A double-layer microcapsule structure flame retardant, flame retardant polyurethane material, and preparation method and application thereof

Abstract

The present invention discloses a double-layer microcapsule structure flame retardant, a flame retardant polyurethane material, and its preparation method and application, belonging to the technical field of flame retardants. This material is a multifunctional flame retardant with a double-layer core-shell structure. The outer shell layer is calixarene boric acid resin, the middle shell layer is melamine phthalic anhydride resin, and the core layer is aluminum hypophosphite modified by hydroxyapatite. Due to the high degree of cross-linking between polymers in the present invention, while improving the flame retardancy of polyurethane, its mechanical properties are also improved. The hydroxyapatite dispersed in the core layer synergistically enhances the flame retardant performance and seawater corrosion resistance of the material. The double shell layer has excellent hydrophobicity, preventing the internal aluminum hypophosphite from being affected by moisture, and has an anti-fouling and self-cleaning effect. The dual network of hydrogen bonds and covalent bonds enables the prepared flame retardant polyurethane composite material to have excellent stretchable and flexible characteristics.

Description

Technical Field

[0001] The present invention relates to a flame retardant with a double - layer microcapsule structure, a flame - retardant polyurethane material, and a preparation method and application thereof, belonging to the technical field of flame retardants. Background Art

[0002] Polyurethane (PU), as a thermoplastic resin, has the advantages of low cost, mature processing and molding technology, low thermal conductivity, high compressive strength, and easy processing. It is an important basic raw material for the development of the national economy and scientific and technological progress. However, PU is extremely flammable and produces a large amount of smoke, which can cause serious harm to human health and seriously affect its applications in the fields of marine pipelines, building materials, industry, and injection molding. As a functional additive, flame retardants can endow PU with flame - retardant properties by affecting the combustion process and combustion products. However, the addition of ordinary flame retardants often reduces the mechanical properties of PU, and in the specific application of marine pipeline PU, certain antifouling properties and seawater corrosion resistance are required. Therefore, improving the overall flame retardancy, hydrophobicity, and seawater corrosion resistance without reducing its mechanical properties is the most economical and effective research direction for realizing the high - performance of PU.

[0003] Chinese invention patent CN115246860A discloses a preparation method and use of phosphorus - nitrogen intumescent flame retardant nanosheets. In the first step, an intermediate product is obtained through the nucleophilic substitution reaction of hexachlorocyclotriphosphazene and p - acetaminophen, and then a deamidation reaction is carried out under alkaline conditions followed by a salt - forming reaction with phytic acid to prepare phosphorus - and nitrogen - containing intumescent flame retardant nanosheets. To improve the thermal stability of the product, anhydride substances are introduced in this patent, which affects the flame - retardant effect of the product and ultimately limits the scope of product use.

[0004] Chinese invention patent CN116554549A discloses a nitrogen - phosphorus highly synergistic bifunctional flame retardant, a highly flame - retardant β - crystal polypropylene material, and a preparation method and application thereof. The flame retardant is composed of polyphosphate, a modified polymer, and chitosan, and the modified polymer is a phytic acid - melamine supramolecular polymer modified by polyphosphate. The nitrogen - phosphorus synergistic flame retardant prepared by this patented technology has poor hydrophobicity due to the outer layer being coated with chitosan, which is very limited in application in the field of marine pipelines, and its seawater corrosion resistance is poor, restricting its application. Summary of the Invention

[0005] Aiming at the problems of poor antifouling property, poor thermal stability, flammability, poor seawater corrosion resistance, and poor anti - aging property existing in the existing polyurethane flame retardants, the present invention provides a flame retardant with a double - layer microcapsule structure, a flame - retardant polyurethane material, and a preparation method and application thereof. This flame retardant can simultaneously achieve multifunctional modification of flame retardancy, excellent mechanical properties, and self - cleaning and corrosion resistance.

[0006] To solve the above technical problems, the first aspect of the present invention is to provide a flame retardant with a double-layer microcapsule structure, which includes an outer shell layer, a middle shell layer, and a core layer arranged from outside to inside; wherein the outer shell layer is calixarene boric acid resin, the middle shell layer is melamine phthalic anhydride resin, and the core layer is aluminum hypophosphite modified by hydroxyapatite. This flame retardant with a double-layer microcapsule structure can be prepared by the following preparation method.

[0007] The second aspect of the present invention is to disclose a preparation method of a flame retardant with a double-layer microcapsule structure, which includes the following steps:

[0008] SO1, Add an aqueous solution of melamine to the reaction kettle, add an aqueous solution of phthalic anhydride with a mass fraction of 37wt% - 39wt% to the aqueous solution of melamine, so that the molar ratio of phthalic anhydride to melamine is 3:2.15 - 2.22, add a nitrogen-containing pH regulator dropwise to adjust the pH to 8 - 9, react at 65 - 80°C for 0.5 - 1.5h to obtain a melamine phthalic anhydride resin prepolymer emulsion. Then, according to the mass ratio of aluminum hypophosphite to melamine of 3 - 6:1 and the mass ratio of hydroxyapatite to melamine of 1:8 - 12, add aluminum hypophosphite and hydroxyapatite to the melamine phthalic anhydride prepolymer emulsion, use an acidic pH regulator to adjust the pH to 4 - 5, react at 70 - 90°C for 4 - 6h, let it stand, filter, wash with anhydrous ethanol until neutral, and dry at 60 - 95°C for 12 - 24h to obtain microcapsules (MCAHP) of melamine phthalic anhydride resin coated with hydroxyapatite-modified aluminum hypophosphite;

[0009] SO2, According to the mass ratio of calixarene to N,N-dimethylformamide of 1:20 - 40, stir at 60 - 90°C for 1 - 2h until the solution is clear; mix according to the mass ratio of calixarene to MCAHP of 1:2 - 4, add Tween-80, stir for 0.5 - 1h, add boric acid according to the mass ratio of boric acid to calixarene of 1:15 - 20, stir, react at 80 - 105°C for 5 - 8h, add acetone according to the mass ratio of MCAHP to acetone of 1:3 - 5 and stir for 30min, cool, filter, wash with acetone until neutral, dry at 80 - 120°C for 24 - 48h, and grind into powder to obtain the flame retardant with a double-layer microcapsule structure.

