Static electrospinning phenolic / formaldehyde aramid micro-nano fiber composite filter material, and preparation method and application thereof

Abstract

The application provides a kind of electrostatic spinning phenolic aldehyde / aramid micro-nanofiber composite filter material and its preparation method and application, the composite filter material includes located outer layer's flame-retardant viscose layer, located central layer's phenolic aldehyde / aramid micro-nanofiber membrane and located inner layer's aramid water guide layer, the outer layer and inner layer are formed by through sewing interlocking structure through quilting line penetration sewing.The composite filter material disclosed in the application exhibits synergistically enhanced high-temperature filtration stability, flame retardancy, excellent mechanical durability, excellent moisture permeability and PM 2.5 Capture rate provides a new paradigm for sustainable personal protective equipment development.

Description

Technical Field

[0001] This invention belongs to the field of filter material technology, and in particular relates to an electrospun phenolic / aramid micro / nanofiber composite filter material, its preparation method, and its application. Background Technology

[0002] Fire incidents typically involve complex factors such as extreme high temperatures and toxic fumes containing harmful particulate matter, posing a serious threat to human life and property, and equally severely impacting the health and safety of frontline firefighters. While significant progress has been made in torso protection systems—modern fire suits integrate multiple thermal barriers and perform excellently in standardized heat flux tests—head protection equipment, particularly hoods and face shields, remains underdeveloped. In fact, as the most metabolically active area, the head is responsible for approximately 40% of the body's heat dissipation, making it not only susceptible to heat injury but also a primary entry point for airborne pollutants into the respiratory system. Epidemiological studies show that smoke inhalation injuries account for over 60% of fire-related deaths, and submicron particulate matter (PM2.5) contributes significantly to the spread of the virus. 2.5 Excessive exposure to the alveoli can lead to acute respiratory distress. Therefore, the head area faces extremely high exposure risks, making the development of head protection materials that combine flame retardancy, smoke filtration, and breathability for continuous wear extremely urgent.

[0003] Traditional fire protection equipment primarily uses woven or knitted fabrics of flame-retardant fibers (such as aramid fibers like Nomex and Kevlar) and flame-retardant viscose, providing basic thermal protection through their inherent thermal stability and charring properties. However, these traditional fabric structures have a critical limitation in terms of particulate matter filtration efficiency. The relatively large yarn spacing (typically 20-800 μm) in woven / knitted fabrics allows submicron particles to penetrate freely, impacting PM2.5 filtration efficiency. 2.5 The filtration efficiency is typically below 50%. This deficiency has driven the exploration of nanofiber-based filter layers as a promising enhancement strategy. A significant advancement is DuPont's NomexNanoFlex technology, which uses electrospinning to refine aramid polymers to the nanoscale (fiber diameter approximately 200-400 nm), forming a three-dimensional fiber network with an ultra-high specific surface area, and integrating this nanofiber membrane into the fabric layer of a traditional headgear. Thanks to the abundant interception sites and tortuous airflow channels provided by the nanofibers, NomexNanoFlex achieves over 95% PM filtration efficiency. 2.5 The filtration efficiency represents a qualitative leap compared to traditional fabrics, pioneering the application of nanofibers in the field of fire protection.

[0004] However, despite breakthroughs in filtration performance, nanofiber hoods still face several challenges. First, the limiting oxygen index (LOI) of aramid fibers is limited under extreme fire conditions, and their thermal decomposition produces significant smoke, posing a risk of secondary inhalation. Second, the inherent mechanical fragility of nanofiber membranes makes them prone to structural degradation under repeated deformation, resulting in insufficient durability. Third, high filtration efficiency depends on dense fiber packing (basis weight > 20 g / m³). 2 This inevitably causes discomfort from heat and humidity, leads to waste of raw materials, and is prone to heat stress during strenuous activities. These limitations stem from the fact that existing designs emphasize single-function optimization rather than the synergistic integration of multiple performance aspects, highlighting the urgent need to develop holistic solutions that combine structural reinforcement mechanisms with hierarchical functional design. Summary of the Invention

[0005] In view of this, the present invention aims to overcome the defects in the prior art and proposes an electrospun phenolic / aramid micro / nanofiber composite filter material, its preparation method and application.

[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0007] In a first aspect, the present invention provides an electrospun phenolic / aramid micro / nanofiber composite filter material, comprising an outer flame-retardant adhesive layer, a central phenolic / aramid micro / nanofiber membrane, and an inner aramid water-conducting layer, wherein the outer and inner layers are interlocked by quilting through stitches.

[0008] The flame-retardant adhesive layer is a weft-knitted structure woven from flame-retardant adhesive yarn; the phenolic / aramid micro / nanofiber membrane is formed by electrospinning and thermosetting cross-linking of a mixed solution of phenolic resin and aramid; the aramid water-wicking layer is a double rib knitted structure woven from aramid fiber yarn.

[0009] Preferably, the mass ratio of phenolic resin to aramid in the phenolic / aramid micro / nanofiber membrane is (1-1.42):1. More preferably, it is 1.25:1.

[0010] Preferably, the flame-retardant adhesive layer has a pore size of 522-536 μm, the phenolic / aramid micro / nanofiber membrane has a pore size of 0.3-1.3 μm, and the aramid water-conducting layer has a pore size of 214-237 μm.

[0011] Preferably, the flame-retardant adhesive layer has a weft-knitted structure with continuous V-shaped coil columns on the front and arc-shaped coil rows on the back.

[0012] Preferably, the aramid water-conducting layer has an interlocking structure of upper and lower coils.

[0013] Preferably, the flame-retardant adhesive yarn used in the flame-retardant adhesive layer has a fineness of 14-18S and a weaving density of 15-19 needles / 2.54cm.

[0014] Preferably, the aramid yarn used in the aramid water-wicking layer has a fineness of 18-22S / 2 and a weaving density of 10-14 needles / cm.

[0015] Preferably, the quilting thread is aramid thread, and the stitch width is 1-1.5cm.

[0016] Secondly, the present invention also provides a method for preparing the above-mentioned electrospun phenolic / aramid micro / nanofiber composite filter material, comprising the following steps:

[0017] S1. Phenolic resin, aramid and solvent are mixed to obtain polymer spinning solution. The polymer spinning solution is electrospun to obtain pretreated phenolic / aramid micro / nanofiber membrane. The pretreated phenolic / aramid micro / nanofiber membrane is dried and then subjected to step-by-step temperature rise thermosetting cross-linking to obtain phenolic / aramid micro / nanofiber membrane.

[0018] S2. A flame-retardant adhesive layer with a weft-knitted structure is prepared using flame-retardant viscose yarn on a flat knitting machine;

[0019] S3. An aramid water-conducting layer with a double rib knitted structure is prepared using aramid fiber yarn through a flat knitting machine;

[0020] S4. Arandex water-conducting layer, phenolic / aramid micro / nanofiber membrane, and flame-retardant adhesive layer are arranged in sequence and sewn together with aramid thread to obtain electrospun phenolic / aramid micro / nanofiber composite filter material.

[0021] Preferably, the relative rotation angle between the aramid water-conducting layer and the flame-retardant adhesive layer is 90°.

