Preparation method of phosphorus-containing ionic liquid intumescent flame retardant

Abstract

The application discloses a preparation method of a phosphorus-containing ionic liquid intumescent flame retardant, and the method is based on the advantages of nanomaterials, ionic liquids and intumescent flame retardants, and integrates carbon source and acid source by synthesizing the phosphorus-containing ionic liquid from pentaerythritol phosphate as raw material through molecular design; the phosphorus-containing ionic liquid is self-assembled on the surface of black phosphorus nanosheet by utilizing electrostatic interaction, and a polymeric ionic liquid organic coating is formed through free radical initiation, and a phosphorus-containing ionic liquid intumescent flame retardant system is constructed; the prepared phosphorus-containing ionic liquid has superior thermal stability and charring capacity, and is an ideal carbon source and acid source of the intumescent flame retardant; the phosphorus-containing ionic liquid is combined with the two-dimensional nanomaterial BP as a surfactant and a synergistic flame retardant, and the phosphorus-containing ionic liquid can increase the residual carbon rate and promote the formation of a continuous and dense carbon layer, so that the heat and gas exchange between the polymer material and the flame zone are effectively insulated.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of flame retardants and preparation, and particularly relates to a preparation method of a phosphorus-containing ionic liquid intumescent flame retardant with good flame retardant performance and thermal stability. BACKGROUND

[0002] The combustion of a polymer material is a complex physicochemical change process. Polymer chain segments will decompose when heated to produce highly volatile and flammable small molecules, which provide fuel for combustion. Once they come into contact with oxygen and accumulate to a critical concentration, ignition will occur as the temperature continues to rise to the ignition point. When combustion occurs, a large number of free radicals such as HO· and H· are generated, which initiate a violent free radical chain reaction in the gas phase and release a large amount of heat. These heat feedback to the pyrolysis zone in the condensed phase, causing the substrate to continue to decompose and burn. Flame retardants can be specially designed to delay or inhibit combustion through their chemical or physical effects. They can absorb heat, cover the surface, inhibit chain reactions, and produce non-combustible gases during combustion. According to the location of the flame retardant effect, its mechanism can be divided into the following two kinds: condensed phase flame retardant mechanism and gas phase flame retardant mechanism. The condensed phase flame retardant mechanism mainly occurs in the pyrolysis zone of the polymer. Some flame retardants can react with the polymer or the pyrolysis products of the polymer to make them produce more non-flammable substances, increase the carbon residue after combustion, and reduce heat release. In addition, the catalytic carbonization of the flame retardant leads to the formation of a more dense carbon layer on the surface of the polymer, thereby improving the thermal stability. The carbon layer helps to prevent the transfer of oxygen, flammable volatile molecules and heat, thereby reducing the flame intensity. The gas phase flame retardant mechanism mainly occurs in the gas phase flame zone, which involves releasing non-flammable gases to dilute the fuel concentration, quenching active free radicals to inhibit chain reactions, and producing water vapor to reduce the temperature of the polymer surface.

[0003] Intumescent flame retardants (IFRs) have gradually become one of the most promising flame retardant technologies to replace halogen-based flame retardants due to their environmental friendliness, high efficiency, anti-dripping, low smoke, low toxicity and other advantages. Generally, an IFR system is composed of three parts: acid source, charring agent and blowing agent. The most typical IFR system is ammonium polyphosphate / pentaerythritol / melamine (APP / PER / MEL). During the process of heating and burning, the gas source in the polymer releases a large amount of non-combustible gas, promotes the expansion of the system, and forms a porous intumescent foam carbon. These expanded porous carbon layers act as a barrier to effectively block the heat, oxygen and pyrolysis products from entering the material surface, thereby inhibiting the further decomposition and combustion of the substrate. Pentaerythritol phosphate (PEPA) has a highly symmetrical cage structure, and the cage structure has good thermal stability and carbon layer skeleton, and is easy to form a cross-linked carbon layer. In addition, PEPA has a high phosphorus content (17.6%) and a P-N bond, which increases the Lewis acid and is beneficial to the dehydration and carbonization reaction. The decomposition temperature of PEPA is about 300℃, and PEPA has good thermal stability. PEPA integrates the functions of acid source and carbon source, so it is a potential intumescent flame retardant. Ionic liquids can be used as surfactants to modify inorganic materials to improve the compatibility with the polymer system and further improve the dispersibility, so as to maximize the flame retardant effect. However, there is no good method to apply ionic liquids to intumescent flame retardants. SUMMARY

[0004] The application provides a preparation method of a phosphorus-containing ionic liquid intumescent flame retardant. Pentaerythritol phosphate, which integrates the functions of acid source and carbon source, is used to prepare an ionic liquid which can be used as a surfactant and a synergistic flame retardant. In combination with the inhibition effect and catalytic carbonization effect of two-dimensional nanomaterial BP, the prepared flame retardant can isolate the heat and gas exchange between the polymer material and the flame zone.