[0010] In S01, the molar ratio of phthalic anhydride to melamine is about 3:2.2, so that phthalic anhydride and melamine react fully to form melamine phthalate resin, enhancing the mechanical properties and the synergistic flame retardant effect. At the same time, a part of the amino groups in melamine are reserved in an unreacted state, and the unreacted amino groups are used for subsequent cross-linking with the phenolic hydroxyl groups in the calixarene cavity. An alkaline condition is beneficial to the preliminary polymerization of melamine and phthalic anhydride to form a prepolymer. The mass ratio of aluminum hypophosphite to melamine is 3-6:1. This ratio enables the melamine phthalate resin to fully coat the aluminum hypophosphite of hydroxyapatite, and the amount of melamine phthalate resin is not too large to cause the formation of an overly thick melamine phthalate resin layer. The mass ratio of hydroxyapatite to melamine is 1:8-12. Hydroxyapatite is used to increase the mechanical properties of the core layer of the material and can cooperate with the melamine phthalate resin and aluminum hypophosphite for synergistic flame retardancy.

[0011] In S01, when the pH is adjusted to 4-5, it is beneficial for the prepolymer to continue to polymerize and coat on the surfaces of aluminum hypophosphite and hydroxyapatite.

[0012] In S02, calixarene is uniformly dispersed in N,N-dimethylformamide. The mass ratio of calixarene to MCAHP is 1:2-4 because MCAHP is the main part of this flame retardant, mainly playing the role of nitrogen-phosphorus synergistic flame retardancy. A certain amount of calixarene is required to cross-link and coat MCAHP, and the amount of calixarene cannot be too large, otherwise the flame retardant effect will be reduced. Tween-80 can improve the interfacial properties of the reaction system, promote the interaction of reactants, and catalyze the reaction. The mass ratio of boric acid to calixarene is 1:15-20, and a small amount of boric acid is used to modify calixarene. And acetone can make both the calixarene boric acid resin and the melamine phthalate resin uniformly dispersed in it. In S02, the mass ratio of boric acid to calixarene makes the phenolic hydroxyl groups of calixarene significantly in excess. There are still surplus phenolic hydroxyl groups in the calixarene cavity for cross-linking with the amino groups of the melamine phthalate resin. At the same time, hydrogen bonds are formed between the amide groups of the melamine phthalate resin and the phenolic hydroxyl groups of the calixarene boric acid resin.

[0013] Similarly, aluminum hypophosphite and hydroxyapatite respectively form hydrogen bonds with the melamine phthalate resin, which helps the melamine phthalate resin to tightly coat the core layer.

[0014] Among them, in SO1, melamine is added to the reaction kettle, and deionized water is added according to the mass ratio of melamine to deionized water of 1:100-250 to obtain an aqueous melamine solution.

[0015] In SO1, the nitrogen-containing pH regulator is one of ammonia water, ammonium chloride, and ammonium carbonate; the acidic pH regulator is one of acetic acid, hydrochloric acid, and sulfuric acid. The second aspect of the present invention discloses a flame retardant polyurethane material modified with a double-layer microcapsule structure flame retardant.

[0016] Specifically, the flame-retardant polyurethane material has a UL-94 flame-retardant rating of V-0 and a loss on ignition (LOI) of 32.7-34.4%.

[0017] The third aspect of the present invention is to provide a method for preparing the aforementioned flame-retardant polyurethane material, which includes the following steps: according to the addition amount of 10wt%-20wt% of the double-layer microcapsule structure flame retardant, according to the addition amount of 0.5wt%-1wt% of silica sol, according to the addition amount of 0.1wt%-0.25wt% of film-forming aid, according to the addition amount of 0.1wt%-0.25wt% of thickener, and according to the addition amount of 5wt%-10wt% of ionic conductive agent, adding each component into polyurethane, mixing evenly, then melt-blending at 160-200°C, and finally extruding through a twin-screw extruder and cooling and pelletizing to obtain the flame-retardant polyurethane material. The above wt% are all mass percentages relative to polyurethane.

[0018] Among them, the mass fraction of SiO2 in the silica sol is 20% ± 2%; the thickener is one of alkyl ammonium salts, gelatin or sodium carboxymethyl cellulose; the film-forming aid is one of propylene glycol, propylene glycol monobutyl ether, lauryl alcohol ester or N,N-dimethylformamide; the ionic conductive agent is one or a combination of choline chloride, acetylcholine chloride, carbachol, etc.

[0019] The fourth aspect of the present invention is to provide the application of the aforementioned double-layer microcapsule structure flame retardant or flame-retardant polyurethane material in combustible gas transmission pipelines, offshore pipelines and shale gas fracturing pipelines.

[0020] The present invention uses the principle of polycondensation reaction to prepare melamine phthalic anhydride resin, and coats aluminum hypophosphite modified by hydroxyapatite with melamine phthalic anhydride resin to obtain MCAHP; uses the hydroxyl groups between calixarene (CD) and boric acid (BA) to react to form covalent bonds, thereby achieving crosslinking, and a part of boric acid (BA) is crosslinked and included in the cavity of calixarene, and another part of boric acid is crosslinked with the main component of calixarene; then reacts with MCAHP to obtain a material with calixarene boric acid resin coated on MCAHP; uses calixarene boric acid resin as the outer shell layer, melamine phthalic anhydride resin as the middle shell layer, and aluminum hypophosphite modified by hydroxyapatite as the core layer to obtain a double-layer microcapsule structure flame retardant.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] While improving the flame retardancy, the double-layer microcapsule structure flame retardant also improves the hydrophobicity and mechanical properties of the polyurethane (PU) polymer.

[0023] (1) The outer shell layer of the double-layer microcapsule structure flame retardant is calixarene modified by boric acid, the middle shell layer is melamine phthalic anhydride resin, and the core layer is aluminum hypophosphite and hydroxyapatite. The outer shell layer provides a flame retardant function while coating the middle shell layer and the core layer, playing a hydrophobic coating role; the middle shell layer is melamine resin, and the self-polymerization and cross-linking of the resin provide good mechanical properties. At the same time, melamine salt provides excellent flame retardant properties and protects the internal inorganic flame retardant from moisture; the interior is aluminum hypophosphite and hydroxyapatite, and the phosphorus element plays a role in binding free radicals during the flame retardant process, reducing the free radical reaction generated by combustion, thereby inhibiting combustion.

