A kind of waterborne polyurethane-based flame-retardant microfiber synthetic leather and preparation method thereof

Abstract

The present invention belongs to the technical field of synthetic leather, and discloses a waterborne polyurethane-based flame-retardant ultra-fine synthetic leather and a preparation method thereof. The present invention forms polyalkylsiloxane on the surface of MXene by in-situ condensation of alkylsiloxane, and then caps the polyalkylsiloxane with a silane coupling agent containing an active group primary amine group, thereby improving the reactivity of the modified MXene. After the aromatic aldehyde-capped polyurethane is successfully phase-transferred, the aqueous dispersion of the modified MXene is added for emulsification. Due to the presence of the aqueous medium, the aromatic aldehyde-capped polyurethane and the modified MXene nanosheets can coexist stably without reacting. Only during the drying process, as the water content decreases, the reaction generates a substance with a larger molecular weight, completing the valence bond bonding between the flame retardant and the polyurethane. The present invention can not only increase the solid content of the composite emulsion, but also improve the flame retardant durability of the composite emulsion-modified ultra-fine synthetic leather material.

Description

Technical Field

[0001] The invention relates to the technical field of synthetic leather, and in particular to a waterborne polyurethane-based flame-retardant ultra-fiber synthetic leather and a preparation method thereof. Background Art

[0002] Microfiber synthetic leather (microfiber leather) is composed of microfiber nonwoven fabric as the base material and polyurethane as the surface coating. Microfiber leather has excellent properties such as wear resistance, soft touch, and sun resistance. It has been widely used in automotive interiors, aerospace, medical devices, sports equipment, high-speed rail seats and other fields. The molecular structure of water-based polyurethane (WPU), the main component of microfiber leather, is mainly composed of CH, C=O, CC bonds, etc. It is flammable, and the combustion process is accompanied by severe melting and dripping, which limits the wide application of polyurethane microfiber 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 flame retardant directly in polyurethane substrate to give it flame retardant properties. Its process flow is short and production cost is low, but additive flame retardant has poor compatibility with substrate and easy migration and agglomeration of flame retardant particles, which leads to a sharp deterioration of mechanical properties of waterborne polyurethane composite flame retardant coating. Compared with additive flame retardant, reactive flame retardant molecules can be firmly bound to polyurethane polymer chains, and their influence on mechanical properties of polyurethane is relatively low, and they can be retained in polyurethane for a long time to play a flame retardant role. However, the introduction of reactive flame retardant by copolymerization in the process of polyurethane synthesis will increase the molecular weight of polyurethane and increase the viscosity of the system, which will affect its emulsification, and the amount of flame retardant involved in copolymerization has an important influence on the performance of polyurethane.

[0004] The properties of the flame retardant itself have a decisive influence on the flame retardant properties of the material. 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; 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, but their flame retardant efficiency is low and the amount added is large. MXene (general formula M n+1 X n T x ) is a unique two-dimensional transition metal carbide or nitride layered nanomaterial. Due to its good thermal stability and excellent catalytic activity, it can be used as a highly efficient flame retardant. Currently, the most widely used is metal carbide (Ti3C2T x, T is O, OH and F). 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 for fire 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. The coating is prepared by adding alkylsiloxane-modified MXene and amino carbon nanotube dispersion to polyurethane emulsion by physical blending. Literature search revealed that there have been many reports on the application of MXene in polyurethane materials, but most of them are introduced into polyurethane emulsion as an additive by physical blending. When it is used to prepare flame-retardant products, the flame retardant is easy to fall off during use, affecting the durability of the flame retardant effect. Summary of the invention

[0005] The purpose of the present invention is to provide a waterborne polyurethane-based flame-retardant microfiber synthetic leather and a preparation method 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.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a waterborne polyurethane-based flame-retardant ultra-fiber synthetic leather, comprising the following steps:

[0008] The microfiber synthetic leather base fabric is impregnated in a flame-retardant water-based polyurethane emulsion, and a roller is used to squeeze the microfiber synthetic leather base fabric during the impregnation process; after the impregnation is completed, the base fabric is dried to obtain a water-based polyurethane-based flame-retardant microfiber synthetic leather;

[0009] The method for preparing the flame retardant aqueous polyurethane emulsion comprises the following steps:

[0010] (1) mixing a polymer diol and a diisocyanate to react to obtain a mixture a;

