Method for preparing polyurethane material based on synergistic flame retardance of chlorogenic acid-graphene aerogel and phytic acid

Abstract

The invention discloses a method for preparing a polyurethane material based on synergistic flame retardance of chlorogenic acid-graphene aerogel and phytic acid. The polyurethane material is prepared by taking isocyanate as a hard segment, polyether polyol as a soft segment, deionized water as a foaming agent, triethylene diamine and dibutyltin dilaurate as catalysts, silicone oil as a foam stabilizer and chlorogenic acid-phytic acid / graphene aerogel as a flame retardant. The preparation method is simple, the process is easy to control, the limit oxygen index of the prepared polyurethane material reaches 27.9, the commercial standard of a flame-retardant material and the UL-94 V-0 flame-retardant grade requirement are met, and the polyurethane material can keep high compression strength while having good flame-retardant performance.

Description

Technical Field

[0001] The present invention belongs to the field of polymer composites, and relates to a method for preparing polyurethane materials by synergistic flame retardancy of chlorogenic acid-graphene aerogel and phytic acid. Background Art

[0002] Rigid polyurethane foam (RPUF) is a lightweight porous material with high mechanical strength, excellent heat insulation, chemical corrosion resistance and adhesiveness. It can be used for the insulation layers of walls, roofs and pipelines; the thermal insulation interlayers of refrigeration equipment such as refrigerators and cold storages; the thermal insulation protection of lightweight storage tanks and pipelines of transportation vehicles such as automobiles and airplanes. However, due to the organic polymer skeleton of RPUF (containing a large number of C-H bonds and ether bonds), it is extremely easy to burn (the limiting oxygen index LOI is only 17%-19%), and a large amount of toxic gases such as CO and HCN are released during combustion, accompanied by the phenomenon of dripping molten matter, posing a serious fire hazard. Therefore, flame retardant modification has become a key requirement for its application.

[0003] Graphene oxide (GO), as a new type of environmentally friendly material, its sheet structure can physically block heat and oxygen, and at the same time inhibit the combustion chain reaction through chemical action, and it is an efficient nano flame retardant. Graphene oxide can not only capture the oxygen-containing free radicals generated by combustion through its surface defects and π-electron structure, delaying the combustion reaction, but also has high thermal conductivity to disperse local heat and inhibit heat accumulation. However, the agglomeration phenomenon of graphene oxide is extremely serious and it is difficult to disperse, thus greatly reducing its performance.

[0004] Chlorogenic acid is a phenylpropanoid compound produced by plants through the shikimic acid pathway during aerobic respiration. It has strong antioxidant ability, and in addition, it also has functions such as anti-HIV virus, anti-tumor cells and antibacterial. It is widely present in the honeysuckle plant with a relatively high content and is a natural green and environmentally friendly substance. Although there are reports on preparing reduced graphene oxide by using chlorogenic acid as a reducing agent, there is no report on preparing chlorogenic acid-graphene aerogel as a flame retardant material under high temperature and high pressure environment.

[0005] Phytic acid is a natural organic phosphorus compound extracted from plants, known for its biodegradability and low toxicity. Phytic acid contains six phosphate groups and is a typical phosphorus-based flame retardant. At high temperatures, phytic acid can decompose to produce phosphoric acid and polyphosphoric acid, catalyzing the dehydration of polyurethane to form a dense carbon layer. In addition, when phytic acid burns, it can not only release phosphorus-containing free radicals to quench the combustion chain reaction, but also the generated phosphoric acid derivatives combine with smoke particles to reduce smoke release. However, due to its three-dimensional structure, if phytic acid is directly grafted onto the polyurethane chain segment, it will not only reduce the mechanical properties of polyurethane, but also pose a risk of explosive polymerization. Its acidity will not only cause foaming and reduce the service life of foaming equipment, but also affect the cell structure of rigid polyurethane foam. In addition, phytic acid is a strongly water-absorbing substance and usually appears in the form of an aqueous solution. However, polyurethane reacts rapidly with water. Therefore, phytic acid needs to be modified to reduce the damage to the polyurethane chain segment.

[0006] Based on this, the present invention aims to provide a polyurethane material with good flame retardant effect. The prepared polyurethane material can be applied to various industries. While having excellent flame retardant effect, it also has characteristics such as green environmental protection. It can be widely used in the thermal insulation interlayers of houses, cars, etc., and can be used as fertilizer for crops after combustion. Summary of the Invention

[0007] In view of the above technical problems, the present invention aims to provide a method for preparing a polyurethane material based on the synergistic flame retardancy of chlorogenic acid-graphene aerogel and phytic acid. The polyurethane material is prepared with isocyanate as the hard segment, polyether polyol as the soft segment, deionized water as the foaming agent, triethylenediamine and dibutyltin dilaurate as the catalysts, silicone oil as the foam stabilizer, and chlorogenic acid-phytic acid / graphene aerogel as the flame retardant; the preparation method of the present invention is simple, the process is easy to control, the limiting oxygen index of the prepared polyurethane material reaches 27.9, meeting the commercial standards of flame retardant materials and the requirements of UL-94 V-0 flame retardant grade, and the polyurethane material can maintain a relatively high compressive strength while having good flame retardant performance.

