Bio-based halogen-free flame-retardant rigid polyether polyol, method of making same, and rigid polyurethane foam compositions comprising same

Abstract

This invention relates to the field of polyurethane materials technology, specifically to a bio-based halogen-free flame-retardant rigid foam polyether polyol, its preparation method, and a rigid polyurethane foam composition containing the polyether polyol. Phytic acid and glycerol are esterified at a molar ratio of 1:(1-3) to obtain a phosphorus-containing reactive flame-retardant polyol initiator. This initiator is then compounded with a small molecule polyol and subjected to a staged polymerization reaction with propylene oxide under alkaline catalysis: in the first stage, 30%-40% of the total mass of propylene oxide is added at 80-85°C to obtain an intermediate; in the second stage, the temperature is raised to 100-110°C, the remaining propylene oxide is added, and polymerization continues. After post-treatment, the final product is obtained. This invention achieves efficient conversion of phytic acid through molecular structure design and polymerization process control. The resulting polyether polyol has advantages such as being halogen-free and environmentally friendly, reactive and permanently flame-retardant, having moderate viscosity, and good foaming properties.

Description

Technical Field

[0001] This invention relates to the field of polyurethane materials technology, specifically to bio-based halogen-free flame-retardant rigid foam polyether polyol, its preparation method, and rigid polyurethane foam compositions containing the polyether polyol. Background Technology

[0002] Rigid polyurethane foam (PU rigid foam) is widely used in building exterior wall insulation, cold storage energy storage, and home appliance insulation due to its good thermal insulation performance, high specific strength, and good molding processability. However, polyurethane materials are highly flammable, posing a significant fire safety hazard. Therefore, flame-retardant modification of polyurethane is an unavoidable and crucial issue.

[0003] Currently, flame retardant modification of rigid polyurethane foam is mainly divided into two categories: "additive" and "reactive." While additive flame retardants are lower in cost and simpler to process, they suffer from poor compatibility, easy migration, and insufficient flame retardant durability. Furthermore, halogenated flame retardants produce toxic and corrosive gases during combustion, which contradicts the trend towards halogen-free and environmentally friendly practices. Reactive flame retardant modification introduces flame-retardant elements into the polyether molecular chain through chemical bonds, achieving permanent flame retardancy. However, existing reactive flame-retardant polyether polyols largely rely on petroleum-based raw materials, with low bio-based content, making it difficult to meet the technical requirements for bio-based alternatives to petrochemical raw materials.

[0004] To reduce reliance on petroleum-based raw materials, the development of bio-based polyether polyols has become a research hotspot. Chinese patent application CN116178696A, published on May 30, 2023, discloses a rosin-based polyether polyol and its preparation method, using rosin glycerol ester and polyol as mixed initiators for polymerization with epoxide alkane. However, this method does not involve flame-retardant modification, and the rosin glycerol ester does not contain flame-retardant elements. Chinese patent application CN116948163A, published on October 27, 2023, discloses a dihydroxy DOPO halogen-free flame-retardant polyether polyol and its preparation method, using a synthetic phosphorus-containing compound DOPO derivative as an initiator. However, its raw material DOPO is derived from petrochemicals, resulting in weak bio-based properties. Chinese patent application CN117327266A, published on January 2, 2024, discloses a method for preparing a flame-retardant rigid foam polyether polyol with increased bio-based content. It uses epoxy oil and nitrogen-containing compounds as initiators, with a phosphorus-containing compound added later to achieve flame retardancy. However, the phosphorus element is introduced "post-addition," which easily leads to uneven distribution, and the product stability needs improvement. Chinese patent application CN109320709A, published on February 12, 2019, discloses a method for preparing reactive flame-retardant polyether polyol by phosphoric acid reaction of epoxidized soybean oil. This method introduces phosphorus through a ring-opening reaction of phosphoric acid with epoxidized soybean oil. However, the product is a phosphorylated macromolecular oil with a complex structure and wide molecular weight distribution, making it difficult to control the functionality and viscosity of the polyether when used as an initiator.

[0005] In addition, Chinese patent application CN109293910A, published on February 1, 2019, discloses a method for preparing bio-based modified rigid foam polyether polyol, which uses modified vegetable oil added in the later stages of polymerization, but it does not involve flame retardancy; Chinese patent application CN110885437A, published on March 17, 2020, discloses a method for preparing high-functionality rigid foam polyether polyol, which uses waste cooking oil for modification, but it also does not involve flame retardancy; Chinese patent application CN116120536A, published on May 16, 2023, discloses a method for preparing polylactic acid bio-based polyester polyol, but it does not involve flame retardant modification.

[0006] In summary, existing bio-based flame-retardant polyethers and related technologies generally suffer from the following technical bottlenecks: First, it is difficult to achieve a synergistic balance between flame-retardant properties, mechanical strength, and foaming flowability; second, the processes are complex, and the functionality and molecular weight distribution of the products are uncontrollable; third, the actual bio-based content is still relatively low; and fourth, the methods for introducing phosphorus-containing flame-retardant elements (such as later addition or macromolecular modification) are difficult to balance product stability and process simplicity. Therefore, there is a significant demand for developing a polyether polyol preparation method that is process-stable and controllable, possesses both high bio-based content and inherently halogen-free flame-retardant properties, and has moderate viscosity, enabling rigid polyurethane foam to exhibit certain mechanical and thermal insulation properties. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the purpose of this invention is to provide a bio-based halogen-free flame-retardant rigid foam polyether polyol. Through molecular structure design and polymerization process control, the efficient conversion of phytic acid is achieved. The prepared polyether polyol has the advantages of being halogen-free and environmentally friendly, permanently flame-retardant, having moderate viscosity, and good foaming process.

[0008] Another objective of this invention is to provide a method for preparing bio-based halogen-free flame-retardant rigid foam polyether polyols. This method is characterized by stable processes, mild reaction conditions, few side reactions, and ease of industrial production. It can achieve efficient conversion of phytic acid and glycerol esterification products, and precisely control the molecular weight, hydroxyl value, and viscosity of the products through a segmented polymerization process, thereby obtaining rigid foam polyether polyols with excellent comprehensive performance.

