Preparation method of flame composite yellowing resistant and low-odor polyurethane sponge

Abstract

The invention discloses a preparation method of flame-resistant composite yellowing and low-odor polyurethane sponge, and relates to the technical field of polyurethane materials.The method comprises the steps of preparation of a supramolecular functional precursor and a polyol mixture, mixed foaming and curing, and the supramolecular functional precursor is of a core-shell structure; an inner core is a cyclodextrin derivative modified by an amine recognition group, a shell is a hindered phenol unit containing a long alkyl chain and connected to the outer edge of the inner core through a thermosensitive linking bond, the precursor is mixed with polyether polyol, a catalyst, a foam stabilizer and water to form a polyol mixture, then the polyol mixture and polyisocyanate are mixed and foamed according to a specific isocyanate index, and the polyurethane foam material is obtained. And curing to obtain the target sponge. When the sponge is laminated and attached to PVC artificial leather in the flame compounding process, yellowing and peculiar smell can be effectively inhibited, good appearance stability and smell safety are kept, and meanwhile the sponge has excellent rebound resilience and machinability.

Description

Technical Field

[0001] This invention relates to the field of polyurethane materials technology, specifically to a method for preparing a flame-resistant, low-odor polyurethane foam that exhibits composite yellowing resistance. Background Technology

[0002] Polyurethane foam, due to its excellent resilience, softness, and processability, is widely used in automotive interiors, furniture, and home furnishings. In these applications, flame lamination is often used to quickly and efficiently bond polyurethane foam to surface materials such as PVC artificial leather. This process utilizes a flash flame to melt the surface of the foam, thereby achieving adhesion to the leather. However, the extreme high-temperature conditions during flame lamination present a significant technical challenge.

[0003] Numerous attempts have been made in this field to improve the appearance stability and odor of polyurethane products. For example, in addressing the yellowing problem of sponges, some technical solutions focus on adding conventional antioxidant and light stabilizer systems to resist oxidative aging under light and at room temperature. Regarding odor control, some existing technologies aim to reduce the release of small-molecule volatiles from foam under normal usage conditions by using specific polyether polyol mixtures and controlling the isocyanate index. However, these existing technical solutions have significant limitations. First, regarding the yellowing problem, ordinary antioxidants are prone to self-decomposition or inactivation under the instantaneous high temperatures encountered during flame lamination. This not only fails to effectively prevent the migration of substances such as amines released during thermal decomposition of the sponge matrix, but the decomposition products themselves may also become new chromophores. Second, regarding the odor problem, formulation designs aimed at reducing normal odors cannot cope with the small-molecule odor substances produced by the new round of intense chemical reactions triggered by the high temperature of the flame. More importantly, existing technologies often treat yellowing and odor as two separate issues, using physical blending of multiple functional additives. However, under extreme conditions, the components may have poor compatibility, delayed response, or mutual interference, making it difficult to form a synergistic, efficient, and stable protection in the specific and harsh temporal and spatial scenario of flame composite.

[0004] Therefore, the technical problem this invention aims to solve is: how to design a polyurethane foam specifically for flame lamination processes, so that when subjected to the instantaneous high temperature of a flame, it can fundamentally inhibit the migration and contamination of alkaline amines and oxidized chromophores generated within the foam due to thermal oxidation to the surface of PVC leather, thereby effectively preventing irreversible yellowing of the leather interface after lamination, and simultaneously controlling the odor generated during this process. The key to this problem lies in the need for a dynamic mechanism that can intelligently respond to the high temperature of a flame and actively play a synergistic interception role along the contamination migration path, rather than the simple static addition of various additives. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for preparing flame-resistant, low-odor polyurethane foam. By designing a core-shell structured supramolecular functional precursor, the core captures amine substances generated under high temperatures during flame lamination, while the outer shell releases hindered phenolic units at high temperatures via thermosensitive linkages, forming a dynamic synergistic protection that inhibits yellowing and odor from the source. This provides a polyurethane foam preparation scheme adapted to flame lamination processes.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: On one hand, a method for preparing flame-resistant, yellowing-resistant, low-odor polyurethane foam, the method comprising the following steps:

[0007] Step 1, Preparation of supramolecular functional precursor: The supramolecular functional precursor is a core-shell structure molecule consisting of a core and a shell. The core is a cyclodextrin derivative modified with an amine recognition group, and the shell is a plurality of hindered phenol units containing long alkyl chains connected to the outer edge of the core by thermosensitive linkages.

[0008] Step 2, preparation of polyol mixture: The polyether polyol, the supramolecular functional precursor prepared in Step 1, the catalyst, the foam stabilizer, and water are mixed at room temperature and stirred evenly to form a polyol mixture. The amount of supramolecular functional precursor added is 0.5% to 2.0% of the total mass of the polyurethane foam.

[0009] Step 3, Mixing and foaming: The polyol mixture obtained in Step 2 is rapidly mixed with the polyisocyanate at an isocyanate index of 1:0.4 to 1:0.6, and then injected into a mold for free foaming;

[0010] Step 4, Curing: Place the foamed polyurethane sponge product in a curing room at 90℃ to 120℃ for 1 to 3 hours, and then let it stand at room temperature for more than 24 hours to obtain flame-resistant, yellowing-resistant, low-odor polyurethane sponge.

