A method for preparing polyurethane material based on chlorogenic acid-graphene aerogel and phytic acid synergistic flame retardancy

Abstract

The present invention discloses 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 using isocyanate as a hard segment, polyether polyol as a soft segment, deionized water as a foaming agent, triethylenediamine 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 of the present invention is simple and the process is easy to control. The limiting oxygen index of the prepared polyurethane material reaches 27.9, meeting the commercial standards for flame retardant materials and the UL-94 V-0 flame retardant grade requirements. In addition, the polyurethane material can maintain a high compressive strength while having good flame retardant properties.

Description

Technical Field

[0001] The present invention belongs to the field of polymer composite materials and relates to a method for preparing a polyurethane material based on the 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 thermal insulation, chemical resistance, and strong adhesion. It can be used as thermal insulation for walls, roofs, and pipes; as thermal insulation interlayers for refrigeration equipment such as refrigerators and cold storage; and as thermal insulation for lightweight storage tanks and pipes in vehicles such as automobiles and aircraft. However, due to its organic polymer backbone (containing numerous CH and ether bonds), RPUF is extremely flammable (with a limiting oxygen index (LOI) of only 17%-19%). Combustion also releases large amounts of toxic gases such as CO and HCN, accompanied by molten dripping, posing a serious fire hazard. Therefore, flame retardant modification is a key requirement for its application.

[0003] Graphene oxide (GO), a new environmentally friendly material, is a highly effective nano-flame retardant. Its layered structure physically blocks heat and oxygen while chemically inhibiting the combustion chain reaction. GO not only traps oxygen-containing free radicals generated by combustion through its surface defects and π-electron structure, slowing the combustion reaction, but also possesses high thermal conductivity, dispersing localized heat and inhibiting heat accumulation. However, GO exhibits severe agglomeration, making it difficult to disperse, significantly reducing its performance.

[0004] Chlorogenic acid is a phenylpropanoid compound produced by plants via the shikimic acid pathway during aerobic respiration. It possesses potent antioxidant properties and also possesses anti-HIV, anti-tumor, and antibacterial properties. It is widely found in high concentrations in honeysuckle plants and is a natural, green, and environmentally friendly substance. While there have been reports of using chlorogenic acid as a reducing agent to prepare reduced graphene oxide, there have been no reports of preparing chlorogenic acid-graphene aerogels as flame-retardant materials under high temperature and high pressure.

[0005] Phytic acid is a natural organophosphorus compound extracted from plants, renowned 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 decomposes to form phosphoric acid and polyphosphoric acid, which catalyze the dehydration of polyurethane to form a dense char layer. Furthermore, when phytic acid burns, it not only releases phosphorus-containing free radicals that quench the combustion chain reaction, but also produces phosphoric acid derivatives that bind to smoke particles, reducing smoke emissions. However, due to its steric structure, direct grafting of phytic acid onto polyurethane segments can not only reduce the mechanical properties of the polyurethane but also pose a risk of implosion. Its acidity not only reduces the life of foaming equipment but also affects the cell structure of rigid polyurethane foam. Furthermore, phytic acid is a highly hygroscopic substance and is typically present as an aqueous solution. However, polyurethane reacts rapidly with water. Therefore, phytic acid modification is necessary to minimize damage to the polyurethane segments.

[0006] Based on this, the present invention aims to provide a polyurethane material with excellent flame retardancy. The resulting polyurethane material can be applied in a variety of industries. While exhibiting excellent flame retardancy, it is also environmentally friendly. It can be widely used in thermal insulation layers in buildings and automobiles, and can also be used as fertilizer for crops after combustion. Summary of the Invention

[0007] In response to 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 a hard segment, polyether polyol as a soft segment, deionized water as a foaming agent, triethylenediamine 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 of the present invention is simple and the process is easy to control. The limiting oxygen index of the prepared polyurethane material reaches 27.9, which meets the commercial standards for flame retardant materials and the UL-94 V-0 flame retardant grade requirements. In addition, the polyurethane material can maintain a high compressive strength while having good flame retardant properties.

