Technical Field
The polyurethane is a high molecular compound and is named polyurethane. Polyurethane has excellent mechanical properties and good chemical reagent resistance, acid and alkali resistance, weather resistance, water resistance, high adhesion and other properties, so that the polyurethane can be widely applied, such as being used as a polyurethane coating. The polyurethane is further classified into solvent type polyurethane and water-based polyurethane, and the application of the solvent type polyurethane coating is limited due to the pollution problem of the solvent type polyurethane coating, and the water-based polyurethane coating belongs to an environment-friendly coating with less pollution compared with the solvent type polyurethane coating, so the research on the development of the performance and the functionalization of the water-based polyurethane coating is a current hotspot. The performance of the polyurethane coating is mainly determined by the performance of the film-forming agent polyurethane, and the polyurethane coating is changed from a solvent type polyurethane coating to a water-based polyurethane coating, and the difference is that the process of a process method for preparing the polyurethane is changed, so that the application process and the performance of the polyurethane are greatly changed, and particularly, the strength, the glossiness, the chemical reagent resistance, the acid and alkali resistance, the heat conduction performance and other performances of the water-based polyurethane coating after film forming are obviously reduced. Furthermore, with the rapid development of electronic information technology, the application requirements of the current aqueous polyurethane coating with heat conduction, flame retardation, antistatic property, corrosion resistance and other functions are more urgent and wider, for example, the functional aqueous polyurethane has important and wide application in the aspects of heat dissipation sheets, integrated circuits, circuit boards, CPUs, memories and the like of computers and other electronic devices. Therefore, the research and development of the waterborne polyurethane coating film-forming agent with excellent mechanical properties and good heat conduction, flame retardance, antistatic property and corrosion resistance have important significance.
Compared with a solvent type aqueous polyurethane coating, the aqueous polyurethane coating has greatly reduced mechanical properties, chemical reagent resistance, acid and alkali resistance, weather resistance, water resistance, high adhesion and other properties, and can be made up by strengthening a crosslinking structure formed in a polyurethane film forming process. The functional aqueous polyurethane coating such as heat conduction, electric conduction, flame retardance, corrosion resistance and the like is modified by adding different fillers such as heat conduction, electric conduction, flame retardance, corrosion resistance and the like, and the current aqueous polyurethane modification method has the following problems: (1) different fillers are required to be added for different functions of heat conduction, electric conduction, flame retardance, static resistance, corrosion resistance and the like of the waterborne polyurethane, the preparation processes and the preparation processes are different, and the multifunctional coating is difficult to prepare and has the functions; (2) the functional water-based polyurethane coating prepared by adding heat-conducting, electric-conducting, flame-retardant, antistatic and anti-corrosion additives has large filler mixing amount, which can reach about 20-40% of the total mass of the coating, causes the reduction of the comprehensive performance of the coating, and also leads to higher preparation cost. (3) By the conventional preparation method, the comprehensive properties of heat conduction, flame retardance, static resistance, good mechanical strength, strong adhesive force and the like of the waterborne polyurethane coating are difficult to achieve.
Graphene is the best nano material with good heat conduction and electric conduction and excellent mechanical property at present, the thickness of a single-layer is about 0.35nm, and the specific surface area is 2630m2The strength is as high as 130GPa, the heat conductivity coefficient is as high as 5300W/(m.K), and the electric conductivity reaches 106S/m, electron mobility up to 2.0 × 105cm2V · s, its thermal, electrical and mechanical properties are the best differences among all materials at present. The preparation of the coating film forming agent with heat conduction, flame retardance, static resistance and corrosion resistance by modifying the waterborne polyurethane through the graphene nanosheet layer is also a hotspot of current research.
However, graphene is a hydrophobic substance, graphene nanosheets are easy to agglomerate and agglomerate, and uniform dispersion in the coating is a technical problem. The graphene oxide is an oxidation product of graphene, contains chemical groups such as carboxyl, hydroxyl, epoxy and the like on the structure, has hydrophilicity and good dispersibility, and is suitable for application in an aqueous polyurethane coating system. However, the hexahydric cyclic regular crystal structure part in the graphene oxide is easily damaged, so that the performances of heat conduction, electric conduction and the like of the graphene oxide are reduced. Researches find that the dispersion performance, the heat and electricity conducting performance and the oxidation degree of the graphene oxide are related, and the dispersion performance and the heat and electricity conducting performance can be considered at the same time by regulating and controlling the oxidation degree of the graphene oxide.
Disclosure of Invention
The invention aims to provide a graphene oxide modified waterborne polyurethane heat-conducting flame-retardant antistatic coating film-forming agent which is low in manufacturing cost, has heat-conducting, heat-resisting, flame-retardant, antistatic and corrosion-resisting properties and is excellent in various properties, and a preparation method thereof.
