Nano sepiolite / MXene-based flame-retardant material as well as preparation method and application thereof

Abstract

The invention discloses a nano sepiolite / MXene-based flame-retardant material as well as a preparation method and application thereof, and belongs to the technical field of flame-retardant materials. According to the invention, nano sepiolite and MXene cooperate with ammonium polyphosphate to enhance the flame retardant property and mechanical property of the ethylene-vinyl acetate copolymer, and nano sepiolite and MXene respectively exert the effects of skeleton enhancement and catalytic graphitization, and cooperate with ammonium polyphosphate to form a compact continuous carbon layer, thereby effectively inhibiting mass and heat transfer, and enhancing the flame retardant property and mechanical property of the ethylene-vinyl acetate copolymer. The flame retardant property of the ethylene-vinyl acetate copolymer is enhanced; nano sepiolite and MXene cooperate with ammonium polyphosphate to physically limit molecular chain movement of the ethylene-vinyl acetate copolymer, so that the ductility of the material is reduced, and meanwhile, the rigidity or strength of the material is remarkably improved through self-bearing and effective stress transfer; the flame retardant property of the ethylene-vinyl acetate copolymer is improved, and meanwhile, the mechanical property of the ethylene-vinyl acetate copolymer is guaranteed.

Description

Technical Field

[0001] This invention belongs to the field of flame retardant materials technology, and particularly relates to a nano-sepiolite / MXene-based flame retardant material, its preparation method, and its application. Background Technology

[0002] Ethylene-vinyl acetate copolymer (EVA), with its lightweight, flexibility, and excellent processing properties, is widely used in cable sheathing, photovoltaic encapsulation, footwear materials, and electronic equipment protection. However, EVA's limiting oxygen index (LOI) is only 17-19%, classifying it as a highly flammable material. Its combustion process releases large amounts of heat and toxic fumes, posing a serious threat to personnel safety and equipment reliability. With the rapid development of the new energy industry, high-voltage cables, energy storage systems, and electric vehicles are placing higher demands on the flame-retardant properties of EVA materials. While traditional flame-retardant technologies can improve fire resistance ratings, they often come at the cost of deteriorated mechanical properties or increased environmental risks. Therefore, developing efficient, environmentally friendly, and mechanically stable flame-retardant EVA composite materials has become a crucial issue in the field of polymer materials.

[0003] Intumescent flame retardant (IFR) systems are considered environmentally friendly flame retardant solutions due to their low smoke and low toxicity. Ammonium polyphosphate (APP), as the core component of IFR, forms an expanded char layer on the material surface through the synergistic effects of an acid source (decomposing to generate phosphoric acid), a gas source (releasing inert gases), and a carbon source (promoting char formation), effectively isolating heat and oxygen transfer. However, the single APP / EVA system has significant drawbacks: high addition levels (typically 25-35 wt%) severely reduce material flexibility; the char layer formed during combustion is prone to cracking, limiting flame retardant efficiency; furthermore, the poor interfacial compatibility between APP and the EVA matrix easily leads to filler agglomeration, further impairing the overall material performance.

[0004] In recent years, the introduction of nanofillers (such as clay, layered double hydroxides, and two-dimensional materials) has provided new solutions to the aforementioned problems. These materials can optimize flame-retardant pathways through mechanisms such as physical barrier effects, catalytic char formation, or free radical capture, while simultaneously improving the mechanical and thermal stability of the matrix. Among them, nano-sepiolite (NS) is a natural fibrous silicate mineral with a unique needle-like structure and a high specific surface area (200~300 m²). 2The presence of NS (saturated styrene) and abundant surface silanol groups (Si-OH) endows it with excellent adsorption properties and char-forming catalytic activity. Studies have shown that NS can construct a three-dimensional network structure in the polymer matrix, delaying the diffusion of pyrolysis gases and producing a synergistic effect with phosphorus-based flame retardants (such as APP), promoting the formation of a denser and more stable char layer. However, the flame-retardant synergistic effect of NS is limited by its dispersibility in the matrix and the interfacial bonding strength with the polymer; excessive addition can easily lead to a decrease in mechanical properties. Therefore, how to improve the flame-retardant properties of ethylene-vinyl acetate copolymers while ensuring their mechanical properties has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a nano-sepiolite / MXene-based flame retardant material, its preparation method, and its application.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a nano-sepiolite / MXene-based flame retardant material, comprising nano-sepiolite, MXene, ammonium polyphosphate, and ethylene-vinyl acetate copolymer; The mass ratio of the nano-sepiolite, MXene, ammonium polyphosphate and ethylene-vinyl acetate copolymer is (0.4~1.2):(0.1~0.3):(9.5~28.5):40.

