Flame retardant finishing method for polyester knitted fabric

Abstract

The invention relates to the field of textile processing, and discloses a flame retardant finishing method for polyester knitted fabrics. The modified waterborne polyurethane emulsion is finished on the washed and dried polyester knitted fabrics by an immersion drying method. The modified waterborne polyurethane emulsion comprises isophorone diisocyanate, an amine chain extender, a flame retardant crosslinking agent, modified nano titanium dioxide, etc. The amine chain extender is prepared by reacting 2-(2,4-dihydroxyphenyl)-2H-benzotriazole and 2-chloro-4,6-diamino-1,3,5-triazine; the flame retardant crosslinking agent is prepared by reacting 1,3,5-tris(2-hydroxyethyl)cyanuric acid and dimethyl methylphosphonate; the modified nano titanium dioxide is prepared by modified silane coupling agent obtained by reacting tetramethyldisiloxane and vinyltrimethoxysilane to modify nano titanium dioxide hybrid silica sol, which can give the material good flame retardant performance while improving its ultraviolet protection performance and ensuring its mechanical properties.

Description

Technical Field

[0001] The invention belongs to the technical field of textile processing, and particularly relates to a flame retardant finishing method for polyester knitted fabrics. Background Art

[0002] Polyester fabrics have many advantages such as good thermal stability, chemical resistance and excellent mechanical properties, and are widely used in clothing, home furnishings and packaging. However, polyester fabrics have a low limiting oxygen index and are flammable. When burning, they will produce a large amount of molten drippings and quickly spread the flame to other combustible materials. In addition, polyester fabrics will release a large amount of toxic smoke when burning. Therefore, it is very important to flame retardant finish polyester knitted fabrics.

[0003] Waterborne polyurethane is a new type of polyurethane with water as the dispersion medium, which is widely used in the field of polyester fabric coating. However, the limiting oxygen index of waterborne polyurethane is also low, and it is flammable. When finishing polyester fabric, it is also easy to produce molten dripping and smoke when burning, and the flame retardant performance does not meet the requirements. In addition, polyester, as the largest type of textile fiber, will also undergo light aging under long-term ultraviolet light irradiation, mainly because the polymer material contains weaknesses that are easy to absorb ultraviolet light and break, which in turn causes the degradation of polyester macromolecules. Summary of the invention

[0004] In order to solve the deficiencies mentioned in the above-mentioned background technology, the purpose of the present invention is to provide a flame retardant finishing method for polyester knitted fabrics, by introducing amine chain extenders and flame retardant crosslinking agents into the main chain of waterborne polyurethane molecules, and adding modified nano titanium dioxide to prepare modified waterborne polyurethane, which is then finished on polyester knitted fabrics by an impregnation and drying method, thereby giving the polyester knitted fabrics good flame retardant properties while improving their ultraviolet protection properties and ensuring their mechanical properties.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A flame retardant finishing method for polyester knitted fabrics, comprising the following steps: using an immersion drying method to finish a modified aqueous polyurethane emulsion onto the washed and dried polyester knitted fabrics, placing the fabrics in an oven for drying, and taking them out after they are completely dried;

[0007] The modified waterborne polyurethane emulsion comprises the following raw materials in parts by weight: 15-20 parts of isophorone diisocyanate, 25-32 parts of polypropylene glycol 2000, 2-5 parts of 2,2-dihydroxymethylpropionic acid, 0.5-1 parts of dibutyltin dilaurate, 2.5-5 parts of amine chain extender, 2-5 parts of flame retardant crosslinking agent, 3-6 parts of triethylamine, 60-75 parts of deionized water, and 4-7 parts of modified nano titanium dioxide;

[0008] The amine chain extender is prepared by substitution reaction between 2-(2,4-dihydroxyphenyl)-2H-benzotriazole and 2-chloro-4,6-diamino-1,3,5-triazine; the flame retardant crosslinker is prepared by transesterification reaction between 1,3,5-tris(2-hydroxyethyl)cyanuric acid and dimethyl methylphosphonate; the modified nano titanium dioxide is prepared by sol-gel method using nano titanium dioxide hybrid silica sol and modified by modified silane coupling agent obtained by hydrosilylation reaction between tetramethyldisiloxane and vinyltrimethoxysilane.

