Carbon nanotube synergistic flame retardant modified waterborne polyurethane coating and preparation method thereof

Abstract

The present invention relates to the field of polyurethane technology, and discloses a carbon nanotube synergistic flame-retardant modified waterborne polyurethane coating and a preparation method thereof. The hydroxyl groups of the acidified carbon nanotubes serve as polymerization reaction sites, and 4,4'-methylenebis(phenyl isocyanate) and triphenylenediamine-based PEPA are subjected to an in-situ graft polymerization reaction to obtain PEPA-based polymer-grafted carbon nanotubes through covalent bonding. After polymer grafting modification, the carbon nanotubes have better compatibility with the waterborne polyurethane matrix and excellent dispersibility, thus playing a better reinforcing role and significantly improving the tensile strength, elongation at break, and tensile modulus of the polyurethane film. The grafted polymer molecular chain contains a PEPA phosphate flame-retardant structure and a urea-based nitrogen-containing structure, as well as a high-carbon triphenyl aromatic ring structure, forming a nitrogen-phosphorus-carbon expansion flame-retardant system, which enables the polyurethane to exhibit excellent flame retardant properties.

Description

Technical Field

[0001] The present invention relates to the technical field of polyurethane, and in particular to a carbon nanotube synergistic flame-retardant modified waterborne polyurethane coating and a preparation method thereof. Background Art

[0002] Polyurethane has excellent elasticity, high chemical stability, and good sound insulation, and can be made into a wide range of products, including foams, fibers, and plastics. Water-based polyurethane, among others, has the advantages of being solvent-free, low in VOCs, and having good film-forming properties. As water-based coatings and inks, it is widely used in wood paints, electronic coatings, and anti-corrosion coatings. Traditional water-based polyurethane coatings lack flame retardancy, hindering their practical application in fire-retardant coatings. Water-based polyurethane coatings also suffer from poor mechanical strength. Carbon nanotubes are a type of carbon nanomaterial with excellent overall properties. They can be used as synergistic flame retardants, toughening agents, and conductive agents, and have important applications in polymer materials. However, carbon nanotubes have significant agglomeration issues and poor compatibility with polyurethane polymers. Patent CN111117466B discloses the preparation of modified flame-retardant polyurethane coatings and adhesives using tannic acid, boron nitride nanosheets, polymer polyols, isocyanates, and carbon nanotubes as raw materials, resulting in reduced combustion smoke and improved pressure-sensitive properties. However, this patent does not improve the agglomeration problem of carbon nanotubes, nor does it significantly improve the mechanical strength of polyurethane materials. Summary of the Invention

[0003] Technical problem solved: Provides a carbon nanotube synergistic flame-retardant modified waterborne polyurethane coating, which solves the problems of easy agglomeration of carbon nanotubes and poor flame retardancy of waterborne polyurethane coating.

[0004] Technical solution:

[0005] A method for preparing a carbon nanotube synergistic flame-retardant modified waterborne polyurethane coating:

[0006] Step (1) adds acidified carbon nanotubes and N,N-dimethylformamide into a reaction container, disperses them by ultrasonication, adds 4,4'-methylenebis(phenyl isocyanate) and triphenylenediamine-based PEPA, and carries out graft polymerization reaction in a nitrogen atmosphere, cools, filters the solvent, washes with ethanol, and dries to obtain PEPA-based polymer-grafted carbon nanotubes.

[0007] Step (2): adding 0.5-10 parts of PEPA-based polymer grafted carbon nanotubes to 100 parts by weight of aqueous polyurethane resin, and then uniformly dispersing the mixture. Then, adding 0.6-1 parts of defoaming agent and 0.5-1 parts of wetting and dispersing agent, and then uniformly dispersing the mixture, to obtain a carbon nanotube synergistic flame-retardant modified aqueous polyurethane coating.

[0008] In step (1), the ratio of acidified carbon nanotubes, N,N-dimethylformamide, 4,4'-methylenebis(phenyl isocyanate), and triphenylenediamine-based PEPA is (80-300) g: (30-50) L: (1.12-1.3) mol: 1 mol.

