A cellulose composite membrane loaded with hyperbranched boron nitride, preparation method and application

Abstract

The application discloses a kind of cellulose composite films loaded hyperbranched boron nitride, preparation method and application, belong to high polymer material technical field.The application solves how to provide the problem of the composite film with better dielectric property.The application includes nanocellulose matrix, the nanofiber base body is loaded with hyperbranched boron nitride, the hyperbranched boron nitride is arranged along nanofiber base body axis direction, and forms bricklaying structure, and the hyperbranched boron nitride is obtained by boron nitride graft hyperbranched polymer.The hyperbranched structure in the application plays the role of molecular bridge, and forges robust CNF-BN interface, and the configuration of hyperbranched boron nitride / nanofiber base body promotes efficient charge dissipation and heat transport, so that the cellulose composite films loaded hyperbranched boron nitride have potential application prospect in high-voltage insulation system of advanced electronic and electrical equipment.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a cellulose composite membrane loaded with hyperbranched boron nitride, its preparation method, and its application. Background Technology

[0002] The rapid development of high-voltage transmission networks, electrified transportation systems, and high-power electronic devices exposes dielectric materials to superimposed extreme operating stresses during service. These challenges include escalating thermal loads, enhanced electric field strength, and complex three-dimensional field distributions. Such harsh service conditions demand improved performance of material systems, particularly in terms of insulation reliability, thermal stability, and environmental compatibility. Traditional polymer dielectrics (such as polyethylene and epoxy resins) exhibit inherent limitations: their low thermal conductivity (κ < 0.3 W) ˙ m -1 ˙ K -1 This exacerbates Joule heating under high electric fields (>50 kV / mm), while weak interfacial interactions with inorganic fillers often lead to premature dielectric breakdown. Addressing these challenges requires innovative material designs that synergistically integrate superior dielectric properties, suppression of space charge accumulation, and improved insulation performance. Composite films, through the strategic fusion of advanced nanomaterials and innovative structural engineering techniques, represent a breakthrough solution. By leveraging the synergy between nanoscale material structures and macroscopic design principles, these films transcend the inherent performance limitations of traditional dielectric insulators, becoming one of the most promising candidates for next-generation electrical insulation systems.

[0003] Boron nitride (BN) is characterized by its unique ultrawide bandwidth (>6 eV) and anisotropic thermal conductivity (κ). ∥ = 300–400W ˙ m -1 ˙ K -1 , κ ⊥ = 30–40 W ˙ m -1 ˙ K -1 The combination of these properties has become a conversion filler for dielectric composites. Theoretically, these properties enable BN composites to achieve exceptional dielectric strength (>40 kV / mm) while effectively dissipating heat energy, a key requirement for high-voltage insulation systems. However, traditional hexagonal BN (h-BN) suffers from severe plate aggregation due to strong interlayer van der Waals forces, resulting in poor dispersion in the polymer matrix and interfacial debonding under combined electrothermal stress.

[0004] Surface functionalization via covalent grafting remains a primary method for improving boron nitride (BN) dispersion and interfacial interactions within polymer matrices. Traditional strategies often utilize silane coupling agents or plasma to treat boron nitride and introduce functional groups (-OH, -NH2) to enhance polymer-filler compatibility. While these methods partially alleviate aggregation, they exhibit low grafting density and limited spatial configuration control. The resulting linear or planar molecular structures fail to establish sufficient mechanical interlocking with the polymer chains, leading to limited modification effects and consequently, limited dielectric properties in composite films using modified boron nitride as filler. Therefore, developing composite films with superior dielectric properties is a problem that needs to be addressed in this field. Summary of the Invention

[0005] To address the problem of how to provide a composite film with better dielectric properties in the prior art, this invention provides a cellulose composite film loaded with hyperbranched boron nitride, its preparation method, and its application.

[0006] The technical solution adopted in this invention is as follows:

[0007] A cellulose composite membrane loaded with hyperbranched boron nitride includes a nanofiber matrix, wherein the nanofiber matrix is ​​loaded with hyperbranched boron nitride, the hyperbranched boron nitride being arranged along the axial direction of the nanofiber matrix and forming a brick-like structure, the hyperbranched boron nitride being obtained by grafting boron nitride with a hyperbranched polymer, and the structural formula of the hyperbranched boron nitride is:

[0008] .

[0009] Preferably, the doping amount of hyperbranched boron nitride is 30-50%.

[0010] Preferably, the thickness of the cellulose composite membrane loaded with hyperbranched boron nitride is 50-200 μm.

[0011] Preferably, the nanofibers forming the nanofiber matrix have a diameter of 5-10 nm and a length of 1-5 μm.

[0012] A method for preparing a cellulose composite membrane loaded with hyperbranched boron nitride includes the following steps:

[0013] S1: Prepare hyperbranched boron nitride solution and nanocellulose suspension respectively;

[0014] S2: Mix the hyperbranched boron nitride solution and the nanocellulose suspension according to the specified ratio to obtain the hyperbranched boron nitride / cellulose suspension;

[0015] S3: A composite membrane is obtained by vacuum-assisted self-assembly of a hyperbranched boron nitride / cellulose suspension.

[0016] S4: After drying the composite membrane, a cellulose composite membrane loaded with hyperbranched boron nitride is obtained.

[0017] As a preferred embodiment, the specific steps for preparing the hyperbranched boron nitride solution in S1 are as follows:

[0018] S101: Add 0.05-0.25 g of hyperbranched boron nitride to 30 ml of solvent;

[0019] S102: Ultrasonic dispersion for 15-30 minutes to obtain hyperbranched boron nitride solution.

[0020] Preferably, a cellulose solution with a concentration of 1.69 wt% is added to a hyperbranched boron nitride solution and mixed thoroughly to obtain a hyperbranched boron nitride / cellulose suspension.