[0011] (2) Mixing mixture a, dibutyltin dilaurate and N,N-dimethylformamide to react to obtain mixture b;

[0012] (3) Mixing the mixture b, the chain extender and N,N-dimethylformamide to carry out a chain extension reaction to obtain a mixture c;

[0013] (4) Mixing the mixture c and the capping agent to perform a capping reaction to obtain a mixture d;

[0014] (5) Mixing mixture d, an antioxidant, triethylamine and N,N-dimethylformamide for neutralization reaction to obtain mixture e;

[0015] (6) Mixing the mixture e with water, and after the phase inversion is successful, adding the aqueous dispersion of modified MXene and diethylenetriamine to mix and emulsify, removing N,N-dimethylformamide, and obtaining a flame-retardant waterborne polyurethane emulsion;

[0016] 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;

[0017] The modifier containing active groups is one or more of 3-aminopropyltrimethoxysilane, 3-aminopropyl(diethoxy)methylsilane, 3-ureapropyltriethoxysilane, N-(β-aminoethyl-γ-aminopropyl)methyldimethoxysilane and 3-aminopropyltriethoxysilane.

[0018] Preferably, in the above-mentioned method for preparing waterborne polyurethane-based flame-retardant microfiber synthetic leather, the bath ratio of the impregnation is 1:5-10; and the impregnation time is preferably 10-30 min.

[0019] Preferably, in the above-mentioned method for preparing a waterborne polyurethane-based flame-retardant microfiber synthetic leather, 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 60~100 g / L; the concentration of the modifier containing an active group in the mixed solution is 10~20 g / L.

[0020] Preferably, in the above-mentioned method for preparing a waterborne polyurethane-based flame-retardant microfiber synthetic leather, 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.

[0021] Preferably, in the above-mentioned method for preparing a waterborne polyurethane-based flame-retardant microfiber synthetic leather, in the method for preparing the modified MXene, after adding alkyl siloxane, react at 25°C for 60 to 90 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.

[0022] Preferably, in the above-mentioned method for preparing a waterborne polyurethane-based flame-retardant microfiber synthetic leather, in the method for preparing the flame-retardant waterborne polyurethane emulsion, the mass ratio of the polymer diol to the diisocyanate in step (1) is 30-40:20-30; the reaction temperature in step (1) is 60-65°C; the reaction time in step (1) is 60-90 min;

[0023] The ratio of the polymer diol in step (1) to the dibutyltin dilaurate and N,N-dimethylformamide in step (2) is 30-40 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;

[0024] The ratio of the polymer diol in step (1) to the chain extender and N,N-dimethylformamide in step (3) is 30-40 g: 5-10 g: 15-20 mL; the temperature of the chain extension reaction in step (3) is 80-90° C.; the time of the chain extension reaction in step (3) is 60-90 min;

[0025] The mass ratio of the polymer diol in step (1) to the end-capping agent in step (4) is 30-40:4-8; the temperature of the end-capping reaction in step (4) is 80-90° C.; the time of the end-capping reaction in step (4) is 20-30 min;

[0026] The amount ratio of the polymer diol in step (1) to the antioxidant, triethylamine, and N,N-dimethylformamide in step (5) is 30-40 g: 0.05-0.1 g: 3-5 g: 10 mL; the temperature of the neutralization reaction in step (5) is 55° C.; and the time of the neutralization reaction in step (5) is 30-60 min.

[0027] Preferably, in the above-mentioned method for preparing an aqueous polyurethane-based flame-retardant microfiber synthetic leather, in the method for preparing the flame-retardant aqueous polyurethane emulsion, the amount ratio of the polymer diol in step (1) to the water, the aqueous dispersion of modified MXene, and diethylenetriamine in step (6) is 30~40g:40~60mL:150~200mL:0.5~1mL; the emulsification temperature in step (6) is 25°C; and the emulsification time in step (6) is 60~120min.

[0028] Preferably, in the above-mentioned method for preparing an aqueous polyurethane-based flame-retardant microfiber synthetic leather, in the method for preparing the flame-retardant aqueous polyurethane emulsion, the mass fraction of the modified MXene in the aqueous dispersion of the modified MXene is 30~50%.

[0029] Preferably, in the above-mentioned method for preparing a waterborne polyurethane-based flame-retardant microfiber synthetic leather, in the method for preparing the flame-retardant waterborne polyurethane emulsion, the capping agent is one of p-hydroxybenzaldehyde, p-hydroxymethylbenzaldehyde, and 2-(2-hydroxyethoxy)benzaldehyde.