[0008] To achieve the above object, the technical solution adopted by the present invention is:

[0009] A method for preparing a polyurethane material based on the synergistic flame retardancy of chlorogenic acid-graphene aerogel and phytic acid is carried out in the following steps in sequence:

[0010] S1. Preparation of graphene oxide

[0011] Weigh 5 g of 325-mesh flake graphite and 2 g of NaNO3, mix them evenly, add 120 mL of concentrated H2SO4, place them in a 0°C ice bath and stir for 30 min, add 20 g of KMnO4 and react for 60 min, then move them into a 40°C warm water bath and continue to react for 30 min, then slowly add 230 mL of deionized water while maintaining the reaction temperature at 90°C, stir for 5 min, then add H2O2 until no bubbles are generated, filter while hot, and centrifuge them several times with deionized water and 5 wt.% hydrochloric acid until neutral, then dry them in a 60°C drying oven for 24 h to obtain graphene oxide;

[0012] S2. Preparation of chlorogenic acid-graphene aerogel

[0013] Graphene oxide and chlorogenic acid were stirred at 25°C for 30 minutes, then transferred to a high-pressure reactor and reacted under high temperature and high pressure conditions for 12 hours to obtain chlorogenic acid-graphene hydrogel, which was then freeze-dried to obtain chlorogenic acid-graphene aerogel.

[0014] S3. Preparation of chlorogenic acid-phytic acid / graphene aerogel flame retardant

[0015] The chlorogenic acid-graphene aerogel was immersed in a 70 wt.% phytic acid aqueous solution for 10 min, and then placed in a vacuum drying oven at 80°C and -0.1 MPa for 15 min. This step was repeated 5 times to obtain a chlorogenic acid-phytic acid / graphene aerogel flame retardant.

[0016] S4. Preparation of polyurethane material

[0017] 3.5 g of flame retardant was ground into 325 mesh powder and added 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, 4.5 g of diphenylmethane diisocyanate was added to the mixed solution. After stirring for 1 min, the mixture was foamed and cured at room temperature for 2 h to obtain a polyurethane material.

[0018] As a limitation of the preparation method of the present invention, in step S1, the centrifugal speed is 10000 rpm.

[0019] As another limitation of the preparation method of the present invention, in step S2, the chlorogenic acid is a chlorogenic acid aqueous solution with a mass fraction of 70 wt.%.

[0020] As a third limitation of the preparation method of the present invention, in step S2, the mass ratio of the graphene oxide to the chlorogenic acid is 2:0.65.

[0021] In the present invention, the mass ratio of graphene oxide to chlorogenic acid is crucial, affecting the formation of the aerogel cross-linked structure and the flame retardant effect on polyurethane. When the mass ratio of graphene oxide to chlorogenic acid is 2:0.65, esterification reaction, addition reaction, and π-π conjugation between graphene oxide and chlorogenic acid occur, which just makes the graphene oxide form 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, thereby greatly reducing the specific surface area of ​​the graphene oxide, forming agglomerates and failing to form an aerogel; if the mass ratio is less than this ratio, it will cause the chlorogenic acid to remain, causing the graphene oxide aerogel to be in an acidic environment and causing the graphene oxide aerogel to have serious slagging.

[0022] As a fourth limitation of the preparation method of the present invention, 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.

[0023] 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 are 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 too stable, resulting in an inability to react. If the temperature is greater than 200°C, the oxygen-containing functional groups on the graphene oxide are too active, causing the hydroxyl and carboxyl groups of the graphene oxide itself to react and cause agglomeration. The pressure is set to 3 MPa because it can limit the volatilization of the aqueous solvent and the escape of oxygen, reduce the risk of reoxidation of the graphene oxide, and ensure that the reduction reaction is thorough. In addition, at this pressure, the phenolic hydroxyl groups of chlorogenic acid are more likely to release protons, promoting close contact between chlorogenic acid and the graphene oxide sheets, thereby improving the efficiency of esterification reactions, epoxy addition, and π-π interactions with graphene oxide.

[0024] As a fifth limitation of the preparation method of the present invention, in step S2, the freeze-drying temperature is -65°C to -50°C, and the time is 72 to 85 hours.

[0025] As a sixth limitation of the preparation method of the present invention, in step S3, the mass ratio of the chlorogenic acid-graphene aerogel to the phytic acid aqueous solution with a mass fraction of 70 wt.% is 1:3.

