A pure para-aramid paper based on nanofiber hydrogel and an integrated preparation method thereof

Abstract

The application discloses a kind of pure para aramid paper based on nanofiber hydrogel and its integrated preparation method, belong to high-performance fiber paper-based material technical field.The application first utilizes pressurized CO2 method to induce aramid fiber gelation, and realizes efficient in-situ extraction and closed-loop recovery of dimethyl sulfoxide (DMSO) solvent by pre-position mechanical pressure filtration, then water washing is prepared to keep high hydration activity nanofiber hydrogel slurry.In the process of papermaking, the hydrogel slurry is used as the only functional medium in the system, and is co-dispersed with homogeneous para aramid short fibers, relying on the high-density hydrogen bonding between isomorphic molecular chains, realizing the dense in-situ coating of nanofiber on the surface of short-cut skeleton.The application avoids the dependence on heterogeneous binder or chemical dispersant in conventional process, under very low solvent recovery energy consumption, constructs the pure para aramid cooperative structure of nanophase-macroscopic skeleton penetrated by continuous three-dimensional hydrogen bond network, realizes the effective unity of pure aramid paper in the premise of lightweight high modulus and high tear toughness, provides technical support for large-scale green manufacturing.

Description

Technical Field

[0001] This invention relates to high-performance synthetic fiber paper-based materials and their manufacturing technology, specifically to a pure para-aramid paper based on nanofiber hydrogel and its integrated preparation method. Background Technology

[0002] Para-aramid paper is widely used in cutting-edge fields such as aerospace, rail transportation, and new energy power due to its excellent high-temperature resistance, high strength, high modulus, and superior insulation properties. Traditional aramid paper production typically relies on the physical mixing of chopped fibers and precipitated fibers (pulp). Because precipitated fibers have poor dispersibility and limited bonding strength with chopped fibers, additional chemical dispersants or binders are often required. This not only increases the complexity of the process but may also affect the paper's heat resistance and insulation properties under extreme environments due to the presence of heterogeneous components.

[0003] In previous research (authorization announcement number: CN118065169B), the inventors proposed a method for preparing high-strength, high-heat-resistant para-aramid nanopaper. This method directly converts macroscopic para-aramid fibers into nanofiber gel via a pressurized CO2 method, and utilizes vacuum suction, pressing, and drying processes to achieve the preparation of 100% pure nanofiber paper without any heterogeneous components. The technical contribution of this method lies in achieving a continuous, simple, and efficient conversion from macroscopic fibers to nanopaper, as well as the in-situ construction of a three-dimensional hydrogen-bonded cross-linked network of nanofibers. While maintaining 100% pure aramid components, significant breakthroughs in mechanical and thermal properties were achieved.

[0004] However, in the process of further industrialization and performance improvement, the previous case still has the following technical bottlenecks that urgently need to be optimized: Solvent recovery and environmental pressure: The previous case involved vacuum suction and water washing of the gel directly during the papermaking process, which resulted in the loss or high dilution of high concentrations of dimethyl sulfoxide (DMSO) solvent with the washing water, making it difficult to recycle at low cost and causing high production costs and environmental treatment pressure.

[0005] Limitations in mechanical properties: Although the pure nanopaper prepared in the previous case has excellent tensile strength, it lacks a macroscopic stress transfer framework because it is composed entirely of nanoscale fibers. When subjected to tearing loads, cracks tend to propagate rapidly in the highly cross-linked nanonetwork, resulting in insufficient paper toughness (low tear strength). If macroscopic short-cut fibers are physically doped into it using conventional processes, the extremely high water filtration resistance of the pure nanosystem will lead to paper inhomogeneity and interlayer delamination, failing to meet the application requirements of dynamic load conditions.

