A special fiber material and a method for producing the same

Abstract

The application provides a special fiber material and a preparation method thereof, and belongs to the technical field of polymer composites, and comprises the following steps: mixing cellulose and an ethanol solution, adding polyvinyl alcohol and a 3-glycidoxypropyltrimethoxysilane solution, adjusting pH to be acidic, heating, performing suction filtration and drying to obtain modified cellulose; mixing expanded graphite, deionized water, ammonium persulfate and dilute sulfuric acid, heating, cooling, dropwise adding aminopolyethylene glycol silane, heating, washing and drying to obtain modified expanded graphite; mixing the modified cellulose, the modified expanded graphite, phosphate ester-based montmorillonite, 3-(isobutenoyloxy)propyltrimethoxysilane, bisphenol A diglycidyl ether and 2-methylimidazole, stirring, heating, defoaming, and performing two-stage constant-temperature treatment to prepare the special fiber material. The special fiber material has good flame retardancy, mechanical strength, water resistance and filtration performance, and can be applied to various high-quality organic composite boards, filter membranes and the like.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, specifically to a special fiber material and its preparation method. Background Technology

[0002] Cellulose is a safe and non-toxic natural polymer material derived from renewable resources such as wood, cotton, and straw. Its advantages, including abundant reserves, low price, renewability, and environmental friendliness, have made it a focus of attention in the field of green and sustainable materials. With social development and increasing environmental protection requirements, special fiber materials prepared using cellulose are gradually being applied in areas such as flame-retardant boards and filter membranes.

[0003] Specialty fiber materials based on cellulose not only possess inherent advantages such as lightweight and low cost, but their flame-retardant properties can also be enhanced through compounding with functional inorganic fillers, thereby expanding their applications in the field of flame-retardant materials. To improve the flame retardancy of materials, a common method is to add inorganic flame-retardant fillers such as expanded graphite to the material system. For example, patent application CN105694505A discloses a surface powdering flame-retardant process for hemp fiber composite materials. In this scheme, expanded graphite is added to the hemp fiber composite material through blending, thereby improving the flame retardancy of the hemp fiber composite material to a certain extent. However, the expanded graphite in this scheme does not form an effective chemical bond with the surrounding material, causing the expanded graphite to enlarge the material pores when heated and to detach from the pores when cooled and contracted, resulting in powder shedding and thus reducing the long-term flame retardancy of the material.

[0004] Furthermore, cellulose contains a large number of hydroxyl groups on its surface, making it highly hydrophilic and hygroscopic. In humid environments, the interaction forces between fibers weaken, and as the moisture content increases, the network structure expands and deforms, leading to a decrease in the overall mechanical strength of the special fiber material.

[0005] In summary, there is a need to provide a special fiber material and its preparation method to solve the problems existing in the prior art. Summary of the Invention

[0006] In view of this, the present invention provides a special fiber material and its preparation method, which can not only avoid the shedding of expanded graphite to provide good long-term flame retardancy, but also improve the water resistance and mechanical strength of the special fiber material.

[0007] To achieve the above objectives, a special fiber material and its preparation method are provided, comprising the following steps:

[0008] S1. Disperse cellulose in an ethanol solution, stir, add polyvinyl alcohol and 3-glycidoxypropyltrimethoxysilane solution, adjust the pH of the solution to acidic, heat the reaction, filter, wash, vacuum dry, and cool to obtain modified cellulose;

[0009] S2. Mix expanded graphite and deionized water, add ammonium persulfate and dilute sulfuric acid, heat to react, cool, add amino polyethylene glycol silane dropwise, heat and stir, filter, wash, vacuum dry, and sieve to obtain modified expanded graphite.

[0010] S3. Mix and stir modified cellulose and modified expanded graphite, add 3-(isobutenoyloxy)propyltrimethoxysilane, bisphenol A diglycidyl ether and 2-methylimidazole, heat and shear to disperse, degas, pour into a mold, and after two stages of constant temperature treatment, cool to demold, dry to obtain special fiber material.

[0011] This invention modifies cellulose with 3-glycidoxypropyltrimethoxysilane, introducing epoxy groups onto its surface. Simultaneously, the hydroxyl groups of cellulose are substituted to form siloxane bonds and organosilicon segments, giving cellulose durable hydrophobicity and thus suppressing its hygroscopicity in humid environments. Furthermore, due to its high surface mineralization, expanded graphite is neither hydrophilic nor oleophilic, often making it difficult to disperse uniformly in conventional systems and leading to poor compatibility with cellulose. This invention acidifies expanded graphite and then treats it with amino-polyethylene glycol silane to obtain modified expanded graphite with surface-grafted amino and hydroxyl groups. The epoxy groups of the modified cellulose can undergo ring-opening reactions with the amino and hydroxyl sites on the modified expanded graphite. Under the catalysis of 2-methylimidazole and under two-stage isothermal treatment conditions, it crosslinks with 3-(isobutenoyloxy)propyltrimethoxysilane to form a three-dimensional network structure. This not only improves the compatibility and dispersibility of expanded graphite in materials but also enhances the overall mechanical strength of the special fiber material.