[0026] 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 aerogel will be balanced, so that the flame retardant effect is optimized. If the mass ratio is less than this ratio, there will be too little phytic acid, and it will not be possible to generate enough polyphosphoric acid to catalyze carbonization, resulting in insufficient thickness and density of the carbon layer; in addition, a mass ratio less than this ratio will also lead to a reduction in the amount of PO· free radicals generated, and the free radical quenching ability is weak and cannot 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 multi-level pore structure to collapse, the specific surface area to decrease, and the physical barrier efficiency to decrease. In addition, excessive 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 will easily crack during combustion, reducing the flame retardant effect.

[0027] As a seventh limitation of the preparation method of the present invention, in step S4, the stirring rate is 300 rpm.

[0028] In the present invention, chlorogenic acid, graphene oxide and phytic acid can synergistically perform flame retardancy, as follows:

[0029] (1) Under specific high temperature and high pressure conditions, the carboxyl groups (-COOH) on the surface of graphene oxide and the phenolic hydroxyl groups (-ArOH) of chlorogenic acid undergo esterification, the hydroxyl groups of chlorogenic acid undergo addition reaction with the epoxy groups of graphene oxide, and the benzene rings on chlorogenic acid undergo π-π conjugation with the carbon-carbon double bonds of graphene oxide. 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. The 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.

[0030] (2) The modification of chlorogenic acid on three-dimensional functionalized graphene oxide aerogel can make the graphene oxide aerogel better dispersed in polyurethane. The phenolic hydroxyl group of chlorogenic acid can form hydrogen bonds with the carbamate group (-NHCOO-) in the polyurethane molecular chain, while its ester group produces polar interactions with the ether bond (-O-) or ester bond (-COO-) of polyurethane, thereby enhancing the interfacial bonding force. After the surface of the graphene oxide aerogel is modified with chlorogenic acid, the hydrophobicity is transformed into a hydrophilic-hydrophobic equilibrium 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 multi-level pore structure with a large pore size distribution. This structure can be embedded in the polyurethane molecular chain during the polyurethane foaming process, forming a "mechanical interlocking" effect, inhibiting the migration and agglomeration of the aerogel. The specific surface area of ​​the aerogel modified with chlorogenic acid is increased, and the high specific surface area provides more active sites in contact with polyurethane, promoting uniform dispersion. The phenolic hydroxyl groups of chlorogenic acid dynamically break and reassemble during the polyurethane curing process, forming reversible crosslinks. This alleviates stress concentration during processing and prevents structural damage to the aerogel due to external forces. Furthermore, the antioxidant properties of chlorogenic acid inhibit the oxidative degradation of graphene oxide aerogels during processing or use, maintaining their structural stability and ensuring long-term dispersibility.

[0031] (3) Nucleophilic substitution occurs between the carboxyl groups (-COOH) on the graphene oxide surface and the phenolic hydroxyl groups (-ArOH) of chlorogenic acid to form a special structure called -COOAr-. This structure allows the graphene oxide surface to contain a large number of benzene rings. This rigid structure can provide skeletal support for the graphene oxide aerogel, thereby providing a wide gap for the cross-linking of phytic acid. In addition, because the benzene rings inside -COOAr- contain a large number of carbon atoms, these carbon atoms can quickly form a dense carbon layer on the polyurethane surface during combustion, thereby blocking the polyurethane from contact with oxygen and achieving a flame retardant effect.

[0032] (4) Because chlorogenic acid-graphene aerogel contains a large number of soft voids and -COOAr- structures, it forms a large number of hydrogen bonds with the hydroxyl groups (-OH) on phytic acid, which makes a large amount of phytic acid tightly cross-linked in the voids and surface of the aerogel, thereby 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 isolate the flame. Since hydrogen bonds are not as stable as chemical bonds, it can quickly release a large amount of phytic acid, generating a large number of phosphorus-containing free radicals to capture oxygen, isolating oxygen and achieving the purpose of quenching the combustion process.