[0007] Furthermore, the average particle size of the nano-sepiolite is 500 nm, and the specific surface area of ​​the nano-sepiolite is 183 m². 2 / g.

[0008] Furthermore, the MXene is selected from Ti3C2.

[0009] Furthermore, the MXene is multilayered, and the average particle size of the MXene is 5 μm.

[0010] Furthermore, the degree of polymerization of the ammonium polyphosphate is 1000.

[0011] This invention provides a method for preparing the nano-sepiolite / MXene-based flame retardant material described above, comprising the following steps: weighing each raw material according to the mass ratio and then blending them, followed by pressing to obtain the nano-sepiolite / MXene-based flame retardant material.

[0012] Furthermore, the blending temperature is 90°C.

[0013] Furthermore, the pressing process specifically involves pre-pressing at 110°C for 5 minutes followed by hot pressing for 3 minutes.

[0014] This invention also provides an application of the nano-sepiolite / MXene-based flame-retardant material described above in the field of new energy cable protection.

[0015] Compared with the prior art, the present invention has the following advantages and technical effects: This invention utilizes nano-sepiolite and MXene in synergistic polyphosphate ammonium to enhance the flame retardant and mechanical properties of ethylene-vinyl acetate copolymers. Nano-sepiolite and MXene respectively play the roles of skeletal reinforcement and catalytic graphitization, synergistically forming a dense and continuous carbon layer with polyphosphate ammonium, effectively inhibiting mass and heat transfer and enhancing the flame retardant properties of ethylene-vinyl acetate copolymers. Nano-sepiolite and MXene, in synergistic polyphosphate ammonium, physically restrict the molecular chain movement of ethylene-vinyl acetate copolymers, reducing the material's ductility. At the same time, through its own load-bearing capacity and effective stress transfer, it significantly improves the material's rigidity or strength, thus achieving the goal of improving the flame retardant properties of ethylene-vinyl acetate copolymers while ensuring their mechanical properties. Attached Figure Description

[0016] 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 XRD patterns of the flame-retardant materials prepared in Example 1 and Comparative Examples 1-3; Figure 2 SEM images of the flame-retardant materials prepared in Example 1 and Comparative Examples 1-3, where a is Comparative Example 1, b is Comparative Example 2, c is Comparative Example 3, and d is Example 1; Figure 3 The graph shows the changes in elongation at break and tensile strength of the flame-retardant materials prepared in Examples 1-5 and Comparative Examples 1-3. Figure 4 The volume resistivity of the flame-retardant materials prepared in Example 1 and Comparative Examples 1-3; Figure 5 Thermogravimetric curves of the flame retardant materials prepared in Example 1 and Comparative Examples 1-3 are shown, where a is TGA and b is DTG. Figure 6 The graph shows the changes in LOI values ​​of the flame-retardant materials prepared in Examples 1-5 and Comparative Examples 1-3. Figure 7 Optical images of the ash after combustion of the flame-retardant materials prepared in Example 1 and Comparative Examples 1-3, from left to right: Comparative Example 1, Comparative Example 2, Comparative Example 3, and Example 1; Figure 8 The combustion mass loss curves of the flame-retardant materials prepared in Example 1 and Comparative Examples 1-3 are shown. Figure 9The graphs show the HRR and THR curves of the flame retardant materials prepared in Example 1 and Comparative Examples 1-3, where the left graph represents HRR and the right graph represents THR. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0019] This invention provides a nano-sepiolite / MXene-based flame retardant material, comprising nano-sepiolite (NS), MXene, ammonium polyphosphate (APP), and ethylene-vinyl acetate copolymer (EVA). The mass ratio of the nano-sepiolite, MXene, ammonium polyphosphate and ethylene-vinyl acetate copolymer is (0.4~1.2):(0.1~0.3):(9.5~28.5):40.

[0020] In a preferred embodiment, the average particle size of the nano-sepiolite is 500 nm, and the specific surface area of ​​the nano-sepiolite is 183 m². 2 / g. The nano-sepiolite in this invention has a nanofiber structure and acts as a carbon layer reinforcing agent, synergist, and physical reinforcing framework. It can be embedded in the expanded carbon layer, enhancing its strength like steel bars and preventing it from collapsing and cracking under the impact of heat or airflow. The silanol groups (-Si-OH) on the surface of sepiolite may also react with the polyphosphoric acid produced by the decomposition of APP to form PO-Si bonds. This not only stabilizes the polyphosphoric acid and prolongs its catalytic effect, but may also promote the formation of a more stable and graphitized carbon layer, thereby improving the flame retardant properties of the material. Nano-sepiolite can also effectively transfer loads, acting like steel bars, bridging cracks and preventing their rapid propagation, thereby improving the mechanical properties of the material.

