A vermiculite nanosheet reinforced polyvinyl chloride composite film based on interface engineering modification and a preparation method and application thereof

Abstract

The application provides a vermiculite nanosheet reinforced polyvinyl chloride composite film based on interface engineering modification and a preparation method and application thereof, and belongs to the technical field of flame-retardant materials.The raw materials of the composite film include polyvinyl chloride and polymethyl methacrylate grafted modified vermiculite nanosheets;the vermiculite raw materials are mechanically exfoliated into vermiculite nanosheets in the presence of sodium carboxymethyl cellulose, then treated by a silane coupling agent, and then grafted with polymethyl methacrylate on the surface of the vermiculite nanosheets through emulsion polymerization to obtain the polymethyl methacrylate grafted modified vermiculite nanosheets.The synergistic effect of efficient and green exfoliation of CMC and covalent grafting of PMMA enables the vermiculite nanosheets to be highly oriented and uniformly dispersed in the matrix, forming a continuous physical barrier and stress transfer network, achieving multifunctional integration improvement, and achieving the purposes of simultaneous reinforcement, toughening, flame retardation, smoke suppression and gas barrier.

Description

Technical Field

[0001] This invention belongs to the field of flame retardant materials technology, and particularly relates to a polyvinyl chloride composite film reinforced by interface engineering modified vermiculite nanosheets, its preparation method and application. Background Technology

[0002] Flexible polyvinyl chloride (fPVC) gains its flexibility through the addition of plasticizers, but this also weakens intermolecular forces and increases free volume, resulting in a significant decrease in the material's structural strength, heat resistance, and gas barrier properties. FPVC is inherently flammable, releasing a large amount of heat and producing substantial amounts of smoke and toxic gases when burned, posing a serious fire hazard.

[0003] To improve the aforementioned properties, existing technologies introduce two-dimensional layered silicates (such as vermiculite) as nanofillers. Vermiculite is a natural 2:1 type layered silicate mineral with wide availability, large interlayer spacing, and good thermodynamic properties. Theoretically, after being exfoliated into single-layer or few-layer nanosheets, it has the potential for enhancement and flame retardancy. However, ordinary vermiculite has a hydrophilic surface, resulting in extremely poor compatibility with hydrophobic PVC matrices. It is difficult to disperse uniformly, easily agglomerates, and cannot exert its nano-effect.

[0004] Traditional exfoliation methods suffer from drawbacks such as long processing times, the use of harsh chemical reagents, and limited lateral dimensions of the resulting nanosheets. To improve interfacial compatibility, small-molecule surfactants are commonly used to modify the surface of vermiculite. However, such modifications rely solely on weak van der Waals forces, resulting in interfacial instability and easy migration of the modifier during processing or use, leading to limited improvements in macroscopic properties. Therefore, how to synergistically improve the mechanical strength, flame retardancy, smoke suppression, and gas barrier properties of flexible PVC while maintaining its flexibility remains an unsolved problem. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a polyvinyl chloride composite film reinforced with interface engineering-modified vermiculite nanosheets, its preparation method, and its application. This invention utilizes sodium carboxymethyl cellulose (CMC) to assist in the exfoliation of vermiculite and combines it with polymethyl methacrylate (PMMA) surface grafting to prepare functionalized vermiculite nanosheets, which are then used to fill modified soft PVC to obtain a composite film.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a polyvinyl chloride composite film reinforced with interface-engineered modified vermiculite nanosheets. The raw materials of the composite film include polyvinyl chloride and polymethyl methacrylate (PMMA)-grafted modified vermiculite nanosheets dispersed therein. The PMMA-grafted modified vermiculite nanosheets are prepared by the following method: first, vermiculite raw material is mechanically exfoliated into vermiculite nanosheets in the presence of sodium carboxymethyl cellulose; then, it is treated with a silane coupling agent; and then PMMA is grafted onto the surface of the vermiculite nanosheets via emulsion polymerization to obtain the PMMA-grafted modified vermiculite nanosheets.

[0007] Furthermore, the amount of polymethyl methacrylate grafted modified vermiculite nanosheets added is 0.5% to 5% of the mass of the polyvinyl chloride.

[0008] Furthermore, the preparation method of the polymethyl methacrylate grafted modified vermiculite nanosheets specifically includes the following steps: (1) Vermiculite powder was mixed with an aqueous solution containing sodium carboxymethyl cellulose, mechanically ball-milled and exfoliated, and then centrifuged and dried to obtain vermiculite nanosheets (VNs). (2) The vermiculite nanosheets obtained in step (1) are surface-treated with a silane coupling agent to obtain organic vermiculite nanosheets; (3) Using the organic vermiculite nanosheets as seeds, methyl methacrylate monomer (MMA) was added dropwise in the presence of emulsifier, initiator and crosslinking agent to carry out emulsion polymerization, and the polymethyl methacrylate grafted modified vermiculite nanosheets (P-VNs) were obtained after purification.

[0009] Furthermore, in step (2), the silane coupling agent is γ-methacryloyloxypropyltrimethoxysilane (silane coupling agent KH570), the surface treatment reaction temperature is 110 °C, and the time is 10 h.

[0010] Furthermore, in step (3), the emulsion polymerization temperature is 60~80℃ and the time is 6~12h.

[0011] Furthermore, in step (3), the ratio of the amount of the organic vermiculite nanosheets, emulsifier, initiator, crosslinking agent and methyl methacrylate monomer is 5g:1.2g:0.2g:0.2g:40g; The emulsifier is sodium dodecyl sulfate (SDS), the initiator is potassium persulfate, and the crosslinking agent is divinylbenzene.

[0012] This invention also provides a method for preparing the above-mentioned polyvinyl chloride composite film based on interface engineering modified vermiculite nanosheets, comprising the following steps: Polymethyl methacrylate-grafted vermiculite nanosheets and plasticizers were dispersed in an organic solvent, and then polyvinyl chloride powder was added and mixed evenly. The resulting mixture was then cast and dried to prepare the interface engineering-modified vermiculite nanosheet-reinforced polyvinyl chloride composite film.

[0013] Furthermore, the organic solvent is tetrahydrofuran, the plasticizer is dioctyl phthalate (DOP), and the amount of plasticizer used is 50% of the mass of the polyvinyl chloride powder.

[0014] Furthermore, the thickness of the prepared interface-engineered modified vermiculite nanosheet-reinforced polyvinyl chloride composite film is 0.1~0.3 mm.

[0015] The present invention also provides an application of the above-mentioned interface engineering modified vermiculite nanosheet reinforced polyvinyl chloride composite film in the fields of flame retardancy, gas barrier or mechanical reinforcement.