[0005] A preparation method of a phosphorus-containing ionic liquid intumescent flame retardant, comprising the following steps:

[0006] (1) dispersing pentaerythritol phosphate (PEPA) in acetonitrile at 50-80℃ to obtain a PEPA solution, dispersing a phosphorus oxychloride compound in a four-necked flask containing acetonitrile under a nitrogen atmosphere to obtain a phosphorus oxychloride compound solution, and adding the PEPA solution at 50-80℃ to the phosphorus oxychloride compound solution by using a peristaltic pump, and refluxing under the condition of 80℃ and vigorous stirring until no HCl gas is released, and then cooling the product to crystallize, and then filtering and drying to obtain white crystals;

[0007] (2) dissolving the product obtained in step (1) and 1-vinylimidazole in acetonitrile, and then adding them into a three-necked flask equipped with a magnetic stirrer and a reflux condenser, and then heating to 70-100℃ under a nitrogen atmosphere and stirring for 10-12h;

[0008] (3) The product of step (2) is filtered, washed for several times and dried under vacuum to obtain the phosphorus-containing ionic liquid;

[0009] (4) 0.001-0.004 g of the radical initiator is weighed and dissolved in DMF to obtain a radical initiator solution;

[0010] 0.5-2 g of two-dimensional nano black phosphorus is ultrasonically dispersed in 100-500 mL of DMF to obtain a nano black phosphorus dispersion liquid, 1-4 g of the phosphorus-containing ionic liquid is added to the above nano black phosphorus dispersion liquid to assist the exfoliation process, and after sufficient stirring, the radical initiator solution is added dropwise to start the self-polymerization of the phosphorus-containing ionic liquid on the surface of the BP, and the polymerization reaction is carried out at 80-100℃ for 3-5 h, and the product is freeze-dried for 48-72 h to obtain the phosphorus-containing ionic liquid intumescent flame retardant.

[0011] The phosphorus oxychloride compound in step (1) is one or a mixture of two or more of methyl phosphorus oxychloride, ethyl phosphorus oxychloride, phenyl phosphorus oxychloride, chloroacetyl dichloride, etc.

[0012] The molar ratio of the pentaerythritol phosphate to the phosphorus oxychloride compound in step (1) is 1:1-1.7.

[0013] The rotation speed of the vigorous stirring condition in step (1) is 300-500 r / min; and the reflux reaction time is 8-12 h.

[0014] The molar ratio of the product of step (1) to 1-vinylimidazole in step (2) is 1:1-1.5.

[0015] The vacuum drying temperature in step (3) is 70-90℃, and the time is 12-24 h.

[0016] The radical initiator in step (4) is one or a mixture of two or more of azobisisobutyronitrile (AIBN), azobisisoheptyl nitrile (AVBN), benzoyl peroxide (BPO), diisopropyl peroxydicarbonate, etc.

[0017] The beneficial effects of the present application are:

[0018] The present application first synthesizes the phosphorus-containing ionic liquid (PBVI) which can be used as a surfactant and a synergistic flame retardant by taking the pentaerythritol phosphate which integrates acid source and carbon source as a raw material, combines the electrostatically driven self-assembly process, and then performs in-situ radical polymerization on the surface of nano black phosphorus. Meanwhile, the presence of the vinyl structure can form a polymerized IL coating on the surface of the nano black phosphorus, thereby more effectively enhancing the interface interaction between the BP and the polymer matrix than ordinary micromolecules. The lubrication and compatibilization of the phosphorus-containing IL can greatly reduce the viscosity of the melt and improve the dispersion of the black phosphorus in the polymer matrix, thereby maximizing the flame retardant effect and imparting good processing performance and mechanical properties to the material.

[0019] The phosphorus-containing ionic liquid prepared by the application has excellent thermal stability and carbon formation capacity, and is an ideal carbon source and acid source of intumescent flame retardant. By combining the inhibiting effect and catalytic carbon formation of the two-dimensional nanomaterial BP with the effect of the phosphorus-containing ionic liquid as a surfactant and synergistic flame retardant, the heat and gas exchange between the polymer material and the flame zone can be isolated. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The infrared spectra of PEPA-BPOD prepared in step (1), PBVI prepared in step (2), PBVIBP prepared in step (3), raw material PEPA, phenylphosphoryl dichloride BPOD and 1-vinylimidazole VI of Example 1;

[0021] Figure 2 The thermal gravimetric curves of the flame retardants PBVI and PBVIBP prepared in Example 1 and BP. DETAILED DESCRIPTION

[0022] The application will be further described below in combination with specific examples.