[0008] To achieve the above object, the technical solution adopted by the present invention is as follows: A method for preparing a polyurethane material based on the synergistic flame retardancy of chlorogenic acid-graphene aerogel and phytic acid, which is carried out in the following order of steps: S1. Prepare graphene oxide Weigh 5 g of 325-mesh flake graphite and 2 g of NaNO3, mix them evenly, add 120 mL of concentrated H2SO4, place it in an ice bath at 0 °C and stir for 30 min. After adding 20 g of KMnO4 and reacting for 60 min, transfer it to a warm water bath at 40 °C and continue to react for 30 min. Then slowly add 230 mL of deionized water, keep the reaction temperature at 90 °C, stir for 5 min, add H2O2 until no bubbles are produced, filter while it is hot, and use deionized water and hydrochloric acid with a mass fraction of 5 wt.% for centrifugation multiple times until it is neutral. Subsequently, dry it in a drying oven at 60 °C for 24 h to obtain graphene oxide; S2. Preparation of chlorogenic acid-graphene aerogel Stir graphene oxide and chlorogenic acid at 25 °C for 30 min, then transfer it to a high-pressure reactor and react under high temperature and high pressure conditions for 12 h to obtain chlorogenic acid-graphene hydrogel. After freeze-drying, chlorogenic acid-graphene aerogel is obtained; S3. Preparation of chlorogenic acid-phytic acid / graphene aerogel flame retardant Immerse chlorogenic acid-graphene aerogel in an aqueous solution of phytic acid with a mass fraction of 70 wt.% for 10 min, then place it in a vacuum drying oven at 80 °C and -0.1 MPa and dry for 15 min. Repeat this step 5 times to obtain chlorogenic acid-phytic acid / graphene aerogel flame retardant; S4. Preparation of polyurethane material Grind 3.5 g of the flame retardant into 325-mesh powder, and add it together with 0.15 g of deionized water, 0.03 g of dibutyltin dilaurate, 0.03 g of triethylenediamine, and 0.05 g of silicone oil to 5 g of polybutylene glycol. After stirring evenly, add 4.5 g of diphenylmethane diisocyanate to the mixed solution, stir for 1 min, and then foam and cure at room temperature for 2 h to obtain the polyurethane material.

[0009] As a limitation of the preparation method of the present invention, in step S1, the centrifugation rate is 10,000 rpm.

[0010] As another limitation of the preparation method of the present invention, in step S2, the chlorogenic acid is an aqueous solution of chlorogenic acid with a mass fraction of 70 wt.%.

[0011] As the third limitation of the preparation method of the present invention, in step S2, the mass ratio of graphene oxide to chlorogenic acid is 2:0.65.

[0012] In the present invention, the mass ratio of graphene oxide to chlorogenic acid is crucial, which affects the formation of the crosslinked structure of the aerogel and the flame retardant effect on polyurethane. When the mass ratio of graphene oxide to chlorogenic acid is 2:0.65, the esterification reaction, addition reaction and π-π conjugation of graphene oxide and chlorogenic acid will occur, so that the graphene oxide just forms a loose 3D aerogel structure; if the mass ratio is greater than this ratio, the oxygen-containing functional groups on the graphene oxide will remain, resulting in a significant reduction in the specific surface area of the graphene oxide and agglomeration, making it impossible to form an aerogel; if the mass ratio is less than this ratio, there will be a surplus of chlorogenic acid, resulting in the graphene oxide aerogel being in an acidic environment and causing serious slagging phenomenon of the graphene oxide aerogel.

[0013] As the fourth limitation of the preparation method of the present invention, in step S2, the temperature under the high temperature and high pressure condition is 180°C to 200°C, and the pressure is 3 MPa.

[0014] In the present invention, high temperature and high pressure are crucial for the preparation of chlorogenic acid-graphene aerogel. When the temperature is 180°C to 200°C, the oxygen-containing functional groups on the graphene oxide will be activated, thereby increasing the activity of the graphene oxide and reacting with chlorogenic acid; if the temperature is less than 180°C, the oxygen-containing functional groups on the graphene oxide are in an overly stable state, resulting in the reaction being unable to proceed; if the temperature is greater than 200°C, it will cause the oxygen-containing functional groups on the graphene oxide to be overly active, resulting in the reaction of the hydroxyl and carboxyl groups of the graphene oxide itself and causing agglomeration. The pressure is set to 3 MPa because it can limit the volatilization of the water solvent and the escape of oxygen, reduce the risk of re-oxidation of graphene oxide, and ensure the thorough progress of the reduction reaction. In addition, at this pressure, the phenolic hydroxyl group of chlorogenic acid is more likely to release protons, promoting the close contact between chlorogenic acid and the graphene oxide sheet layer, thereby improving the efficiency of the esterification reaction, epoxy addition and π-π interaction with graphene oxide.

[0015] As the fifth limitation of the preparation method of the present invention, in step S2, the temperature during freeze-drying is -65°C to -50°C, and the time is 72 to 85 h.

