the graphite precursor dispersion and improve its compatibility with the vinyl chloride suspension polymerization system.

[0046] In step S2 of this invention, the polymerization formulation contains a dispersant, an N-doped nitrogen atom source, and an initiator. The dispersant is preferably one or more of polyvinyl alcohol or hydroxypropyl methylcellulose, more preferably hydroxypropyl methylcellulose, and even more preferably a 2% aqueous solution of hydroxypropyl methylcellulose, which forms a protective layer around the monomer droplets to prevent droplet aggregation during the polymerization reaction. The initiator is preferably one or more of bis(2-ethylhexyl) percarbonate (EHP), benzoyl peroxide, or diisobutyronitrile peroxide. The selection of the initiator should be based on the required reaction kinetics and polymerization temperature; in this invention, bis(2-ethylhexyl) percarbonate (EHP) is recommended as the initiator.

[0047] It is particularly important to note that the polymerization formulation components added to the reactor in this invention contain an N-doped nitrogen atom source, which can be one or a combination of ammonium bicarbonate, ammonia, or both. The presence of nitrogen atoms in ammonium bicarbonate and ammonia is a crucial factor in the final formation of the honeycomb graphene carbon cage. Because the precursor dispersion in step S1 undergoes free radical polymerization in the in-situ polymerization system of polyvinyl chloride under the action of an initiator, electron capture and charge transfer occur between free radicals and graphene interfaces and edge defect sites during polymerization, leading to localized electrostatic accumulation between graphene layers. As the thermal expansion of the polymerization reaction intensifies, the combined effect of the interlayer electrostatic repulsion exceeds the van der Waals force constraint, triggering microscale Coulombic burst disintegration. Due to the presence of the N-doped nitrogen atom source, local bridging occurs between graphene layers, resulting in bending, closure, and honeycomb reconstruction of the two-dimensional graphene, forming a multilayered anchored carbon cage structure.

[0048] Specifically, the exothermic polymerization reaction further induces local thermal expansion. Ammonium bicarbonate or ammonia, components of the polymerization formulation, also decompose and release gases, promoting interlayer expansion and the formation of honeycomb channels. The instantaneous release of local electrostatics generates a plasma region, creating favorable conditions for N atom doping. With the participation of the N source, N-doped carbon cages containing pyridine nitrogen, graphitic nitrogen, and pyrrole nitrogen structures are formed.

[0049] In step S2 of the present invention, the relative proportions of the components added to the reactor can be reasonably optimized according to the actual effect. In the embodiments of the present invention, the following other components need to be added relative to 100 parts by mass of vinyl chloride monomer: 100-300 parts by weight of deionized water; 0.1~0.5 parts by weight of dispersant; 0.05~0.3 parts by mass of N-doped nitrogen atom source; 1-30 parts by weight of precursor dispersion; 0.05~0.2 parts by weight of initiator.

[0050] Furthermore, suspension polymerization requires sufficient pressure and temperature to initiate the reaction; the reactor pressure can be set to 6 to 10 bar, and the temperature can be controlled between 50°C and 60°C. This temperature range provides the necessary thermal energy to drive the polymerization reaction while effectively controlling reaction kinetics and polymer molecular weight distribution. Errors in temperature control can lead to variations in the viscosity and performance properties of the composite material.

[0051] Therefore, based on the in-situ polymerization-induced coulombic micro-explosion method for preparing honeycomb graphene carbon cage materials described in steps S1 and S2 above, this invention uses flake graphite as a carbon source. Through surfactant intercalation, power ultrasonic pre-exfoliation, in-situ polymerization of polyvinyl chloride, and thermally induced expansion, electron capture and interlayer electrostatic repulsion effects are formed in a free radical polymerization environment, thereby inducing microscale coulombic explosions between graphene layers, and finally forming an N-doped graphene carbon cage composite material with a honeycomb, porous, multi-layered anchoring structure.

[0052] This invention prepares a honeycomb porous structure and a multi-layered anchored carbon cage structure PVC in-situ polymer composite material, which has characteristics such as multiple scattering interfaces, dipole polarization loss, conductivity loss, and defect polarization loss, and can simultaneously achieve excellent electromagnetic shielding, microwave absorption, thermal management, and heat storage functions. Therefore, this honeycomb graphene carbon cage composite material can be widely used in various electromagnetic and microwave shielding materials, or in battery thermal management scenarios. For example, it can be used as an EMI shielding material, a microwave absorbing material, or as a stealth skin for drones, an electromagnetic shielding coating for new energy vehicles, and an electromagnetic interference protection coating for electronic devices, etc.

