Preparation method of waterproof and flame-retardant multifunctional fabric

Abstract

The present application provides a method for preparing a waterproof and flame-retardant multifunctional fabric, which belongs to the technical field of functional textiles. After heating the diol until it is completely melted, diisocyanate, flame retardant and catalyst are added to react to obtain a polyurethane prepolymer, a chain extender is added to extend the chain, and then a capping agent is added to cap the end, and the mixture is cooled, and an emulsifier is added to obtain a waterproof and flame-retardant emulsion, and water is added to form a finishing agent. The polyacrylonitrile preoxidized fiber fabric is immersed in the finishing agent and treated, and then pre-baked and baked to obtain a multifunctional fabric. The present invention uses a polyol with a long alkane chain to extend the polyurethane prepolymer. The obtained waterproof agent has good film-forming properties and can be firmly fixed on the fiber surface without the aid of a cross-linking agent or adhesive when used, giving the modified textile excellent washing resistance.

Description

Technical Field

[0001] The present application relates to a method for preparing a waterproof and flame-retardant multifunctional fabric, and belongs to the technical field of functional textiles. Background Art

[0002] Polyacrylonitrile pre-oxidized fiber is widely used in flame-retardant fabrics, high-temperature resistant, acid- and alkali-resistant, and relatively inexpensive. However, there are certain structural defects inside the polyacrylonitrile fiber, and some new defects will continue to appear during the carbonization process due to high-temperature treatment, resulting in low fiber curl, weak cohesion, and decreased strength after carbonization, which directly affects the subsequent spinning process. In addition, when polyacrylonitrile pre-oxidized fiber is subjected to external forces during use and processing, carbonized fragments or residues often fall off, which seriously affects the promotion and application of the product.

[0003] Based on the problems existing in current flame-retardant fibers, this application aims to prepare a multifunctional fabric with both waterproof function and permanent flame-retardant properties to solve the defects of polyacrylonitrile pre-oxidized fibers in the application of textile field. Summary of the invention

[0004] In view of this, the present application provides a method for preparing a waterproof and flame-retardant multifunctional fabric, which imparts the provided fabric with both waterproofness and permanent flame retardancy, so as to solve the problems of existing polyacrylonitrile pre-oxidized flame-retardant fibers such as low strength, poor wearing performance and poor waterproof effect.

[0005] Specifically, the present application is implemented through the following scheme:

[0006] A method for preparing a waterproof and flame-retardant multifunctional fabric, comprising the following steps:

[0007] Step 1, preparing a waterproof flame retardant: heating the diol until it is completely melted, cooling to 50-60°C, adding diisocyanate and flame retardant, stirring, heating to 60-80°C, adding a catalyst, continuing the reaction to obtain a polyurethane prepolymer, adding a chain extender, continuing the reaction, then adding a capping agent, continuing the reaction, cooling to 50-60°C, adding an emulsifier twice under stirring conditions, the first emulsifier is added in an amount until the emulsion completes the water-in-oil phase transition, and then the remaining emulsifier is added to continue emulsification to obtain a waterproof flame retardant emulsion, wherein the emulsifier is deionized water containing 1-2 g / L of a defoamer and 30-60 g / L of a surfactant.

[0008] Step 2, preparing multifunctional fabrics: After the polyacrylonitrile pre-oxidized fiber fabric is immersed in the finishing agent, it is pre-baked and baked to obtain the multifunctional fabric. The finishing agent is an aqueous solution of the waterproof flame retardant prepared in step 1, with a concentration of 30-60 g / L, an immersion time of 5-10 min, and a rolling residue of 60-80%.

[0009] The above scheme uses diol, diisocyanate and flame retardant as raw materials, first catalyzes to obtain polyurethane prepolymer, then performs water-in-oil phase transformation on the chain extension reactant to obtain an emulsion of polyurethane-based fluorine-free waterproof flame retardant, and the obtained emulsion is used for padding treatment of polyacrylonitrile pre-oxidized fiber fabric to obtain a finished multifunctional fabric with both flame retardancy and waterproofness.