[0012] Furthermore, expanded graphite undergoes significant expansion and contraction at high temperatures. The periodic changes in its interlayer volume can easily lead to increased porosity in the network structure of specialty fiber materials, causing expanded graphite to peel off and detach from the fiber materials, thereby weakening their physicochemical properties. In this invention, expanded graphite is surface-modified with amino-polyethylene glycol silane. The silane ends form stable Si-O anchoring bonds on the expanded graphite surface, while the amino groups can undergo ring-opening reactions with the epoxy groups on the modified cellulose surface, resulting in chemical bonding. The PEG segments of the amino-polyethylene glycol silane molecules possess flexible and reversible stretchability: when the expanded graphite layer expands, the PEG segments moderately contract to offset the volume change; when the expanded graphite contracts, the PEG segments extend to fill the interfacial voids. Through this dynamic adaptation mechanism, the increase in interfacial porosity is effectively avoided, preventing expanded graphite from detaching from the fiber material. Meanwhile, modified expanded graphite can still expand rapidly when heated, forming a dense carbonaceous heat insulation layer that acts as a barrier to the transfer of heat and oxygen, thereby improving the long-term flame retardant performance of special fiber materials.

[0013] Optionally, in step S3, when the modified cellulose and modified expanded graphite are mixed and stirred, phosphate-based montmorillonite is also added, wherein the phosphate-based montmorillonite is obtained by treating montmorillonite with triethyl phosphate.

[0014] In this invention, montmorillonite is treated with triethyl phosphate to introduce phosphate groups into its lamellar structure, resulting in phosphate-based montmorillonite. Phosphate-based montmorillonite no longer exhibits strong hydrophilic properties but instead shows better compatibility with modified cellulose, making it easier to disperse in the fiber network and form a uniformly distributed layered structure. Simultaneously, under heat curing conditions, the phosphate groups can undergo ring-opening condensation reactions with the epoxy groups on the surface of the modified cellulose, forming phosphate ester bonds and ether bonds that crosslink, thereby constructing an organic-inorganic crosslinked network. Phosphate-based montmorillonite acts as a framework embedded between the fiber pores. When the fiber network changes under external force, the interlamellar spacing can offset the stress through slippage or re-stacking, preventing the fiber network from collapsing and improving the mechanical strength of the material. Furthermore, the phosphate groups promote the carbonization of the surrounding modified cellulose when heated, forming a carbonaceous thermal insulation barrier in synergy with the modified expanded graphite, further enhancing the flame-retardant properties of the material.

[0015] Optionally, the phosphate-based montmorillonite is prepared by mixing montmorillonite and deionized water, ultrasonically dispersing for 10-15 min, adding anhydrous ethanol, stirring for 10-20 min, adding triethyl phosphate, heating to 50-70°C, stirring for 60-90 min, filtering, washing 2-3 times with anhydrous ethanol and deionized water, vacuum drying at 80-90°C for 1-2 h, and passing through a 50-mesh sieve.

[0016] In this invention, triethyl phosphate is allowed to fully interact with the surface of montmorillonite through ultrasonic dispersion, temperature-controlled reaction, and washing, resulting in uniform and stable modification. By passing the 50-mesh sieve, the uniformity of the particle size of the phosphate-based montmorillonite is further improved, which is beneficial for its dispersion in fiber systems.

[0017] Optionally, dry cellulose and 70 wt% ethanol solution are mixed and stirred for 20-25 min, polyvinyl alcohol and 1 wt% 3-glycidoxypropyltrimethoxysilane solution are added, glacial acetic acid is added dropwise to adjust the pH of the solution to 4-5, and the mixture is stirred at 50-60℃ for 60-90 min. The mixture is then filtered, washed 2-3 times with anhydrous ethanol and deionized water, dried under vacuum at 80-90℃ for 2-3 h, and cooled to room temperature to obtain modified cellulose.

