Combination of polyester polyols, flame-retardant rigid polyurethane foam and their preparation methods

Abstract

This application relates to the field of polymer materials technology, and particularly to a composite polyester polyol, a flame-retardant rigid polyurethane foam, and a method for preparing the same. The composite polyester polyol comprises a first polyester polyol and an additive flame retardant; the structure of the first polyester polyol is shown in Formula I, where n is 0, 1, 2, or 3. When the composite polyester polyol of this application is prepared into rigid polyurethane foam, it can significantly reduce the peak heat release rate and the total heat release. Formula I.

Description

Technical Field

[0001] This application relates to the field of polymer materials technology, and in particular to a combination of polyester polyol, flame-retardant rigid polyurethane foam and its preparation method. Background Technology

[0002] With the development of social life and the increasing abundance of production resources, the sources of fire hazards are constantly increasing, especially the rapid development of the polyurethane insulation market for buildings and cold storage in recent years, which has brought potential fire dangers. A fire generally goes through four stages: the initial stage (ignition period), the development stage (development phase), the intense combustion stage (full combustion phase), and the extinguishing stage (final combustion phase). The best time to extinguish a fire is during the initial stage, when the fire area is smallest and the ambient temperature is low. The use of flame-retardant materials can effectively prevent the spread of flames and reduce the intensity of combustion, prolonging the time it takes for the material to reach the intense combustion stage, thus providing more time for people to escape and for firefighting and rescue efforts. Even if the fire develops into the intense combustion stage, highly effective flame-retardant materials can reduce the maximum intensity of the fire and weaken its destructive power.

[0003] Due to its organic components and highly honeycomb structure, rigid polyurethane foam is flammable. Therefore, improving its flame retardant properties is crucial in insulation applications such as construction and cold storage, as it directly relates to the safety of the material and the risk of fire. Summary of the Invention

[0004] Based on this, the first aspect of this application provides a composite polyester polyol, which aims to reduce the peak heat release rate and total heat release of rigid polyurethane foam and improve its flame retardant properties. The technical solution is as follows:

[0005] A composite polyester polyol comprising a first polyester polyol and an additive flame retardant;

[0006] The structure of the first polyester polyol is shown in Formula I: Formula I, where n is 0, 1, 2 or 3.

[0007] Compared with traditional solutions, this application has the following advantages:

[0008] The composite polyester polyol of this application includes a first polyester polyol, which, compared with ordinary polyester polyol, introduces N and P flame-retardant elements in its structure. Due to the increased electronegativity of N atoms, the electrophilicity of P atoms is increased, resulting in a decrease in electron cloud density on P atoms and enhanced Lewis acidity. This facilitates dehydration and carbonization to form a graphitic carbon layer, thus better exerting the flame-retardant effect of P-based condensed phase. At the same time, when used in conjunction with additive flame retardants, the peak heat release rate and total heat release can be significantly reduced after preparing rigid polyurethane foam.

[0009] Optionally, the functionality of the first polyester polyol is 2 to 2.3. For example, the functionality is 2, 2.1, 2.2, or 2.3.

[0010] Optionally, the hydroxyl value of the first polyester polyol is 225±5 mgKOH / g. For example, the hydroxyl value is 225±4 mgKOH / g, 225±3 mgKOH / g, 225±2 mgKOH / g, or 225±1 mgKOH / g.

[0011] Optionally, the preparation method of the first polyester polyol includes the following steps:

[0012] Phthalic anhydride, N,P-based flame-retardant polyol, and diethylene glycol undergo a ring-opening polymerization reaction in the presence of a catalyst; wherein the structure of the N,P-based flame-retardant polyol is shown in Formula II. .

[0013] Optionally, the reaction catalyst is selected from one or more of tetraethyl titanate, tetraisopropyl titanate, tetrapropyl titanate, and tetrabutyl titanate.

[0014] Optionally, the reaction conditions for the ring-opening polymerization reaction include a reaction temperature of 200℃ to 230℃. For example, reaction temperatures of 200℃, 210℃, 220℃, and 230℃.

[0015] Optionally, the reaction conditions for the ring-opening polymerization reaction include a vacuum level of 50 Mbar to 200 Mbar. For example, vacuum levels of 50 Mbar, 100 Mbar, 150 Mbar, and 200 Mbar.

[0016] Understandably, after the ring-opening polymerization reaction is completed, the reaction products are also subjected to a neutralization and purification process.