[0010] Further, as a preference:

[0011] In step one,

[0012] The molar ratio of the diol, diisocyanate, chain extender and flame retardant is 2-6:3-15:2-4:2-10, and more preferably, the molar ratio of the diol, diisocyanate, chain extender and flame retardant is 3-5:6:5. The catalyst addition amount is 0.02-0.03% of the molar amount of diisocyanate, and the end-capping agent is 5-10% of the molar amount of diisocyanate.

[0013] The diol is a composite of any one or more of polycaprolactone diol (PCL), polyether diol (PPG), polyether diol (PTMG), polytetramethylene glycol (PTMEG), and 1,12-dodecane diol. More preferably, the diol is a composite of polycaprolactone diol (such as PCL2000) and 1,12-dodecane diol, and the composite molar ratio of polycaprolactone diol to 1,12-dodecane diol is 1:0.1-0.3.

[0014] The diisocyanate is one or a mixture of hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), dicyclohexylmethane-4,4'-diisocyanate (HMDI), 1,4-cyclohexane diisocyanate (CHDI), and methylcyclohexane diisocyanate (HTDI). More preferably, the diisocyanate is a mixture of isophorone diisocyanate (IPDI) and dicyclohexylmethane-4,4'-diisocyanate (HMDI), and the molar ratio of isophorone diisocyanate (IPDI) to dicyclohexylmethane-4,4'-diisocyanate (HMDI) is preferably 1:2-5.

[0015] The chain extender is a sorbitol stearate substance, such as Span 60, Span 80, Span 40, Span 20, preferably Span 60.

[0016] The flame retardant is one or more of nano silicon carbide, nano graphene, nano graphene oxide, MXene nanosheets, carbon nanotubes, carbon nanowires, nano MgO, nano ZrO2, nano SiO2, and nano ZnO, preferably nano silicon carbide.

[0017] The end-capping agent refers to R-OH, where the number of C atoms in R is 8 to 20, and hexadecanol is preferred.

[0018] The catalyst is dibutyltin dilaurate.

[0019] The defoamer is defoamer DM 8317.

[0020] The surfactant is one or more of alkylphenol polyoxyethylene ether, high-carbon fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene ester, and fatty acid methyl ester ethoxylate, preferably high-carbon fatty alcohol polyoxyethylene ether, and more preferably: fatty alcohol polyoxyethylene ether O-20.

[0021] The volume ratio of the first drop of deionized water containing defoamer and surfactant to the second drop of deionized water containing defoamer and surfactant is 30-40%. The present invention does not use common hydrophilic chain extenders. During emulsification, deionized water containing defoamer and surfactant is added as an emulsifier, and it is carried out twice. The first addition is carried out in a slow dripping manner, which can realize the oil-in-water to water-in-oil phase transition. After the phase transition is successful, the remaining deionized water containing defoamer and surfactant can be added quickly and in large quantities. When the emulsifier is added once, the polyurethane prepared by the reaction is a polymer with poor hydrophilicity. This one-time addition will cause the water addition speed to be too fast, resulting in oil-water separation and emulsification failure, and the incremental speed is slow. Therefore, this case is added in batches and the first addition amount is controlled at 30-40%, which can significantly improve processing efficiency and reduce production time. The formed waterproof flame retardant is in the form of an emulsion, which can not only store stability, but also help the waterproof flame retardant to spread on the fiber surface and penetrate into the fiber when used, thereby improving waterproof performance and durability.

[0022] In step 2,

[0023] The polyacrylonitrile pre-oxidized fiber fabric is one of a polyacrylonitrile pre-oxidized fiber woven fabric and a polyacrylonitrile pre-oxidized fiber knitted fabric.

[0024] The pre-baking temperature is 80-100° C. and the pre-baking time is 3-10 minutes.

[0025] The baking temperature is 130-170° C. and the baking time is 3-6 minutes.