[0018] Optionally, expandable graphite is mixed with deionized water and soaked for 10-15 minutes. Anhydrous ethanol is added and stirred for 20-30 minutes. Ammonium persulfate and dilute sulfuric acid are added and stirred at 50-60°C for 30-60 minutes. After cooling to room temperature, amino-polyethylene glycol silane is slowly added dropwise and stirred at 40-50°C for 60-90 minutes. The mixture is then filtered, washed 2-3 times with anhydrous ethanol and deionized water, and dried under vacuum at 80-85°C for 1-2 hours. The resulting product is passed through a 60-mesh sieve to obtain modified expandable graphite.

[0019] In this invention, in step S2, ammonium persulfate and dilute sulfuric acid are reacted at 50-60°C to gently introduce active sites and avoid damage to the graphite structure. Then, amino-polyethylene glycol silane is added dropwise and reacted under acidic conditions to make it uniformly bonded to the surface of expanded graphite. After filtration, washing and vacuum drying, by-products and solvents are removed. Finally, after sieving, modified expanded graphite with uniform particle size is obtained.

[0020] Optionally, the modified cellulose and modified expanded graphite are mixed and stirred for 10-20 minutes, 3-(isobutenoyloxy)propyltrimethoxysilane, bisphenol A diglycidyl ether and 2-methylimidazole are added, and the mixture is sheared and dispersed at 60-70℃ for 3-5 minutes, degassed for 5-8 minutes, poured into a mold, and after two stages of constant temperature treatment, cooled to room temperature and demolded. The mixture is then dried at 50-60℃ for 1-2 hours to obtain the special fiber material.

[0021] Optionally, the two-stage constant temperature treatment is as follows: constant temperature treatment at 90~100℃ for 30~40 min, followed by heating to 125~130℃ for curing for 1~1.5 h.

[0022] In this invention, a pre-reaction is first carried out at 90~100℃ to avoid stress concentration caused by sudden cross-linking of the reaction system; then, the final curing is completed at 125~130℃ to fully cross-link the fiber network structure, which is beneficial to improving the structural density and performance stability of the special fiber material.

[0023] A special fiber material comprising the following raw materials in parts by weight: 50-60 parts modified cellulose, 5-6 parts modified expanded graphite, 2-5 parts 3-(isobutenoyloxy)propyltrimethoxysilane, 5-8 parts bisphenol A diglycidyl ether, and 0.5-0.8 parts 2-methylimidazole.

[0024] Optionally, the modified cellulose comprises the following raw materials in parts by weight: 50-60 parts of cellulose, 660-750 parts of 70wt% ethanol solution, 1.5-2.5 parts of polyvinyl alcohol, and 10-20 parts of 1wt% 3-glycidoxypropyltrimethoxysilane solution.

[0025] The modified expanded graphite comprises the following raw materials in parts by weight: 5-6 parts expanded graphite, 200-250 parts deionized water, 620-720 parts anhydrous ethanol, 0.6-1 parts ammonium persulfate, 0.2-0.4 parts 5wt% dilute sulfuric acid, and 0.6-1 parts amino-polyethylene glycol silane.

[0026] Optionally, the special fiber material also contains phosphate-based montmorillonite, which comprises the following raw materials in parts by weight: 1-2.5 parts montmorillonite, 200-250 parts deionized water, 310-400 parts anhydrous ethanol, and 0.5-1 parts triethyl phosphate.

[0027] The above-described technical solution of the present invention has at least the following beneficial effects:

[0028] This invention modifies cellulose with 3-glycidoxypropyltrimethoxysilane, introducing epoxy groups onto its surface. Simultaneously, the hydroxyl groups of cellulose are substituted to form siloxane bonds and organosilicon segments, giving the cellulose durable hydrophobicity and thus inhibiting its hygroscopicity. Furthermore, due to the high surface mineralization of expanded graphite, it is difficult to disperse uniformly in conventional systems, easily leading to poor compatibility with cellulose. This invention obtains modified expanded graphite by acidifying it and then treating it with amino-polyethylene glycol silane. The epoxy groups of the modified cellulose can undergo ring-opening reactions with the amino and hydroxyl sites on the modified expanded graphite. Under the catalysis of 2-methylimidazole and under two-stage isothermal treatment conditions, it crosslinks with 3-(isobutenoyloxy)propyltrimethoxysilane to form a three-dimensional network structure. This not only improves the compatibility and dispersibility of expanded graphite in materials but also enhances the overall mechanical strength of the special fiber material.

