A flame retardant aqueous polyurethane emulsion and its preparation method and application

Abstract

The present invention belongs to the technical field of polyurethane, and discloses a flame-retardant water-based polyurethane emulsion, a preparation method thereof and an application thereof. The present invention forms polyalkylsiloxane on the surface of MXene by in-situ condensation of alkylsiloxane, and then uses a silane coupling agent containing an active group (amino group or epoxy group) for end-capping to improve the reactivity of the modified MXene. The prepared modified MXene nanosheets are introduced into the polyurethane molecular chain by copolymerization, which not only improves the storage stability of the emulsion, but also improves the uniformity and durability of the flame retardant performance. After the polymer diol and diisocyanate react to form a prepolymer, the present invention uses a polyalkylsiloxane-modified MXene nanosheet containing an active group for chain extension, and the prepared water-based polyurethane is easy to form a film, and the film has good flexibility and good bonding strength with fiber products.

Description

Technical Field

[0001] The invention relates to the technical field of polyurethane, and in particular to a flame retardant waterborne polyurethane emulsion and a preparation method and application thereof. Background Art

[0002] Waterborne polyurethane (WPU) has a lower volatile organic compound (VOC), excellent chemical resistance, wear resistance and wide applicability to substrates, and its application in leather and microfiber leather finishing is becoming more and more extensive. However, the molecular structure mainly composed of CH, C=O, CC bonds, etc. makes WPU extremely flammable, and the combustion process is accompanied by severe melting and dripping, which limits the wide application of polyurethane synthetic leather in confined spaces such as subways, locomotives, ships and large public buildings.

[0003] According to the existence mode of flame retardant components in waterborne polyurethane, it can be divided into additive flame retardant waterborne polyurethane physically combined with waterborne polyurethane and reactive flame retardant waterborne polyurethane as part of waterborne polyurethane chain segment. Additive flame retardant waterborne polyurethane is to disperse the flame retardant directly in the polyurethane substrate to give it flame retardant properties. It has a short process flow and low production cost, but additive flame retardants have poor compatibility with the substrate and flame retardant particles are easy to migrate and agglomerate, which leads to a sharp deterioration in the mechanical properties of waterborne polyurethane composite flame retardant coatings. Compared with additive flame retardants, reactive flame retardant molecules can be firmly combined with polyurethane polymer chains, have less impact on the mechanical properties of polyurethane, and can be retained in polyurethane for a long time to play a flame retardant role.

[0004] At present, the commonly used flame retardants are mainly halogen compounds, phosphorus compounds and inorganic flame retardants. Phosphorus and nitrogen flame retardants have high flame retardant efficiency, but they will produce a lot of black smoke during the combustion process, and cannot be used in confined spaces such as subways, locomotives, ships and large public buildings; when halogen compounds burn, they will release toxic gases that harm the environment and humans, and their use has been restricted; inorganic flame retardants such as aluminum hydroxide (ATH) and magnesium hydroxide have the advantages of environmental protection and low cost, and are widely used in cable sheath materials, but their flame retardant efficiency is low and the amount added is large, which will have a certain impact on the physical and mechanical properties of the material.

[0005] MXene (general formula: M n+1 X n T x ) is a unique two-dimensional transition metal carbide or nitride layered nanomaterial. Currently, the most widely used is metal carbide (Ti 3 C 2 T x, T is O, OH and F). MXene can be used as a highly efficient flame retardant due to its good thermal stability and excellent catalytic activity. However, unmodified MXene materials tend to aggregate and re-stack, which in turn affects the flame retardant effect and uniformity of the modified materials. In order to overcome the shortcomings of MXene and improve its flame retardant properties, domestic and foreign scholars have studied modifications such as doping, chemical modification, surface functional group modification or defect modification, and have achieved certain results. Yu et al. used tetrabutylphosphine chloride and hexadecyltrimethylammonium bromide to functionalize the surface of MXene to reduce the polarity of the material, so that it can be better dispersed in weakly polar polymers (Yu B, Tawiah B, Wang LQ, et al. Interface decoration of exfoliated MXene ultra-thin nanosheets forfire and smoke suppressions of thermoplastic polyurethane elastomer[J]. Journal of Hazardous Materials, 2019, 374: 110-119). ZL 202111319586.4 discloses a method for preparing a polyurethane anticorrosive coating synergistically modified with MXene and carbon nanotubes, which is prepared by adding alkylsiloxane-modified MXene and amino carbon nanotube dispersion to polyurethane emulsion by physical blending. Through searching, it was found that there have been many reports on the application of MXene in polyurethane materials, but most of them are introduced into polyurethane emulsions as additives by physical blending, and such emulsions have the defect of poor storage stability. Summary of the invention