[0021] Preferably, the method for preparing hyperbranched boron nitride in S101 includes the following steps:

[0022] S1011: Hexagonal boron nitride is modified with a silane coupling agent to obtain hydroxylated boron nitride;

[0023] S1012: Raise the reaction temperature from room temperature to 80-90℃ to allow the remaining silane coupling agent to continue the silanization reaction with hydroxylated boron nitride to obtain aminolated boron nitride.

[0024] S1013: 3,5-Diaminobenzoic acid and amino boron nitride are dissolved in the same system, then a reaction aid is added, and a polymerization reaction is carried out under a nitrogen atmosphere and a temperature of 100-120℃ to obtain hyperbranched boron nitride.

[0025] As a preferred option, the vacuum-assisted self-assembly technology uses a filter membrane with a pore size of 0.45-2 μm, and the vacuum filtration time is 10-30 minutes.

[0026] An application of a cellulose composite membrane, in which a cellulose composite membrane loaded with hyperbranched boron nitride is used as a dielectric material.

[0027] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0028] This invention presents a high-performance composite membrane prepared by vacuum-assisted filtration self-assembly of one-dimensional (1D) cellulose (CNF) and two-dimensional (2D) boron nitride (BN). This method utilizes negative pressure to drive the solvent to rapidly pass through the filter membrane, enabling efficient and controllable layer-by-layer deposition and tight stacking of CNF and surface-functionalized BN nanosheets on the membrane. Hyperbranched polymer (HBP)-mediated surface functionalization optimizes the dispersion of BN in the CNF matrix. HBP was chosen for modifying boron nitride due to its highly branched structure and abundant terminal functional groups, which not only modify the BN surface but also establish multiple hydrogen bonds with CNF, significantly enhancing interfacial interactions. Studies show that the hyperbranched structure acts as a molecular bridge, forming a robust CNF-BN interface, while the 1D / 2D structure contributes to efficient charge dissipation and heat transfer. These findings demonstrate that hyperbranched surface functionalization provides a simple and effective strategy for integrating superior electrical and thermal properties into composite materials, driving the development of customized dielectric materials for high-voltage applications. Attached Figure Description

[0029] Figure 1 The images show the detection results of boron nitride and cellulose, where (a) is the TEM image of BN, (b) is the HRTEM image of BN, and (c) and (d) are the TEM images of CNFs at different magnifications, respectively.

[0030] Figure 2 The synthesis route diagram for HBP-BN;

[0031] Figure 3 The images show the detection results of HBP-BN, where (a) is the FTIR result of BN and HBP-BN, (b) is the XPS image of BN and HBP-BN, (c) is the C1s spectrum of HBP-BN, and (d) is the Si2p spectrum of HBP-BN.

[0032] Figure 4 Synthesis route diagram for HBP-BN / CNF composite membrane;

[0033] Figure 5 Images of finished HBP-BN / CNF composite membranes obtained with different HBP-BN dosages;

[0034] Figure 6The images show the detection results of HBP-BN / CNF composite films. (a), (b), (c), (d), (e), and (f) are SEM images of pure CNF, HBP-BN10wt% / CNF, HBP-BN20wt% / CNF, HBP-BN30wt% / CNF, HBP-BN40wt% / CNF, and HBP-BN50wt% / CNF, respectively. (d1), (e1), and (f1) are high-resolution SEM images of HBP-BN30wt% / BNF, HBP-BN40wt% / BNF, and HBP-BN50wt% / CNF, respectively. (g) shows the dielectric loss detection results, (h) shows the dielectric constant detection results, (i) shows the volume resistivity detection results, (j) shows the TGA curve, and (k) shows the HBP-BN / CNF... DTG curve of the composite membrane;

[0035] Figure 7 shows the carrier trapping characteristics detection results of the HBP-BN / CNF composite film. (a) is the carrier trap distribution diagram of the HBP-BN / CNF composite film, (b) is the depth detection result of the trap energy level of the HBP-BN / CNF composite film, and (c), (d), (e), (f), (g), and (h) are the shallow trap and deep trap distribution detection results of pure CNF, HBP-BN10wt% / CNF, HBP-BN20wt% / CNF, HBP-BN30wt% / CNF, HBP-BN40wt% / CNF, and HBP-BN50wt% / CNF, respectively.

[0036] Figure 8 The image shows the flashover voltage detection results for pure CNF and HBP-BN / CNF composite films. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0038] The raw materials used in this embodiment are from the following sources:

[0039] Nanocellulose was provided by the Quzhou Institute of Zhejiang University.

[0040] Hexagonal boron nitride (h-BN, 1~2 μm) was provided by Shanghai Aladdin Biochemical Technology Co., Ltd.

[0041] The accompanying chemicals, including 3,5-diaminobenzoic acid (DABA), pyridine, 3-aminopropyltriethoxysilane (KH-550) and triphenyl phosphate (TPP), as well as solvents and reagents, including N-methylpyrrolidone (NMP), lithium chloride (LiCl), acetic acid and ethanol, were all purchased from China Maclean Biochemical Co., Ltd.

[0042] In this embodiment, the microstructural characteristics of BN and CNF were studied using transmission electron microscopy (TEM, JEOL JEM-F200, Japan) to analyze the surface morphology of nanoscale materials. The results are as follows: Figure 1 As shown. From Figure 1 As can be seen in (a), the ultrasonic ablation process effectively reduces the lateral size of BN to the submicron level while producing an ultrathin layered structure; from Figure 1 As can be seen in (b), the (100) crystal plane of h-BN has clear lattice fringes with a spacing of 0.224 nm, thus confirming the structural integrity maintained during the exfoliation process. This intact crystal structure ensures an effective lattice vibration transmission path, which is a key factor in the thermal management of dielectric composites. Figure 1 As shown in (c) and (d), CNF exhibits a characteristic high aspect ratio morphology with a diameter of 5-10 nm and a length on the micrometer scale. The extended nanofiber geometry promotes the formation of a three-dimensional percolation network through interlocking fiber nodes, constructing a mechanically robust architecture with stress dispersion capabilities. This hierarchical structure enhances electrical insulation performance synergistically by constructing tortuous carrier migration paths, while reducing the generation of interface defects.