[0029] Expanded graphite undergoes significant expansion and contraction at high temperatures, causing it to detach from the fiber network and weakening the material's physicochemical properties. In this invention, expanded graphite is surface-modified with amino-polyethylene glycol silane, which then chemically bonds to modified cellulose, improving stability. The PEG segments of the amino-polyethylene glycol silane molecules also possess flexible and reversible stretchability, dynamically adapting to the expansion and contraction of the expanded graphite and preventing it from detaching from the fibers. Simultaneously, the modified expanded graphite continues to expand rapidly upon heating, forming a dense carbonaceous insulating layer that acts as a barrier against heat and oxygen transfer, thereby further enhancing the material's flame-retardant properties while maintaining structural stability. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. The described embodiments are some embodiments of the present invention, and all other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0031] Example 1

[0032] 50g of dried cellulose was dispersed in 660g of 70wt% ethanol solution and mechanically stirred for 20min. 1.5g of polyvinyl alcohol and 10g of 1wt% 3-glycidoxypropyltrimethoxysilane (KH560) solution were added, and glacial acetic acid was added dropwise to adjust the pH to 4. The mixture was stirred at 50℃ for 60min. The precipitate was collected by filtration and washed twice with anhydrous ethanol and deionized water, respectively. The precipitate was then vacuum dried at 80℃ for 2h and cooled to room temperature to obtain modified cellulose.

[0033] 5g of expanded graphite was placed in a beaker and pre-soaked in 200g of deionized water for 10min. Then, 620g of anhydrous ethanol was added and the mixture was magnetically stirred and dispersed for 20min. 0.6g of ammonium persulfate and 0.2g of 5wt% dilute sulfuric acid were added and the mixture was stirred continuously at 50℃ for 30min. After cooling to room temperature, 0.6g of aminopolyethylene glycol silane was slowly added dropwise and the mixture was stirred at 40℃ for 60min. The mixture was then filtered, washed twice with anhydrous ethanol and deionized water, and dried under vacuum at 80℃ for 1h. The resulting product was passed through a 60-mesh sieve to obtain modified expanded graphite.

[0034] 1 g of montmorillonite was added to 200 g of deionized water and ultrasonically dispersed for 10 min. Then, 310 g of anhydrous ethanol was added and stirred for 10 min. 0.5 g of triethyl phosphate (TEP) was added, the temperature was raised to 50 °C, and the mixture was stirred for 60 min. The mixture was then filtered and washed twice with anhydrous ethanol and deionized water, respectively. The mixture was then vacuum dried at 80 °C for 1 h and passed through a 50-mesh sieve to obtain phosphate-based montmorillonite.

[0035] 50g of modified cellulose, 5g of modified expanded graphite, and 1g of phosphate-based montmorillonite were mixed and stirred for 10 minutes. Then, 2g of 3-(isobutenoyloxy)propyltrimethoxysilane, 5g of bisphenol A diglycidyl ether, and 0.5g of 2-methylimidazole were added. After shearing and dispersing at 60℃ for 3 minutes, the mixture was placed in a vacuum jar and degassed for 5 minutes. The mixture was then poured into a mold, and excess material was slowly scraped off to make the sample surface smooth. The sample was then treated at 90℃ for 30 minutes, heated to 125℃ and cured for 1 hour. After cooling to room temperature, the sample was demolded and dried at 50℃ for 1 hour to obtain the special fiber material.

[0036] Example 2

[0037] 55g of dried cellulose was dispersed in 700g of 70wt% ethanol solution and mechanically stirred for 23min. 2g of polyvinyl alcohol and 15g of 1wt% 3-glycidoxypropyltrimethoxysilane (KH560) solution were added, and glacial acetic acid was added dropwise to adjust the pH to 4.5. The mixture was stirred at 55℃ for 75min, and the precipitate was collected by filtration. The precipitate was washed twice with anhydrous ethanol and deionized water, and then vacuum dried at 85℃ for 2.5h. After cooling to room temperature, modified cellulose was obtained.

[0038] 5.5g of expanded graphite was placed in a beaker and pre-soaked in 225g of deionized water for 12min. Then, 680g of anhydrous ethanol was added, and the mixture was dispersed by magnetic stirring for 25min. 0.7g of ammonium persulfate and 0.3g of 5wt% dilute sulfuric acid were added, and the mixture was stirred continuously at 55℃ for 40min. After cooling to room temperature, 0.8g of aminopolyethylene glycol silane was slowly added dropwise, and the mixture was stirred at 45℃ for 70min. After filtration, the graphite was washed three times with anhydrous ethanol and three times with deionized water, and then dried under vacuum at 85℃ for 1.5h. The resulting product was passed through a 60-mesh sieve to obtain modified expanded graphite.

[0039] Add 2g of montmorillonite to 230g of deionized water and sonicate for 12min. Add 350g of anhydrous ethanol and stir for 16min. Add 0.8g of triethyl phosphate (TEP), heat to 60℃, stir for 80min, filter, wash three times with anhydrous ethanol and deionized water, dry under vacuum at 85℃ for 1.5h, and pass through a 50-mesh sieve to obtain phosphate-based montmorillonite.