[0033] (5) Since the phenolic hydroxyl group (-ArOH) on chlorogenic acid can form a hydrogen bond cross-linking network with the isocyanate group (R-NCO) on polyurethane, it produces non-combustible gases such as N2 and CO2 when combustion occurs, thereby diluting oxygen and combustible free radicals and further quenching the combustion reaction.

[0034] (6) Chlorogenic acid, as a natural polyphenol compound, can decompose rapidly at high temperatures, thereby promoting the dehydration and carbonization of polyurethane; phytic acid contains 6 phosphate groups, which decomposes thermally to form polyphosphoric acid, catalyzing the carbonization of the polymer and forming an expanded carbon layer; and graphene oxide itself contains a six-membered carbon ring 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 of polyurethane during combustion, forming a synergistic physical flame retardant effect. In addition, the phenolic hydroxyl and quinone structures produced by the decomposition of chlorogenic acid can capture active free radicals (such as HO·, H·) in the combustion chain reaction, inhibiting gas phase combustion; and phytic acid releases PO· free radicals at high temperatures, which form a "dual 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.

[0035] The above technical solution of the present invention is taken as a whole, and the various steps are closely related and influence each other, which jointly determine the morphological characteristics and performance of the product.

[0036] The above technical solution has the following advantages or beneficial effects:

[0037] 1. The polyurethane material prepared by the present invention has a limiting oxygen index value of 27.9 and a flame retardant grade of V-0 according to the UL-94 test. It also has good flame retardant properties and can maintain high compressive strength.

[0038] 2. The preparation method of the present invention is simple, the process is easy to control, the preparation cycle is short, and the cost is low;

[0039] 3. The raw materials used in the present invention are green and environmentally friendly, and the flame retardant can be used as fertilizer for fertilizing crops after burning.

[0040] The present invention is suitable for preparing a polyurethane material based on the synergistic flame retardancy of chlorogenic acid-graphene aerogel and phytic acid.

[0041] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific implementation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1Structural 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, wherein: (a) is a Raman spectrum, (b) is an X-ray diffraction pattern, and (c) is a Fourier transform infrared spectrum;

[0043] Figure 2 These are LOI test graphs 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 graph of the polyurethane material prepared in Comparative Example 1, (b) is the LOI test graph of the polyurethane material prepared in Comparative Example 2, (c) is the LOI test graph of the polyurethane material prepared in Comparative Example 5, and (d) is the LOI test graph of the polyurethane material prepared in Example 1;

[0044] Figure 3 These are vertical combustion 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 a vertical combustion test diagram of the polyurethane material prepared in Comparative Example 1, (b) is a vertical combustion test diagram of the polyurethane material prepared in Comparative Example 2, (c) is a vertical combustion test diagram of the polyurethane material prepared in Comparative Example 5, and (d) is a vertical combustion test diagram of the polyurethane material prepared in Example 1. DETAILED DESCRIPTION

[0045] The following embodiments are merely some of the embodiments of the present invention, rather than all of them. Therefore, the detailed description of the embodiments of the present invention provided below is not intended to limit the scope of the claimed invention, but rather merely represents selected embodiments of the present invention. All other embodiments derived by those skilled in the art based on the embodiments of the present invention without creative effort are intended to fall within the scope of protection of the present invention.

[0046] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments, unless otherwise specified, are all conventional methods in the art.

[0047] Example 1

[0048] In this embodiment, a polyurethane material with chlorogenic acid-graphene aerogel and phytic acid synergistic flame retardancy is prepared, and the preparation process and steps are as follows:

[0049] S1. Preparation of graphene oxide

[0050] Weigh 5 g of 325-mesh flake graphite and 2 g of NaNO3, mix them evenly, add 120 mL of concentrated H2SO4, place them in a 0°C ice bath and stir for 30 min, add 20 g of KMnO4 and react for 60 min, then move them into a 40°C warm water bath and continue to react for 30 min, then slowly add 230 mL of deionized water, and keep the reaction temperature at 90°C. After stirring for 5 min, add H2O2 until no bubbles are generated, filter while hot, and centrifuge them several times at 10,000 rpm with deionized water and 5 wt.% hydrochloric acid until neutral, then dry them in a 60°C drying oven for 24 h to obtain graphene oxide;

[0051] S2. Preparation of chlorogenic acid-graphene aerogel

[0052] 2 g of graphene oxide and 0.65 g of a 70 wt.% aqueous solution of chlorogenic acid were stirred at 25°C for 30 min, transferred to a high-pressure reactor, and reacted at 180°C and 3 MPa for 12 h to obtain a chlorogenic acid-graphene hydrogel. The hydrogel was then freeze-dried at -50°C for 85 h to obtain a chlorogenic acid-graphene aerogel.