[0009] The third objective of this invention is to provide a composition of bio-based halogen-free flame-retardant rigid polyurethane foam polyether polyol, which comprises the above-mentioned bio-based halogen-free flame-retardant rigid polyurethane foam polyether polyol, isocyanate and foaming agent and other additives. It has good foaming process flowability and compatibility. The rigid polyurethane foam produced has high flame retardancy (high limiting oxygen index), high compressive strength, low thermal conductivity and good dimensional stability, and can be applied to building insulation, cold storage energy storage, home appliance insulation and other fields.

[0010] This invention is achieved using the following technical solution: The preparation method of the bio-based halogen-free flame-retardant rigid foam polyether polyol includes the following steps: (1) Phytic acid and glycerol are mixed in a molar ratio of 1:(1-3) to undergo esterification. After the reaction is completed, acidic substances are removed by neutralization treatment to obtain a phosphorus-containing polyol initiator. (2) The phosphorus-containing polyol initiator obtained in step (1) is compounded with a small molecule polyol to form a mixed initiator; under the action of an alkaline catalyst, the mixed initiator is subjected to a segmented polymerization reaction with propylene oxide; wherein, the temperature of the first stage polymerization reaction is 80-85℃, and the propylene oxide added in the first stage polymerization reaction accounts for 30%-40% of the total mass of propylene oxide used in the polymerization reaction; after the first stage polymerization reaction is completed, a bio-based halogen-free flame-retardant rigid foam polyether polyol intermediate is obtained. (3) Heat the reaction system obtained in step (2) to carry out the second stage of polymerization reaction, add the remaining propylene oxide dropwise to continue polymerization, and after the reaction is completed, perform post-treatment to obtain the bio-based halogen-free flame-retardant rigid foam polyether polyol.

[0011] Preferably, the small molecule polyol mentioned in step (2) is diethylene glycol; and in the mixed initiator, the mass ratio of the phosphorus-containing polyol initiator to the diethylene glycol is (4-6):1.

[0012] Phytic acid has significant steric hindrance due to its six phosphate groups. While its esterification with glycerol produces a product with good flame retardancy, its molecular skeleton is rigid and its viscosity is high. Using phytic acid alone as an initiator leads to excessively high viscosity in the final polyether, which is detrimental to subsequent polyurethane foaming processes. This invention introduces diethylene glycol for compounding. Diethylene glycol contains flexible ether bonds, which effectively improves the flowability of the initiator system and imparts a certain degree of toughness to the final polyurethane foam. By controlling the mass ratio of the two to (4-6):1, the hydroxyl value and viscosity of the product can be adjusted to a suitable range for foaming without sacrificing phosphorus content (flame retardancy).

[0013] Preferably, the esterification reaction in step (1) is carried out in the presence of an acidic catalyst and an organic solvent; the acidic catalyst is p-toluenesulfonic acid, and its amount is 0.6% to 0.8% of the total mass of phytic acid and glycerol; the organic solvent is toluene or isopropanol, and its amount is 10% to 30% of the total mass of phytic acid and glycerol; the temperature of the esterification reaction is 90 to 100°C, and the reaction time is 1 to 2 hours. The phytic acid is preferably an aqueous solution with a mass fraction ≥ 70%, and the glycerol has a purity ≥ 99.5%.

[0014] Phytic acid contains water, and water is also generated during the esterification process. This invention selects p-toluenesulfonic acid as a catalyst. Compared to strong inorganic acids (such as sulfuric acid), p-toluenesulfonic acid provides sufficient protons to catalyze esterification without causing excessive dehydration and carbonization of glycerol or carbon chain cleavage side reactions. The addition of an organic solvent (toluene or isopropanol) not only reduces the initial viscosity of the system but also acts as an azeotropic agent, promoting the forward esterification reaction at a temperature of 90–100°C and increasing the conversion rate of phytic acid.

[0015] Furthermore, after the esterification reaction described in step (1), a dehydration and neutralization process is also included: dehydration is carried out at a vacuum of -0.08 to -0.09 MPa for 2 to 3 hours; then, 1.0% to 1.5% of the total mass of the esterification product is added to KOH, and neutralization and dehydration are carried out at 80 to 90°C under vacuum for 1 to 2 hours. After filtration, the phosphorus-containing polyol initiator is obtained. This step eliminates free water in the system and neutralizes the residual acidic catalyst and the incompletely esterified phosphate hydroxyl groups, avoiding catalyst poisoning or a large number of by-products in the subsequent alkaline-catalyzed ring-opening polymerization.

[0016] Preferably, the alkaline catalyst in step (2) is selected from 2,4,6-tris(dimethylaminomethyl)phenol or dimethylamine, and its dosage is 0.7% to 0.9% of the total mass of the bio-based halogen-free flame-retardant rigid foam polyether polyol finally prepared. In step (2), the polymerization pressure of the first stage polymerization reaction is controlled at 0.1 to 0.4 MPa, and the pressure is maintained for 1 to 2 hours after the propylene oxide feed is completed; in step (3), the reaction system is heated to 100 to 110°C in the second stage polymerization reaction, the pressure is maintained at 0.1 to 0.4 MPa, the remaining propylene oxide is added dropwise, and when the reaction pressure is basically unchanged after the feed is completed, the pressure is increased to 0.2 to 0.3 MPa and the reaction continues for 2 to 3 hours; the post-treatment is to remove residual small molecules by bubbling with nitrogen and filtering.

[0017] The key process of this invention lies in the "two-stage" polymerization control of propylene oxide.

[0018] (A) Because phosphorus-containing initiators have high functionality and large steric hindrance, if conventional high-temperature single-stage drop addition is used, the initial local concentration of propylene oxide is too high, which can easily cause violent exothermic reactions, leading to uncontrolled system temperature, intensified chain transfer side reactions, and the generation of a large number of terminal unsaturated double bonds. This not only reduces the quality of polyether but also deepens the color.

[0019] (B) Therefore, the first stage of polymerization uses a relatively low temperature (80-85°C), and the amount of propylene oxide added in the first batch is strictly controlled (30%-40%). At this time, due to the low temperature, the reaction is milder, and propylene oxide can orderly combine with the sterically hindered hydroxyl groups of the initiator, uniformly "expanding" the spatial structure of the initiator molecules to form a low-polymerization-degree intermediate, thereby eliminating the steric hindrance of subsequent reactions.