[0040] 55g of modified cellulose, 5.5g of modified expanded graphite, and 1.8g of phosphate-based montmorillonite were mixed and stirred for 15 minutes. Then, 3.5g of 3-(isobutenoyloxy)propyltrimethoxysilane, 6.5g of bisphenol A diglycidyl ether, and 0.6g of 2-methylimidazole were added. After shearing and dispersing at 65℃ for 4 minutes, the mixture was placed in a vacuum jar and degassed for 6 minutes. The mixture was then poured into a mold, and excess material was slowly scraped off to make the sample surface smooth. The sample was then treated at 95℃ for 35 minutes, heated to 128℃ and cured for 1.2 hours. After cooling to room temperature, the sample was demolded and dried at 55℃ for 1.5 hours to obtain the special fiber material.

[0041] Example 3

[0042] 60g of dried cellulose was dispersed in 750g of 70wt% ethanol solution and mechanically stirred for 25min. 2.5g of polyvinyl alcohol and 20g of 1wt% 3-glycidoxypropyltrimethoxysilane (KH560) solution were added, and glacial acetic acid was added dropwise to adjust the pH to 5. The mixture was stirred at 60℃ for 90min, and the precipitate was collected by filtration. The precipitate was washed three times with anhydrous ethanol and deionized water, and then vacuum dried at 90℃ for 3h. After cooling to room temperature, modified cellulose was obtained.

[0043] 6g of expanded graphite was placed in a beaker and pre-soaked in 250g of deionized water for 15min. Then, 720g of anhydrous ethanol was added and the mixture was magnetically stirred and dispersed for 30min. 1g of ammonium persulfate and 0.4g of 5wt% dilute sulfuric acid were added and the mixture was stirred continuously at 60℃ for 60min. After cooling to room temperature, 1g of aminopolyethylene glycol silane was slowly added dropwise and the mixture was stirred at 50℃ for 90min. The mixture was then filtered, washed three times with anhydrous ethanol and three times with deionized water, and dried under vacuum at 85℃ for 2h. The resulting modified expanded graphite was passed through a 60-mesh sieve.

[0044] Add 2.5g of montmorillonite to 250g of deionized water and sonicate for 15min. Add 400g of anhydrous ethanol and stir for 20min. Add 1g of triethyl phosphate (TEP), heat to 70℃, stir for 90min, filter, wash three times with anhydrous ethanol and deionized water, dry under vacuum at 90℃ for 2h, and pass through a 50-mesh sieve to obtain phosphate-based montmorillonite.

[0045] 60g of modified cellulose, 6g of modified expanded graphite, and 2.5g of phosphate-based montmorillonite were mixed and stirred for 20 minutes. Then, 5g of 3-(isobutenoyloxy)propyltrimethoxysilane, 8g of bisphenol A diglycidyl ether, and 0.8g of 2-methylimidazole were added. After shearing and dispersing at 70℃ for 5 minutes, the mixture was placed in a vacuum jar and degassed for 8 minutes. The mixture was then poured into a mold, and excess material was slowly scraped off to make the sample surface smooth. The sample was then treated at 100℃ for 40 minutes, heated to 130℃ and cured for 1.5 hours. After cooling to room temperature, the sample was demolded and dried at 60℃ for 2 hours to obtain the special fiber material.

[0046] Example 4

[0047] 50g of dried cellulose was dispersed in 660g of 70wt% ethanol solution and mechanically stirred for 20min. 1.5g of polyvinyl alcohol and 10g of 1wt% 3-glycidoxypropyltrimethoxysilane (KH560) solution were added, and glacial acetic acid was added dropwise to adjust the pH to 4. The mixture was stirred at 50℃ for 60min. The precipitate was collected by filtration and washed twice with anhydrous ethanol and deionized water, respectively. The precipitate was then vacuum dried at 80℃ for 2h and cooled to room temperature to obtain modified cellulose.

[0048] 5g of expanded graphite was placed in a beaker and pre-soaked in 200g of deionized water for 10min. Then, 620g of anhydrous ethanol was added and the mixture was magnetically stirred and dispersed for 20min. 0.6g of ammonium persulfate and 0.2g of 5wt% dilute sulfuric acid were added and the mixture was stirred continuously at 50℃ for 30min. After cooling to room temperature, 0.6g of aminopolyethylene glycol silane was slowly added dropwise and the mixture was stirred at 40℃ for 60min. The mixture was then filtered, washed twice with anhydrous ethanol and deionized water, and dried under vacuum at 80℃ for 1h. The resulting product was passed through a 60-mesh sieve to obtain modified expanded graphite.