[0009] Preferably, the preparation method of the modified waterborne polyurethane emulsion comprises the following steps: weighing each raw material by weight, placing isophorone diisocyanate, polypropylene glycol 2000, 2,2-dihydroxymethylpropionic acid and dibutyltin dilaurate in a reactor, placing at 75-85° C. under a nitrogen atmosphere, stirring for 2-3 hours, heating to 85-95° C., adding an amine chain extender and a flame retardant crosslinking agent, and continuing the reaction for 1-2 hours, cooling to 40-50° C. after the reaction is completed, adding triethylamine and stirring for 0.5-1 hour, then adding deionized water for emulsification, and finally adding modified nano titanium dioxide, stirring and dispersing to prepare a modified waterborne polyurethane emulsion.

[0010] Preferably, the preparation method of the amine chain extender comprises the following steps: taking 2-(2,4-dihydroxyphenyl)-2H-benzotriazole and triethylamine in a reactor, adding a mixed solution of 2-chloro-4,6-diamino-1,3,5-triazine and 1,4-dioxane, placing the mixture at 80°C and stirring for 6-8h, and after the reaction is completed, filtering, washing and drying to prepare the amine chain extender.

[0011] Preferably, the molar ratio of the 2-(2,4-dihydroxyphenyl)-2H-benzotriazole to 2-chloro-4,6-diamino-1,3,5-triazine is 1:1-1.2.

[0012] Preferably, the preparation method of the flame retardant crosslinking agent comprises the following steps: taking 1,3,5-tris(2-hydroxyethyl)cyanuric acid, dimethyl methylphosphonate and sodium hydroxide in a reactor, reacting at 160°C for 10-12 hours, cooling to 95-100°C after the reaction is completed, and vacuum rotary evaporating at 195-205°C for 2-3 hours to prepare a flame retardant crosslinking agent.

[0013] Preferably, the molar ratio of 1,3,5-tris(2-hydroxyethyl)cyanuric acid to dimethyl methylphosphonate is 1:1.3-3.5.

[0014] Preferably, the preparation method of the modified nano titanium dioxide comprises the following steps:

[0015] (1) Put ethanol, deionized water and ammonia water in a reactor, stir at 45-55°C and drop tetraethyl orthosilicate, keep in a constant temperature water bath for 22-25 hours, then add nano-titanium dioxide and stir to prepare nano-titanium dioxide hybrid silica sol;

[0016] (2) Tetramethyldisiloxane and vinyltrimethoxysilane are placed in a reactor containing toluene, nitrogen is introduced into the reaction, the temperature is raised to 75-85°C, Wilkinson catalyst is added, and the reaction is stirred for 5-8 hours. After the reaction is completed, the reaction is cooled to room temperature, the solvent is removed by rotary evaporation, and the modified silane coupling agent is prepared by silica gel column chromatography;

[0017] (3) Place the nano-titanium dioxide hybrid silica sol in a reactor, add a modified silane coupling agent, and stir the reaction at 60-85°C for 4-8 hours to prepare modified nano-titanium dioxide.

[0018] Preferably, in step (1), the molar ratio of ethanol, deionized water, ammonia water and tetraethyl orthosilicate is 16-19:7-10:0.05-0.15:1.

[0019] Preferably, in step (2), the molar ratio of tetramethyldisiloxane to vinyltrimethoxysilane is 1:1-2.

[0020] Preferably, in step (3), the mass ratio of nano-titanium dioxide hybrid silica sol to modified silane coupling agent is 1:0.5-1.