[0022] Preferably, in step S2, the flame-retardant adhesive layer is made of 16S flame-retardant adhesive yarn, and the parameters of the flat knitting machine are set as follows: needle pitch is 12-16G, knitting density is 15-19 needles / 2.54cm, knitting speed is 0.9-1.2m / s, and yarn feeding tension is 4-5cN, resulting in a weft plain knit structure with continuous V-shaped loop columns on the front and arc-shaped loop rows on the back.

[0023] Preferably, in step S3, the aramid water-wicking layer uses 20S / 2 double-ply aramid 1313 filament as the aramid yarn, and the parameters of the flat knitting machine are set as follows: needle pitch is 10-14G, knitting density is 10-14 needles / cm, knitting speed is 0.9-1.2m / s, and yarn feeding tension is 5-6cN. The front and rear needle beds of the flat knitting machine simultaneously complete the knitting of the knitting needles and the purl needles, so that the fabric forms a rib knitting structure with loops on both sides.

[0024] Preferably, the parameters for electrospinning in step S1 are: spinning needle 18-23G, feed speed 0.2-1.0mL / h, receiving speed 239-350rpm, applied voltage 15-30kV, ambient temperature 32±2℃, relative humidity 25±3%, and receiving distance 50-80cm.

[0025] Preferably, the step-by-step temperature-increasing thermosetting crosslinking process in step S1 is as follows:

[0026] The temperature is raised to 70-80℃ within 0.5-1 hour and held for 4-5 hours; then raised to 80-90℃ within 0.5-1 hour and held for 4-5 hours; next, raised to 90-100℃ within 0.5-1 hour and held for 4-5 hours; then raised to 100-110℃ within 0.5-1 hour and held for 3-4 hours; then raised to 110-120℃ within 0.5-1 hour and held for 2-3 hours; then raised to 120-130℃ within 0.5-1 hour and held for 2-3 hours; then raised to 140-150℃ at a rate of 10-20℃ / h; finally, raised to 180-200℃ within 0.5-1 hour to complete the thermosetting crosslinking.

[0027] This invention employs a non-uniform stepwise heating and curing crosslinking process. This method ensures full crosslinking of fibers while avoiding fiber melting and adhesion, and effectively shortens the curing time.

[0028] Thirdly, the present invention also provides the application of the above-mentioned electrospun phenolic / aramid micro / nanofiber composite filter material in fire protection equipment and high-temperature industrial fields.

[0029] Preferably, the fire protection equipment is a fire hood.

[0030] This invention designs an interlocking structure to achieve vertical locking between fiber layers. This interlocking structure consists of two layers of knitted fabric connected by quilting threads. The loops of the knitted fabric are arranged vertically along the thickness direction, forming a multi-layered support network. The quilting threads pass through the upper and lower loops, tightly locking them together and achieving effective force transfer between layers. The flame-retardant adhesive layer adopts a weft plain knit structure. The loops of this structure are arranged regularly in the same plane, providing stable planar support, but it is still prone to local deformation under external force. The aramid water-wicking layer introduces a double rib structure, characterized by the nesting and interlocking of the front and back loops, forming a stronger constraint force in the thickness direction. After placing the phenolic / aramid micro / nanofiber membrane between the two layers of knitted fabric, the quilting process allows the quilting threads to pass vertically through the outer weft plain knitted fabric, the middle phenolic / aramid micro / nanofiber membrane, and the inner double rib knitted fabric, forming a connection point that runs through the entire thickness. This vertically penetrating quilting thread locks the loops of the upper and lower knitted layers within the same vertical plane, forcing the composite filter material to deform collaboratively under external force. This effectively limits localized stress concentration in the brittle phenolic / aramid micro / nanofiber in the middle layer. The individual loops of the flame-retardant adhesive layer are uniformly distributed in the plane, providing basic planar support and stability. The double rib of the aramid water-wicking layer exhibits a more complex interlocking loop morphology, with the front and back loops nested together, creating additional toughness and constraint in the thickness direction, effectively limiting the deformation range of the outer weft knit. Through this combination of differentiated knitting design between the upper and lower layers and the middle phenolic / aramid micro / nanofiber membrane, along with the vertically penetrating quilting thread, mechanical interlocking and collaborative stress distribution between the layers are achieved, significantly improving the overall mechanical stability and protective performance of the fabric.

[0031] Furthermore, flame-retardant viscose fibers, with their abundant hydroxyl groups, exhibit the fastest moisture absorption rate, enabling the efficient establishment of stable capillary transport channels. The weft-plain weave design achieves a balanced approach in pore size distribution and pore connectivity, ensuring not only the long-lasting capillary driving force but also overall breathability and uniformity. Therefore, flame-retardant viscose weft-plain fabrics outperform other comparative samples in terms of initial water absorption rate and uniform transport, making them the most suitable hydrophilic layer choice for fire protection equipment and high-temperature industrial applications.

[0032] A composite fabric system with a micro-nano hierarchical structure was constructed by using the hydrophilic layer of the flame-retardant adhesive layer as the outer layer, the water-repellent layer of the phenolic / aramid micro / nanofiber membrane as the central layer, and the aramid water-conducting layer as the inner layer. This hierarchical design not only achieves a gradually enhanced wetting gradient from the inside out, but also effectively improves the synergistic mechanical stability with the phenolic / aramid micro / nanofiber membrane through the reasonable arrangement of the structures. Specifically, the weft-flat weave of the flame-retardant adhesive layer, with its uniform coil arrangement and moderate pore size, can quickly establish stable capillary channels. However, it also suffers from slippage and expansion during lateral coil stretching. Without effective restraint, this excessive lateral deformation can be transmitted to the core phenolic / aramid micro / nanofiber membrane, damaging its structure and severely affecting its thermal protection performance. The introduction of the inner double-rib structure effectively limits the slippage of the weft-flat weave coils. The double-rib coils are interlaced, with high longitudinal density and smaller pore size. They not only perform the function of water conduction, but also restrain the expansion of the outer weft-flat structure through lateral restraint, thus enabling the composite filter material to form a synergistic response during deformation.

[0033] The phenolic / aramid micro / nanofiber membrane is formed by electrospinning and thermosetting crosslinking of a mixed solution of phenolic resin and aramid. During the thermosetting crosslinking reaction, the aramid skeleton remains stable, while the phenolic resin completes its network formation through the thermosetting crosslinking reaction. During the heating process, the thermosetting phenolic resin first undergoes hydroxymethyl (-CH2OH) activation and condensation: hydroxymethyl groups on adjacent aromatic ring active sites (ortho / para positions) undergo electrophilic substitution and dehydration condensation via active intermediates such as quinone methyl groups under thermal drive, gradually generating a three-dimensional crosslinked structure dominated by -CH2- (methylene bridges). A small amount of -CH2-O-CH2- (ether bridges) can also be formed in the early stages, but as curing progresses and the temperature increases, the ether bridges further rearrange / break and transform into more stable methylene bridges. This effect, through the construction of a physical cross-linking network between molecules, restricts the thermal motion of chain segments and increases the thermal decomposition initiation temperature. On the other hand, it promotes the further aggregation of aromatic structures and densification of carbonaceous structures during high-temperature pyrolysis, which is conducive to the formation of a stable and continuous carbon layer barrier. Multiple levels synergistically enhance the overall thermal stability and heat protection performance of the composite system.