[0006] The purpose of the present invention is to provide a flame retardant waterborne polyurethane emulsion and a preparation method and application thereof, so as to solve the problems that the flame retardant in the existing flame retardant waterborne polyurethane emulsion is easy to fall off, the flame retardant effect is poor, and the flame retardant is easy to affect the performance of polyurethane.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] The present invention provides a method for preparing a flame retardant aqueous polyurethane emulsion, comprising the following steps:

[0009] (1) mixing a polymer diol and a diisocyanate to react to obtain a mixture a;

[0010] (2) Mixing mixture a, dibutyltin dilaurate and N,N-dimethylformamide to react to obtain mixture b;

[0011] (3) Mixing mixture b, modified MXene and N,N-dimethylformamide to carry out a chain extension reaction to obtain mixture c;

[0012] (4) Mixing mixture c, an antioxidant, triethylamine and N,N-dimethylformamide for neutralization reaction to obtain mixture d;

[0013] (5) Mixing mixture d with part of water, and after the phase inversion is successful, adding the remaining water and diethylenetriamine to mix and emulsify, removing N,N-dimethylformamide, and obtaining a flame retardant waterborne polyurethane emulsion;

[0014] The preparation method of the modified MXene comprises the following steps: ultrasonically dispersing MXene nanosheets in a mixed solution, and then sequentially adding alkyl siloxane and a modifier containing an active group to react to obtain the modified MXene.

[0015] Preferably, in the above-mentioned method for preparing a flame-retardant aqueous polyurethane emulsion, in the method for preparing the modified MXene, the mixed solution is a mixture of a surfactant, a defoaming agent, hydrochloric acid, and water; the concentration of the MXene nanosheets in the mixed solution is 5~10 g / L; the concentration of the alkyl siloxane in the mixed solution is 100~200 g / L; the concentration of the modifier containing an active group in the mixed solution is 10~20 g / L.

[0016] Preferably, in the above-mentioned method for preparing a flame-retardant aqueous polyurethane emulsion, in the method for preparing the modified MXene, the alkyl siloxane is one or more of methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, n-butyltrimethoxysilane, isobutyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, propyltriethoxysilane, n-butyltriethoxysilane, and isobutyltriethoxysilane.

[0017] Preferably, in the above-mentioned method for preparing a flame-retardant aqueous polyurethane emulsion, in the method for preparing the modified MXene, the modifier containing an active group is one or more of 3-aminopropyltrimethoxysilane, 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropyl(dimethoxy)methylsilane, 3-aminopropyl(diethoxy)methylsilane, 3-ureapropyltriethoxysilane, N-(β-aminoethyl-γ-aminopropyl)methyldimethoxysilane, and 3-aminopropyltriethoxysilane.

[0018] Preferably, in the above-mentioned method for preparing a flame-retardant aqueous polyurethane emulsion, in the method for preparing the modified MXene, after adding the alkyl siloxane, react at 25°C for 60 to 120 minutes, heat to 40 to 60°C and react for 30 to 60 minutes, then add a modifier containing an active group, and react at 40 to 60°C for 30 to 60 minutes.