[0026] The finished waterproof and flame-retardant multifunctional fabric obtained by the above scheme has the following beneficial effects:

[0027] (1) Polyurethane monomers are obtained by reacting diols and diisocyanates as raw materials. Under the action of a catalyst, nano-scale flame retardants are evenly mixed with polyurethane monomers, and then a polymerization reaction is carried out to form a polyurethane prepolymer, which effectively improves the uniformity of the distribution of nano-flame retardant materials in polyurethane. This is also the premise for the waterproof flame retardant to have uniform flame retardant characteristics.

[0028] (2) The flame-retardant polyurethane prepolymer is chain extended, and a long alkane chain polyol is used as a chain extender, and a long alkane chain monool is used as a capping agent. The prepared chain extension product has a small number of hydrophilic groups in its structure, and has excellent hydrophobicity, water resistance and good film-forming properties. When used, it can be firmly fixed on the fiber surface without the help of a cross-linking agent or adhesive, giving the modified textile excellent washing resistance. In particular, when the chain extender is a sorbitol stearate substance such as Span 60, Span 80, Span 40, Span 20, etc., which contains 3 hydroxyl groups in its structure, it can react with the isocyanate-terminated polyurethane prepolymer to form a polymer with a network structure, which can improve the waterproof performance and its durability. Its water-repellent level reaches level 5. After 50 washes, the water-repellent level can still be maintained at level 5, and the film-forming property is excellent.

[0029] (3) The waterproof and flame-retardant multifunctional fabric provided by the above scheme has not only waterproof and flame-retardant functions, but also has the function of forming a dense film on the fiber surface, which can resist external tensile force together with the fiber. In addition, the waterproof and flame-retardant can also penetrate into the fiber and repair the original defects of the fiber to a certain extent, thereby improving the mechanical strength of the fabric. DETAILED DESCRIPTION

[0030] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application clearer, the technical solutions of this application will be further described in detail below in combination with the specific cases in the embodiments of this application. It should be understood that the specific embodiments described herein are only used to explain this application and are not used to limit the technical solutions of this application. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0031] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features. "Multiple" means two or more, unless otherwise clearly and specifically defined.

[0032] The waterproof and flame-retardant multifunctional fabrics and unmodified polyacrylonitrile pre-oxidized fiber fabrics prepared in the comparative examples and the examples were analyzed for hydrophobic effect, washing resistance, mechanical strength and flame retardant properties. The washing method during the washing resistance test was carried out in accordance with the provisions of "GB / T 8629-2017 Household washing and drying procedures for textile testing"; the hydrophobic effect was carried out in accordance with the provisions of "GB / T4745-2012 Testing and evaluation of the waterproof performance of textiles by water dipping method"; the flame retardant performance was carried out in accordance with the provisions of "GB / T 5455-2014 Textile combustion performance vertical direction damage length, smoldering and afterflaming time determination"; the mechanical strength was carried out in accordance with the provisions of "GB / T 3923.1-2013 Textile fabric tensile properties Part 1: Determination of breaking strength and elongation at break (strip method)".

[0033] Example 1

[0034] (1) Preparation of waterproof flame retardant:

[0035] 0.15 mol of diol (the molar ratio of polycaprolactone diol PCL2000 and 1,12-dodecane diol is 1:0.2) was added to a 500 mL three-necked round-bottom flask, heated in an oven until completely melted, cooled to 50 ° C, added 0.30 mol of diisocyanate (the molar ratio of IPDI to HMDI is 1:3) and 10 g of flame retardant nano-silicon carbide, stirred at 500 r / min for 60 min, heated to 80 ° C, added 0.05 g of catalyst dibutyltin dilaurate and 7 mL of DMF, continued to react for 90 min to obtain a polyurethane prepolymer, added 0.1 mol of chain extender Span 60 and 10 mL of DMF, continued to react for 90 min, then added 0.07 mol of end-capping agent hexadecanol, continued to react for 60 min, cooled to 50 ° C, and added dropwise with 2 g / L defoamer DM under stirring at 1500 r / min. 8317 and 40g / L surfactant fatty alcohol polyoxyethylene ether O-20 70mL of deionized water, after the emulsion completes the water-in-oil phase transition, add the remaining 130mL of deionized water containing the above defoaming agent and surfactant, and continue emulsification for 120 min to obtain a polyurethane-based fluorine-free waterproof flame retardant emulsion.