[0021] Beneficial effects of the present invention:

[0022] The present invention utilizes the hydroxyl group in the 2-(2,4-dihydroxyphenyl)-2H-benzotriazole structure and the chlorine atom in the 2-chloro-4,6-diamino-1,3,5-triazine structure to undergo a substitution reaction, thereby preparing an amine chain extender with a benzotriazole group as a parent structure and a nitrogen-containing element introduced therein, thereby improving the UV protection ability and flame retardant effect of the material. In addition, the present invention utilizes the ester exchange reaction between 1,3,5-tris(2-hydroxyethyl)cyanuric acid and dimethyl methylphosphonate to prepare a flame retardant crosslinking agent containing nitrogen and phosphorus elements, and then introduces the amine chain extender and the flame retardant crosslinking agent into the waterborne polyurethane structure chain, and simultaneously adds modified nano titanium dioxide to improve the mechanical properties of the waterborne polyurethane emulsion, and the modified nano titanium dioxide and the amine chain extender play a synergistic UV protection effect, while ensuring the modified The treated fabric has good water washing stability, wherein the modified nano titanium dioxide first uses tetraethyl orthosilicate as a silicon source, and the titanium on the surface of the nano titanium dioxide is bonded to the silicon formed by the hydrolysis of tetraethyl orthosilicate, and hydrolyzes and condenses to prepare a nano titanium dioxide hybrid silica sol with a Si-O-Ti structure, and then tetramethyldisiloxane and vinyltrimethoxysilane are used for a silylation reaction to prepare a modified silane coupling agent, and the silicon hydroxyl group in the structure of the modified silane coupling agent and the hydroxyl group in the structure of the nano titanium dioxide hybrid silica sol undergo a condensation reaction to prepare the modified nano titanium dioxide, which has good interface bonding ability with the surface of the fabric, giving the material excellent UV resistance and water washing stability, and the introduction of silicon-oxygen bonds can give the material excellent heat resistance and mechanical properties. The invention introduces an amine chain extender and a flame retardant crosslinking agent into the main chain of a waterborne polyurethane molecule, and adds modified nano titanium dioxide to prepare a modified waterborne polyurethane, which is then applied to a polyester knitted fabric through an impregnation and drying method, thereby giving the polyester knitted fabric good flame retardancy and improving its ultraviolet protection performance, and ensuring its mechanical properties. DETAILED DESCRIPTION

[0023] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] Example 1 A method for preparing an amine chain extender comprises the following steps:

[0025] 11.4 g of 2-(2,4-dihydroxyphenyl)-2H-benzotriazole and 7 mL of triethylamine were placed in a reactor, and a mixed solution of 7.28 g of 2-chloro-4,6-diamino-1,3,5-triazine and 20 mL of 1,4-dioxane was added. The mixture was stirred at 80°C for 7 hours. After the reaction was completed, the mixture was filtered, washed and dried to prepare an amine chain extender.

[0026] Example 2 A method for preparing a flame retardant crosslinking agent comprises the following steps:

[0027] 65.6 g of 1,3,5-tris(2-hydroxyethyl)cyanuric acid, 49.6 g of dimethyl methylphosphonate and 3.24 g of sodium hydroxide were placed in a reactor and reacted at 160° C. for 12 h. After the reaction was completed, the mixture was cooled to 100° C. and subjected to vacuum rotary evaporation at 200° C. for 2.5 h to prepare a flame retardant crosslinking agent.

[0028] Example 3 A method for preparing modified nano titanium dioxide comprises the following steps:

[0029] (1) 20.7 g of ethanol, 3.6 mL of deionized water and 0.09 g of ammonia water were placed in a reactor, stirred at 50 °C and 6.6 g of tetraethyl orthosilicate was added dropwise, and the mixture was kept in a constant temperature water bath for 24 h. Then, 5 g of nano-titanium dioxide was added and stirred to prepare nano-titanium dioxide hybrid silica sol;

[0030] (2) 7.1 g of tetramethyldisiloxane and 7.8 g of vinyltrimethoxysilane were placed in a reactor containing 50 mL of toluene, nitrogen was introduced into the reaction, the temperature was raised to 80°C, 5 mg of Wilkinson catalyst was added, and the reaction was stirred for 6 h. After the reaction was completed, the mixture was cooled to room temperature, the solvent was removed by rotary evaporation, and the mixture was subjected to silica gel column chromatography. A mixed eluent of 60 mL of n-hexane and 30 mL of ethyl acetate was poured into the chromatography column for washing, and then the solvent was removed by rotary evaporation to prepare a modified silane coupling agent;

[0031] (3) Take 10g of nano-titanium dioxide hybrid silica sol into a reactor, add 5g of modified silane coupling agent, place it at 80°C and stir for 7h to prepare modified nano-titanium dioxide.