In order to achieve the above purpose, the preparation method of the invention comprises the following steps:
step one, preparation of hydroxyl-terminated hyperbranched graphene oxide
Adding 1-2 parts by mass of graphene oxide nanosheet layer powder into 60-80 parts by mass of N, N' -dimethylformamide for ultrasonic treatment to uniformly disperse the graphene oxide nanosheet layer powder, sequentially adding 6-9 parts by mass of hydroxyl-terminated hyperbranched polyester, 0.9-1.2 parts by mass of catalyst dicyclohexylcarbodiimide and 0.1-0.2 part by mass of 4-dimethylaminopyridine, stirring and reacting at 25-30 ℃, carrying out reduced pressure suction filtration after the reaction is finished, washing and freeze-drying a product obtained by the reduced pressure suction filtration to obtain hydroxyl-terminated hyperbranched graphene oxide powder;
step two, preparation of waterborne polyurethane prepolymer
Sequentially adding 9-12 parts by mass of isocyanate, 15-18 parts by mass of polycarbonate diol and 20-30 parts by mass of acetone into a reactor, stirring and heating to 70-80 ℃, preserving heat, stirring, reacting to obtain a polyurethane prepolymer, then adding 30-40 parts by mass of acetone under stirring at 70-80 ℃, stirring uniformly, and then adding 1.2-1.6 parts by mass of dimethylolpropionic acid to react to obtain a waterborne polyurethane prepolymer;
step three, preparing method of graphene oxide modified waterborne polyurethane heat-conducting flame-retardant antistatic coating film-forming agent
And (2) adding 1-2 parts by mass of the hydroxyl-terminated hyperbranched graphene oxide powder prepared in the first step into the aqueous polyurethane prepolymer prepared in the second step, stirring at 70-80 ℃, performing chain extension intercalation reaction, cooling to 40-50 ℃, adding 0.9-1.1 part of triethylamine, neutralizing, stirring, adding 90-120 parts of deionized water, stirring, emulsifying, standing, removing acetone at 40-50 ℃ by using a rotary evaporator, and thus obtaining the graphene oxide modified aqueous polyurethane heat-conducting flame-retardant antistatic coating film-forming agent with the solid content of 18-22%.
In the first step, the graphene oxide nanosheet layer powder is prepared by a wet milling oxidation method, and the specific steps include: mixing 8-16 parts of concentrated sulfuric acid and 2-4 parts of concentrated phosphoric acid according to the mass parts, adding a mixture of 1-2 parts of flaky graphite powder and 3-5 parts of potassium permanganate powder into the mixture of concentrated sulfuric acid and concentrated phosphoric acid in a fractional manner while stirring within 20-30 minutes, continuing stirring for 0.5-1.0 hour after the addition to obtain a mixture, transferring the mixture into a ball milling tank of a ball mill, and carrying out ball milling for 1-1.5 hours at a ball milling rotation speed of 100-150 r/min, ball milling for 1.5-2.0 hours at a ball milling rotation speed of 300-350 r/min and ball milling for 2.0-2.5 hours at a ball milling rotation speed of 500-550 r/min to obtain a ball milling product; transferring the ball mill into a reactor after the ball milling is finished, adding 100-150 parts of water into the reactor within 25-30 minutes while stirring, controlling the temperature of the system to be 35-40 ℃, dropwise adding 5-10 parts of hydrogen peroxide within 10-15 minutes, repeatedly performing centrifugal precipitation and washing by using deionized water on the product until no sulfate radical is detected by using a barium chloride solution in a washing liquid, obtaining the graphene oxide dispersion liquid, and performing freeze drying to control the mass fraction of the graphene oxide in the dispersion liquid to be 0.5% to obtain the graphene oxide nanosheet powder.
The particle size of the flaky graphite powder is 13-15 mu m, and the carbon content is more than or equal to 98%; the concentrated sulfuric acid is chemically pure, and the mass fraction concentration is 98%; the concentrated phosphoric acid is chemically pure, and the mass fraction concentration is 85%; the hydrogen peroxide is chemically pure, and the mass fraction concentration is 30%; the barium chloride solution is a solution with the mass fraction concentration of 25% obtained by dissolving analytically pure barium chloride in deionized water; the mass ratio of ball materials during ball milling is 300-400: 1, the grinding balls are made of stainless steel with the diameter of 2mm, 4mm, 6mm, 8mm, 10mm, 12mm and 15mm in a corresponding mass ratio of 10-15: 15-20: 20-25: 25-30: 30-35: 35-40: 40-45, and the ball milling tank is made of nylon.
In the first step, the N, N '-dimethylformamide solution is chemically pure, the mass fraction of the N, N' -dimethylformamide solution is more than or equal to 99.5%, the hydroxyl number of the hydroxyl-terminated hyperbranched polyester is 20-24/mol, the hydroxyl value is 560mgKOH/g, the acid value is less than 25mgKOH/g, and the relative molecular mass is 2400 g/mol; the dicyclohexylcarbodiimide and the 4-dimethylaminopyridine are both chemically pure, and the mass fractions of the dicyclohexylcarbodiimide and the 4-dimethylaminopyridine are both greater than or equal to 99%.
In the step one, the reaction is carried out for 10 to 12 hours under stirring at a temperature of between 25 and 30 ℃.
And in the step one, the product obtained by decompression and suction filtration is washed by N, N' -dimethylformamide to remove redundant dicyclohexylcarbodiimide, 4-dimethylaminopyridine and hydroxyl-terminated hyperbranched polyester.