[0017] Optionally, the additive flame retardant includes chlorine-based flame retardants and phosphorus-based flame retardants. Based on the flame-retardant effect of the first polyester polyol in the P-based condensed phase, the addition of chlorine-based and phosphorus-based flame retardants further enhances the flame-retardant effect.

[0018] Optionally, the mass ratio of total phosphorus (P) in the first polyester polyol and the additive flame retardant to the mass ratio of chlorine (Cl) in the additive flame retardant is 0.5~1.25. Preferably, the mass ratio of total phosphorus (P) in the first polyester polyol and the additive flame retardant to the mass ratio of Cl (P / Cl mass ratio) is 0.7±0.05. For example, the P / Cl mass ratios are 0.65, 0.66, 0.67, 0.68, 0.69, 0.7, 0.71, 0.72, 0.73, 0.74, and 0.75. When the P / Cl mass ratio is controlled within the above range, the synergistic flame retardant effect of P-based condensed phase flame retardant, P-based flame retardant, and Cl-based flame retardant is highest, and the oxygen index reaches its relative maximum, which is beneficial for reducing the peak heat release rate and the total heat release.

[0019] Optionally, the additive flame retardant includes one or more of tris(2-chloropropyl) phosphate (TCPP), tris(2-chloroethyl) phosphate (TCEP), triethyl phosphate (TEP), and dimethyl methylphosphonate (DMMP). Preferably, the additive flame retardant includes TCPP and TEP. When TCPP and TEP are combined with the first polyester polyol, they facilitate the simultaneous exertion of flame retardant effects by the condensed phase and the gas phase, thereby improving the flame retardant performance. Optionally, the mass ratio of TCPP to TEP is (20~30):(5~15).

[0020] Optionally, the components of the composite polyester polyol may further include one or more of a foam stabilizer, a catalyst, a blowing agent, an organic acid, and water.

[0021] Optionally, the foam stabilizer is selected from silicone oils. It may be one or more of Evonik's B84806 or B84813.

[0022] Optionally, the catalyst comprises at least one of a foaming catalyst and a gel-type catalyst, and a trimer catalyst. The foaming catalyst is selected from one or more of bis(dimethylaminoethyl) ether (DMDEE), pentamethyldiethylenetriamine (PMDETA), N,N-dimethylcyclohexylamine (DMCHA), and N,N-dimethylbenzylamine (BDMA). The trimer catalyst is selected from one or more of tris(dimethylaminopropyl)hexahydrotriazine, 2-hydroxy-N,N,N-trimethyl-1-propylaminocarbamate (TMR-2), potassium acetate, potassium formate, and potassium isooctanoate.

[0023] Optionally, the organic acid is selected from one or more of formic acid, acetic acid, and alkyd. Preferably, the organic acid is selected from one or both of formic acid and acetic acid.

[0024] Optionally, the blowing agent is selected from one or more of n-pentane (NP), isopentane (IP), and cyclopentane (CP). Blowing agents are commonly used additives in polyurethane foam production. Traditional physical blowing agents are mainly chlorofluorocarbons (CFCs), but due to the ozone-depleting effect of trifluorochloromethane (CFC-11), CFCs have been completely banned in polyurethane foam production. Currently, hydrochlorofluorocarbons (HCFCs) are mainly used as blowing agents. HCFC-141B is a transitional blowing agent for polyurethane foam production, but HCFC-141B is also an ozone-depleting substance with high ozone depletion potential (ODP) and global warming potential (GWP). The production and use of HCFC blowing agents will be completely stopped by 2030. Hydrofluorocarbons (HFCs) are non-flammable and low in toxicity, but HFC-134a and HFC-152a are gaseous at room temperature, making them inconvenient to handle and unstable to store, requiring immediate foaming. Alkane compounds (HC) have an ODP value of zero, exhibiting characteristics such as minimal greenhouse effect, non-toxicity, and minimal environmental impact. Cyclopentane (CP), n-pentane (NP), and isopentane (IP) are the three most commonly used alkane blowing agents. They are liquid at room temperature and have high boiling points, facilitating storage and enabling online addition to continuous polyurethane foam boards. Using these alkane compounds offers advantages such as low cost, strong environmental friendliness, and convenient process operation. Compared to 141B, due to its higher vapor pressure and smaller molecular weight, it can rapidly vaporize in the early stages, significantly improving foam strength and ensuring foam stability.