[0020] (C) In the second polymerization stage, the temperature is increased to 100–110°C. At this point, since the steric hindrance of the intermediate has been eliminated, increasing the temperature can accelerate the reaction rate, promote the rapid and complete reaction of the remaining propylene oxide, and also benefit the increase in molecular weight. Through secondary polymerization at 100–110°C, the molecular weight distribution can be effectively narrowed, ensuring the stability of the viscosity and hydroxyl value of the final product.

[0021] The present invention also provides a bio-based halogen-free flame-retardant rigid foam polyether polyol prepared by the above preparation method, wherein the polyether polyol has a hydroxyl value of 240-270 mgKOH / g and a viscosity of 4000-6000 mPa·s at 25°C.

[0022] The hydroxyl value and viscosity of polyethers directly determine their reactivity and mixing state in polyurethane foaming. This invention utilizes a precise esterification ratio of phytic acid to glycerol (1:(1-3), more preferably 1:2), combined with diethylene glycol compounding and segmented polymerization, to achieve a stable hydroxyl value of 240-270 mgKOH / g in the prepared polyether. This hydroxyl value range allows for the formation of a three-dimensional network with moderate crosslinking density with isocyanate, imparting good compressive strength and low dimensional shrinkage to rigid foam. Simultaneously, the viscosity is controlled at 4000-6000 mPa·s, overcoming the pumpability limitations of traditional phosphorus-modified polyethers (often >10000 mPa·s), ensuring compatibility and emulsification dispersion with other additives and isocyanate (component B) in the foaming system, resulting in fine, uniform cells and a high closed-cell rate.

[0023] This invention also provides a rigid polyurethane foam composition comprising the above-mentioned bio-based halogen-free flame-retardant rigid foam polyether polyol, isocyanate, blowing agent, water, polyurethane catalyst, foam leveling agent, and TEP flame retardant; wherein the blowing agent is 245fa blowing agent. Specifically, by weight, it is foamed by mixing component A (white component) containing polyether polyol and other components with component B (black component) of isocyanate in a weight ratio of 1:1.

[0024] Compared with the prior art, the beneficial effects of the present invention are: (1) This invention utilizes bio-based phytic acid as a precursor, stably grafting its high phosphorus content onto the polyether molecular backbone via chemical bonds, thus belonging to an inherently reactive flame retardant. During combustion, the phosphate ester structure decomposes upon heating to generate phosphoric acid or polyphosphoric acid. These acidic substances catalyze the dehydration and carbonization reaction of the polyurethane matrix, forming a dense, expanded carbon layer on the material surface. This carbon layer has multiple functions, including heat insulation, oxygen isolation, and inhibition of combustible gas escape, thereby achieving highly efficient flame retardancy and isolating oxygen and heat transfer; at the same time, it avoids the problems of high smoke production, release of toxic and corrosive gases, and easy migration and loss of additive flame retardants, which are common with traditional halogenated flame retardants.

[0025] (2) The core starting materials of this invention are all derived from renewable natural products, which greatly replace petrochemical-based raw materials and increase the bio-based carbon content of the final polyurethane material. The raw materials used are renewable bio-based sources, and the sources are relatively wide and the cost is relatively stable.

[0026] (3) The functionality and flexibility of the polyether were precisely controlled through the synergistic design of "phytic acid-glycerol-diethylene glycol". At a specific ratio, the flame retardancy provided by the phosphate ester structure, the high crosslinking density provided by glycerol, and the flexibility provided by diethylene glycol were balanced. The prepared polyurethane rigid foam had a high limiting oxygen index, while the compressive strength, thermal conductivity and dimensional stability were kept within acceptable ranges. Compared with the existing flame retardant modification schemes, the degradation of mechanical and thermal insulation properties was improved.

[0027] (4) To address the issues of steric hindrance and the susceptibility to side reactions caused by phosphorus-containing initiators, a two-stage polymerization process of low-temperature, low-load initiation and high-temperature curing is adopted. This process has relatively mild reaction conditions and a stable exothermic process, which can reduce the risk of explosive polymerization and discoloration of the product. The resulting polyether polyol can be directly used in existing PU rigid foam production equipment. Attached Figure Description

[0028] Figure 1 This is a gel permeation chromatography (GPC) elution curve of the phosphorus-containing polyol initiator in Example 2 of the present invention; Figure 2 This is the mid-infrared spectral analysis of the phosphorus-containing polyol initiator in Example 2 of the present invention; Figure 3 This is a gel permeation chromatography (GPC) elution curve of the bio-based halogen-free flame-retardant rigid foam polyether polyol obtained in Example 2 of the present invention. Figure 4 The image shows the infrared analysis of the bio-based halogen-free flame-retardant rigid foam polyether polyol obtained in Example 2 of this invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below, combining the core mechanism and the physicochemical basis for parameter settings. The specific process mechanism and parameter range selection criteria described herein are a full discussion of the core concept of this invention.

[0030] The main sources of raw materials used in the examples and comparative examples are shown in Table 1.

[0031] Table 1: Sources of main raw materials used in the examples and comparative examples

[0032] Performance testing standards: (1) Hydroxyl value determination: Refer to GB / T12008.3-2009 "Plastic polyether polyols Part 3: Determination of hydroxyl value".

[0033] (2) Viscosity determination: Refer to GB / T12008.7-2010 "Plastic Polyether Polyols Part 7: Determination of Viscosity", and use a rotational viscometer to determine the viscosity at 25°C.

[0034] (3) Compression strength test: Refer to GB / T8813-2020 "Determination of compression properties of rigid foamed plastics", take the core sample of the test sample, and measure the compressive stress at the ultimate yield or 10% deformation. The first one shall be taken as the standard. The direction of the applied load is parallel to the direction of foam initiation.

[0035] (4) Thermal conductivity measurement: Refer to GB / T10294-2021, the sample size is 200mm×200mm×25mm, the thermal conductivity is measured at an average temperature of 10℃ and 23℃, the temperature difference is not greater than 25℃, and the thermal conductivity tester is used.

[0036] (5) Limiting oxygen index (LOI) determination: The test was conducted using a WK5155A digital display oxygen index tester, referring to GB / T2406.2-2009 "Determination of combustion behavior of plastics by oxygen index method". The cured polyurethane foam was cut into cubic samples of 150mm×10mm×10mm.