[0006] The lack of post-processing technology for the gel: Although the previous study achieved a continuous transformation from macroscopic fibers to nanopaper, the microstructure of the resulting aramid nanofiber gel exhibited a highly entangled cross-linked network. The previous study did not systematically study and optimize the gel dissociation process. The dissociation method directly determines the degree of nanofiber dissociation, aspect ratio retention rate, and surface activity, thus profoundly affecting the fiber recombination and cross-linking behavior during subsequent papermaking, ultimately resulting in significant differences in the mechanical properties and thermal stability of the paper. Summary of the Invention

[0007] The purpose of this invention is to overcome the technical deficiencies of existing pure aramid paper and heterogeneous composite aramid paper in terms of mechanical toughness, interfacial compatibility, and environmentally friendly processes, and to provide an integrated preparation method based on nanofiber hydrogel slurry. This invention uses homogeneous aramid nanofiber hydrogel as an intermediate state, and constructs a dual-state synergistic structure of nanonetwork and macroscopic framework through an in-situ aqueous phase coating process. This achieves a comprehensive improvement in the strength and toughness of aramid paper and low-cost closed-loop solvent recovery without the need for any heterogeneous additives.

[0008] On the one hand, an integrated preparation method for pure para-aramid paper based on nanofiber hydrogel slurry includes the following steps: S1. Gel preparation and closed-loop pretreatment: Para-aramid fibers are placed in a mixed system containing alkali, water, and dimethyl sulfoxide. Under a CO2 pressure of 2-20 MPa, the mixture is stirred for 5-10 min to induce the aramid fibers to exfoliate and form a para-aramid nanofiber gel. Subsequently, the gel is mechanically filtered directly without fiber desorption to separate and recover the dimethyl sulfoxide solvent, resulting in a wet filter cake. The wet filter cake is washed and decomposed with water to obtain a nanofiber hydrogel slurry with a solid content of 1-5 wt%, ensuring that the nanofibers in the slurry remain highly hydrated and have surface activity. S2. In-situ homogeneous composite and defiberization: The nanofiber hydrogel slurry obtained in step S1 is mixed with para-aramid chopped fibers at an oven-dry mass ratio of (0.5-3):1, and co-defiberization is carried out in the aqueous phase. Utilizing the abundant active functional groups on the surface of the highly hydrated nanofibers and their excellent affinity with the homogeneous chopped fibers, the nanofibers in the hydrogel are dissociated under hydraulic shear and densely deposited in situ on the surface of the chopped fibers to form a composite dispersion. In this process, the hydrogel slurry serves as the only functional suspension medium and interface reinforcing phase in the system, and the addition of any heterogeneous chemical dispersants or binders is excluded. S3. Synergistic Structure Construction: The composite dispersion is formed by wet papermaking, and the nanofibers coated on the surface are driven to undergo densification shrinkage under pressing and dehydration conditions. Subsequently, after drying and hot pressing, the abundant active functional groups on the surface of the nanofibers undergo dense hydrogen bond closure to form a continuous three-dimensional hydrogen bond network. At the same time, relying on the high binding force of this hydrogen bond network and the geometric locking effect generated by dehydration shrinkage, a double dense coating of the macroscopic short-cut skeleton is achieved, and finally a 100% pure aramid homogeneous reinforcement structure without interface gaps is constructed.

[0009] In some embodiments: In step S1, the solid-liquid separation adopts a pressure filtration process to directly remove the mother liquor in the gel state. The pressure filtration pressure is 0.5-2.0 MPa, and the content of dimethyl sulfoxide (DMSO) in the filtrate recovered after pressure filtration is not less than 60 wt%.

[0010] In some embodiments: In step S1, during the process of preparing the wet filter cake into a hydrogel slurry, a refining machine and a fiber disintegrator are used in combination. The refining speed is 10,000-20,000 rpm, the disintegration speed is 1,500-3,000 rpm, and the disintegration time is 5-15 min, so as to ensure that the nanofibers in the hydrogel slurry are uniformly dispersed and maintain a high aspect ratio before they are completely dried and agglomerated.

[0011] In some embodiments: in step S2, the solid content of the composite fiber dispersion is controlled between 0.01-0.1 wt%, and no chemical dispersant, heterogeneous binder or precipitated fiber is added during the entire dispersion process.

[0012] In some embodiments: in step S2, the length of the para-aramid chopped fiber is 3-12 mm and the fineness is 1.0-2.5 dtex.

[0013] In some implementations: In step S3, the pressing process employs multi-stage pressing with a pressure range of 0.1-0.5 MPa.

[0014] In some embodiments: in step S3, the temperature of the hot pressing treatment is 180-280℃ and the pressure is 80-200 N / mm.

[0015] In some implementations: Throughout the entire preparation process, a closed-loop water circulation is achieved through a washing and filtration system, and the recycling rate of the washing water is not less than 80%.