[0049] 50g of modified cellulose and 5g of modified expanded graphite were mixed and stirred for 10 minutes. Then, 2g of 3-(isobutenoyloxy)propyltrimethoxysilane, 5g of bisphenol A diglycidyl ether and 0.5g of 2-methylimidazole were added. After shearing and dispersing at 60℃ for 3 minutes, the mixture was placed in a vacuum jar and degassed for 5 minutes. The mixture was then poured into a mold, and excess material was slowly scraped off to make the sample surface smooth. The sample was then treated at 90℃ for 30 minutes, heated to 125℃ and cured for 1 hour. After cooling to room temperature, the sample was demolded and dried at 50℃ for 1 hour to obtain the special fiber material.

[0050] Example 5

[0051] 55g of dried cellulose was dispersed in 700g of 70wt% ethanol solution and mechanically stirred for 23min. 2g of polyvinyl alcohol and 15g of 1wt% 3-glycidoxypropyltrimethoxysilane (KH560) solution were added, and glacial acetic acid was added dropwise to adjust the pH to 4.5. The mixture was stirred at 55℃ for 75min, and the precipitate was collected by filtration. The precipitate was washed twice with anhydrous ethanol and deionized water, and then vacuum dried at 85℃ for 2.5h. After cooling to room temperature, modified cellulose was obtained.

[0052] 5.5g of expanded graphite was placed in a beaker and pre-soaked in 225g of deionized water for 12min. Then, 680g of anhydrous ethanol was added, and the mixture was dispersed by magnetic stirring for 25min. 0.7g of ammonium persulfate and 0.3g of 5wt% dilute sulfuric acid were added, and the mixture was stirred continuously at 55℃ for 40min. After cooling to room temperature, 0.8g of aminopolyethylene glycol silane was slowly added dropwise, and the mixture was stirred at 45℃ for 70min. After filtration, the graphite was washed three times with anhydrous ethanol and three times with deionized water, and then dried under vacuum at 85℃ for 1.5h. The resulting product was passed through a 60-mesh sieve to obtain modified expanded graphite.

[0053] 55g of modified cellulose and 5.5g of modified expanded graphite were mixed and stirred for 15 min. Then, 3.5g of 3-(isobutenoyloxy)propyltrimethoxysilane, 6.5g of bisphenol A diglycidyl ether and 0.6g of 2-methylimidazole were added. After shearing and dispersing at 65℃ for 4 min, the mixture was placed in a vacuum jar and degassed for 6 min. The mixture was then poured into a mold, and excess material was slowly scraped off to make the sample surface smooth. The sample was then treated at 95℃ for 35 min, heated to 128℃ and cured for 1.2 h. After cooling to room temperature, the sample was demolded and dried at 55℃ for 1.5 h to obtain the special fiber material.

[0054] Example 6

[0055] 60g of dried cellulose was dispersed in 750g of 70wt% ethanol solution and mechanically stirred for 25min. 2.5g of polyvinyl alcohol and 20g of 1wt% 3-glycidoxypropyltrimethoxysilane (KH560) solution were added, and glacial acetic acid was added dropwise to adjust the pH to 5. The mixture was stirred at 60℃ for 90min, and the precipitate was collected by filtration. The precipitate was washed three times with anhydrous ethanol and deionized water, and then vacuum dried at 90℃ for 3h. After cooling to room temperature, modified cellulose was obtained.

[0056] 6g of expanded graphite was placed in a beaker and pre-soaked in 250g of deionized water for 15min. Then, 720g of anhydrous ethanol was added and the mixture was magnetically stirred and dispersed for 30min. 1g of ammonium persulfate and 0.4g of 5wt% dilute sulfuric acid were added and the mixture was stirred continuously at 60℃ for 60min. After cooling to room temperature, 1g of aminopolyethylene glycol silane was slowly added dropwise and the mixture was stirred at 50℃ for 90min. The mixture was then filtered, washed three times with anhydrous ethanol and three times with deionized water, and dried under vacuum at 85℃ for 2h. The resulting modified expanded graphite was passed through a 60-mesh sieve.

[0057] 60g of modified cellulose and 6g of modified expanded graphite were mixed and stirred for 20min. Then, 5g of 3-(isobutenoyloxy)propyltrimethoxysilane, 8g of bisphenol A diglycidyl ether and 0.8g of 2-methylimidazole were added. After shearing and dispersing at 70℃ for 5min, the mixture was placed in a vacuum jar and degassed for 8min. The mixture was then poured into a mold, and excess material was slowly scraped off the mold to make the sample surface smooth. The sample was then treated at 100℃ for 40min, heated to 130℃ and cured for 1.5h. After cooling to room temperature, the sample was demolded and dried at 60℃ for 2h to obtain the special fiber material.