[0021] In a preferred embodiment, the MXene is selected from Ti3C2; the MXene is multilayered, and the average particle size of the MXene is 5 μm. The MXene used in this invention can not only withstand huge stresses, but its two-dimensional planar structure can also significantly increase the interface area for load transfer, providing excellent reinforcement efficiency. The lamellar structure can also hinder the propagation of cracks perpendicular to the tensile direction, which is beneficial to improving the mechanical properties of the material. MXene has excellent physical barrier properties. This barrier is extremely effective in blocking oxygen penetration and heat feedback. During combustion, it has efficient heat conduction and dissipation. In synergy with APP and sepiolite, MXene may also promote the formation of PO-Ti bonds in the APP and sepiolite system, constructing an "organic-inorganic hybrid" carbon layer, achieving a significant improvement in strength, density, and thermal stability (ternary synergistic effect).

[0022] In a preferred embodiment, the degree of polymerization of the ammonium polyphosphate is 1000; the particle size of the ammonium polyphosphate is 1~5μm. The ammonium polyphosphate in this invention acts as a physical barrier during combustion; the expanded char layer prevents oxygen from diffusing into the matrix and blocks heat transfer to the interior. Furthermore, APP can suppress molten droplets, and the char layer increases the melt viscosity, reducing the amount of molten droplets that could ignite other substances.

[0023] This invention provides a method for preparing a nano-sepiolite / MXene-based flame retardant material, comprising the following steps: weighing each raw material according to the mass ratio and then blending them, followed by pressing to obtain the nano-sepiolite / MXene-based flame retardant material.

[0024] In a preferred embodiment, the blending temperature is 90°C.

[0025] In a preferred embodiment, the pressing specifically involves pre-pressing at 110°C for 5 minutes followed by hot pressing for 3 minutes.

[0026] This invention also provides an application of the nano-sepiolite / MXene-based flame-retardant material described above in the field of new energy cable protection.

[0027] In this embodiment of the invention, room temperature refers to "25±2℃".

[0028] Unless otherwise specified, all raw materials used in the embodiments of this invention were purchased through commercial channels.

[0029] In the following examples and comparative examples: 1. Raw materials Ethylene-vinyl acetate copolymer (EVA), DuPont, USA; MXene (Ti3C2), multilayer, average particle size 5μm, Nangong Fenghui Nanotechnology Co., Ltd.; Ammonium polyphosphate (APP), degree of polymerization 1000, Guangzhou Runzhan Chemical Co., Ltd.; Nano-sepiolite, average particle size 500nm, specific surface area 183m².2 / g, Hebei Runri Mineral Products Co., Ltd.

[0030] 2. Equipment and Instruments Two-roll open mill, SK-160B, Dongguan Tin Testing Instruments Co., Ltd.; Tableting machine, YST-100T, Dongguan Tin Testing Instruments Co., Ltd.; Shore hardness tester, LX-D, Wenzhou Haibao Instruments Co., Ltd.; High resistance meter, ZC-36, Shanghai Sixth Electric Meter Factory Co., Ltd.; Microcomputer-controlled electronic universal testing machine, ETM-A, Shenzhen Wanchuang Testing Equipment Co., Ltd.; X-ray diffractometer (XRD), D8 ADVANCE, Bruker AXS GmbH, Germany; Fourier transform infrared spectrometer (FT-IR), Tensor II, Bruker AG, Germany; Scanning electron microscope (SEM), Phenom Pro, Phenom-world BV GmbH, Netherlands; Differential scanning calorimeter, DSC822e, Mettler Toledo GmbH, Switzerland; Thermogravimetric analyzer (TGA), Q50, TA Instruments, USA; Limiting oxygen index tester, HC-2, Nanjing Jiangning District Analytical Instrument Factory; Cone calorimeter, FTT0030, FTT Instruments, UK.

[0031] 3. Performance Testing and Structural Characterization 1) Mechanical property testing: The sample was made to a thickness of 4mm. The dumbbell shape is 7.5mm in diameter and tested according to GB / T 1040-1992. 2) Volume resistivity test: The sample was prepared into a circular sheet with a thickness of 1 mm and a suitable diameter. The test was conducted on a ZC-36 high resistance meter according to GB / T 1410-2006. The test temperature was 25℃ and the test voltage was 1000V. 3) FTIR analysis: The sample was placed on a Fourier transform infrared spectrometer and tested using the reflectance method; 4) XRD test: Cut an appropriate size sheet sample and place it on an X-ray diffractometer for scanning. The scanning speed is 8 (°) / min and the X-ray wavelength is 0.154 nm. 5) SEM analysis: The sample was fractured in liquid nitrogen, sputtered with gold under vacuum, and then the fracture surface was observed by SEM with an acceleration pressure of 10kV. 6) TGA analysis: Take about 10 mg of sample and place it in an aluminum crucible. Test under a nitrogen atmosphere at a rate of 50 mL / min, and heat to 650 °C at a rate of 20 °C / min. 7) Limiting oxygen index: Tested according to standard GB 5454-1985; 8) Cone-shaped calorimetry: 50kW / m² according to ISO 5660-1 standard. 2 The experiment was conducted under thermal irradiation power, and the sample size was 100mm×100mm×3mm.