[0043] Preparation of HBP-BN

[0044] like Figure 2 As shown, 1 g of BN and 20 g of KH-550 were ultrasonically dispersed in 300 g of anhydrous ethanol for 60 minutes under ice-water bath conditions (0-5°C) to obtain hydroxylated BN-OH. The suspension containing hydroxylated BN-OH was transferred to a three-necked flask equipped with a condenser and refluxed at 80°C. Subsequently, a mixed solvent containing 40 g of deionized water and 100 g of anhydrous ethanol was added dropwise to the reaction system (the refluxed suspension containing hydroxylated BN-OH). Under continuous mechanical stirring at 80°C, BN-OH in the reaction system continued to undergo silanization with KH-550 for 12 hours. After the reaction, the product was separated by thermal centrifugation (8000 rpm, 60°C) and washed eight times with deionized water to remove unreacted silane coupling agent. The purified product was freeze-dried in a vacuum freeze dryer (-50°C, 10 Pa) for 48 hours to obtain BN-NH2.

[0045] The preparation method of HBP-BN is the same as that in the literature [Hyperbranched boron nitride structure-based epoxy composite: Simultaneous enhancement of mechanical properties, thermal conductivity, and superior electrical insulation at cryogenic temperatures. Polymer Composites. 45(9), 7967-7978 (2024)] and [Hyperbranched polymers: from synthesis to applications. Progress in Polymer Science. 29(3), 183-275 (2004)]. In short, as... Figure 2 As shown, 0.6 g of BN-NH2 prepared according to the above method and 0.6 g of DABA were dispersed in 50 ml of NMP until completely dissolved. Then, 2 ml of pyridine (catalyst) and 6 ml of TPP (stabilizer) were added to the reaction system, followed by 0.2 g of LiCl (stabilizer for ionic intermediates). Polymerization was carried out for 12 hours under a nitrogen atmosphere and at 100°C with constant magnetic stirring (500 rpm). After the reaction was completed, the crude product was thermally centrifuged (10000 rpm, 80°C) to separate the grafted HBP-BN from the residual monomer. The product was continuously washed with NMP (3 × 20 ml) to remove unreacted DABA, and the final product was dried under vacuum freeze-drying conditions (-50°C, 10 Pa) for 48 hours to obtain HBP-BN.

[0046] This embodiment further analyzes the modification effect of BN, and the results are as follows: Figure 3 As shown; from Figure 3 As can be seen from 'a', complementary spectral analysis clearly confirms that BN has achieved covalent functionalization through HBP grafting. Compared with the original BN, HBP-BN exhibits four emission absorption bands, with a maximum of 3220 cm⁻¹. -1 The broad peak at 2925 cm⁻¹ corresponds to the bending vibration of the NH bond, while the peak at 2925 cm⁻¹ corresponds to the bending vibration of the NH bond. -1 The characteristic peak at 1631 cm⁻¹ originates from the CH stretching vibration in the methylene (-CH₂-) group. -1 With 1139 cm -1The appearance of the peaks confirmed the formation of amide bonds (-CO-NH-) and the generation of siloxane bridges (-Si-O-), respectively, demonstrating the successful anchoring of the hyperbranched polymer (HBP) via silane coupling agents. XPS energy dispersive spectroscopy analysis verified this surface modification process at the atomic scale: from Figure 3 As can be seen from b, the wide-field spectroscopy shows characteristic peaks at 154 eV (Si2s) and 103 eV (Si2p) for both BN-NH2 and HBP-BN materials, confirming the effectiveness of the KH-550 silanization treatment. Figure 3 As can be seen from 'c', the high-resolution C1s spectrum resolves four chemical states: carboxyl carbon (OC=O, 288.5 eV), amine-bonded carbon (CN, 285.5 eV), aromatic carbon (C=C, 284.8 eV), and aliphatic chain carbon (CC, 284.2 eV), collectively mapping the molecular structure configuration of HBP. Simultaneously, from... Figure 3 As can be seen from d, the Si2p spectrum distinguishes two bonding environments: Si-OC (102.79 eV) and Si-C (102.14 eV), elucidating the interfacial dual anchoring mechanism. These spectroscopic features and Figure 2 The reaction pathways shown are highly consistent, in which the KH-550 silanol groups undergo a condensation reaction with the hydroxyl groups on the BN surface, and are subsequently subjected to nucleophilic attack by the terminal amine groups of HBP. Synergistic evidence from FTIR and XPS confirms the robust chemical bonding nature of the BN-HBP interface, fundamentally explaining that the enhanced dielectric stability of the composite material stems from the suppression of interfacial polarization and the synergistic optimization of phonon transport / charge transport pathways.

[0047] like Figure 4 As shown, a method for preparing a cellulose composite membrane loaded with hyperbranched boron nitride includes the following steps:

[0048] S1: Dissolve 0.05g HBP-BN in 30 ml of deionized water and sonicate for 20 minutes to ensure uniform distribution to obtain a hyperbranched boron nitride solution; add nanocellulose to deionized water to obtain a nanocellulose suspension with a concentration of 1.69wt%;

[0049] S2: Mix the hyperbranched boron nitride solution and the nanocellulose suspension according to the specified ratio to obtain the hyperbranched boron nitride / cellulose suspension;

[0050] S3: Transfer the hyperbranched boron nitride / cellulose suspension to a sand core funnel and perform vacuum filtration using a filter membrane with a pore size of 0.45 μm for 10 minutes.

[0051] S4: After drying the composite membrane at 80℃ for 24 hours, a cellulose composite membrane loaded with hyperbranched boron nitride was obtained.