The isocyanate in the second step is industrial grade, the mass fraction of the isocyanate is more than 98%, and the isocyanate is one or a mixture of more of toluene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate and dicyclohexylmethane diisocyanate; the polycarbonate diol has a value of 100-120 mgKOH/g, an acid value of less than 0.1mgKOH/g and a relative molecular mass of 1000 g/mol; the acetone and the dimethylolpropionic acid are both chemically pure, and the mass fraction is not less than 99%.
And in the second step, the polyurethane prepolymer is prepared after the heat preservation stirring reaction is carried out for 3-4 hours, and the aqueous polyurethane prepolymer is obtained after the dimethylolpropionic acid is added for the reaction for 2.5-3.0 hours.
In the third step, the reaction time of chain extension intercalation is 4-5 hours, and the emulsification time is 2-3 hours.
The graphene oxide modified waterborne polyurethane heat-conducting flame-retardant antistatic coating film-forming agent prepared by the preparation method has the characteristics of heat conduction, heat resistance, flame retardance, smoke suppression, static resistance, corrosion resistance and strong chemical property;
the heat conductivity coefficient of the polyurethane film is improved from 0.17W/(m.K) of the pure polyurethane film to 1.55-1.76W/(m.K), the heat conductivity coefficient is improved by more than 20 times compared with that of the pure polyurethane film, and the modified polyurethane coating can reduce the temperature of a matrix by 8.3-10.5 ℃ under a heat source of 100 ℃.
Compared with pure polyurethane, the glass transition temperature of the heat resistance is increased by 56.7-64.3 ℃, and the working temperature reaches 190-200 ℃.
The limit oxygen index of the flame retardance is improved from 17 percent of pure polyurethane to 29 to 33 percent, and the maximum heat release rate is 412.3KW/m of the pure polyurethane2Reducing the voltage to 204.6-211.5 KW/m2The smoke density is reduced from 276.5 to 105.8-115.3, and the flame retardant and smoke suppression effects are achieved.
The antistatic property has a volume resistivity of 5.6 x 10-2~8.7ⅹ10-2Omega · m, surface resistivity of 6.82-8.45 omega · m, have antistatic ability.
The salt spray resistance of the corrosion-resistant polyurethane coating reaches 1300-1500 hours, and is improved by more than 40 hours compared with the salt spray resistance of a pure polyurethane coating in 36 hoursThe self-corrosion potential of the coating is improved from-1.6V of pure polyurethane to-0.6 to-0.7V of modified polyurethane, and the corrosion current density is 0.86 muA/cm of pure polyurethane2The temperature is reduced to 0.02-0.03 mu A/cm of the modified polyurethane2The modified polyurethane coating film forming agent has good corrosion resistance.
The tearing strength of the high-mechanical-property polyurethane film is 136.7-143.5 kN/m, which is 83.5% -93.5% higher than that of a pure polyurethane film; the tensile strength is 47.6-51.8 MPa, the tensile strength is improved by 80.6-96.2% compared with a pure polyurethane film, and the adhesion reaches II level.
Compared with the prior art, the invention has the beneficial effects that:
according to the invention, the graphene oxide and the waterborne polyurethane prepolymer are subjected to crosslinking reaction, so that the formation of a crosslinked network structure by the waterborne polyurethane is increased and promoted, the mechanical property and the adhesive force of the waterborne polyurethane are improved, meanwhile, the graphene oxide is uniformly dispersed in a polyurethane system in the form of few-layer powder, and the crosslinking structure is formed, and the graphene oxide nanosheet layer has the heat conduction, flame retardance, antistatic property and corrosion resistance and generates a nano effect, so that the performances of the waterborne polyurethane such as mechanical property, heat conduction, flame retardance, antistatic property and corrosion resistance are considered and the optimal effect is achieved after the waterborne polyurethane is formed into a film, and the requirements of an electronic product on the performances of a coating material such as heat conduction, flame retardance, antistatic property and corrosion resistance are met; according to the invention, the modified material can simultaneously have multiple performances only by modifying the water-based polyurethane coating film forming agent by using the graphene oxide, and a large number of additives with various types are not required to be added, so that the emission of pollutants is reduced, the manufacturing cost is reduced, and the method is suitable for large-area popularization and use.
Furthermore, the graphene oxide nanosheet layer prepared by the wet milling oxidation method has low oxidation degree, high dispersibility and good heat conduction and electric conductivity, and then forms the water-based coating with the heat conduction, flame retardance and antistatic functions with the hydroxyl-terminated multi-branched polyester and the polyurethane prepolymer, so that the heat conduction, electric conduction, mechanical properties, adhesion and other properties of the modified water-based polyurethane coating film forming agent can be improved.
