Aerogel composite floe and method of making same

Abstract

The application discloses an aerogel composite floccus and a preparation method thereof, and belongs to the technical field of new materials. The aerogel composite floccus is aramid aerogel composite floccus; the aerogel composite floccus is composed of an upper layer of PP fiber, a middle layer of short-chopped aramid aerogel fiber and a lower layer of PP fiber from top to bottom; the upper layer, the middle layer and the lower layer of the aerogel composite floccus have a dry weight ratio of (37.5%-42.5%):(15%-25%):(37.5%-42.5%); and the aerogel composite floccus has an area density of 80-100. The application further discloses a preparation method of the aerogel composite floccus and application of the aerogel composite floccus in preparation of heat insulation and thermal insulation materials. The aerogel composite floccus is modified and grafted on aramid fiber based on dimethyl sulfoxide anion, the intramolecular / intermolecular hydrogen bond of aramid is destroyed, a flexible side group is introduced on the main chain, and the solubility of aramid fiber is greatly improved, so that the aramid fiber has more excellent properties.

Description

Technical Field

[0001] This invention relates to the field of new materials technology, and in particular to an aerogel composite flocculent and its preparation method. Background Technology

[0002] Fluff refers to small, thin flakes of flocculent sediment. It can also refer to sheet-like, cotton-like materials made of plant, animal, or chemical fibers for warmth, insulation, or shock absorption. Fluffy flakes are loose, sheet-like filling materials that must be attached to the inner lining when made into garments and undergo machine or hand quilting. In winter clothing materials, fluffy flakes provide good heat insulation and warmth due to their loose, air-filled structure.

[0003] With the development of technology, people's demand for thermal insulation materials is increasing. Existing main thermal insulation materials include: polystyrene foam, but it has poor fire resistance, low physical strength, average weather resistance, poor air permeability, and also suffers from dimensional instability and environmental problems; extruded polystyrene foam has poor fire resistance, poor air permeability, poor adhesion, dimensional instability, and environmental problems, and its price is relatively high; rigid polyurethane foam is expensive, highly flammable, has weather resistance and aging problems, requires high-precision on-site spraying processes, and also has environmental problems; rock wool and slag wool have problems with water absorption, strength, dust and fiber, and sedimentation, and their thermal conductivity is relatively high; glass wool suffers from a significant decrease in thermal insulation performance after water absorption, and its compressive and tensile strengths are low, and it also suffers from sedimentation and high thermal conductivity. Based on the above-mentioned defects in existing technologies, providing a thermal insulation material with good thermal insulation performance, lightweight flexibility, fire safety, and strong temperature and weather resistance has become a pressing technical problem to be solved. Summary of the Invention

[0004] Based on the technical problems to be solved by the present invention, the present invention proposes an aerogel composite flocculant and its preparation method based on the preparation of aramid aerogel fibers and the preparation of aramid aerogel composite flocculant.

[0005] One objective of this invention is to provide an aerogel composite filament, wherein the aerogel composite filament is an aramid aerogel composite filament; the aerogel composite filament is composed of an upper layer of PP fibers, a middle layer of chopped aramid aerogel fibers, and a lower layer of PP fibers from top to bottom; the dry weight ratio of the upper layer:middle layer:lower layer of the aerogel composite filament is (37.5%~42.5%):(15%~25%):(37.5%~42.5%); and the areal density of the aerogel composite filament is 80~100. .

[0006] Furthermore, the basis weight of the aerogel composite flocculent is no greater than 90 g / m². .

[0007] Further, the clo value of the aerogel composite flocculent is 1.70-1.90clo; preferably, the clo value of the aerogel composite flocculent is 1.81clo.

[0008] A second objective of this invention is to provide a method for preparing aerogel composite flocculent sheets, comprising: S1. Cut the aramid aerogel fibers into short pieces, add dimethyl sulfoxide and potassium hydroxide aqueous solution to obtain an aramid nanofiber dispersion; S2. The aramid nanofiber dispersion is squeezed into a coagulation bath through a syringe needle, and the wet gel fibers are collected by rotation and traction to obtain aramid wet gel fibers. S3. Add the aramid wet gel fiber to anhydrous ethanol and supercritically dry to obtain aramid aerogel fiber. S4. Select the short-cut fibers in the aramid aerogel fibers as the middle layer, and select PP fibers as the upper and lower layers respectively. After opening, removing impurities, laying web, needle punching and consolidation, and drying, the aerogel composite flocs are obtained.