[0053] S3. Preparation of chlorogenic acid-phytic acid / graphene aerogel flame retardant

[0054] 1 g of chlorogenic acid-graphene aerogel was immersed in 3 g of 70 wt.% phytic acid aqueous solution for 10 min, then placed in a vacuum drying oven at 80°C and -0.1 MPa for 15 min. This step was repeated 5 times to obtain a chlorogenic acid-phytic acid / graphene aerogel flame retardant.

[0055] S4. Preparation of polyurethane material

[0056] 3.5 g of flame retardant was ground into 325 mesh powder and added 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 at 300 rpm, 4.5 g of diphenylmethane diisocyanate was added to the mixed solution. After stirring at 300 rpm for 1 min, the mixture was foamed and cured at room temperature for 2 h to obtain a polyurethane material.

[0057] Example 2

[0058] In this embodiment, a polyurethane material with chlorogenic acid-graphene aerogel and phytic acid synergistic flame retardancy is prepared, and the preparation process and steps are as follows:

[0059] S1. Preparation of graphene oxide

[0060] Weigh 5 g of 325-mesh flake graphite and 2 g of NaNO3, mix them evenly, add 120 mL of concentrated H2SO4, place them in a 0°C ice bath and stir for 30 min, add 20 g of KMnO4 and react for 60 min, then move them into a 40°C warm water bath and continue to react for 30 min, then slowly add 230 mL of deionized water, and keep the reaction temperature at 90°C. After stirring for 5 min, add H2O2 until no bubbles are generated, filter while hot, and centrifuge them several times at 10,000 rpm with deionized water and 5 wt.% hydrochloric acid until neutral, then dry them in a 60°C drying oven for 24 h to obtain graphene oxide;

[0061] S2. Preparation of chlorogenic acid-graphene aerogel

[0062] 2 g of graphene oxide and 0.65 g of a 70 wt.% chlorogenic acid aqueous solution were stirred at 25°C for 30 min, transferred to a high-pressure reactor, and reacted at 190°C and 3 MPa for 12 h to obtain a chlorogenic acid-graphene hydrogel. The hydrogel was then freeze-dried at -60°C for 80 h to obtain a chlorogenic acid-graphene aerogel.

[0063] S3. Preparation of chlorogenic acid-phytic acid / graphene aerogel flame retardant

[0064] 1 g of chlorogenic acid-graphene aerogel was immersed in 3 g of 70 wt.% phytic acid aqueous solution for 10 min, then placed in a vacuum drying oven at 80°C and -0.1 MPa for 15 min. This step was repeated 5 times to obtain a chlorogenic acid-phytic acid / graphene aerogel flame retardant.

[0065] S4. Preparation of polyurethane material

[0066] 3.5 g of flame retardant was ground into 325 mesh powder and added 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 at 300 rpm, 4.5 g of diphenylmethane diisocyanate was added to the mixed solution. After stirring at 300 rpm for 1 min, the mixture was foamed and cured at room temperature for 2 h to obtain a polyurethane material.

[0067] Example 3

[0068] In this embodiment, a polyurethane material with chlorogenic acid-graphene aerogel and phytic acid synergistic flame retardancy is prepared, and the preparation process and steps are as follows:

[0069] S1. Preparation of graphene oxide

[0070] Weigh 5 g of 325-mesh flake graphite and 2 g of NaNO3, mix them evenly, add 120 mL of concentrated H2SO4, place them in a 0°C ice bath and stir for 30 min, add 20 g of KMnO4 and react for 60 min, then move them into a 40°C warm water bath and continue to react for 30 min, then slowly add 230 mL of deionized water, and keep the reaction temperature at 90°C. After stirring for 5 min, add H2O2 until no bubbles are generated, filter while hot, and centrifuge them several times at 10,000 rpm with deionized water and 5 wt.% hydrochloric acid until neutral, then dry them in a 60°C drying oven for 24 h to obtain graphene oxide;