[0016] On the other hand, the pure para-aramid paper obtained by the above-mentioned integrated preparation method is formed by a para-aramid nanofiber network tightly coating the surface of para-aramid chopped fibers, and its longitudinal tear index is not less than 20 mN·m. 2 / g, and the initial thermal decomposition temperature is not lower than 520℃.

[0017] Compared with the prior art, the present invention has the following outstanding advantages: 1. Overcoming the bottleneck of mutual exclusion between strength and toughness in the pure aramid system, achieving homogeneous synergistic enhancement. While existing technologies can construct composite frameworks by physically doping chopped fibers or nanomaterials, this often comes at the cost of sacrificing the purity of the aramid matrix or introducing phase boundary defects. This invention takes a different approach, co-dissolving pure para-aramid nanofiber hydrogels with homogeneous chopped fibers in an aqueous phase. This allows the nanofibers to be deposited in situ and densely, continuously coating the surface of the chopped fibers in a highly hydrated state. During subsequent dehydration and hot pressing, the coated nanofibers, relying on their extremely high specific surface area and abundant surface active functional groups, undergo dense hydrogen bond closure, forming a continuous three-dimensional hydrogen bond network that runs through the entire paper substrate. Simultaneously, combined with the volume shrinkage of this network during drying, a dual enhancement effect of hydrogen bonding and physical locking is achieved on the macroscopic chopped framework. This structure perfectly reconstructs the macroscopic load-bearing framework of pure para-aramid without introducing any heterogeneous interfaces, eliminating phase boundary gaps in traditional composite processes.

[0018] In this homogeneous synergistic structure, macroscopically chopped fibers bear the skeletal load, while the surface nano-hydrogen bond network effectively transfers stress and inhibits inter-fiber slippage. Experiments show that at 30 g / m², 2 At low basis weights, the longitudinal tear index of the paper reaches 20.11-32.17. (Compared to the basic patent pure nanopaper 1.42) (The yield is increased by more than ten times); at the same time, the longitudinal elastic modulus reaches 7200-10300 MPa, successfully overcoming the technical problem of low basis weight aramid paper being too stiff and brittle.

[0019] To avoid heterogeneous defects, a pure interface-binding phase is reconstructed using a hydrogel intermediate. Existing high-strength aramid paper typically relies on adding low-melting-point meta-aramid precipitated fibers as a binder phase, or adding chemical dispersants to improve the uniformity of chopped fibers. This inevitably introduces thermodynamic and electrical weaknesses into the paper matrix, impairing the heat resistance and electrical insulation properties of the para-aramid matrix. This invention eliminates any heterogeneous additives, utilizing a homogeneous para-aramid nanofiber hydrogel with a solid content of 1-5 wt% as the core intermediate state. This hydrogel retains active surface groups, acting as a uniform suspension and dispersion medium for chopped fibers during pulping and co-disintegration, and directly transforming into an interfacial bonding phase under pressing and hot-pressing conditions.

[0020] Innovative process decoupling design solves the problems of extreme dilution and high-cost recovery of organic solvents. Existing technologies (such as patent CN119593243A) typically involve directly mixing an aramid nanofiber dispersion system containing organic solvents such as dimethyl sulfoxide (DMSO) into a large volume of aqueous papermaking phase. This results in extreme dilution of the high-boiling-point solvent, leading to extremely high energy consumption for subsequent distillation recovery and a lack of industrial feasibility. This invention innovatively decouples solvent separation from the fiber aqueous dispersion process: after gelation and before adding water for fiber dissociation, the mother liquor is directly extracted from the solid-phase gel state via mechanical pressure filtration (0.5-2.0 MPa), ensuring a DMSO recovery rate of no less than 60%. This fundamentally avoids the diffusion and dilution of organic solvents into the massive white water system.

[0021] After removing most of the organic solvents, the wet filter cake is converted into a pure aqueous hydrogel slurry for subsequent papermaking. Combined with a washing and filtration system, a washing water recycling rate of no less than 80% is achieved. This dual physical closed loop of solvent and water significantly reduces the energy consumption of thermal separation and the pressure on environmental wastewater treatment, effectively opening up the engineering link for pure aramid nanocomposite paper from the laboratory to low-cost, large-scale production.