[0030] The invention also provides a waterborne polyurethane-based flame-retardant super-fiber synthetic leather prepared by a method for preparing the waterborne polyurethane-based flame-retardant super-fiber synthetic leather.

[0031] It can be seen from the above technical solution that compared with the prior art, the present invention has the following beneficial effects:

[0032] (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 the modified MXene nanosheets in polyurethane prepolymers; secondly, a silane coupling agent containing an active primary amine group (-NH2) is used to end-cap the polyalkylsiloxane to give the modified MXene nanosheets reactive activity. Moreover, the use of alkylsiloxane to modify MXene nanosheets can achieve a synergistic effect, thereby improving the flame retardant effect.

[0033] (2) After the aromatic aldehyde-terminated polyurethane is successfully phase-transferred, the present invention adds a deionized water dispersion of MXene nanosheets modified with polyalkylsiloxane containing primary amine groups for emulsification. In the emulsion, due to the presence of the aqueous medium, the aromatic aldehyde-terminated polyurethane and the MXene nanosheets modified with polyalkylsiloxane containing primary amine groups can stably coexist without reacting. Only during the drying process, as the water content decreases, do they react to generate substances with a larger molecular weight, and at the same time, the valence bond between the flame retardant and the polyurethane is completed. The preparation method of the flame-retardant water-based polyurethane emulsion provided by the present invention can not only increase the solid content of the composite emulsion, but also improve the flame retardant durability of the composite emulsion-modified microfiber synthetic leather material.

[0034] (3) The present invention can generate multiple active groups on the surface of MXene by controlling the amount of silane coupling agent. After the MXene is prepared into a composite emulsion with a benzaldehyde-terminated polyurethane, a film with a spatial network structure can be generated during the drying and dehydration process (the reaction process is as follows Figure 1 As shown), it can effectively improve the mechanical strength of the film. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for describing the embodiments or the prior art are briefly introduced below.

[0036] 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

[0037] The present invention provides a method for preparing a waterborne polyurethane-based flame-retardant ultra-fiber synthetic leather, comprising the following steps:

[0038] The microfiber synthetic leather base fabric is impregnated in a flame-retardant water-based polyurethane emulsion, and a roller is used to squeeze the microfiber synthetic leather base fabric during the impregnation process; and the microfiber synthetic leather base fabric is dried after the impregnation is completed to obtain a water-based polyurethane-based flame-retardant microfiber synthetic leather.

[0039] In the present invention, the immersion temperature is preferably room temperature; the immersion bath ratio is preferably 1:5-10, more preferably 1:6-8, more preferably 1:8; the immersion time is preferably 10-30 min, more preferably 13-20 min, more preferably 15 min.

[0040] In the present invention, the uptake of the flame retardant aqueous polyurethane emulsion by the microfiber synthetic leather base fabric during the impregnation process is preferably 28-32wt%, more preferably 29-31wt%, and more preferably 30wt%.

[0041] In the present invention, after the impregnation is completed, a scraper is used to scrape off the excess flame-retardant aqueous polyurethane emulsion on the surface of the microfiber synthetic leather base fabric.

[0042] In the present invention, the microfiber synthetic leather base fabric can be any conventional base fabric in the art, and the present invention does not limit the type of the microfiber synthetic leather base fabric.

[0043] In the present invention, the drying may be carried out under conventional drying conditions in the art, and the present invention does not limit the drying conditions.

[0044] The present invention also provides a method for preparing the flame retardant aqueous polyurethane emulsion, comprising the following steps:

[0045] (1) mixing a polymer diol and a diisocyanate to react to obtain a mixture a;

[0046] (2) Mixing mixture a, dibutyltin dilaurate and N,N-dimethylformamide to react to obtain mixture b;

[0047] (3) Mixing the mixture b, the chain extender and N,N-dimethylformamide to carry out a chain extension reaction to obtain a mixture c;

[0048] (4) Mixing the mixture c and the capping agent to perform a capping reaction to obtain a mixture d;

[0049] (5) Mixing mixture d, an antioxidant, triethylamine and N,N-dimethylformamide for neutralization reaction to obtain mixture e;

[0050] (6) Mix the mixture e with water. After the phase inversion is successful, add the modified MXene aqueous dispersion and diethylenetriamine to mix and emulsify, remove N,N-dimethylformamide, and obtain a flame-retardant water-based polyurethane emulsion.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] In the present invention, the mass ratio of the polymer diol to the diisocyanate in step (1) is preferably 30-40:20-30, more preferably 30-36:22-27, and more preferably 30:25; the reaction temperature in step (1) is preferably 60-65°C, more preferably 60-63°C, and more preferably 60°C; the reaction time in step (1) is preferably 60-90 min, more preferably 60-80 min, and more preferably 60 min.