[0009] Further, the step of cutting aramid aerogel fibers into short pieces and adding dimethyl sulfoxide and potassium hydroxide aqueous solution to obtain an aramid nanofiber dispersion includes: taking 40-60g of aramid fibers into short pieces, adding dimethyl sulfoxide, slowly adding 0.8-1.2g / mL of potassium hydroxide aqueous solution, stirring under nitrogen protection for 20-28h, and after the solution changes from colorless and transparent to dark red, taking it out and sealing it for storage to obtain the aramid nanofiber dispersion.

[0010] Further, the step of extruding the aramid nanofiber dispersion through a syringe needle into a coagulation bath, and then rotating and collecting the wet gel fibers to obtain aramid wet gel fibers includes: using a constant flow peristaltic pump to extrude the aramid nanofiber dispersion through a 200~2000μm syringe needle into a coagulation bath of a proton donor solution or metal salt solution; rotating and collecting the wet gel fibers using a constant speed motor; the color of the extruded aramid nanofiber dispersion gradually changes from dark red to light yellow in the coagulation bath, thus obtaining aramid wet gel fibers.

[0011] Further, the step of adding the aramid wet gel fiber to anhydrous ethanol and supercritically drying to obtain aramid aerogel fiber includes: adding 6 to 10 times the mass of the aramid wet gel fiber to anhydrous ethanol, letting it stand; replacing the anhydrous ethanol once every 6 to 10 hours, for a total of 5 to 7 times; supercritical drying; and depressurizing and cooling to obtain aramid aerogel fiber.

[0012] Further, the chopped fibers from the aramid aerogel fibers are selected as the middle layer of the floc, and PP fibers are selected as the upper and lower layers of the floc, respectively. After opening, impurity removal, web formation, needle punching and consolidation, and drying, the aerogel composite floc is obtained, comprising: S41. Select the short-cut fibers in the aramid aerogel fibers as the middle layer of the aerogel composite filament, and select PP fibers as the upper and lower layers of the aerogel composite filament respectively; mix and loosen the PP fibers in the upper and lower layers of the aerogel composite filament, comb to remove impurities, and lay the web to obtain a two-dimensional PP fiber web. S42. The two-dimensional PP fiber mesh is added to the chopped aramid aerogel fiber, and needle-punched to consolidate it. The needle-punching density is 60~62 needles / min. The upper, middle and lower layers of the aerogel composite floc are reinforced with fibers and placed in an oven at 75℃~85℃ for 12~36h to obtain the aramid aerogel composite floc consisting of the upper, middle and lower layers.

[0013] Furthermore, the proton donor solution is deionized water, ethanol, or hydrochloric acid.

[0014] The third objective of this invention is to provide an application of aerogel composite flocs in the preparation of thermal insulation and heat preservation materials.

[0015] Compared with the prior art, the present invention proposes an aerogel composite flocculent and its preparation method, which has the following beneficial effects: The aerogel composite flocs proposed in this invention are based on the modification and grafting of aramid fibers with dimethyl sulfoxide anions. The intramolecular / intermolecular hydrogen bonds of aramid are broken, and flexible side groups are introduced into the main chain, thereby greatly improving the solubility of aramid fibers and endowing aramid fibers with more excellent properties.

[0016] Furthermore, the aerogel composite wadding prepared by this invention has superior thermal insulation performance compared with traditional wadding, and its clo value is much greater than that of down. Attached Figure Description

[0017] Figure 1 A diagram illustrating a method for preparing aramid nanofiber aerogel yarn according to an embodiment of the present invention is shown. Figure 2 The following is a SEM image of an aramid aerogel fiber according to an embodiment of the present invention, wherein (a) is a 100 μm surface SEM image; (b) is a 4 μm surface SEM image; (c) is a 20 μm surface SEM image; and (d) is a cross-sectional SEM image. Figure 3 The figure showing the effect of a coagulation bath component on the mechanical strength of aramid aerogel fibers according to an embodiment of the present invention is illustrated. Figure 4A graph showing the effect of spinning solution concentration and draw ratio on the mechanical properties of fibers according to an embodiment of the present invention is shown. Detailed Implementation

[0018] Exemplary embodiments of the present application will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present application are shown in the drawings, it should be understood that the present application may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this application will be thorough and complete, and will fully convey the scope of the present application to those skilled in the art.