[0036] (2) Preparation of waterproof and flame-retardant multifunctional fabrics

[0037] The waterproof and flame-retardant multifunctional fabric is prepared by a padding method: the waterproof and flame-retardant emulsion prepared in step (1) is added with water to form a finishing solution with a waterproof and flame-retardant concentration of 40 g / L, and the polyacrylonitrile pre-oxidized fiber fabric is immersed in the finishing solution for 8 minutes, with a padding rate of 60%, and then pre-baked at 80°C for 6 minutes and then baked at 150°C for 4 minutes.

[0038] Comparative Example 1

[0039] The configuration of this comparative example is the same as that of Example 1, except that no flame retardant is added in step (1). The preparation process of the waterproof flame retardant is as follows:

[0040] 0.15 mol of diol (the molar ratio of polycaprolactone diol PCL2000 and 1,12-dodecane diol is 1:0.2) was added to a 500 mL three-necked round-bottom flask, heated in an oven until completely melted, cooled to 50°C, added 0.30 mol of diisocyanate (the molar ratio of IPDI to HMDI is 1:3), stirred at 500 r / min for 60 min, heated to 80°C, added 0.05 g of catalyst dibutyltin dilaurate and 7 mL of DMF, continued to react for 90 min to obtain a polyurethane prepolymer, added 0.1 mol of chain extender Span 60 and 10 mL of DMF, continued to react for 90 min, then added 0.07 mol of end-capping agent hexadecanol, continued to react for 60 min, cooled to 50°C, and added dropwise a mixture containing 2 g / L defoamer DM under stirring at 1500 r / min. 8317 and 40g / L surfactant fatty alcohol polyoxyethylene ether O-20 in deionized water 70mL, after the emulsion completes the water-in-oil phase transition, add the remaining 130mL of deionized water containing the above defoaming agent and surfactant, and continue emulsification for 120 minutes to complete the emulsification.

[0041] The performance of the unmodified fabric (i.e., the polyacrylonitrile pre-oxidized fiber fabric before impregnation), the fabric treated in Example 1 and Comparative Example 1 was tested, as shown in Table 1.

[0042] Table 1: Effect of flame retardants on fabric properties

[0043] .

[0044] As can be seen from Table 1,

[0045] The afterflaming time of the unmodified fabric is about 0.17s, the smoldering time is 0.16s, the damaged length is 60mm, the breaking strength is 400N, and the water-wetting level is 2~3.

[0046] Compared with the unmodified fabric, the afterflame time of Example 1 was reduced to 0.13s, the ignition time was less than 0.10s, and the damaged length was reduced to about 43mm, and its flame retardant performance was significantly improved. However, in the preparation process of Comparative Example 1, no flame retardant was added, and the flame retardant performance of the fabric was slightly reduced. The reason for this phenomenon may be that the polyurethane film is flammable, which prolongs the afterflame time. However, since the polyurethane film is relatively thin, the change in flame retardancy is not obvious.

[0047] Compared with the unmodified fabric, the preparation method of this case has significantly improved mechanical properties and waterproof properties. The water-repellent level of Example 1 and Comparative Example 1 is increased from level 2 to 3 of the unmodified fabric to level 5, and the breaking strength is increased from 400N of the unmodified fabric to 570N and 550N respectively, and the breaking strength and water-repellent level are significantly improved. The difference in breaking strength between Example 1 and Comparative Example 1 also shows that under the same preparation conditions, whether to add a flame retardant and make it participate in the synthesis process of the waterproof flame retardant has no obvious effect on the waterproof performance of the fabric, but has a certain improvement effect on the breaking strength.