[0019] Preferably, in the above-mentioned method for preparing a flame-retardant aqueous polyurethane emulsion, the mass ratio of the polymer diol to the diisocyanate in step (1) is 15-25:20-30; the reaction temperature in step (1) is 60-65° C.; the reaction time in step (1) is 60-90 min;

[0020] The ratio of the polymer diol in step (1) to the dibutyltin dilaurate and N,N-dimethylformamide in step (2) is 15-25 g: 0.1-0.3 g: 10-20 mL; the reaction temperature in step (2) is 70-75° C.; the reaction time in step (2) is 90-120 min;

[0021] The ratio of the polymer diol in step (1) to the antioxidant, triethylamine, and N,N-dimethylformamide in step (4) is 15-25 g: 0.05-0.1 g: 3-5 g: 10 mL; the temperature of the neutralization reaction in step (4) is 55° C.; the time of the neutralization reaction in step (4) is 30-60 min;

[0022] The ratio of the polymer diol in step (1) to the total volume of the partial water and the remaining water in step (5) and diethylenetriamine is 15-25 g: 200-300 mL: 0.5-1 mL; the emulsification temperature in step (5) is 25° C.; and the emulsification time in step (5) is 60-120 min.

[0023] Preferably, in the above-mentioned method for preparing a flame-retardant aqueous polyurethane emulsion, the amount ratio of the polymer diol in step (1) to the modified MXene and N,N-dimethylformamide in step (3) is 15-25 g: 20-30 g: 20-40 mL; the temperature of the chain extension reaction in step (3) is 80-90° C.; and the time of the chain extension reaction in step (3) is 60-90 min.

[0024] Preferably, in the above-mentioned method for preparing a flame-retardant aqueous polyurethane emulsion, the polymer diol in step (1) is a mixture of polycaprolactone polyol and polyester diol in a mass ratio of 1:2; and the diisocyanate in step (1) is a mixture of isophorone diisocyanate and dicyclohexylmethane diisocyanate in a mass ratio of 2:1.

[0025] The invention also provides a flame retardant waterborne polyurethane emulsion prepared by a method for preparing the flame retardant waterborne polyurethane emulsion.

[0026] The invention also provides an application of the flame retardant aqueous polyurethane emulsion in finishing of fiber products.

[0027] It can be seen from the above technical solution that compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The present invention first forms polyalkylsiloxane on the surface of MXene by in-situ condensation of alkylsiloxane, which can effectively reduce the polarity of the surface of MXene nanosheets and improve the dispersibility of modified MXene nanosheets in polyurethane prepolymers; secondly, the polyalkylsiloxane is capped with a silane coupling agent containing an active group (amino or epoxy), and the modified MXene nanosheets can be introduced into the polyurethane molecular chain through copolymerization, which not only improves the storage stability of the emulsion, but also improves the uniformity and durability of the flame retardant performance. The present invention uses alkylsiloxane to modify MXene nanosheets, which can achieve a synergistic effect and thus improve the flame retardant effect.

[0029] (2) In the present invention, after the polymer diol and diisocyanate react to form a prepolymer, the chain is extended by using a polyalkylsiloxane-modified MXene nanosheet containing an active group. The resulting waterborne polyurethane is easy to form a film, and the film has good flexibility and good bonding strength with fiber products.

[0030] (3) The present invention can generate multiple active groups on the surface of MXene by controlling the amount of silane coupling agent, and use them to extend the chain to generate modified polyurethane with a spatial network structure (taking epoxy as an active group as an example, the reaction process is as follows Figure 1 As shown), improve the mechanical strength of the polyurethane film. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required to be used in the description of the embodiments or the prior art are briefly introduced below.

[0032] Figure 1 It is a schematic diagram of the reaction process of the flame retardant waterborne polyurethane emulsion of the present invention to form a spatial network structure. DETAILED DESCRIPTION

[0033] The present invention provides a method for preparing a flame retardant aqueous polyurethane emulsion, comprising the following steps:

[0034] (1) mixing a polymer diol and a diisocyanate to react to obtain a mixture a;

[0035] (2) Mixing mixture a, dibutyltin dilaurate and N,N-dimethylformamide to react to obtain mixture b;

[0036] (3) Mixing mixture b, modified MXene and N,N-dimethylformamide to carry out a chain extension reaction to obtain mixture c;

[0037] (4) Mixing mixture c, an antioxidant, triethylamine and N,N-dimethylformamide for neutralization reaction to obtain mixture d;

[0038] (5) Mix the mixture d with part of the water. After the phase inversion is successful, add the remaining water and diethylenetriamine to mix and emulsify, remove N,N-dimethylformamide, and obtain a flame-retardant water-based polyurethane emulsion.