[0019] Unless otherwise specified, the technical means used in the following embodiments are conventional means well known to those skilled in the art, and the reagents and materials in this invention are obtained from the market or other public channels.

[0020] The experimental materials and equipment involved in this invention mainly include, but are not limited to: Reagents (see Table 1): Table 1 List of Main Reagents and Raw Materials instrument: The main components include: supercritical drying equipment (Fanrui Yihui Composite Materials Co., Ltd.); forced-air drying oven (Zhengzhou Shengyuan Instrument Co., Ltd., model DHG-9140A); thermal conductivity tester (JW-III, China Academy of Building Research, Zhongji Group); field emission scanning electron microscope (SEM), (Germany - ZEISS-GeminiSEM360); vacuum freeze dryer (LGJ-12A, Beijing Sihuan Qihang Technology Co., Ltd.); and universal testing machine (UTM4204, Shenzhen Sansi Zongheng Technology Co., Ltd.).

[0021] The technical principle of the aerogel composite flocculent sheet and its preparation method described in this invention mainly includes: The presence of numerous hydrogen bonds between the molecular chains of aramid fibers gives them strong resistance to chemical corrosion; only high-concentration strong acids (concentrated sulfuric acid and hydrofluoric acid) can dissolve them. Under anhydrous conditions, strong bases such as sodium hydride (NaH) react with DMSO to generate dimethyl sulfoxide (DMSO) anions. DMSO anions are highly reactive and can react with protons containing weak acids (such as amines, amides, acetylene, and weak acid hydrocarbons). Therefore, DMSO anions can be used to modify and graft aramid fibers. The DMSO anions cause the amide bonds on PPTA molecules to lose protons, forming highly reactive nitrogen anions. These nitrogen anions then undergo related substitution reactions to obtain N-substituted aramid fibers with better solubility. In this process, the intramolecular / intermolecular hydrogen bonds of aramid are broken, introducing various flexible side groups into the main chain, thereby significantly improving the solubility of aramid fibers and endowing them with more superior properties.

[0022] The aerogel composite flocs prepared in this invention use aramid fibers, which exhibit fast gelation speed, stable gelation, and good mechanical properties after gelation, as the nanobuilding unit material. The aramid fibers are dehydrogenated from the amide bonds on their molecular chains by a strong base, generating a large number of negative charges on the molecular chain surface. This ultimately leads to the detachment of the aramid fibrils from the fiber matrix, yielding aramid nanofibers. The aramid nanofibers obtained by the deprotonation method are high-strength one-dimensional polymer nanowire nanobuilding units with diameters ranging from 5 nm to 40 nm and average lengths exceeding 1 μm. The average diameter and length vary depending on the strong base used. Due to the electrostatic interactions caused by the large number of negative charges on the surface of the aramid nanofibers, they are highly stable in the dispersion, showing no sedimentation even after a year of sealed storage. Similarly, because of the deprotonation exfoliation method, when a certain amount of proton donor is added to the dispersion, the negative charges on the surface of the aramid nanofibers combine with hydrogen ions to restore the amide bonds, the electrostatic repulsion disappears, and the nanofiber dispersion becomes unstable and settles. When nanofibers come into contact, the hydrogen bonding between the amide bonds on their surfaces firmly binds them together, forming stable connection points. A large number of nanofibers overlap to form a three-dimensional network, thus forming an aramid nanofiber gel. The formation of the aramid nanofiber gel is a typical assembly method of nano-building units, which forms the basis for the preparation of the aerogel composite flocs of this invention.