[0037] (6) Determination of dimensional change rate: Refer to GB / T8811-2021 "Test method for dimensional stability of rigid foam plastics", the sample size is 100mm×100mm×25mm, and it is placed at 80℃±2℃ for 48h to determine the dimensional change rate before and after the test.

[0038] I. Esterification reaction and synthesis stage of phosphorus-containing initiator The first step of this invention involves synthesizing a phosphorus-containing precursor using phytic acid and glycerol. Phytic acid contains six phosphate groups and exhibits significant steric hindrance.

[0039] The molar ratio of phytic acid to glycerol (1:(1~3)): If the molar ratio is less than 1:1 (i.e., too little glycerol), the large amount of unreacted phosphate hydroxyl groups in phytic acid will lead to excessive acidity and polarity of the product, making it difficult to carry out subsequent ring-opening polymerization of propylene oxide, and will also cause side reactions that result in the product turning black; if the molar ratio is greater than 1:3 (i.e., too much glycerol), it will lead to too much free glycerol in the synthesized initiator that has not participated in esterification, which will not only reduce the mass fraction of phosphorus in the final polyether (weakening the flame retardancy), but also lead to an excessively wide molecular weight distribution of the generated polyether, affecting the mechanical properties of the foam.

[0040] p-Toluenesulfonic acid (0.6%–0.8%) is used instead of strong inorganic acids because inorganic acids readily induce etherification or dehydration carbonization between glycerol molecules. The 0.6%–0.8% dosage ensures the esterification reaction rate (90–100℃, 1–2 h) while preventing the catalyst from inducing polymerization side reactions at subsequent high temperatures. After esterification, a vacuuming process and the addition of 1.0%–1.5% KOH for neutralization are necessary. Without adding KOH to neutralize the residual phosphate groups and p-toluenesulfonic acid, the acidity of the system will directly lead to the inactivation of subsequent amine (or phenolic) basic catalysts, preventing the epoxy ring-opening polymerization from proceeding.

[0041] The esterification reaction product of phytic acid and glycerol is a mixture containing multiple phosphate ester bonds and free hydroxyl groups. Its average functionality and phosphorus content can be controlled by adjusting the molar ratio of phytic acid to glycerol. As a starting agent, the overall properties of this mixture (such as hydroxyl value, acid value, and phosphorus content) can be characterized by conventional analytical methods without the need to separate individual components.

[0042] II. Initiator Formulation Stage The role and ratio of diethylene glycol in the compound (4-6):1): Phytic acid-glycerol esters, due to their multifunctional crosslinking, have highly rigid cage-like or star-shaped molecular structures, and direct polymerization can lead to polyether viscosity exceeding 10,000. This invention introduces diethylene glycol as a co-initiator. Diethylene glycol has flexible ether bonds (-COC-), which can act as an "internal plasticizer," improving the overall flowability of the initiator mixture. Simultaneously, diethylene glycol has a small molecular weight and low steric hindrance, and its hydroxyl groups have high reactivity. When used as a co-initiator in polymerization, it can introduce more flexible segments into the system, thereby balancing the viscosity increase caused by the rigid structure of phosphorus-containing initiators. The critical window for blending it with phosphorus-containing polyols in a ratio of 1:4 to 1:6 was determined through extensive experimental screening: if the ratio is less than 1:6 (too little diethylene glycol), the viscosity reduction and flexibility enhancement effects are not obvious, the product viscosity is still too high, and the foam is brittle; if the ratio is greater than 1:4 (too much diethylene glycol), it will cause a sharp decrease in the average functionality of the system, and the crosslinking density of the generated rigid polyurethane foam will be insufficient, resulting in low compressive strength and large dimensional shrinkage, which cannot meet the requirements of rigid foam.

[0043] III. Core Segmented Polymerization Process The ring-opening polymerization of propylene oxide (PO) is the core step of this invention. Because the initiator system contains large-volume phosphorus-containing groups, it has a steric shielding effect against the attack of propylene oxide, making it prone to localized overheating and explosive polymerization using the traditional single-stage continuous dropwise addition method. Therefore, this invention strictly defines a two-stage polymerization process: The first stage of polymerization (initiating chain extension stage): the temperature is strictly controlled at 80-85℃, and the added propylene oxide accounts for 30%-40% of the total amount.

[0044] 80–85℃ is a mild polymerization temperature, effectively preventing localized and intense exothermic reactions caused by insufficient diffusion of PO. At this temperature, 30%–40% of the total PO is slowly added dropwise. The first stage of polymerization uses a relatively low temperature (80–85℃), and the initial amount of propylene oxide is controlled (30%–40%). Under these conditions, the ring-opening polymerization of propylene oxide is relatively mild, preferentially reacting with sterically less hindered hydroxyl groups (such as primary hydroxyl groups) in the initiator molecule to generate short polyether chains with low polymerization degrees. As the polyether chain grows, the active center gradually extends from the initiator core to the end of the flexible polyether chain, effectively reducing the steric shielding effect of the initiator core and creating favorable conditions for the subsequent high-temperature rapid polymerization. If the temperature of the first stage is higher than 85℃, the system will overheat and the pressure will rise sharply due to the rapid reaction, which may cause danger and may also generate unsaturated end groups. If the proportion of PO added in the first stage is less than 30%, it is not enough to fully "expand" all the rigid sites. If it is higher than 40%, too much unreacted free PO will accumulate at low temperature, which may cause runaway polymerization when the temperature is raised in the future.

[0045] Second stage of polymerization (maturation and growth stage): The temperature is raised to 100-110℃, the remaining PO is added dropwise and the pressure is increased to 0.2-0.3 MPa to continue the reaction.

[0046] After the first stage of polymerization, the steric hindrance of the intermediate has been eliminated. Increasing the temperature to 100–110°C at this point significantly improves the reaction kinetic constant, promoting rapid and complete ring-opening polymerization of the remaining propylene oxide to achieve the target molecular weight increase. This temperature ensures the highest reaction conversion rate while effectively narrowing the molecular weight distribution of the product.

[0047] IV. Product Specifications and Composition Based on the above-described precisely controlled preparation method, the polyether polyol obtained by this invention has a stable hydroxyl value of 240–270 mg KOH / g and a stable viscosity of 4000–6000 mPa·s at 25°C.