[0052] To investigate the effect of hyperbranched boron nitride (HBP-BN) addition on the performance of cellulose membranes, this embodiment prepared cellulose composite membranes with HBP-BN contents of 0 wt%, 10 wt%, 20 wt%, 30 wt%, 40 wt%, and 50 wt%, respectively, while controlling the weight of each layer of cellulose composite membrane loaded with HBP-BN to be 0.01 g (with the same water content). The resulting composite membrane products are shown below. Figure 5 ;from Figure 5 It can be seen that when the amount of hyperbranched boron nitride added is as high as 50%, a cellulose composite membrane loaded with hyperbranched boron nitride with an intact morphology can still be obtained in this invention, and it is not damaged after bending, which proves that it has good flexibility.

[0053] In this embodiment, cross-sectional analysis of the HBP-BN / CNF composite film was performed using a field emission scanning electron microscope (SEM, Zeiss Sigma 360, Germany). The results are as follows: Figure 6 As shown in Figure af, the test results for the dielectric properties of the composite film are as follows: Figure 6 As shown in gi, the thermal stability test results are as follows: Figure 6 As shown in jk;

[0054] from Figure 6 As can be seen from d1-f1, high-resolution SEM characterization confirms the molecular-level interpenetrating structure of the HBP-BN / CNF interface, where continuous transition domains are formed between the nanosheet edges and the fiber surface. This unique interfacial architecture endows the composite film with excellent macroscopic flexibility. Figure 5 This allows it to withstand repeated bending and folding without structural failure. This study elucidates a multi-scale ordered assembly paradigm for inorganic-organic nanocomposites by synergistically integrating interface engineering and structural control, establishing new design principles for advanced flexible functional materials.

[0055] from Figure 6 As can be seen from the curves, the dielectric loss factor (tanδ) versus frequency reveals a systematic correlation between HBP-BN content and the dielectric dissipation behavior of cellulose nanofiber (CNF) composites. Pure CNF exhibits the lowest tanδ value across the entire spectrum, consistent with its homogeneous hydrogen bond network effectively suppressing interfacial polarization. The characteristic tanδ curves of CNF show that in the low-frequency region (<10 Ω·cm), the tanδ value is highest at lower frequencies. 4 Interfacial polarization induced by hydroxyl (-OH) and hydrogen bond networks in the high-frequency region (>10 Hz) leads to increased dielectric loss as frequency decreases; while in the high-frequency region (>10 Hz), dielectric loss increases with decreasing frequency. 4 (Hz), due to the lag of polarization relaxation behind the change in electric field, the loss gradually tends to stabilize. All CNF composite films containing HBP-BN maintain a similar tanδ variation trend as pure CNF, confirming that the CNF matrix continues to dominate.

[0056] Low frequency band (<10) 4 The increase in tanδ (Hz) with increasing HBP-BN content stems from a multi-scale cooperative mechanism: the HBP-BN / CNF interface of the interpenetrating structure (e.g., Figure 6 The df diagram significantly increases the heterostructure interface density, enhances the Maxwell-Wagner-Sillars (MWS) interface polarization effect, and promotes the accumulation and relaxation of interface-bound charges as the main low-frequency energy dissipation pathways. Simultaneously, unreacted polar groups (-OH, -NH2, etc.) on the HBP form continuous ion migration channels under high filling levels, activating low-frequency ion conductivity losses. Furthermore, the BN nanosheets act as a physical barrier, extending the carrier migration path and exacerbating energy dissipation through a shallow trap-assisted hopping mechanism.

[0057] In the high-frequency region (>10) 4 Even with increased HBP-BN content, the tanδ value remained below 0.016, mainly due to intrinsic polarization kinetics and material properties. Sub-nanosecond electronic displacement polarization dominates polarization behavior under high-frequency electric fields, while filler-induced dipole polarization and interface effects are suppressed due to relaxation time mismatch. The wide bandgap (~5.9 eV) and high crystallinity of BN (XRD confirmed (002) interplanar spacing of 0.334 nm) fundamentally limit the intrinsic carrier concentration, effectively blocking ohmic conduction paths. In addition, the steric hindrance of HBP significantly reduces the defect state density of the HBP-BN / CNF interface, weakening the probability of high-frequency localized state-assisted quantum tunneling. This interface optimization and the continuous transition structure observed by SEM ( Figure 6 The results are consistent with d1-f1, which corroborates the structure-property relationship between microstructure and performance.

[0058] like Figure 6 As shown in h, the dielectric constant-frequency curve of the HBP-BN / CNF composite film exhibits a significant concentration-dependent evolution. The similar curve morphology and parallel decay trend under different filler contents indicate the existence of a unified polarization mechanism—changes in filler content primarily regulate the dielectric response intensity through interfacial density, rather than altering the fundamental polarization kinetics. Pure CNF films exhibit stable dielectric behavior across the entire frequency domain, with their weak frequency dependence stemming from the dipole relaxation of -OH groups in the CNF molecular chain and weak interfacial polarization within the hydrogen bond network. After introducing HBP-BN, the dielectric behavior exhibits a nonlinear concentration effect: the dielectric constant of the 10 wt% HBP-BN / CNF composite film is lower than that of pure CNF in all frequency bands. This is due to a dual inhibition mechanism—the wide bandgap of HBP-BN hinders the inherent ion migration polarization of the CNF matrix, while the discrete HBP-BN nanosheets introduce interfacial defects that distort the local electric field, further reducing polarization efficiency.

[0059] When the HBP-BN content increases to 20 wt%, the low-frequency region (<10 wt%)4 The dielectric constant of the high-frequency response (>10 Hz) exceeds that of pure CNF, while the high-frequency response (>10 Hz) is higher. 4 The frequency response crossover phenomenon (Hz) is still slightly lower. This frequency response crossover phenomenon reveals a competitive polarization mechanism: in the low frequency range, MWS interface polarization induced by the heterostructure interface dominates, while in the high frequency range, the rapid electronic displacement polarization in the CNF matrix is ​​slightly suppressed due to the restriction of molecular chain mobility by the filler.