[0023] Based on the above principles, this invention proposes an aerogel composite flocculent sheet and its preparation method. Please refer to [link to relevant documentation]. Figure 1 Aerogel fiber material was prepared by combining aramid (ANF) aerogel fiber with PP meltblown fiber, and then the aerogel fiber material was used to prepare flocs, resulting in aramid aerogel composite flocs. The preparation method includes: S1. Take 40-60g of aramid fiber short cuts and put them into an Erlenmeyer flask. Add dimethyl sulfoxide to prepare aramid short cut fibers with a concentration of 8-12g / L. Slowly add 0.8-1.2g / mL potassium hydroxide aqueous solution. Stir for 20-28h under nitrogen protection. After the solution changes from colorless and transparent to dark red, take it out, seal and store it to obtain aramid nanofiber dispersion. S2. The aramid nanofiber dispersion is extruded through a 200-2000 μm syringe needle into a coagulation bath containing a proton donor solution or a metal salt solution using a constant-flow peristaltic pump. A constant-speed motor is used to rotate and collect the wet gel fibers, preventing the fine streams of the aramid nanofiber dispersion from stacking and agglomerating, thus avoiding loss of fiber morphology and effectively controlling the uniformity of fiber diameter. The color of the extruded aramid nanofiber dispersion stream gradually changes from dark red to light yellow in the coagulation bath, yielding aramid wet gel fibers. By adjusting the diameter of the extrusion needle and the composition and concentration of the coagulation bath, different aramid wet gel fibers can be obtained. S3. Place the aramid wet gel fiber in a beaker, add 6-10 times the mass of the aramid wet gel fiber in anhydrous ethanol, and let stand. Replace the anhydrous ethanol every 6-10 hours, for a total of 5-7 times. Supercritical drying replaces the ethanol inside the condensed fiber with supercritical ethanol. By reducing the pressure and temperature, aramid aerogel fibers are obtained.

[0024] S4. Select chopped aramid aerogel fibers as the middle layer of the floc, and select PP fibers as the upper and lower layers of the floc, respectively. The dry weight ratio of the upper layer:middle layer:lower layer is (37.5%~42.5%):(15%~25%):(37.5%~42.5%). Mix and loosen the PP fibers in the upper and lower layers, comb to remove impurities, and obtain a two-dimensional PP fiber web through a cross-curtain web laying machine. Add the two-dimensional PP fiber web to the chopped aramid aerogel fibers, needle-punch to consolidate, and needle-punch at a density of 60~62 needles / min. Reinforce the three layers of fibers (upper, middle, and lower) and place them in an oven at 75℃~85℃ for 12~36 hours to obtain an aramid aerogel composite floc consisting of the upper, middle, and lower layers.

[0025] The prepared aramid aerogel fibers had a diameter of 400-600 μm, consistent with the inner diameter of the syringe needle, indicating that the traction rate of the gel fibers was consistent with the extrusion rate of the dispersion. The cross-section showed that the internal structure of the aramid aerogel fibers was a three-dimensional nanonetwork with nano-overlapping structures, representing a stable gel structure. The basis weight of the floc was tested according to the national standard GB / T 4669-2008, and the basis weight of the floc was ≤90. According to the national standard GB / T 35762-2017, the thermal insulation performance was tested using the flat plate method. Compared with traditional wadding, aramid aerogel composite wadding has excellent thermal insulation performance, with a Clo value far greater than that of down, reaching 1.81 Clo.

[0026] Example 1 This invention proposes a method for preparing aramid nanofibers.

[0027] Mainly includes: Add 50g of aramid fiber to a three-necked flask, then add dimethyl sulfoxide (DMSO). The total volume of the chopped aramid fiber and DMSO is 5L. Dissolve 50g of potassium hydroxide in 50mL of deionized water. Stir under nitrogen protection for 24h. After the solution changes from colorless and transparent to dark red, remove it, seal it, and store it. This yields a 10mg / mL aramid nanofiber dispersion.

[0028] result: Aramid nanofibers have a diameter of 5–40 nm and a length >1 μm, and the dispersion is a dark red homogeneous phase. The nanofibers carry a negative charge on their surface, which imparts long-term stability to the dispersion and provides high-strength building blocks for the gel network.

[0029] Example 2 This invention proposes a method for preparing aramid wet gel fibers.

[0030] Mainly includes: A constant-flow peristaltic pump was used to expel 50-100 mL of a 10 mg / mL (i.e., 1.0 wt%) aramid nanofiber dispersion through a 500 μm needle with a 10 mL syringe volume into a coagulation bath composed of deionized water proton donor solution. The needle diameter was 500 μm. A constant-speed motor was used to rotate the pump at a traction rate of 5-10 cm / min for 1-2 hours to traction and collect the wet gel fibers. Approximately 5 g of wet gel fibers could be obtained from every 100 mL of dispersion. This method avoids the stacking and adhesion of fine streams of aramid nanofiber dispersion, loss of fiber morphology, and ensures uniform fiber diameter.