[0016] Compared with the prior art, the present invention has the following advantages and technical effects: This invention relates to a polyvinyl chloride (PVC) composite film reinforced with vermiculite nanosheets based on interface engineering. Using CMC as a green exfoliating agent, it not only yields vermiculite nanosheets with a high aspect ratio, but also preliminarily improves the surface properties of the inorganic sheets through its adsorption layer. Furthermore, a silane coupling agent is used to introduce double bond anchors on the vermiculite nanosheet surface, and PMMA chains are chemically grafted onto the sheet surface via emulsion polymerization, achieving a transformation of the inorganic sheet surface from hydrophilic to hydrophobic, forming an organic-inorganic interface layer compatible with the PVC matrix. Within the PVC matrix, the PMMA-grafted vermiculite nanosheets can be uniformly oriented and dispersed, forming a physical cross-linked network, while simultaneously constructing a "maze"-like barrier structure, achieving the simultaneous goals of reinforcement, toughening, flame retardancy, smoke suppression, and gas barrier properties. This invention utilizes the synergistic effect of efficient and green CMC exfoliation and PMMA covalent grafting to enable vermiculite nanosheets to be highly oriented and uniformly dispersed in the matrix, forming a continuous physical barrier and stress transfer network, achieving multifunctional integrated enhancement. The resulting interface-engineered vermiculite nanosheet-reinforced PVC composite film exhibits excellent performance. 1. Synergistic improvement of mechanical properties: The amount of polymethyl methacrylate grafted modified vermiculite nanosheets added is 0.5%~5% of the mass of polyvinyl chloride. With only 3wt% of modified vermiculite nanosheets added, the tensile strength of the prepared composite film can reach 21.13MPa, which is 19.72% higher than that of pure soft PVC; the elongation at break reaches 322%, which is 32.51% higher, achieving both reinforcement and toughening.

[0017] 2. Significantly improved gas barrier performance: The oxygen permeability of the polyvinyl chloride composite film reinforced with interface engineering-modified vermiculite nanosheets obtained in this invention is reduced to 1.60 × 10⁻⁶. 13 cm 3·cm / cm 2 The water vapor permeability (·s·Pa) is reduced by approximately 35.7% compared to pure soft PVC, and the water vapor permeability can be modulated through the interface.

[0018] 3. Significantly improved flame retardant performance: In the cone calorimeter test of the P-VNs-reinforced polyvinyl chloride composite film based on interface engineering modified vermiculite nanosheets obtained in this invention, the peak heat release rate was reduced to 378 kW / m³. 2 The total heat release remained stable at 30 MJ / m 2 about.

[0019] 4. Significant smoke suppression and toxicity reduction effects: The total smoke emission of the polyvinyl chloride composite film reinforced with interface engineering modified vermiculite nanosheets obtained in this invention is reduced to 9.5m³. 2 The rates of CO and CO2 generation both decreased, while the rate of smoke release remained at a low level.

[0020] 5. Enhanced hydrophobicity and interfacial adhesion: The water contact angle of the polyvinyl chloride composite film reinforced by interface engineering modified vermiculite nanosheets obtained in this invention increased from 81° of the pure film to 97.4°, indicating enhanced surface hydrophobicity; dynamic mechanical analysis showed that the glassy energy storage modulus increased, the loss peak shifted to higher temperatures and increased in intensity, indicating enhanced interfacial confinement and energy dissipation capacity. Attached Figure Description

[0021] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic diagram illustrating the preparation principle of the polyvinyl chloride composite film reinforced by interface engineering modified vermiculite nanosheets in an embodiment of the present invention. Figure 2 The images show the microstructure of vermiculite raw material (VMT), vermiculite nanosheets (VNs), and PMMA-grafted modified vermiculite nanosheets (P-VNs). In the images, (A) is a scanning electron microscope (SEM) image of VMT, (B) is a scanning electron microscope (SEM) image of VNs, (C) is a scanning electron microscope (SEM) image of VNs, (D) is a transmission electron microscope (TEM) image of VMT, (E) is a transmission electron microscope (TEM) image of P-VNs, (F) is an atomic force microscope (AFM) image of VNs, and (G) is an energy dispersive spectroscopy (EDS) image of P-VNs. Figure 3(A) is a comparison of Fourier transform infrared (FT-IR) spectra of VMT, VNs, and P-VNs; (B) is an X-ray diffraction (XRD) pattern of VMT, VNs, and P-VNs; (C) is a full X-ray photoelectron spectroscopy (XPS) pattern of VMT, VNs, and P-VNs; (D) is a high-resolution Si 2p spectrum of VMT and VNs; (E) is a high-resolution O 1s spectrum of VMT and VNs; (F) and (G) are high-resolution Si 2p and O 1s spectra of P-VNs, respectively; (H) is a thermogravimetric (TG) curve of VMT, VNs, and P-VNs; and (I) is a differential thermogravimetric (DTG) curve of VMT, VNs, and P-VNs. Figure 4 The composite films in Example 1 (fPVC / P-VNs 3%) and Comparative Examples 1-3 (fPVC / VNs 3%, fPVC / VMT 3%, and fPVC) are characterized by their structure and performance. (A) is an infrared spectrum (FTIR), (B) is an X-ray diffraction pattern (XRD), (C) is the water contact angle test result, (D) is the thermogravimetric curve (TG curve), (E) is the differential thermogravimetric curve (DTG curve), (F) is a comparison chart of T5% (initial degradation temperature), (G) is the storage modulus-temperature curve, (H) is the loss modulus-temperature curve, and (I) is a comparison chart of oxygen permeability and water vapor permeability. Figure 5 Mechanical properties of the composite films in Example 1 (fPVC / P-VNs 3%) and Comparative Examples 2-3 (fPVC / VMT 3% and fPVC) were tested. Among them, (A) is a comparison diagram of tensile strength, (B) is a comparison diagram of elongation at break, (C) is a representative stress-strain curve, (D) and (G) are SEM images of tensile sections of fPVC at different magnifications, (E) and (H) are SEM images of tensile sections of fPVC / VMT 3% at different magnifications, and (F) and (I) are SEM images of tensile sections of fPVC / P-VNs 3% at different magnifications. Figure 6 The results show the flame retardancy and smoke suppression performance of the composite films in Example 1 (fPVC / P-VNs 3%) and Comparative Examples 2-3 (fPVC / VMT 3% and fPVC). Among them, (A) is the heat release rate (HRR) curve measured by cone calorimeter, (B) is the total heat release (THR) curve, (C) is the smoke release rate (SPR) curve, (D) is the total smoke production (TSP) curve, (E) is the carbon monoxide production (COP), (F) is the carbon dioxide production (CO2P), (G) is the mass loss curve, (H) is a comparison graph of heat release rate (HRR) curves, and (I) is a comparative analysis of the SPR and TSP performance of various flame retardants. Detailed Implementation

[0022] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0023] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0024] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0025] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0026] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0027] This invention provides a polyvinyl chloride composite film reinforced with interface-engineered modified vermiculite nanosheets. The raw materials of the composite film include polyvinyl chloride and polymethyl methacrylate (PMMA)-grafted modified vermiculite nanosheets dispersed therein. The PMMA-grafted modified vermiculite nanosheets are prepared by the following method: first, vermiculite raw material is mechanically exfoliated into vermiculite nanosheets in the presence of sodium carboxymethyl cellulose; then, it is treated with a silane coupling agent; and then PMMA is grafted onto the surface of the vermiculite nanosheets by emulsion polymerization to obtain PMMA-grafted modified vermiculite nanosheets.