[0032] Example 4 A modified waterborne polyurethane emulsion comprises the following raw materials in parts by weight:

[0033] 16 parts of isophorone diisocyanate, 25 parts of polypropylene glycol 2000, 2.5 parts of 2,2-dihydroxymethylpropionic acid, 0.5 parts of dibutyltin dilaurate, 2.5 parts of amine chain extender prepared in Example 1, 2 parts of flame retardant crosslinking agent prepared in Example 2, 3 parts of triethylamine, 63 parts of deionized water, and 4 parts of modified nano titanium dioxide prepared in Example 3.

[0034] The preparation method of the modified waterborne polyurethane emulsion comprises the following steps: weighing each raw material by weight, placing isophorone diisocyanate, polypropylene glycol 2000, 2,2-dihydroxymethyl propionic acid and dibutyltin dilaurate in a reactor, stirring at 80°C for 2 hours under a nitrogen atmosphere, heating to 90°C, adding an amine chain extender and a flame retardant crosslinking agent and continuing the reaction for 2 hours, cooling to 45°C after the reaction is completed, adding triethylamine and stirring for 0.5 hours, then adding deionized water for emulsification, and finally adding modified nano titanium dioxide, stirring and dispersing to prepare the modified waterborne polyurethane emulsion.

[0035] A flame retardant finishing method for polyester knitted fabrics comprises the following steps: using an immersion drying method to finish a modified aqueous polyurethane emulsion onto the polyester knitted fabrics that have been washed and dried with acetone and deionized water, placing the fabrics in an oven at 80°C for drying for 72 hours, and taking the fabrics out after they are completely dried.

[0036] Example 5 A modified waterborne polyurethane emulsion comprises the following raw materials in parts by weight:

[0037] 17 parts of isophorone diisocyanate, 28 parts of polypropylene glycol 2000, 3.5 parts of 2,2-dihydroxymethylpropionic acid, 0.5 parts of dibutyltin dilaurate, 3.5 parts of amine chain extender prepared in Example 1, 3 parts of flame retardant crosslinking agent prepared in Example 2, 5 parts of triethylamine, 68 parts of deionized water, and 5 parts of modified nano titanium dioxide prepared in Example 3.

[0038] The preparation method of the modified aqueous polyurethane emulsion and the flame retardant finishing method of polyester knitted fabric are the same as those in Example 4.

[0039] Example 6 A modified waterborne polyurethane emulsion comprises the following raw materials in parts by weight:

[0040] 20 parts of isophorone diisocyanate, 30 parts of polypropylene glycol 2000, 4.5 parts of 2,2-dihydroxymethylpropionic acid, 1 part of dibutyltin dilaurate, 5 parts of the amine chain extender prepared in Example 1, 5 parts of the flame retardant crosslinking agent prepared in Example 2, 6 parts of triethylamine, 72 parts of deionized water, and 6.5 parts of modified nano titanium dioxide prepared in Example 3.

[0041] The preparation method of the modified aqueous polyurethane emulsion and the flame retardant finishing method of polyester knitted fabric are the same as those in Example 4.

[0042] Comparative Example 1 A modified waterborne polyurethane emulsion comprises the following raw materials in parts by weight:

[0043] 20 parts of isophorone diisocyanate, 30 parts of polypropylene glycol 2000, 4.5 parts of 2,2-dihydroxymethylpropionic acid, 1 part of dibutyltin dilaurate, 5 parts of 1,4-butanediol, 5 parts of the flame retardant crosslinking agent prepared in Example 2, 6 parts of triethylamine, 72 parts of deionized water, and 6.5 parts of the modified nano titanium dioxide prepared in Example 3.