[0016] As the sixth limitation of the preparation method of the present invention, in step S3, the mass ratio of the chlorogenic acid-graphene aerogel to the aqueous solution of phytic acid with a mass fraction of 70wt.% is 1:3.

[0017] In the present invention, the mass ratio of chlorogenic acid-graphene aerogel to phytic acid aqueous solution is crucial and will affect the final flame retardant effect on polyurethane. When the mass ratio is 1:3, the catalytic carbonization ability of phytic acid and the physical barrier effect of the aerogel reach a balance, thus making the flame retardant effect reach the best. If the mass ratio is less than this ratio, there will be too little phytic acid, and insufficient polyphosphoric acid can be generated to catalyze carbonization, resulting in insufficient thickness and compactness of the carbon layer. In addition, when the mass ratio is less than this ratio, the generation amount of PO· free radicals will also decrease, and the free radical quenching ability is weak, unable to effectively neutralize the H· and OH· free radicals in the combustion chain reaction. If the mass ratio is greater than this ratio, there will be too much phytic acid, which will cause the collapse of the hierarchical pore structure, reduce the specific surface area, and decrease the physical barrier efficiency. In addition, too much phytic acid will hydrolyze and destroy the hydrogen bond cross-linking network between chlorogenic acid and graphene oxide, weaken the mechanical strength of the aerogel, and the carbon layer is prone to cracking during combustion, reducing the flame retardant effect.

[0018] As the seventh limitation of the preparation method of the present invention, in step S4, the stirring rate is 300 rpm.

[0019] In the present invention, chlorogenic acid, graphene oxide and phytic acid can cooperate in flame retardancy, specifically as follows: (1) Under specific high temperature and high pressure conditions, the carboxyl group (-COOH) on the surface of graphene oxide and the phenolic hydroxyl group (-ArOH) of chlorogenic acid undergo an esterification reaction, the hydroxyl group of chlorogenic acid and the epoxy group of graphene oxide undergo an addition reaction, and the benzene ring on chlorogenic acid and the π-π conjugation of the carbon-carbon double bond of graphene oxide occur. The synergistic effect of these chemical reactions not only increases the specific surface area of graphene oxide and solves the agglomeration phenomenon of graphene oxide solution, but also forms a functionalized graphene oxide 3D aerogel containing a large number of soft voids. This chlorogenic acid-functionalized graphene oxide 3D aerogel has the characteristics of low mass and large volume, which determines that it can have a strong flame retardant effect with a small content.

[0020] (2)The modification of chlorogenic acid on three-dimensional functionalized graphene oxide aerogel enables the better dispersion of graphene oxide aerogel in polyurethane. The phenolic hydroxyl group of chlorogenic acid can form hydrogen bonds with the carbamate group (-NHCOO-) in the polyurethane molecular chain. Meanwhile, its ester group has polar interactions with the ether bond (-O-) or ester bond (-COO-) of polyurethane, thus enhancing the interfacial binding force. After the surface of graphene oxide aerogel is modified by chlorogenic acid, it changes from hydrophobic to a hydrophilic-hydrophobic balance state, which is more compatible with the polarity of the polyurethane matrix and reduces the agglomeration phenomenon caused by interfacial tension. Chlorogenic acid promotes the formation of a three-dimensional network of graphene oxide sheets through π-π stacking and hydrogen bonding, forming a hierarchical pore structure with a pore size distribution. This structure can be embedded in the polyurethane molecular chain during the polyurethane foaming process, forming a "mechanical interlocking" effect to inhibit the migration and agglomeration of the aerogel. The specific surface area of the aerogel modified by chlorogenic acid increases, and the high specific surface area provides more active sites for contact with polyurethane, promoting uniform dispersion. The phenolic hydroxyl group of chlorogenic acid can dynamically break and recombine during the curing process of polyurethane, forming reversible cross-linking points to relieve stress concentration during processing and avoid structural damage of the aerogel due to external forces. In addition, the antioxidant property of chlorogenic acid can inhibit the oxidative degradation of graphene oxide aerogel during processing or use, maintaining its structural stability and thus ensuring long-term dispersibility.

[0021] (3)Nucleophilic substitution occurs between the carboxyl group (-COOH) on the surface of graphene oxide and the phenolic hydroxyl group (-ArOH) of chlorogenic acid to obtain a special structure of -COOAr-. This structure makes the surface of graphene oxide contain a large number of benzene rings. This rigid structure can provide a framework support for the graphene oxide aerogel, thus providing a broad void for the cross-linking of phytic acid. In addition, due to the large number of carbon atoms in the internal benzene ring of -COOAr-, when combustion occurs, these carbon atoms can quickly form a dense carbon layer on the surface of polyurethane, thereby blocking the contact between polyurethane and oxygen to achieve a flame retardant effect.