[0028] In a preferred embodiment of the present invention, the amount of polymethyl methacrylate grafted modified vermiculite nanosheets added is 0.5% to 5% of the mass of polyvinyl chloride.

[0029] In a preferred embodiment of the present invention, the preparation method of polymethyl methacrylate grafted modified vermiculite nanosheets specifically includes the following steps: (1) Vermiculite powder was mixed with an aqueous solution containing sodium carboxymethyl cellulose, mechanically ball-milled and exfoliated, and then centrifuged and dried to obtain vermiculite nanosheets (VNs). (2) The vermiculite nanosheets obtained in step (1) are surface-treated with a silane coupling agent to obtain organic vermiculite nanosheets; (3) Using organic vermiculite nanosheets as seeds, methyl methacrylate monomers were added dropwise in the presence of emulsifiers, initiators and crosslinking agents to carry out emulsion polymerization. After purification, polymethyl methacrylate grafted modified vermiculite nanosheets (P-VNs) were obtained.

[0030] In the preferred embodiment of the present invention, in the preparation method of polymethyl methacrylate grafted modified vermiculite nanosheets, in step (2), the silane coupling agent is γ-methacryloyloxypropyltrimethoxysilane (silane coupling agent KH570), the surface treatment reaction temperature is 110℃, and the time is 10h.

[0031] In the preferred embodiment of the present invention, in the preparation method of polymethyl methacrylate grafted modified vermiculite nanosheets, in step (3), the emulsion polymerization temperature is 60~80℃ and the time is 6~12h.

[0032] In the preferred embodiment of the present invention, in the preparation method of polymethyl methacrylate grafted modified vermiculite nanosheets, in step (3), the ratio of the amount of organic vermiculite nanosheets, emulsifier, initiator, crosslinking agent and methyl methacrylate monomer is 5g∶1.2g∶0.2g∶0.2g∶40g; The emulsifier is sodium dodecyl sulfate (SDS), the initiator is potassium persulfate, and the crosslinking agent is divinylbenzene.

[0033] For example, the preparation method of polymethyl methacrylate grafted modified vermiculite nanosheets in this embodiment of the invention specifically includes the following steps: (1) Preparation of vermiculite nanosheets (VNs): Layered vermiculite powder (VMT) was mixed with a CMC aqueous solution (mass ratio 1:100, CMC aqueous solution mass concentration 1%) and placed in a ball mill, and ground at 400 rpm for 6 hours. Utilizing the numerous hydroxyl and carboxyl groups on the CMC molecular chain to form hydrogen bonds with the hydroxyl groups on the vermiculite surface, CMC inserts into the vermiculite interlayers, increasing the interlayer spacing, weakening the interlayer bonding force, and using the shear force of ball milling to exfoliate the vermiculite layer by layer, resulting in a two-dimensional vermiculite nanosheet dispersion. Then, a large amount of polymer was removed by centrifugation (8000 rpm, 5 minutes), followed by centrifugation at 3000 rpm for 5 minutes. The supernatant was collected and freeze-dried to obtain VNs.

[0034] (2) Organic treatment of vermiculite nanosheets 1 g of VNs was dispersed in 50 mL of toluene solution, and 6.2 mL of silane coupling agent KH570 was slowly added at 70 °C. The mixture was sonicated for 30 minutes and reacted at 110 °C for 10 hours. The precipitate was separated by filtration, ground, and then vacuum dried at 70 °C for 12 hours to obtain KH570 organo-modified vermiculite (KH570@VNs).

[0035] (3) Preparation of PMMA-grafted modified vermiculite nanosheets (P-VNs): Using a seed emulsion polymerization method, 1.2 g of emulsifier SDS, 0.2 g of initiator potassium persulfate, 0.2 g of crosslinking agent divinylbenzene, and 5 g of the obtained KH570@VNs were dispersed in 200 mL of deionized water. Nitrogen gas was purged to remove oxygen, and the temperature was raised to 70 °C under mechanical stirring. 40 g of methyl methacrylate monomer (MMA) was added dropwise, and the reaction was carried out for 8 hours. After demulsification, the polymer was repeatedly dispersed with toluene and centrifuged four times to remove free polymer. The polymer was then vacuum dried at 70 °C for 24 hours to obtain PMMA-grafted modified vermiculite nanosheets (P-VNs).

[0036] This invention also proposes a method for preparing the above-mentioned polyvinyl chloride composite film based on interface engineering modified vermiculite nanosheets, comprising the following steps: Polymethyl methacrylate-grafted vermiculite nanosheets and plasticizers were dispersed in an organic solvent, and then polyvinyl chloride powder was added and mixed evenly. The resulting mixture was then cast and dried to prepare a polyvinyl chloride composite film reinforced with interface engineering-modified vermiculite nanosheets.

[0037] In a preferred embodiment of the present invention, the organic solvent is tetrahydrofuran, the plasticizer is dioctyl phthalate (DOP), and the amount of plasticizer is 50% of the mass of polyvinyl chloride powder.

[0038] In a preferred embodiment of the present invention, the thickness of the polyvinyl chloride composite film reinforced by interface engineering modified vermiculite nanosheets is 0.1~0.3 mm.

[0039] For example, the preparation method of the polyvinyl chloride composite film based on interface engineering modified vermiculite nanosheets in this embodiment of the invention specifically includes the following steps: Weigh out P-VNs (0.5%~5% of PVC mass) and plasticizer dioctyl phthalate (DOP, 50wt% of PVC mass) according to the raw material amount, disperse them in tetrahydrofuran, and sonicate for 60 minutes; then add PVC powder, continue mechanical stirring at room temperature for 1 hour to obtain a uniform dispersion; cast the dispersion onto a glass plate, dry at 40℃ for 48 hours, and demold to obtain a PVC composite film with a thickness of 0.1~0.3 mm based on interface engineering modified vermiculite nanosheets.

[0040] This invention also proposes an application of the above-mentioned interface-engineered modified vermiculite nanosheet-reinforced polyvinyl chloride composite film in the fields of flame retardancy, gas barrier, or mechanical reinforcement.