[0039] In the present invention, the polymer diol in step (1) further includes a dehydration treatment before use; the temperature of the dehydration treatment is preferably 100° C.; the time of the dehydration treatment is preferably 1 to 2 hours, more preferably 1.5 to 2 hours, and more preferably 2 hours.

[0040] In the present invention, the polymer diol in step (1) is preferably a mixture of polycaprolactone polyol (PLG) and polyester diol (PBA2000) in a mass ratio of 1:2.

[0041] In the present invention, the diisocyanate in step (1) is preferably a mixture of isophorone diisocyanate (IPDI) and dicyclohexylmethane diisocyanate (HMDI) in a mass ratio of 2:1.

[0042] In the present invention, the mass ratio of the polymer diol to the diisocyanate in step (1) is preferably 15-25:20-30, more preferably 17-22:23-27, and more preferably 20:25; the reaction temperature in step (1) is preferably 60-65°C, more preferably 64-65°C, and more preferably 65°C; the reaction time in step (1) is preferably 60-90 min, more preferably 60-80 min, and more preferably 60 min.

[0043] In the present invention, the amount ratio of the polymer diol in step (1) to the dibutyltin dilaurate and N,N-dimethylformamide in step (2) is preferably 15-25 g: 0.1-0.3 g: 10-20 mL, more preferably 17-22 g: 0.1-0.2 g: 10-15 mL, more preferably 20 g: 0.1 g: 10 mL; the reaction temperature in step (2) is preferably 70-75 ° C, more preferably 70-72 ° C, more preferably 70 ° C; the reaction time in step (2) is preferably 90-120 min, more preferably 90-100 min, more preferably 90 min.

[0044] In the present invention, the mixing in step (2) is preferably performed by preliminarily mixing dibutyltin dilaurate and mixture a at the reaction temperature of step (1), and then, during the process of heating from the reaction temperature of step (1) to the reaction temperature of step (2), adding N,N-dimethylformamide in equal amounts twice to the mixed system consisting of mixture a and dibutyltin dilaurate to complete the mixing.

[0045] In the present invention, the amount ratio of the polymer diol in step (1) to the modified MXene and N,N-dimethylformamide in step (3) is preferably 15-25 g: 20-30 g: 20-40 mL, more preferably 17-22 g: 20-25 g: 25-30 mL, and more preferably 20 g: 20 g: 25 mL; the temperature of the chain extension reaction in step (3) is preferably 80-90 ° C, more preferably 82-88 ° C, and more preferably 85 ° C; the time of the chain extension reaction in step (3) is preferably 60-90 min, more preferably 60-70 min, and more preferably 60 min.

[0046] In the present invention, the antioxidant in step (4) is preferably antioxidant 1010.

[0047] In the present invention, the usage ratio of the polymer diol in step (1) to the antioxidant, triethylamine and N,N-dimethylformamide in step (4) is preferably 15-25 g: 0.05-0.1 g: 3-5 g: 10 mL, more preferably 17-22 g: 0.05-0.06 g: 4-5 g: 10 mL, and more preferably 20 g: 0.05 g: 5 g: 10 mL; the temperature of the neutralization reaction in step (4) is preferably 55° C.; the time of the neutralization reaction in step (4) is preferably 30-60 min, more preferably 50-60 min, and more preferably 60 min.

[0048] In the present invention, the method of mixing the mixture d with a portion of water in step (5) is preferably: adding a portion of water at 5° C. to the mixture d at a stirring rate of 1500 rpm.

[0049] In the present invention, the ratio of the polymer diol in step (1) to the total volume of the partial water and the remaining water in step (5) and the amount of diethylenetriamine is preferably 15-25 g: 200-300 mL: 0.5-1 mL, more preferably 17-22 g: 270-300 mL: 0.8-1 mL, and more preferably 20 g: 300 mL: 1 mL; the emulsification temperature in step (5) is preferably 25° C.; the emulsification time in step (5) is preferably 60-120 min, more preferably 90-120 min, and more preferably 120 min.