[0031] result: Please see Figure 3 It can be observed that the extruded aramid nanofiber dispersion gradually changes color from dark red to pale yellow in the coagulation bath, indicating the formation of gel fibers. The extrusion needle diameter ranges from 200 μm to 2000 μm, and the coagulation bath consists of a proton donor solution (deionized water, ethanol, hydrochloric acid) or a metal salt solution. The concentration of the aramid nanofiber dispersion is 10 mg / mL. Different gel fibers are obtained by adjusting the diameter of the extrusion needle, the composition of the coagulation bath, and its concentration. The wet gel fibers are pale yellow, with a diameter consistent with the needle (500 μm), and their mechanical strength is controlled by the coagulation bath. The color change indicates that protonation is complete, and hydrogen bonds are rebuilt to form a three-dimensional network.

[0032] Example 3 This invention proposes a method for preparing aramid aerogel fibers.

[0033] Mainly includes: There are two methods for preparing aerogel fibers from gel fibers: freeze drying and supercritical drying.

[0034] Method 1, freeze-drying technology: Place 10-20g of wet aerogel fibers in a beaker, add 80-160mL, or 80-160g (8 times the mass) of deionized water, and let stand. Replace the deionized water every 6 hours, for a total of 6 replacements. After 6 replacements, replace the deionized water with an equal volume of 80-160mL of tert-butanol aqueous solution (concentration gradient of 0%, 20%, 40%, 60%, 80%, 100%), and then replace the deionized water with 100-200mL of tert-butanol aqueous solution every 8 hours, for a total of 2 replacements. The above replacements are performed using tert-butanol aqueous solutions with concentrations of 0%, 20%, 40%, 60%, 80%, and 100%, respectively, to obtain different aerogel fibers. The wet aerogel fibers after different solvent replacements, through gradient tert-butanol replacement, reduce capillary forces and prevent network collapse during freeze-drying. After the solvent replacement is completed, the gel fiber is frozen at -20°C for 8 hours and then transferred to a freeze dryer for vacuum drying for 24 hours. The internal pressure of the freeze dryer is 0.5 Mbar and the cooling temperature is -50°C.

[0035] Method 2, Supercritical Drying Technology: Place 10-20g of wet gel fiber in a beaker, add 80-160mL of anhydrous ethanol (8 times its mass), and let it stand. Replace the anhydrous ethanol every 8 hours, for a total of 6 replacements. Use a supercritical carbon dioxide drying device to replace the ethanol inside the gel fiber with supercritical carbon dioxide. Aerogel fibers are obtained by depressurizing and cooling.

[0036] result: Although freeze drying can be used to prepare aramid aerogel fibers, this method is not suitable for the present invention due to the scale of the dried samples and the time cost.

[0037] Please see Figure 2 Scanning electron microscopy images show that the diameter of the aramid aerogel fibers is approximately 500 μm. Figure 2 a) The traction rate is consistent with the inner diameter of the syringe needle, indicating that the traction rate of the aramid aerogel fiber is consistent with the extrusion speed of the dispersion. If the traction rate is too fast, the fiber will become thinner and break, preventing stable and continuous preparation of gel fibers. If the traction rate is too slow, the gel will stack and adhere, losing its fiber morphology. High-magnification observation of the fiber surface revealed a relatively dense structure with surface wrinkles. Figure 2 b and Figure 2 c). Its cross-section ( Figure 2d) Magnified observation reveals that the internal structure of aramid aerogel fibers is a three-dimensional nanonetwork of overlapping nanofibers, indicating that disordered aramid nanofibers overlap to form a stable gel structure after instability in the dispersion. The gelation process occurs with solvent diffusion, and a gel network gradually forms along the solvent diffusion path. At this point, the diffusion rate of nanofibers is lower than that of the solvent, thus forming a stable gel after instability. The coagulation bath composition (DMSO / pH) and spinning parameters (concentration / draw ratio) can regulate the mechanical properties of the fibers, providing a high-strength intermediate layer for composite flocs.