[0009] Wherein, in step (1), the temperature of the graft polymerization reaction is controlled to be 75-90° C. and the time is 12-24 hours.

[0010] The preparation method of triphenyldiamine-based PEPA comprises the following steps:

[0011] Step (3): Place the reaction vessel in an ice bath, add 1-oxo-4-hydroxymethyl-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane, pyridine, solvent, and 4-formylbenzoyl chloride, and react for 0.5-1 h. Then remove the ice bath and react at room temperature for 3-8 h. Concentrate the solvent and recrystallize the product from ethyl acetate to obtain 4-formylbenzoate PEPA. The structural formula is:

[0012] Step (4): 4-formylbenzoate-based PEPA and aniline are added to a reaction vessel, and aniline hydrochloride is added in a nitrogen atmosphere to carry out a condensation reaction. After cooling, the mixture is added to an aqueous potassium carbonate solution and stirred to precipitate. The solvent is filtered, and the precipitate is washed with methanol. The product is recrystallized from toluene to obtain triphenyldiamino-based PEPA. The structural formula is:

[0013] Wherein, in step (3), the ratio of 1-oxo-4-hydroxymethyl-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane, pyridine, solvent, and 4-formylbenzoyl chloride is (1-1.2) mol: (1-1.4) mol: (3-5) L: 1 mol.

[0014] Wherein, the solvent in step (3) is any one of ethyl acetate, acetonitrile and toluene.

[0015] Wherein, in step (4), the ratio of 4-formylbenzoate PEPA, aniline, and aniline hydrochloride is 1 mol: (3.8-4.5) mol: (0.13-0.18) mol.

[0016] Wherein, in step (4), potassium carbonate aqueous solution is added to adjust the pH of the reaction solution to neutral.

[0017] Wherein, the condensation reaction in step (4) is controlled at a temperature of 140-155° C. and a time of 2-6 hours.

[0018] Technical Effect: 1-Oxo-4-hydroxymethyl-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane and 4-formylbenzoyl chloride are used for an esterification reaction to obtain 4-formylbenzoate-based PEPA. Aniline hydrochloride is then used as a promoter to undergo a condensation reaction with the CH atom at the 4-position of aniline to obtain 4-formylbenzoate-based PEPA, which contains two active aromatic amine groups that can react with the isocyanate group of 4,4'-methylenebis(phenylisocyanate).

[0019] This invention utilizes the principle that the hydroxyl groups on the surface of acidified carbon nanotubes can react with isocyanate groups. The hydroxyl groups on the acidified carbon nanotubes serve as polymerization sites for an in-situ graft polymerization reaction of 4,4'-methylenebis(phenyl isocyanate) and triphenylenediamine-based PEPA. Through covalent bonding, PEPA-based polymer-grafted carbon nanotubes are produced. These polymers are then added to a waterborne polyurethane resin along with additives such as a defoamer to produce a synergistic flame-retardant carbon nanotube-modified waterborne polyurethane coating. The polymer grafting modification of the carbon nanotubes helps overcome agglomeration issues, improves compatibility with the waterborne polyurethane matrix, and offers excellent dispersibility, providing enhanced reinforcement and significantly increasing the tensile strength, elongation at break, and tensile modulus of the polyurethane film.

[0020] The polymer molecular chain grafted with carbon nanotubes contains PEPA phosphate flame retardant structure and urea nitrogen-containing structure, as well as a triphenyl aromatic ring structure with a high carbon content, forming a nitrogen-phosphorus-carbon expansion flame retardant system. During combustion, it promotes the dehydration of polyurethane into carbon, and forms a continuous and stable composite carbon layer structure with carbon nanotubes, reducing the peak heat release rate and total heat release of the polyurethane film during combustion, showing excellent flame retardant properties. DETAILED DESCRIPTION

[0021] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0022] The main raw materials of the present invention are:

[0023] Waterborne polyurethane resin, solid content 40%;

[0024] 4-Formylbenzoyl chloride, CAS No. 16173-52-7.