Detailed Description
Example 1:
step one, preparation of hydroxyl-terminated hyperbranched graphene oxide
Adding 1 part of graphene oxide nanosheet layer powder into 60 parts of N, N '-dimethylformamide according to the mass part, performing ultrasonic treatment to uniformly disperse the graphene oxide nanosheet layer powder, sequentially adding 6 parts of hydroxyl-terminated hyperbranched polyester, 0.9 part of catalyst dicyclohexylcarbodiimide and 0.1 part of 4-dimethylaminopyridine, stirring and reacting at 25 ℃ for 10 hours, performing reduced pressure filtration, washing a product obtained by the reduced pressure filtration by using the N, N' -dimethylformamide to remove redundant dicyclohexylcarbodiimide, 4-dimethylaminopyridine and hydroxyl-terminated hyperbranched polyester, and performing freeze drying to obtain hydroxyl-terminated hyperbranched graphene oxide powder;
the graphene oxide nanosheet layer powder is prepared by a wet milling oxidation method, and the specific steps include: mixing 8 parts of 98% concentrated sulfuric acid and 2 parts of 85% concentrated phosphoric acid in parts by mass, adding a mixture of 1 part of flaky graphite powder with the particle size of 13-15 mu m and the carbon content of more than or equal to 98% and 3.5 parts of potassium permanganate powder into the mixture of concentrated sulfuric acid and concentrated phosphoric acid in 20 minutes while stirring, continuously stirring for 0.5 hour after adding to obtain a mixture, transferring the mixture into a ball mill made of a nylon material, and controlling the mass ratio of ball materials to be 300: 1, the grinding ball consists of a grinding ball with the diameter of 2mm, 4mm, 6mm, 8mm, 10mm, 12mm and 15mm, and the corresponding mass ratio is 10: 16: 20: 26: 30: 35: 40, ball milling for 1 hour at the ball milling rotating speed of 100 revolutions per minute, ball milling for 1.5 hours at the ball milling rotating speed of 350 revolutions per minute, and ball milling for 2.5 hours at the ball milling rotating speed of 520 revolutions per minute to obtain a ball milling product; transferring the ball mill into a reactor after the ball milling is finished, adding 100 parts of water into the reactor within 25 minutes while stirring, controlling the temperature of the system to be 35 ℃, dropwise adding 10 parts of 30% hydrogen peroxide within 10 minutes, then repeatedly performing centrifugal precipitation and washing by using deionized water on the product until no sulfate radical exists in the washing liquid detected by 25% barium chloride solution, namely obtaining graphene oxide dispersion liquid, and performing freeze drying to control the mass fraction of the graphene oxide in the dispersion liquid to be 0.5% to obtain graphene oxide nanosheet powder;
the N, N '-dimethylformamide solution is chemically pure, the mass fraction of the N, N' -dimethylformamide solution is more than or equal to 99.5%, the hydroxyl number of the hydroxyl-terminated hyperbranched polyester is 20-24/mol, the hydroxyl value is 560mgKOH/g, the acid value is less than 25mgKOH/g, and the relative molecular mass is 2400 g/mol; the dicyclohexylcarbodiimide and the 4-dimethylaminopyridine are both chemically pure, and the mass fractions of the dicyclohexylcarbodiimide and the 4-dimethylaminopyridine are both more than or equal to 99%;
step two, preparation of waterborne polyurethane prepolymer
Sequentially adding 9 parts by mass of toluene diisocyanate with the mass fraction of more than 98%, 15 parts by mass of polycarbonate diol and 20 parts by mass of acetone with the mass fraction of not less than 99% into a reactor, stirring and heating to 70 ℃, keeping the temperature and stirring for 3 hours to obtain a polyurethane prepolymer, then adding 30 parts by mass of acetone with the mass fraction of not less than 99% into the reactor under stirring at 70 ℃, uniformly stirring, and then adding 1.2 parts by mass of dimethylolpropionic acid with the mass fraction of not less than 99% into the reactor to react for 2.5 hours to obtain a waterborne polyurethane prepolymer;
the polycarbonate diol has a value of 100-120 mgKOH/g, an acid value of less than 0.1mgKOH/g and a relative molecular mass of 1000 g/mol;
step three, preparing method of graphene oxide modified waterborne polyurethane heat-conducting flame-retardant antistatic coating film-forming agent
And (2) adding 1 part of the hydroxyl-terminated hyperbranched graphene oxide powder prepared in the first step into the aqueous polyurethane prepolymer prepared in the second step in parts by mass, stirring at 70 ℃ for chain extension intercalation reaction for 4 hours, cooling to 40 ℃, adding 0.9 part of triethylamine for neutralization and stirring, adding 90 parts of deionized water for stirring and emulsification reaction for 2 hours, standing, and removing acetone at 40 ℃ by using a rotary evaporator to obtain the graphene oxide modified aqueous polyurethane heat-conducting flame-retardant antistatic coating film forming agent with the solid content of 18%.