[0060] When the HBP-BN loading reaches 30 wt% or higher, the dielectric constant of the HBP-BN / CNF composite material exhibits a systematic enhancement, and the curve remains strictly parallel. This transformation stems from the complete formation of the interfacial polarization network: the -OH groups on the HBP-BN surface are strongly coupled with the CNF hydrogen bond network, promoting the uniform dispersion of nanosheets. Figure 6 The presence of no agglomerates in the BF SEM images confirms this, forming a high-density heterogeneous interface. Simultaneously, the nanocapacitors constructed between adjacent HBP-BN nanosheets amplify the polarization effect through the superposition of local electric fields. The high crystallinity of the BN layer acts as a physical barrier, extending the carrier migration path and forcing charge transport to rely on a shallow trap-assisted hopping mechanism, thus strictly limiting the enhanced polarization to the range of interface-bound charge accumulation. Notably, even at a high filling amount (50 wt%), the dielectric constant still increases steadily without exhibiting the overpercolation threshold characteristic (i.e., a sudden inflection point in conductive network formation), confirming that HBP modification inhibits conductive network formation by blocking direct contact with the filler.

[0061] Furthermore, the parallel decay of the dielectric constant with increasing frequency in all samples indicates that the polarization response dynamics are jointly governed by the intrinsic relaxation characteristics of the matrix and the interfacial polarization behavior. (High frequency region > 10) 4 The behavior at high frequencies (Hz) is particularly striking: although the absolute dielectric constant of the HBP-BN 50 wt% / CNF composite film is significantly higher than that of the pure CNF film, its decay slope is highly consistent with that of the low-filled sample. This confirms that electronic displacement polarization remains the core mechanism dominating the high-frequency response, while HBP-BN mainly provides additional polarization contributions through microcapacitor coupling (local charge redistribution between adjacent nanosheets). The stability of such polarization dynamics ensures performance predictability, making it possible to precisely control the dielectric constant through filler content—a crucial foundation for the gradient design of flexible devices.

[0062] The comparison with the unmodified BN / polymer system further highlights the crucial role of interface engineering. Traditional BN nanosheet composites often exhibit a sharp increase in dielectric constant at 20-30 wt% filler content due to percolation effects. However, the gradual reinforcement trend and low-loss characteristics observed in this study confirm that HBP modification suppresses electron tunneling between fillers through chemical and steric hindrance effects, ensuring that polarization enhancement is dominated solely by interfacial mechanisms. This performance decoupling strategy, achieved through customized surface chemistry and microstructure design, provides a new approach for developing advanced composite materials that combine high dielectric constant, low loss, and mechanical flexibility.

[0063] The volume resistivity of the HBP-BN / CNF composite film increases significantly with increasing filler content (6i in the figure), further confirming the dominance of the interfacial polarization mechanism. Pure CNF films exhibit moderate resistivity due to the limited carrier migration capacity within the hydrogen bond network, while the introduction of HBP-BN enhances insulation performance through a triple synergistic mechanism:

[0064] Intrinsic bandgap suppression—The wide bandgap (~5.9 eV) of HBP-BN, combined with insulating surface modification, suppresses the generation and migration of free charges;

[0065] Three-dimensional barrier effect: Uniformly dispersed BN nanosheets construct a three-dimensional insulating barrier network in the matrix, forcing charge carriers to migrate along highly tortuous paths, resulting in an exponential decrease in mobility with filler content;

[0066] Microcapacitor manipulation—the nanocapacitors between adjacent BN nanosheets amplify interface polarization through localized bound charge accumulation, while simultaneously blocking long-range charge transport, achieving synergistic optimization of dielectric constant enhancement and conduction loss suppression.

[0067] When the HBP-BN filling amount reaches 50 wt%, the volume resistivity is increased by more than an order of magnitude compared to pure CNF, consistent with the dielectric enhancement trend. This correlation demonstrates that the formation of the interfacial polarization network not only optimizes the dielectric response but also synergistically suppresses charge leakage through physical barrier effects and chemical modifications.

[0068] These composite films achieve superior dielectric and insulating properties through interface engineering mediated by hyperbranched polymers:

[0069] Three-dimensional topological effects: The three-dimensional branching topology of HBP promotes the synergistic hydrogen bonding and π-π stacking of terminal polar groups (-OH / -COOH) and CNF hydroxyl groups;

[0070] Structural evidence: uniform dispersion at 50 wt% filler (6f in the figure) and axial nanosheet arrangement along CNF fibers ( Figure 6 The word "be" directly corroborates this effect;

[0071] Performance breakthrough: The above-mentioned interactions inhibit agglomeration and optimize stress transfer, ultimately achieving a volume resistivity improvement of >10 times, a flashover voltage of 15.61 kV, and stable dielectric properties (ε=5.8, tanδ<0.016 at 10 MHz).

[0072] The simultaneous improvement of insulation performance and dielectric constant provides a new design paradigm for cutting-edge applications such as high voltage insulation and high frequency flexible electronics that require high dielectric strength and signal stability.

[0073] Through TGA ( Figure 6 The synergistic analysis of j) and derivative thermogravimetric (DTG) curves (6k in the figure) systematically reveals the multi-stage thermal degradation behavior of the HBP-BN / CNF composite membrane and its correlation with filler concentration. Figure 6 As shown in Figure j, the pure CNF film exhibits a mass loss of 98.02% at 800°C, while the mass loss of the composite material with added 10-50 wt% HBP-BN decreases sequentially to 81.13%, 75.08%, 63.03%, 55.61%, and 44.64%. This gradient change confirms the effect of HBP-BN on improving thermal stability. The mechanism is further elucidated through the characteristic degradation stages of the DTG curve, revealing a three-stage degradation mechanism:

[0074] Desorption stage (75-85°C)

[0075] Classification: Removal of adsorbed water / residual solvent

[0076] Characteristics: The peak area is negligible, indicating that there are very few volatile impurities and that the concentration is independent of the filler.