[0025] 1-Oxo-4-hydroxymethyl-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane, CAS No. 5301-78-0.

[0026] Aniline, CAS No. 62-53-3.

[0027] Aniline hydrochloride, CAS No. 142-04-1.

[0028] 4,4'-Methylenebis(phenyl isocyanate), CAS No. 101-68-8.

[0029] Defoamer, brand Efka SI 2741.

[0030] Wetting and dispersing agent, brand TS-9100.

[0031] 0.2 g of carbon nanotubes were acidified in 15 mL of concentrated sulfuric acid and 5 mL of concentrated nitric acid at room temperature by ultrasonication for 8 h to obtain acidified carbon nanotubes.

[0032] Example 1

[0033] The reaction vessel was placed in an ice bath, and 1 mmol of 1-oxo-4-hydroxymethyl-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane, 1.4 mmol of pyridine, 3 mL of acetonitrile solvent, and 1 mmol of 4-formylbenzoyl chloride were added. The reaction was carried out for 0.5 h. The ice bath was then removed, and the reaction was carried out at room temperature for 8 h. The solvent was concentrated, and the product was recrystallized from ethyl acetate to obtain 4-formylbenzoate PEPA.

[0034] 2 mmol of 4-formylbenzoate-based PEPA and 9 mmol of aniline were added to a reaction vessel. 0.32 mmol of aniline hydrochloride was added under a nitrogen atmosphere. The condensation reaction was carried out at 155°C for 2 hours. After cooling, the reaction solution was added to an aqueous potassium carbonate solution. The pH of the reaction solution was adjusted to neutral. The precipitate was stirred and the solvent was filtered. The product was washed with methanol and recrystallized from toluene to obtain triphenyldiamino-PEPA. Reaction route:

[0035]

[0036] 0.4 g of acidified carbon nanotubes and 150 mL of N,N-dimethylformamide were added to a reaction vessel and dispersed by ultrasound. 5.6 mmol of 4,4'-methylenebis(phenyl isocyanate) and 5 mmol of triphenylenediamine-based PEPA were added. Graft polymerization was carried out in a nitrogen atmosphere at 75°C for 24 h. The mixture was cooled, the solvent was filtered, the mixture was washed with ethanol, and the mixture was dried to obtain PEPA-based polymer-grafted carbon nanotubes.

[0037] 0.5 g of PEPA-based polymer grafted carbon nanotubes was added to 100 g of waterborne polyurethane resin and dispersed evenly. Then, 1 g of defoamer and 0.6 g of wetting and dispersing agent were added and dispersed evenly to obtain a carbon nanotube synergistic flame retardant modified waterborne polyurethane coating.

[0038] Example 2

[0039] The reaction vessel was placed in an ice bath, and 1.2 mmol of 1-oxo-4-hydroxymethyl-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane, 1 mmol of pyridine, 5 mL of ethyl acetate solvent, and 1 mmol of 4-formylbenzoyl chloride were added. The reaction was continued for 1 h. The ice bath was then removed, and the reaction was continued at room temperature for 3 h. The solvent was concentrated, and the product was recrystallized from ethyl acetate to obtain 4-formylbenzoate PEPA.

[0040] 2 mmol of 4-formylbenzoate-based PEPA and 7.6 mmol of aniline were added to a reaction vessel. 0.36 mmol of aniline hydrochloride was added in a nitrogen atmosphere. The condensation reaction was carried out at 150°C for 6 hours. After cooling, the reaction solution was added to an aqueous potassium carbonate solution. The pH of the reaction solution was adjusted to neutral. The precipitate was precipitated by stirring, the solvent was filtered, and the product was washed with methanol. The product was recrystallized from toluene to obtain triphenyldiamino-PEPA.

[0041] 1 g of acidified carbon nanotubes and 200 mL of N,N-dimethylformamide were added to a reaction vessel and dispersed by ultrasound. 6 mmol of 4,4'-methylenebis(phenyl isocyanate) and 5 mmol of triphenyldiamine-based PEPA were added. Graft polymerization was carried out in a nitrogen atmosphere at 90°C for 12 h. The reaction was cooled, the solvent was filtered, the mixture was washed with ethanol, and the mixture was dried to obtain PEPA-based polymer-grafted carbon nanotubes.