[0024] (2) The cavity size of calixarene is larger than the molecular size of melamine phthalic anhydride, which is conducive to the coating effect; moreover, the phenolic hydroxyl groups at the lower edge of calixarene can cross-link with the amino groups in melamine resin and form hydrogen bonds with the amide groups in melamine resin. The combination of multiple cross-linking sites and hydrogen bond sites can enhance the stability after coating; there is an aromatic structure in melamine phthalic anhydride resin, which can undergo Π-Π stacking with the benzene ring in calixarene, and melamine phthalic anhydride has strong hydrophobicity. The hydrophobicity of the calixarene cavity is significantly stronger than that of the calixarene main body. The Π-Π stacking effect, combined with the similar hydrophobicity of melamine phthalic anhydride and the calixarene cavity, quickly attracts the melamine phthalic anhydride resin into the calixarene cavity rather than the calixarene main body. The hydrophobic melamine phthalic anhydride resin is completely and tightly enclosed in the calixarene cavity. At the same time, the overall structure enhances its hydrophobicity. Utilizing the high hydrophobicity obtained by the synergistic effect of the shell layer melamine phthalic anhydride resin and calixarene boric acid resin, it plays an anti-fouling and self-cleaning role and prevents the moisture absorption of aluminum hypophosphite, which reduces the flame retardant performance. In addition, covalent bond cross-linking and hydrogen bond formation can generally make the coating tighter, enhance the hydrophobic and mechanical properties, and the char layer formed during combustion is also tighter, synergistically improving the flame retardant effect.

[0025] (3) When the calixarene cavity is successively modified by boric acid and included with melamine phthalic anhydride, the calixarene cavity is filled.

[0026] (4) In the initial stage of combustion, the calixarene boric acid resin generates water vapor and a small amount of boric acid vapor or gas containing B element. These gases can dilute the oxygen concentration in the flame zone, reduce the flame temperature, and thus inhibit the progress of the combustion reaction. After a small amount of borate decomposes under high temperature (170 - 220 °C) conditions, boron oxides (such as B2O3) and borates with aromatic structures will be formed. The boron oxides can improve the flame retardant effect to a certain extent, and the borates with aromatic structures react with the char layer formed by the combustion of the benzene ring in calixarene to form a glassy covering layer. Calixarene can form a tighter inclusion compound with the glassy covering layer, together promoting the formation of a more stable char layer on the material surface (calixarene boric acid resin layer), further slowing down the transfer of heat and oxygen, and thus reducing the speed of flame spread.

[0027] (5) During further combustion, the borate will also form a vitreous coating layer with calcium in the hydroxyapatite of the nuclear layer and aluminum in the aluminum hypophosphite, jointly promoting the formation of a more stable carbonized layer in the material, slowing down the transfer of heat and oxygen, and reducing the flame propagation speed.

[0028] (6) In the middle stage of combustion, as the temperature rises (330 - 350 °C), the borate will synergistically catalyze the decomposition of the organic melamine phthalic anhydride resin (the products are water, nitrogen oxides, nitrogen, ammonia, etc.), promoting the decomposition of the melamine phthalic anhydride resin to produce nitrogen (used to dilute the oxygen concentration), ammonia, etc. to dilute the oxygen concentration in the flame zone. Ammonia reacts with free radicals in the combustion area, especially with hydrogen free radicals and hydroxyl free radicals (OH·) generated during combustion. This can effectively reduce the concentration of free radicals, inhibit free radical reactions, lower the flame temperature, and thus reduce the rate of the combustion reaction.

[0029] (7) In the late stage of combustion, the N element in the melamine phthalic anhydride resin and the P element in the aluminum hypophosphite and hydroxyapatite can play a synergistic flame retardant effect. The aluminum hypophosphite modified by hydroxyapatite will form a relatively stable protective carbonized layer at high temperature. This carbonized layer can effectively block the transfer of oxygen and heat. The aluminum hypophosphite itself can also react with the combustion products to generate low-volatility substances (aluminum oxide, aluminum salts). The aluminum hypophosphite can also adsorb and react with nitrogen oxides decomposed from melamine, further reducing the combustion reaction. In addition, the P - O bonds in the aluminum hypophosphite and hydroxyapatite will break, and phosphorus oxygen free radicals will be generated in the gas phase to capture active hydrogen and hydroxyl free radicals during the pyrolysis process of the polyurethane substrate, inhibiting the further cracking and combustion of the PU main chain.

[0030] To prevent the flame retardant from being easily damaged in a humid environment, resulting in a deterioration of the flame retardant performance, the double-layer microcapsule structure flame retardant uses melamine phthalic anhydride resin as the middle shell layer and calixarene borate resin as the outer shell layer. Utilizing the cavity formed by the calixarene borate resin, through the cross-linking interaction and hydrogen bond interaction between the melamine phthalic anhydride resin and the calixarene borate resin, the aluminum hypophosphite modified by hydroxyapatite is coated therein;

[0031] Hydroxyapatite is doped in the double-layer microcapsule structure flame retardant. While having a synergistic flame retardant effect, hydroxyapatite endows the material with certain seawater corrosion resistance and anti-aging properties. Description of the Drawings

[0032] Figure 1 It is a scanning electron microscope image of the raw materials or products involved in the preparation process of the double-layer microcapsule structure flame retardant in Example 1. a and c are the scanning electron microscope images of aluminum hypophosphite, e and f are the scanning electron microscope images when the melamine phthalic anhydride resin is singly coated (Comparative Example 2), and b and d are the scanning electron microscope images of the double-layer microcapsule structure flame retardant (Example 1);

[0033] Figure 2 Hydrophobic effect diagrams of flame retardants prepared by using the method of the present invention and flame retardants not prepared by using the method of the present invention. a is aluminum hypophosphite modified polyurethane prepared in Comparative Example 1, and b is polyurethane modified by a flame retardant with a double-layer microcapsule structure (Example 1);

[0034] Figure 3 EDS spectrum of the flame retardant with a double-layer microcapsule structure. a and b are the EDS spectra of aluminum hypophosphite and the flame retardant with a double-layer microcapsule structure (Example 1) respectively. Detailed implementation manners

[0035] The technical solution of the present invention will be further described in detail below through examples and drawings.