[0032] Example 1 A method for preparing a nano-sepiolite / MXene-based flame retardant material includes the following steps: Weigh 40g of EVA, 9.5g of APP, 0.4g of nano-sepiolite, and 0.1g of MXene, mix them evenly on a two-roll mill at a mixing temperature of 90℃, and then pre-press them at 110℃ for 5min using a tablet press, followed by hot pressing for 3min to prepare sheet samples with thicknesses of 1mm, 2mm, and 3mm, respectively; wherein, MXene is Ti3C2, and the particle size of ammonium polyphosphate is 1~5μm.

[0033] Example 2 A method for preparing a nano-sepiolite / MXene-based flame retardant material includes the following steps: Weigh 40g of EVA, 14.25g of APP, 0.6g of nano-sepiolite, and 0.15g of MXene, mix them evenly on a two-roll mill at a mixing temperature of 90℃, and then pre-press them at 110℃ for 5min using a tablet press, followed by hot pressing for 3min to prepare sheet samples with thicknesses of 1mm, 2mm, and 3mm, respectively; wherein, MXene is Ti3C2, and the particle size of ammonium polyphosphate is 1~5μm.

[0034] Example 3 A method for preparing a nano-sepiolite / MXene-based flame retardant material includes the following steps: Weigh 40g of EVA, 19.0g of APP, 0.8g of nano-sepiolite, and 0.2g of MXene, mix them evenly on a two-roll mill at a mixing temperature of 90℃, and then pre-press them at 110℃ for 5min using a tablet press, followed by hot pressing for 3min to prepare sheet samples with thicknesses of 1mm, 2mm, and 3mm, respectively; wherein, MXene is Ti3C2, and the particle size of ammonium polyphosphate is 1~5μm.

[0035] Example 4 A method for preparing a nano-sepiolite / MXene-based flame retardant material includes the following steps: Weigh 40g of EVA, 23.75g of APP, 1g of nano-sepiolite, and 0.25g of MXene, mix them evenly on a two-roll mill at a mixing temperature of 90℃, and then pre-press them at 110℃ for 5min using a tablet press, followed by hot pressing for 3min to prepare sheet samples with thicknesses of 1mm, 2mm, and 3mm, respectively; wherein, MXene is Ti3C2, and the particle size of ammonium polyphosphate is 1~5μm.

[0036] Example 5 A method for preparing a nano-sepiolite / MXene-based flame retardant material includes the following steps: Weigh 40g of EVA, 28.5g of APP, 1.2g of nano-sepiolite, and 0.3g of MXene, mix them evenly on a two-roll mill at a mixing temperature of 90℃, and then pre-press them at 110℃ for 5min using a tablet press, followed by hot pressing for 3min to prepare sheet samples with thicknesses of 1mm, 2mm, and 3mm, respectively; wherein, MXene is Ti3C2, and the particle size of ammonium polyphosphate is 1~5μm.

[0037] Comparative Examples 1-3 A method for preparing a flame retardant material includes the following steps: weighing each raw material according to Table 1, mixing them evenly on a two-roll mill at a mixing temperature of 90°C, and then pre-pressing them at 110°C for 5 minutes using a tablet press, followed by hot pressing for 3 minutes to prepare sheet samples with thicknesses of 1 mm, 2 mm, and 3 mm, respectively; wherein, the particle size of ammonium polyphosphate is 1~5 μm.

[0038] Table 1. Composition of flame-retardant materials in Examples 1-5 and Comparative Examples 1-3 Figure 1 The images show the XRD patterns of the flame-retardant materials prepared in Example 1 and Comparative Examples 1-3. Figure 1 As can be seen, EVA exhibits a typical amorphous diffraction peak at 22.5°, indicating a high vinyl acetate (VA) content in EVA, which hinders the crystallization of the ethylene segment, resulting in low crystallinity of EVA. In the XRD curve of the EVA-A sample, strong diffraction peaks appear at 15.3°, 27.5°, and 30.5°, corresponding to the ammonium polyphosphate (APP) crystal structure. Simultaneously, the EVA peak position shifts to the right, reflecting the interaction (hydrogen bonding) between APP and EVA molecular chains, indicating that APP interferes with the regular arrangement of EVA chain segments, leading to decreased crystallinity. While APP, as a rigid particle, hinders EVA crystallization, the absence of new peaks suggests the absence of chemical bonding. In the XRD curve of the EVA-AS sample, the characteristic peak of nano-sepiolite at 7.4° (110 crystal plane) was not observed, indicating that sepiolite was exfoliated or highly dispersed; further weakening of the EVA peak can be observed, possibly due to the large specific surface area of ​​sepiolite, which inhibits EVA crystallization. The leftward shift of the APP peak position may be due to the interaction between some sepiolite and APP through PO-Si bonds. In the XRD curve of the EVA-ASM sample, the characteristic peak of MXene in the 6~9° (002 crystal plane) was not observed. This may be because the content is too low, resulting in a weak X-ray signal, or it may be due to partial exfoliation or increased interlayer spacing in the EVA caused by shear force during processing.