Example 2:
step one, preparation of hydroxyl-terminated hyperbranched graphene oxide
Adding 1.5 parts of graphene oxide nanosheet layer powder into 70 parts of N, N '-dimethylformamide according to the mass part, performing ultrasonic treatment to uniformly disperse the graphene oxide nanosheet layer powder, sequentially adding 7 parts of hydroxyl-terminated hyperbranched polyester, 1 part of dicyclohexylcarbodiimide as a catalyst and 0.15 part of 4-dimethylaminopyridine, stirring and reacting at 28 ℃ for 11 hours, performing reduced pressure filtration, washing a product obtained by the reduced pressure filtration by using the N, N' -dimethylformamide to remove redundant dicyclohexylcarbodiimide, 4-dimethylaminopyridine and hydroxyl-terminated hyperbranched polyester, and performing freeze drying to obtain hydroxyl-terminated hyperbranched graphene oxide powder;
the graphene oxide nanosheet layer powder is prepared by a wet milling oxidation method, and the specific steps include: mixing 10 parts by mass of 98% concentrated sulfuric acid and 3 parts by mass of 85% concentrated phosphoric acid, adding a mixture of 2 parts of flaky graphite powder with the particle size of 13-15 mu m and the carbon content of more than or equal to 98% and 3 parts of potassium permanganate powder into the mixture of concentrated sulfuric acid and concentrated phosphoric acid in 25 minutes while stirring, continuously stirring for 1.0 hour after the mixture is added to obtain a mixture, transferring the mixture into a ball mill nylon ball-milling tank, and controlling the mass ratio of ball materials to be 320: 1, grinding balls are composed of a grinding ball with the diameter of 2mm, 4mm, 6mm, 8mm, 10mm, 12mm and 15mm, and the corresponding mass ratio is 12: 15: 23: 28: 32: 37: 41, ball-milling for 1.5 hours at a ball-milling rotating speed of 120 revolutions per minute, ball-milling for 2.0 hours at a ball-milling rotating speed of 320 revolutions per minute, and ball-milling for 2.5 hours at a ball-milling rotating speed of 510 revolutions per minute to obtain a ball-milling product; transferring the ball mill into a reactor after the ball milling is finished, adding 120 parts of water into the reactor within 28 minutes while stirring, controlling the system temperature at 38 ℃, dropwise adding 8 parts of hydrogen peroxide with the mass fraction of 30% within 13 minutes, then repeatedly performing centrifugal precipitation and washing the product by using deionized water until no sulfate radical exists in the washing liquid detected by a barium chloride solution with the mass fraction of 25%, obtaining graphene oxide dispersion liquid, and performing freeze drying to control the mass fraction of the graphene oxide in the dispersion liquid to be 0.5% to obtain graphene oxide nanosheet layer powder;
the N, N '-dimethylformamide solution is chemically pure, the mass fraction of the N, N' -dimethylformamide solution is more than or equal to 99.5%, the hydroxyl number of the hydroxyl-terminated hyperbranched polyester is 20-24/mol, the hydroxyl value is 560mgKOH/g, the acid value is less than 25mgKOH/g, and the relative molecular mass is 2400 g/mol; the dicyclohexylcarbodiimide and the 4-dimethylaminopyridine are both chemically pure, and the mass fractions of the dicyclohexylcarbodiimide and the 4-dimethylaminopyridine are both more than or equal to 99%;
step two, preparation of waterborne polyurethane prepolymer
Sequentially adding 11 parts by mass of isophorone diisocyanate with the mass fraction of more than 98%, 17 parts by mass of polycarbonate diol and 25 parts by mass of acetone with the mass fraction of not less than 99% into a reactor, stirring and heating to 75 ℃, keeping the temperature and stirring for 3.5 hours to obtain a polyurethane prepolymer, then adding 35 parts by mass of acetone with the mass fraction of not less than 99% into the reactor under stirring at 75 ℃, uniformly stirring, and then adding 1.5 parts by mass of dimethylolpropionic acid with the mass fraction of not less than 99% into the reactor to react for 2.8 hours to obtain a waterborne polyurethane prepolymer;
the polycarbonate diol has a value of 100-120 mgKOH/g, an acid value of less than 0.1mgKOH/g and a relative molecular mass of 1000 g/mol;
step three, preparing method of graphene oxide modified waterborne polyurethane heat-conducting flame-retardant antistatic coating film-forming agent
And (2) adding 1.5 parts by mass of the hydroxyl-terminated hyperbranched graphene oxide powder prepared in the first step into the aqueous polyurethane prepolymer prepared in the second step, stirring at 75 ℃ for chain extension intercalation reaction for 4.5 hours, cooling to 45 ℃, adding 1 part of triethylamine for neutralization stirring, adding 110 parts of deionized water for stirring and emulsification reaction for 2.5 hours, standing, and removing acetone at 45 ℃ by using a rotary evaporator to obtain the graphene oxide modified aqueous polyurethane heat-conducting flame-retardant antistatic coating film-forming agent with the solid content of 20%.