[0058] The present invention also includes comparative examples and related experiments.

[0059] Comparative Example 1

[0060] The only difference from Example 1 is that in step S2, amino polyethylene glycol silane was not added. The other components and preparation steps are completely the same, and a special fiber material is obtained.

[0061] Comparative Example 2

[0062] The only difference from Example 1 is that 3-glycidoxypropyltrimethoxysilane was not added in step S1. The other components and preparation steps are completely the same, and a special fiber material is obtained.

[0063] Comparative Example 3

[0064] The only difference from Example 1 is that no modified expanded graphite was added in step S3. The other components and preparation steps are completely the same, and a special fiber material is obtained.

[0065] Boards with a thickness of 5 mm were prepared using the special fiber materials of Examples 1-6 and Comparative Examples 1-3. The water resistance of the boards was tested by boiling test for moisture resistance according to standard GB / T 11718-2021, and the internal bonding strength was tested after treatment. The mechanical strength of the boards was tested by static bending strength according to standard GB / T 11718-2021. The flame retardancy of the boards was tested by combustion performance according to standard GB / T 18958-2022. After testing the samples according to this standard, they were naturally cooled to room temperature, and the flame retardancy test was repeated on the samples. After three repeated tests, the combustion performance rating of the samples was recorded based on the results of the last test. The test results are shown in Table 1.

[0066] Thin film materials with a thickness of 0.4 mm were prepared using the special fiber materials of Examples 1-6 and Comparative Examples 1-3, respectively. The filtration performance of the thin film materials was tested for filtration efficiency in accordance with QB / T 4031-2024. The test results are shown in Table 1.

[0067] Table 1

[0068]

[0069] As shown in Table 1, compared to Examples 4-6, the addition of phosphate-modified montmorillonite in Examples 1-3 resulted in better static bending strength and filtration efficiency in the materials. Triethyl phosphate-modified montmorillonite can be uniformly dispersed in the three-dimensional network structure and acts as a supporting framework to resist external forces, thereby improving the overall mechanical strength of the special fiber material. Simultaneously, the introduction of phosphate-modified montmorillonite increases the density of the three-dimensional network structure, thereby improving the membrane's interception efficiency for particulate matter and ultimately enhancing the filtration performance of the special fiber material.

[0070] Compared to Comparative Example 1, Example 1, due to the introduction of amino-polyethylene glycol silane, exhibits flexible and reversible stretching properties in its PEG segments: when expanded graphite expands due to heat, the segments contract to offset the volume change; when cooled and contracted, the segments extend to fill the gaps, thereby preventing the expanded graphite from detaching and resulting in better flame retardancy. In contrast, Comparative Example 1 lacks amino-polyethylene glycol silane, causing the expanded graphite to detach from the special fiber material due to repeated expansion and contraction, leading to a decrease in the material's flame retardancy.

[0071] Compared to Comparative Example 2, Example 1 introduced 3-glycidoxypropyltrimethoxysilane, which generates silicon-oxygen bonds and organosilicon segments on the cellulose surface, forming a stable hydrophobic barrier, reducing water penetration, and thus enhancing water resistance. In contrast, the cellulose in Comparative Example 2 lacked 3-glycidoxypropyltrimethoxysilane modification, resulting in the material's tendency to absorb moisture and expand, which in turn led to a decrease in the internal bonding strength of the special fiber material after the boiling test.

[0072] Compared to Comparative Example 3, Example 1 introduced modified expanded graphite, which can rapidly expand at high temperatures to form a dense carbon layer, blocking heat and oxygen transfer and thus improving flame retardant performance. Simultaneously, its surface-active groups form a stable bond with the modified cellulose, preventing powdering. In contrast, Comparative Example 3 lacked modified expanded graphite, resulting in a lack of carbon layer protection during combustion and a decrease in the flame retardancy of the special fiber material.

[0073] The above are preferred embodiments of the present invention. Those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a special fiber material, characterized in that, Includes the following steps: S1. Disperse cellulose in an ethanol solution, stir, add polyvinyl alcohol and 3-glycidoxypropyltrimethoxysilane solution, adjust the pH of the solution to acidic, heat the reaction, filter, wash, vacuum dry, and cool to obtain modified cellulose; S2. Mix expanded graphite and deionized water, add ammonium persulfate and dilute sulfuric acid, heat to react, cool, add amino polyethylene glycol silane dropwise, heat and stir, filter, wash, vacuum dry, and sieve to obtain modified expanded graphite. S3. Mix and stir modified cellulose and modified expanded graphite, add 3-(isobutenoyloxy)propyltrimethoxysilane, bisphenol A diglycidyl ether and 2-methylimidazole, heat and shear to disperse, degas, pour into a mold, and after two stages of constant temperature treatment, cool to demold, dry to obtain special fiber material.