[0042] 5 g of PEPA-based polymer grafted carbon nanotubes were added to 100 g of waterborne polyurethane resin and dispersed evenly. Then, 0.6 g of defoaming agent and 1 g of wetting and dispersing agent were added and dispersed evenly to obtain a carbon nanotube synergistic flame retardant modified waterborne polyurethane coating.

[0043] Example 3

[0044] The reaction vessel was placed in an ice bath, and 1.2 mmol of 1-oxo-4-hydroxymethyl-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane, 1.2 mmol of pyridine, 5 mL of toluene solvent, and 1 mmol of 4-formylbenzoyl chloride were added. The reaction was continued for 1 h. The ice bath was then removed, and the reaction was continued at room temperature for 8 h. The solvent was concentrated, and the product was recrystallized from ethyl acetate to obtain 4-formylbenzoate PEPA.

[0045] 2 mmol of 4-formylbenzoate-based PEPA and 8.2 mmol of aniline were added to a reaction vessel. 0.26 mmol of aniline hydrochloride was added in a nitrogen atmosphere. The condensation reaction was carried out at 140°C for 5 hours. After cooling, the reaction solution was added to an aqueous potassium carbonate solution. The pH of the reaction solution was adjusted to neutral. The precipitate was precipitated by stirring, the solvent was filtered, and the product was washed with methanol. The product was recrystallized from toluene to obtain triphenyldiamino-based PEPA.

[0046] 1.5 g of acidified carbon nanotubes and 250 mL of N,N-dimethylformamide were added to a reaction vessel and dispersed by ultrasound. 6.5 mmol of 4,4'-methylenebis(phenyl isocyanate) and 5 mmol of triphenylenediamine-based PEPA were added. Graft polymerization was carried out in a nitrogen atmosphere at a temperature of 75°C for 18 h. The mixture was cooled, the solvent was filtered, the mixture was washed with ethanol, and the mixture was dried to obtain PEPA-based polymer-grafted carbon nanotubes.

[0047] 10g of PEPA-based polymer grafted carbon nanotubes was added to 100g of waterborne polyurethane resin and dispersed evenly. Then, 1g of defoamer and 0.5g of wetting and dispersing agent were added and dispersed evenly to obtain a carbon nanotube synergistic flame retardant modified waterborne polyurethane coating.

[0048] Comparative Example 1

[0049] 1 g of defoaming agent and 0.6 g of wetting and dispersing agent were added to 100 g of waterborne polyurethane resin and dispersed uniformly to obtain a waterborne polyurethane coating.

[0050] Comparative Example 2

[0051] 0.5 g of acidified carbon nanotubes were added to 100 g of waterborne polyurethane resin and dispersed evenly. Then, 1 g of defoamer and 0.6 g of wetting and dispersing agent were added and dispersed evenly to obtain a modified waterborne polyurethane coating.

[0052] Comparative Example 3

[0053] 150 mL of N,N-dimethylformamide was added to a reaction vessel and dispersed by ultrasound. 5.6 mmol of 4,4'-methylenebis(phenyl isocyanate) and 5 mmol of triphenyldiamine-based PEPA were added. Graft polymerization was carried out in a nitrogen atmosphere at 75°C for 24 hours. The mixture was cooled, the solvent was filtered, the mixture was washed with ethanol, and dried to obtain a PEPA-based polymer.

[0054] 0.5 g of PEPA-based polymer was added to 100 g of waterborne polyurethane resin and dispersed evenly. Then, 1 g of defoamer and 0.6 g of wetting and dispersing agent were added and dispersed evenly to obtain a modified waterborne polyurethane coating.