Example 3:
step one, preparation of hydroxyl-terminated hyperbranched graphene oxide
Adding 2 parts of graphene oxide nanosheet layer powder into 80 parts of N, N '-dimethylformamide according to the mass part, performing ultrasonic treatment to uniformly disperse the graphene oxide nanosheet layer powder, sequentially adding 9 parts of hydroxyl-terminated hyperbranched polyester, 1.2 parts of dicyclohexylcarbodiimide as a catalyst and 0.2 part of 4-dimethylaminopyridine, stirring and reacting at 30 ℃ for 12 hours, performing reduced pressure filtration, washing a product obtained by the reduced pressure filtration by using the N, N' -dimethylformamide to remove redundant dicyclohexylcarbodiimide, 4-dimethylaminopyridine and hydroxyl-terminated hyperbranched polyester, and performing freeze drying to obtain hydroxyl-terminated hyperbranched graphene oxide powder;
the graphene oxide nanosheet layer powder is prepared by a wet milling oxidation method, and the specific steps include: mixing 12 parts by mass of 98% concentrated sulfuric acid and 4 parts by mass of 85% concentrated phosphoric acid, adding a mixture of 1.8 parts of flaky graphite powder with the particle size of 13-15 mu m and the carbon content of more than or equal to 98% and 4 parts of potassium permanganate powder into the mixture of concentrated sulfuric acid and concentrated phosphoric acid in 30 minutes while stirring, continuously stirring for 0.5 hour after adding to obtain a mixture, transferring the mixture into a ball mill made of a nylon material, and controlling the mass ratio of ball materials to be 380: 1, grinding balls are composed of grinding balls with the diameters of 2mm, 4mm, 6mm, 8mm, 10mm, 12mm and 15mm, and the corresponding mass ratio is 14: 18: 22: 25: 31: 38: 43, ball-milling for 1.5 hours at the ball-milling rotating speed of 140 revolutions per minute, ball-milling for 1.5 hours at the ball-milling rotating speed of 340 revolutions per minute, and ball-milling for 2 hours at the ball-milling rotating speed of 550 revolutions per minute to obtain a ball-milled product; transferring the ball mill into a reactor after the ball milling is finished, adding 150 parts of water into the reactor within 30 minutes while stirring, controlling the temperature of the system to be 36 ℃, dropwise adding 7 parts of hydrogen peroxide with the mass fraction of 30% within 14 minutes, then repeatedly performing centrifugal precipitation and washing the product by using deionized water until no sulfate radical exists in the washing liquid detected by a barium chloride solution with the mass fraction of 25%, obtaining graphene oxide dispersion liquid, and performing freeze drying to control the mass fraction of the graphene oxide in the dispersion liquid to be 0.5% to obtain graphene oxide nanosheet layer powder;
the N, N '-dimethylformamide solution is chemically pure, the mass fraction of the N, N' -dimethylformamide solution is more than or equal to 99.5%, the hydroxyl number of the hydroxyl-terminated hyperbranched polyester is 20-24/mol, the hydroxyl value is 560mgKOH/g, the acid value is less than 25mgKOH/g, and the relative molecular mass is 2400 g/mol; the dicyclohexylcarbodiimide and the 4-dimethylaminopyridine are both chemically pure, and the mass fractions of the dicyclohexylcarbodiimide and the 4-dimethylaminopyridine are both more than or equal to 99%;
step two, preparation of waterborne polyurethane prepolymer
Sequentially adding 12 parts by mass of hexamethylene diisocyanate with the mass fraction of more than 98%, 18 parts by mass of polycarbonate diol and 30 parts by mass of acetone with the mass fraction of not less than 99% into a reactor, stirring and heating to 80 ℃, keeping the temperature and stirring for 4 hours to obtain a polyurethane prepolymer, then adding 40 parts by mass of acetone with the mass fraction of not less than 99% into the reactor under stirring at 80 ℃, uniformly stirring, and then adding 1.6 parts by mass of dimethylolpropionic acid with the mass fraction of not less than 99% into the reactor to react for 3 hours to obtain a waterborne polyurethane prepolymer;
the polycarbonate diol has a value of 100-120 mgKOH/g, an acid value of less than 0.1mgKOH/g and a relative molecular mass of 1000 g/mol;
step three, preparing method of graphene oxide modified waterborne polyurethane heat-conducting flame-retardant antistatic coating film-forming agent
And 2 parts by mass of the hydroxyl-terminated hyperbranched graphene oxide powder prepared in the first step is added into the aqueous polyurethane prepolymer prepared in the second step, the mixture is stirred at 80 ℃ for chain extension intercalation reaction for 5 hours, then the temperature is reduced to 50 ℃, 1.1 part of triethylamine is added for neutralization stirring, 120 parts of deionized water is added for stirring and emulsification reaction for 3 hours, and then the mixture is kept stand and acetone is removed at 50 ℃ by using a rotary evaporator to obtain the graphene oxide modified aqueous polyurethane heat-conducting flame-retardant antistatic coating film forming agent with the solid content of 22%.