[0077] Main degradation phase (311-327°C)

[0078] Classification: CNF cellulose chain and HBP component decomposition.

[0079] Key phenomenon: The peak area ratio systematically decreases with increasing HBP-BN content.

[0080] Mechanism: Uniformly dispersed BN nanosheets delay matrix degradation by extending the thermal diffusion path and inhibiting the release of volatiles;

[0081] High-temperature oxidation stage (422-462°C)

[0082] Attribution: Oxidation of residual carbonaceous products or complete decomposition of BN surface modifiers.

[0083] Dynamic response: The peak temperature shifts towards higher temperatures as the filler content increases.

[0084] Mechanism: The BN-matrix stabilizes the interfacial phase, inhibiting high-temperature oxidation reactions;

[0085] The essence of improved thermal stability:

[0086] Although the HBP component decomposes at 200-400°C (corresponding to the main degradation peak), the high thermal inertness of the BN nanosheets (decomposition at >1000°C) dominates the final residual mass. The improved thermal stability of the composite film (55.36% residual mass at 800°C) stems from a triple synergistic effect:

[0087] Carbonization barrier effect: HBP can be controlled to aromatize to form a dense carbon layer that encapsulates BN, blocking oxygen diffusion and volatile release;

[0088] Interface bonding protection: The multi-point hydrogen bonds between the HBP terminal group (-OH / -COOH) and the CNF hydroxyl group stabilize the glycosidic bond and delay CNF decomposition;

[0089] Nanosheet shielding: BN blocks thermal radiation and dissipates local heat through its high thermal conductivity (~300 W / mK);

[0090] Experimental verification showed that the residual mass of the 50 wt% composite material (55.36%) was significantly higher than the theoretical value of physical mixing (52.89%), confirming the interfacial synergistic effect.

[0091] Evidence of the structure-performance correlation

[0092] The evolution of DTG peaks directly reflects the dispersion state of the packing material.

[0093] The main peak narrows and stabilizes (311-327°C) ⇔ SEM observations show no aggregation or dispersion ( Figure 6 (bf in the middle)

[0094] Full width at half maximum (FWHM) narrowing ⇔ High thermal conductivity of BN inhibits local heat accumulation;

[0095] Although no covalent bonds were detected at the interface, the physical entanglement of the hyperbranched polymer chains and cellulose filaments, as well as the hydrogen bonding tendency between the BN edge groups and CNF hydroxyl groups, together maintained the structural integrity under thermal stress.

[0096] In general, Figure 6 The synergistic effect of thermal stability and dielectric properties reveals the dual functional mechanism of HBP-BN: while achieving precise dielectric control, BN nanosheets act as a physical barrier to simultaneously inhibit thermal degradation and charge leakage, while HBP-mediated interface homogenization effectively prevents localized heat accumulation. These two factors work together to ensure ultra-low mass loss (<5%) and wide-band dielectric stability (1 kHz–1 MHz) within the operating temperature range (<150°C) of flexible electronic devices, making this composite material an ideal candidate for high-frequency applications such as 5G circuit packaging. Future research could focus on designing flame-retardant hyperbranched polymers or optimizing BN surface functionalization strategies to directionally control degradation pathways in the mid-to-high temperature range (300–500°C), expanding its application potential in extreme environments.

[0097] The carrier trapping characteristics of the cellulose composite membrane loaded with hyperbranched boron nitride are as follows: Figure 7 As shown, when the surface potential decay (SPD) curve is fitted with a double exponential function, the calculated trap curve always exhibits two types of characteristic peaks. Specifically, the trap energy level is calculated using a rigorously normalized method based on double exponential fitting, resolving the charge trapping kinetics into two independent stages: rapid decay (shallow trap) and slow decay (deep trap). The trap depth is quantified by Arrhenius analysis of the temperature-dependent trapping time constant, a method consistently applied across all samples, such as... Figure 7 As shown in the figure, shallow traps (0.761–0.802 eV) originate from hydroxyl defects and hydrogen bond breaking in CNF, while deep traps (0.845–0.861 eV) are generated by the interfacial barrier induced by HBP-BN. The trap density is derived by normalizing the relative amplitude contribution per unit film thickness and electrode area.

[0098] like Figure 7 As shown, SPD analysis of the HBP-BN / CNF composite film revealed a strong correlation between charge transport behavior and interface trap energy levels. The bi-exponential fitting of the decay curves clarified the synergistic mechanism between shallow traps (0.761–0.802 eV) and deep traps (0.845–0.861 eV). Figure 7 a). For pure CNF ( Figure 7 In the cellulose molecule (c), the shallow trap energy level (0.761 eV) and deep trap energy level (0.845 eV) originate from hydroxyl defects and hydrogen bond breakage in the cellulose molecular chain. The distribution of shallow traps promotes rapid charge release, while the limited density of deep traps restricts the long-term retention of bulk charge. With the introduction of HBP-BN, the shallow trap energy level shows a fluctuating upward trend with increasing filler content, while the deep trap energy level only slightly increases compared to pure CNF. Figure 7 (b) indicates that the filler incorporation has a limited effect on regulating deep charge traps.

[0099] At low HBP-BN loading (10-20 wt%) Figure 7 In the context of (de), the increase in shallow trap energy levels likely stems from enhanced interfacial polarization. The introduction of BN nanosheets increases the heterogeneous interface density within the CNF matrix, inducing local electric field distortion and forming shallow traps with slightly elevated energy levels (<0.8 eV). While these shallow traps moderately delay charge release, their low energy level limits surface charge capture efficiency, causing some charge to dissipate rapidly. Simultaneously, the slight increase in deep trap energy levels indicates that BN nanosheets extend the carrier migration path through a physical barrier effect, forcing charges to be captured by deeper traps, thereby suppressing leakage current—which is consistent with... Figure 6This is consistent with the observed increase in volume resistivity in i.