[0041] In other embodiments, the stripping agent can also be other water-soluble polymers or biomacromolecules containing a large number of hydroxyl and carboxyl groups, but CMC is preferred due to its low cost and good stripping effect. Besides MMA, other acrylate monomers or copolymers with good compatibility with PVC can also be used as grafting monomers, but PMMA is more ideal because it matches the refractive index of PVC and has good interfacial adhesion.

[0042] In the embodiments of this invention, unless otherwise specified, "parts" refers to "number of parts by weight".

[0043] In the embodiments of this invention, "room temperature" refers to "25±3℃".

[0044] A schematic diagram illustrating the preparation principle of the polyvinyl chloride composite film reinforced with interface engineering modified vermiculite nanosheets in this embodiment of the invention is shown below. Figure 1This figure illustrates the intermolecular interactions and polymer chain movement to elucidate the microstructure formed at the P-VNs and PVC interface during composite material preparation. First, the hydroxyl and carboxymethyl groups on the CMC molecular chains form hydrogen bonds and electrostatic adsorption with oxygen-containing groups on the surface and interlayer of the VMT sheets. Under mechanical shearing, the embedding and adsorption of CMC weakens the interlayer interactions of VMT, promoting relative sliding between layers, thereby achieving the effective exfoliation of VMT into monolayer or few-layer VNs. The exfoliated VNs have higher specific surface area and aspect ratio, providing a structural basis for the subsequent construction of continuous interfacial networks and channel closure. Subsequently, PMMA is grafted onto the surface of the VNs, forming a stable organic coating layer, which alters the surface polarity and interfacial energy of the inorganic layer. The PMMA segments enhance the thermodynamic compatibility between the VNs and the fPVC matrix and prevent secondary aggregation of nanosheets during solution mixing. This flexible grafted layer can also serve as a transition interface between rigid VNs and the flexible PVC matrix, alleviating stress concentration caused by sudden changes in modulus. Simultaneously, the C=O groups in the PMMA segments can form dipole-dipole interactions with the polar C–Cl structural units in the PVC molecular chain, thereby creating a more stable interfacial adhesion region between PMMA-VNs and fPVC.

[0045] In the composite system, PMM-VNs together form a confined interface layer through interfacial adsorption, chain segment entanglement, and polar interactions. This interface layer can suppress the relaxation movement of PVC chains, improve load transfer efficiency, and enable external forces to be effectively transferred from the flexible matrix to the high-modulus VNs layer. When the material is subjected to external forces, the two-dimensional flakes can induce crack deformation and lengthen the crack propagation path, thereby enhancing the material's strength and crack propagation resistance. Simultaneously, the flexible PMMA interface layer can disperse some stress, preventing significant loss of material toughness. Furthermore, the high aspect ratio VNs particles form a typical "bent path" effect within the matrix, hindering the diffusion of oxygen, heat, and volatile pyrolysis products, and playing an inorganic shielding role during thermal degradation or combustion. In summary, the synergistic optimization of VNs dispersion, interfacial bonding, and barrier structure is achieved through CMC-assisted exfoliation and PMMA grafting modification. This fundamentally reveals the reasons for the excellent mechanical properties, barrier properties, and flame retardancy of fPVC composites.

[0046] The technical solution of the present invention will be further illustrated by the following embodiments.

[0047] Example 1 A method for preparing a polyvinyl chloride composite film reinforced with interface engineering-modified vermiculite nanosheets includes the following steps: (1) Preparation of vermiculite nanosheets (VNs): Take 1g of layered vermiculite powder (VMT) and mix it with 100g of CMC aqueous solution (containing 1g of CMC). Place the mixture in a ball mill jar and grind it at 400rpm for 6 hours. Then, remove a large amount of polymer by centrifugation (8000rpm, 5 minutes) and discard the supernatant. Redisperse the precipitate and centrifuge it again at 3000rpm for 5 minutes. Collect the supernatant and freeze-dry it to obtain VNs.

[0048] (2) Organic treatment of vermiculite nanosheets: 1 g of VNs was dispersed in 50 mL of toluene solution, and 6.2 mL of silane coupling agent KH570 was slowly added at 110 °C. The mixture was sonicated for 30 minutes and reacted at 110 °C for 10 hours. The precipitate was separated by filtration, ground, and then vacuum dried at 70 °C for 12 hours to obtain KH570 organo-converted vermiculite (KH570@VNs).

[0049] (3) Preparation of PMMA-grafted modified vermiculite nanosheets (P-VNs): Using a seed emulsion polymerization method, 1.2 g of emulsifier SDS, 0.2 g of initiator potassium persulfate, 0.2 g of crosslinking agent divinylbenzene, and 5 g of the obtained KH570@VNs were dispersed in 200 mL of deionized water. Nitrogen gas was purged to remove oxygen, and the temperature was raised to 70 °C under mechanical stirring. 40 g of methyl methacrylate monomer (MMA) was added dropwise, and the reaction was carried out for 8 hours. After demulsification, the polymer was repeatedly dispersed with toluene and centrifuged four times to remove free polymer. The polymer was then vacuum dried at 70 °C for 24 hours to obtain PMMA-grafted modified vermiculite nanosheets (P-VNs).

[0050] (4) Preparation of composite films: Weigh out 0.09g of P-VNs (3% of PVC mass) and 1.5g of dioctyl phthalate (DOP, 50wt% of PVC) according to the formula, disperse them in 30 mL of tetrahydrofuran, and sonicate for 60 minutes. Then add 3.0g of PVC powder and continue mechanical stirring at room temperature for 1 hour to obtain a uniform dispersion. Cast the dispersion onto a glass plate and dry it at 40℃ for 48 hours. Demold to obtain a polyvinyl chloride composite film (fPVC / P-VNs 3%) based on interface engineering modified vermiculite nanosheets.

[0051] Comparative Example 1 Preparation of fPVC / VNs 3%: Weigh 0.09g of VNs (VNs added at 3% of PVC mass, prepared in the same way as step (1) in Example 1) and 1.5g of plasticizer dioctyl phthalate (DOP, 50wt% of PVC) and disperse them in 30 mL of tetrahydrofuran. Sonicate for 60 minutes. Then add 3.0g of PVC powder and continue mechanical stirring at room temperature for 1 hour to obtain a uniform dispersion. Cast the dispersion onto a glass plate and dry at 40℃ for 48 hours. Demold to obtain fPVC / VNs 3% composite film.