[0036] Example 1

[0037] A preparation method of a flame retardant with a double-layer microcapsule structure, comprising the following steps:

[0038] SO1, according to the mass ratio of melamine to deionized water of 1:100, add deionized water to obtain an aqueous melamine solution; add the aqueous melamine solution (containing 12.6 g of melamine) to a three-necked flask, add a 37 wt% aqueous phthalic anhydride solution (containing 20.2 g of phthalic anhydride) to the aqueous melamine solution, and adjust the pH to 8.5 by dropping 25 wt% ammonia water. React at 80 °C for 1 h to obtain a melamine phthalic anhydride resin prepolymer emulsion. Disperse 60 g of aluminum hypophosphite in 200 ml of water, add it to the prepolymer, add 1.5 g of hydroxyapatite (Sigma-Aldrich, N#A8069, the same below) to the three-necked flask, adjust the pH to 4.5 with acetic acid, react at 70 °C for 4 h, let it stand, filter, wash with absolute ethanol until neutral, and dry in an oven at 80 °C for 24 h to obtain microcapsules (MCAHP) of aluminum hypophosphite modified by melamine phthalic anhydride resin-coated hydroxyapatite;

[0039] SO2, add 20 g of calixarene and 400 g of N,N-dimethylformamide to the reaction kettle, stir at 60 °C for 2 h until the solution is clear; add 60 g of MCAHP in the first step to the reaction kettle, add 0.5 g of Tween-80, and stir for 1 h. Add a 1 mol / L boric acid solution (containing 1.1 g of boric acid) and stir, react at 80 °C for 8 h, add 200 mL of acetone and stir for 30 min, cool, filter, wash with acetone until neutral, dry at 80 °C for 24 h, and grind into powder to obtain a flame retardant with a double-layer microcapsule structure.

[0040] Preparation method of flame-retardant polyurethane material, comprising the following steps: adding 50 g of double-layer microcapsule structure flame retardant, 5 g of silica sol, 1 g of propylene glycol, 1 g of sodium carboxymethyl cellulose, and 25 g of choline chloride into 418 g of polyurethane, mixing evenly, performing melt blending at 180 °C, and finally extruding through a twin-screw extruder, cooling and pelletizing to obtain the flame-retardant polyurethane material.

[0041] Example 2

[0042] Preparation method of a double-layer microcapsule structure flame retardant, comprising the following steps:

[0043] SO1, adding deionized water according to the mass ratio of melamine to deionized water of 1:100 to obtain an aqueous melamine solution; adding the aqueous melamine solution (containing 12.6 g of melamine) into a three-necked flask, adding a 38 wt% aqueous phthalic anhydride solution (containing 20.2 g of phthalic anhydride) into the aqueous melamine solution, dropping 25 wt% ammonia water to adjust the pH to 8.5, reacting at 70 °C for 1 h to obtain a melamine phthalic anhydride resin prepolymer emulsion, dispersing 60 g of aluminum hypophosphite in 200 ml of water, adding it into the prepolymer, adding 1.5 g of hydroxyapatite into the three-necked flask, adjusting the pH to 4.5 with acetic acid, reacting at 70 °C for 4 h, standing, filtering, washing with absolute ethanol until neutral, and drying in an oven at 80 °C for 24 h to obtain microcapsules (MCAHP) of aluminum hypophosphite modified with melamine phthalic anhydride resin-coated hydroxyapatite;

[0044] SO2, adding 20 g of calixarene and 400 g of N,N-dimethylformamide into a reaction kettle, stirring at 60 °C for 2 h until the solution is clear; adding 60 g of MCAHP in the first step into the reaction kettle, adding 0.5 g of Tween-80, and stirring for 1 h. Adding a 1 mol / L boric acid solution (containing 1.3 g of boric acid) and stirring, reacting at 100 °C for 6 h, adding 200 mL of acetone and stirring for 30 min, cooling, filtering, washing with acetone until neutral, drying at 80 °C for 24 h, and grinding into powder to obtain the double-layer microcapsule structure flame retardant.

[0045] Preparation method of flame-retardant polyurethane material, comprising the following steps: adding 50 g of double-layer microcapsule structure flame retardant, 5 g of silica sol, 1 g of propylene glycol, 1 g of sodium carboxymethyl cellulose, and 25 g of choline chloride into 418 g of polyurethane, mixing evenly, performing melt blending at 160 °C, and finally extruding through a twin-screw extruder, cooling and pelletizing to obtain the flame-retardant polyurethane material.

[0046] Example 3

[0047] Preparation method of a double-layer microcapsule structure flame retardant, comprising the following steps:

[0048] SO1, Add deionized water according to the mass ratio of melamine to deionized water of 1:100 to obtain an aqueous melamine solution; Add the aqueous melamine solution (containing 12.6 g of melamine) to a three-necked flask, add a 39 wt% phthalic anhydride aqueous solution (containing 20.2 g of phthalic anhydride) to the aqueous melamine solution, dropwise add 25 wt% ammonia water to adjust the pH to 8.5, and react at 80 °C for 1 h to obtain a melamine phthalate resin prepolymer emulsion. Disperse 60 g of aluminum hypophosphite in 200 ml of water, add it to the prepolymer, add 1.5 g of hydroxyapatite to the three-necked flask, adjust the pH to 4.5 with acetic acid, react at 80 °C for 4 h, let it stand, filter, wash with absolute ethanol until neutral, and dry in an oven at 80 °C for 24 h to obtain microcapsules (MCAHP) of melamine phthalate resin-coated aluminum hypophosphite;

[0049] SO2, Add 30 g of calixarene and 400 g of N,N-dimethylformamide to the reaction kettle, stir at 60 °C for 2 h until the solution is clear; Add 60 g of MCAHP from the first step to the reaction kettle, add 0.5 g of Tween-80, and stir for 1 h. Add a 1 mol / L boric acid solution (containing 1.6 g of boric acid) and stir, react at 90 °C for 8 h, add 200 mL of acetone and stir for 30 min, cool, filter, wash with acetone until neutral, dry at 80 °C for 24 h, and grind into powder to obtain a flame retardant with a double-layer microcapsule structure.