[0038] Example 4 This invention proposes an experiment on the effect of aramid nanofiber dispersion concentrations of 2 mg / ml, 4 mg / ml, 6 mg / ml, 8 mg / ml, and 10 mg / ml on the mechanical properties of aramid aerogel fibers.

[0039] Mainly includes: Coagulation bath test: (1) DMSO volume fraction: 0%, 10%, 20%, 30%, 40%, 50%, fixed pH=7; pH values ​​are 1, 3, 5, 7, 9, 11 respectively (fixed DMSO=10%). Spinning experiment: (1) Dispersion concentration: 5, 10, 15, 20 mg / mL (fixed draw ratio 1.5); (2) Draw ratio: 1.0, 1.5, 2.0, 2.5, 3.0 (fixed concentration 10mg / mL); 3 batches of fiber were prepared for each group, and the tensile strength was tested after supercritical drying (ASTM D3822 standard, tensile speed 5mm / min).

[0040] result: The results are as follows Figure 3 and Figure 4 As shown, mechanical strength decreases with increasing DMSO concentration and increases with increasing acidity; high concentration and draw ratio significantly improve fiber strength. When the concentration of the aramid nanofiber dispersion increases from 10 mg / mL to 20 mg / mL, the tensile strength of the aramid aerogel fiber increases from 32.4 MPa to 58.6 MPa; when the draw ratio increases from 1.5 to 3.0, the strength increases from 46.4 MPa to 67.3 MPa. Under the optimal process (concentration 20 mg / mL + draw ratio 3.0), the fiber strength reaches 68.9 MPa, demonstrating that high concentration and high draw ratio synergistically strengthen the fiber network structure.

[0041] This invention analyzes the factors affecting the mechanical properties of fibers and fits a three-dimensional graph. Please refer to [link / reference]. Figure 3The mechanical strength of aramid aerogel fibers decreases with increasing DMSO content in the coagulation bath; however, pH value shows that the fiber mechanical strength increases with increasing acidity. The coagulation bath composition (DMSO / pH) and spinning parameters (concentration / draw ratio) can regulate the fiber mechanical properties.

[0042] Please see Figure 4 The strength of aramid aerogel fibers increases with the increase of aramid nanofiber dispersion concentration; the increase of draw ratio also gradually increases the mechanical strength of aramid aerogel fibers. The coagulation bath composition (DMSO / pH) and spinning parameters (concentration / draw ratio) can regulate the mechanical properties of the fibers.

[0043] Furthermore, the concentration of the aramid nanofiber dispersion is one of the key factors affecting the diameter of aramid aerogel fibers. During the formation of aramid aerogel fibers, such as electrospinning, the concentration of the aramid nanofiber dispersion directly affects the diameter of the aramid aerogel fibers. As the concentration of the aramid nanofiber dispersion increases, the diameter of the aramid aerogel fibers also increases accordingly, because the polymer chains in the high-concentration solution are more likely to entangle with each other, forming larger aramid aerogel fiber bundles. Simultaneously, a high concentration of aramid nanofiber dispersion results in a greater tensile force under the action of an electric field, which is beneficial for forming aramid aerogel fibers with larger diameters.

[0044] Furthermore, during the molding process of aramid aerogel fibers, the concentration of the aramid nanofiber dispersion affects the arrangement and orientation of the polymer chains. In low-concentration solutions, the polymer chains are loosely arranged, making it difficult to form highly oriented aramid aerogel fiber structures; while in high-concentration aramid nanofiber dispersions, the polymer chains are more tightly arranged, which is conducive to forming highly oriented aramid aerogel fiber structures. Therefore, appropriately increasing the solution concentration can improve the orientation degree of aramid aerogel fibers, thereby improving their mechanical properties.

[0045] Furthermore, the effect of aramid nanofiber dispersion concentration on the properties of aramid aerogel fibers is mainly reflected in mechanical properties and thermal stability. In high-concentration solutions, the polymer chains are more tightly packed together, forming a more stable aramid aerogel fiber structure. Therefore, aramid aerogel fibers prepared from high-concentration solutions typically exhibit higher mechanical strength and modulus. Simultaneously, aramid aerogel fibers prepared from high-concentration solutions also possess higher thermal stability, maintaining good performance even at high temperatures.

[0046] Example 5 This invention presents an experimental method for preparing aramid aerogel composite flocculent sheets.