[0023] Example 1

[0024] A preparation method of a phosphorus-containing ionic liquid intumescent flame retardant, comprising the following steps:

[0025] (1) 0.1 mol of pentaerythritol phosphate (PEPA) is dispersed in 100 mL of acetonitrile at 50°C to obtain a PEPA solution, 0.17 mol of phenylphosphoryl dichloride (BPOD) is dispersed in another four-necked flask containing 150 mL of acetonitrile under a nitrogen atmosphere to obtain a phosphoryl dichloride compound solution, the PEPA solution at 50°C is added dropwise into the phenylphosphoryl dichloride solution by using a peristaltic pump within 3 h, the temperature is increased to 80°C, and the product is crystallized after cooling, filtered and dried to obtain a white crystal (PEPA-BPOD) under the condition of vigorous stirring at a speed of 300 r / min and reflux reaction for 12 h until no HCl gas is released;

[0026] (2) 0.1 mol (61.4 g) of PEPA-BPOD and 1-vinylimidazole (VI) are dissolved in 300 mL of acetonitrile at a molar ratio of 1:1, and then added into a three-necked flask equipped with a magnetic stirrer and a reflux condenser, and the temperature is increased to 70°C under a nitrogen atmosphere for stirring and reflux reaction for 12 h;

[0027] (3) The product of step (2) is filtered, washed with acetonitrile for 3 times, and then vacuum dried in a vacuum drying box at 70°C for 24 h to obtain a phosphorus-containing ionic liquid (PBVI);

[0028] (4) 0.001 g of radical initiator dibenzoyl peroxide was weighed into 5 mL of DMF to obtain a radical initiator solution;

[0029] 0.5 g of two-dimensional nano black phosphorus was ultrasonically dispersed in 100 mL of DMF to obtain a nano black phosphorus dispersion liquid, 1 g of phosphorus-containing ionic liquid (PBVI) was added to the above nano black phosphorus dispersion liquid to assist the exfoliation process, and after sufficient stirring, the radical initiator solution was added dropwise to start the self-polymerization of PBVI on the surface of BP. The polymerization was carried out at 80°C for 5h, and the product was freeze-dried for 48h to obtain a phosphorus-containing ionic liquid intumescent flame retardant (PBVI-BP).

[0030] Example 2

[0031] A method for preparing a phosphorus-containing ionic liquid intumescent flame retardant, comprising the following steps:

[0032] (1) 0.1 mol of pentaerythritol phosphate (PEPA) was dispersed in 100 mL of acetonitrile at 60°C to obtain a PEPA solution. 0.15 mol of methyl phosphorodichloridate (MPDC) was dispersed in another four-necked flask containing 150 mL of acetonitrile under a nitrogen atmosphere to obtain a phosphorodichloridate compound solution. The PEPA solution at 60°C was added dropwise to the methyl phosphorodichloridate solution using a peristaltic pump within 3h, and the temperature was increased to 80°C. The solution was stirred vigorously at a speed of 350 r / min, and the reflux reaction was carried out for 10h until no HCl gas was released. The product was cooled and crystallized, filtered and dried to obtain white crystals (PEPA-MPDC);

[0033] (2) 0.1 mol (27.6 g) of PEPA-MPDC and 1-vinylimidazole (VI) were dissolved in 300 mL of acetonitrile at a molar ratio of 1:1.2, and then added to a three-necked flask equipped with a magnetic stirrer and a reflux condenser. The temperature was increased to 80°C under a nitrogen atmosphere, and the solution was stirred and refluxed for 11h;

[0034] (3) The product of step (2) was filtered, washed with acetonitrile three times, and then vacuum dried at 80°C for 18h to obtain a phosphorus-containing ionic liquid (PMVI);

[0035] (4) 0.002 g of radical initiator dibenzoyl peroxide was weighed into 5 mL of DMF to obtain a radical initiator solution;

[0036] 1 g of two-dimensional nano black phosphorus was ultrasonically dispersed in 200 mL of DMF to obtain a nano black phosphorus dispersion liquid, 2 g of phosphorus-containing ionic liquid (PMVI) was added to the above nano black phosphorus dispersion liquid to assist the exfoliation process, and after sufficient stirring, the radical initiator solution was added dropwise to start the self-polymerization of PMVI on the surface of BP. The polymerization was carried out at 90°C for 4h, and the product was freeze-dried for 48h to obtain a phosphorus-containing ionic liquid intumescent flame retardant (PMVI-BP).