[0055] Comparative Example 4

[0056] 0.4 g of carbon nanotubes and 150 mL of N,N-dimethylformamide were added to a reaction vessel and dispersed by ultrasound. 5.6 mmol of 4,4'-methylenebis(phenyl isocyanate) and 5 mmol of triphenylenediamine-based PEPA were added. The mixture was reacted at 75°C in a nitrogen atmosphere for 24 h. The mixture was cooled, the solvent was filtered, the mixture was washed with ethanol, and the mixture was dried to obtain a PEPA-based polymer-carbon nanotube blend.

[0057] 0.5 g of the PEPA-based polymer-carbon nanotube blend was added to 100 g of the waterborne polyurethane resin and dispersed uniformly. Then, 1 g of a defoamer and 0.6 g of a wetting and dispersing agent were added and dispersed uniformly to obtain a modified waterborne polyurethane coating.

[0058] The waterborne polyurethane coating was cast into a film in a mold and dried at 80°C for 6 hours to obtain a polyurethane film. The tensile properties of the film were tested according to the method of GB / T 1040.1-2006.

[0059] Table 1 Polyurethane film tensile properties test

[0060]

[0061] The combustion performance of the polyurethane film was tested by a microcalorimeter with a sample size of 50 mm × 50 mm × 3 mm and a thermal irradiation condition of 35 kW / m 2 .

[0062] Table 2 Polyurethane combustion performance test

[0063]

[0064]

[0065] The hydroxyl groups on the surface of the acidified carbon nanotubes of Examples 1 to 3 can react with the isocyanate groups of 4,4'-methylenebis(phenyl isocyanate), so that the hydroxyl groups of the acidified carbon nanotubes serve as polymerization reaction sites, and 4,4'-methylenebis(phenyl isocyanate) and triphenylenediamine-based PEPA undergo in-situ graft polymerization reaction, and through covalent bonding, PEPA-based polymer-grafted carbon nanotubes are obtained. Then, with additives such as defoaming agents and water-based polyurethane resin, a carbon nanotube synergistic flame-retardant modified water-based polyurethane coating is obtained; after the carbon nanotubes are grafted with polymers, they are conducive to overcoming their agglomeration problem, and have better compatibility with the water-based polyurethane matrix, excellent dispersibility, and play a better reinforcing role, significantly improving the tensile strength, elongation at break, and tensile modulus of the polyurethane film. At the same time, the grafted polymer molecular chain contains PEPA phosphate Flame retardant structure and Urea nitrogen structure and high carbon content triphenyl aromatic ring structure It forms a nitrogen-phosphorus-carbon expanding flame retardant system, which promotes the dehydration of polyurethane into carbon during combustion, and forms a continuous and stable composite carbon layer structure with carbon nanotubes, which has a synergistic flame retardant effect, reduces the peak heat release rate and total heat release of the polyurethane film during combustion, and exhibits excellent flame retardant properties.

[0066] In Comparative Example 1, no PEPA-based polymer grafted carbon nanotubes were added, and the tensile properties and flame retardancy of the polyurethane film were the worst.

[0067] In Comparative Example 2, only acidified carbon nanotubes were added. The acidified carbon nanotubes were easily agglomerated, had poor compatibility with polyurethane, had a small improvement on the tensile properties of polyurethane, and had poor flame retardant properties.

[0068] In Comparative Example 3, no carbon nanotubes were added during the preparation of the PEPA-based polymer. The resulting PEPA-based polymer formed a nitrogen-phosphorus-carbon intumescent flame retardant system, which improved the flame retardant properties of the polyurethane. However, no carbon nanotubes were added to form a synergistic flame retardant effect. The peak heat release rate and total heat release were higher than those in the other examples; and the tensile properties of the polyurethane were not improved.

[0069] In Comparative Example 4, when preparing a PEPA-based polymer, unacidified carbon nanotubes were added. Since the carbon nanotubes did not contain hydroxyl groups on their surfaces, they could not undergo an in-situ graft polymerization reaction with 4,4'-methylenebis(phenyl isocyanate) and triphenylenediamine-based PEPA. The resulting PEPA-based polymer did not form chemical covalent bonds with the carbon nanotubes, and only a physical blend of the PEPA-based polymer and the carbon nanotubes was obtained. This did not significantly improve the agglomeration problem of the carbon nanotubes, and the tensile properties of the polyurethane were only slightly improved.