[0025] In some embodiments, the composite polyester polyol comprises the following components in parts by weight:

[0026] 25-60 parts of the first polyester polyol

[0027] 25-40 parts of added flame retardant

[0028] 2-3 parts foam stabilizer

[0029] Catalyst 0.5~5 parts

[0030] 0.5-1.5 parts water

[0031] Organic acids 0.5~2 and

[0032] 5-10 parts of foaming agent.

[0033] The mass fraction of the first polyester polyol includes, but is not limited to, 25 parts, 35 parts, 45 parts, 50 parts, 55 parts, and 60 parts. Preferably, the mass fraction of the first polyester polyol is 45 to 60 parts.

[0034] The mass fractions of the additive flame retardant include, but are not limited to, 25 parts, 30 parts, 35 parts, 40 parts, and 45 parts.

[0035] The mass fractions of the foam stabilizer include, but are not limited to, 2 parts, 2.5 parts, and 3 parts.

[0036] The mass fractions of the catalyst include, but are not limited to, 0.5 parts, 1 part, 2 parts, 3 parts, 4 parts, and 5 parts.

[0037] The mass fractions of water include, but are not limited to, 0.5 parts, 1 part, and 1.5 parts.

[0038] The organic acid is present in parts by weight, including but not limited to 0.5 parts, 1 part, 1.5 parts, and 2 parts.

[0039] The mass fractions of the foaming agent include, but are not limited to, 5, 6, 7, 8, 9, and 10 parts.

[0040] Optionally, the composite polyester polyol may further comprise a second polyester polyol, the polymerization raw material of which includes two or more selected from phthalic anhydride, terephthalic anhydride, diethylene glycol, glycerol, trimethylolpropane, and pentaerythritol. For example, the polymerization raw material of the second polyester polyol may include two or more selected from diethylene glycol, glycerol, trimethylolpropane, and pentaerythritol, as well as phthalic anhydride; or the polymerization raw material of the second polyester polyol may include two or more selected from diethylene glycol, glycerol, trimethylolpropane, and pentaerythritol, as well as terephthalic anhydride.

[0041] Optionally, the functionality of the second polyester polyol is 2 to 2.5.

[0042] Optionally, the hydroxyl value of the second polyester polyol is 180 mg KOH / g to 300 mg KOH / g.

[0043] Optionally, the mass ratio of the second polyester polyol to the first polyester polyol is (0.1~35):(25~60).

[0044] The aforementioned composite polyester polyols not only possess excellent flame retardant properties, but also exhibit good mechanical properties.

[0045] The second aspect of this application provides a flame-retardant rigid polyurethane foam, the technical solution of which is as follows:

[0046] A flame-retardant rigid polyurethane foam, the raw materials of which include the combination of polyester polyol and isocyanate as described above.

[0047] The flame-retardant rigid polyurethane foam of this application comprises the above-mentioned blend of polyester polyols, has a low total heat release and peak heat release rate, can achieve a flame retardancy rating of B1, and has good mechanical properties.

[0048] Optionally, the isocyanate is selected from polyphenylmethane polyisocyanates. More preferably, the polyphenylmethane polyisocyanate is selected from polymeric MDI. Preferably, the NCO content in the polymeric MDI is 30wt%~32wt%. More preferably, the isocyanate is selected from one or more of Wanhua PM200, PM400, and PM700, and even more preferably, the isocyanate is selected from one of PM400 and PM700.

[0049] Optionally, the mass ratio of the combined polyester polyol and isocyanate is 1:(1.5~2). For example, the mass ratio of the combined polyester polyol and isocyanate is 1:1.5, 1:1.7, 1:1.8, or 1:2.

[0050] The third aspect of this application provides a method for preparing flame-retardant rigid polyurethane foam, the technical solution of which is as follows:

[0051] A method for preparing flame-retardant rigid polyurethane foam includes the following steps:

[0052] The mixture is obtained by mixing the combined polyester polyol and isocyanate as described above and then molding and curing it.

[0053] The combined polyester polyol and isocyanate can be mixed in a high-pressure foaming machine, and the combined polyester polyol and isocyanate are added to the high-pressure foaming machine in the above mass ratio and mixed thoroughly.

[0054] The resulting mixture can be evenly sprayed onto a moving metal plate through a cloth rod, and then enters the press mold for molding and curing.

[0055] Optionally, the molding curing temperature is 50℃~70℃.