[0022] Optimize defibrillation kinetics, inhibit polymer degradation and improve intrinsic heat resistance. Aramid polymer chains are prone to hydrolysis and chain breakage, as well as molecular weight reduction, when treated in strongly alkaline organic solvents for extended periods. This invention significantly alters the swelling and peeling kinetics of aramid fibers through the physicochemical synergistic effect of a specific ratio of alkali / water / organic solvent system and pressurized CO2 (2-20 MPa), drastically reducing the nano-sizing reaction time from several hours to less than 5-10 minutes.

[0023] The extremely short depolymerization time effectively suppresses the risk of excessive degradation of para-aramid macromolecules in strong solvent systems, maximizing the integrity and crystallinity of the polymer molecular chains. Pure para-aramid paper prepared by this closed-loop process has an initial thermal decomposition temperature of no less than 520℃, achieving a nanoscale toughened structure while retaining the bulk reliability of para-aramid materials under extreme high-temperature environments. Attached Figure Description

[0024] Figure 1 This is a complete process flow diagram of the preparation method of the present invention.

[0025] Figure 2 This is a schematic diagram comparing the cross-section of paper obtained by the conventional process (Comparative Example 1) and the process of the present invention (Example 1) using a scanning electron microscope (SEM). Detailed Implementation

[0026] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims. Example 1:

[0027] The entire process flow diagram is as follows: Figure 1 As shown: S1. Preparation of aramid nanofiber gel: Take 60g of para-aramid short-cut fibers (1.5D, 6mm), mix para-aramid fibers, potassium hydroxide, water and dimethyl sulfoxide in a mass ratio of 1:3:12:330 to obtain an aramid fiber mixture; transfer the mixture to a 10L pilot reactor, inject CO2 into the apparatus to 2MPa, and react at 80℃ for 10min to obtain an aramid nanofiber gel with a solid content of 1wt%.

[0028] S2. General preparation of nanofiber hydrogel slurry: Transfer all the gel from step S1 to a plate and frame filter press (filter cloth pore size...) The DMSO mother liquor was dehydrated by pressure filtration at 1.0 MPa for 15 minutes, and approximately 5 kg of DMSO was collected (for later use), yielding a wet filter cake. The wet filter cake was then processed in a refiner for 20,000 rpm, followed by a fiber disintegration apparatus with 2 L of deionized water added. The mixture was then subjected to deep washing and homogenization at 3000 rpm for a cumulative 25,000 rpm. Finally, approximately 2 kg of nanofiber hydrogel slurry with a solid content of 3.0 wt% was obtained after dehydration and set aside for later use.

[0029] S3. Integrated composite dispersion: Weigh 69.4g of the slurry prepared in step S2, place it in a descaling apparatus and descaling for 5000 rpm, then add 0.8g of oven-dry para-aramid short-cut fibers, wherein the ratio of nanofibers to short-cut fibers is 2.6:1, and descaling is carried out together at a speed of 2000 rpm for 20000 rpm to obtain a uniform dispersion.

[0030] S4. Papermaking: The entire dispersion was formed on a standard hand-made sheet forming machine, pressed (0.3 MPa, 3 min), dried (105℃, 10 min), and then hot-pressed at 200℃, machine speed 1 m / min, and pressure 100 N / mm to obtain sample E1. Example 2:

[0031] Weigh 57.7g of the slurry prepared in S2 of Example 1 and place it in a spalling apparatus to spall at 5000 rpm. Then add 1.15g of oven-dry para-aramid chopped fibers, wherein the ratio of nanofibers to chopped fibers is 1.5:1. Subsequent spalling, papermaking, and hot-pressing conditions are the same as in Example 1 to obtain sample E2. Example 3:

[0032] Weigh 42.7g of the slurry prepared in S2 of Example 1 and place it in a spalling apparatus to spall at 5000 rpm. Then add 1.60g of oven-dry chopped fibers, wherein the ratio of nanofibers to chopped fibers is 0.8:1. Subsequent spalling, papermaking, and hot pressing conditions are the same as in Example 1, yielding sample E3. Example 4:

[0033] Weigh 32.0 g of the slurry prepared in S2 of Example 1 and place it in a spalling apparatus to spall at 5000 rpm. Then add 1.92 g of oven-dry chopped fibers, wherein the ratio of nanofibers to chopped fibers is 0.5:1. Subsequent spalling, papermaking, and hot-pressing conditions are the same as in Example 1, yielding sample E4.