[0055] In the present invention, the usage ratio of the polymer diol in step (1) to the dibutyltin dilaurate and N,N-dimethylformamide in step (2) is preferably 30-40 g: 0.1-0.3 g: 10-20 mL, more preferably 30-35 g: 0.1-0.2 g: 12-18 mL, more preferably 30 g: 0.1 g: 15 mL; the reaction temperature in step (2) is preferably 70-75° C., more preferably 70-73° C., more preferably 70° C.; the reaction time in step (2) is preferably 90-120 min, more preferably 90-110 min, more preferably 90 min.

[0056] 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.

[0057] In the present invention, the chain extender in step (3) is preferably dimethylolpropionic acid (DMPA).

[0058] In the present invention, the ratio of the amount of the polymer diol in step (1) to the chain extender and N,N-dimethylformamide in step (3) is preferably 30-40 g: 5-10 g: 15-20 mL, more preferably 30-35 g: 5-8 g: 15-18 mL, more preferably 30 g: 5 g: 15 mL; the temperature of the chain extension reaction in step (3) is preferably 80-90° C., more preferably 80-85° C., more preferably 80° C.; the time of the chain extension reaction in step (3) is preferably 60-90 min, more preferably 60-70 min, more preferably 60 min.

[0059] In the present invention, the end-capping agent in step (4) is preferably one of p-hydroxybenzaldehyde, p-hydroxymethylbenzaldehyde and 2-(2-hydroxyethoxy)benzaldehyde, more preferably p-hydroxybenzaldehyde or p-hydroxymethylbenzaldehyde, and more preferably p-hydroxymethylbenzaldehyde.

[0060] In the present invention, the mass ratio of the polymer diol in step (1) to the end-capping agent in step (4) is preferably 30-40:4-8, more preferably 30-35:6-8, and more preferably 30:8; the temperature of the end-capping reaction in step (4) is preferably 80-90°C, more preferably 80-85°C, and more preferably 80°C; the time of the end-capping reaction in step (4) is preferably 20-30 min, more preferably 25-30 min, and more preferably 30 min.

[0061] In the present invention, the antioxidant in step (5) is preferably antioxidant 1010.

[0062] In the present invention, the amount ratio of the polymer diol in step (1) to the antioxidant, triethylamine and N,N-dimethylformamide in step (5) is preferably 30-40 g: 0.05-0.1 g: 3-5 g: 10 mL, more preferably 30-35 g: 0.05-0.07 g: 3-4 g: 10-15 mL, more preferably 30 g: 0.05 g: 3 g: 10 mL; the temperature of the neutralization reaction in step (5) is preferably 55° C.; the time of the neutralization reaction in step (5) is preferably 30-60 min, more preferably 40-60 min, more preferably 60 min.

[0063] In the present invention, the mass fraction of the modified MXene in the aqueous dispersion of the modified MXene in step (6) is preferably 30-50%, more preferably 35-40%, and more preferably 35%.

[0064] In the present invention, the method of mixing the mixture e with water in step (6) is preferably: adding 5° C. deionized water to the mixture e at a stirring rate of 1500 rpm.

[0065] In the present invention, the amount ratio of the polymer diol in step (1) to the water, the aqueous dispersion of modified MXene, and diethylenetriamine in step (6) is preferably 30-40 g: 40-60 mL: 150-200 mL: 0.5-1 mL, more preferably 30-35 g: 45-60 mL: 150-170 mL: 0.5-0.7 mL, and more preferably 30 g: 50 mL: 150 mL: 0.5 mL; the emulsification temperature in step (6) is preferably 25° C.; the emulsification time in step (6) is preferably 60-120 min, more preferably 100-120 min, and more preferably 120 min.

[0066] 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.

[0067] 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 Ti3C2T x(T=OH, O)via Alkali Treatment[J]. Angewandte Chemie, 2018, 57(21):6115-6119.