[0050] The present invention also provides a method for preparing the modified MXene, comprising the following steps: ultrasonically dispersing MXene nanosheets in a mixed solution, and then sequentially adding alkyl siloxane and a modifier containing an active group to react to obtain the modified MXene.

[0051] In the present invention, the MXene nanosheets are prepared by alkaline etching. The preparation method is described in the existing literature: Li T, Yao L, Liu Q, et al. Fluorine-free synthesis of high-purity Ti 3 C 2 T x (T=OH, O)via Alkali Treatment[J]. Angewandte Chemie, 2018, 57(21):6115-6119.

[0052] In the present invention, the mixed solution is preferably a mixture of a surfactant, a defoamer, hydrochloric acid and water; the concentration of the surfactant in the mixed solution is preferably 1-2 g / L, more preferably 1.1-1.5 g / L, more preferably 1.2 g / L; the concentration of the defoamer in the mixed solution is preferably 0.1-0.3 g / L, more preferably 0.2-0.3 g / L, more preferably 0.2 g / L; the concentration of hydrochloric acid in the mixed solution is preferably 4-6 g / L, more preferably 4-5.5 g / L, more preferably 4 g / L; the surfactant is preferably a mixture of sodium dodecylbenzene sulfonate and twain-80 in a mass ratio of 1:0.1-0.3, more preferably 1:0.3; the defoamer is preferably defoamer DM 8317.

[0053] In the present invention, the concentration of the MXene nanosheets in the mixed solution is preferably 5-10 g / L, more preferably 7-9 g / L, and more preferably 8 g / L; the concentration of the alkyl siloxane in the mixed solution is preferably 100-200 g / L, more preferably 100-130 g / L, and more preferably 100 g / L; the concentration of the modifier containing the active group in the mixed solution is preferably 10-20 g / L, more preferably 14-19 g / L, and more preferably 15 g / L.

[0054] In the present invention, the alkyl siloxane is preferably one or more of methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, n-butyltrimethoxysilane, isobutyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, propyltriethoxysilane, n-butyltriethoxysilane, and isobutyltriethoxysilane, and is further preferably one or more of methyltrimethoxysilane, propyltrimethoxysilane, n-butyltrimethoxysilane, and isobutyltriethoxysilane, and is more preferably propyltrimethoxysilane.

[0055] In the present invention, the modifier containing an active group is preferably one or more of 3-aminopropyltrimethoxysilane, 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropyl(dimethoxy)methylsilane, 3-aminopropyl(diethoxy)methylsilane, 3-ureapropyltriethoxysilane, N-(β-aminoethyl-γ-aminopropyl)methyldimethoxysilane, and 3-aminopropyltriethoxysilane, and is further preferably one or more of 3-aminopropyltrimethoxysilane, 3-glycidyloxypropyl(dimethoxy)methylsilane, 3-aminopropyl(diethoxy)methylsilane, and 3-aminopropyltriethoxysilane, and is more preferably 3-glycidyloxypropyl(dimethoxy)methylsilane.

[0056] In the present invention, the ultrasonic dispersion time is preferably 5 to 10 min, more preferably 7 to 10 min, and more preferably 10 min.

[0057] In the present invention, stirring is also performed during the process of adding the alkylsiloxane and the modifier containing active groups; the stirring rate is preferably 600 rpm.

[0058] In the present invention, after adding the alkyl siloxane, it is preferred to react at 25°C for 60-90min, heat to 40-60°C for 30-60min, then add a modifier containing an active group, and react at 40-60°C for 30-60min; more preferably, react at 25°C for 60-80min, heat to 45-55°C for 40-50min, then add a modifier containing an active group, and react at 45-55°C for 30-40min; more preferably, react at 25°C for 60min, heat to 50°C for 40min, then add a modifier containing an active group, and react at 50°C for 30min.

[0059] The invention also provides a flame retardant waterborne polyurethane emulsion prepared by a method for preparing the flame retardant waterborne polyurethane emulsion.

[0060] The invention also provides an application of the flame retardant aqueous polyurethane emulsion in finishing of fiber products.

[0061] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. 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.