[0034] Examples 1-4 in this series aim to investigate the effect of fiber ratio on performance. The target quantitative basis for all samples was fixed at 30 g / m². 2 (Corresponding to ISO 536 A4 paper area of ​​0.0961 m²) 2 The total amount of oven-dried fiber is approximately 2.883g.

[0035] Comparative Example C1 (Mesoprecipitation Pathway) Commercially available para-aramid paper with meta-precipitation as an adhesive.

[0036] Comparative Example C2 (pure para-aramid nanopaper) This comparative example is pure nanofiber paper prepared by the method described in the basic patent of this invention (CN118065169B), used to compare the performance of a single nanofiber system.

[0037] Following the method described in Example 1 of CN118065169B, para-aramid nanofiber gel was first obtained using a pressurized CO2 method. The resulting gel was then subjected to subsequent pressure filtration and water washing according to step S2, followed by wet forming and drying. A weight of approximately 32 g / m³ was achieved without hot pressing. 2 Pure nanofiber paper was used as a control sample C2. This sample did not contain macroscopically chopped fibers.

[0038] Comparative Example C3 (Preparation of pure para-aramid nanopaper from recycled DMSO) Following the method described in Example 1 of CN118065169B, para-aramid nanofiber gel was first obtained using a pressurized CO2 method. DMSO was then recovered via pressure filtration and used for preparing the gel slurry in this case. The resulting gel underwent subsequent pressure filtration and washing according to step S2, followed by wet forming and drying, achieving a quantitative yield of approximately 26 g / m³ without hot pressing. 2 Pure nanofiber paper was used as a control sample C3. This sample did not contain macroscopically chopped fibers.

[0039] Performance Comparison and Data Analysis Figure 2 This is a schematic diagram comparing the cross-section of paper obtained by the conventional process (Comparative Example 1) and the process of the present invention (Example 1) using a scanning electron microscope (SEM).

[0040] Comparative Example 1 (traditional meta-precipitation route) exhibits a typical two-phase structure of chopped fibers and precipitated fibers. The interface between the two is clearly visible, with obvious phase boundary gaps, indicating that the bonding between the precipitated fibers and chopped fibers mainly relies on physical interweaving and limited hydrogen bonding, lacking tight interfacial fusion. This loose microstructure results in a low elastic modulus—under external forces, the interfacial region is prone to become a stress concentration point and crack initiation source.

[0041] The morphology of Embodiment 1 of this invention exhibits a distinctly different synergistic structure of a nano-network encapsulating a macroscopic framework. Para-aramid chopped fibers maintain their intact morphology, serving as the macroscopic mechanical framework of the paper. The nanofiber hydrogel slurry, after co-disintegration, is uniformly dispersed and fully dissociated in the aqueous phase. During the papermaking process, through vacuum suction and pressing dehydration, the nanofibers are uniformly deposited and tightly encapsulated on the surface of the chopped fibers, forming a continuous three-dimensional hydrogen-bonded cross-linked network. As shown in the figure, there are no obvious interfacial gaps between the chopped fibers and the nanofiber network. The nanofibers not only fill the gaps between the chopped fibers but also form a dense coating layer on their surface, achieving a point-to-surface reinforcement mechanism. This unique structure endows the paper with a dual mechanical response: the chopped fiber network bears the main load, providing tensile strength and modulus; the nanofiber network, through its high specific surface area and dense hydrogen-bonded cross-linking, effectively transfers stress and inhibits relative slippage between fibers, thereby significantly improving tear strength.

[0042] Performance tests were performed on all samples, and the results are summarized in Table 1.

[0043] Test standards: Quantitative analysis GB / T 451.2; Tear index GB / T 455; Tensile index, elongation, and modulus of elasticity GB / T12914.