[0056] Optionally, the molding curing time is 5 min to 20 min.

[0057] After molding and curing, flame-retardant rigid polyurethane foam is formed on the metal plate.

[0058] The above-mentioned method for preparing flame-retardant rigid polyurethane foam can be carried out on a continuous production line for polyurethane sandwich panels. The production line is mature and has low cost. Detailed Implementation

[0059] The present application will be further described in detail below with reference to specific embodiments. The present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0060] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0061] the term

[0062] Unless otherwise stated or in case of contradiction, the terms or phrases used herein shall have the following meanings:

[0063] In this application, the terms "multiple", "various", "multiple times", "multi-dimensional", etc., unless otherwise specified, refer to a quantity greater than or equal to 2. For example, "one or more" means one or more or more.

[0064] In this application, the terms "optionally," "optionally," and "optional" refer to options that are optional, meaning they can be selected from either "with" or "without." If multiple "optional" options appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" option is independent.

[0065] In this application, the terms "first aspect," "second aspect," "third aspect," and "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," and "fourth," etc., serve only a non-exhaustive enumeration purpose and should be understood not to constitute a closed limitation on quantity.

[0066] In this application, numerical intervals (i.e. numerical ranges) are involved. Unless otherwise specified, the selected numerical distributions within the above-mentioned numerical intervals are considered continuous, and include the two numerical endpoints (i.e., the minimum value and the maximum value) of the numerical range, as well as every value between the two numerical endpoints.

[0067] Unless otherwise specified, the temperature parameters in this application are permitted to be either constant-temperature treatment or variations within a certain temperature range. It should be understood that the constant-temperature treatment allows temperature fluctuations within the precision range of the instrument control, such as ±5℃, ±4℃, ±3℃, ±2℃, or ±1℃.

[0068] In this application, %(w / w) and wt% both represent weight percentage, %(v / v) refers to volume percentage, and %(w / v) refers to mass-volume percentage.

[0069] The following description, in conjunction with specific embodiments and comparative examples, will provide further details. Unless otherwise specified, all raw materials and instruments used in the following specific embodiments are commercially available. Unless otherwise specified, all processes involved are conventionally selected by those skilled in the art.

[0070] The first polyester polyol was prepared in-house. The preparation method was as follows: 296.4g of phthalic anhydride, 233.4g of diethylene glycol, and 510g of N,P-based flame-retardant polyol with the structure shown in Formula II were added to a reaction vessel. Nitrogen gas was introduced at a flow rate of 10mL / min. The temperature was raised to 200℃ and reacted for 2 hours. The temperature was then raised to 230℃ and reacted until the material was clear. 0.5g of tetrabutyl titanate catalyst was added, and the vacuum was reduced to a vacuum degree of 150mbar. The reaction was carried out for 6 hours to obtain the first polyester polyol with the structure shown in Formula I. The prepared first polyester polyol had a functionality of 2 and a hydroxyl value of 225mgKOH / g.

[0071] The polymerization raw materials for the second polyester polyol include phthalic anhydride and diethylene glycol, with a functionality of 2 and a hydroxyl value of 245 mgKOH / g, and are sourced from Stepan (Nanjing) Chemical Co., Ltd.

[0072] TCPP and TEP are additive flame retardants from Jiahe Chemical Co., Ltd.

[0073] B84806 is a silicone oil foam stabilizer from Evonik Specialty Chemicals (Shanghai) Co., Ltd.

[0074] PC5 is pentamethyldiethylenetriamine, PC8 is N,N-dimethylcyclohexylamine, and the potassium formate and potassium isooctanoate of PC5 and PC8 are all catalysts, sourced from Evonik Specialty Chemicals (Shanghai) Co., Ltd.

[0075] The organic acid mentioned is formic acid, which comes from Jinan Century Tongda Chemical Co., Ltd.

[0076] n-Pentane is a foaming agent, sourced from Yantai Haida Chemical Co., Ltd.

[0077] PM400 is a polyphenylmethane polyisocyanate sourced from Wanhua Chemical Group Co., Ltd.