[0053] In other embodiments of the present invention, the multilayer honeycomb graphene carbon cage composite material prepared based on the above steps S1 and S2 can be further dissolved in an organic solvent to dissolve polyvinyl chloride (PVC), and then purified to obtain pure graphene. The organic solvent used to dissolve PVC can be one or more of tetrahydrofuran, cyclohexanone, and DMF. The purified graphene obtained in this way has a three-dimensional cage structure and can be applied in energy storage, catalysis, or sensor fields. For example, it can be used as a hydrogen storage material, or to prepare supercapacitors, or as a load carrier for high-sensitivity sensors. The high specific surface area and excellent electronic properties of graphene effectively improve the performance of various devices. Therefore, in addition to the graphene carbon cage PVC composite material, the further purified graphene has broad application potential in energy, catalysis, and biomedicine.

[0054] The following examples will demonstrate the specific preparation method and technical effects of the above-mentioned honeycomb graphene carbon cage composite material.

[0055] Example 1 In this embodiment, a honeycomb graphene carbon cage material was prepared by in-situ polymerization-induced coulombic micro-explosion. The preparation method is as follows: Step 1: Preparation of graphene polymerization precursor dispersion: Add 1000L of deionized water to a 1 cubic meter stainless steel stirred tank, then add 3kg of SDBS surfactant and stir until fully dissolved to form a dispersion system. Slowly add 10kg of flake graphite and 100kg of nano-calcium carbonate to the dispersion system in sequence, stir and heat to 70℃ to form a pre-dispersed slurry. Then add 1000ml of emulsifier Tween, 2.4kg of C16 alcohol, and 200ml of silicone defoamer. Use high-power ultrasonic treatment to achieve molecular intercalation of SDBS, while some nano-calcium carbonate particles are embedded between the graphite layers to achieve mechanical isolation. The ultrasonic power density is 1000W / L, and the ultrasonic frequency is 20-40KHz with dual-frequency synergy. Specifically, 24 sets of probe-type and water bath-type ultrasonic generators are connected in series for cyclic processing. A dual-frequency combination of 40 kHz and 23 kHz is used. The low frequency is conducive to the exfoliation of graphene layers, while the high frequency is conducive to the nano-calcium carbonate particles obtaining ultrasonic cavitation pulse energy to force them to embed into the interlayer gaps of graphite. After about 4 hours of ultrasonic treatment, some monolayer graphene will be exfoliated. Hydrogel phenomenon occurs in the presence of divalent calcium ions in the system. The online viscometer of the device will automatically stop the 24 sets of ultrasonic generators in batches when the system viscosity rises. When the temperature of the system material drops below 60 degrees Celsius, 1500 ml of 2% hydroxypropyl methylcellulose aqueous solution, which is the dispersant used in the later polymerization reaction, is added to the stirred mixing vessel. (The polymerization engineer can calculate the total amount of dispersant to be included in the polymerization formula.) Stir for another 25 minutes. After the treatment is completed, the polymerization precursor dispersion is sent to the finished product storage tank for cooling and packaging for later use.

[0056] Step 2: Preparation of PVC in-situ polymerized graphene carbon cage composite material: 10 kg of deionized water was added to a 20 L stainless steel reactor, followed by 500 ml of the precursor dispersion prepared in step 1 (approximately 5 g of flake graphite and 50 g of nano-calcium carbonate) and other polymerization formulation components (specifically: 800 ml of 2 wt.% hydroxypropyl methylcellulose solution, 2.5 g of ammonium bicarbonate, and 10 g of EHP initiator). Air was removed from the reactor by vacuuming. Then, 5 kg of vinyl chloride monomer was added. Before polymerization, the reactor was stirred cold for 30 minutes at 400 rpm. After heating, in-situ polymerization began. During the reaction, the reaction temperature was maintained at 57.5 °C, and the reactor pressure was maintained at 0.87 MPa. After about 1 hour of reaction, the stirring speed was adjusted to 300 rpm to maintain the stability of monomer droplet dispersion. The reaction was maintained for 6 hours. When the reaction pressure dropped by 0.1 MPa, a chain terminator was added to stop the reaction. Unreacted monomer was recovered, and after nitrogen purging, the reaction product was removed, washed, and dried, ultimately yielding a composite material of N-doped honeycomb graphene carbon cage PVC in-situ polymerization.