[0052] Comparative Example 2 Preparation of fPVC / VMT 3%: Weigh out 0.09g of VMT (VMT added at 3% of PVC mass) and 1.5g of dioctyl phthalate (DOP, plasticizer at 50wt% of PVC) according to the raw material amount, disperse them in 30 mL of tetrahydrofuran, and sonicate for 60 minutes; then add 3.0g of PVC powder, and continue mechanical stirring at room temperature for 1 hour to obtain a uniform dispersion; cast the dispersion onto a glass plate, dry at 40℃ for 48 hours, and demold to obtain fPVC / VMT 3% composite film.

[0053] Comparative Example 3 Pure soft PVC (fPVC): Based on SG-5 grade polyvinyl chloride (PVC, degree of polymerization 1000~1200, purchased from Xinjiang Zhongtai Chemical Co., Ltd.), the amount of dioctyl phthalate (DOP, Shanghai Maclean Biochemical Technology Co., Ltd.) added was 50% of the mass of PVC. 3g of PVC and 1.5g of DOP were dispersed in 30 mL of tetrahydrofuran and sonicated for 60 minutes. Then, 3.0g of PVC powder was added, and mechanical stirring was continued at room temperature for 1 hour to obtain a uniform dispersion. The dispersion was cast onto a glass plate and dried at 40℃ for 48 hours. After demolding, fPVC was obtained.

[0054] The performance of the raw materials and composite films in Example 1, and the composite films in Comparative Examples 1-3 were tested: (1) Microscopic morphological characterization Figure 2The images show the microstructure of vermiculite raw material (VMT), vermiculite nanosheets (VNs), and PMMA-grafted modified vermiculite nanosheets (P-VNs). In the images, (A) is a scanning electron microscope (SEM) image of VMT, (B) is a scanning electron microscope (SEM) image of VNs (400 nm), (C) is a scanning electron microscope (SEM) image of VNs (100 nm), (D) is a transmission electron microscope (TEM) image of VMT, (E) is a transmission electron microscope (TEM) image of P-VNs, (F) is an atomic force microscope (AFM) image of VNs, and (G) is an energy dispersive spectroscopy (EDS) image of P-VNs. Figure 2 As can be seen in (A), the vermiculite raw material (VMT) exhibits a densely stacked layered structure. After CMC-assisted exfoliation, the product displays a typical two-dimensional sheet-like morphology (see Figure 1). Figure 2 (B) and (C)). Figure 2 The transmission electron microscopy comparison between (D) and (E) shows that the unexfoliated vermiculite VMT is an electronically opaque mass, while P-VNs are electronically translucent and have surface wrinkles, indicating that the lamellae are extremely thin and that the insertion and grafting of polymer chains disrupt the long-range ordered stacking of vermiculite. Figure 2 The atomic force microscopy height image in (F) shows that the vermiculite nanosheets are only about 1.81 nm thick, which quantitatively proves that few-layer vermiculite nanosheets have been successfully prepared. Figure 2 The elemental distribution diagram of G shows that, in addition to Si, Al, and O which constitute the vermiculite framework, a large amount of uniform C signal covers the inorganic framework, indicating that KH570 and PMMA form a continuous organic modification layer on the nanosheet surface. Overall, this demonstrates that the exfoliation and grafting process of the present invention can obtain functionalized two-dimensional nanofillers with high aspect ratio and uniform organic coating.

[0055] (2) Fourier transform infrared spectroscopy determination Figure 3 Image (A) shows a comparison of the Fourier transform infrared (FT-IR) spectra of VMT, VNs, and P-VNs. It can be seen that, compared to VMT, the characteristic absorption peak of VNs is lower at 1610.0 cm⁻¹. -1 and 1400.0cm -1 They shifted to lower wavenumbers up to 1593.1 cm. -1 and 1361.6cm -1 This significant low wavenumber shift provides spectroscopic evidence for hydrogen bonding between functional groups on the CMC molecular chain and exposed hydroxyl groups on the vermiculite surface, confirming the CMC-mediated intercalation-exfoliation mechanism. More importantly, compared to vermiculite and vermiculite nanosheets, the spectrum of PMMA-grafted modified vermiculite nanosheets (P-VNs) shows a higher intensity at 1720.0 cm⁻¹. -1A distinct new absorption peak appeared at the point, which corresponds to the characteristic stretching vibration of the C=O bond, indicating that the PMMA macromolecular chain has been successfully grafted in situ onto the surface of the two-dimensional nanosheet, fundamentally changing the surface chemical environment of the filler.

[0056] Figure 3 (B) shows the X-ray diffraction (XRD) patterns of VMT, VNs, and P-VNs. It can be seen that the VMT peak at 8.92° corresponds to the (002) crystal plane. The VNs peak on the (002) crystal plane shifts to the left to 8.83°, indicating an increase in the interlayer spacing of this plane. Furthermore, the diffraction peak intensity of P-VNs is significantly enhanced. This result indicates that the initial layered morphology and crystal properties are largely preserved after modification. Expanded vermiculite was successfully separated into nanosheets, consistent with the results observed in the SEM images.

[0057] Figure 3 (C) shows the full X-ray photoelectron spectroscopy (XPS) spectra of VMT, VNs, and P-VNs. It can be seen that, compared to the original vermiculite, the surface of the exfoliated vermiculite nanosheets exhibits a Na 1s signal. This signal originates from sodium ions in the exfoliating agent CMC, indirectly confirming the interaction between CMC and the vermiculite surface during the exfoliation process. In PMMA-grafted modified vermiculite nanosheets, the C 1s peak intensity significantly increases, preliminarily indicating the successful loading of organic polymers onto inorganic surfaces.

[0058] Figure 3 (D) and (E) are high-resolution spectra of Si 2p and O 1s in VMT and VNs, respectively. It can be seen that, compared to the original vermiculite, the characteristic binding energies of Si-O-Si and Si-OH in VNs have shifted slightly towards higher values. This change in binding energy is generally related to the hydrogen bonding between the CMC macromolecular chains and the exposed hydroxyl groups on the two-dimensional mineral surface, further confirming the CMC intercalation and exfoliation mechanism at the chemical state level.

[0059] Figure 3 In the image, (F) and (G) are high-resolution spectra of Si 2p and O 1s, respectively, for P-VNs. It can be seen that after KH570 silanization treatment and in-situ PMMA grafting, a new characteristic peak belonging to the Si-C bond appears at 101.5 eV in the Si 2p spectrum, indicating that the silane coupling agent KH570 is covalently anchored to the nanosheet surface through a dehydration condensation reaction. Simultaneously, a characteristic peak belonging to the C=O bond appears at 531.3 eV in the O 1s spectrum. The simultaneous appearance of spectral signals from both the Si-C covalent bond and the C=O double bond proves that this interface engineering strategy successfully achieved chemical bonding of polymer chains on the surface of two-dimensional vermiculite nanosheets.