[0071] S2. Preparation of chlorogenic acid-graphene aerogel

[0072] 2 g of graphene and 0.65 g of a 70 wt.% chlorogenic acid aqueous solution were stirred at 25°C for 30 min, transferred to a high-pressure reactor, and reacted at 200°C and 3 MPa for 12 h to obtain a chlorogenic acid-graphene hydrogel. The hydrogel was then freeze-dried at -65°C for 72 h to obtain a chlorogenic acid-graphene aerogel.

[0073] S3. Preparation of chlorogenic acid-phytic acid / graphene aerogel flame retardant

[0074] 1 g of chlorogenic acid-graphene aerogel was immersed in 3 g of 70 wt.% phytic acid aqueous solution for 10 min, then placed in a vacuum drying oven at 80°C and -0.1 MPa for 15 min. This step was repeated 5 times to obtain a chlorogenic acid-phytic acid / graphene aerogel flame retardant.

[0075] S4. Preparation of polyurethane material

[0076] 3.5 g of flame retardant was ground into 325 mesh powder and added 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 at 300 rpm, 4.5 g of diphenylmethane diisocyanate was added to the mixed solution. After stirring at 300 rpm for 1 min, the mixture was foamed and cured at room temperature for 2 h to obtain a polyurethane material.

[0077] Comparative Example

[0078] In order to explore the effects of different substances on the performance of the product of the present invention during the preparation process of the present invention, the following comparative experiments were conducted. Different polyurethane materials were prepared in the following comparative examples, as follows:

[0079] Comparative Example 1

[0080] In this comparative example, a polyurethane material is prepared. The preparation process is similar to that of Example 1, except that no flame retardant is added in step S4.

[0081] Comparative Example 2

[0082] In this comparative example, a polyurethane material is prepared. The preparation process is similar to that of Example 1, except that in step S4, the flame retardant is graphene oxide, and the other parameters are the same as those of Example 1.

[0083] Comparative Example 3

[0084] In this comparative example, a polyurethane material is prepared. The preparation process is similar to that of Example 1, except that in step S4, the flame retardant is a phytic acid aqueous solution with a mass fraction of 70 wt.%, and the other parameters are the same as those of Example 1.

[0085] Comparative Example 4

[0086] In this comparative example, a polyurethane material was prepared. The preparation process was similar to that of Example 1, except that, in step S4, the flame retardant was a chlorogenic acid aqueous solution with a mass fraction of 70 wt.%, and the other parameters were the same as those of Example 1.

[0087] Comparative Example 5

[0088] In this comparative example, a polyurethane material is prepared. The preparation process is similar to that of Example 1, except that, in step S4, the flame retardant is chlorogenic acid-graphene aerogel, and the other parameters are the same as those of Example 1.

[0089] Comparative Example 6

[0090] In this comparative example, a polyurethane material is prepared. The preparation process is similar to that of Example 1, except that, in step S4, the flame retardant is phytic acid-graphene aerogel, and the other parameters are the same as those of Example 1.

[0091] Comparative Example 7

[0092] In this comparative example, a polyurethane material was prepared. The preparation process was similar to that in Example 1, except that, in step S4, the flame retardant was a chlorogenic acid and phytic acid aqueous solution with a mass fraction of 70 wt.%, and the other parameters were the same as those in Example 1.

[0093] Comparative Example 8

[0094] In this comparative example, a polyurethane material was prepared. The preparation process was similar to that of Example 1, except that, in steps S2 and S3, a phytic acid-graphene aerogel was first formed and then immersed in a chlorogenic acid aqueous solution with a mass fraction of 70 wt.%.

[0095] Comparative Example 9

[0096] In this comparative example, a polyurethane material was prepared. The preparation process was similar to that of Example 1, except that in step S2, the pressure was 0.1 MPa, and the other parameters were the same as those of Example 1.

[0097] Comparative Example 10

[0098] In this comparative example, a polyurethane material was prepared. The preparation process was similar to that in Example 1, except that in step S2, the pressure was 0.1 MPa, and the soaking process in step S3 was not adopted. Instead, phytic acid was directly mixed with chlorogenic acid and graphene oxide.