[0044] The preparation method of the modified waterborne polyurethane emulsion comprises the following steps: weighing each raw material by weight, placing isophorone diisocyanate, polypropylene glycol 2000, 2,2-dihydroxymethyl propionic acid and dibutyltin dilaurate in a reactor, stirring at 80°C for 2 hours under a nitrogen atmosphere, heating to 90°C, adding 1,4-butanediol and a flame retardant crosslinking agent and continuing the reaction for 2 hours, cooling to 45°C after the reaction is completed, adding triethylamine and stirring for 0.5 hours, then adding deionized water for emulsification, and finally adding modified nano titanium dioxide, stirring and dispersing to prepare the modified waterborne polyurethane emulsion.

[0045] A flame retardant finishing method for polyester knitted fabric is the same as that of Example 4.

[0046] Comparative Example 2 A modified waterborne polyurethane emulsion comprises the following raw materials in parts by weight:

[0047] 20 parts of isophorone diisocyanate, 30 parts of polypropylene glycol 2000, 4.5 parts of 2,2-dihydroxymethylpropionic acid, 1 part of dibutyltin dilaurate, 5 parts of the amine chain extender prepared in Example 1, 5 parts of trimethylolpropane, 6 parts of triethylamine, 72 parts of deionized water, and 6.5 parts of modified nano titanium dioxide prepared in Example 3.

[0048] The preparation method of the modified waterborne polyurethane emulsion comprises the following steps: weighing each raw material by weight, placing isophorone diisocyanate, polypropylene glycol 2000, 2,2-dihydroxymethylpropionic acid and dibutyltin dilaurate in a reactor, stirring at 80°C for 2 hours under a nitrogen atmosphere, heating to 90°C, adding an amine chain extender and trimethylolpropane to continue the reaction for 2 hours, cooling to 45°C after the reaction is completed, adding triethylamine and stirring for 0.5 hours, then adding deionized water for emulsification, and finally adding modified nano titanium dioxide, stirring and dispersing to prepare the modified waterborne polyurethane emulsion.

[0049] A flame retardant finishing method for polyester knitted fabric is the same as that of Example 4.

[0050] Comparative Example 3 A modified waterborne polyurethane emulsion comprises the following raw materials in parts by weight:

[0051] 20 parts of isophorone diisocyanate, 30 parts of polypropylene glycol 2000, 4.5 parts of 2,2-dihydroxymethylpropionic acid, 1 part of dibutyltin dilaurate, 5 parts of the amine chain extender prepared in Example 1, 5 parts of the flame retardant crosslinking agent prepared in Example 2, 6 parts of triethylamine, 72 parts of deionized water, and 6.5 parts of nano titanium dioxide.

[0052] The preparation method of the modified waterborne polyurethane emulsion comprises the following steps: weighing each raw material by weight, placing isophorone diisocyanate, polypropylene glycol 2000, 2,2-dihydroxymethylpropionic acid and dibutyltin dilaurate in a reactor, stirring at 80°C for 2 hours under a nitrogen atmosphere, heating to 90°C, adding an amine chain extender and a flame retardant crosslinking agent and continuing the reaction for 2 hours, cooling to 45°C after the reaction is completed, adding triethylamine and stirring for 0.5 hours, then adding deionized water for emulsification, and finally adding nano titanium dioxide, stirring and dispersing to prepare the modified waterborne polyurethane emulsion.

[0053] A flame retardant finishing method for polyester knitted fabric is the same as that of Example 4.

[0054] Performance Testing

[0055] The polyester knitted fabrics prepared in Examples 4-6 and Comparative Examples 1-3 were subjected to performance tests:

[0056] (1) Mechanical properties test: The breaking strength and breaking elongation were tested according to GB / T 3923.1-2013. The sample size was 20 cm × 5 cm. The test was performed 5 times and the average value was taken. The wear resistance was tested according to GB / T 21196.1-2007. The data results are shown in Table 1.

[0057] (2) Flame retardant performance test: Referring to GB / T 5454-1997, the limiting oxygen index of the sample was measured using a limiting oxygen index tester, and the sample size was 15 cm × 5.8 cm; the vertical burning test was conducted using a fabric flame retardant performance tester, and the sample size was 40 cm × 10 cm. The vertical burning experiment was conducted using the vertical damage length method, and the changes in the fabric during the burning process and the final damage length were recorded. The data results are shown in Table 1.