[0022] (4)Due to the large number of soft voids and -COOAr- structures in chlorogenic acid-graphene aerogel, a large number of hydrogen bonds are formed with the hydroxyl groups (-OH) on phytic acid, so that a large amount of phytic acid is tightly cross-linked in the voids and on the surface of the aerogel, thus better promoting the dispersion of phytic acid on the surface of graphene oxide. During combustion, graphene oxide can form a dense carbon layer covering the surface of polyurethane foam to play a role in isolating the flame. Also, because hydrogen bonds are not as stable as chemical bonds, a large amount of phytic acid can be quickly released, generating a large number of phosphorus-containing free radicals to capture oxygen, playing a role in isolating oxygen and achieving the quenching of the combustion process.

[0023] (5) Since the specific phenolic hydroxyl groups (-ArOH) on chlorogenic acid can form hydrogen bond cross - linked networks with the specific isocyanate groups (R - NCO) on polyurethane, non - combustible gases such as N2 and CO2 are generated during combustion, thereby diluting oxygen and combustible free radicals and further quenching the combustion reaction.

[0024] (6) As a natural polyphenol compound, chlorogenic acid can decompose rapidly at high temperatures, thus promoting the dehydration and carbonization of polyurethane; phytic acid contains six phosphate groups, and its thermal decomposition generates polyphosphoric acid, which catalyzes the carbonization of polymers and forms an intumescent carbon layer; while graphene oxide itself contains six - membered carbon rings and also has the ability to form an expanded carbon layer. Therefore, the carbonization of chlorogenic acid and the catalytic carbonization of phytic acid and graphene oxide form a "three - core drive", which significantly increases the thickness and density of the carbon layer during the combustion of polyurethane, forming a synergistic physical flame - retardant effect. In addition, the phenolic hydroxyl groups and quinone structures generated by the decomposition of chlorogenic acid can capture active free radicals (such as HO·, H·) in the combustion chain reaction, inhibiting gas - phase combustion; while phytic acid releases PO· free radicals at high temperatures, forming a "double - path" quenching mechanism with the free - radical capture effect of chlorogenic acid, further reducing the combustion intensity and forming a synergistic gas - phase flame - retardant effect.

[0025] As an integrated whole, the above - mentioned technical solutions of the present invention are closely related and interact with each other, jointly determining the morphological characteristics and properties of the product.

[0026] The above - mentioned technical solutions have the following advantages or beneficial effects: 1. The limiting oxygen index value of the polyurethane material prepared by the present invention reaches 27.9, and the UL - 94 test reaches the V - 0 flame - retardant grade. Moreover, it can maintain a relatively high compressive strength while having good flame - retardant performance; 2. The preparation method of the present invention is simple, the process is easy to control, the preparation period is short, and the cost is low; 3. The raw materials used in the present invention are green and environmentally friendly, and the flame retardant can be used as fertilizer for crop fertilization after combustion.

[0027] The present invention is applicable to the preparation of polyurethane materials with synergistic flame retardancy based on chlorogenic acid - graphene aerogel and phytic acid.

[0028] The technical solutions of the present invention will be further described in detail below in conjunction with the accompanying drawings of the specification and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is the structural characterization diagram of graphene oxide, chlorogenic acid - graphene aerogel and chlorogenic acid - phytic acid / graphene (flame retardant) prepared in Example 1 of the present invention, where: (a) is the Raman spectrum diagram, (b) is the X - ray diffraction diagram, and (c) is the Fourier transform infrared spectrum diagram; Figure 2 LOI test diagrams of the polyurethane materials prepared in Comparative Example 1, Comparative Example 2, Comparative Example 5 and Example 1 of the present invention, wherein: (a) is the LOI test diagram of the polyurethane material prepared in Comparative Example 1, (b) is the LOI test diagram of the polyurethane material prepared in Comparative Example 2, (c) is the LOI test diagram of the polyurethane material prepared in Comparative Example 5, and (d) is the LOI test diagram of the polyurethane material prepared in Example 1; Figure 3 Vertical burning test diagrams of the polyurethane materials prepared in Comparative Example 1, Comparative Example 2, Comparative Example 5 and Example 1 of the present invention, wherein: (a) is the vertical burning test diagram of the polyurethane material prepared in Comparative Example 1, (b) is the vertical burning test diagram of the polyurethane material prepared in Comparative Example 2, (c) is the vertical burning test diagram of the polyurethane material prepared in Comparative Example 5, and (d) is the vertical burning test diagram of the polyurethane material prepared in Example 1. Specific embodiments

[0030] The following embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Therefore, the detailed descriptions in the embodiments of the present invention provided below are not intended to limit the scope of the claimed invention, but merely represent selected embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts fall within the protection scope of the present invention.