[0099] Performance Testing

[0100] The performance of the polyurethane materials prepared in the examples of the present invention and the comparative examples was characterized as follows:

[0101] like Figure 1 , are structural 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, wherein: (a) is a Raman spectrum diagram, (b) is an X-ray diffraction diagram, and (c) is a Fourier transform infrared spectrum diagram. Figure 1 As can be seen in (a), the three samples of graphene oxide, chlorogenic acid-graphene aerogel, and chlorogenic acid-phytic acid / graphene aerogel have uniform and obvious peaks, and the overall curve trend is relatively clear without the appearance of other impurities, indicating that the samples are successfully composited. In addition, graphene oxide has a peak at 1347 cm -1 The D peak appears at 1332 cm-1 for chlorogenic acid-graphene aerogel and chlorogenic acid-phytic acid / graphene aerogel. -1 The D peak appears at this location, indicating that the sp 3 The size of the hybrid region decreases and the defect region increases; the graphene oxide has a -1 The G peak appears at 1581 cm-1 for chlorogenic acid-graphene aerogel and chlorogenic acid-phytic acid / graphene aerogel. -1 The G peak of both samples is close to that of natural graphite at 1580 cm -1 The G peak of the two samples indicates that the sp 2 The hybrid carbon structure is partially repaired. I D / I G =1.18, slightly larger than that of chlorogenic acid-graphene aerogel and chlorogenic acid-phytic acid / graphene aerogel I D / I G =1.05, indicating that there are fewer C atomic crystal defects. Figure 1As can be seen from (b), graphene oxide has a ° The characteristic diffraction peak appeared at 2θ=23, and the peak shape was narrow, which corresponded to the characteristic diffraction peak of graphene oxide, indicating that the sample contained a large number of oxidized functional groups. ° The diffraction peak at is relatively broad and thick, indicating that graphene oxide has been functionalized. Figure 1 As can be seen in (c), at 2860 cm -1 ~2030 cm -1 The graphene oxide has a relatively broad and long absorption peak at 825 cm, which is due to the large number of oxygen-containing functional groups in graphene oxide. -1 The characteristic peak of CO appears at 1210 cm -1 The COC stretching vibration peak appears at 1510 cm -1 The C=C stretching vibration peak appears at 1620 cm -1 The CO stretching vibration peak appears at , indicating that graphene is fully oxidized.

[0102] like Figure 2 , which are the LOI test graphs of the polyurethane materials prepared in Comparative Examples 1, 2, 5, and Example 1 of the present invention. (a) is the LOI test graph of the polyurethane material prepared in Comparative Example 1, (b) is the LOI test graph of the polyurethane material prepared in Comparative Example 2, (c) is the LOI test graph of the polyurethane material prepared in Comparative Example 5, and (d) is the LOI test graph of the polyurethane material prepared in Example 1. As can be seen from the graphs, the LOIs of the polyurethane materials prepared in Comparative Examples 1, 2, 5, and 1 are 17.2%, 19.1%, 23.8%, and 27.9%, respectively. The polyurethane material prepared in Example 1 has the highest LOI, indicating that the chlorogenic acid-phytic acid / graphene aerogel has the best flame retardant effect.