[0037] Example 3

[0038] A method for preparing a phosphorus-containing ionic liquid intumescent flame retardant, comprising the following steps:

[0039] (1) 0.1 mol of pentaerythritol phosphate (PEPA) was dispersed in 100 mL of acetonitrile at 70°C to obtain a PEPA solution, 0.13 mol of ethyl phosphorodichloridate (EDOP) was dispersed in another four-necked flask containing 150 mL of acetonitrile under a nitrogen atmosphere to obtain a phosphorodichloridate compound solution, the PEPA solution at 70°C was added dropwise to the ethyl phosphorodichloridate solution within 3 h using a peristaltic pump, the temperature was raised to 80°C, and the product was crystallized under the condition of vigorous stirring at a speed of 400 r / min and refluxing for 9 h until no HCl gas was released, and then the product was filtered, dried and obtained as white crystals (PEPA-EDOP);

[0040] (2) 0.1 mol (30.6 g) of PEPA-EDOP and 1-vinylimidazole (VI) were dissolved in 300 mL of acetonitrile at a molar ratio of 1:1.3, and then added to a three-necked flask equipped with a magnetic stirrer and a reflux condenser, and heated to 90°C under a nitrogen atmosphere and stirred for 10 h;

[0041] (3) The product of step (2) was filtered, washed with acetonitrile three times, and then vacuum dried in a vacuum drying oven at 90°C for 12 h to obtain a phosphorus-containing ionic liquid (PEVI);

[0042] (4) 0.003 g of a free radical initiator, dibenzoyl peroxide, was dissolved in 5 mL of DMF to obtain a free radical initiator solution;

[0043] 1.5 g of two-dimensional nano black phosphorus was ultrasonically dispersed in 300 mL of DMF to obtain a nano black phosphorus dispersion liquid, 3 g of the phosphorus-containing ionic liquid (PEVI) was added to the above nano black phosphorus dispersion liquid to assist the exfoliation process, and then the free radical initiator solution was added dropwise to start the self-polymerization of PEVI on the surface of BP, and the polymerization was carried out at 90°C for 4 h, and then the product was freeze-dried for 60 h to obtain a phosphorus-containing ionic liquid intumescent flame retardant (PEVIBP).

[0044] Example 4

[0045] A method for preparing a phosphorus-containing ionic liquid intumescent flame retardant, comprising the following steps:

[0046] (1) 0.1 mol of pentaerythritol phosphate (PEPA) was dispersed in 100 mL of acetonitrile at 80°C to obtain a PEPA solution, 0.1 mol of chloroacetyl dichloride (CAC) was dispersed in another four-necked flask containing 150 mL of acetonitrile under a nitrogen atmosphere to obtain a phosphorus oxychloride compound solution, the PEPA solution at 80°C was added dropwise into the chloroacetyl dichloride solution by using a peristaltic pump within 3 h, the temperature was raised to 80°C, and the product was crystallized after cooling, filtered and dried to obtain white crystals (PEPA-CAC) under the condition of vigorous stirring at a speed of 500 r / min and refluxing for 8 h until no HCl gas was released;

[0047] (2) 0.1 mol (17.1 g) of PEPA-CAC was dissolved in 300 mL of acetonitrile together with 1-vinylimidazole at a molar ratio of 1:1.5, and then added to a three-necked flask equipped with a magnetic stirrer and a reflux condenser, and the temperature was raised to 100°C under a nitrogen atmosphere and stirred to reflux for 10 h;

[0048] (3) The product of step (2) was filtered, washed with acetonitrile three times, and then vacuum dried in a vacuum drying oven at 90°C for 12 h to obtain a phosphorus-containing ionic liquid (PCVI);

[0049] (4) 0.004 g of a free radical initiator, dibenzoyl peroxide, was dissolved in 5 mL of DMF to obtain a free radical initiator solution;

[0050] 2 g of two-dimensional nano black phosphorus was ultrasonically dispersed in 500 mL of DMF to obtain a nano black phosphorus dispersion liquid, 4 g of the phosphorus-containing ionic liquid (PCVI) was added to the above nano black phosphorus dispersion liquid to assist the exfoliation process, and after sufficient stirring, the free radical initiator solution was added dropwise to start the self-polymerization of PBVI on the surface of BP, and the polymerization was carried out at 100°C for 3 h, and the product was freeze-dried for 72 h to obtain a phosphorus-containing ionic liquid intumescent flame retardant (PCVIBP).