[0034] Compared with the prior art, the present invention has the following advantages:

[0035] The interlocking composite filter material described in this invention exhibits synergistically enhanced multifunctional properties: limiting oxygen index (LOI=31%, 11% higher than aramid), and excellent high-temperature filtration stability (maintaining >99% PM filtration efficiency even after treatment at 250°C for 4 hours). 2.5 It exhibits excellent filtration efficiency, superior mechanical durability (maintaining 96.7% filtration efficiency at 10% deformation), and outstanding moisture permeability (WVTR = 585.5 g·m³). -2·day -1 (24.6% higher than commercial hoods). More notably, thanks to the ultra-high filtration efficiency of nanofibers, this composite material achieves an ultra-low basis weight (0.77 g / m³). 2 ) can achieve 99.90% PM. 2.5 The capture rate provides a new paradigm for the development of sustainable protective equipment. More importantly, this "structural interlocking-functional gradient" co-design approach can be extended to other extreme environmental protection scenarios that require simultaneous thermal protection, air filtration, and moisture management, providing new ideas for the design of next-generation multifunctional protective materials in aerospace, industrial safety, and other fields. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the structure of the electrospun phenolic / aramid micro / nanofiber composite filter material of the present invention;

[0037] Figure 2 This is a diagram of the loop structure of the weft-knitted structure of the present invention, wherein a is the front loop structure diagram and b is the back loop structure diagram;

[0038] Figure 3 This is a diagram of the loop structure of the double rib knitting structure of the present invention;

[0039] Figure 4 These are the results of high-temperature filtration performance tests, where 'a' represents the effect of the phenolic / aramid micro / nanofiber membrane on PM2.5 at different temperatures. 2.5 b represents the filtration efficiency of different filter fiber membranes at 25℃ and 250℃ for PM2.5. 2.5 Comparison of filtration efficiency; c is electron micrograph of different filter fiber membranes after heat treatment;

[0040] Figure 5 Tensile curves of composite materials with different locking angles (TPNM in the figure is phenolic / aramid micro / nanofiber membrane).

[0041] Figure 6 The images show the tensile cycle curves of the composite filter material at a 90° locking angle, where a is the tensile cycle curve with 5% deformation, b is a photograph of the composite filter material after 5% deformation and stretching, c is the tensile cycle curve with 10% deformation, and d is a photograph of the composite filter material after 10% deformation and stretching.

[0042] Figure 7 Comparative photographs of the breathability of the phenolic / aramid micro / nanofiber membrane (IKPNC) and the commercial headgear membrane (Nomex) from Example 1;

[0043] Figure 8 The results show the unidirectional moisture wicking performance test results, where a is a fluorescent droplet tracer image of the composite filter material, and b is a comparison of the moisture absorption rates of the composite filter materials. Detailed Implementation

[0044] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0045] In this document, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0046] In this document, when values ​​are described as ranges, it should be understood that such disclosure includes disclosure of all possible subranges within that range, as well as the specific numerical values ​​falling within that range, regardless of whether the specific numerical value or specific subrange is explicitly specified.

[0047] In this article, the terms "multiple" or "more than" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0048] In this document, the terms "preferred" and "more preferred" are used only to describe implementation methods or embodiments with better effects, and should be understood as not constituting a limitation on the scope of protection of this invention.

[0049] In this document, terms such as "further" are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of this invention.

[0050] In this article, the term "and / or" describes an association between objects, indicating that three relationships can exist. For example, A and / or B means: A or B, or A and B.

[0051] In this document, the term "about" means a specified value of + / - 10%, preferably + / - 5%, and more preferably + / - 1%.

[0052] In this article, the terms “include,” “including,” “have,” “contain,” etc., are all open-ended terms, meaning that they include but are not limited to.

[0053] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0054] The present invention will be described in detail below with reference to embodiments.

[0055] Example 1

[0056] S1: Preparation of phenolic / aramid micro / nanofiber membranes, the specific steps are as follows:

[0057] Phenolic resin and aramid were dissolved in dimethylacetamide (DMAC) at a mass ratio of 1.25:1 and stirred at 70°C for 5 hours to obtain a uniform and transparent polymer spinning solution. This ratio of polymer spinning solution achieves an optimal balance between viscosity and flowability, allowing the jet to fully extend under electric field stretching. The resulting fibers have a smooth and dense surface, with a uniform and densely distributed secondary nanonetwork structure.

[0058] Phenolic / aramid micro / nanofiber membranes were prepared using a commercially available electrospinning apparatus. The spinning needle was 23G, and the spinning conditions were set as follows: feed rate 0.5 mL / h, receiving rate 239 rpm, applied voltage 25 kV, ambient temperature 32 ± 2℃, relative humidity 25 ± 3%, and receiving distance 50 cm. During the stretching process, the polymer spinning solution evaporated, and nanofibers deposited on the receiving substrate, forming a pretreated phenolic / aramid micro / nanofiber membrane.

[0059] The pretreated phenolic / aramid micro / nanofiber membrane was first completely dried in an oven at 50°C to remove residual solvent. Then, a thermosetting crosslinking process was performed in the oven, with the following steps: First, the temperature was raised to 70°C within 1 hour and held for 4 hours; then, the temperature was raised to 80°C within 1 hour and held for 4 hours; next, the temperature was raised to 90°C within 1 hour and held for 4 hours; then, the temperature was raised to 100°C within 1 hour and held for 3 hours. After that, the temperature was raised to 110°C within 1 hour and held for 2 hours; then, the temperature was raised to 120°C within 1 hour and held for 2 hours; subsequently, the temperature was raised to 140°C at a rate of 10°C / hour; finally, the temperature was raised to 180°C within 1 hour. After the heating process was completed, the phenolic / aramid micro / nanofiber membrane was obtained.

[0060] S2. A flame-retardant viscose layer with a weft-knitted structure is prepared using flame-retardant viscose yarn on a flat knitting machine. The specific steps are as follows:

[0061] Flame-retardant adhesive layers are prepared using 16S flame-retardant viscose yarn. Three yarns are drawn from yarn bobbins fixed on a yarn frame and then guided by a yarn guide to a plying machine for simultaneous plying, ensuring the three single yarns are combined into a single yarn under uniform tension. During the plying process, the yarn tension is precisely controlled by a tensioner and a yarn guide to prevent uneven plying caused by inconsistent yarn tension. After plying, the resulting yarn bobbins are wound for use on a flat knitting machine.