[0068] 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 0.3 g / L; the concentration of hydrochloric acid in the mixed solution is preferably 4-6 g / L, more preferably 4.5-6 g / L, more preferably 5 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 1:0.2; the defoamer is preferably defoamer DM 8317.

[0069] In the present invention, the concentration of the MXene nanosheets in the mixed solution is preferably 5-10 g / L, more preferably 8-10 g / L, and more preferably 10 g / L; the concentration of the alkyl siloxane in the mixed solution is preferably 60-100 g / L, more preferably 70-90 g / L, and more preferably 80 g / L; the concentration of the modifier containing the active group in the mixed solution is preferably 10-20 g / L, more preferably 12-18 g / L, and more preferably 15 g / L.

[0070] 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.

[0071] In the present invention, the modifier containing an active group is preferably one or more of 3-aminopropyltrimethoxysilane, 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-aminopropyl(diethoxy)methylsilane, and 3-aminopropyltriethoxysilane, and is more preferably 3-aminopropyl(diethoxy)methylsilane.

[0072] In the present invention, the ultrasonic dispersion time is preferably 5 to 10 min, more preferably 5 to 7 min, and more preferably 5 min.

[0073] 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.

[0074] 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 50-60min, 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 60min, then add a modifier containing an active group, and react at 50°C for 30min.

[0075] The invention also provides a waterborne polyurethane-based flame-retardant super-fiber synthetic leather prepared by a method for preparing the waterborne polyurethane-based flame-retardant super-fiber synthetic leather.

[0076] 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.

[0077] Example 1

[0078] This embodiment provides a method for preparing a flame retardant aqueous polyurethane emulsion, comprising the following steps:

[0079] (1) Preparation of modified MXene nanosheets: Surfactant (sodium dodecylbenzene sulfonate and twain-80 mixed in a mass ratio of 1:0.2), 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, 0.3 g / L and 5 g / L respectively. The mixture was stirred at 300 rpm for 45 min at 25 °C. After the surfactant was fully dissolved, MXene nanosheets were added to make the concentration of the MXene nanosheets 10 g / L. Ultrasonic dispersion was performed for 5 min. Propyl trimethoxy silane was added within 10 min under the stirring condition of 600 rpm to make the concentration of 80 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 60 min. Then, 3-aminopropyl (diethoxy) 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 modified MXene nanosheets.

[0080] (2) Preparation of flame-retardant waterborne polyurethane emulsion: 30 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 60 °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 15 mL of N,N-dimethylformamide (DMF), continue to react for 90 minutes; then add 15mL of DMF solution containing 5g of dihydroxymethylpropionic acid for chain extension, then heat to 80℃, and react at constant temperature for 60min; then add 8g of blocking agent p-hydroxymethylbenzaldehyde to block the isocyanate group, and the reaction time is 30min; then cool to 55℃, add 10mL of DMF solution containing 0.05g of antioxidant 1010 and 3g of triethylamine, and neutralize for 60min; slowly add 50mL of 5℃ deionized water under stirring at 1500rpm, and after the phase inversion is successful, quickly add 150mL of deionized water dispersion of modified MXene nanosheets (the mass fraction of modified MXene nanosheets is 35%), and then add 0.5mL of diethylenetriamine, continue emulsification at 25℃ for 120min, remove the organic solvent, and obtain a flame-retardant water-based polyurethane emulsion.

[0081] Example 2

[0082] This embodiment provides a method for preparing a waterborne polyurethane-based flame-retardant microfiber synthetic leather, comprising the following steps:

[0083] The microfiber synthetic leather base fabric was immersed in the flame retardant water-based polyurethane emulsion prepared in Example 1 at a bath ratio of 1:8 at room temperature for 15 minutes. During the impregnation process, a roller was used to squeeze the microfiber synthetic leather base fabric, and the pressure between the upper and lower rollers was controlled to control the intake amount at 30wt%. After the impregnation, a scraper was used to scrape off the excess flame retardant water-based polyurethane emulsion on the surface of the microfiber synthetic leather base fabric, and then dried to obtain a water-based polyurethane-based flame retardant microfiber synthetic leather.

[0084] Comparative Example 1

[0085] This comparative example provides a method for preparing an aqueous polyurethane emulsion, which is specifically referred to in Example 1, except that a deionized water dispersion of modified MXene nanosheets is not added in the preparation of the aqueous polyurethane emulsion.