[0048] Comparative Example 2

[0049] This comparative example is similar to Example 1 except that no end-capping agent is added in step (1). The preparation process of the waterproof flame retardant is as follows:

[0050] In a 500 mL three-necked round-bottom flask, 0.15 mol of diol (the molar ratio of polycaprolactone diol PCL2000 and 1,12-dodecane diol is 1:0.2) was added, heated in an oven until completely melted, cooled to 50 ° C, 0.30 mol of diisocyanate (the molar ratio of IPDI to HMDI is 1:3) and 10 g of flame retardant nano-silicon carbide were added, stirred at 500 r / min for 60 min, heated to 80 ° C, 0.05 g of catalyst dibutyltin dilaurate and 7 mL of DMF were added, and the reaction was continued for 90 min to obtain a polyurethane prepolymer, 0.1 mol of chain extender Span 60 and 10 mL of DMF were added, and the reaction was continued for 90 min, cooled to 50 ° C, and under the stirring condition of 1500 r / min, 2 g / L defoamer DM was added dropwise. 8317 and 40g / L surfactant fatty alcohol polyoxyethylene ether O-20 70mL of deionized water, after the emulsion completes the water-in-oil phase transition, add the remaining 130mL of deionized water containing the above defoaming agent and surfactant, and continue emulsification for 120 min to obtain a polyurethane-based fluorine-free waterproof flame retardant emulsion.

[0051] The waterproof performance of the fabric obtained by impregnation modification in Comparative Example 2 was tested, and its water-repellent performance was 4-5. This is because if no end-capping agent is added, the chain extension product will not be end-capped, and its molecular chain end contains a small amount of hydroxyl and carboxyl groups, while in Example 1, an end-capping agent is added, and after the chain extension reaction is completed and the end of the molecular chain of the obtained waterproof flame retardant is an alkyl chain. Compared with the alkyl chain, the hydrophilic group hydroxyl group will cause the hydrophobicity and water resistance to be weakened.

[0052] Comparative Example 3

[0053] This comparative example is similar to Example 1 in configuration, except that the chain extender in step (1) is replaced with 2,2-dimethylolpropionic acid. The preparation process of the waterproof flame retardant is as follows:

[0054] 0.15 mol of diol (the molar ratio of polycaprolactone diol PCL2000 and 1,12-dodecane diol is 1:0.2) was added to a 500 mL three-necked round-bottom flask, heated in an oven until completely melted, cooled to 50 ° C, 0.30 mol of diisocyanate (the molar ratio of IPDI to HMDI is 1:3) and 10 g of flame retardant nano-silicon carbide were added, stirred at 500 r / min for 60 min, heated to 80 ° C, 0.05 g of catalyst dibutyltin dilaurate and 7 mL of DMF were added, and the reaction was continued for 90 min to obtain a polyurethane prepolymer, 0.1 mol of chain extender 2,2-dihydroxymethylpropionic acid and 10 mL of DMF were added, and the reaction was continued for 90 min, and then 0.07 mol of end-capping agent hexadecanol was added, and the reaction was continued for 60 min, cooled to 50 ° C, and under the stirring condition of 1500 r / min, 2 g / L defoamer DM was added dropwise. 8317 and 40g / L surfactant fatty alcohol polyoxyethylene ether O-20 70mL of deionized water, after the emulsion completes the water-in-oil phase transition, add the remaining 130mL of deionized water containing the above defoaming agent and surfactant, continue emulsification for 120 min, and obtain an emulsion.

[0055] The emulsion prepared by the above scheme was used for impregnation modification of polyacrylonitrile pre-oxidized fiber fabric (the process was the same as in Example 1), and the waterproof performance of the modified fabric was tested, and its water-repellent performance was level 2-3; after washing 50 times, the water-repellent performance was level 2.

[0056] By using the chain extender of this comparative example, the structure of the obtained emulsion contains a large number of hydrophilic carboxyl groups and a certain amount of terminal hydrophilic hydroxyl groups, so the hydrophobic performance is not as good as that of Example 1; while Example 1 uses a long alkane chain polyol for chain extension, which gives the extended chain product a structure that does not contain hydrophilic groups and performs better in the corresponding water repellency grade parameters.

[0057] Comparative Example 4

[0058] CN116396454A is taken as comparative example 4, in which no prepolymer is prepared during the preparation process.