[0062] Example 1

[0063] This embodiment provides a method for preparing a flame retardant aqueous polyurethane emulsion, comprising the following steps:

[0064] (1) Preparation of modified MXene nanosheets: Surfactant (sodium dodecylbenzene sulfonate and twain-80 mixed in a mass ratio of 1:0.3), defoamer DM 8317 was added to the hydrochloric acid aqueous solution so that the concentrations of the surfactant, defoamer and hydrochloric acid were 1.2 g / L, 0.2 g / L and 4 g / L respectively. The mixture was stirred at 300 rpm for 60 min at 25 °C. After the surfactant was fully dissolved, MXene nanosheets were added to make the concentration of the MXene nanosheets 8 g / L. Ultrasonic dispersion was performed for 10 min. Propyl trimethoxy silane was added within 10 min under the stirring condition of 600 rpm to make the concentration of 100 g / L. After the addition, stirring was continued for 60 min. Then, the temperature was raised to 50 °C at a heating rate of 2 °C / min. The mixture was reacted at 600 rpm for 40 min. Then, 3-glycidoxypropyl (dimethoxy) methyl silane was slowly added to make the concentration of 15 g / L. The end-capping reaction was carried out for 30 min. After the reaction was completed, the mixture was centrifuged and washed to obtain polyalkylsiloxane-modified MXene nanosheets containing active groups on the surface.

[0065] (2) Preparation of flame-retardant waterborne polyurethane emulsion: 20 g of polymer diol (PLG and PBA2000 mixed in a mass ratio of 1:2) was added to the reaction equipment, heated to 100 °C under vacuum conditions, dehydrated for 2 h, cooled to 50 °C, added 25 g of diisocyanate (IPDI and HMDI mixed in a mass ratio of 2:1), heated to 65 °C, and reacted at a constant temperature for 60 min; then 0.1 g of dibutyltin dilaurate was added, the temperature was raised to 70 °C, and 10 mL of N,N-dimethylformamide (DMF), continue to react for 90 minutes; then add 25mL of DMF solution containing 20g of modified MXene nanosheets for chain extension, then raise the temperature to 85°C and react at constant temperature for 60min; then cool to 55°C, add 10mL of DMF solution containing 0.05g of antioxidant 1010 and 5g of triethylamine, and neutralize for 60min; slowly add 200mL of 5°C deionized water under stirring at 1500rpm, and after the phase transfer is successful, quickly add 100mL of deionized water, and then add 1mL of diethylenetriamine, continue emulsification at 25°C for 120min, remove the organic solvent, and obtain a flame-retardant water-based polyurethane emulsion.

[0066] Comparative Example 1

[0067] This comparative example provides a method for preparing an aqueous polyurethane emulsion, which is specifically described in Example 1, except that modified MXene nanosheets are not added during the preparation of the aqueous polyurethane emulsion, and a chain extender DMPA is used instead of the modified MXene nanosheets.

[0068] Comparative Example 2

[0069] This comparative example provides a method for preparing a flame retardant aqueous polyurethane emulsion, which is specifically referred to in Example 1, except that no MXene nanosheets are added during the preparation of the modified MXene nanosheets in step (1) of Example 1, that is, the polyalkylsiloxane containing active groups on the surface is prepared in step (1) of this comparative example, and in the preparation of the flame retardant aqueous polyurethane emulsion, the modified MXene nanosheets in Example 1 are replaced by the polyalkylsiloxane containing active groups on the surface.

[0070] Comparative Example 3

[0071] This comparative example provides a method for preparing a flame-retardant aqueous polyurethane emulsion, which is specifically referred to in Example 1, except that during the preparation of the flame-retardant aqueous polyurethane emulsion, diisocyanate is added and then a DMF solution of modified MXene nanosheets is added.

[0072] The mechanical properties of the aqueous polyurethane emulsions prepared in Comparative Example 1, Comparative Example 3 and Example 1 were tested. The aqueous polyurethane emulsions prepared in Comparative Example 1, Comparative Example 3 and Example 1 were evenly spread on a polytetrafluoroethylene plate to form a film, then dried at room temperature, and finally placed in a 70°C oven for drying for 24 hours to obtain a polyurethane coating film, and the film thickness was controlled at 2.0±0.05mm. Referring to GB / T 3923.1-2013 "Determination of breaking strength and breaking elongation of tensile properties of textile fabrics (strip method)", the tensile test of the polyurethane film was carried out using an Instron 3655 universal material testing machine, and each sample was tested 5 times to take the average value. The results are shown in Table 1.