[0058] (3) Water wash resistance test: Referring to GB / T 3921-2008, the sample was cut into a specimen of 15 cm × 5.8 cm in size, and 200 mL of a detergent with a mass fraction of 0.5% (the detergent adopts AATCC 1993 WOB standard detergent) was prepared. The test sample was placed in the detergent and 50 steel balls with a diameter of 6 mm were added. The sample was washed at 50°C and the flame retardant properties of the sample after washing were tested. The water wash resistance was evaluated by the change in the flame retardant properties. The data results are shown in Table 1.

[0059] Table 1 Test results of sample performance

[0060]

[0061] From the data in Table 1, it can be seen that the polyester knitted fabrics prepared by Examples 4-6 of the present invention have excellent mechanical properties, flame retardant properties and water washability. In Comparative Example 1, the amine chain extender is replaced by a small molecule chain extender 1,4-butanediol in equal amounts, and in Comparative Example 2, the flame retardant crosslinker is replaced by trimethylolpropane in equal amounts. The flame retardant properties of Comparative Examples 1-2 are significantly lower than those of Examples 4-6, indicating that the addition of amine chain extenders and flame retardant crosslinkers can improve the flame retardant properties of the material. In Comparative Example 3, nano titanium dioxide is not modified, and the measured breaking strength, elongation at break and wear resistance times are lower than those of Examples 4-6. The possible reason is that the Si-O-Ti structure and silicon-oxygen bond are not introduced, and the mechanical properties are reduced due to the agglomeration of nano titanium dioxide.

[0062] (4) UV protection performance test: Referring to GB / T 18830-2009, the UV protection performance of the samples was tested on the NF2021 UV transmittance and protection performance tester. Referring to GB / T 8629-2017, the fabric was washed in a XQB50-A2039 computer automatic washing machine, and the accompanying laundry and detergent were added. After washing, the fabric was laid flat on the screen drying rack of the oven to dry. The data results are shown in Table 2.

[0063] Table 2 Test results of UV protection performance of samples

[0064]

[0065] It can be seen from the data in Table 2 that the polyester knitted fabrics finished by Examples 4-6 of the present invention have excellent ultraviolet protection performance and water washing stability. The ultraviolet protection performance measured in Comparative Example 1 is worse than that of Examples 4-6, indicating that the introduction of benzotriazole groups can improve the ultraviolet protection performance of the material, and the water washing resistance effect of the ultraviolet protection performance measured in Comparative Example 3 is worse than that of Examples 4-6, indicating that the addition of modified nano titanium dioxide can improve the water washing stability of the ultraviolet protection performance of the material.

[0066] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0067] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A flame retardant finishing method for polyester knitted fabrics, characterized in that: The following steps are involved: The modified waterborne polyurethane emulsion is applied to the washed and dried polyester knitted fabric by the dipping and drying method, and then placed in an oven for drying and taken out after being completely dried. The modified waterborne polyurethane emulsion comprises the following raw materials in parts by weight: 15-20 parts of isophorone diisocyanate, 25-32 parts of polypropylene glycol 2000, 2-5 parts of 2,2-dihydroxymethylpropionic acid, 0.5-1 parts of dibutyltin dilaurate, 2.5-5 parts of amine chain extender, 2-5 parts of flame retardant crosslinking agent, 3-6 parts of triethylamine, 60-75 parts of deionized water, and 4-7 parts of modified nano titanium dioxide; The amine chain extender is prepared by substitution reaction between 2-(2,4-dihydroxyphenyl)-2H-benzotriazole and 2-chloro-4,6-diamino-1,3,5-triazine; the flame retardant crosslinker is prepared by transesterification reaction between 1,3,5-tris(2-hydroxyethyl)cyanuric acid and dimethyl methylphosphonate; the modified nano titanium dioxide is prepared by sol-gel method using nano titanium dioxide hybrid silica sol and modified by modified silane coupling agent obtained by hydrosilylation reaction between tetramethyldisiloxane and vinyltrimethoxysilane.