[0048] When this polyether is combined with isocyanate and other additives (such as a combination of 245fa foaming agent, TEP, water, and foam leveling agent), the viscosity of 4000-6000 mPa·s ensures the fluidity of component A (white component), allowing it to achieve nanoscale molecular uniformity with component B (black component, isocyanate) within a very short stirring time (usually within a few seconds). The hydroxyl value of 240-270 mgKOH / g ensures reactivity (avoiding foam collapse) and endows the foamed polyurethane material with a high-density three-dimensional network skeleton, which macroscopically manifests as good closed-cell rate, low thermal conductivity, and long-term dimensional stability. At the same time, the phosphorus element in the skeleton achieves long-lasting intrinsic flame retardancy.

[0049] In the following embodiments, the foaming temperature conditions are: ambient temperature 22°C; material temperature 22°C; mold temperature 45°C.

[0050] The theoretical phosphorus content in phosphorus-containing polyol initiators is as follows: The theoretical phosphorus content is approximately 25.30% when phytic acid:glycerol = 1:1; approximately 22.96% when phytic acid:glycerol = 1:2; and approximately 21.02% when phytic acid:glycerol = 1:3.

[0051] The preparation method and composition of the present invention will be described in detail below with reference to specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0052] Example 1 The present invention will be further described below with reference to embodiments and comparative examples. Unless otherwise specified, the raw materials used in the embodiments are all commercially available conventional raw materials: (1) In a reaction vessel, phytic acid and glycerol are mixed in a molar ratio of 1:1. 0.6% of the total mass of p-toluenesulfonic acid is added as a catalyst, and 10% of the total mass of toluene solvent is added. The esterification reaction is carried out at 90°C with a stirring rate of 200 r / min for 1 h. The vacuum degree is controlled at -0.08 MPa for 2 h of dehydration. 1.0% of the total mass of the esterification product of KOH is added. The reaction is neutralized and dehydrated at 80°C under vacuum for 1 h. The phosphorus-containing polyol initiator is obtained by filtration. (2) Add 712g of phosphorus-containing bio-based polyol initiator and 178g of diethylene glycol to the reactor, add 13g of 2,4,6-tris(dimethylaminomethyl)phenol as an alkaline catalyst, heat to 82℃, control the pressure at 0.25MPa, add 282g of propylene oxide dropwise for polymerization, and hold the pressure for 1.5h after the feed is completed to obtain the intermediate; (3) Heat to 105℃ and maintain pressure at 0.25MPa, add the remaining 658g of propylene oxide dropwise. After the feed is completed, pressurize to 0.25MPa and react for 2.5h. Finally, remove residual small molecules by bubbling with nitrogen gas, and filter to obtain bio-based halogen-free flame-retardant rigid foam polyether polyol. The total mass of the polyether polyol is 1843g, and the bio-based content is about 38.6%.

[0053] Example 2 (1) In a reaction vessel, phytic acid and glycerol were mixed at a molar ratio of 1:2. 0.7% of the total mass of p-toluenesulfonic acid was added as a catalyst, and 20% of the total mass of toluene solvent was added. The esterification reaction was carried out at 95°C with a stirring rate of 250 r / min for 1.5 h. The vacuum degree was controlled at -0.085 MPa for dehydration for 2.5 h. 1.25% of the total mass of the esterification product of KOH was added. The mixture was neutralized and dehydrated at 85°C under vacuum for 1.5 h. The phosphorus-containing polyol initiator was obtained by filtration. (2) Add 712g of phosphorus-containing bio-based polyol initiator and 142g of diethylene glycol to the reactor, add 11g of dimethylamine as an alkaline catalyst, heat to 80℃, control the pressure at 0.1MPa, add 184g of propylene oxide dropwise for polymerization, and hold the pressure for 2h after the feed is completed to obtain the intermediate. (3) Heat to 100℃, maintain pressure at 0.1MPa, add the remaining 342g of propylene oxide dropwise, and after the feed is completed, pressurize to 0.2MPa and react for 3h. Finally, remove residual small molecules by bubbling with nitrogen gas, and filter to obtain bio-based halogen-free flame-retardant rigid foam polyether polyol. The total mass of polyether polyol is 1391g, and the bio-based content is about 51.2%.

[0054] The average molecular weight of the phosphorus-containing polyol initiator in Example 2 is shown in Table 2; the chromatographic peak retention time range of the phosphorus-containing polyol initiator in Example 2 is shown in Table 3; the chromatographic peak parameters of the phosphorus-containing polyol initiator in Example 2 are shown in Table 4; the gel permeation chromatography (GPC) elution curve of the phosphorus-containing polyol initiator in Example 2 is shown in Table 4. Figure 1 The mid-infrared spectroscopy analysis of the phosphorus-containing polyol initiator in Example 2 is shown below. Figure 2 The average molecular weight of the bio-based halogen-free flame-retardant rigid foam polyether polyols obtained in Example 2 is shown in Table 5; the retention time range of the chromatographic peaks of the bio-based halogen-free flame-retardant rigid foam polyether polyols obtained in Example 2 is shown in Table 6; the chromatographic peak parameters of the bio-based halogen-free flame-retardant rigid foam polyether polyols obtained in Example 2 are shown in Table 7; the gel permeation chromatography (GPC) elution curve of the bio-based halogen-free flame-retardant rigid foam polyether polyols obtained in Example 2 is shown in Table 7. Figure 3 The infrared analysis chromatogram of the bio-based halogen-free flame-retardant rigid foam polyether polyol obtained in Example 2 is shown below. Figure 4 .