[0031] In the present invention, unless otherwise specified, all devices and raw materials can be purchased from the market or are commonly used in this industry. The methods in the following embodiments are conventional methods in this field unless otherwise specified. Example 1

[0032] In this example, a polyurethane material flame-retarded synergistically by chlorogenic acid-graphene aerogel and phytic acid is prepared, and its preparation process and steps are as follows: S1. Preparation of graphene oxide Weigh 5 g of 325-mesh flake graphite and 2 g of NaNO3, mix them evenly, add 120 mL of concentrated H2SO4, place it in an ice bath at 0 °C and stir for 30 min. Add 20 g of KMnO4 and react for 60 min, then transfer it to a warm water bath at 40 °C and continue to react for 30 min. Then slowly add 230 mL of deionized water, keep the reaction temperature at 90 °C, stir for 5 min, add H2O2 until no bubbles are generated, filter while it is hot, and perform centrifugation at a speed of 10000 rpm with deionized water and hydrochloric acid with a mass fraction of 5wt.% for multiple times until it is neutral. Then dry it in a drying oven at 60 °C for 24 h to obtain graphene oxide; S2. Preparation of chlorogenic acid-graphene aerogel 2 g of graphene oxide was stirred with 0.65 g of an aqueous solution of chlorogenic acid with a mass fraction of 70 wt.% at 25 °C for 30 min. It was transferred to a high-pressure reactor and reacted at 180 °C and 3 MPa for 12 h to obtain a chlorogenic acid-graphene hydrogel. Then, it was freeze-dried at -50 °C for 85 h to obtain a chlorogenic acid-graphene aerogel; S3. Preparation of a chlorogenic acid-phytic acid / graphene aerogel flame retardant 1 g of the chlorogenic acid-graphene aerogel was immersed in 3 g of an aqueous solution of phytic acid with a mass fraction of 70 wt.% for 10 min, and then it was placed in a vacuum drying oven at 80 °C and -0.1 MPa and dried for 15 min. This step was repeated 5 times to obtain a chlorogenic acid-phytic acid / graphene aerogel flame retardant; S4. Preparation of a polyurethane material 3.5 g of the flame retardant was ground into a powder with 325 mesh, and 0.15 g of deionized water, 0.03 g of dibutyltin dilaurate, 0.03 g of triethylenediamine, and 0.05 g of silicone oil were added to 5 g of polybutylene glycol. After stirring evenly at a rotation speed of 300 rpm, 4.5 g of diphenylmethane diisocyanate was added to the mixed solution. After stirring at a rotation speed of 300 rpm for 1 min, it was foamed and cured at room temperature for 2 h to obtain a polyurethane material. Example 2

[0033] In this example, a polyurethane material with synergistic flame retardancy of chlorogenic acid-graphene aerogel and phytic acid was prepared, and its preparation process and steps are as follows: S1. Preparation of graphene oxide 5 g of 325-mesh flake graphite and 2 g of NaNO3 were weighed and mixed evenly, 120 mL of concentrated H2SO4 was added, and it was stirred in an ice bath at 0 °C for 30 min. After adding 20 g of KMnO4 and reacting for 60 min, it was transferred to a water bath at 40 °C and continued to react for 30 min. Then, 230 mL of deionized water was slowly added, and the reaction temperature was maintained at 90 °C. After stirring for 5 min, H2O2 was added until no bubbles were generated. It was filtered while it was hot, and centrifuged at a rotation speed of 10000 rpm with deionized water and hydrochloric acid with a mass fraction of 5 wt.% for multiple times until it was neutral. Subsequently, it was dried in a drying oven at 60 °C for 24 h to obtain graphene oxide; S2. Preparation of chlorogenic acid-graphene aerogel 2 g of graphene oxide was stirred with 0.65 g of an aqueous solution of chlorogenic acid with a mass fraction of 70 wt.% at 25 °C for 30 min. It was transferred to a high-pressure reactor and reacted at 190 °C and 3 MPa for 12 h to obtain a chlorogenic acid-graphene hydrogel. Then, it was freeze-dried at -60 °C for 80 h to obtain a chlorogenic acid-graphene aerogel; S3. Preparation of Chlorogenic Acid-Phytic Acid / Graphene Aerogel Flame Retardant Immerse 1 g of chlorogenic acid-graphene aerogel into 3 g of aqueous phytic acid solution with a mass fraction of 70 wt.% for 10 min, then place it in a vacuum drying oven at 80 °C and -0.1 MPa, and dry for 15 min. Repeat this step 5 times to obtain the chlorogenic acid-phytic acid / graphene aerogel flame retardant; S4. Preparation of Polyurethane Material Grind 3.5 g of the flame retardant into a powder with 325 mesh, and add it together with 0.15 g of deionized water, 0.03 g of dibutyltin dilaurate, 0.03 g of triethylenediamine, and 0.05 g of silicone oil into 5 g of polybutylene glycol. After stirring evenly at a rotation speed of 300 rpm, add 4.5 g of diphenylmethane diisocyanate to the mixed solution, stir at a rotation speed of 300 rpm for 1 min, and then foam and cure at room temperature for 2 h to obtain the polyurethane material. Example 3