[0047] Mainly includes: Raw material preparation To improve the warmth retention and resilience of the wadding, this invention uses a combination of aramid aerogel chopped fibers and PP meltblown fibers to prepare the aerogel wadding. This combination improves the longitudinal and transverse tensile strength of the wadding and forms a two-component warm wadding. The two-component wadding raw materials are as follows: This wadding is assembled from three parts: an upper layer, a middle layer, and a lower layer. The upper and lower layers are made of PP fibers, with the dry weight ratio of PP fibers in the upper and lower layers being 75%~85%. The middle layer contains 15%~25% aramid aerogel chopped fibers, with an areal density of 80~100. PP fiber specifications: fineness 2~3 denier, length 5~7cm During the preparation of the fibrous flakes, the upper and lower layers of PP fibers are first opened. To reduce the generation of excessive fibrous material during processing, 5% deionized water (relative to the mass of the PP fibers) is atomized and sprayed before mixing. The PP fibers are then calculated based on their areal density, ranging from 15 to 25. The fibers were placed in a constant temperature oven at 80°C for 24 hours and then removed to obtain the prepared fibers.

[0048] The prepared fibers are mixed and opened by a cotton feeder and an opening machine. After the opened fibers are further combed to remove impurities, they are then passed through a cross-laid web machine to finally form a two-dimensional PP fiber web. The web laying process mainly includes an opening machine → a combing machine → a cross-laid web machine.

[0049] The prepared aramid aerogel chopped fibers (uniform basis weight two-dimensional PP fiber web with an areal density of 40) were added to the upper and lower two-dimensional PP fiber webs. Then, the needle-punching consolidation method is used, with a needle-punching density of 60-62 needles / min, to consolidate the three layers of fibers. The semi-finished product is then placed in an 80℃ oven for 24 hours to obtain a semi-finished wadding. After needle-punching consolidation, the finished wadding is dried at 80℃ for 24 hours, requiring no further processing.

[0050] result: Please refer to Table 2. The thermal conductivity of the aramid aerogel composite flocculent is the lowest and the thermal insulation performance is the best when the length is 11cm.

[0051] Table 2 Comparison of flocs prepared with different fiber lengths Comparative Example This invention presents a performance comparison experiment between aramid aerogel composite flocs and existing flocs.

[0052] Mainly includes: Take the same areal density (90) The aramid aerogel composite wadding, down, 3M cotton, and wool wadding were tested for clo value and thermal conductivity according to GB / T35762-2017.

[0053] result: Please refer to Table 3. When the prepared aramid aerogel composite fiber is cut to 11cm, the thickness of the three-layer wadding is approximately 10.04mm, exhibiting the best warmth retention effect. The basis weight of the wadding was tested according to the national standard GB / T 4669-2008, and the basis weight of the wadding is ≤90. Furthermore, according to the national standard GB / T 35762-2017, the heat insulation performance was tested using the plate method. It was found that compared with traditional wadding, ANF-PP aerogel fiber composite wadding has excellent heat insulation performance, with a Clo value much greater than that of down, reaching 1.81 Clo. This invention adopts a three-layer structure (PP / aramid aerogel / PP) + aramid nanofiber gelation technology, and its advantages include: (1) heat insulation: Clo value 1.81 Clo, 50% higher than down (1.2 Clo); (2) lightweight: surface density ≤90 (3) Stability: Aramid network is resistant to high temperature (>450℃), and PP layer enhances mechanical properties; (4) Process controllability: Coagulation bath / spinning parameters are adjustable (see Figure 3 and Figure 4 ).

[0054] Table 3 Clo values ​​of aramid aerogel fiber composite sheets and common fiber sheets It should be noted that the term "comprising," or any other variation thereof, is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0055] The above are merely embodiments of this application and are not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. An aerogel composite flocculent sheet, characterized in that, The aerogel composite flocculent is an aramid aerogel composite flocculent; The aerogel composite sheet is composed of an upper layer of PP fibers, a middle layer of chopped aramid aerogel fibers, and a lower layer of PP fibers from top to bottom. The dry weight ratio of the upper, middle, and lower layers of the aerogel composite flocculent is (37.5%~42.5%): (15%~25%): (37.5%~42.5%). The areal density of the aerogel composite flocs is 80~100. .