[0059] Comparative Example 4: A super-hydrophobic polymer compound is constructed by the condensation reaction of polyurethane and a long-chain hydroxyl compound. The super-hydrophobic polymer compound is applied to the surface of a fabric to significantly reduce the surface energy of the fabric. At the same time, the hard segment of the polyurethane effectively enhances the bonding strength between the product and the fiber. The present invention is applied to the fluorine-free waterproof finishing of fabrics, which can give the fabrics efficient waterproof performance and excellent washing resistance. Its water-repellent performance is level 5; after washing 50 times, the water-repellent performance is level 3-4.

[0060] The present invention uses a polyol with a long alkane chain to extend the polyurethane prepolymer, and the obtained waterproofing agent has good film-forming properties. When used, it can be firmly fixed on the fiber surface without the help of a cross-linking agent or an adhesive, but the washing resistance is better than that of Comparative Example 4. Taking Example 1 as an example, it uses a polyol with a long alkane chain to extend the polyurethane prepolymer prepared by diol and diisocyanate. The prepared waterproofing agent not only has good bonding strength with the fiber, but also has good flexibility and is not easy to break during washing. The obtained modified fabric is washed 50 times, and its water-wetting performance is still maintained at level 5. However, the polyurethane waterproofing agent directly prepared by diol and isocyanate in Comparative Example 4 has poor flexibility, and breaks or even falls off due to external force during washing.

[0061] Example 2

[0062] The configuration of this embodiment is the same as that of embodiment 1, except that the amount of diol added is 0.05 mol, and the amount of chain extender Span 60 added is 0.17 mol.

[0063] Example 3

[0064] The configuration of this embodiment is the same as that of embodiment 1, except that the amount of diol added is 0.25 mol, and the amount of chain extender Span 60 added is 0.03 mol.

[0065] The performance of the unmodified fabric (i.e., the polyacrylonitrile pre-oxidized fiber fabric before impregnation), the fabric treated in Example 1 and Comparative Example 1 was tested, as shown in Table 2.

[0066] Table 2: Effect of diol and chain extender dosage on fabric waterproof performance

[0067] .

[0068] Table 2 shows that:

[0069] 1) Before washing, the water level of the fabric prepared in Example 1 was the best, and the water level of the waterproof agent prepared in Example 3 was the lowest. After washing 50 times, the water level of the fabric prepared in Example 1 did not change significantly, while the water level of the fabrics prepared in Examples 2 and 3 decreased significantly, and the degree of decrease in the water level of the fabric prepared in Example 2 was greater than that of Example 3.

[0070] 2) The influence of chain extenders and diols is mainly manifested in waterproof performance. Comparative Example 1, Example 1-1 to Example 1-5 show that: when the amount of chain extender is small, the small amount of isocyanate groups remaining in the polyurethane molecular structure are easy to react with water, affecting the emulsification performance, and then affecting the waterproof performance; when the amount of chain extender is too much, the unreacted chain extender molecules contain hydrophilic hydroxyl groups, which reduces the waterproof performance. Comparative Example 1, Example 1-6 to Example 1-9 show that: when the amount of diol is small, the molecular chain of the polyurethane prepolymer is short, the prepared waterproof agent has poor film-forming properties, and it is easy to fall off during the washing process, resulting in poor waterproof performance. When the amount of diol is large, the terminal group of the prepolymer is hydroxyl, which cannot react with the chain extender, so the finished product contains more terminal hydroxyl groups, which in turn affects the waterproof performance of the product. Therefore, the optimal molar ratio of diol, diisocyanate and chain extender is 0.15:0.30:0.10.

[0071] The above-mentioned embodiments only express several feasible implementation methods of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention, and the embodiments are not used to limit the scope of protection in the claims of the present invention. For ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, and all equivalent implementations or changes that do not depart from the present invention should be included in the technology of the present invention.