[0034] This example prepares a polyurethane material with synergistic flame retardancy of chlorogenic acid-graphene aerogel and phytic acid. The preparation process and steps are as follows: S1. Preparation of Graphene Oxide Weigh 5 g of 325-mesh flake graphite and 2 g of NaNO3, mix them evenly, add 120 mL of concentrated H2SO4, place it in an ice bath at 0 °C and stir for 30 min. Add 20 g of KMnO4 and react for 60 min, then transfer it to a water bath at 40 °C and continue to react for 30 min. Then slowly add 230 mL of deionized water, and keep the reaction temperature at 90 °C. Stir for 5 min, then add H2O2 until no bubbles are generated. Filter while it is hot, and perform centrifugation at a rotation speed of 10000 rpm with deionized water and hydrochloric acid with a mass fraction of 5 wt.% for multiple times until it is neutral. Subsequently, dry it in a drying oven at 60 °C for 24 h to obtain graphene oxide; S2. Preparation of Chlorogenic Acid-Graphene Aerogel Stir 2 g of graphene and 0.65 g of aqueous chlorogenic acid solution with a mass fraction of 70 wt.% at 25 °C for 30 min, transfer it to a high-pressure reactor, react at 200 °C and 3 MPa for 12 h to obtain chlorogenic acid-graphene hydrogel, and then freeze-dry it at -65 °C for 72 h to obtain chlorogenic acid-graphene aerogel; S3. Preparation of Chlorogenic Acid-Phytic Acid / Graphene Aerogel Flame Retardant Immerse 1 g of chlorogenic acid-graphene aerogel into 3 g of aqueous phytic acid solution with a mass fraction of 70 wt.% for 10 min, then place it in a vacuum drying oven at 80 °C and -0.1 MPa, and dry for 15 min. Repeat this step 5 times to obtain the chlorogenic acid-phytic acid / graphene aerogel flame retardant; S4. Preparation of polyurethane material Grind 3.5 g of the flame retardant into a powder with a mesh size of 325, and add it together with 0.15 g of deionized water, 0.03 g of dibutyltin dilaurate, 0.03 g of triethylenediamine, and 0.05 g of silicone oil to 5 g of polybutylene glycol. After stirring evenly at a rotation speed of 300 rpm, add 4.5 g of diphenylmethane diisocyanate to the mixed solution. Stir for 1 min at a rotation speed of 300 rpm, and then foam and cure at room temperature for 2 h to obtain the polyurethane material. Comparative example

[0035] In order to explore the influence of different substances in the preparation process of the present invention on the performance of the products of the present invention, the following comparative experiments were specifically carried out. The following comparative examples respectively prepared different polyurethane materials, specifically as follows: Comparative example 1 A polyurethane material was prepared in this comparative example. The preparation process was similar to that of Example 1, except that in step S4, the flame retardant was not added.

[0036] Comparative example 2 A polyurethane material was prepared in this comparative example. The preparation process was similar to that of Example 1, except that in step S4, the flame retardant was graphene oxide, and the other parameters were the same as those in Example 1.

[0037] Comparative example 3 A polyurethane material was prepared in this comparative example. The preparation process was similar to that of Example 1, except that in step S4, the flame retardant was an aqueous solution of phytic acid with a mass fraction of 70 wt.%, and the other parameters were the same as those in Example 1.

[0038] Comparative example 4 A polyurethane material was prepared in this comparative example. The preparation process was similar to that of Example 1, except that in step S4, the flame retardant was an aqueous solution of chlorogenic acid with a mass fraction of 70 wt.%, and the other parameters were the same as those in Example 1.

[0039] Comparative example 5 A polyurethane material was prepared in this comparative example. The preparation process was similar to that of Example 1, except that in step S4, the flame retardant was chlorogenic acid-graphene aerogel, and the other parameters were the same as those in Example 1.

[0040] Comparative example 6 A polyurethane material was prepared in this comparative example. The preparation process was similar to that of Example 1, except that in step S4, the flame retardant was phytic acid-graphene aerogel, and the other parameters were the same as those in Example 1.

[0041] Comparative example 7 This comparative example prepares a polyurethane material. The preparation process is similar to that of Example 1, except that in step S4, the flame retardant is an aqueous solution of chlorogenic acid and phytic acid with a mass fraction of 70 wt.%, and the remaining parameters are the same as those in Example 1.

[0042] Comparative Example 8 This comparative example prepares a polyurethane material. The preparation process is similar to that of Example 1, except that in steps S2 and S3, a phytic acid-graphene aerogel is first formed and then immersed in an aqueous solution of chlorogenic acid with a mass fraction of 70 wt.%.

[0043] Comparative Example 9 This comparative example prepares a polyurethane material. The preparation process is similar to that of Example 1, except that in step S2, the pressure is 0.1 MPa, and the remaining parameters are the same as those in Example 1.