Example 4:
step one, preparation of hydroxyl-terminated hyperbranched graphene oxide
Adding 1.3 parts of graphene oxide nanosheet layer powder into 75 parts of N, N '-dimethylformamide according to the mass part, performing ultrasonic treatment to uniformly disperse the graphene oxide nanosheet layer powder, sequentially adding 8 parts of hydroxyl-terminated hyperbranched polyester, 1.1 parts of catalyst dicyclohexylcarbodiimide and 0.13 part of 4-dimethylaminopyridine, stirring and reacting at 26 ℃ for 10 hours, performing reduced pressure filtration, washing a product obtained by the reduced pressure filtration by using the N, N' -dimethylformamide to remove redundant dicyclohexylcarbodiimide, 4-dimethylaminopyridine and hydroxyl-terminated hyperbranched polyester, and performing freeze drying to obtain hydroxyl-terminated hyperbranched graphene oxide powder;
the graphene oxide nanosheet layer powder is prepared by a wet milling oxidation method, and the specific steps include: mixing 15 parts by mass of 98% concentrated sulfuric acid and 2.5 parts by mass of 85% concentrated phosphoric acid, adding a mixture of 1.5 parts of flaky graphite powder with the particle size of 13-15 mu m and the carbon content of more than or equal to 98% and 4.5 parts of potassium permanganate powder into the mixture of concentrated sulfuric acid and concentrated phosphoric acid in 28 minutes while stirring, continuously stirring for 1.0 hour after the mixture is added to obtain a mixture, transferring the mixture into a ball milling tank made of a ball mill nylon material, and controlling the mass ratio of ball materials to be 400: 1, grinding balls are composed of grinding balls with the diameters of 2mm, 4mm, 6mm, 8mm, 10mm, 12mm and 15mm, and the corresponding mass ratio is 15: 20: 25: 27: 33: 36: 44, ball-milling for 1 hour at the ball-milling rotating speed of 130 r/min, ball-milling for 2.0 hours at the ball-milling rotating speed of 300 r/min, and ball-milling for 2 hours at the ball-milling rotating speed of 530 r/min to obtain a ball-milled product; transferring the ball mill into a reactor after the ball milling is finished, adding 110 parts of water into the reactor within 26 minutes while stirring, controlling the system temperature at 39 ℃, dropwise adding 9 parts of hydrogen peroxide with the mass fraction of 30% within 12 minutes, then repeatedly performing centrifugal precipitation and washing the product by using deionized water until no sulfate radical exists in the washing liquid detected by a barium chloride solution with the mass fraction of 25%, obtaining graphene oxide dispersion liquid, and performing freeze drying to control the mass fraction of the graphene oxide in the dispersion liquid to be 0.5% to obtain graphene oxide nanosheet layer powder;
the N, N '-dimethylformamide solution is chemically pure, the mass fraction of the N, N' -dimethylformamide solution is more than or equal to 99.5%, the hydroxyl number of the hydroxyl-terminated hyperbranched polyester is 20-24/mol, the hydroxyl value is 560mgKOH/g, the acid value is less than 25mgKOH/g, and the relative molecular mass is 2400 g/mol; the dicyclohexylcarbodiimide and the 4-dimethylaminopyridine are both chemically pure, and the mass fractions of the dicyclohexylcarbodiimide and the 4-dimethylaminopyridine are both more than or equal to 99%;
step two, preparation of waterborne polyurethane prepolymer
Sequentially adding 10 parts by mass of a mixture of diphenylmethane diisocyanate and dicyclohexylmethane diisocyanate with the mass fraction of more than 98%, 16 parts by mass of polycarbonate diol and 28 parts by mass of acetone with the mass fraction of not less than 99% into a reactor, stirring and heating to 77 ℃, keeping the temperature and stirring for 4 hours to obtain a polyurethane prepolymer, then adding 33 parts by mass of acetone with the mass fraction of not less than 99% into the reactor under stirring at 77 ℃, stirring uniformly, and adding 1.3 parts by mass of dimethylolpropionic acid with the mass fraction of not less than 99% into the reactor to react for 3 hours to obtain a waterborne polyurethane prepolymer;
the polycarbonate diol has a value of 100-120 mgKOH/g, an acid value of less than 0.1mgKOH/g and a relative molecular mass of 1000 g/mol;
step three, preparing method of graphene oxide modified waterborne polyurethane heat-conducting flame-retardant antistatic coating film-forming agent
And (2) adding 1.3 parts by mass of the hydroxyl-terminated hyperbranched graphene oxide powder prepared in the first step into the aqueous polyurethane prepolymer prepared in the second step, stirring at 77 ℃ for chain extension intercalation reaction for 5 hours, cooling to 49 ℃, adding 0.9 part of triethylamine for neutralization stirring, adding 100 parts of deionized water for stirring and emulsification reaction for 2 hours, standing, and removing acetone at 43 ℃ by using a rotary evaporator to obtain the graphene oxide modified aqueous polyurethane heat-conducting flame-retardant antistatic coating film-forming agent with the solid content of 21%.