Claims

1. A method for preparing a waterproof and flame-retardant multifunctional fabric, characterized in that: Here are the steps: Step 1, heating the diol until it is completely melted, cooling to 50-60°C, adding diisocyanate and flame retardant, stirring, heating to 60-80°C, adding catalyst, continuing reaction to obtain polyurethane prepolymer, adding chain extender, continuing reaction, then adding end-capping agent, continuing reaction, cooling to 50-60°C, under stirring conditions, adding emulsifier twice, the amount of emulsifier added for the first time is enough to complete the water-in-oil phase transition of the emulsion, and then adding the remaining emulsifier to continue emulsification to obtain a waterproof flame retardant emulsion, wherein the emulsifier is deionized water containing 1-2 g / L defoamer and 30-60 g / L surfactant; The molar ratio of the diol, diisocyanate, chain extender and flame retardant is 2-6:3-15:2-4:2-10, the amount of catalyst added is 0.02-0.03% of the molar amount of diisocyanate, the end-capping agent is 5-10% of the molar amount of diisocyanate, and the molar ratio of the diol, diisocyanate and chain extender meets 0.15:0.30:0.

10. The diol is a composite of any one or more of polycaprolactone diol PCL, polyether diol PPG, polyether diol PTMG, polytetrahydrofuran diol PTMEG, and 1,12-dodecane diol. The chain extender is a sorbitol stearate compound, The end-capping agent refers to R-OH, where the number of C atoms in R is 8 to 20. Step 2: The polyacrylonitrile pre-oxidized fiber fabric is immersed in a finishing agent, pre-baked, and baked to obtain a multifunctional fabric. The finishing agent is an aqueous solution of the waterproof flame retardant emulsion prepared in step 1, with a concentration of 30-60 g / L, an immersion time of 5-10 min, and a rolling residue of 60-80%.

2. The method for preparing a waterproof and flame-retardant multifunctional fabric according to claim 1, characterized in that: The diol is a composite of polycaprolactone diol PCL and 1,12-dodecane diol, and the composite molar ratio of polycaprolactone diol PCL to 1,12-dodecane diol is 1:0.1-0.

3.

3. The method for preparing a waterproof and flame-retardant multifunctional fabric according to claim 1, characterized in that: The diisocyanate is one or a mixture of hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, 1,4-cyclohexane diisocyanate, and methylcyclohexane diisocyanate.

4. The method for preparing a waterproof and flame-retardant multifunctional fabric according to claim 3, characterized in that: The diisocyanate is a mixture of isophorone diisocyanate and dicyclohexylmethane-4,4'-diisocyanate, and the molar ratio of isophorone diisocyanate to dicyclohexylmethane-4,4'-diisocyanate is 1:2-5.

5. The method for preparing a waterproof and flame-retardant multifunctional fabric according to claim 1, characterized in that: The flame retardant is one or more of nano silicon carbide, nano graphene, nano graphene oxide, MXene nano sheets, carbon nanotubes, carbon nanowires, nano MgO, nano ZrO2, nano SiO2, and nano ZnO.

6. The method for preparing a waterproof and flame-retardant multifunctional fabric according to claim 1, characterized in that: The chain extender is one of Span 60, Span 80, Span 40 and Span 20.

7. The method for preparing a waterproof and flame-retardant multifunctional fabric according to claim 1, characterized in that: The volume percentage of the emulsifier added for the first time is 30~40% of the total emulsifier.

8. The method for preparing a waterproof and flame-retardant multifunctional fabric according to claim 1, characterized in that: The defoamer is defoamer DM 8317, and the surfactant is one or more of alkylphenol polyoxyethylene ether, high-carbon fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene ester, and fatty acid methyl ester ethoxylate.

9. The method for preparing a waterproof and flame-retardant multifunctional fabric according to claim 1, characterized in that: The polyacrylonitrile pre-oxidized fiber fabric is one of a polyacrylonitrile pre-oxidized fiber woven fabric and a polyacrylonitrile pre-oxidized fiber knitted fabric.

10. The method for preparing a waterproof and flame-retardant multifunctional fabric according to claim 1, characterized in that: The pre-baking temperature is 80-100° C., and the duration is 3-10 minutes; the baking temperature is 130-170° C., and the duration is 3-6 minutes.