[0044] Comparative Example 10 This comparative example prepares a polyurethane material. The preparation process is similar to that of Example 1, except that in step S2, the pressure is 0.1 MPa, and instead of adopting the immersion process in step S3, phytic acid is directly mixed with chlorogenic acid and graphene oxide. Performance Test

[0045] The polyurethane materials prepared in the examples and comparative examples of the present invention are subjected to performance characterization, which is specifically as follows: As Figure 1 , are the structure characterization diagrams of graphene oxide, chlorogenic acid-graphene aerogel, and chlorogenic acid-phytic acid / graphene (flame retardant) prepared in Example 1 of the present invention, where: (a) is the Raman spectrum diagram, (b) is the X-ray diffraction diagram, and (c) is the Fourier transform infrared spectrum diagram. From Figure 1 In (a), it can be seen that overall, the three samples of graphene oxide, chlorogenic acid-graphene aerogel, and chlorogenic acid-phytic acid / graphene aerogel have obvious peaks evenly and well, and the overall curve trend is relatively clear without the appearance of other impurities, indicating that the sample composite is relatively successful. In addition, graphene oxide shows a D peak at 1347 cm -1 , and chlorogenic acid-graphene aerogel and chlorogenic acid-phytic acid / graphene aerogel show a D peak at 1332 cm -1 , indicating that the size of the sp 3 hybridization region at this position of the two samples decreases and the defect region increases; graphene oxide shows a G peak at 1775 cm -1 , and chlorogenic acid-graphene aerogel and chlorogenic acid-phytic acid / graphene aerogel show a G peak at 1581 cm -1 . The G peaks of the two samples are close to the G peak of natural graphite at 1580 cm -1 , indicating that the sp of the two samples2 The hybrid carbon structure is partially repaired. Among them, the I D / I G = 1.18 is slightly greater than that of chlorogenic acid-graphene aerogel and chlorogenic acid-phytic acid / graphene aerogel I D / I G = 1.05, indicating that the C atomic crystal defects of NH2-GO2 / PANI are less. As can be seen from Figure 1 (b), characteristic diffraction peaks appear at 2θ = 11 ° for graphene oxide, and the peak shape is narrow, corresponding to the characteristic diffraction peak of graphene oxide, indicating that the sample at this place contains a large number of oxygen-containing functional groups. The diffraction peaks at 2θ = 23 ° for chlorogenic acid-graphene aerogel and chlorogenic acid-phytic acid / graphene aerogel have a relatively wide and thick peak shape, indicating that graphene oxide has been functionalized. In addition, as can be seen from Figure 1 (c), graphene oxide has a relatively wide and long absorption peak at 2860 cm -1 ~ 2030 cm -1 due to the large number of oxygen-containing functional groups in graphene oxide. Chlorogenic acid-graphene aerogel and chlorogenic acid-phytic acid / graphene aerogel show a C-O characteristic peak at 825 cm -1 and a C-O-C stretching vibration peak at 1210 cm -1 , a C=C stretching vibration peak at 1510 cm -1 , and a C-O stretching vibration peak at 1620 cm -1 , indicating that graphene has been fully oxidized.

[0046] Such as Figure 2 , are the LOI test diagrams of the polyurethane materials prepared in Comparative Example 1, Comparative Example 2, Comparative Example 5 and Example 1 of the present invention, where: (a) is the LOI test diagram of the polyurethane material prepared in Comparative Example 1, (b) is the LOI test diagram of the polyurethane material prepared in Comparative Example 2, (c) is the LOI test diagram of the polyurethane material prepared in Comparative Example 5, and (d) is the LOI test diagram of the polyurethane material prepared in Example 1. As can be seen from the figure, the LOIs of the polyurethane materials prepared in Comparative Example 1, Comparative Example 2, Comparative Example 5 and Example 1 are 17.2%, 19.1%, 23.8%, and 27.9% respectively. The LOI of the polyurethane material prepared in Example 1 is the highest, indicating that the flame retardant effect of chlorogenic acid-phytic acid / graphene aerogel is the best.

[0047] Such as Figure 3, is the vertical combustion test diagram of the polyurethane materials prepared in Comparative Example 1, Comparative Example 2, Comparative Example 5 and Example 1 of the present invention, where: (a) is the vertical combustion test diagram of the polyurethane material prepared in Comparative Example 1, (b) is the vertical combustion test diagram of the polyurethane material prepared in Comparative Example 2, (c) is the vertical combustion test diagram of the polyurethane material prepared in Comparative Example 5, and (d) is the vertical combustion test diagram of the polyurethane material prepared in Example 1. It can be seen from the figure that the pure polyurethane material (Comparative Example 1) shows obvious combustion phenomenon in the vertical combustion test and has no quenching effect. After re-ignition for 5 s, there is basically no fire, indicating that the polyurethane burns almost completely during the first ignition; after adding graphene oxide (Comparative Example 2), although the combustion situation is improved and the oxygen index LOI is increased compared with pure polyurethane, the combustion situation has not been completely improved and the combustion time exceeds 30 s; after adding chlorogenic acid-graphene (Comparative Example 5), no melt dripping occurs after the first and second ignitions for 10 s, but the combustion time also exceeds 30 s; while after adding chlorogenic acid-phytic acid / graphene (Example 1), the limiting oxygen index of the polyurethane material reaches 27.9, and no melt dripping occurs after the first and second ignitions for 10 s, so the UL-94 flame retardant rating is improved from no rating to V-0 rating. (UL-94 flame retardant rating standard: V-2: After two 10-s combustion tests on the sample, the flame extinguishes within 60 s, and combustion products can fall off; V-1: After two 10-s combustion tests on the sample, the flame extinguishes within 60 s, and no combustion products can fall off; V-0: After two 10-s combustion tests on the sample, the flame extinguishes within 30 s, and no combustion products can fall off; no rating means that the test sample burns out and cannot self-extinguish.) The polyurethane materials prepared in Examples 1-3 and Comparative Examples 1-10 were tested for flame retardancy and compressive strength. The specific test results are shown in the following table:

[0048] It can be seen from the above table that the limiting oxygen index, UL-94 flame retardant rating and compressive strength of the polyurethane materials prepared in Examples 1-3 are significantly higher than those in Comparative Examples 1-10. Thus, it can be shown that the chlorogenic acid-phytic acid / graphene aerogel flame retardant prepared in the present invention has the best flame retardant effect and can keep the polyurethane with a relatively high compressive strength.