[0039] Figure 2SEM images of the flame-retardant materials prepared in Examples 1 and Comparative Examples 1-3 are shown, where a is Comparative Example 1, b is Comparative Example 2, c is Comparative Example 3, and d is Example 1. Figure 2 As can be seen from part a, the cross-section of the pure EVA sample is smooth and uniform, exhibiting typical ductile fracture characteristics (accompanied by stringing). Figure 2 In part b, APP particles (1~5μm) can be seen dispersed in the matrix. Figure 2 As can be seen from part c, sepiolite has a nanofiber structure, but due to its small addition amount, it is uniformly dispersed in the EVA substrate without agglomeration, and tightly bonded to the matrix interface. Figure 2 More particles, namely APP and MXene, were observed in the d portion, which were embedded in the polymer and showed no stacking.

[0040] The breaking strength and elongation at break of the flame-retardant materials prepared in Examples 1-5 and Comparative Examples 1-3 are shown in Table 2 and 3. Figure 3 .

[0041] Table 2. Fracture strength and elongation at break of different flame-retardant materials Figure 3 The graph shows the changes in elongation at break and tensile strength of the flame-retardant materials prepared in Examples 1-5 and Comparative Examples 1-3. Figure 3As can be seen, with the sequential addition of ammonium polyphosphate, nano-sepiolite, and MXene, the elongation at break of the flame-retardant material slowly decreased from 1500% to 1200%; while the tensile strength gradually increased from 4 MPa to 6.8 MPa. The fundamental reason for this is that the addition of rigid fillers significantly affected the molecular chain movement and stress transfer mechanism of the EVA matrix. The sequential addition of APP, nano-sepiolite, and MXene reduced the material's ductility by physically restricting the movement of EVA molecular chains, while significantly improving the material's rigidity or strength through its own load-bearing capacity and effective stress transfer. The EVA-ASM sample (containing MXene) had the highest strength and the lowest elongation, demonstrating the outstanding role of MXene two-dimensional sheets in reinforcing efficiency and restricting chain movement. Specifically, pure EVA is a low-crystallinity elastomer with highly flexible molecular chains, capable of large-scale slippage, orientation, and crystal rearrangement during stretching, thus exhibiting extremely high elongation at break (1500%) and relatively low strength. In the EVA-A sample, ammonium polyphosphate consists of rigid inorganic particles (micrometer-sized). These hard particles, dispersed within the EVA matrix, act as physical barriers, hindering the free movement and slippage of the EVA molecular chains. During stretching, the molecular chains cannot fully extend and rearrange as they would in a pure matrix, resulting in a decrease in macroscopic plastic deformation capacity and elongation at break. In the EVA-AS sample (containing nano-sepiolite), the nano-sepiolite, a high aspect ratio nanofiber filler, exerts a stronger binding effect (interfacial effect) on the surrounding EVA molecular chains due to its large specific surface area and rigid structure. This binding not only restricts chain segment movement but may also hinder or disrupt the formation of crystalline regions (consistent with the decrease in EVA diffraction intensity in XRD), further weakening the matrix's ductility. In the EVA-ASM sample (containing MXene), MXene is an ultrathin two-dimensional sheet with an extremely large specific surface area and a strong physical barrier effect. It can penetrate the matrix like a "nanowall," significantly restricting the movement path of EVA molecular chains in three-dimensional space. This restriction is stronger than that of particles and fibers, leading to a further decrease in elongation at break to 1200%. Regarding the enhancement mechanism from the perspective of increased fracture strength, particle reinforcement (APP) involves hard particles bearing stress and hindering crack propagation. High aspect ratio sepiolite can more effectively transfer loads, acting like reinforcing steel, bridging cracks and preventing their rapid propagation. MXene sheets have extremely high modulus and strength, not only able to bear enormous stress, but their two-dimensional planar structure also significantly increases the interface area for load transfer, providing excellent reinforcement efficiency. The sheets also hinder crack propagation perpendicular to the tensile direction. Combined with XRD results, the addition of filler leads to a decrease in EVA crystallinity (weakened peak intensity). Although a decrease in crystallinity usually slightly reduces strength, in the system of this invention, the strength improvement effect of filler reinforcement far outweighs the negative impact of decreased crystallinity.In addition, nanofillers may act as heterogeneous nucleation sites, altering the crystal morphology of EVA (such as generating smaller spherulites), and small-sized spherulites are beneficial to strength.