[0050] A preparation method of a flame-retardant polyurethane material, comprising the following steps: Add 50 g of the flame retardant with a double-layer microcapsule structure, 5 g of silica sol, 1 g of propylene glycol, 1 g of sodium carboxymethylcellulose, and 25 g of choline chloride to 418 g of polyurethane, mix evenly, and then melt-blend at 200 °C, and finally extrude through a twin-screw extruder and cool and pelletize to obtain the flame-retardant polyurethane material.

[0051] Example 4

[0052] A preparation method of a flame retardant with a double-layer microcapsule structure, comprising the following steps:

[0053] SO1, Add deionized water according to the mass ratio of melamine to deionized water of 1:100 to obtain an aqueous melamine solution; Add the aqueous melamine solution (containing 12.6 g of melamine) to a three-necked flask, add a 38 wt% phthalic anhydride aqueous solution (containing 20.2 g of phthalic anhydride) to the aqueous melamine solution, dropwise add 25 wt% ammonia water to adjust the pH to 8.5, and react at 70 °C for 1 h to obtain a melamine phthalate resin prepolymer emulsion. Disperse 60 g of aluminum hypophosphite in 200 ml of water, add it to the prepolymer, add 1.5 g of hydroxyapatite to the three-necked flask, adjust the pH to 4.5 with acetic acid, react at 70 °C for 4 h, let it stand, filter, wash with absolute ethanol until neutral, and dry in an oven at 80 °C for 24 h to obtain microcapsules (MCAHP) of melamine phthalate resin-coated aluminum hypophosphite;

[0054] SO2, 20 g of calixarene and 400 g of N,N-dimethylformamide were added to the reaction kettle, and stirred at 60 °C for 2 h until the solution became clear; 60 g of MCAHP from the first step was added to the reaction kettle, 0.5 g of Tween-80 was added, and stirred for 1 h. 1 mol / L boric acid solution (containing 1.3 g of boric acid) was added and stirred, and reacted at 100 °C for 8 h. 200 mL of acetone was added and stirred for 30 min, cooled, filtered, washed with acetone until neutral, dried at 80 °C for 24 h, ground into powder to obtain the flame retardant with double-layer microcapsule structure.

[0055] The preparation method of the flame retardant polyurethane material includes the following steps: 50 g of the flame retardant with double-layer microcapsule structure, 5 g of silica sol, 1 g of propylene glycol, 1 g of sodium carboxymethyl cellulose, and 25 g of choline chloride were added to 418 g of polyurethane. After mixing evenly, melt-blended at 180 °C, and finally extruded through a twin-screw extruder, cooled and pelletized to obtain the flame retardant polyurethane material.

[0056] Comparative Example 1 (This comparative example did not use double-layer resin-coated aluminum hypophosphite and did not use hydroxyapatite modification)

[0057] The preparation method of the flame retardant polyurethane material includes the following steps: 50 g of aluminum hypophosphite, 5 g of silica sol, 1 g of propylene glycol, 1 g of sodium carboxymethyl cellulose, and 25 g of choline chloride were added to 418 g of polyurethane. After mixing evenly, melt-blended at 180 °C, and finally extruded through a twin-screw extruder, cooled and pelletized to obtain the flame retardant polyurethane material.

[0058] Comparative Example 2 (This comparative example did not use calixarene boric acid resin-coated MCAHP)

[0059] SO1, Deionized water was added according to the mass ratio of melamine to deionized water of 1:100 to obtain an aqueous melamine solution; the aqueous melamine solution (containing 12.6 g of melamine) was added to a three-necked flask, and 37 wt% aqueous phthalic anhydride solution (containing 20.2 g of phthalic anhydride) was added to the aqueous melamine solution. 25 wt% ammonia water was added dropwise to adjust the pH to 8.5, and reacted at 80 °C for 1 h to obtain a melamine phthalic anhydride resin prepolymer emulsion. 60 g of aluminum hypophosphite was dispersed in 200 ml of water and added to the prepolymer. 1.5 g of hydroxyapatite was added to the three-necked flask, and the pH was adjusted to 4.5 with acetic acid, and reacted at 70 °C for 4 h, allowed to stand, filtered, washed with absolute ethanol until neutral, and dried in an oven at 80 °C for 24 h to obtain the microcapsule (MCAHP) of melamine phthalic anhydride resin-coated aluminum hypophosphite.

[0060] Preparation method of flame-retardant polyurethane material, comprising the following steps: adding 50 g of aluminum hypophosphite microcapsules (MCAHP) coated with melamine phthalate resin, 5 g of silica sol, 1 g of propylene glycol, 1 g of sodium carboxymethyl cellulose, and 25 g of choline chloride into 418 g of polyurethane, mixing evenly, melt-blending at 180 °C, and finally extruding through a twin-screw extruder and cooling and pelletizing to obtain the flame-retardant polyurethane material.

[0061] Comparative example 3 (no flame retardant was used in this comparative example)

[0062] Preparation method of flame-retardant polyurethane material, comprising the following steps: adding 5 g of silica sol, 1 g of propylene glycol, 1 g of sodium carboxymethyl cellulose, and 25 g of choline chloride into 468 g of polyurethane, mixing evenly, melt-blending at 180 °C, and finally extruding through a twin-screw extruder and cooling and pelletizing to obtain the flame-retardant polyurethane material.

[0063] Comparative example 4 (calixarene was replaced with chitosan in this comparative example)

[0064] In this comparative example, calixarene was replaced with chitosan, and the others were the same as in Example 1.

[0065] Comparative example 5 (boric acid was not added in this comparative example)

[0066] The step of "adding 1 mol / L boric acid solution (containing 1.1 g of boric acid) and stirring" was omitted, and the others were the same as in Example 1.

[0067] Comparative example 6 (the mass ratio of aluminum hypophosphite to melamine was modified in this comparative example)

[0068] In this comparative example, the addition amount of aluminum hypophosphite was 30 g, and the mass ratio of aluminum hypophosphite to melamine was 30:12.6 (equivalent to 2.38:1), and the others were the same as in Example 1.