[0051] Figure 1 The infrared spectra of PEPA-BPOD prepared in step (1) of Example 1, PBVI prepared in step (2), PBVIBP prepared in step (3), raw materials PEPA, phenyl phosphorus oxychloride BPOD and 1-vinylimidazole VI, in the spectrum of PEPA-BPOD, the disappearance of -OH belonging to PEPA and the wide peak of P-Cl belonging to BPOD changed into a sharp peak, indicating that substitution reaction occurred between PEPA and BPOD to obtain the product PEPA-BPOD, indicating that PEPA-BPOD was successfully prepared; in the FTIR spectrum of PBVI, C=C absorption peaks belonging to 1-vinylimidazole appeared at 1648 cm -1 and 1494 cm -1 , indicating the successful preparation of the phosphorus-containing IL; in the FTIR spectrum of PBVIBP, 1648 cm -1and 1494 cm -1 The disappearance of the C=C absorption peak belonging to 1-vinylimidazole indicates the successful polymerization of PBVI on the surface of black phosphorus.

[0052] Figure 2 The thermal gravimetric curves of the flame retardant PBVIBP and PBVI prepared in Example 1 and BP are shown in the figure, from which it can be seen that the initial decomposition temperature (T d5％ ) of PBVIBP is higher than that of PBVI, and the introduction of PBVI improves the carbon residue of BP, indicating that the phosphorus-containing ionic liquid intumescent flame retardant (PBVIBP) obtained in Example 1 has a better catalytic carbonization effect on flame retardation.

[0053] Finally, it should be pointed out that the above examples are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing examples, or equivalently replace some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a phosphorus-containing ionic liquid intumescent flame retardant, characterized in that: The following steps are involved: (1) Pentaerythritol phosphate is dispersed in acetonitrile at 50-80°C to obtain a PEPA solution. A phosphorus oxychloride compound is dispersed in a four-necked flask filled with acetonitrile under a nitrogen atmosphere to obtain a phosphorus oxychloride compound solution. The 50-80°C PEPA solution is added dropwise to the phosphorus oxychloride compound solution. The mixture is vigorously stirred and refluxed at 80°C to react. The product is cooled and crystallized, and filtered and dried to obtain white crystals. The phosphorus oxychloride compound is one or a mixture of two or more of methyl phosphorus oxychloride, ethyl phosphorus oxychloride, and phenyl phosphorus oxychloride; (2) dissolving the product obtained in step (1) and 1-vinylimidazole in acetonitrile, heating to 70-100°C under a nitrogen atmosphere, and stirring to react for 10-12 hours; (3) filtering and washing the product of step (2) for multiple times and then vacuum drying to obtain a phosphorus-containing ionic liquid; (4) Weigh 0.001-0.004 g of a free radical initiator and dissolve it in DMF to obtain a free radical initiator solution; 0.5-2 g of two-dimensional nano-black phosphorus is weighed and ultrasonically dispersed in 100-500 mL of DMF to obtain a nano-black phosphorus dispersion. 1-4 g of phosphorus-containing ionic liquid is added to the nano-black phosphorus dispersion and stirred thoroughly. A free radical initiator solution is then added dropwise. The polymerization reaction is carried out at 80-100° C. for 3-5 hours. The product is freeze-dried for 48-72 hours to obtain a phosphorus-containing ionic liquid intumescent flame retardant.

2. The method for preparing the phosphorus-containing ionic liquid intumescent flame retardant according to claim 1, characterized in that: In step (1), the molar ratio of pentaerythritol phosphate to phosphorus oxychloride is 1:1-1.7; the rotation speed of the vigorous stirring condition is 300-500 r / min, and the reflux reaction time is 8-12 h.

3. The method for preparing the phosphorus-containing ionic liquid intumescent flame retardant according to claim 1, characterized in that: In step (2), the molar ratio of the product of step (1) to 1-vinylimidazole is 1:1-1.

5.

4. The method for preparing the phosphorus-containing ionic liquid intumescent flame retardant according to claim 1, characterized in that: In step (3), the vacuum drying temperature is 70-90°C and the time is 12-24 hours.

5. The method for preparing the phosphorus-containing ionic liquid intumescent flame retardant according to claim 1, characterized in that: In step (4), the free radical initiator is one or a mixture of two or more of azobisisobutyronitrile, azobisisoheptanenitrile, dibenzoyl peroxide, and diisopropyl peroxydicarbonate.

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