2. The aerogel composite flocculent sheet according to claim 1, characterized in that, The basis weight of the aerogel composite flocculent is no more than 90 g / m². .

3. The aerogel composite flocculent sheet according to claim 1, characterized in that, The clo value of the aerogel composite flocs is 1.70~1.90clo.

4. The method for preparing the aerogel composite flocculent sheet according to any one of claims 1 to 3, characterized in that, include: S1. Cut the aramid aerogel fibers into short pieces, add dimethyl sulfoxide and potassium hydroxide aqueous solution to obtain an aramid nanofiber dispersion; S2. The aramid nanofiber dispersion is squeezed into a coagulation bath through a syringe needle, and the wet gel fibers are collected by rotation and traction to obtain aramid wet gel fibers. S3. Add the aramid wet gel fiber to anhydrous ethanol and supercritically dry to obtain aramid aerogel fiber. S4. Select the short-cut fibers in the aramid aerogel fibers as the middle layer, and select PP fibers as the upper and lower layers respectively. After opening, removing impurities, laying web, needle punching and consolidation, and drying, the aerogel composite flocs are obtained.

5. The method for preparing aerogel composite flocs according to claim 4, characterized in that, The process involves cutting aramid aerogel fibers into short sections and adding dimethyl sulfoxide and potassium hydroxide aqueous solution to obtain an aramid nanofiber dispersion, comprising: Take 40-60g of aramid fiber short pieces, add dimethyl sulfoxide, and slowly add 0.8-1.2g / mL of potassium hydroxide aqueous solution. Stir under nitrogen protection for 20-28h. After the solution changes from colorless and transparent to dark red, take it out, seal and store it to obtain aramid nanofiber dispersion.

6. The method for preparing aerogel composite flocculent sheets according to claim 4, characterized in that, The process of extruding the aramid nanofiber dispersion through a syringe needle into a coagulation bath, and then rotating and collecting the wet gel fibers to obtain aramid wet gel fibers includes: The aramid nanofiber dispersion is extruded through a 200-2000 μm syringe needle using a constant flow peristaltic pump into a coagulation bath containing a proton donor solution or a metal salt solution. The wet gel fibers are collected by rotating a constant speed motor. The extruded aramid nanofiber dispersion gradually changes color from dark red to light yellow in the coagulation bath, yielding wet aramid gel fibers.

7. The method for preparing aerogel composite flocculent sheets according to claim 4, characterized in that, The step of adding the aramid wet gel fiber to anhydrous ethanol and supercritical drying to obtain aramid aerogel fiber includes: Add 6-10 times the mass of the aramid wet gel fiber to anhydrous ethanol and let it stand. Replace the anhydrous ethanol every 6-10 hours for a total of 5-7 times. Perform supercritical drying, reduce pressure and temperature to obtain aramid aerogel fiber.

8. The method for preparing aerogel composite flocculent sheets according to claim 4, characterized in that, The process involves selecting short-cut fibers from the aramid aerogel fibers as the middle layer of the floc, and using PP fibers as the upper and lower layers of the floc, respectively. After opening, impurity removal, web formation, needle punching and consolidation, and drying, the aerogel composite floc is obtained, comprising: S41. Select the short-cut fibers in the aramid aerogel fibers as the middle layer of the aerogel composite filament, and select PP fibers as the upper and lower layers of the aerogel composite filament respectively; mix and loosen the PP fibers in the upper and lower layers of the aerogel composite filament, comb to remove impurities, and lay the web to obtain a two-dimensional PP fiber web. S42. The two-dimensional PP fiber mesh is added to the chopped aramid aerogel fiber, and needle-punched to consolidate it. The needle-punching density is 60~62 needles / min. The upper, middle and lower layers of the aerogel composite floc are reinforced with fibers and placed in an oven at 75℃~85℃ for 12~36h to obtain the aramid aerogel composite floc consisting of the upper, middle and lower layers.

9. The method for preparing aerogel composite flocs according to claim 6, characterized in that, The proton donor solution is deionized water, ethanol, or hydrochloric acid.

10. The application of the aerogel composite flocs according to any one of claims 1 to 3 or the aerogel composite flocs prepared by the preparation method of any one of claims 5 to 8 in the preparation of heat insulation and thermal insulation materials.

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