[0062] The weaving is carried out on a fully automatic computerized flat knitting machine, with the structure set as a weft-plain knitting structure. The yarn goes through actions such as yarn feeding, yarn hooking, closing, needle turning, and loop release in sequence, gradually forming loops in the cyclical movement of the single-sided needle bed, and finally obtaining a face composed of continuous V-shaped loop columns. Figure 2 a), forming an arc-shaped coil array structure on the reverse side ( Figure 2b) The weft-knitted structure. The parameters of the fully automatic computerized flat knitting machine are: needle length set to 14G, knitting density of 17 needles / 2.54cm, width of 40cm, knitting speed of 0.9m / s, yarn tension of 5cN. After knitting, the sample is subjected to a relaxation treatment by restoring moisture for 24 hours under standard atmospheric conditions to eliminate internal stress during the knitting process and maintain dimensional stability.

[0063] S3. The specific steps for preparing an aramid water-wicking layer with a double rib knit structure using aramid fiber yarn on a flat knitting machine are as follows:

[0064] Using 20S / 2 double-ply aramid 1313 filament as raw material, the fabric is knitted on a fully automatic computerized flat knitting machine equipped with a double needle bed, enabling precise and automated shaping of the structure. Before weaving, the aramid yarn is wound into a suitable yarn bobbin, installed into the yarn feeding system, and threaded through the yarn feeder. In one work cycle, the double needle bed simultaneously completes both the knitting of the front and back needles, thus forming a double rib structure on both sides of the fabric. Figure 3 The parameters of the fully automatic computerized flat knitting machine are: needle pitch 12G, knitting density 12 stitches / cm, knitting speed 0.9m / s, and yarn tension adjusted to 6cN. After completing 140 knitting cycles, the sample is removed. After knitting, the sample is rehydrated for 24 hours under standard atmospheric conditions to relax it, eliminating internal stress during the knitting process and maintaining dimensional stability.

[0065] S4. An aramid water-conducting layer, a phenolic / aramid micro / nanofiber membrane, and a flame-retardant adhesive layer are arranged sequentially and sewn together using aramid thread as quilting thread to obtain an electrospun phenolic / aramid micro / nanofiber composite filter material, such as... Figure 1 As shown, the specific steps are as follows:

[0066] The two prepared fabrics and the phenolic / aramid micro / nanofiber membrane were cut to the same size (300mm*300mm), and the orientation of each fabric sample was marked as a reference baseline. According to the interlocking requirements of the experiment, the relative rotation angles of the two knitted layers were designed to be 0°, 45°, 90°, and 135° (i.e., for each sample group, the flame-retardant adhesive layer fabric maintained the reference orientation, and the aramid water-conducting layer fabric rotated to the specified angle relative to the baseline), with the phenolic / aramid micro / nanofiber membrane placed between them. To prevent slippage of the three-layer structure of the composite filter material in subsequent operations, it was sewn together with aramid thread at 10mm intervals, and each sample was numbered for later use.

[0067] The three layers of the sample were sewn together using an industrial sewing machine. To ensure the compatibility of the quilting thread with the base fabric, aramid thread with a diameter of 0.12 cm was selected; a No. 11 sewing needle was used, and the thread tension was adjusted to keep the stitches tight but not to cause wrinkles in the phenolic / aramid micro / nano layer.

[0068] After sewing, retain appropriate seam edges on the sample and reinforce the seam knots. Then, use low-temperature hot rolling to flatten the sample and check whether the seam is uniform, whether there are defects between layers, and whether the phenolic / aramid micro / nanofiber membrane is cracked.

[0069] Measurements showed that the outer layer had a contact angle of ≈0° and a pore size of 508μm, the middle layer had a contact angle of ≈153° and a pore size of 0.5μm, and the inner layer was capable of slowly absorbing water with a pore size of 220μm.

[0070] Example 2

[0071] S1: Preparation of phenolic / aramid micro / nanofiber membranes, the specific steps are as follows:

[0072] Phenolic resin and aramid were dissolved in dimethylacetamide (DMAC) at a mass ratio of 1:1 and stirred at 70°C for 5 hours to obtain a uniform and transparent polymer spinning solution.

[0073] Phenolic / aramid micro / nanofiber membranes were prepared using a commercially available electrospinning apparatus. The spinning needle was 18G, and the spinning conditions were set as follows: feed rate 0.2 mL / h, receiving rate 350 rpm, applied voltage 15 kV, ambient temperature 32 ± 2 °C, relative humidity 25 ± 3%, and receiving distance 80 cm. During the stretching process, the polymer spinning solution evaporated, and nanofibers deposited on the receiving substrate, forming a pretreated phenolic / aramid micro / nanofiber membrane.

[0074] The pretreated phenolic / aramid micro / nanofiber membrane was first completely dried in an oven at 50°C to remove residual solvent. Then, a thermosetting crosslinking process was performed in the oven, with the following steps: First, the temperature was raised to 80°C within 0.5 hours and held for 5 hours; then, the temperature was raised to 90°C within 0.5 hours and held for 5 hours; next, the temperature was raised to 100°C within 0.5 hours and held for 5 hours; then, the temperature was raised to 110°C within 0.5 hours and held for 4 hours. After that, the temperature was raised to 120°C within 0.5 hours and held for 2 hours; then, the temperature was raised to 130°C within 0.5 hours and held for 3 hours. Subsequently, the temperature was raised to 150°C at a rate of 20°C / hour, and finally, the temperature was raised to 200°C within 0.5 hours. After the heating process was completed, the phenolic / aramid micro / nanofiber membrane was obtained.

[0075] S2. A flame-retardant viscose layer with a weft-knitted structure is prepared using flame-retardant viscose yarn on a flat knitting machine. The specific steps are as follows:

[0076] Flame-retardant adhesive layers are prepared using 16S flame-retardant viscose yarn. Three yarns are drawn from yarn bobbins fixed on a yarn frame and then guided by a yarn guide to a plying machine for simultaneous plying, ensuring the three single yarns are combined into a single yarn under uniform tension. During the plying process, the yarn tension is precisely controlled by a tensioner and a yarn guide to prevent uneven plying caused by inconsistent yarn tension. After plying, the resulting yarn bobbins are wound for use on a flat knitting machine.

[0077] The weaving is carried out on a fully automatic computerized flat knitting machine, with the structure set as a plain weft knitting structure. The yarn goes through actions such as feeding, hooking, closing, turning, and looping in sequence, gradually forming loops in the cyclical movement of the single-sided needle bed. Finally, a plain weft knitting structure is obtained, with continuous V-shaped loop columns on the front and arc-shaped loop rows on the back. Figure 2 The parameters of the fully automatic computerized flat knitting machine are as follows: needle length set to 16G, knitting density to 15 needles / 2.54cm, width to 40cm, knitting speed to 1.2m / s, yarn tension to 4cN. After knitting, the sample is subjected to a relaxation treatment by re-moistening under standard atmospheric conditions for 24 hours to eliminate internal stress during the knitting process and maintain dimensional stability.