[0044] Table 1. Performance Comparison of Examples and Comparative Samples The data in Table 1 further validates the correlation between microstructure and macroscopic performance: The longitudinal tear index of the embodiments of the present invention (E1-E4) is generally between 20.11 and 32.17 mN·m. 2 The concentrations were between 1.42 mN·m³ / g, far exceeding those of the pure nanopaper comparative C₂ (1.42 mN·m³). 2 / g) and C3 (1.21 mN·m 2 / g). Among them, the transverse tear index of Example E4 reached 32.68 mN·m. 2 / g, with a longitudinal concentration of 32.17 mN·m 2 / g, compared with the traditional process using meta-precipitation C1 (43.29 / 33.73 mN·m 2 The basis weight of the paper in this invention is only 30 g / m³, which is comparable to that of the paper in the present invention. 2 Compared to C1's 45 g / m 2 The tear strength was reduced by 33%, demonstrating a significant advantage in lightweight design. This leap in tear performance is attributed to the tight wrapping of chopped fibers by the nanofiber network. When a tear load is applied to the paper, the chopped fibers, as the main load-bearing units, are gradually pulled out of the nanofiber network. During this process, the hydrogen bond crosslinks of the nanofiber network are continuously broken and energy is dissipated, which macroscopically manifests as a significant improvement in tear strength.

[0045] Comparative example C2 of pure nanopaper exhibits the highest tensile index (113.94 N·m / g longitudinally and 97.55 N·m / g transversely), which stems from its three-dimensional hydrogen-bonded network composed entirely of nanofibers—the continuous network structure ensures uniform stress distribution, but at the cost of extremely low tear strength (1.42 mN·m). 2 The tensile strength (82.35 N·m / g) exhibits typical high strength-low toughness characteristics. In contrast, embodiment E3 of the present invention, while maintaining excellent tensile strength (82.35 N·m / g longitudinally and 74.47 N·m / g transversely), achieves a significant improvement in tear index (35.26 / 27.99 mN·m / g). 2 The E3 nanopaper, with a basis weight of 79.50 N·m / g, has successfully overcome the performance bottleneck of being "strong but not tough". Compared with the traditional process comparative example C1 (79.50 N·m / g in the longitudinal direction and 78.48 N·m / g in the transverse direction), the E3 nanopaper, with a basis weight reduction of 33% and an elastic modulus increase of nearly 100% at a similar tensile level, demonstrates better material efficiency and structural rigidity.

[0046] The longitudinal elastic modulus of the embodiments of this invention is generally in the range of 7200-10300 MPa, with Example E3 reaching 10305.95 MPa, significantly better than the conventional process comparative example C1 (5702.10 MPa). High modulus means less deformation of the paper under external force, which is crucial for applications involving precision insulating components or structural parts. Microstructural analysis shows that the tight wrapping of chopped fibers by the nanofiber network effectively suppresses relative slippage between fibers, resulting in a mechanical response of the paper that is closer to a continuous body. Meanwhile, the elongation of the embodiments of this invention (0.96%-1.72%) falls between that of conventional processes (3.02%-3.45%) and pure nanopaper (2.05%-3.24%), indicating that by adjusting the ratio of nanofibers to chopped fibers, it is possible to maintain high strength and high modulus while imparting a certain degree of toughness to the paper, avoiding the defects of excessive rigidity and brittleness.

[0047] In summary, this invention, by constructing a microstructure that encapsulates a macroscopic framework with a nanonetwork, successfully achieved a breakthrough in the comprehensive mechanical properties of para-aramid paper while maintaining lightweight characteristics: achieving a performance of 30 g / m². 2 At low basis weight levels, the paper exhibits both high tensile strength (82.35 N·m / g in the longitudinal direction) and high tear index (32.68 mN·m). 2 With a high elastic modulus (10305.95 MPa) and a high basis weight ( / g), its overall performance reaches the advanced level in the industry. This structural design concept fundamentally solves the contradiction between the low tear strength of pure nanopaper and the high basis weight and poor interfacial bonding of traditional aramid paper, providing a new technical path for the lightweight design and green manufacturing of high-performance aramid paper.