Claims

1. A method for preparing a carbon nanotube synergistic flame retardant modified waterborne polyurethane coating, characterized in that: The preparation method comprises the following steps: step (1), adding acidified carbon nanotubes and N,N-dimethylformamide into a reaction container, dispersing them by ultrasonication, adding 4,4'-methylenebis(phenyl isocyanate) and triphenylenediamine-based PEPA, carrying out graft polymerization reaction in a nitrogen atmosphere, cooling, filtering, washing, and drying to obtain PEPA-based polymer-grafted carbon nanotubes; The structural formula of the triphenyldiamine-based PEPA is: ; Step (2): adding 0.5-10 parts of PEPA-based polymer grafted carbon nanotubes to 100 parts by weight of aqueous polyurethane resin, and then uniformly dispersing the mixture. Then, adding 0.6-1 parts of defoaming agent and 0.5-1 parts of wetting and dispersing agent, and then uniformly dispersing the mixture, to obtain a carbon nanotube synergistic flame-retardant modified aqueous polyurethane coating.

2. The method for preparing the carbon nanotube synergistic flame retardant modified waterborne polyurethane coating according to claim 1, characterized in that: In the step (1), the ratio of acidified carbon nanotubes, N,N-dimethylformamide, 4,4'-methylenebis(phenyl isocyanate), and triphenylenediamine-based PEPA is (80-300) g: (30-50) L: (1.12-1.3) mol: 1 mol.

3. The method for preparing the carbon nanotube synergistic flame retardant modified waterborne polyurethane coating according to claim 1, characterized in that: In the step (1), the temperature of the graft polymerization reaction is controlled to be 75-90° C. and the time is controlled to be 12-24 hours.

4. The method for preparing the carbon nanotube synergistic flame retardant modified waterborne polyurethane coating according to claim 1, characterized in that: The preparation method of the triphenyldiamine-based PEPA comprises the following steps: Step (3), placing the reaction vessel in an ice bath, adding 1-oxo-4-hydroxymethyl-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane, pyridine, a solvent, and 4-formylbenzoyl chloride, reacting for 0.5-1 h, then removing the ice bath, reacting at room temperature for 3-8 h, concentrating the solvent, and recrystallizing to obtain 4-formylbenzoate-based PEPA; Step (4), adding 4-formylbenzoate-based PEPA and aniline to a reaction vessel, adding aniline hydrochloride in a nitrogen atmosphere, carrying out a condensation reaction, cooling, adding to a potassium carbonate aqueous solution, stirring to precipitate, filtering, washing, and recrystallizing to obtain triphenyldiamino-PEPA.

5. The method for preparing the carbon nanotube synergistic flame retardant modified waterborne polyurethane coating according to claim 4, characterized in that: In the step (3), the ratio of 1-oxo-4-hydroxymethyl-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane, pyridine, solvent, and 4-formylbenzoyl chloride is (1-1.2) mol: (1-1.4) mol: (3-5) L: 1 mol.

6. The method for preparing the carbon nanotube synergistic flame retardant modified waterborne polyurethane coating according to claim 5, characterized in that: The solvent in step (3) is any one of ethyl acetate, acetonitrile and toluene.

7. The method for preparing the carbon nanotube synergistic flame retardant modified waterborne polyurethane coating according to claim 4, characterized in that: In the step (4), the ratio of 4-formylbenzoate PEPA, aniline, and aniline hydrochloride is 1 mol: (3.8-4.5) mol: (0.13-0.18) mol.

8. The method for preparing the carbon nanotube synergistic flame-retardant modified waterborne polyurethane coating according to claim 4, characterized in that: In the step (4), potassium carbonate aqueous solution is added to adjust the pH of the reaction solution to neutral.

9. The method for preparing the carbon nanotube synergistic flame retardant modified waterborne polyurethane coating according to claim 4, characterized in that: In the step (4), the condensation reaction is carried out at a controlled temperature of 140-155° C. and for a time of 2-6 hours.

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