[0060] Figure 3The thermogravimetric curves (TG) for VMT, VNs, and P-VNs are shown in Figure (H). It can be seen that the original vermiculite exhibits high inherent thermal stability, with almost no mass loss across the entire test temperature range. The vermiculite nanosheets obtained from CMC exfoliation show a small mass loss, mainly attributed to the thermal degradation of a small amount of CMC adsorbed on the surface, providing thermal evidence for the interfacial intercalation and adhesion of CMC during vermiculite exfoliation. In contrast, the PMMA-grafted modified vermiculite nanosheets show a significant mass decrease in the temperature range of 300℃ to 400℃, with a final residual mass of 77.82%, indicating that a large amount of organic polymer is grafted onto the surface of the inorganic sheets.

[0061] Figure 3 In Figure (I), the differential thermogravimetric (DTG) curves of VMT, VNs, and P-VNs are shown. It can be seen that PMMA-grafted vermiculite nanosheets exhibit a sharp peak in the maximum thermal weight loss rate range of 300℃ to 400℃. This concentrated thermal degradation stage is highly consistent with the thermal decomposition process of the silane coupling agent and the long PMMA chain at the interface. This result further demonstrates that the organic polymer achieves effective covalent bonding and structural reorganization on the surface of vermiculite nanosheets.

[0062] (3) Structural characterization and performance testing Figure 4 The structural characterization and performance testing of the composite films in Example 1 (fPVC / P-VNs 3%) and Comparative Examples 1-3 (fPVC / VNs 3%, fPVC / VMT 3%, and fPVC) are shown in the figures. (A) is the Fourier Transform Infrared (FTIR) spectrum, (B) is the X-ray Diffraction (XRD) spectrum, (C) is the water contact angle test result, (D) is the thermogravimetric (TG) curve, (E) is the differential thermogravimetric (DTG) curve, (F) is a comparison of T5% (initial degradation temperature), (G) is the storage modulus-temperature curve, (H) is the loss modulus-temperature curve, and (I) is a comparison of oxygen permeability and water vapor permeability. (It should be noted that fPVC / P-VNs 3%, fPVC / P-VNs, and P-VNs 3% in the figures are all fPVC / P-VNs 3% prepared in Example 1, and fPVC / VMT 3%, fPVC / VMT, and VMT 3% are all fPVC / VMT prepared in Comparative Example 2.) 3%, fPVC / VNs 3%, fPVC / VNs and VNs 3% are all fPVC / VNs 3% prepared in Comparative Example 1. They are just different names for each other.

[0063] according to Figure 4 As can be seen in (A), all samples are at 1720.4 cm. -1Significant characteristic absorption peaks were observed at all locations, which are attributed to the stretching vibration of the carbonyl group in the dioctyl phthalate ester bond of the plasticizer, indicating that the plasticizing system is stable in all formulations. Compared with pure soft PVC matrix, the composite films with the addition of the three fillers all showed a peak at 1037.7 cm⁻¹. -1 A new characteristic absorption peak appeared, corresponding to the asymmetric stretching vibration of the Si-O-Si bonds in the layered vermiculite framework, indicating that the inorganic silicate filler has been successfully introduced into the polymer matrix. Furthermore, the overall spectral profiles of all composite films are highly similar to those of pure soft PVC, indicating that the introduction of PMMA-grafted modified vermiculite nanosheets did not disrupt the main chemical structure of soft PVC, and the blend system maintained good structural stability.

[0064] according to Figure 4 As shown in (B), the (110) crystal plane peak in the composite film remains stable, indicating that the layered silicate framework remains intact during the mixing process. The (002) peaks of VNs and P-VNs shift to lower angles when combined with PVC to form a film. This is consistent with the XRD patterns of powdered VNs and P-VNs. This interlayer network combines the increased interlayer spacing with the highly oriented alignment of the two-dimensional nanosheets, which is beneficial for constructing a highly ordered nacre brick-mortar structure within the matrix.

[0065] according to Figure 4 As shown in Figure (C), the water contact angle of the fPVC film is 81°. After adding unmodified vermiculite and vermiculite nanosheets (fPVC / VMT 3%, fPVC / VNs 3%), the contact angles decreased to 80.1° and 71.9°, respectively. The enhanced hydrophilicity is mainly due to the exposure of a large number of inherent polar hydroxyl groups on the exfoliated two-dimensional nanosheets. However, after adding PMMA-grafted modified vermiculite nanosheets (fPVC / P-VNs 3%), the contact angle significantly increased to 97.4°, exhibiting a clear hydrophobic transition. This transition indicates that the grafted PMMA chains effectively shielded the surface hydrophilic sites, while the uniformly intercalated nanosheets created micro- and nano-scale structural roughness, further amplifying the hydrophobic effect. These drastically different wetting behaviors provide direct evidence of successful surface modification.

[0066] according to Figure 4As shown in Figure (D), the initial degradation temperature of fPVC was 244℃. After adding unmodified vermiculite and vermiculite nanosheets (fPVC / VMT 3% and fPVC / VNs 3%), the initial degradation temperatures decreased to 220℃ and 226℃, respectively. This premature weight loss is usually related to the polar sites exposed on the mineral surface or the accelerated dehydrochlorination of the PVC matrix catalyzed by metal ions. After surface grafting modification, the initial degradation temperature of the PMMA-grafted vermiculite nanosheet composite material (fPVC / P-VNs 3%) recovered to 237℃, indicating that the grafted PMMA chains effectively shielded the catalytically active sites and improved interfacial compatibility, thus inhibiting early catalytic degradation.

[0067] according to Figure 4 As can be seen in Figure (E), compared with the abnormally sharp degradation peak induced by the unmodified filler (fPVC / VMT 3%), the introduction of PMMA-grafted modified vermiculite nanosheets significantly suppressed the maximum thermal degradation rate of the composite material (fPVC / P-VNs 3%), and the degradation peak was significantly broadened and moderated. Combined with the highest residual carbon content at the end of the thermogravimetric curve, the improvement in thermal stability in the high-temperature region is mainly attributed to the fact that the uniformly dispersed two-dimensional nanosheets form a physical maze network, which restricts the dynamic transport of heat and volatile degradation products, while promoting the catalytic carbonization of the polymer matrix, ultimately endowing the composite material with better high-temperature resistance.

[0068] according to Figure 4 As can be seen from Figure (F), the initial degradation temperature of the PMMA-grafted vermiculite nanosheet system is significantly higher than that of the unmodified system, further confirming the effect of interface modification on improving thermal stability.

[0069] according to Figure 4 As can be seen in (G), in the glassy region, the storage modulus of the PMMA-grafted vermiculite nanosheet composite (fPVC / P-VNs 3%) is significantly higher than that of fPVC and other systems. This enhancement is mainly attributed to the fact that PMMA grafting promotes the uniform intercalation and dispersion of nanosheets in the matrix, improves interfacial compatibility, and thus achieves effective stress transfer from the flexible PVC matrix to the high-rigidity two-dimensional inorganic framework under dynamic loading.