[0069] Comparative example 7 (the mass ratio of calixarene to MCAHP was modified in this comparative example)

[0070] In this comparative example, the addition amount of calixarene was 10 g, and the mass ratio of calixarene to MCAHP was 1:6, and the others were the same as in Example 1.

[0071] Comparative example 8 (the reaction temperature of S01 was modified in this comparative example)

[0072] 25 wt% ammonia water was added dropwise to adjust the pH to 8.5, and the reaction was carried out at 90 °C for 1 h, and the rest was the same as in Example 1.

[0073] Comparative example 9 (aluminum hypophosphite was directly coated with calixarene boric acid resin instead of being coated with melamine phthalate resin in this comparative example)

[0074] A preparation method of a microcapsule-structured flame retardant, comprising the following steps:

[0075] SO1, Add 20 g of calixarene and 400 g of N,N-dimethylformamide to the reaction kettle, stir at 60 °C for 2 h until the solution is clear; Disperse 60 g of aluminum hypophosphite and 1.5 g of hydroxyapatite in 200 ml of water, add them to the reaction kettle, add 0.5 g of Tween-80, and stir for 1 h. Add 1 mol / L boric acid solution (containing 1.1 g of boric acid) and stir, react at 80 °C for 8 h, add 200 mL of acetone and stir for 30 min, cool, filter, wash with acetone until neutral, dry at 80 °C for 24 h, grind into powder to obtain the microcapsule structure flame retardant.

[0076] Preparation method of flame retardant polyurethane material, including the following steps: Add 50 g of microcapsule structure flame retardant, 5 g of silica sol, 1 g of propylene glycol, 1 g of sodium carboxymethyl cellulose, and 25 g of choline chloride to 418 g of polyurethane, mix evenly, and then carry out melt blending at 180 °C, and finally extrude through a twin-screw extruder, cool and pelletize to obtain the flame retardant polyurethane material.

[0077] Comparative Example 10 (the core layer is removed in this comparative example)

[0078] SO1, Add deionized water according to the mass ratio of melamine to deionized water of 1:100 to obtain an aqueous melamine solution; Add the aqueous melamine solution (containing 12.6 g of melamine) to a three-necked flask, add 37 wt% aqueous phthalic anhydride solution (containing 20.2 g of phthalic anhydride) to the aqueous melamine solution, dropwise add 25 wt% ammonia water to adjust the pH to 8.5, react at 80 °C for 1 h to obtain a melamine phthalic anhydride resin prepolymer emulsion, let it stand, filter, wash with absolute ethanol until neutral, and dry in an oven at 80 °C for 24 h to obtain melamine phthalic anhydride resin;

[0079] SO2, Add 20 g of calixarene and 400 g of N,N-dimethylformamide to the reaction kettle, stir at 60 °C for 2 h until the solution is clear; Add 60 g of the melamine phthalic anhydride resin in the first step to the reaction kettle, add 0.5 g of Tween-80, and stir for 1 h. Add 1 mol / L boric acid solution (containing 1.1 g of boric acid) and stir, react at 80 °C for 8 h, add 200 mL of acetone and stir for 30 min, cool, filter, wash with acetone until neutral, dry at 80 °C for 24 h, grind into powder to obtain the microcapsule structure flame retardant.

[0080] Preparation method of flame retardant polyurethane material, including the following steps: Add 50 g of microcapsule structure flame retardant, 5 g of silica sol, 1 g of propylene glycol, 1 g of sodium carboxymethyl cellulose, and 25 g of choline chloride to 418 g of polyurethane, mix evenly, and then carry out melt blending at 180 °C, and finally extrude through a twin-screw extruder, cool and pelletize to obtain the flame retardant polyurethane material.

[0081] The flame-retardant polyurethane materials prepared in Examples 1-4 and Comparative Examples 1-10 were subjected to performance tests, and the results are shown in Table 1. Among them, the limiting oxygen index test was carried out on an oxygen index meter 1600 in accordance with GB / T 2406-2009; the flammability test of the spline was carried out on a horizontal and vertical combustion tester CZF-5A in accordance with the UL94 standard; the mechanical properties of the material were investigated with an electronic universal testing machine, and the tensile properties were tested according to the Chinese national standard GB528-2009, and the tensile rate was 25 mm / min.

[0082] Table 1 Test results of the flame-retardant polyurethane materials prepared in Examples 1-4 and Comparative Examples 1-10

[0083]

[0084] From the data of Example 1 and Comparative Example 1, it can be seen that the flame-retardant performance of the flame retardant-modified polyurethane coated with double-layer microcapsules is significantly enhanced, the LOI value is increased from 21.5% to 34.4%, and the flame retardant grade is improved from UL 94V-1 to UL94V-0. Moreover, the tight coating, crosslinking, hydrogen bonding and hydroxyapatite in the double-layer microcapsules synergistically improve the mechanical properties.

[0085] In Comparative Example 2, calixarene borate resin was not used to coat MCAHP, and the core flame-retardant component MCAHP had no coating, resulting in an obvious decrease in LOI. After the lack of calixarene borate resin, there is no crosslinking in the structure and the hydrogen bond binding is significantly reduced, so the mechanical properties also decrease.

[0086] For the unmodified polyurethane in Comparative Example 3, during the vertical combustion and limiting oxygen index tests, due to complete combustion and damage during the test, the continuous combustion time was long, 8-9 molten drops were generated, and these molten drops could ignite absorbent cotton, so the UL-94 test could not be carried out, and the flame retardant performance was poor.

[0087] Compared with Comparative Examples 1 and 2, the flame retardant performance of Example 1 is significantly enhanced, the flame retardant grade is improved to UL-94V-0, and compared with Comparative Example 3, there is no dripping of molten liquid, showing strong flame retardant performance.

[0088] Compared with Example 1, in Comparative Example 4, calixarene was replaced with chitosan. Since chitosan does not contain a cavity, in order to form an effective coating, the relative amount of chitosan required is significantly larger, so the coating effect is slightly inferior when the dosage remains unchanged; chitosan does not contain an aromatic structure and cannot undergo Π-Π stacking with melamine phthalic anhydride, and chitosan has strong hydrophilicity and repels the relatively hydrophobic melamine phthalic anhydride, so tight coating cannot be achieved and the mechanical properties also decrease.