[0078] S3. The specific steps for preparing an aramid water-wicking layer with a double rib knit structure using aramid fiber yarn on a flat knitting machine are as follows:

[0079] Using 20s / 2 double-ply aramid 1313 filament as raw material, the fabric is knitted on a fully automatic computerized flat knitting machine equipped with a double needle bed, enabling precise and automated shaping of the structure. Before weaving, the aramid yarn is wound into a suitable yarn bobbin, installed into the yarn feeding system, and threaded through the yarn feeder. In one work cycle, the double needle bed simultaneously completes both knitting (both purl and back purl), thus forming a double rib structure on both sides of the fabric. Figure 3 The parameters of the fully automatic computerized flat knitting machine are: needle pitch of 14G, knitting density of 10 stitches / cm, knitting speed of 1.2m / s, and yarn tension of 5cN. After completing 140 knitting cycles, the sample is removed. After knitting, the sample is rehydrated for 24 hours under standard atmospheric conditions to relax it, thereby eliminating internal stress during the knitting process and maintaining dimensional stability.

[0080] S4. Arandex water-conducting layer, phenolic / aramid micro / nanofiber membrane, and flame-retardant adhesive layer are arranged sequentially and sewn together using aramid thread as quilting thread to obtain electrospun phenolic / aramid micro / nanofiber composite filter material. The specific steps are as follows:

[0081] The two prepared fabrics and the phenolic / aramid micro / nanofiber membrane were cut to the same size (300mm*300mm), and the orientation of each fabric sample was marked as a reference baseline. Following the interlocking requirements of the experiment, the two knitted layers were arranged with a relative rotation angle of 90° (i.e., for each sample group, the flame-retardant adhesive layer fabric maintained the reference orientation, and the aramid water-wicking layer fabric rotated to the specified angle relative to the baseline), with the phenolic / aramid micro / nanofiber membrane placed between them. To prevent slippage of the three-layer structure in subsequent operations, it was sewn together with aramid thread at 10mm intervals, and each sample was numbered for later use.

[0082] The three layers of the sample were sewn together using an industrial sewing machine. To ensure the compatibility of the quilting thread with the base fabric, aramid thread with a diameter of 0.12 cm was selected; a No. 11 sewing needle was used, and the thread tension was adjusted to keep the stitches tight but not to cause wrinkles in the phenolic / aramid micro / nano layer.

[0083] After sewing, retain appropriate seam edges on the sample and reinforce the seam knots. Then, use low-temperature hot rolling to flatten the sample and check whether the seam is uniform, whether there are defects between layers, and whether the phenolic / aramid micro / nanofiber membrane is cracked.

[0084] Measurements showed that the outer layer had a contact angle of ≈0° and a pore size of 522μm, the middle layer had a contact angle of ≈148° and a pore size of 1.3μm, and the inner layer could slowly absorb water with a pore size of 237μm.

[0085] Example 3

[0086] S1: Preparation of phenolic / aramid micro / nanofiber membranes, the specific steps are as follows:

[0087] Phenolic resin and aramid were dissolved in dimethylacetamide (DMAC) at a mass ratio of 1.42:1 and stirred at 70°C for 5 hours to obtain a uniform and transparent polymer spinning solution.

[0088] Phenolic / aramid micro / nanofiber membranes were prepared using a commercially available electrospinning apparatus. The spinning needle was 20G, and the spinning conditions were set as follows: feed rate 0.2 mL / h, receiving rate 200 rpm, applied voltage 30 kV, ambient temperature 32 ± 2℃, relative humidity 25 ± 3%, and receiving distance 60 cm. During the stretching process, the polymer spinning solution evaporated, and nanofibers deposited on the receiving substrate, forming a pretreated phenolic / aramid micro / nanofiber membrane.

[0089] The pretreated phenolic / aramid micro / nanofiber membrane was first completely dried in an oven at 50°C to remove residual solvent. Then, a thermosetting cross-linking process was performed in the oven, with the following steps: First, the temperature was raised to 70°C within 0.5 hours and held for 5 hours; then, the temperature was raised to 80°C within 0.5 hours and held for 5 hours; next, the temperature was raised to 90°C within 0.5 hours and held for 5 hours; then, the temperature was raised to 100°C within 0.5 hours and held for 4 hours. After that, the temperature was raised to 110°C within 0.5 hours and held for 2 hours; then, the temperature was raised to 120°C within 0.5 hours and held for 3 hours; subsequently, the temperature was raised to 140°C at a rate of 20°C / hour; finally, the temperature was raised to 180°C within 0.5 hours. After the heating process was completed, the phenolic / aramid micro / nanofiber membrane was obtained.

[0090] S2. A flame-retardant viscose layer with a weft-knitted structure is prepared using flame-retardant viscose yarn on a flat knitting machine. The specific steps are as follows:

[0091] Flame-retardant adhesive layers are prepared using 16S flame-retardant viscose yarn. Three yarns are drawn from yarn bobbins fixed on a yarn frame and then guided by a yarn guide to a plying machine for simultaneous plying, ensuring the three single yarns are combined into a single yarn under uniform tension. During the plying process, the yarn tension is precisely controlled by a tensioner and a yarn guide to prevent uneven plying caused by inconsistent yarn tension. After plying, the resulting yarn bobbins are wound for use on a flat knitting machine.

[0092] The weaving is carried out on a fully automatic computerized flat knitting machine, with the structure set as a plain weft knitting structure. The yarn goes through actions such as feeding, hooking, closing, turning, and looping in sequence, gradually forming loops in the cyclical movement of the single-sided needle bed. Finally, a plain weft knitting structure is obtained, with continuous V-shaped loop columns on the front and arc-shaped loop rows on the back. Figure 2 The parameters of the fully automatic computerized flat knitting machine are as follows: needle length set to 12G, knitting density to 19 needles / 2.54cm, width to 40cm, knitting speed to 1.0m / s, yarn tension to 5cN. After knitting, the sample is subjected to a relaxation treatment by re-moistening under standard atmospheric conditions for 24 hours to eliminate internal stress during the knitting process and maintain dimensional stability.

[0093] S3. The specific steps for preparing an aramid water-wicking layer with a double rib knit structure using aramid fiber yarn on a flat knitting machine are as follows:

[0094] Using 20s / 2 double-ply aramid 1313 filament as raw material, the fabric is knitted on a fully automatic computerized flat knitting machine equipped with a double needle bed, enabling precise and automated shaping of the structure. Before weaving, the aramid yarn is wound into a suitable bobbin, installed into the yarn feeding system, and threaded through the yarn feeder. In one work cycle, the double needle bed simultaneously completes both knitting (both purl and back purl), thus forming a double rib structure on both sides of the fabric. Figure 3The parameters of the fully automatic computerized flat knitting machine are: needle pitch 10G, knitting density 14 stitches / cm, knitting speed 1.0m / s, yarn tension up to 6cN. After completing 140 knitting cycles, the sample is removed. After knitting, the sample is rehydrated for 24 hours under standard atmospheric conditions to relax it, eliminating internal stress during the knitting process and maintaining dimensional stability.