[0073]

[0074] As can be seen from the data in Table 1, the fracture strength and elongation at break of the polyurethane film obtained by the waterborne polyurethane of Comparative Example 3 are significantly less than those of Example 1 and Comparative Example 1. In addition, the fracture strength of the polyurethane film obtained by the waterborne polyurethane of Example 1 is greater than that of Comparative Example 1, while the elongation at break is slightly reduced. This is because the flexible segments in the waterborne polyurethane molecular chain obtained by polymerization after the polyalkylsiloxane-modified MXene nanosheets containing active groups on the surface are evenly mixed with the monomers of polymer diols and diisocyanates are then unevenly distributed, making the polyurethane less flexible and easy to break when stretched. After the polymer diols react with diisocyanates to form a prepolymer of a certain molecular weight, the polyalkylsiloxane-modified MXene nanosheets containing active groups on the surface are chain extended, and the obtained waterborne polyurethane molecular chain is controllable, and the flexible segments are evenly distributed, and the molecular chain has a spatial network structure, so the polyurethane fracture strength and elongation at break are good.

[0075] The flame retardant performance of the aqueous polyurethane emulsions prepared in Comparative Examples 1 to 3 and Example 1 was tested, and the aqueous polyurethane emulsions prepared in Comparative Examples 1 to 3 and Example 1 were used to prepare flame retardant microfiber leather. Specific method: The polyurethane emulsion is impregnated into the microfiber leather base cloth to ensure that the polyurethane is fully adhered to the microfiber leather base cloth, and then the microfiber leather base cloth is fully impregnated by roller extrusion, and then the excess polyurethane emulsion on the surface is scraped off with a scraper. During the impregnation process, the pressure between the upper and lower rollers is controlled, and the intake is controlled at 30wt% to ensure the best performance of the microfiber leather product. Finally, the sample impregnated with polyurethane is dried to obtain flame retardant microfiber leather. Among them, the limiting oxygen index test refers to GB / T 5454-1997 "Textile Combustion Performance Test Oxygen Index Method", and the damage length, smoldering time and afterburning time test refer to GB / T 5455-2014 "Determination of vertical damage length, smoldering and afterburning time of textile combustion performance". The results are shown in Table 2.

[0076]

[0077] It can be seen from the data in Table 2 that the polyurethane without flame retardant (Comparative Example 1) is flammable. The polyalkylsilane-modified polyurethane containing active groups on the surface (Comparative Example 2) has a certain flame retardant effect, and the flame retardant effect of the polyurethane prepared by chain extension of polyalkylsiloxane-modified MXene nanosheets containing active groups on the surface (Comparative Example 3 and Example 1) is significantly better than the flame retardant effect of a single polyalkylsilane-modified polyurethane, indicating that polyalkylsiloxane and MXene have a synergistic effect on flame retardant properties. At the same time, the addition time of the polyalkylsiloxane-modified MXene nanosheets containing active groups on the surface in the polyurethane synthesis process has no obvious effect on the flame retardant properties of the polyurethane, because the flame retardant properties of the polyurethane mainly depend on the amount of flame retardant.