[0070] according to Figure 4As shown in Figure (H), the introduction of PMMA-grafted vermiculite nanosheets maximizes the loss peak intensity, while the peak position shifts significantly towards higher temperatures. This high-temperature shift indicates that the large specific surface area and strong interfacial entanglement of the two-dimensional nanosheets significantly restrict the relaxed motion degrees of freedom of adjacent polymer chain segments. The significant increase in loss peak intensity implies that under alternating stress, the dense physical interface network dissipates a large amount of energy through interfacial friction between the polymer chains and the nanosheets. These rheological characteristics demonstrate that the interfacial engineering of PMMA-grafted vermiculite nanosheets not only enhances the dynamic stiffness of the material but also endows the system with excellent deformation energy dissipation capabilities, providing a microstructure and dynamic basis for enhancing macroscopic mechanical properties and toughness.

[0071] according to Figure 4 As can be seen from Figure (I), the oxygen permeability of the PMMA-grafted modified vermiculite nanosheet composite film (fPVC / P-VNs 3%) decreased to 1.60 × 10⁻⁶. 13 cm 3 ·cm / cm 2 The water vapor permeability (Pa) was reduced by approximately 35.7% compared to fPVC. This improvement stems from the dense brick-and-mortar barrier structure formed by uniformly intercalated, highly oriented two-dimensional vermiculite nanosheets, which significantly extends the tortuous diffusion path of nonpolar oxygen molecules. Simultaneously, the water vapor permeability of the PMMA-grafted vermiculite nanosheet composite film rebounded compared to the unmodified vermiculite nanosheet system. Based on the dissolution-diffusion model, this is because the grafted macromolecules introduce polar ester groups, increasing the thermodynamic affinity for water, and the effectively expanded interlayer spacing and free volume provide additional transport channels for polar water molecules.

[0072] (4) Mechanical performance testing Figure 5 Mechanical property tests were conducted on the composite films in Example 1 (fPVC / P-VNs 3%) and Comparative Examples 2-3 (fPVC / VMT 3% and fPVC). Among them, (A) is a comparison diagram of tensile strength, (B) is a comparison diagram of elongation at break, (C) is a representative stress-strain curve, (D) and (G) are SEM images of tensile sections of fPVC at different magnifications, (E) and (H) are SEM images of tensile sections of fPVC / VMT 3% at different magnifications, and (F) and (I) are SEM images of tensile sections of fPVC / P-VNs 3% at different magnifications.

[0073] according to Figure 5As shown in Figure (A), the tensile strength of fPVC is 17.65 MPa. The addition of 3 wt% unmodified vermiculite (fPVC / VMT 3%) significantly reduced the tensile strength. This is due to the poor interfacial compatibility and weak adhesion between the hydrophilic mineral and the hydrophobic polymer matrix, leading to localized stress concentration, limiting the uniform plastic deformation of the matrix, and prematurely inducing interfacial debonding and microcracks. After transitioning from unmodified vermiculite to exfoliated vermiculite nanosheets (fPVC / VNs 3%), the tensile strength rebounded to 19.24 MPa, demonstrating the geometric advantages of high aspect ratio two-dimensional nanomaterials: the exfoliated silicate sheets provided a larger interfacial contact area, promoting a more uniform stress distribution. Based on this, the surface-grafted PMMA-modified vermiculite nanosheet system (fPVC / P-VNs 3%) achieved the most significant reinforcing effect, with a tensile strength of 21.13 MPa, an increase of 19.72% compared to fPVC.

[0074] according to Figure 5 As shown in Figure (B), the elongation at break of fPVC is 243%. The elongation at break of the unmodified vermiculite (fPVC / VMT 3%) system is reduced, which is related to premature fracture caused by interfacial defects. The elongation at break of the exfoliated vermiculite nanosheets (fPVC / VNs 3%) system is increased to approximately 280%, and the unmodified two-dimensional nanosheets play a toughening role to some extent. The elongation at break of the PMMA-grafted modified vermiculite nanosheets (fPVC / P-VNs 3%) system is further increased to 322%, which is 32.51% higher than that of fPVC, achieving the best comprehensive effect of simultaneous reinforcement and toughening.

[0075] according to Figure 5 As shown in Figure (C), the curve for the PMMA-grafted vermiculite nanosheet composite film (fPVC / P-VNs 3%) exhibits a steeper initial slope, indicating improved material stiffness; simultaneously, the largest area under the curve indicates the highest energy required for fracture. This comprehensive performance leap demonstrates that in-situ grafting of PMMA chains effectively optimizes interfacial interactions, constructing a robust load transfer bridge between the inorganic nanosheets and the polymer matrix. During deformation, the improved interfacial compatibility ensures effective load transfer to the high-stiffness two-dimensional skeleton for reinforcement, while also allowing the polymer chains to dissipate a significant amount of mechanical energy along the nanosheet surface through slippage and orientation, ultimately endowing the composite material with excellent ductility.

[0076] according to Figure 5 As can be seen from (D) and (G), the fPVC cross-section is relatively smooth, exhibiting typical uniform fracture characteristics of an unreinforced amorphous matrix, indicating that the matrix without filler is mainly characterized by uniform deformation and fracture. Based on... Figure 5As can be seen in (E) and (H), significant phase separation is observed in the unmodified vermiculite composite film (fPVC / VMT 3%). This is because the unmodified vermiculite particles have poor dispersion, forming micro-agglomerates with obvious interfacial debonding resulting in voids and gaps. These agglomerates become stress concentration points and crack initiation sites, consistent with the decrease in mechanical properties observed in tensile tests. According to... Figure 5 As shown in (F) and (I), the PMMA-grafted vermiculite nanosheet composite film (fPVC / P-VNs 3%) exhibits a rougher and more tortuous ductile tear morphology, indicating significant plastic deformation and energy dissipation during fracture. The vermiculite nanosheets are uniformly dispersed and deeply embedded in the matrix. Even after fracture, the exposed nanosheets remain well wetted and coated by the PVC matrix, with no obvious macroscopic voids observed. This directly reflects the successful establishment of a good organic-inorganic interfacial bond through PMMA surface modification. This tightly bonded interfacial structure provides a basis for effective stress transfer and matrix yielding, which is beneficial for passivating microcracks and improving the ultimate tensile strength and ductility of the nanocomposite material.

[0077] (5) Flame retardancy and smoke suppression performance test Figure 6 The results show the flame retardancy and smoke suppression performance of the composite films in Example 1 (fPVC / P-VNs 3%) and Comparative Examples 2-3 (fPVC / VMT 3% and fPVC). Among them, (A) is the heat release rate (HRR) curve measured by cone calorimeter, (B) is the total heat release (THR) curve, (C) is the smoke release rate (SPR) curve, (D) is the total smoke production (TSP) curve, (E) is the carbon monoxide production (COP) curve, and (F) is the carbon dioxide production (CO2P) curve.