[0095] S4. Arandex water-conducting layer, phenolic / aramid micro / nanofiber membrane, and flame-retardant adhesive layer are arranged sequentially and sewn together using aramid thread as quilting thread to obtain electrospun phenolic / aramid micro / nanofiber composite filter material. The specific steps are as follows:

[0096] The two prepared fabrics and the phenolic / aramid micro / nanofiber membrane were cut to the same size (300mm*300mm), and the orientation of each fabric sample was marked as a reference baseline. Following the interlocking requirements of the experiment, the two knitted fabrics were arranged with a relative rotation angle of 90° (i.e., for each sample group, the flame-retardant adhesive layer fabric maintained the reference orientation, and the aramid water-wicking layer fabric rotated to the specified angle relative to the baseline), with the phenolic / aramid micro / nanofiber membrane placed between them. To prevent slippage of the three-layer structure in subsequent operations, it was sewn together with aramid thread at 15mm intervals, and each sample was numbered for later use.

[0097] The three layers of the sample were sewn together using an industrial sewing machine. To ensure the compatibility of the quilting thread with the base fabric, aramid thread with a diameter of 0.12 cm was selected; a No. 11 sewing needle was used, and the thread tension was adjusted to keep the stitches tight but not to cause wrinkles in the phenolic / aramid micro / nano layer.

[0098] After sewing, retain appropriate seam edges on the sample and reinforce the seam knots. Then, use low-temperature hot rolling to flatten the sample and check whether the seam is uniform, whether there are defects between layers, and whether the phenolic / aramid micro / nanofiber membrane is cracked.

[0099] Measurements showed that the outer layer had a contact angle of ≈0° and a pore size of 522μm, the middle layer had a contact angle of ≈168° and a pore size of 0.3μm, and the inner layer could slowly absorb water with a pore size of 214μm.

[0100] Comparative Example 1

[0101] The difference between this comparative example and Example 1 is that: there is no intermediate phenolic / aramid micro / nanofiber membrane, and the aramid water-conducting layer and flame-retardant adhesive layer are directly stitched together.

[0102] Comparative Example 2

[0103] The difference between this comparative example and Example 1 is that the intermediate phenolic / aramid micro / nanofiber membrane is replaced with a PP membrane with a pore size of 0.5 μm.

[0104] Comparative Example 3

[0105] The difference between this comparative example and Example 1 is that the aramid water-wicking layer has a weft-knitted structure.

[0106] Comparative Example 4

[0107] The difference between this comparative example and Example 1 is that the flame-retardant adhesive layer has a double rib knit structure.

[0108] Comparative Example 5

[0109] The difference between this comparative example and Example 1 is that the pore size of the aramid water-conducting layer is 600 μm.

[0110] Comparative Example 6

[0111] The difference between this comparative example and Example 1 is that the mass ratio of phenolic resin to aramid in the phenolic / aramid micro / nanofiber membrane is 1:1.2.

[0112] Comparative Example 7

[0113] The difference between this comparative example and Example 1 is that the mass ratio of phenolic resin to aramid in the phenolic / aramid micro / nanofiber membrane is 1.58:1.

[0114] The composite filter materials of Examples 1-3 and Comparative Examples 1-7 were subjected to the following tests:

[0115] Test Example 1: High Temperature Filtration Performance Test

[0116] The testing method was as follows: different membranes were placed at different temperatures for a certain period of time, and then tested using a German TOPASAFC131 multi-functional filter stage. The samples were prepared as 15cm discs and fixed in a clamp. The aerosol particulate matter concentration was set to 3000 mg / m³. 2 The airflow velocity was set to 32 L / min. The filtration efficiency under different particle size conditions was calculated by monitoring the difference in the number of aerosol particles upstream and downstream of the test chamber. To ensure repeatability, each filtration performance test was repeated three times using an independent sample.

[0117] Example 1: The particulate matter interception efficiency of phenolic / aramid micro / nanofiber membranes was first evaluated under different treatment conditions (25-400℃, 30 min). Since the inner and outer layers only provide support, high-temperature filtration was used to investigate the performance of the middle layer—the phenolic / aramid micro / nanofiber membrane. Figure 4 It can be seen that even after high-temperature treatment, its effect on PM2.5 is... 2.5The removal efficiency remained consistently above 99%, fully demonstrating the excellent heat-resistant filtration capability of the phenolic / aramid micro / nanofiber membrane based on its structural stability. Next, the filtration performance of the phenolic / aramid micro / nanofiber membrane (TPNM) prepared in Example 1 was compared with that of common polypropylene (PP), polyacrylonitrile (PAN), and polytetrafluoroethylene (PTFE) after simultaneous heat treatment at 250°C for 4 hours. Figure 4 As can be seen from b, PP, PAN, and PTFE membranes all completely lost their filtration capacity after high-temperature treatment due to melting and cracking or structural collapse. However, the phenolic / aramid fiber membrane, with its highly cross-linked molecular skeleton, maintained structural integrity and avoided the loss of core performance. This difference is closely related to the thermal transformation behavior of the polymers. PP has a melting temperature of approximately 160-170℃, and at 250℃, the material will undergo significant melting and fiber breakage. PAN has a glass transition temperature of approximately 95℃, and its thermal decomposition initiation temperature is close to 250℃. Therefore, the molecular chain segments will undergo violent thermal decomposition, causing rapid collapse of the fiber structure. PTFE has a higher thermal decomposition temperature, but its melting temperature is 327℃. At 250℃, the crystalline region will soften and rearrange, causing morphological instability. (Electron microscopy images after high-temperature treatment are shown.) Figure 4 c) This further confirms that after high-temperature treatment, the phenolic / aramid micro / nanofiber membrane still maintains a complete, continuous, and uniform fiber network morphology without morphological damage, which verifies its excellent structural stability at the microscopic level.

[0118] The composite filter material of Example 2 was subjected to heat treatment at 250°C for 4 hours before PM... 2.5 The filtration efficiency was 99.36%. The composite filter material in Example 3, after heat treatment at 250°C for 4 hours, showed PM2.5% filtration efficiency. 2.5 Its filtration efficiency is 99.78%.

[0119] In Comparative Example 1, the middle core layer is the main interception layer for fine particulate matter. When only the upper and lower knitted layers are present, the pore size of both layers is much larger than the size of fine particulate matter (2.5 μm), resulting in almost no capture effect on fine particles and a filtration efficiency as low as 11.3% at high temperatures. In Comparative Example 2, the PP meltblown membrane collapses completely at 250℃, losing all functionality. Therefore, under high-temperature conditions, Comparative Example 2 not only loses its filtration performance but also its one-way moisture wicking. In Comparative Example 6, the filtration efficiency is significantly reduced (97.53%) due to the incomplete formation of the secondary nanomesh. In Comparative Example 7, the pore size of the secondary nanomesh is significantly reduced, resulting in more small pores and a better interception effect on fine particulate matter, with a significantly increased filtration efficiency (99.99%). However, at the same time, the friction between the airflow and the fibers increases, leading to increased energy consumption and a shorter lifespan for the material.

[0120] Test Example 2: Tensile Fracture Test

[0121] (1) Tensile fracture tests were conducted on the four sets of samples prepared in Example 1 (two layers of knitted fabric arranged with relative rotation angles of 0°, 45°, 90°, and 135°) and the phenolic / aramid micro / nanofiber membrane. The test method was as follows: a universal tensile testing machine TSE502B was used to perform tensile fracture tests on the samples, with a load of 100N, a tensile rate of 1mm / min, a sample width of 10mm, and a length of 100mm. The results are as follows. Figure 5 As shown, the curves with 90° interlocking arrangement are closest to those of a single-layer phenolic nanofiber membrane, indicating that this angle can maintain the fabric's mechanical properties while dispersing stress through interlaced coils, preventing excessive local deformation. The fracture stresses of curves at other angles are much higher than those of the single-layer phenolic nanofiber membrane, indicating that the inner layer fractures before the outer layer fails, causing premature collapse of the overall structure and severely impacting its performance.