[0086] Comparative Example 2

[0087] This comparative example provides a method for preparing a flame-retardant aqueous polyurethane emulsion, which is specifically referred to in Example 1, except that 3-aminopropyl(diethoxy)methylsilane is not added in the preparation of the modified MXene nanosheets.

[0088] Comparative Example 3

[0089] This comparative example provides a method for preparing a waterborne polyurethane-based microfiber synthetic leather. For details, refer to Example 2, except that the flame-retardant waterborne polyurethane emulsion is replaced by the waterborne polyurethane emulsion of Comparative Example 1.

[0090] Comparative Example 4

[0091] This comparative example provides a method for preparing a waterborne polyurethane-based flame-retardant microfiber synthetic leather, comprising the following steps:

[0092] (1) Preparation of polyalkylsiloxane containing primary amine groups on the surface: For details, refer to step (1) of Example 1 for preparation of modified MXene nanosheets, except that no MXene nanosheets are added;

[0093] (2) Preparation of flame-retardant aqueous polyurethane emulsion: For details, refer to step (2) of Example 1 for preparation of flame-retardant aqueous polyurethane emulsion, except that the modified MXene nanosheets of Example 1 are replaced by polyalkylsiloxane having primary amine groups on the surface of this comparative example;

[0094] (3) Preparation of waterborne polyurethane-based flame-retardant microfiber synthetic leather: See Example 2 for details, except that the flame-retardant waterborne polyurethane emulsion in Example 2 is replaced by the flame-retardant waterborne polyurethane emulsion of this comparative example.

[0095] The waterborne polyurethane emulsions prepared in Comparative Example 1, Comparative Example 2 and Example 1 were subjected to mechanical property tests. The method is as follows: the waterborne polyurethane emulsion is 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 is 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.

[0096]

[0097] As can be seen from the data in Table 1, the breaking strength of the polyurethane film obtained from the aqueous polyurethane emulsion of Comparative Example 1 is the smallest, while the breaking elongation is the largest. It is shown that the polyalkylsiloxane-modified MXene has a reinforcing effect on polyurethane, but the breaking elongation is slightly reduced. In addition, the breaking strength of the polyurethane film obtained from the aqueous polyurethane emulsion of Comparative Example 2 is significantly smaller than that of Example 1, while the breaking elongation is greater than the latter. This is because the aromatic aldehyde group and the primary amine group do not react in the emulsion, and only react to generate a substance with a larger molecular weight as the water content decreases during the drying process, while completing the valence bond bonding of the flame retardant to the polyurethane. In Example 1, the polyalkylsiloxane-modified MXene nanosheets containing primary amine groups and the benzaldehyde-terminated polyurethane reacted during the drying process to generate macromolecular substances, and the breaking strength of the film became larger, but the breaking elongation decreased slightly.

[0098] The flame retardant properties of the microfiber synthetic leathers prepared in Comparative Example 3, Comparative Example 4 and Example 2 were tested, wherein the limiting oxygen index test was based on GB / T 5454-1997 "Oxygen Index Method for Textile Combustion Performance Test", and the damage length, smoldering time and afterflame time tests were based on GB / T 5455-2014 "Determination of Vertical Damage Length, Smoldering and Afterflame Time of Textile Combustion Performance". The results are shown in Table 2.

[0099]

[0100] It can be seen from the data in Table 2 that the ultra-fine synthetic leather prepared from polyurethane emulsion without adding flame retardant (Comparative Example 3) is flammable, the ultra-fine synthetic leather prepared from polyalkylsiloxane blended polyurethane (Comparative Example 4) has a certain flame retardant effect, and the flame retardant effect of the ultra-fine synthetic leather prepared from polyurethane blended with MXene nanosheets modified by primary amine group (Example 2) is significantly better than the flame retardant effect of single polyalkylsiloxane blended polyurethane, indicating that polyalkylsiloxane and MXene have a synergistic effect in flame retardant properties.