[0100] When the HBP-BN content reaches 30 wt% ( Figure 7 In the f-value, the shallow trap energy level drops to its lowest point (0.784 eV), while the deep trap energy level reaches its peak (0.861 eV). This phenomenon originates from the critical transition of filler dispersion: hyperbranched polymer chains form a dense interface layer through molecular extension, optimizing BN-CNF compatibility and reducing the shallow trap energy level. The rapid charge dissipation of shallow traps and the efficient charge fixation of deep traps form a dynamic balance, synergistically enhancing the surface charge dissipation and volume charge suppression capabilities, corresponding to a flashover voltage peak of 14.94 kV. Figure 8 ).

[0101] When the HBP-BN content increases to 40-50 wt% ( Figure 7 In the sample (gh), the shallow trap energy level rebounds to 0.796–0.802 eV, while the deep trap energy level tends to stabilize. This indicates that when the filler approaches the percolation threshold, high-density BN dispersion amplifies interfacial polarization, slightly pushing up the shallow trap energy level. However, the stabilization of the deep trap energy level reflects the inherent limitation of the wide bandgap characteristics of BN—there is an upper limit to its energy level rise. Although the increase in shallow trap energy level slows down the charge dissipation rate, the dominant role of deep traps still ensures the long-term stability of the volume charge, supporting excellent insulation performance under high electric fields (e.g., the flashover voltage of the 50 wt% sample reaches 15.61 kV).

[0102] In summary, the SPD analysis results elucidate the differentiated regulation mechanisms of shallow and deep traps: the energy level of shallow traps fluctuates with the dynamic evolution of interfacial polarization and changes in dispersion state, while the energy level of deep traps is constrained by the inherent properties of BN, only experiencing a slight increase through the physical barrier effect. The synergistic effect of these two mechanisms balances the rapid dissipation of surface charge (dominated by shallow traps) with the long-term stability of volume charge (controlled by deep traps), providing a crucial basis for the design of advanced insulating materials.

[0103] like Figure 8 As shown, the surface flashover voltage of the HBP-BN / CNF composite film exhibits a significant non-monotonic dependence on the filler content: it decreases from 13.82 kV for pure CNN to 12.56 kV for 10 wt% HBP-BN, then gradually increases to 14.47 kV (20 wt% HBP-BN), reaching a peak of 14.94 kV at 30 wt%, and after a brief decline to 14.36 kV at 40 wt%, it finally reaches a record high of 15.61 kV at 50 wt%. This phenomenon stems from the dynamic interaction between the HBP-BN dispersion state, interfacial polarization intensity, and the competition among the insulation network.

[0104] When the HBP-BN content is 10 wt%, the uneven dispersion of nanosheets generates interfacial micropores and weak bonding regions, forming electric field distortion "hot spots" that accelerate pre-discharge initiation. Simultaneously, the partial coverage of CNF intrinsic surface traps by HBP reduces charge trapping efficiency, both contributing to a voltage drop. When the content increases to 20 wt%, the wide bandgap physical barrier effect of BN becomes dominant, suppressing carrier migration and extending the surface discharge path, thus restoring the flashover voltage to 14.47 kV.

[0105] Peak flashover voltage (14.94 kV) of 30 wt% HBP-BN / CNF thin film corresponding to critical interface optimization state: SEM image ( Figure 6 Figure d) shows that BN nanosheets are uniformly dispersed in the CNF matrix, and HBP chains form a dense interface layer. This configuration reduces the shallow trap energy level to 0.784 eV. Figure 7 (f) to enhance surface charge dissipation, while the deep trap energy level rises to 0.861 eV to achieve volume charge fixation, thereby increasing the volume resistivity by more than an order of magnitude ( Figure 6 (i) The Maxwell-Wagner-Sillars polarization at the BN-CNF heterostructure further redistributes the local electric field, effectively suppressing charge accumulation.

[0106] When the HBP-BN content reaches 40 wt%, the high-density BN dispersion system, approaching the percolation threshold, induces complex interfacial charge migration paths, instantaneously reducing the shallow trap dissipation efficiency and causing the voltage to drop back to 14.36 kV. However, in the 50 wt% HBP-BN system, the continuous BN insulation network blocks long-range charge transport, stabilizing the deep trap energy level at 0.858 eV. Figure 7 (h in the figure), and through enhanced interface polarization to optimize electric field homogeneity, synergistically drive the flashover voltage to jump to 15.61 kV. Significantly improved thermal stability (55.36% residual mass fraction at 800°C), Figure 6 (j) further corroborates the key role of the BN barrier effect in the synergistic regulation of electro-thermal performance.

[0107] This invention achieves a performance breakthrough in HBP-modified BN with high filler content by optimizing the interfacial charge transport path. The non-monotonic voltage evolution process reveals the transition path from a defect-dominated interface to a percolation network, which is essentially controlled by the competitive regulation of shallow and deep trap charge dissipation mechanisms. These findings highlight the decisive role of interface engineering in improving the dielectric and insulating properties of polymer-ceramic composites.

[0108] This invention develops a dielectric insulating composite film through HBP-mediated functionalization of the BN interface and vacuum-assisted self-assembly of 1D CNF and 2D HBP-BN. The composite material exhibits superior overall performance: flexible bending (adaptable to complex deformations), high thermal stability (55.36% residual mass at 800°C), optimized dielectric properties (dielectric constant ε=5.8 at 10 MHz, dielectric loss tanδ<0.016). These optimizations stem from dynamically adjusting the shallow well energy levels (0.761–0.802 eV) and stabilizing the deep well energy distribution (0.845–0.861 eV), as well as significantly improved insulation performance (volume resistivity increased by >1 order of magnitude, and surface flashover voltage increased from 13.82 kV to 15.61 kV). The improved performance is mainly attributed to two mechanisms: (1) The three-dimensional branched topology of HBP enables in-situ crosslinking between its terminal active groups and CNF hydroxyl groups, effectively inhibiting BN nanosheet aggregation and optimizing interfacial compatibility. (2) The synergistic effect between the template effect of one-dimensional CNF and the barrier function of two-dimensional HBP-BN constructs a three-dimensional charge blocking network, achieving a uniform electric field distribution and controllable carrier migration pathway. Compared with traditional polyethylene (PE) and epoxy resin (EP), the HBP-BN / CNF composite film exhibits excellent comprehensive dielectric insulation performance: providing ultra-low dielectric loss (tanδ<0.016, EP: 0.02-0.04) and higher flashover voltage (15.61 kV, EP: <12 kV). In addition, the thermal stability exceeds the degradation threshold of PE (>80°C) and the glass transition temperature of EP (approximately 150°C), and it possesses mechanical flexibility that cannot be achieved in the brittle EP system. In summary, this study demonstrates that hyperbranched interface engineering overcomes the traditional trade-off between filler dispersion and dielectric insulation properties, providing a promising approach for developing BN-based functional materials with potential applications in high-voltage insulation systems for advanced electronic and electrical equipment.