[0078] Example 1

[0079] This embodiment provides a polyurethane foam and its preparation method, the steps of which are as follows:

[0080] Accurately weigh the first polyester polyol, additive flame retardant, foam stabilizer, catalyst, organic acid, and water according to the mass ratio in Table 1, and add them to the reactor. Stir at a high speed of 2000 r / min for 1 hour to mix them evenly. Then, add the foaming agent to the mixture according to the ratio to form a composite polyester polyol. Add the composite polyester polyol and PM400 to the black and white material tank of the high-pressure press, control the material temperature at 19℃~22℃ and the pressure at 100bar~120bar. Mix the composite polyester polyol and PM400 at a mass ratio of 1:1.67, and then spray the mixture evenly onto the moving metal plate through the nozzle of the high-pressure press and the mold at about 60℃ for 10 minutes to cure and form polyurethane foam board. Take samples for testing after 48 hours.

[0081] Examples 2 to 4

[0082] Examples 2 to 4 provide a polyurethane foam and its preparation method. The raw material mass ratio is shown in Table 1, and the preparation method is shown in Example 1.

[0083] Example 5

[0084] This embodiment provides a polyurethane foam and its preparation method, the steps of which are as follows:

[0085] Accurately weigh the first polyester polyol, second polyester polyol, additive flame retardant, foam stabilizer, catalyst, organic acid, and water according to the mass ratio in Table 1, and add them to the reactor. Stir at a high speed of 2000 r / min for 1 hour to mix them evenly. Then, add the foaming agent to the mixture according to the ratio to form a composite polyester polyol. Add the composite polyester polyol and PM400 to the black and white material tank of the high-pressure press, control the material temperature at 19℃~22℃ and the pressure at 100bar~120bar. Mix the composite polyester polyol and PM400 at a mass ratio of 1:1.67, and then spray the mixture evenly onto the moving metal plate through the nozzle of the high-pressure press and the mold at about 60℃ for 10 minutes to obtain polyurethane foam board. Take samples for testing after 48 hours.

[0086] Table 1

[0087]

[0088] Comparative Example 1

[0089] This comparative example provides a polyurethane foam and its preparation method, which is basically the same as that in Example 1, except that the first polyester polyol is replaced with the second polyester polyol. The steps are as follows:

[0090] According to the mass ratio in Table 2, accurately weigh the second polyester polyol, additive flame retardant, foam stabilizer, catalyst, organic acid, and water, and add them to the reactor. Stir at a high speed of 2000 r / min for 1 hour to mix them evenly. Then, add the foaming agent to the mixture in proportion to form a composite polyester polyol. Add the composite polyester polyol and PM400 to the black and white material tank of the high-pressure press, control the material temperature at 19℃~22℃ and the pressure at 100bar~120bar. Mix the composite polyester polyol and PM400 at a mass ratio of 1:1.67 and then spray the mixture evenly onto the moving metal plate through the nozzle of the high-pressure press and into the press mold at about 60℃ for 10 minutes to obtain polyurethane foam board. Take samples for testing after 48 hours.

[0091] Comparative Examples 2 to 3

[0092] Comparative Examples 2 and 3 provide a polyurethane foam and its preparation method. The raw material mass ratio is shown in Table 2, and the preparation method is shown in Comparative Example 1.

[0093] Table 2

[0094]

[0095] The polyurethane foams of the above embodiments and comparative examples were tested.

[0096] The test method for the P / Cl mass ratio is as follows: Calculate the mass of P in the first polyester polyol and the added flame retardant separately to obtain the total mass of P. Calculate the mass of Cl in the added flame retardant. The value calculated as Mp / Mcl is the P / Cl mass ratio. Foam core density is tested according to GB / T 6343-2009. Compressive strength is tested according to GB / T 8813-2008. Linear deformation at -30℃ for 48h is tested according to GB / T 8811-2008. Linear deformation at 70℃ for 48h is tested according to GB / T 8811-2008. Oxygen index is tested according to GB / T 2406.2-2009. Peak heat release rate is tested according to ISO 5660-1:2015. Total heat release is tested according to ISO 5660-1:2015.

[0097] The test results are shown in Tables 3 and 4.

[0098] Table 3

[0099]

[0100] Table 4

[0101]

[0102] As can be seen from Tables 3 and 4:

[0103] a. Introducing N,P-based flame-retardant polyester polyols can significantly improve the oxygen index and provide excellent flame-retardant performance; compared with ordinary polyester polyols, it can significantly reduce the heat release rate and total heat release, and has good mechanical properties.

[0104] b. When the P / Cl mass ratio is around 0.7, the heat release rate and total heat release can reach their lowest points, while the oxygen index is the highest, resulting in a highly efficient flame retardant effect.