[0101] 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 waterborne polyurethane-based flame-retardant microfiber synthetic leather, characterized in that: The following steps are involved: The microfiber synthetic leather base fabric is impregnated in a flame-retardant water-based polyurethane emulsion, and a roller is used to squeeze the microfiber synthetic leather base fabric during the impregnation process; after the impregnation is completed, the base fabric is dried to obtain a water-based polyurethane-based flame-retardant microfiber synthetic leather; The method for preparing the flame retardant aqueous polyurethane emulsion comprises the following steps: (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 the mixture b, the chain extender and N,N-dimethylformamide to carry out a chain extension reaction to obtain a mixture c; (4) Mixing the mixture c and the capping agent to perform a capping reaction to obtain a mixture d; (5) Mixing mixture d, an antioxidant, triethylamine and N,N-dimethylformamide for neutralization reaction to obtain mixture e; (6) Mixing the mixture e with water, and after the phase inversion is successful, adding the aqueous dispersion of modified MXene and diethylenetriamine to mix and emulsify, removing N,N-dimethylformamide, and obtaining a flame-retardant waterborne polyurethane emulsion; The end-capping agent in step (4) is one of p-hydroxybenzaldehyde, p-hydroxymethylbenzaldehyde, and 2-(2-hydroxyethoxy)benzaldehyde; 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 modifier containing active groups is one or more of 3-aminopropyltrimethoxysilane, 3-aminopropyl(diethoxy)methylsilane, 3-ureapropyltriethoxysilane, N-(β-aminoethyl-γ-aminopropyl)methyldimethoxysilane and 3-aminopropyltriethoxysilane.

2. The method for preparing a waterborne polyurethane-based flame-retardant microfiber synthetic leather according to claim 1, characterized in that: The bath ratio of the immersion is 1:5-10; and the immersion time is 10-30 minutes.

3. The method for preparing a waterborne polyurethane-based flame-retardant microfiber synthetic leather 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 60-100 g / L; and the concentration of the modifier containing an active group in the mixed solution is 10-20 g / L.

4. The method for preparing a waterborne polyurethane-based flame-retardant microfiber synthetic leather according to claim 3, characterized in that: In the preparation method of the modified MXene, the alkyl siloxane is one or more of methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, n-butyltrimethoxysilane, isobutyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, propyltriethoxysilane, n-butyltriethoxysilane, and isobutyltriethoxysilane.

5. The method for preparing a waterborne polyurethane-based flame-retardant microfiber synthetic leather according to claim 4, characterized in that: In the preparation method of the modified MXene, after adding alkyl siloxane, the reaction is carried out at 25° C. for 60 to 90 minutes, the temperature is raised to 40 to 60° C. for reaction for 30 to 60 minutes, and then a modifier containing an active group is added and the reaction is carried out at 40 to 60° C. for 30 to 60 minutes.

6. The method for preparing a waterborne polyurethane-based flame-retardant microfiber synthetic leather according to claim 1 or 4, characterized in that: In the method for preparing the flame-retardant aqueous polyurethane emulsion, the mass ratio of the polymer diol to the diisocyanate in step (1) is 30-40:20-30; 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 30-40 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 chain extender and N,N-dimethylformamide in step (3) is 30-40 g: 5-10 g: 15-20 mL; the temperature of the chain extension reaction in step (3) is 80-90° C.; the time of the chain extension reaction in step (3) is 60-90 min; The mass ratio of the polymer diol in step (1) to the end-capping agent in step (4) is 30-40:4-8; the temperature of the end-capping reaction in step (4) is 80-90° C.; the time of the end-capping reaction in step (4) is 20-30 min; The amount ratio of the polymer diol in step (1) to the antioxidant, triethylamine, and N,N-dimethylformamide in step (5) is 30-40 g: 0.05-0.1 g: 3-5 g: 10 mL; the temperature of the neutralization reaction in step (5) is 55° C.; and the time of the neutralization reaction in step (5) is 30-60 min.

7. The method for preparing a waterborne polyurethane-based flame-retardant microfiber synthetic leather according to claim 6, characterized in that: In the method for preparing the flame-retardant aqueous polyurethane emulsion, the amount ratio of the polymer diol in step (1) to the water, the aqueous dispersion of modified MXene, and diethylenetriamine in step (6) is 30-40 g: 40-60 mL: 150-200 mL: 0.5-1 mL; the emulsification temperature in step (6) is 25° C.; and the emulsification time in step (6) is 60-120 min.

8. The method for preparing a waterborne polyurethane-based flame-retardant microfiber synthetic leather according to claim 7, characterized in that: In the method for preparing the flame-retardant aqueous polyurethane emulsion, the mass fraction of the modified MXene in the aqueous dispersion of the modified MXene is 30-50%.

9. A waterborne polyurethane based flame retardant microfiber synthetic leather obtained by the method for preparing a waterborne polyurethane based flame retardant microfiber synthetic leather according to any one of claims 1 to 8.

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