Example 5:
step one, preparation of hydroxyl-terminated hyperbranched graphene oxide
Adding 1.8 parts of graphene oxide nanosheet layer powder into 65 parts of N, N '-dimethylformamide according to the mass part, performing ultrasonic treatment to uniformly disperse the graphene oxide nanosheet layer powder, sequentially adding 7 parts of hydroxyl-terminated hyperbranched polyester, 1.2 parts of catalyst dicyclohexylcarbodiimide and 0.18 part of 4-dimethylaminopyridine, stirring and reacting at 29 ℃ for 12 hours, performing reduced pressure filtration, washing a product obtained by the reduced pressure filtration by using the N, N' -dimethylformamide to remove redundant dicyclohexylcarbodiimide, 4-dimethylaminopyridine and hydroxyl-terminated hyperbranched polyester, and performing freeze drying to obtain hydroxyl-terminated hyperbranched graphene oxide powder;
the graphene oxide nanosheet layer powder is prepared by a wet milling oxidation method, and the specific steps include: mixing 16 parts by mass of 98% concentrated sulfuric acid and 3.5 parts by mass of 85% concentrated phosphoric acid, adding a mixture of 1.3 parts of flaky graphite powder with the particle size of 13-15 mu m and the carbon content of more than or equal to 98% and 5 parts of potassium permanganate powder into the mixture of concentrated sulfuric acid and concentrated phosphoric acid in 26 minutes while stirring, continuously stirring for 1.0 hour after adding to obtain a mixture, transferring the mixture into a ball mill made of a nylon material, and controlling the mass ratio of ball materials to be 350: 1, grinding balls are composed of a grinding ball with the diameter of 2mm, 4mm, 6mm, 8mm, 10mm, 12mm and 15mm, and the corresponding mass ratio is 11: 19: 21: 30: 35: 40: 45, ball milling for 1.5 hours at a ball milling rotating speed of 150 revolutions per minute, ball milling for 2.0 hours at a ball milling rotating speed of 310 revolutions per minute, and ball milling for 2.5 hours at a ball milling rotating speed of 500 revolutions per minute to obtain a ball milling product; transferring the ball mill into a reactor after the ball milling is finished, adding 140 parts of water into the reactor within 29 minutes while stirring, controlling the temperature of the system to be 40 ℃, dropwise adding 5 parts of hydrogen peroxide with the mass fraction of 30% within 15 minutes, then repeatedly performing centrifugal precipitation and washing the product by using deionized water until no sulfate radical exists in the washing liquid detected by a barium chloride solution with the mass fraction of 25%, obtaining graphene oxide dispersion liquid, and performing freeze drying to control the mass fraction of the graphene oxide in the dispersion liquid to be 0.5% to obtain graphene oxide nanosheet layer powder;
the N, N '-dimethylformamide solution is chemically pure, the mass fraction of the N, N' -dimethylformamide solution is more than or equal to 99.5%, the hydroxyl number of the hydroxyl-terminated hyperbranched polyester is 20-24/mol, the hydroxyl value is 560mgKOH/g, the acid value is less than 25mgKOH/g, and the relative molecular mass is 2400 g/mol; the dicyclohexylcarbodiimide and the 4-dimethylaminopyridine are both chemically pure, and the mass fractions of the dicyclohexylcarbodiimide and the 4-dimethylaminopyridine are both more than or equal to 99%;
step two, preparation of waterborne polyurethane prepolymer
Sequentially adding 12 parts by mass of toluene diisocyanate with the mass fraction of more than 98%, a mixture of isophorone diisocyanate and dicyclohexylmethane diisocyanate, 17 parts of polycarbonate diol and 23 parts by mass of acetone with the mass fraction of not less than 99% into a reactor, stirring and heating to 72 ℃, keeping the temperature and stirring for 3 hours to obtain a polyurethane prepolymer, then adding 36 parts by mass of acetone with the mass fraction of not less than 99% into the reactor while stirring at 72 ℃, uniformly stirring, and adding 1.4 parts by mass of dimethylolpropionic acid with the mass fraction of not less than 99% into the reactor to react for 3 hours to obtain a waterborne polyurethane prepolymer;
the polycarbonate diol has a value of 100-120 mgKOH/g, an acid value of less than 0.1mgKOH/g and a relative molecular mass of 1000 g/mol;
step three, preparing method of graphene oxide modified waterborne polyurethane heat-conducting flame-retardant antistatic coating film-forming agent
And (2) adding 1.8 parts by mass of the hydroxyl-terminated hyperbranched graphene oxide powder prepared in the first step into the aqueous polyurethane prepolymer prepared in the second step, stirring at 72 ℃ for chain extension intercalation reaction for 4 hours, cooling to 43 ℃, adding 1.1 parts of triethylamine for neutralization stirring, adding 120 parts of deionized water for stirring and emulsification reaction for 3 hours, standing, and removing acetone at 48 ℃ by using a rotary evaporator to obtain the graphene oxide modified aqueous polyurethane heat-conducting flame-retardant antistatic coating film-forming agent with the solid content of 19%.
The coating performance of the graphene oxide modified waterborne polyurethane heat-conducting flame-retardant antistatic coating film-forming agent is shown in table 1.
TABLE 1 sample application results of the examples
Note: the control sample was a sample without graphene oxide incorporated, and the other preparation processes were consistent with the examples, except that no graphene oxide was added.
The resistivity was measured according to GB/T1410-2006 method.
Thermal conductivity was measured using a TC3000E thermal conductivity meter.
Adhesion was determined according to GB/T9286-1998.
Heat resistance was determined according to GB/T1735-1979.
And (4) performing detection analysis by using a TGA/DSC synchronous analyzer in thermogravimetric analysis.
The corrosion resistance was measured according to GB/T1771-2007.