2. The flame retardant finishing method for polyester knitted fabric according to claim 1, characterized in that: The preparation method of the modified waterborne polyurethane emulsion comprises the following steps: weighing various raw materials by weight, placing isophorone diisocyanate, polypropylene glycol 2000, 2,2-dihydroxymethyl propionic acid and dibutyltin dilaurate in a reactor, stirring at 75-85° C. for 2-3 hours under a nitrogen atmosphere, heating to 85-95° C., adding an amine chain extender and a flame retardant crosslinking agent to continue the reaction for 1-2 hours, cooling to 40-50° C. after the reaction is completed, adding triethylamine and stirring for 0.5-1 hour, then adding deionized water for emulsification, and finally adding modified nano titanium dioxide, stirring and dispersing to prepare the modified waterborne polyurethane emulsion.

3. The flame retardant finishing method for polyester knitted fabric according to claim 1, characterized in that: The preparation method of the amine chain extender comprises the following steps: taking 2-(2,4-dihydroxyphenyl)-2H-benzotriazole and triethylamine in a reactor, adding a mixed solution of 2-chloro-4,6-diamino-1,3,5-triazine and 1,4-dioxane, placing the mixture at 80°C and stirring for reaction for 6-8h, and after the reaction is completed, filtering, washing and drying to prepare the amine chain extender.

4. The flame retardant finishing method for polyester knitted fabric according to claim 3, characterized in that: The molar ratio of the 2-(2,4-dihydroxyphenyl)-2H-benzotriazole to 2-chloro-4,6-diamino-1,3,5-triazine is 1:1-1.

2.

5. The flame retardant finishing method of polyester knitted fabric according to claim 1, characterized in that: The preparation method of the flame retardant crosslinking agent comprises the following steps: taking 1,3,5-tris(2-hydroxyethyl)cyanuric acid, dimethyl methylphosphonate and sodium hydroxide in a reactor, reacting at 160°C for 10-12h, cooling to 95-100°C after the reaction is completed, and vacuum rotary evaporating at 195-205°C for 2-3h to prepare the flame retardant crosslinking agent.

6. The flame retardant finishing method for polyester knitted fabric according to claim 5, characterized in that: The molar ratio of 1,3,5-tris(2-hydroxyethyl)cyanuric acid to dimethyl methylphosphonate is 1:1.3-3.

5.

7. The flame retardant finishing method for polyester knitted fabric according to claim 1, characterized in that: The preparation method of the modified nano titanium dioxide comprises the following steps: (1) Put ethanol, deionized water and ammonia water in a reactor, stir at 45-55°C and drop tetraethyl orthosilicate, keep in a constant temperature water bath for 22-25 hours, then add nano-titanium dioxide and stir to prepare nano-titanium dioxide hybrid silica sol; (2) Tetramethyldisiloxane and vinyltrimethoxysilane are placed in a reactor containing toluene, nitrogen is introduced into the reaction, the temperature is raised to 75-85°C, Wilkinson catalyst is added, and the reaction is stirred for 5-8 hours. After the reaction is completed, the reaction is cooled to room temperature, the solvent is removed by rotary evaporation, and the modified silane coupling agent is prepared by silica gel column chromatography; (3) Place the nano-titanium dioxide hybrid silica sol in a reactor, add a modified silane coupling agent, and stir the reaction at 60-85°C for 4-8 hours to prepare modified nano-titanium dioxide.

8. The flame retardant finishing method for polyester knitted fabric according to claim 7, characterized in that: In the step (1), the molar ratio of ethanol, deionized water, ammonia water and tetraethyl orthosilicate is 16-19:7-10:0.05-0.15:

1.

9. The flame retardant finishing method for polyester knitted fabric according to claim 7, characterized in that: In the step (2), the molar ratio of tetramethyldisiloxane to vinyltrimethoxysilane is 1:1-2.

10. The flame retardant finishing method for polyester knitted fabric according to claim 7, characterized in that: In the step (3), the mass ratio of the nano-titanium dioxide hybrid silica sol to the modified silane coupling agent is 1:0.5-1.

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