[0105] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0106] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A composite polyester polyol, characterized in that, Its components include a first polyester polyol and an additive flame retardant; The structure of the first polyester polyol is shown in Formula I: Formula I, where n is 0, 1, 2, or 3; The additive flame retardant includes chlorine-based flame retardants and phosphorus-based flame retardants, and the mass ratio of the total mass of P in the first polyester polyol and the additive flame retardant to the mass of Cl in the additive flame retardant is 0.5~1.25, and the additive flame retardant includes one or more of tris(2-chloropropyl) phosphate, tris(2-chloroethyl) phosphate, triethyl phosphate and dimethyl methylphosphonate.

2. The composite polyester polyol according to claim 1, characterized in that, The first polyester polyol satisfies at least one of the following conditions: (1) The functionality of the first polyester polyol is 2 to 2.3; (2) The hydroxyl value of the first polyester polyol is 225±5mgKOH / g.

3. The composite polyester polyol according to claim 2, characterized in that, The preparation method of the first polyester polyol includes the following steps: Phthalic anhydride, N,P-based flame-retardant polyol, and diethylene glycol undergo a ring-opening polymerization reaction in the presence of a catalyst; wherein the structure of the N,P-based flame-retardant polyol is shown in Formula II. .

4. The composite polyester polyol according to claim 3, characterized in that, The reaction catalyst is selected from one or more of tetraethyl titanate, tetraisopropyl titanate, tetrapropyl titanate, and tetrabutyl titanate.

5. The composite polyester polyol according to claim 1, characterized in that, The mass ratio of the total mass of P in the first polyester polyol and the additive flame retardant to the mass of Cl in the additive flame retardant is 0.7 ± 0.

05.

6. The composite polyester polyol according to any one of claims 1 to 5, characterized in that, The components of the composite polyester polyol also include one or more of a foam stabilizer, a catalyst, a blowing agent, an organic acid, and water; the blowing agent is selected from one or more of n-pentane, isopentane, and cyclopentane.

7. The composite polyester polyol according to claim 6, characterized in that, The foam stabilizer is selected from silicone oil.

8. The composite polyester polyol according to claim 6, characterized in that, The catalyst comprises at least one of a foaming catalyst and a gel-type catalyst, as well as a trimer catalyst. The foaming catalyst is selected from one or more of bis(dimethylaminoethyl) ether, pentamethyldiethylenetriamine, N,N-dimethylcyclohexylamine, and N,N-dimethylbenzylamine. The trimer catalyst is selected from one or more of tris(dimethylaminopropyl)hexahydrotriazine, 2-hydroxy-N,N,N-trimethyl-1-propylaminocarbamate, potassium acetate, potassium formate, and potassium isooctanoate.

9. The composite polyester polyol according to claim 6, characterized in that, The organic acid is selected from one or more of formic acid, acetic acid, and alkyd.

10. The composite polyester polyol according to claim 6, characterized in that, Components comprising the following parts by weight: 25-60 parts of the first polyester polyol 25-40 parts of added flame retardant 2-3 parts foam stabilizer Catalyst 0.5~5 parts 0.5-1.5 parts water Organic acids 0.5~2 and 5-10 parts of foaming agent.

11. The composite polyester polyol according to any one of claims 1 to 5, 7 to 10, characterized in that, The composite polyester polyol further includes a second polyester polyol, the polymer raw materials of which include two or more of phthalic anhydride, terephthalic anhydride, diethylene glycol, glycerol, trimethylolpropane and pentaerythritol.

12. The composite polyester polyol according to claim 11, characterized in that, The second polyester polyol satisfies at least one of the following conditions: (1) The functionality of the second polyester polyol is 2 to 2.5; (2) The hydroxyl value of the second polyester polyol is 180mgKOH / g~300mgKOH / g.

13. A flame-retardant rigid polyurethane foam, characterized in that, Its raw materials include the combined polyester polyol and isocyanate as described in any one of claims 1 to 8.

14. The flame-retardant rigid polyurethane foam according to claim 13, characterized in that, The isocyanate is selected from polyphenylmethane polyisocyanate.

15. The flame-retardant rigid polyurethane foam according to claim 13, characterized in that, The mass ratio of the combined polyester polyol and isocyanate is 1:(1.5~2).

16. A method for preparing flame-retardant rigid polyurethane foam, characterized in that, Includes the following steps: The mixture obtained by molding and curing a combination of polyester polyol and isocyanate according to any one of claims 1 to 12.

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