[0042] Figure 4 The volume resistivity is shown in Example 1 and Comparative Examples 1-3 for the flame retardant materials prepared. EVA itself is an excellent insulating polymer, but its volume resistivity is typically very high. Its molecular chain structure lacks free electrons or ion carriers, making charge migration difficult. Ammonium polyphosphate (APP) is an ionic flame retardant, but its solid crystal structure does not provide an electronic conduction pathway, and its resistivity is also very high (>10). 8 APP may undergo slight decomposition or moisture absorption during processing or testing, introducing small amounts of mobile ions (such as NH4). + The APP particles exhibit extremely weak ionic conductivity. The interface between the APP particles and the EVA matrix may become a site of charge accumulation and polarization, which may manifest as increased dielectric loss under AC testing, resulting in a slight decrease in resistivity compared to pure EVA. Nano-sepiolite is a magnesium silicate mineral and also an insulator (resistivity > 10¹² Ω·cm). The mechanism by which the addition of nano-sepiolite leads to a decrease in resistivity may be: 1) Reduced crystallinity and increased amorphous regions. As shown in XRD, the addition of sepiolite further inhibits EVA crystallization, and the higher mobility of molecular chain segments in the amorphous regions may be more conducive to the migration of trace ions introduced by APP; 2) Formation of more complex interfaces. The huge specific surface area and nanofiber morphology of sepiolite form more interfaces with APP particles and the EVA matrix. These interface regions may adsorb trace amounts of water or impurity ions, becoming charge traps or promoting interface polarization (especially under AC fields); 3) Potential ion channels. The sepiolite crystal structure contains exchangeable cations (such as Mg). 2+ Na + / Ca 2+ Theoretically, MXene materials may exhibit weak ionic conductivity under specific conditions (such as high humidity), but their contribution in dry polymer composites is negligible. MXene materials possess metal-like conductivity, with intrinsic conductivity ranging from 10,000 to 20,000 S / cm (resistivity as low as approximately 5 × 10⁻⁶). -5 The resistivity of MXene is about 20 orders of magnitude higher than that of the polymer matrix, which theoretically can significantly reduce the resistivity of EVA. Although APP and nano-sepiolite are insulators, their presence plays a key role in the dispersion of MXene and the construction of the final conductive network, resulting in a slow rather than abrupt decrease.

[0043] The thermogravimetric data of the flame-retardant materials prepared in Example 1 and Comparative Examples 1-3 are shown in Table 3.

[0044] Table 3 Thermogravimetric data Figure 5The graphs show the thermogravimetric analysis (TGA) curves of the flame-retardant materials prepared in Example 1 and Comparative Examples 1-3, where a represents TGA and b represents DTG. Figure 5 It can be seen that there are two decomposition stages in the TGA curve of EVA: the thermal decomposition of the EVA side chains (around 365℃) and the main chain (around 480℃). A weight loss of 10% (T...) is defined as... 10% The initial decomposition temperature is T. The maximum thermal decomposition temperatures of EVA's side chains and main chain are T and T, respectively. max1 and T max2 The TGA curves show an initial increase followed by a decrease in both the initial and maximum decomposition temperatures. APP, acting as an acid source, decomposes at a relatively low temperature (approximately 250-300°C) to form polyphosphoric acid (PPA). PPA, as a strong Lewis acid, catalyzes the deacetylation of EVA, accelerating acetic acid removal (below the decomposition temperature of pure EVA). Simultaneously, it promotes dehydration and cross-linking to form carbon, causing EVA molecular chains to cross-link at lower temperatures, forming a carbon layer with higher thermal stability. Overall, the addition of APP alters the thermal decomposition pathway of EVA. Although the initial decomposition (deacidification) may occur slightly earlier, the carbonization reaction significantly increases the heat required for main chain breakage (the severe weight loss stage). The physical barrier formed on the surface of the carbon layer also delays further decomposition of the internal matrix, leading to the severe weight loss peak (T0). max2 The high temperature shift is due to the large specific surface area and surface silanol groups (-Si-OH) of sepiolite nanoparticles, which may adsorb some of the polyphosphoric acid (PPA) or reaction intermediates produced by APP decomposition, thus temporarily restricting the catalytic activity of PPA. Sepiolite, as an inert filler, occupies volume and may slightly reduce the concentration of active catalytic component (PPA) per unit volume. The physical adsorption and dilution effect of sepiolite on PPA may slightly inhibit the catalytic efficiency of APP in the early stages of decomposition, leading to a slightly earlier and more intense decomposition phase (compared to the EVA-A sample). However, this effect is weak, so the decrease is small (only 1.2℃). The addition of MXene shifts the intense char-forming decomposition reaction (intense weight loss phase) towards lower temperatures. Although decomposition starts earlier, the catalytically generated char layer forms earlier and is of higher quality. This char layer can more effectively protect the remaining matrix, resulting in a slower weight loss rate and increased char residue in the later decomposition phase (high-temperature zone). Therefore, T maxThe decrease in the maximum weight loss rate temperature does not indicate a deterioration in thermal stability, but rather a result of the decomposition pathway being efficiently catalyzed and reshaped. In TGA testing, the char residue rate increased sequentially with the addition of ammonium polyphosphate, nano-sepiolite, and MXene. The char residue rates for EVA-0, EVA-A, EVA-AS, and EVA-ASM were 0.3%, 7.3%, 8.8%, and 9.0%, respectively. This stepwise increase in char residue rate is a natural result of the layer-by-layer upgrade and synergistic optimization of the flame retardant system. APP provides the basic catalytic char formation capability, achieving a char layer stability from zero (0.3% to 7.3%). Nano-sepiolite enhances the stability of the char layer through physical reinforcement and chemical synergy (PO-Si) (from 7.3% to 8.8%). MXene, with its superior catalytic activity (Ti... 4+ With the advantages of its two-dimensional structure, it further optimizes the char formation efficiency and char layer quality (from 8.8% to 9.0%) when approaching the upper limit. Although its contribution is the smallest in numerical value, it is the key leap to achieve the top flame retardant performance (highest LOI value).