[0055] Table 2: Average molecular weight of phosphorus-containing polyol initiators in Example 2

[0056] Table 3: Retention time ranges of chromatographic peaks for the phosphorus-containing polyol initiator in Example 2

[0057] Table 4: Chromatographic peak parameters of the phosphorus-containing polyol initiator in Example 2

[0058] Table 5: Average molecular weight of the bio-based halogen-free flame-retardant rigid foam polyether polyols obtained in Example 2

[0059] Table 6: Retention time ranges of chromatographic peaks of the bio-based halogen-free flame-retardant rigid foam polyether polyols obtained in Example 2

[0060] Table 7: Chromatographic peak parameters of the bio-based halogen-free flame-retardant rigid foam polyether polyol obtained in Example 2

[0061] from Figure 1-4 As can be seen from the data, after esterification of phytic acid and glycerol at a molar ratio of 1:2, the molecular weight of the resulting phosphorus-containing polyol initiator is highly consistent with the theoretical value, exhibiting a narrow molecular weight distribution and a clear POC characteristic peak in the infrared spectrum, proving that the esterification reaction proceeded successfully with few side reactions. When this initiator was combined with diethylene glycol to polymerize propylene oxide, the molecular weight of the product increased to Mn = 1255 g / mol, the distribution index further narrowed, and the COC characteristic peak of the polyether in the infrared spectrum was enhanced, proving that the ring-opening polymerization of propylene oxide was successful and the chain growth process was stable and controllable. The POC and P=O characteristic peaks in the infrared spectrum remained stable in the final product, proving that the phosphorus-based flame-retardant units were not destroyed during the entire preparation process, constructing a bio-based polyether polyol with both high reactivity and phosphorus-based flame-retardant function. From the initiator to the final polyether, the molecular weight distribution remained narrow throughout, with no obvious by-product peaks, proving that the entire preparation process was stable, reliable, and highly efficient.

[0062] Example 3 (1) In a reaction vessel, phytic acid and glycerol were mixed at a molar ratio of 1:3. 0.8% of the total mass of p-toluenesulfonic acid was added as a catalyst, and 30% of the total mass of isopropanol was added as solvent. The esterification reaction was carried out at 100°C with a stirring rate of 300 r / min for 2 h. The vacuum degree was controlled at -0.09 MPa for 3 h to dehydrate. 1.5% of the total mass of the esterification product of KOH was added, and the mixture was neutralized and dehydrated at 90°C under vacuum for 2 h. The phosphorus-containing polyol initiator was obtained by filtration. (2) 712g of phosphorus-containing bio-based polyol initiator and 118g of diethylene glycol were added to the reactor, and 9.4g of 2,4,6-tris(dimethylaminomethyl)phenol was added as an alkaline catalyst. The temperature was raised to 85℃ and the pressure was controlled at 0.4MPa. 82g of propylene oxide was added dropwise for polymerization. After the feeding was completed, the pressure was maintained for 1h to obtain the intermediate. (3) Heat to 110℃, maintain pressure at 0.4MPa, add the remaining 124g of propylene oxide dropwise, and after the feed is completed, pressurize to 0.3MPa and react for 2h. Finally, remove residual small molecules by bubbling with nitrogen, and filter to obtain bio-based halogen-free flame-retardant rigid foam polyether polyol. The total mass of polyether polyol is 1045.4g, and the bio-based content is about 68.1%.

[0063] Comparative Example 1 (1) In a reaction vessel, phytic acid and glycerol were mixed at a molar ratio of 1:4. 0.7% of the total mass of p-toluenesulfonic acid was added as a catalyst, and 20% of the total mass of toluene solvent was added. The esterification reaction was carried out at 95°C for 1.5 h. The vacuum degree was controlled at -0.085 MPa for 2.5 h of dehydration. 1.25% of the total mass of the esterification product of KOH was added. The mixture was neutralized and dehydrated at 85°C under vacuum for 1.5 h. The phosphorus-containing polyol initiator was obtained by filtration. (2) Add 712g of phosphorus-containing bio-based polyol initiator and 142g of diethylene glycol to the reactor, add 9.4g of dimethylamine as an alkaline catalyst, heat to 80℃, control the pressure at 0.1MPa, add 92g of propylene oxide dropwise for polymerization, and hold the pressure for 2h after the feeding is completed to obtain the intermediate. (3) Heat to 100℃, maintain pressure at 0.1MPa, add the remaining 214g of propylene oxide, pressurize to 0.2MPa after feeding, react for 3h, finally remove residual small molecules by nitrogen bubbling, and obtain bio-based halogen-free flame-retardant rigid foam polyether polyol after filtration.

[0064] Comparative Example 2 (1) In a reaction vessel, phytic acid and glycerol were mixed at a molar ratio of 1:2. 0.7% of the total mass of p-toluenesulfonic acid was added as a catalyst, and 20% of the total mass of toluene solvent was added. The esterification reaction was carried out at 95°C for 1.5 h. The vacuum degree was controlled at -0.085 MPa for 2.5 h of dehydration. 1.0% of the total mass of the esterification product of KOH was added. The mixture was neutralized and dehydrated at 80°C under vacuum for 1 h. The phosphorus-containing polyol initiator was obtained by filtration. (2) Add 712g of phosphorus-containing bio-based polyol initiator and 236g of diethylene glycol to the reactor, add 14.2g of dimethylamine as an alkaline catalyst, heat to 80℃, control the pressure at 0.1MPa, add 248g of propylene oxide dropwise for polymerization, and hold the pressure for 2h after the feed is completed to obtain the intermediate. (3) Heat to 100℃, maintain pressure at 0.1MPa, add the remaining 580g of propylene oxide, pressurize to 0.2MPa after feeding, react for 3h, finally remove residual small molecules by nitrogen bubbling, and obtain bio-based halogen-free flame-retardant rigid foam polyether polyol after filtration.

[0065] Comparative Example 3 (1) Using a conventional petroleum-based polyol system, without adding phytic acid and glycerol, without esterification reaction, glycerol and diethylene glycol are directly used as mixed initiators. 236g of diethylene glycol and 200g of glycerol are added to the reactor, and 17.4g of 2,4,6-tris(dimethylaminomethyl)phenol is added as an alkaline catalyst. The temperature is raised to 80℃, the pressure is controlled at 0.1MPa, and 520g of propylene oxide is added dropwise for polymerization. After the feeding is completed, the pressure is maintained for 2h to obtain the intermediate. (2) Heat to 100℃, maintain pressure at 0.1MPa, add the remaining 1214g of propylene oxide, pressurize to 0.2MPa after feeding, react for 3h, and finally remove residual small molecules by bubbling with nitrogen to obtain ordinary petroleum-based rigid foam polyether polyol.