[0057] Step 3: The composite material sample prepared in the previous step was subjected to performance characterization tests and evaluations. The results showed that the composite material had a viscosity of 104 mL / g, a pseudo specific gravity of 0.45 g / mL, an oil absorption rate of 27.8 g / 100 g, a residual VCM content of 1.9 ug / g, and a thermal aging decomposition time of PVC resin tested using the Congo red test method of 15 min. Example 2 In this embodiment, the preparation process of the composite material is the same as in Example 1, except that the amount of polymerization precursor dispersion added to the reactor is increased from 500 ml to 1000 ml. All other aspects are the same as in Example 1. The final composite material sample test results are as follows: composite material viscosity 102 mL / g, apparent density 0.42 g / mL, oil absorption rate 27.8 g / 100g, residual VCM content 0.1 ug / g, and the thermal aging decomposition time of PVC resin tested using the Congo red test method increased to 28 min.

[0058] Example 3 In this embodiment, the preparation process of the composite material is the same as in Example 1, except that the amount of polymerization precursor dispersion added to the reactor is increased from 500 ml to 1500 ml, while the rest is the same as in Example 1. The final test results of the composite material sample are as follows: composite material viscosity 100 mL / g, apparent density 0.49 g / mL, oil absorption rate 27.8 g / 100g, residual VCM content 0.4 ug / g, and the thermal aging decomposition time of PVC resin tested by the Congo red test method is increased to 33 min.

[0059] Comparative Example 1 This comparative example did not add a polymerization precursor dispersion. It followed conventional PVC polymerization using the same 20L reactor as Example 1, and the process formulation and control methods were all the same as in Example 1. The test data of the obtained sample are as follows: viscosity number 100mL / g, apparent density 0.45 g / mL, oil absorption rate 15.7 g / 100g, residual VCM content 81 ug / g, and the thermal aging decomposition time of PVC resin tested by the Congo red test method was 1 min.

[0060] It should be noted that in Examples 1-3 and the comparative examples above, the samples of the prepared composite materials were tested according to the HG / T3791-2015 standard, and the electron microscopy (TEM) sample preparation was carried out according to the GB / T45469-2025 standard. A horizontal comparison of the results shows that, compared with materials obtained by traditional PVC polymerization methods, the composite materials prepared in Examples 1-3 of this invention have a thermal decomposition time that is 15-30 times longer. Furthermore, taking the composite material prepared in Example 1 as an example, the concentration of conjugated double bonds on the PVC molecular chain in this composite material was tested using ultraviolet spectroscopy. The results show that it is 20 times lower than the concentration of conjugated double bonds in the traditional PVC molecular chain, proving that the graphene carbon cage structure can achieve π-π stacking with the conjugated double bonds on the PVC molecular chain during in-situ polymerization through the delocalized electrons of the large π bonds, thereby stabilizing the PVC molecular chain. The composite materials prepared according to the graphene precursor formulation in Examples 1-3 of this invention generally have lower PVC viscosity than those in Comparative Example 1, indicating a slight decrease in average molecular weight. This may be related to the premature chain termination after free radicals gain electrons from the graphene interface. In contrast, the composite materials prepared by this invention show a significant reduction in residual VCM, which should be directly related to the decrease in the concentration of conjugated double bonds on the PVC molecular chain. This provides a huge potential for reducing energy consumption in the stripping process of PVC production.

[0061] Taking the composite material prepared in Example 1 as an example, Figure 1 , Figure 2 and Figure 3 TEM results of the composite material samples at three different scales are presented, revealing numerous honeycomb graphene carbon cage structures and plasma pores left by electrostatic micro-explosion charge release within the PVC particle slices. The microwave absorbing layer prepared using the composite materials of the various embodiments of this invention does not require compounding with other resins during construction; instead, it is directly dissolved in a solvent and sprayed onto the surface of the object requiring microwave absorption. A recommended solvent is a mixture of tetrahydrofuran (THF) and cyclohexanone in a 7:3 volume ratio. During spraying, the amount of honeycomb graphene carbon cage structure microwave absorbing material can be adjusted by regulating the thickness of the sprayed layer. Test results show that when the sprayed layer thickness is between 0.25 and 2.2 mm, the minimum reflection loss (RL) value in the X-band is below -20 dB. While PVC composite materials have lower strength and lifespan than epoxy resins, their low manufacturing cost and ease of construction give them a unique advantage in EMI shielding for autonomous vehicles and stealth applications for disposable drones.

[0062] The embodiments described above are only some implementations of the present invention and are not intended to limit the invention. Various implementation schemes can be adjusted without departing from the spirit and scope of the invention. Therefore, all technical solutions obtained by equivalent substitution or equivalent transformation are requested to be included within the protection scope of the present invention.