[0078] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a flame retardant aqueous polyurethane emulsion, characterized in that: The following steps are involved: (1) mixing a polymer diol and a diisocyanate to react to obtain a mixture a; (2) Mixing mixture a, dibutyltin dilaurate and N,N-dimethylformamide to react to obtain mixture b; (3) Mixing mixture b, modified MXene and N,N-dimethylformamide to carry out a chain extension reaction to obtain mixture c; (4) Mixing mixture c, an antioxidant, triethylamine and N,N-dimethylformamide for neutralization reaction to obtain mixture d; (5) Mixing mixture d with part of water, and after the phase inversion is successful, adding the remaining water and diethylenetriamine to mix and emulsify, removing N,N-dimethylformamide, and obtaining a flame retardant waterborne polyurethane emulsion; The preparation method of the modified MXene comprises the following steps: ultrasonically dispersing MXene nanosheets in a mixed solution, and then sequentially adding alkyl siloxane and a modifier containing an active group to react to obtain a modified MXene; The alkyl siloxane is one or more of methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, n-butyltrimethoxysilane, isobutyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, propyltriethoxysilane, n-butyltriethoxysilane and isobutyltriethoxysilane; The modifier containing active groups is one or more of 3-aminopropyltrimethoxysilane, 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropyl(dimethoxy)methylsilane, 3-aminopropyl(diethoxy)methylsilane, 3-ureapropyltriethoxysilane, N-(β-aminoethyl-γ-aminopropyl)methyldimethoxysilane, and 3-aminopropyltriethoxysilane.

2. The method for preparing a flame retardant aqueous polyurethane emulsion according to claim 1, characterized in that: In the preparation method of the modified MXene, the mixed solution is a mixture of a surfactant, a defoaming agent, hydrochloric acid, and water; the concentration of the MXene nanosheets in the mixed solution is 5-10 g / L; the concentration of the alkyl siloxane in the mixed solution is 100-200 g / L; and the concentration of the modifier containing an active group in the mixed solution is 10-20 g / L.

3. The method for preparing a flame retardant aqueous polyurethane emulsion according to claim 1 or 2, characterized in that: In the preparation method of the modified MXene, the modifier containing active groups is 3-glycidoxypropyl(dimethoxy)methylsilane or 3-aminopropyl(diethoxy)methylsilane.

4. The method for preparing a flame retardant aqueous polyurethane emulsion according to claim 3, characterized in that: In the preparation method of the modified MXene, after adding alkyl siloxane, react at 25° C. for 60 to 120 minutes, heat to 40 to 60° C. for 30 to 60 minutes, then add a modifier containing an active group, and react at 40 to 60° C. for 30 to 60 minutes.

5. The method for preparing a flame retardant aqueous polyurethane emulsion according to claim 1, characterized in that: The mass ratio of the polymer diol to the diisocyanate in step (1) is 15-25:20-30; the reaction temperature in step (1) is 60-65° C.; the reaction time in step (1) is 60-90 min; The ratio of the polymer diol in step (1) to the dibutyltin dilaurate and N,N-dimethylformamide in step (2) is 15-25 g: 0.1-0.3 g: 10-20 mL; the reaction temperature in step (2) is 70-75° C.; the reaction time in step (2) is 90-120 min; The ratio of the polymer diol in step (1) to the antioxidant, triethylamine, and N,N-dimethylformamide in step (4) is 15-25 g: 0.05-0.1 g: 3-5 g: 10 mL; the temperature of the neutralization reaction in step (4) is 55° C.; the time of the neutralization reaction in step (4) is 30-60 min; The ratio of the polymer diol in step (1) to the total volume of the partial water and the remaining water in step (5) and diethylenetriamine is 15-25 g: 200-300 mL: 0.5-1 mL; the emulsification temperature in step (5) is 25° C.; and the emulsification time in step (5) is 60-120 min.

6. The method for preparing a flame retardant aqueous polyurethane emulsion according to claim 5, characterized in that: The ratio of the amount of the polymer diol in step (1) to the amount of the modified MXene and N,N-dimethylformamide in step (3) is 15-25 g: 20-30 g: 20-40 mL; the temperature of the chain extension reaction in step (3) is 80-90° C.; and the time of the chain extension reaction in step (3) is 60-90 min.

7. The method for preparing a flame retardant aqueous polyurethane emulsion according to claim 6, characterized in that: The polymer diol in step (1) is a mixture of polycaprolactone polyol and polyester diol in a mass ratio of 1:2; the diisocyanate in step (1) is a mixture of isophorone diisocyanate and dicyclohexylmethane diisocyanate in a mass ratio of 2:

1.

8. A flame retardant aqueous polyurethane emulsion prepared by the method for preparing a flame retardant aqueous polyurethane emulsion according to any one of claims 1 to 7.

9. Use of the flame retardant aqueous polyurethane emulsion according to claim 8 in finishing of fiber products.

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