[0089] Compared with Example 1, in Comparative Example 5, the limiting oxygen index decreased due to the absence of boric acid.

[0090] Comparative Example 6 compared with Example 1. Due to the modification of the mass ratio of aluminum hypophosphite to melamine, the content of aluminum hypophosphite in the core layer was reduced, resulting in a decrease in the phosphorus content of the overall flame retardant. During the flame retardant process, phosphorus combines with free radicals, weakening the free radical reaction during combustion, thereby causing a decrease in the limiting oxygen index. The mechanical properties also decreased.

[0091] Comparative Example 7 compared with Example 1. Due to the modification of the mass ratio of calixarene to MCAHP, there was less calixarene, resulting in insufficient coating of the melamine phthalic anhydride resin by calixarene, and the flame retardant properties and mechanical properties decreased to a certain extent. Moreover, the mass ratio of calixarene to MCAHP is also important for the synergistic improvement of hydrophobicity between the calixarene boric acid resin and the melamine phthalic anhydride resin, and the hydrophobicity also showed a decrease.

[0092] Comparative Example 8 compared with Example 1. Due to the modification of the reaction temperature in S01, the polymerization effect of the melamine phthalic anhydride resin prepolymer was affected, resulting in a decrease in the limiting oxygen index and mechanical properties.

[0093] Comparative Example 9 compared with Example 1. Since aluminum hypophosphite was not coated with melamine phthalic anhydride resin, but directly coated with calixarene boric acid resin, due to the lack of melamine phthalic anhydride resin, the flame retardancy decreased significantly; and there was no crosslinking in the structure of Comparative Example 9, and the hydrogen bond binding decreased significantly, and the mechanical properties also decreased significantly.

[0094] Comparative Example 10 compared with Example 1. Since the core layer was deleted, the flame retardant properties decreased significantly, and the mechanical properties also decreased.

[0095] Among them, the materials that improve or maintain the mechanical properties are the polymers in the shell layer and the crosslinking and hydrogen bond interactions between the polymers. If the content in the shell layer is reduced or the ratio is not the best, the mechanical properties will decrease to a certain extent.

[0096] The water contact angles of the surfaces of Examples 1-4 were measured and compared with those of Comparative Examples 1-10. The detection process was as follows: At room temperature, a liquid droplet with a volume of 5 μL was used, and an optical goniometer (JC2000D3R, Shanghai Zhongchen Digital Technology Instrument Co., Ltd., China) was used to measure the contact angle of the sample surface.

[0097] Table 2 Contact angles of examples and comparative examples

[0098] Example Contact Angle (°) Example 1 132.4 Comparative Example 1 72.5 Example 2 130.5 Comparative Example 2 115.5 Example 3 134.8 Comparative Example 3 92.1 Example 4 130.6 Comparative Example 4 74.5 Comparative Example 5 133.5 Comparative Example 6 132.6 Comparative Example 7 125.3 Comparative Example 8 130.5 Comparative Example 9 112.5 Comparative Example 10 135.6

[0099] Based on the data in Table 1 and Table 2, it can be seen from Example 1 and Comparative Example 4 that although replacing calixarene with chitosan has a certain coating effect and similar flame retardant properties, the hydrophobicity decreases significantly, not meeting the application requirements.

[0100] Comparative Example 2 compared with Example 1. Since calixarene boronic acid resin was not used to coat MCAHP, the π-π stacking interaction could not be formed and it could not cooperate with calixarene boronic acid resin to improve hydrophobicity. Therefore, the hydrophobicity decreased.

[0101] Comparative Example 3 compared with Example 1. Since it was not modified with a flame retardant, the hydrophobic property also decreased significantly.

[0102] In Comparative Example 8, the reaction temperature was too high. During the prepolymerization of melamine phthalic anhydride resin, the degree of polymerization was relatively high, which was not conducive to subsequent coating. Therefore, the hydrophobic angle decreased slightly.

[0103] It can be seen from Example 1 and Comparative Example 9 that the hydrophobicity of the flame retardant with a single-layer microcapsule structure decreased significantly. Double-layer coating can achieve a better coating effect through the hydrophobicity of the shell layer and the tight crosslinking of the double shell layer, and can cooperate to play a better hydrophobic role.

[0104] It can be seen from Example 1 and Comparative Example 1 that the hydrophobic property of the flame retardant modified polyurethane without double-layer resin coating of aluminum hypophosphite also decreased significantly. The reason is the hydrophilicity of aluminum hypophosphite itself.

[0105] Figure 1 It is the scanning electron microscope image of the raw materials or products involved in the preparation process of the flame retardant with a double-layer microcapsule structure in Example 1. a and c are the scanning electron microscope images of aluminum hypophosphite, and e and f are the scanning electron microscope images when melamine phthalic anhydride resin is used for single-layer coating (Comparative Example 2). It can be clearly seen that melamine phthalic anhydride resin polymerized on the surface of aluminum hypophosphite. b and d are the scanning electron microscope images of the flame retardant after double-layer microencapsulation (Example 1). After layer-by-layer coating and assembly, it can be clearly seen that the double-layer microcapsule-coated flame retardant is successfully prepared.

[0106] Figure 2 It is the hydrophobic effect diagram of the flame retardant prepared by the method of the present invention and the flame retardant not prepared by the method of the present invention. a is the polyurethane modified with aluminum hypophosphite prepared in Comparative Example 1, and b is the polyurethane modified with the flame retardant with a double-layer microcapsule structure (Example 1). By comparison, it can be found that the contact angle of the polyurethane modified with the double-layer microcapsule prepared by this method is greater than 130 degrees, and the hydrophobicity is stronger;

[0107] Figure 3 It is the EDS energy spectrum diagram of the flame retardant with a double-layer microcapsule structure in Example 1. a and b are the EDS energy spectrum diagrams of aluminum hypophosphite and the flame retardant with a double-layer microcapsule structure (Example 1) respectively. It can be clearly seen that N element is coated on the shell layer, which confirms the successful preparation of the flame retardant with a double-layer microcapsule structure.