[0066] Comparative Example 4 (1) In a reaction vessel, dihydroxy DOPO (10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide, CAS No. 99208-50-1) and glycerol were mixed in a molar ratio of 1:2. 0.7% of the total mass of p-toluenesulfonic acid was added as a catalyst, and 20% of the total mass of toluene solvent was added. The esterification reaction was carried out at 95°C with a stirring rate of 250 r / min for 1.5 h. The vacuum degree was controlled at -0.085 MPa for dehydration for 2.5 h. 1.25% of the total mass of the esterification product of KOH was added, and the product was neutralized and dehydrated at 85°C under vacuum for 1.5 h. The phosphorus-containing polyol initiator was obtained by filtration.

[0067] (2) Add 712g of the above-mentioned phosphorus-containing polyol initiator and 142g of diethylene glycol to the reactor, add 11g of dimethylamine as an alkaline catalyst, heat to 80℃, control the pressure at 0.1MPa, add 420g of propylene oxide for polymerization, and hold the pressure for 2h after the feeding is completed to obtain the intermediate.

[0068] (3) Heat to 100℃, maintain pressure at 0.1MPa, add the remaining 780g of propylene oxide, pressurize to 0.2MPa after feeding, react for 3h, finally remove residual small molecules by bubbling with nitrogen, and obtain DOPO-based flame-retardant polyether polyol after filtration.

[0069] Test results: The DOPO-based polyether polyol had a hydroxyl value of 238 mg KOH / g and a viscosity of 7850 mPa·s at 25°C, significantly higher than that of the embodiment of this invention (viscosity ≤ 6000 mPa·s). It exhibited poor flowability during foaming, with a foam compressive strength of only 0.19 MPa and an oxygen index of 25.1%. These results indicate that the rigid phenanthrene ring structure of the DOPO derivative leads to an increase in polyether viscosity.

[0070] Comparative Example 5 (1) Dissolve 100g of epoxidized soybean oil (epoxidation value: about 6.2%, Qilu Lanfan: LF-ESO) in 30g of acetone, and add it dropwise to a solution containing 10g of phosphoric acid and 30g of acetone under nitrogen protection. The reaction temperature is 90℃, the dropping rate is 1g / min, and the reaction continues for 3h after the addition is completed. Remove the solvent to obtain phosphorylated epoxidized soybean oil. Then add triethanolamine to adjust the pH to 13.

[0071] (2) Mix 400g of phosphorylated epoxidized soybean oil with 142g of diethylene glycol and 11g of dimethylamine, heat to 80℃, control the pressure at 0.1MPa, add 184g of propylene oxide for polymerization, and hold the pressure for 2 hours after feeding to obtain the intermediate.

[0072] (3) Heat to 100℃, maintain pressure at 0.1MPa, add the remaining 342g of propylene oxide, pressurize to 0.2MPa after feeding, react for 3h, and finally remove residual small molecules by bubbling with nitrogen. After filtration, obtain phosphorylated soybean oil-based polyether polyol.

[0073] Test results: The polyether polyol had a hydroxyl value of 215 mg KOH / g, a viscosity of 9320 mPa·s at 25℃, and appeared cloudy. It separated into layers after standing for 24 hours. The foam compressive strength after foaming was only 0.11 MPa, and the oxygen index was 22.3%. These results indicate that phosphorylated epoxidized soybean oil, as a macromolecular modifier, has poor compatibility with the initiator system, resulting in poor product stability and making it impossible to obtain a uniform and stable polyether polyol.

[0074] Comparative Example 6 (1) Prepare a phosphorus-containing polyol initiator by following the same steps (1) as in Example 2.

[0075] (2) Add 712g of phosphorus-containing bio-based polyol initiator and 142g of diethylene glycol to the reactor, add 11g of dimethylamine as an alkaline catalyst, heat to 100℃, control the pressure at 0.1MPa, and continuously add 526g of propylene oxide (without distinguishing between the first and second stages) dropwise. After the addition is complete, maintain the pressure for 2 hours to obtain the intermediate. Then, remove the residual small molecules by bubbling with nitrogen, and obtain the polyether polyol after filtration.

[0076] Test results: The polyether polyol had a hydroxyl value of 251 mg KOH / g, a viscosity of 6850 mPa·s at 25℃, and a dark brown appearance (significantly darker than in Example 2). The foamed product had a compressive strength of 0.16 MPa and an oxygen index of 24.5%. The results indicate that without a segmented polymerization process, localized overheating during the reaction exacerbated side reactions, resulting in a darker product color, increased viscosity, and a decrease in both the foam's mechanical properties and flame retardant properties.

[0077] Comparative Example 7 (1) Same as step (1) in Example 2, but after esterification and dehydration, KOH is not added for neutralization and dehydration, and the phosphorus-containing polyol initiator is obtained directly by filtration.

[0078] (2) The remaining steps are the same as steps (2) and (3) in Example 2.

[0079] Test results: After adding the alkaline catalyst in step (2), the reaction system could not initiate polymerization normally. After a long reaction period, the pressure did not change, and the final product had a hydroxyl value of only 182 mg KOH / g and a low viscosity (1250 mPa·s). A large amount of unreacted propylene oxide remained. The results indicate that if neutralization is not carried out, the residual acidic substances will poison the alkaline catalyst, and the ring-opening polymerization of propylene oxide cannot proceed.

[0080] The test results of the indicators for Examples 1-3 and Comparative Examples 1-7 are shown in Table 8 below: Table 8: Test results of indicators for Examples 1-3 and Comparative Examples 1-7

[0081] Examples 1-3 and Comparative Examples 1-7 were prepared according to the following mass ratio: polyether polyol: 100 parts; water: 1.5 parts; catalyst (N,N-dimethylcyclohexylamine): 1 part; foaming agent: 2 parts; TEP flame retardant: 10 parts; 245fa foaming agent: 28 parts; component A was prepared; component B, PM200, was a commercially available product from Wanhua Chemical (Yantai) Sales Co., Ltd., with an NCO content of 31.26% and a viscosity of 200 mPa.s / 25℃. Components A and B were mixed evenly in a 1:1 ratio and then foamed to obtain rigid polyether polyol samples.

[0082] The performance test results of rigid polyurethane foams in Examples 1-3 and Comparative Examples 1-7 are shown in Table 9.