[0122] After determining the optimal locking angle, cyclic tensile tests were conducted on the composite filter materials prepared in the examples and comparative examples to further assess their mechanical stability during repeated tensile loading-unloading processes. The test method was as follows: a TSE502B universal tensile testing machine was used to perform tensile fracture tests on the samples, with loads of 3N and 13N, a tensile rate of 1mm / min, and sample widths of 10mm and lengths of 100mm. The results are as follows:

[0123] Example 1: Under 5% cyclic deformation conditions ( Figure 6 a) The stress-strain curves maintain a high degree of consistency over 100 consecutive cycles, initially exhibiting minimal hysteresis, indicating that the material can achieve a stable elastic response under small deformations, without significant plastic accumulation or performance degradation. When the deformation amplitude is increased to 10% ( Figure 6 (c) The curve also maintained good repeatability; despite a significant increase in stress level, the overall return curve remained intact, without any breakage or instability. (From the actual photograph in the illustration...) Figure 6 b、 Figure 6 d) It can also be seen that after repeated stretching and deformation, the overall shape of the composite structure remains intact, without any obvious relaxation, slippage, or damage. These results fully demonstrate that the interlocking structure can maintain robust mechanical responsiveness under multiple cyclic strains, exhibiting excellent fatigue resistance of the material and durability of the structure, providing strong support for its long-term use.

[0124] Measurements showed that the elongation of Comparative Example 3 was 182%, and the elastic recovery rate was 85%. Due to the high tensile deformation and low elastic recovery rate of the weft-faced fabric, the fabric deformed after repeated stretching and did not return to its original shape. Comparative Example 4, due to its tight double-rib structure, required a greater force (>4N) to perform tensile cycles under the same deformation, exceeding the tensile breaking strength of the interlayer. Therefore, during cyclic stretching, the phenolic / aramid micro / nanofiber membrane was damaged, leading to the loss of functionality of the entire material. Comparative Example 5, due to the change in pore size, showed weakened inter-fiber binding, and under the same tensile cycle conditions, the material exhibited relaxation, with an elastic recovery rate of only 80%.

[0125] Test Example 3: Breathability Test

[0126] (1) Gas permeation experiment:

[0127] Gas permeation experiments were conducted using highly volatile concentrated hydrochloric acid as an indicator, and the results were as follows: Figure 7 As shown, when the composite filter material prepared in Example 1 (IKPNC in the figure) is used as the covering layer, the acid gas can turn the test paper significantly purple-red within 15s, proving that the gas can quickly penetrate the material; the head cover film made of commercially available material (the commercially available material is Nomex® Nano Flex manufactured by DuPont, referred to as Nomex in the figure) only shows a light purple-red color on the acid-base indicator test paper after 115s, indicating the lag in gas diffusion.

[0128] (2) Water vapor permeation experiment

[0129] Test Method: Pour 10 mL of water into a clean, dry cup. Place the sample face down on the cup, install the gasket and pressure ring, screw on the nut, and seal the test assembly (cup, gasket, and pressure ring) from the side with vinyl tape. Place the test assembly horizontally in a test chamber preheated to 38℃, 2% humidity, and 0.5 m / s airflow. After equilibration for 0.5 hours, weigh each sample in the chamber according to its number, accurate to 0.001 g. After 1 hour of testing, weigh again in the same order. If weighing is required outside the chamber, the difference between the ambient temperature and the specified test temperature should not exceed 3℃.

[0130] The moisture permeability of the sample is calculated using the following formula:

[0131] WVTR=Δm*24 / (s·t)

[0132] In the formula: WVTR is the moisture permeability per square meter per day, g / (m²). 2 .d); Δm is the difference between two weighings of the same test combination, in g; s is the test area of ​​the sample, in m. 2t represents the test time, in hours. The moisture permeability is the arithmetic mean of the moisture permeability of the three samples [rounded to 10 g / (m³)]. 2 .d)).

[0133] The results are shown in Table 1:

[0134] Table 1. Results of air permeability test

[0135]

[0136] Note: The commercially available material is Nomex® Nano Flex manufactured by DuPont.

[0137] As shown in the table above, the air permeability of Example 1 is significantly higher than that of commercially available materials, proving that the gradient structure achieves efficient gas permeability while ensuring flame retardancy, effectively guaranteeing the exchange of heat and volatile gases during long-term wear. The three-layer stacked fiber network structure of the composite filter fiber material of the present invention provides a large number of interconnected diffusion channels for gas molecules. This structure significantly reduces the detour and retention of molecules during the passage process, improving the overall transmission rate. Compared with the two-level spider web structure of "coarse skeleton + fine branches" in Comparative Example 2, the PP electrospun membrane usually needs to rely on a more uniform and denser fiber web to achieve the same 0.5μm pore size. Due to the lack of the hierarchical channel maintenance mechanism of "skeleton support - branch filling" provided by the spider web structure, its pore structure is more likely to become dense and form a longer tortuous flow path, increasing the tortuosity and decreasing the proportion of through holes, thus exhibiting higher flow resistance under the same test air volume / pressure difference conditions. Comparative Example 7 has a denser pore structure under the same structural conditions, which is not conducive to the passage of water vapor molecules.

[0138] Test Example 4: Unidirectional Moisture Conductivity Test

[0139] (1) Fluorescent droplet tracing experiment

[0140] The test method is as follows: When using fluorescent droplet tracers for unidirectional moisture wicking tests, the sample is first cut into uniform size and labeled with upper / lower layers and direction. A 0.6 g / L fluorescent tracer solution is prepared (a small amount of fluorescent dye is added to deionized water or simulated sweat and mixed thoroughly). The sample is laid flat and fixed on a transparent support and a black background. Under fixed light source conditions, ultraviolet / blue light excitation and camera are turned on, and the exposure, distance, and angle are kept consistent. Then, a fixed volume of fluorescent droplets is added at the specified position using a micropipette. Two sets of experiments are conducted: "forward" (dropping on the upper layer and observing downward transmission) and "reverse" (dropping on the lower layer and observing upward transmission). Each set is repeated at least three times. After the droplets are added, continuous photography or video recording is taken at set time intervals to record the spread of the droplets on the surface and the time and intensity change of fluorescence on the other side, which serves as a qualitative and semi-quantitative evaluation of the unidirectional moisture wicking effect.

[0141] The results of the fluorescent droplet tracing experiment in Example 1 are as follows: Figure 8 As shown in Figure a, when the outer layer is flame-retardant adhesive, the droplets spread rapidly on the surface and are bound by its surface tension. At the same time, they are prevented from penetrating downward by the phenolic / aramid micro / nanofiber membrane, and more water remains on the surface. When the aramid layer is placed on the upper layer, the combined effect of the continuous capillary channels formed between the layers and the strong hydrophilicity of the adhesive causes the droplets to pass through the middle layer and reach the adhesive layer below.