[0078] according to Figure 6 As can be seen from (A), the peak heat release rate (pHRR) of fPVC is approximately 518.6 KW / m². 2 This is because it has high flammability. The peak heat release rate (pHRR) of the composite material containing 3% VNs and P-VNs decreased to 328.6 KW / m². 2 and 378.8 KW / m 2 This indicates that the uniform distribution of P-VNs helps suppress the rapid heat release that occurs in the early stages of combustion. Compared to VNs, although PMMA releases volatile products such as MMA upon heating, which reduces flame retardant efficiency, PMMA mainly exists as a surface graft layer in PMMA-VNs. Its negative impact cannot offset the shielding effect caused by nanosheet detachment. Therefore, the flame retardant performance of PMMA-VNs is still superior to VMT.

[0079] according to Figure 6 As shown in Figure (B), although unmodified vermiculite delayed the initial heat release, its final total heat release increased to its highest value. This performance degradation can be attributed to the severe agglomeration of the hydrophilic raw material clay: the agglomerates could not form a continuous protective char layer, but instead destroyed the structural integrity of the char layer, forming channels that promoted the transport of heat and combustible volatiles, thereby accelerating further degradation. In contrast, the composite material with PMMA-grafted modified vermiculite nanosheets (fPVC / P-VNs 3%) maintained a stable total heat release of 30 MJ / m³. 2 No deterioration was observed in the later stages.

[0080] according to Figure 6 As can be seen from (C) and (D), the total smoke emission of fPVC is 11m³. 2 Furthermore, the smoke release rate is relatively high. Similar to the overall heat release trend, incomplete combustion due to agglomeration of unmodified vermiculite increases the total smoke release of fPVC / VMT by 3% to 11.5m³. 2 The well-dispersed PMMA-grafted modified vermiculite nanosheet composite (fPVC / P-VNs 3%) maintained a low smoke release rate and reduced the total smoke release to 9.5 m³. 2 It exhibits a significant smoke-suppressing effect. This smoke-suppressing effect is related to the "maze effect" generated by the highly oriented vermiculite nanosheets with a high aspect ratio: the tortuous layered network prolongs the diffusion path of smoke precursors and promotes the retention of carbonaceous soot particles in the condensed phase.

[0081] according to Figure 6 As can be seen from (E) and (F), the addition of PMMA-grafted modified vermiculite nanosheets reduces the generation rates of both toxic CO and greenhouse CO2, which helps to extend the safe evacuation time window in actual fire scenarios.

[0082] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A polyvinyl chloride composite film reinforced with interface-engineered modified vermiculite nanosheets, characterized in that, The raw materials for the composite film include polyvinyl chloride and polymethyl methacrylate-grafted modified vermiculite nanosheets dispersed therein. The polymethyl methacrylate-grafted modified vermiculite nanosheets are prepared by the following method: vermiculite raw material is mechanically exfoliated into vermiculite nanosheets in the presence of sodium carboxymethyl cellulose, then treated with a silane coupling agent, and then polymethyl methacrylate is grafted onto the surface of the silane coupling agent-treated vermiculite nanosheets by emulsion polymerization to obtain the polymethyl methacrylate-grafted modified vermiculite nanosheets.

2. The polyvinyl chloride composite film reinforced with interface engineering modified vermiculite nanosheets according to claim 1, characterized in that, The amount of polymethyl methacrylate grafted modified vermiculite nanosheets added is 0.5% to 5% of the mass of the polyvinyl chloride.

3. The polyvinyl chloride composite film reinforced with interface engineering modified vermiculite nanosheets according to claim 1, characterized in that, The preparation method of the polymethyl methacrylate grafted modified vermiculite nanosheets specifically includes the following steps: (1) Vermiculite powder was mixed with an aqueous solution containing sodium carboxymethyl cellulose, mechanically ball-milled and exfoliated, and then centrifuged and dried to obtain vermiculite nanosheets; (2) The vermiculite nanosheets obtained in step (1) are surface-treated with a silane coupling agent to obtain organic vermiculite nanosheets; (3) Using the organic vermiculite nanosheets as seeds, methyl methacrylate monomers were added dropwise in the presence of emulsifiers, initiators and crosslinking agents to carry out emulsion polymerization, and the polymethyl methacrylate grafted modified vermiculite nanosheets were obtained after purification.

4. The polyvinyl chloride composite film reinforced with interface engineering modified vermiculite nanosheets according to claim 3, characterized in that, In step (2), the silane coupling agent is γ-methacryloxypropyltrimethoxysilane, and the surface treatment reaction temperature is 110°C and the time is 10h.

5. The polyvinyl chloride composite film reinforced with interface engineering modified vermiculite nanosheets according to claim 3, characterized in that, In step (3), the emulsion polymerization temperature is 60~80℃ and the time is 6~12h.

6. The polyvinyl chloride composite film reinforced with interface engineering modified vermiculite nanosheets according to claim 3, characterized in that, In step (3), the organic vermiculite nanosheets, emulsifier, initiator, crosslinking agent and methyl methacrylate monomer are in the ratio of 5g:1.2g:0.2g:0.2g:40g; The emulsifier is sodium dodecyl sulfate, the initiator is potassium persulfate, and the crosslinking agent is divinylbenzene.

7. A method for preparing a polyvinyl chloride composite film based on interface engineering modified vermiculite nanosheets as described in any one of claims 1 to 6, characterized in that, Includes the following steps: Polymethyl methacrylate-grafted vermiculite nanosheets and plasticizers were dispersed in an organic solvent, and then polyvinyl chloride powder was added and mixed evenly. The resulting mixture was then cast and dried to prepare the interface engineering-modified vermiculite nanosheet-reinforced polyvinyl chloride composite film.

8. The method for preparing a polyvinyl chloride composite film based on interface engineering modified vermiculite nanosheets according to claim 7, characterized in that, The organic solvent is tetrahydrofuran, the plasticizer is dioctyl phthalate, and the amount of plasticizer used is 50% of the mass of polyvinyl chloride powder.

9. The method for preparing a polyvinyl chloride composite film based on interface engineering modified vermiculite nanosheets according to claim 7, characterized in that, The thickness of the prepared interface-engineered vermiculite nanosheet-reinforced polyvinyl chloride composite film is 0.1~0.3 mm.

10. The application of the interface-engineered modified vermiculite nanosheet-reinforced polyvinyl chloride composite film according to any one of claims 1 to 6 in the fields of flame retardancy, gas barrier or mechanical reinforcement.

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