[0048] Finally, it should be noted that those skilled in the art should understand that this invention is not limited to the above-described embodiments. The above embodiments and descriptions are merely illustrative of the principles of this invention. Various changes and modifications can be made to this invention without departing from its spirit and scope, and all such changes and modifications should fall within the scope of the invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for the integrated preparation of pure para-aramid paper based on nanofiber hydrogel, characterized in that, Includes the following steps: S1. Gel preparation and ring-closure pretreatment: Para-aramid fibers were placed in a mixed system containing alkali, water and dimethyl sulfoxide, and stirred for 5-10 min under CO2 pressure of 2-20 MPa to induce the exfoliation of aramid fibers to form para-aramid nanofiber gel. Subsequently, the gel was mechanically filtered directly in the unde-fiber state to separate and recover the dimethyl sulfoxide solvent, resulting in a wet filter cake. The wet filter cake was then washed and decomposed with water to obtain a nanofiber hydrogel slurry with a solid content of 1-5 wt%, so that the nanofibers in the slurry maintained a highly hydrated state and surface activity. S2. In-situ homogeneous composite and defiberization: The nanofiber hydrogel slurry obtained in step S1 is mixed with para-aramid chopped fibers at an oven-dry mass ratio of (0.5-3):1, and co-defiberization is carried out in the aqueous phase. Utilizing the abundant active functional groups on the surface of the highly hydrated nanofibers and their excellent affinity with the homogeneous chopped fibers, the nanofibers in the hydrogel are dissociated under hydraulic shear and densely deposited in situ on the surface of the chopped fibers to form a composite dispersion. In this process, the hydrogel slurry serves as the only functional suspension medium and interface reinforcing phase in the system, and the addition of any heterogeneous chemical dispersants or binders is excluded. S3. Synergistic Structure Construction: The composite dispersion is formed by wet papermaking, and the nanofibers coated on the surface are driven to undergo densification shrinkage under pressing and dehydration conditions. Subsequently, after drying and hot pressing, the abundant active functional groups on the surface of the nanofibers undergo dense hydrogen bond closure to form a continuous three-dimensional hydrogen bond network. At the same time, relying on the high binding force of this hydrogen bond network and the geometric locking effect generated by dehydration shrinkage, a double dense coating of the macroscopic short-cut skeleton is achieved, and finally a 100% pure aramid homogeneous reinforcement structure without interface gaps is constructed.

2. The integrated preparation method according to claim 1, characterized in that: In step S1, the solid-liquid separation adopts a mechanical pressure filtration process, with the pressure controlled at 0.5-2.0 MPa. By directly removing the mother liquor in the gel state, the mass fraction of dimethyl sulfoxide (DMSO) in the filtrate recovered after pressure filtration is not less than 60 wt%.

3. The integrated preparation method according to claim 1, characterized in that: In step S1, during the process of preparing the wet filter cake into a hydrogel slurry, a refining machine and a fiber disintegrator are used in combination. The refining speed is 10,000-20,000 rpm, the disintegration speed is 1,500-3,000 rpm, and the disintegration time is 5-15 min, so as to ensure that the nanofibers in the hydrogel slurry are uniformly dispersed and maintain a high aspect ratio before they are completely dried and agglomerated.

4. The integrated preparation method according to claim 1, characterized in that: In step S2, the solid content of the composite fiber dispersion is controlled between 0.01 and 0.1 wt%, and no chemical dispersant, heterogeneous binder, or precipitated fiber is added during the entire dispersion process.

5. The integrated preparation method according to claim 1, characterized in that: In step S2, the length of the para-aramid chopped fiber is 3-12 mm and the fineness is 1.0-2.5 dtex.

6. The integrated preparation method according to claim 1, characterized in that: In step S3, the pressing process employs multi-stage pressing with a pressure range of 0.1-0.5 MPa.

7. The integrated preparation method according to claim 1, characterized in that: In step S3, the temperature of the hot pressing treatment is 180-280℃ and the pressure is 80-200 N / mm.

8. The integrated preparation method according to claim 1, characterized in that: Throughout the entire preparation process, a closed-loop water circulation is achieved through a washing and filtration system, with a washing water recycling rate of no less than 80%.

9. A pure para-aramid paper obtained by the integrated preparation method according to any one of claims 1-8, characterized in that: This paper is made of 100% pure para-aramid fiber, and its microstructure consists of a three-dimensional cross-linked network of para-aramid nanofibers continuously coating the surface of the chopped para-aramid fiber skeleton without interfacial gaps; with a basis weight of 30 g / m³. 2 Under these conditions, its longitudinal tear index is not less than 20 mN·m 2 / g, longitudinal elastic modulus not less than 7200 MPa, and initial thermal decomposition temperature not less than 520℃.

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