[0108] It should be understood that the above embodiments do not limit the present invention in any form. All technical solutions obtained by using equivalent replacement or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A double-layer microcapsule structure flame retardant, characterized in that: It includes an outer shell layer, a middle shell layer and a core layer arranged from the outside to the inside; wherein the outer shell layer is a calixarene boric acid resin, the middle shell layer is a melamine phthalic anhydride resin, and the core layer is hydroxyapatite-modified aluminum hypophosphite; The preparation method of the double-layer microcapsule structure flame retardant comprises the following steps: SO1, add melamine aqueous solution into a reaction kettle, add phthalic anhydride aqueous solution with a mass fraction of 37wt% to 39wt% into the melamine aqueous solution, so that the molar ratio of phthalic anhydride to melamine is 3:2.15-2.22, drop a nitrogen-containing pH regulator to adjust the pH to 8-9, react at 65-80°C for 0.5-1.5h to obtain a melamine phthalic anhydride resin prepolymer emulsion, then add aluminum hypophosphite and hydroxyapatite to the melamine phthalic anhydride prepolymer emulsion at a mass ratio of aluminum hypophosphite to melamine of 3-6:1 and a mass ratio of hydroxyapatite to melamine of 1:8-12, adjust the pH to 4-5 with an acidic pH regulator, react at 70-90°C for 4-6h, let stand, filter, wash with anhydrous ethanol to neutrality, and dry at 60-95°C for 12-24h to obtain melamine phthalic anhydride resin-coated modified aluminum hypophosphite microcapsules; SO2, mix calixarene with N,N-dimethylformamide in a mass ratio of 1:20-40, stir at 60-90°C for 1-2h, until the solution is clear; then add the modified aluminum hypophosphite microcapsules obtained from SO1 in a mass ratio of 2-4:1 to calixarene, add Tween-80, stir for 0.5-1h, add boric acid in a mass ratio of boric acid to calixarene of 1:15-20, stir, react at 80-105°C for 5-8h, add acetone in a mass ratio of 1:3-5 to acetone and stir for 30min, cool, filter, wash with acetone until neutral, dry at 80-120°C for 24-48h, grind into powder, and obtain a double-layer microcapsule structure flame retardant.

2. A method for preparing a double-layer microcapsule structure flame retardant, characterized in that: The steps include: SO1, add melamine aqueous solution into a reaction kettle, add phthalic anhydride aqueous solution with a mass fraction of 37wt% to 39wt% into the melamine aqueous solution, so that the molar ratio of phthalic anhydride to melamine is 3:2.15-2.22, drop a nitrogen-containing pH regulator to adjust the pH to 8-9, react at 65-80°C for 0.5-1.5h to obtain a melamine phthalic anhydride resin prepolymer emulsion, then add aluminum hypophosphite and hydroxyapatite to the melamine phthalic anhydride prepolymer emulsion at a mass ratio of aluminum hypophosphite to melamine of 3-6:1 and a mass ratio of hydroxyapatite to melamine of 1:8-12, adjust the pH to 4-5 with an acidic pH regulator, react at 70-90°C for 4-6h, let stand, filter, wash with anhydrous ethanol to neutrality, and dry at 60-95°C for 12-24h to obtain melamine phthalic anhydride resin-coated modified aluminum hypophosphite microcapsules; SO2, mix calixarene with N,N-dimethylformamide in a mass ratio of 1:20-40, stir at 60-90°C for 1-2h, until the solution is clear; then add the modified aluminum hypophosphite microcapsules obtained with SO1 in a mass ratio of 2-4:1 to calixarene, add Tween-80, stir for 0.5-1h, add boric acid in a mass ratio of boric acid to calixarene of 1:15-20, stir, react at 80-105°C for 5-8h, add acetone in a mass ratio of 1:3-5 to acetone, stir for 30min, cool, filter, wash with acetone until neutral, dry at 80-120°C for 24-48h, grind into powder, and obtain a double-layer microcapsule structure flame retardant; The double-layer microcapsule structure flame retardant comprises an outer shell layer, a middle shell layer and a core layer arranged from outside to inside; wherein the outer shell layer is calixarene boric acid resin, the middle shell layer is melamine phthalic anhydride resin, and the core layer is hydroxyapatite-modified aluminum hypophosphite.

3. The method for preparing a double-layer microcapsule structure flame retardant according to claim 2, characterized in that: In SO1, the nitrogen-containing pH adjuster is one of ammonia water, ammonium chloride and ammonium carbonate.

4. The method for preparing a double-layer microcapsule structure flame retardant according to claim 2, characterized in that: In SO1, the acidic pH adjuster is one of acetic acid, hydrochloric acid and sulfuric acid.

5. A flame-retardant polyurethane material prepared using the double-layer microcapsule structure flame retardant according to claim 1.

6. The method for preparing the flame retardant polyurethane material according to claim 5, characterized in that: The method comprises the following steps: uniformly mixing the components with polyurethane according to the addition amount of 10wt% to 20wt% of a double-layer microcapsule structure flame retardant, 0.5wt% to 1wt% of silica sol, 0.1wt% to 0.25wt% of a film-forming aid, 0.1wt% to 0.25wt% of a thickener and 5wt% to 10wt% of an ion conductive agent, melt blending at 160 to 200°C, and finally extruding through a twin-screw extruder and cooling and granulating to obtain a flame-retardant polyurethane material.

7. The method for preparing a flame retardant polyurethane material according to claim 6, characterized in that: The mass fraction of SiO2 in the silica sol is 20%±2%; the thickener is one of alkyl ammonium salt, gelatin or sodium carboxymethyl cellulose; and the film-forming aid is one of propylene glycol, propylene glycol butyl ether, dodecyl alcohol ester or N,N-dimethylformamide.

8. The method for preparing a flame retardant polyurethane material according to claim 6, characterized in that: The ion conductive agent is a combination of one or more of choline chloride, acetylcholine chloride and carbachol.

9. Use of the double-layer microcapsule structure flame retardant according to claim 1 or the flame retardant polyurethane material according to claim 5 in combustible gas transmission pipelines, marine pipelines and shale gas fracturing pipelines.

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