[0045] The limiting oxygen indices of the flame-retardant materials prepared in Examples 1-5 and Comparative Examples 1-3 are shown in Table 4 and... Figure 6 .

[0046] Table 4 Limiting Oxygen Index (LOI) of Different Flame Retardant Materials Figure 6 This is a graph showing the LOI value changes of the flame-retardant materials prepared in Examples 1-5 and Comparative Examples 1-3. From... Figure 6As can be seen, the LOI of the sample gradually increases with the gradual addition of flame retardants. APP is a classic intumescent flame retardant that acts as a physical barrier during combustion, preventing oxygen diffusion into the matrix and blocking heat transfer to the interior. The non-combustible gases produced during combustion dilute the fuel and oxygen concentration in the gas phase combustion zone. In addition, APP can also suppress droplets, and the char layer increases the melt viscosity, reducing droplets that ignite other substances. Sepiolite acts as a char layer reinforcing agent and synergist, and a physical reinforcing "skeleton": the nanofiber structure of sepiolite is embedded in the intumescent char layer, acting like "steel bars" to enhance the strength of the char layer and prevent it from collapsing and cracking under the impact of heat or airflow. The silanol groups (-Si-OH) on the surface of sepiolite may react with the polyphosphoric acid produced by the decomposition of APP to form PO-Si bonds. This not only stabilizes the polyphosphoric acid and prolongs its catalytic effect, but may also promote the formation of a more stable char layer with a higher degree of graphitization. MXene is an emerging two-dimensional flame retardant and catalytic material with excellent physical barrier properties. This barrier effectively blocks oxygen penetration and heat feedback, and provides efficient heat conduction and dissipation during combustion. MXene possesses ultra-high planar thermal conductivity, enabling rapid lateral diffusion of heat from the combustion zone, reducing localized surface temperatures, and inhibiting pyrolysis and combustion. It catalyzes char formation and modifies the char layer, increasing residual char content. It promotes graphitization, resulting in a more graphitized, stable, and barrier-like char layer. Synergistically with APP and sepiolite, MXene may promote the formation of PO-Ti bonds in the APP and sepiolite system, constructing an "organic-inorganic hybrid" char layer with significantly improved strength, density, and thermal stability (ternary synergistic effect). Furthermore, MXene components may capture free radicals (·H, ·OH) in the combustion chain reaction, inhibiting gas-phase combustion. In summary, the gradual increase in LOI is the inevitable result of the complementary and deep synergistic effects of APP (the basis for expanded char formation), nano-sepiolite (char layer enhancement and synergistic catalysis), and MXene (top-tier two-dimensional barrier, highly efficient char formation, and thermal conductivity).