[0142] (2) Moisture absorption rate (MMT) test

[0143] The testing method was as follows: The moisture transport properties of the samples were quantitatively assessed using a humidity management tester (M290, SDLATlas, USA). The test solution simulated human sweat and was a mixture of sodium chloride and distilled water, with a conductivity maintained at 16 ± 0.2 mS. Before testing, the samples were cut into 8cm × 8cm squares and pre-treated for humidity regulation.

[0144] The results are as follows Figure 8 As shown in b, when the aramid layer is on the outside, the water initially remains in the upper layer, but under the combined drive of capillary force and gravity, it successfully penetrates the three-layer structure within 120 seconds. However, when the orientation is reversed, the water mainly remains in the surface layer and fails to reach the bottom layer. This quantitative difference is highly consistent with the results of the fluorescent droplet tracing experiment.

[0145] In Comparative Example 1, the lack of an intermediate water-repellent layer causes the entire material to lose its unidirectional moisture-wicking properties. In Comparative Example 3, both the inner and outer knitted fabrics are changed to flame-retardant viscose weft plain weave fabric, exhibiting highly hydrophilic characteristics. Lacking the construction of pore size and humidity gradients, the entire material loses its unidirectional moisture-wicking properties. In Comparative Example 4, both the inner and outer knitted fabrics are changed to aramid double rib fabric, exhibiting slow water-wicking characteristics. Lacking the construction of pore size and humidity gradients, the entire material loses its unidirectional moisture-wicking properties. In Comparative Example 5, with the lower layer pore size increased to 600 μm, capillary suction in the lower layer is significantly weakened, interfacial liquid supply is more discontinuous, and drainage is more inclined towards "large-pore free flow," making it difficult to directionally trigger the "valve effect" of the intermediate layer. The reverse seepage path becomes smoother, ultimately resulting in a decrease in unidirectional moisture-wicking directionality and an increase in the risk of backflow.

[0146] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An electrospun phenolic / aramid micro / nanofiber composite filter material, characterized in that: It includes an outer flame-retardant adhesive layer, a central phenolic / aramid micro / nanofiber membrane, and an inner aramid water-conducting layer. The outer and inner layers are interlocked by quilting stitches. The flame-retardant adhesive layer is a weft-knitted structure woven from flame-retardant adhesive yarn; the phenolic / aramid micro / nanofiber membrane is formed by electrospinning and thermosetting cross-linking of a mixed solution of phenolic resin and aramid; the aramid water-wicking layer is a double rib knitted structure woven from aramid fiber yarn. The mass ratio of phenolic resin to aramid in the phenolic / aramid micro / nanofiber membrane is (1-1.42):1; The flame-retardant adhesive layer has a pore size of 522-536 μm, the phenolic / aramid micro / nanofiber membrane has a pore size of 0.3-1.3 μm, and the aramid water-conducting layer has a pore size of 214-237 μm. The relative rotation angle between the aramid water-conducting layer and the flame-retardant adhesive layer is 90°.

2. The electrospun phenolic / aramid micro / nanofiber composite filter material according to claim 1, characterized in that: The flame-retardant adhesive layer uses flame-retardant adhesive yarn with a fineness of 14-18S and a weaving density of 15-19 needles / 2.54cm; the aramid water-wicking layer uses aramid yarn with a fineness of 18-22S / 2 and a weaving density of 10-14 needles / cm.

3. The electrospun phenolic / aramid micro / nanofiber composite filter material according to claim 1, characterized in that: The quilting thread is aramid thread, and the stitch width is 1-1.5cm.

4. The method for preparing the electrospun phenolic / aramid micro / nanofiber composite filter material according to any one of claims 1-3, characterized in that: Includes the following steps: S1. Phenolic resin, aramid and solvent are mixed to obtain polymer spinning solution. The polymer spinning solution is electrospun to obtain pretreated phenolic / aramid micro / nanofiber membrane. The pretreated phenolic / aramid micro / nanofiber membrane is dried and then subjected to step-by-step temperature rise thermosetting cross-linking to obtain phenolic / aramid micro / nanofiber membrane. S2. A flame-retardant adhesive layer with a weft-knitted structure is prepared using flame-retardant viscose yarn on a flat knitting machine; S3. An aramid water-conducting layer with a double rib knitted structure is prepared using aramid fiber yarn through a flat knitting machine; S4. Arandex water-conducting layer, phenolic / aramid micro / nanofiber membrane, and flame-retardant adhesive layer are arranged in sequence and sewn together with aramid thread to obtain electrospun phenolic / aramid micro / nanofiber composite filter material.

5. The method for preparing the electrospun phenolic / aramid micro / nanofiber composite filter material according to claim 4, characterized in that: The parameters for electrospinning in step S1 are as follows: the spinning needle is 18-23G, the feed speed is 0.2-1.0mL / h, the receiving speed is 239-350rpm, the applied voltage is 15-30kV, the ambient temperature is 32±2℃, the relative humidity is 25±3%, and the receiving distance is 50-80cm. In step S2, the flame-retardant adhesive layer uses 16S flame-retardant adhesive yarn, and the knitting machine parameters are set as follows: needle pitch 12-16G, knitting density 15-19 stitches / kg. With a yarn length of 2.54cm, a weaving speed of 0.9-1.2m / s, and a yarn feeding tension of 4-5cN, a weft plain knitting structure is obtained with continuous V-shaped loop columns on the front and arc-shaped loop rows on the back. In step S3, the aramid water-wicking layer uses 20S / 2 double-strand aramid 1313 filament as the aramid yarn. The parameters of the flat knitting machine are set as follows: needle pitch is 10-14G, knitting density is 10-14 needles / cm, knitting speed is 0.9-1.2m / s, and yarn feeding tension is 5-6cN. The front and rear needle beds of the flat knitting machine simultaneously complete the knitting of the knitting needles and the purl needles, so that the fabric forms a rib knitting structure with loops on both sides.

6. The method for preparing the electrospun phenolic / aramid micro / nanofiber composite filter material according to claim 4, characterized in that: The step-by-step temperature-increasing thermosetting crosslinking process in step S1 is as follows: The temperature is raised to 70-80℃ within 0.5-1 hour and held for 4-5 hours; then raised to 80-90℃ within 0.5-1 hour and held for 4-5 hours; next, raised to 90-100℃ within 0.5-1 hour and held for 4-5 hours; then raised to 100-110℃ within 0.5-1 hour and held for 3-4 hours; then raised to 110-120℃ within 0.5-1 hour and held for 2-3 hours; then raised to 120-130℃ within 0.5-1 hour and held for 2-3 hours; then raised to 140-150℃ at a rate of 10-20℃ / h; finally, raised to 180-200℃ within 0.5-1 hour and the heating process is stopped.

7. The application of the electrospun phenolic / aramid micro / nanofiber composite filter material according to any one of claims 1-3 in fire protection equipment and high-temperature industrial fields.

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