2. The method for preparing a special fiber material according to claim 1, characterized in that, In step S3, when the modified cellulose and modified expanded graphite are mixed and stirred, phosphate-based montmorillonite is also added. The phosphate-based montmorillonite is obtained by treating montmorillonite with triethyl phosphate.

3. The method for preparing a special fiber material according to claim 2, characterized in that, The phosphate-based montmorillonite was prepared by mixing montmorillonite and deionized water, ultrasonically dispersing for 10-15 min, adding anhydrous ethanol, stirring for 10-20 min, adding triethyl phosphate, heating to 50-70℃, stirring for 60-90 min, filtering, washing 2-3 times with anhydrous ethanol and deionized water, vacuum drying at 80-90℃ for 1-2 h, and passing through a 50-mesh sieve.

4. The method for preparing a special fiber material according to claim 1, characterized in that, Dry cellulose and 70 wt% ethanol solution are mixed and stirred for 20-25 min. Polyvinyl alcohol and 1 wt% 3-glycidoxypropyltrimethoxysilane solution are added. The pH of the solution is adjusted to 4-5 by adding glacial acetic acid dropwise. The mixture is stirred at 50-60℃ for 60-90 min, filtered, and washed 2-3 times with anhydrous ethanol and deionized water. The mixture is then vacuum dried at 80-90℃ for 2-3 h and cooled to room temperature to obtain modified cellulose.

5. The method for preparing a special fiber material according to claim 1, characterized in that, Expanded graphite and deionized water were mixed and soaked for 10-15 minutes. Anhydrous ethanol was added and the mixture was stirred and dispersed for 20-30 minutes. Ammonium persulfate and dilute sulfuric acid were added and stirred at 50-60°C for 30-60 minutes. After cooling to room temperature, amino-polyethylene glycol silane was slowly added dropwise and stirred at 40-50°C for 60-90 minutes. The mixture was filtered and washed 2-3 times with anhydrous ethanol and deionized water, respectively. The mixture was then vacuum dried at 80-85°C for 1-2 hours and passed through a 60-mesh sieve to obtain modified expanded graphite.

6. The method for preparing a special fiber material according to claim 1, characterized in that, Modified cellulose and modified expanded graphite were mixed and stirred for 10-20 minutes. 3-(isobutenoyloxy)propyltrimethoxysilane, bisphenol A diglycidyl ether and 2-methylimidazole were added. The mixture was sheared and dispersed at 60-70℃ for 3-5 minutes and degassed for 5-8 minutes. The mixture was poured into a mold and subjected to two stages of constant temperature treatment. After cooling to room temperature, the mixture was demolded and dried at 50-60℃ for 1-2 hours to obtain the special fiber material.

7. The method for preparing a special fiber material according to claim 6, characterized in that, The two-stage isothermal treatment is as follows: isothermal treatment at 90~100℃ for 30~40 min, followed by curing at 125~130℃ for 1~1.5 h.

8. A special fiber material, prepared by the method for preparing a special fiber material according to claim 1, characterized in that, The raw materials include the following parts by weight: 50-60 parts modified cellulose, 5-6 parts modified expanded graphite, 2-5 parts 3-(isobutenoyloxy)propyltrimethoxysilane, 5-8 parts bisphenol A diglycidyl ether, and 0.5-0.8 parts 2-methylimidazole.

9. A special fiber material according to claim 8, characterized in that, The modified cellulose comprises the following raw materials in parts by weight: 50-60 parts cellulose, 660-750 parts 70wt% ethanol solution, 1.5-2.5 parts polyvinyl alcohol, and 10-20 parts 1wt% 3-glycidoxypropyltrimethoxysilane solution. The modified expanded graphite comprises the following raw materials in parts by weight: 5-6 parts expanded graphite, 200-250 parts deionized water, 620-720 parts anhydrous ethanol, 0.6-1 parts ammonium persulfate, 0.2-0.4 parts 5wt% dilute sulfuric acid, and 0.6-1 parts amino-polyethylene glycol silane.

10. A special fiber material according to claim 8, characterized in that, The special fiber material also contains phosphate-based montmorillonite, which comprises the following raw materials in parts by weight: 1-2.5 parts montmorillonite, 200-250 parts deionized water, 310-400 parts anhydrous ethanol, and 0.5-1 parts triethyl phosphate.

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