[0103] like Figure 3, are vertical combustion 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 a vertical combustion test diagram of the polyurethane material prepared in Comparative Example 1, (b) is a vertical combustion test diagram of the polyurethane material prepared in Comparative Example 2, (c) is a vertical combustion test diagram of the polyurethane material prepared in Comparative Example 5, and (d) is a vertical combustion test diagram of the polyurethane material prepared in Example 1. As can be seen from the figure, the pure polyurethane material (Comparative Example 1) burned obviously in the vertical combustion test and had no quenching effect. After re-ignition for 5 seconds, basically no flame appeared, indicating that the polyurethane was basically completely burned during the first ignition; after adding graphene oxide (Comparative Example 2), the combustion situation improved, and the oxygen index LOI was improved compared with pure polyurethane, but the combustion situation was not completely improved, and the burning time exceeded 30 seconds; after adding chlorogenic acid-graphene (Comparative Example 5), no molten droplets were produced after 10 seconds of the first and second ignition, but the burning time also exceeded 30 seconds; after adding chlorogenic acid-phytic acid / graphene (Example 1), the limiting oxygen index of the polyurethane material reached 27.9, and no molten droplets were produced after 10 seconds of the first and second ignition, so the UL-94 flame retardant grade was improved from no grade to V-0 grade. (UL-94 flame retardant rating standard: V-2: After two 10-second combustion tests, the sample flame goes out within 60 seconds, and the burning material may fall off; V-1: After two 10-second combustion tests, the sample flame goes out within 60 seconds, and no burning material can fall off; V-0: After two 10-second combustion tests, the sample flame goes out within 30 seconds, and no burning material can fall off; No rating means the test sample burns out completely and cannot self-extinguish.)

[0104] The polyurethane materials prepared in Examples 1-3 and Comparative Examples 1-10 were subjected to flame retardancy and compressive strength tests. The specific test results are shown in the following table:

[0105]

[0106] As can be seen from the above table, the limiting oxygen index, UL-94 flame retardant grade and compressive strength of the polyurethane materials prepared in Examples 1-3 are significantly higher than those in Comparative Examples 1-10. This shows that the chlorogenic acid-phytic acid / graphene aerogel flame retardant prepared in the present invention has the best flame retardant effect and can enable the polyurethane to maintain a high compressive strength.

[0107] In addition, since Comparative Examples 3, 4, and 7 respectively use phytic acid aqueous solution, chlorogenic acid aqueous solution, and phytic acid-chlorogenic acid aqueous solution as flame retardants for polyurethane materials, isocyanate will react rapidly with water in the flame retardant to cause explosion, so that polyurethane material cannot be formed and relevant performance tests cannot be performed.

[0108] Finally, it should be noted that the above descriptions are merely 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 aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles 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 a polyurethane material based on the synergistic flame retardancy of chlorogenic acid-graphene aerogel and phytic acid, characterized in that: Follow the steps below in order: 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 them in a 0°C ice bath and stir for 30 min, then add 20 g of KMnO4 and react for 60 min. Move them into a 40°C warm water bath and continue to react for 30 min. Then slowly add 230 mL of deionized water and keep the reaction temperature at 90°C. After stirring for 5 min, add H2O2 until no bubbles are generated. Filter while hot and centrifuge them several times with deionized water and 5 wt.% hydrochloric acid until neutral. Then dry them in a 60°C drying oven for 24 h to obtain graphene oxide. S2. Preparation of chlorogenic acid-graphene aerogel Graphene oxide and chlorogenic acid were stirred at 25°C for 30 min, wherein the chlorogenic acid was a chlorogenic acid aqueous solution with a mass fraction of 70 wt.%, and then transferred to a high-pressure reactor, reacted at 180°C to 200°C and 3 MPa for 12 h to obtain a chlorogenic acid-graphene hydrogel, and then freeze-dried to obtain a chlorogenic acid-graphene aerogel; The mass ratio of graphene oxide to chlorogenic acid is 2:0.65; S3. Preparation of chlorogenic acid-phytic acid / graphene aerogel flame retardant The chlorogenic acid-graphene aerogel was immersed in a 70 wt.% phytic acid aqueous solution for 10 min, wherein the mass ratio of the chlorogenic acid-graphene aerogel to the 70 wt.% phytic acid aqueous solution was 1:3, and then placed in a vacuum drying oven at 80°C and -0.1 MPa for 15 min. This step was repeated 5 times to obtain a chlorogenic acid-phytic acid / graphene aerogel flame retardant. S4. Preparation of polyurethane material 3.5 g of flame retardant was ground into 325 mesh powder and added 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, 4.5 g of diphenylmethane diisocyanate was added to the mixed solution. After stirring for 1 min, the mixture was foamed and cured at room temperature for 2 h to obtain a polyurethane material.

2. The 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 S1, the centrifugal speed is 10000 rpm.

3. The 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 freeze-drying temperature is -65 to -50°C and the time is 72 to 85 hours.

4. The 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 S4, the stirring rate is 300 rpm.

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