[0049] In addition, since Comparative Example 3, Comparative Example 4 and Comparative Example 7 used aqueous phytic acid solution, aqueous chlorogenic acid solution and aqueous phytic acid-chlorogenic acid solution as flame retardants for polyurethane materials respectively, the isocyanate would react rapidly with the water in the flame retardant and cause explosive polymerization, so polyurethane materials could not be formed and relevant property tests could not be carried out.

[0050] Finally, it should be noted that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing polyurethane materials by synergistic flame retardancy of chlorogenic acid-graphene aerogel and phytic acid, characterized in that, Proceed in sequence according to the following steps: S1. Prepare graphene oxide Weigh 5 g of 325-mesh flake graphite and 2 g of NaNO3, mix them evenly, add 120 mL of concentrated H2SO4, place it in an ice bath at 0 °C and stir for 30 min. Then add 20 g of KMnO4 and react for 60 min. Transfer it to a warm water bath at 40 °C and continue to react for 30 min. Then slowly add 230 mL of deionized water, keep the reaction temperature at 90 °C, stir for 5 min, add H2O2 until no bubbles are produced, filter while it is hot, and centrifuge with deionized water and hydrochloric acid with a mass fraction of 5wt.% for multiple times until it is neutral. Then dry it in a drying oven at 60 °C for 24 h to obtain graphene oxide; S2. Prepare chlorogenic acid-graphene aerogel Stir graphene oxide and chlorogenic acid at 25 °C for 30 min, then transfer it to a high-pressure reaction kettle and react for 12 h under high temperature and high pressure conditions to obtain chlorogenic acid-graphene hydrogel, and then freeze-dry it to obtain chlorogenic acid-graphene aerogel; S3. Prepare chlorogenic acid-phytic acid / graphene aerogel flame retardant Immerse the chlorogenic acid-graphene aerogel in an aqueous solution of phytic acid with a mass fraction of 70wt.% for 10 min, then place it in a vacuum drying oven at 80 °C and -0.1 MPa and dry for 15 min. Repeat this step 5 times to obtain chlorogenic acid-phytic acid / graphene aerogel flame retardant; S4. Prepare polyurethane material Grind 3.5 g of the flame retardant into 325-mesh powder, add it together with 0.15 g of deionized water, 0.03 g of dibutyltin dilaurate, 0.03 g of triethylenediamine, and 0.05 g of silicone oil to 5 g of polybutylene glycol. After stirring evenly, add 4.5 g of diphenylmethane diisocyanate to the mixed solution, stir for 1 min, then foam and cure at room temperature for 2 h to obtain the polyurethane material.

2. A method for preparing a polyurethane material by synergistic flame retardancy of chlorogenic acid-graphene aerogel and phytic acid according to claim 1, characterized in that, In step S1, the centrifugation rate is 10000 rpm.

3. A method for preparing a polyurethane material based on the synergistic flame retardancy of chlorogenic acid-graphene aerogel and phytic acid according to claim 1, characterized in that, In step S2, the chlorogenic acid is an aqueous solution of chlorogenic acid with a mass fraction of 70wt.%.

4. A method for preparing a polyurethane material based on the synergistic flame retardancy of chlorogenic acid-graphene aerogel and phytic acid according to claim 1, characterized in that, In step S2, the mass ratio of graphene oxide to chlorogenic acid is 2:0.

65.

5. A method for preparing a polyurethane material by synergistic flame retardancy of chlorogenic acid-graphene aerogel and phytic acid according to claim 1, characterized in that, In step S2, the temperature under the high temperature and high pressure conditions is 180 °C to 200 °C, and the pressure is 3 MPa.

6. A method for preparing a polyurethane material by synergistic flame retardancy of chlorogenic acid-graphene aerogel and phytic acid according to claim 1, characterized in that In step S2, the temperature during freeze-drying is -65 °C to -50 °C, and the time is 72 to 85 h.

7. A method for preparing a polyurethane material based on the synergistic flame retardancy of chlorogenic acid-graphene aerogel and phytic acid according to claim 1, characterized in that, In step S3, the mass ratio of the chlorogenic acid-graphene aerogel to the aqueous solution of phytic acid with a mass fraction of 70wt.% is 1:

3.

8. A method for preparing a polyurethane material by synergistic flame retardancy of chlorogenic acid-graphene aerogel and phytic acid according to claim 1, characterized in that, In step S4, the stirring rate is 300 rpm.

Images