Claims

1. A method for exfoliating graphene and its honeycomb carbon cage structure during PVC in-situ polymerization, characterized in that, include: Flake graphite is dispersed in a surfactant to form a dispersion system. Then, nano-calcium carbonate and an emulsifier are added. The surfactant and nano-calcium carbonate are then injected into the spaces between the flake graphite layers by high-power ultrasonic treatment to obtain an in-situ polymerization precursor dispersion. Deionized water, the precursor dispersion, and a polymerization formulation containing a dispersant, an N-doped nitrogen atom source, and an initiator are added to a reaction vessel. The N-doped nitrogen atom source is ammonium bicarbonate and / or ammonia. After mixing, vinyl chloride monomer is added under vacuum or nitrogen protection. The polymerization reaction is then carried out at a pressure and temperature sufficient to initiate the polymerization reaction. The graphene honeycomb carbon cage structure is obtained by in-situ exfoliation of flake graphite through the residual heat of the polymerization reaction and the electron-induced coulombic repulsion force at the free radical trapping interface. After the reaction is terminated, a composite material containing graphene and its honeycomb carbon cage structure is obtained.

2. The method of claim 1, wherein the PVC in-situ polymerization process exfoliates graphene and its honeycomb carbon cage structure, and is characterized by, The mass ratio of flake graphite to nano calcium carbonate in the precursor dispersion is 1:8~12, and the amount of precursor dispersion added to the reactor during the polymerization reaction is 0.2 wt%~30 wt% of the mass of the added vinyl chloride monomer.

3. The method of claim 1, wherein the PVC in-situ polymerization process exfoliates graphene and its honeycomb carbon cage structure, and is characterized by, The high-power ultrasonic treatment is configured with an ultrasonic power density of 500-1000 W / L, an ultrasonic frequency of 10-40 kHz with two frequencies working in tandem, and an ultrasonic treatment time of 4-6 hours.

4. The method of claim 1, wherein the PVC in-situ polymerization process exfoliates graphene and its honeycomb carbon cage structure, and is characterized by, The raw materials used in this method are selected to satisfy one or more of the following: Preferably, the surfactant is sodium dodecylbenzenesulfonate (SDBS) or sodium dodecyl sulfate (SDS). Preferably, the diameter of the flake graphite is 2~10μm; more preferably, the flake graphite is pre-treated mechanically to present an arched structure; Preferably, the particle size of the nano-calcium carbonate particles is 30~100 nm; Preferably, the dispersant is one or more of polyvinyl alcohol or hydroxypropyl methylcellulose; Preferably, the emulsifier is one or more selected from Tween, n-hexadecyl alcohol, n-heptadecyl alcohol, or n-octadecyl alcohol; Preferably, the initiator is one or more of bis(2-ethylhexyl) peroxide dicarbonate (EHP), benzoyl peroxide, or diisobutyronitrile peroxide.

5. The method of exfoliating graphene and its honeycomb carbon cage structure in a PVC in-situ polymerization process as claimed in claim 1, wherein, In the aforementioned reactor, relative to every 100 parts by mass of vinyl chloride monomer, the following should be added: 100-300 parts by weight of deionized water; 0.1~0.5 parts by weight of dispersant; 0.05~0.3 parts by mass of N-doped nitrogen atom source; 1-30 parts by weight of precursor dispersion; 0.05~0.2 parts by weight of initiator.

6. The method of exfoliating graphene and its honeycomb carbon cage structure in a PVC in-situ polymerization process as claimed in claim 1, wherein, The polymerization reaction is controlled at a temperature of 50-60°C and a pressure of 6-10 bar.

7. The method of exfoliating graphene and its honeycomb carbon cage structure in a PVC in-situ polymerization process as claimed in claim 1, wherein, The multi-layered honeycomb graphene carbon cage composite material is further added to an organic solvent to dissolve polyvinyl chloride, and then separated and purified to obtain pure graphene carbon cages; preferably, the organic solvent is one or more of tetrahydrofuran, cyclohexanone, and DMF.

8. A graphene-PVC composite material prepared according to the method described in claims 1 to 7.

9. The application of the composite material as described in claim 8 as an EMI shielding material and a microwave absorbing material.

10. The application of the composite material as described in claim 8 in stealth skin for unmanned aerial vehicles, electromagnetic shielding for new energy vehicles, electromagnetic protection for electronic equipment, or battery thermal management.

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