[0083] Table 9: Performance test results of rigid polyurethane foam in Examples 1-3 and Comparative Examples 1-7

[0084] As shown in Table 9, the foam performance is best when the molar ratio of phytic acid to glycerol is 1:2. The fundamental reason for this is that the microstructure, cross-linking density, phosphorus content, and bio-based content achieve an optimal synergistic balance. At the 1:2 ratio, the phosphorus-based flame-retardant units provided by phytic acid and the long chains of bio-based polyols provided by glycerol are well-matched, the cross-linking density of the system is moderate, and the resulting cells are small, uniform, and have a high closed-cell rate. Therefore, the compressive strength, dimensional change rate, thermal conductivity, and flame retardancy are all at their best simultaneously.

[0085] When the molar ratio of phytic acid to glycerol is 1:1, the product has high functionality and high phosphorus content, resulting in strong flame retardancy, but also significant acid residue and high viscosity. When the molar ratio of phytic acid to glycerol is 1:3, excess glycerol reduces phosphorus content and increases hydroxyl groups, leading to good polyether flowability and easy polymerization, but also a decrease in flame retardancy. The differences among these three products are determined by functionality, phosphorus content, and system activity. Comparative Example 3 is a conventional petroleum-based rigid polyether, lacking a phosphorus-based flame-retardant structure and having zero bio-based content. It exhibits large pores, low closed-cell rate, and slight shrinkage at high temperatures, with overall performance far inferior to the embodiments of this invention. Only at a ratio of 1:2, with a suitable phytic acid to glycerol ratio and sufficient esterification reaction, can the phosphorus content, bio-based content, crosslinking density, and pore microstructure be balanced, which is beneficial for preparing rigid polyurethane foam with good processability and performance.

Claims

1. A method for preparing a bio-based halogen-free flame-retardant rigid foam polyether polyol, characterized in that, Includes the following steps: (1) Phytic acid and glycerol are mixed in a molar ratio of 1:(1-3) to undergo esterification. After the reaction is completed, acidic substances are removed by neutralization treatment to obtain a phosphorus-containing polyol initiator. (2) The phosphorus-containing polyol initiator obtained in step (1) is compounded with a small molecule polyol to form a mixed initiator; under the action of an alkaline catalyst, the mixed initiator is subjected to a segmented polymerization reaction with propylene oxide; wherein, the temperature of the first stage polymerization reaction is 80-85℃, and the propylene oxide added in the first stage polymerization reaction accounts for 30%-40% of the total mass of propylene oxide used in the polymerization reaction; after the first stage polymerization reaction is completed, a bio-based halogen-free flame-retardant rigid foam polyether polyol intermediate is obtained. (3) Heat the reaction system obtained in step (2) to carry out the second stage of polymerization reaction, add the remaining propylene oxide dropwise to continue polymerization, and after the reaction is completed, perform post-treatment to obtain the bio-based halogen-free flame-retardant rigid foam polyether polyol.

2. The method for preparing bio-based halogen-free flame-retardant rigid foam polyether polyol according to claim 1, characterized in that, The small molecule polyol mentioned in step (2) is diethylene glycol; and in the mixed initiator, the mass ratio of the phosphorus-containing polyol initiator to the diethylene glycol is (4-6):

1.

3. The method for preparing bio-based halogen-free flame-retardant rigid foam polyether polyol according to claim 1, characterized in that, The esterification reaction in step (1) is carried out in the presence of an acidic catalyst and an organic solvent; the acidic catalyst is p-toluenesulfonic acid, and its amount is 0.6% to 0.8% of the total mass of phytic acid and glycerol; the organic solvent is toluene or isopropanol, and its amount is 10% to 30% of the total mass of phytic acid and glycerol; the temperature of the esterification reaction is 90 to 100°C, and the reaction time is 1 to 2 hours.

4. The method for preparing bio-based halogen-free flame-retardant rigid foam polyether polyol according to claim 3, characterized in that, The esterification reaction described in step (1) further includes a dehydration and neutralization process: the vacuum degree is controlled at -0.08 to -0.09 MPa for 2 to 3 hours of dehydration; then 1.0% to 1.5% of the total mass of the esterification product of KOH is added, and the mixture is neutralized and dehydrated under vacuum conditions at 80 to 90°C for 1 to 2 hours. After filtration, the phosphorus-containing polyol initiator is obtained.

5. The method for preparing bio-based halogen-free flame-retardant rigid foam polyether polyol according to claim 1, characterized in that, The alkaline catalyst mentioned in step (2) is selected from 2,4,6-tris(dimethylaminomethyl)phenol or dimethylamine, and its amount is 0.7% to 0.9% of the total mass of the bio-based halogen-free flame-retardant rigid foam polyether polyol finally prepared.

6. The method for preparing bio-based halogen-free flame-retardant rigid foam polyether polyol according to claim 1, characterized in that, In step (2), the polymerization pressure of the first polymerization reaction is controlled at 0.1-0.4 MPa, and the pressure is maintained for 1-2 hours after the propylene oxide feed is completed; In step (3), the second polymerization reaction heats the reaction system to 100-110°C, maintains the pressure at 0.1-0.4 MPa, and adds the remaining propylene oxide dropwise. After the feed is completed and the reaction pressure remains basically unchanged, the pressure is increased to 0.2-0.3 MPa and the reaction continues for 2-3 hours. The post-treatment is to remove residual small molecules by bubbling with nitrogen and then filtering.

7. A bio-based halogen-free flame-retardant rigid foam polyether polyol, characterized in that, The polyether polyol is prepared by the method for preparing bio-based halogen-free flame-retardant rigid foam polyether polyol according to any one of claims 1-6; The polyether polyol has a hydroxyl value of 240–270 mg KOH / g and a viscosity of 4000–6000 mPa·s at 25°C.

8. A rigid polyurethane foam composition, characterized in that, It comprises the bio-based halogen-free flame-retardant rigid foam polyether polyol, isocyanate, blowing agent, water, polyurethane catalyst, foam leveling agent, and TEP flame retardant as described in claim 7; the blowing agent is 245fa blowing agent.

9. The rigid polyurethane foam composition according to claim 8, characterized in that, The composition comprises component A and component B, wherein the mass ratio of component A to component B is 1:1; By mass, material A comprises the following components: 100 parts of the polyether polyol of claim 7, 1.5 parts of water, 1 part of polyurethane catalyst, 2 parts of foam stabilizer, 10 parts of TEP flame retardant, and 28 parts of 245fa foaming agent. Material B is isocyanate.

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