[0047] Figure 7 The images show the optical images of the ash after combustion of the flame-retardant materials prepared in Example 1 and Comparative Examples 1-3. From left to right, they are Comparative Example 1, Comparative Example 2, Comparative Example 3, and Example 1. Figure 8 The combustion mass loss curves are for the flame-retardant materials prepared in Example 1 and Comparative Examples 1-3. From... Figure 7 and Figure 8It can be seen that pure EVA burns completely with almost no residue, and the combustion mass loss curve decreases rapidly, exhibiting a very high combustion rate. The EVA-A sample (containing APP) leaves light gray, porous char residue after combustion; APP decomposes to produce polyphosphoric acid (PPA), catalyzing the dehydration and cross-linking of EVA to form an expanded char layer. The EVA-AS sample (containing APP and sepiolite) leaves structurally intact, gray-black, blocky char residue after combustion, which is not easily broken; sepiolite acts as a framework embedded in the char layer, reducing pore merging and structural collapse. The EVA-ASM sample leaves dark black, smooth, dense, and relatively intact char residue after combustion, producing a metallic sound when struck; MXene sheets migrate to the surface to form a dense "ceramicized" barrier; ternary synergy (PO-Ti bonds, etc.) constructs an organic-inorganic hybrid char, exhibiting extremely high thermal stability; simultaneously, due to catalysis, the high degree of graphitization results in a dark black color. These factors also contribute to the gradual decrease in the combustion mass loss rate of the samples.

[0048] Figure 9 The graphs show the HRR and THR curves of the flame-retardant materials prepared in Examples 1 and Comparative Examples 1-3, where the left graph represents HRR and the right graph represents THR. Figure 9 As can be seen in the cone calorimetry test, with the sequential addition of ammonium polyphosphate, nano-sepiolite, and MXene, the maximum heat release peak in the heat release rate curve (HRR) shifts sequentially to the later stages, and the peak heat release rate (pHRR) decreases from 718 kW / m³. 2 Reduced to 308kW / m 2 The total heat release (THR) decreases sequentially, starting with the EVA sample which has a total heat release of 91.7 MJ / m³. 2 Reduced to 74.7 MJ / m 2 . Figure 9 The HRR curves show a delayed peak HRR, reflecting a gradual postponement of the combustion process. This is because, starting with the EVA-A sample, the flame retardant (APP) and its synergistic components (sepiolite, MXene) form an increasingly effective, stable, and durable physical barrier layer (expanded char layer) on the material surface. This barrier layer significantly slows down the transfer of heat to the internal matrix and the transport of internal combustible volatiles to the flame zone, resulting in a longer time required to reach the maximum heat release rate after ignition. The more additives and the better the synergistic effect, the higher the effectiveness of the barrier layer and the more pronounced the delay effect. Figure 9The THR curves show a progressively decreasing THR, reflecting increasingly incomplete combustion. The presence of highly efficient barrier layers (especially in the EVA-AS and EVA-ASM samples) significantly limits the release of combustible volatiles and the supply of oxygen to the material interior. A large amount of carbonaceous material is retained in the condensed phase to form a char layer, rather than being converted into combustible gases for combustion. Simultaneously, the catalytic effect of MXene significantly improves char formation efficiency, further reducing the amount of combustible gases generated. Therefore, the total amount of material capable of complete combustion and releasing heat decreases progressively, leading to a stepwise decrease in THR.

[0049] 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 nano-sepiolite / MXene-based flame retardant material, characterized in that, Including nano-sepiolite, MXene, ammonium polyphosphate, and ethylene-vinyl acetate copolymer; The mass ratio of the nano-sepiolite, MXene, ammonium polyphosphate and ethylene-vinyl acetate copolymer is (0.4~1.2):(0.1~0.3):(9.5~28.5):

40.

2. The nano-sepiolite / MXene-based flame retardant material according to claim 1, characterized in that, The nano-sepiolite has an average particle size of 500 nm and a specific surface area of ​​183 m². 2 / g.

3. The nano-sepiolite / MXene-based flame retardant material according to claim 1, characterized in that, The MXene is selected from Ti3C2.

4. The nano-sepiolite / MXene-based flame retardant material according to claim 3, characterized in that, The MXene is multilayered, and the average particle size of the MXene is 5 μm.

5. The nano-sepiolite / MXene-based flame retardant material according to claim 1, characterized in that, The degree of polymerization of the ammonium polyphosphate is 1000.

6. A method for preparing the nano-sepiolite / MXene-based flame retardant material as described in any one of claims 1 to 5, characterized in that, Includes the following steps: After weighing each raw material according to the mass ratio, they are blended and then pressed to obtain nano-sepiolite / MXene-based flame retardant material.

7. The preparation method of the nano-sepiolite / MXene-based flame retardant material according to claim 6, characterized in that, The blending temperature is 90°C.

8. The preparation method of the nano-sepiolite / MXene-based flame retardant material according to claim 6, characterized in that, The pressing process specifically involves pre-pressing at 110°C for 5 minutes, followed by hot pressing for another 3 minutes.

9. The application of the nano-sepiolite / MXene-based flame retardant material according to any one of claims 1 to 5 in the field of new energy cable protection.

Images