[0109] The embodiments described above merely illustrate specific implementation methods of this application, and while the descriptions are detailed and specific, they should not be construed as limiting the scope of protection of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the technical solution of this application, and these modifications and improvements all fall within the scope of protection of this application.

Claims

1. A cellulose composite membrane loaded with hyperbranched boron nitride, characterized in that: The membrane comprises a nanofiber matrix loaded with hyperbranched boron nitride. The cellulose composite membrane loaded with hyperbranched boron nitride is obtained through vacuum-assisted filtration self-assembly of the nanofiber matrix and the hyperbranched boron nitride. The hyperbranched boron nitride is arranged axially along the nanofiber matrix, forming a brick-like structure. The hyperbranched boron nitride is obtained by grafting hyperbranched polymers with boron nitride. The structural formula of the hyperbranched boron nitride is: ； The doping concentration of hyperbranched boron nitride is 30-50%; The nanofibers forming the nanofiber matrix have a diameter of 5-10 nm and a length of 1-5 μm; The method for preparing a cellulose composite membrane loaded with hyperbranched boron nitride includes the following steps: S1: Prepare hyperbranched boron nitride solution and nanocellulose suspension respectively; the specific steps for preparing hyperbranched boron nitride solution are as follows: S101: Add 0.05-0.25 g of hyperbranched boron nitride to 30 ml of solvent; S102: Ultrasonic dispersion for 15-30 minutes to obtain hyperbranched boron nitride solution; S2: A cellulose solution with a concentration of 1.69 wt% was added to a hyperbranched boron nitride solution and mixed thoroughly to obtain a hyperbranched boron nitride / cellulose suspension; S3: Obtain a composite membrane from a hyperbranched boron nitride / cellulose suspension using vacuum-assisted self-assembly technology. The vacuum-assisted self-assembly technology uses a filter membrane with a pore size of 0.45-2 μm and a vacuum filtration time of 10-30 minutes. S4: The composite membrane is dried to obtain the cellulose composite membrane loaded with hyperbranched boron nitride. The preparation method of hyperbranched boron nitride includes the following steps: S1011: Hexagonal boron nitride is modified with silane coupling agent KH-550 to obtain hydroxylated boron nitride; S1012: Raise the reaction temperature from room temperature to 80-90℃, so that the remaining silane coupling agent KH-550 can continue to undergo silylation reaction with hydroxylated boron nitride to obtain aminolated boron nitride. S1013: 3,5-Diaminobenzoic acid and amino boron nitride are dissolved in the same system, then a reaction aid is added, and a polymerization reaction is carried out under a nitrogen atmosphere and a temperature of 100-120℃ to obtain hyperbranched boron nitride.

2. The cellulose composite membrane loaded with hyperbranched boron nitride according to claim 1, characterized in that: The thickness of the cellulose composite membrane loaded with hyperbranched boron nitride is 50-200 μm.

3. A method for preparing a cellulose composite membrane loaded with hyperbranched boron nitride, characterized in that: Includes the following steps: S1: Prepare hyperbranched boron nitride solution and nanocellulose suspension respectively; the specific steps for preparing hyperbranched boron nitride solution are as follows: S101: Add 0.05-0.25 g of hyperbranched boron nitride to 30 ml of solvent to obtain a hyperbranched boron nitride solution. The preparation method of hyperbranched boron nitride includes the following steps: S1011: Hexagonal boron nitride is modified with silane coupling agent KH-550 to obtain hydroxylated boron nitride; S1012: Raise the reaction temperature from room temperature to 80-90℃, so that the remaining silane coupling agent KH-550 can continue to undergo silylation reaction with hydroxylated boron nitride to obtain aminolated boron nitride. S1013: 3,5-Diaminobenzoic acid and amino boron nitride are dissolved in the same system, then a reaction auxiliary is added, and a polymerization reaction is carried out under a nitrogen atmosphere and a temperature of 100-120℃ to obtain hyperbranched boron nitride. The structural formula of the hyperbranched boron nitride is as follows: ； S102: Ultrasonic dispersion for 15-30 minutes to obtain hyperbranched boron nitride solution; S2: A cellulose solution with a concentration of 1.69 wt% was added to a hyperbranched boron nitride solution and mixed evenly to obtain a hyperbranched boron nitride / cellulose suspension, wherein the nanofibers had a diameter of 5-10 nm and a length of 1-5 μm; S3: A composite membrane is obtained by using a vacuum-assisted self-assembly technique to obtain a hyperbranched boron nitride / cellulose suspension. The vacuum-assisted self-assembly technique uses a filter membrane with a pore size of 0.45-2μm and the vacuum filtration time is 10-30 minutes. S4: After drying the composite membrane, the cellulose composite membrane loaded with hyperbranched boron nitride as described in any one of claims 1-2 is obtained.

4. The application of a cellulose composite membrane loaded with hyperbranched boron nitride as described in any one of claims 1-2, characterized in that: Cellulose composite films loaded with hyperbranched boron nitride are used as dielectric materials.

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