[0011] Further, in step one, the cyclodextrin derivative modified with an amine recognition group, wherein the amine recognition group is a crown ether unit or an azacrown ether unit, and the cyclodextrin is selected from at least one of α-cyclodextrin, β-cyclodextrin, or γ-cyclodextrin, and the modification refers to the amine recognition group being chemically grafted onto the secondary hydroxyl position in the cyclodextrin molecule structure.

[0012] Furthermore, in step one, the thermosensitive linking bond is selected from at least one of disulfide bonds and thermally unstable specific ester bonds, the long alkyl chain is a straight-chain alkyl group with 8 to 18 carbon atoms, and the structure of the hindered phenolic unit is selected from at least one of 2,6-di-tert-butyl-4-methylphenol structure and β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate structure.

[0013] Furthermore, in step one, the method for synthesizing the supramolecular functional precursor includes the following steps:

[0014] First, cyclodextrin is reacted with a modifier containing an amine recognition group under the action of an alkaline catalyst to obtain a modified cyclodextrin intermediate.

[0015] Then, the modified cyclodextrin intermediate and a compound containing a long alkyl chain and a hindered phenolic structure with a terminal reactive functional group corresponding to the thermosensitive link bond are subjected to a second reaction in the presence of a condensation catalyst, and the supramolecular functional precursor is obtained after purification.

[0016] Furthermore, in step two, the catalyst includes an amine catalyst and a metal catalyst. The amine catalyst is at least one of a propylene glycol solution of dimethylaminoethyl ether and a propylene glycol solution of triethylenediamine. The metal catalyst is at least one of stannous octoate and dibutyltin dilaurate.

[0017] Furthermore, in step two, the polyether polyol is at least one of polyoxypropylene polyol and polymer polyol with a functionality of 2 to 4 and a molecular weight of 1,000 to 6,000, the foam stabilizer is a non-hydrolyzable stabilizer of polysiloxane-oxyolefin block copolymer, and the amount of water added accounts for 1.5% to 4.0% of the total mass of the polyol mixture.

[0018] Furthermore, in step three, the polyisocyanate is at least one of diphenylmethane diisocyanate, toluene diisocyanate, or polymethylene polyphenyl polyisocyanate.

[0019] Furthermore, in step four, the curing temperature is 100°C and the curing time is 2 hours.

[0020] Furthermore, after the polyurethane foam and white PVC leather are hot-pressed together at 130°C for 30 seconds, and then aged at 70°C for 72 hours, the color difference value ΔE of the white PVC leather surface is less than or equal to 0.8, and the yellowness change value Δb is less than or equal to 0.3.

[0021] On the other hand, a flame-resistant, low-odor polyurethane foam is provided, which is applicable to the preparation method of a flame-resistant, low-odor polyurethane foam. The polyurethane foam is used in the preparation of composite materials by laminating it with PVC artificial leather using a flame lamination process. The flame temperature of the flame lamination process is 860°C to 980°C, and the lamination linear speed is 15 m / min to 20 m / min.

[0022] Compared with existing technologies, this method for preparing a flame-resistant, yellowing-resistant, low-odor polyurethane foam has the following advantages:

[0023] This invention designs a core-shell structured supramolecular functional precursor. The core, a cyclodextrin derivative modified with an amine recognition group, captures amines generated during the instantaneous high-temperature pyrolysis of sponge in flame lamination. The shell, connected by thermosensitive linkages, releases hindered phenolic units at high temperatures, exerting an anti-thermal oxidation effect and inhibiting the formation of oxidized chromophores, thus forming a synergistic protection mechanism. This mechanism can intervene from both the pollution migration path and the source of the oxidation reaction, effectively preventing the migration of amines and oxidized chromophores to the PVC leather surface. It effectively solves the problem of irreversible yellowing and accompanying odor after polyurethane sponge and PVC leather are laminated in the flame lamination process, ensuring the appearance stability and odor safety of the composite material.

[0024] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0026] Figure 1 This is a schematic diagram of the preparation method of the present invention;

[0027] Figure 2 This is a schematic diagram of the mechanism of action of the supramolecular functional precursor of the present invention. Detailed Implementation

[0028] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0029] Example 1

[0030] like Figures 1 to 2As shown, this embodiment provides a method for preparing flame-resistant composite yellowing and low-odor polyurethane foam. The core of the method lies in synthesizing a supramolecular functional precursor with β-cyclodextrin as the core, crown ether units as amine recognition groups, disulfide bonds as thermosensitive linkages, and 2,6-di-tert-butyl-4-methylphenol containing C12 straight-chain alkyl groups as hindered phenolic units. The amount of the precursor added is 1.0% of the total mass of the polyurethane foam. Polyoxypropylene polyol with a functionality of 3 and a molecular weight of 3000 is selected as the main polyol component. The amount of water added accounts for 2.5% of the total mass of the polyol mixture. The polyol mixture is mixed with diphenylmethane diisocyanate at an isocyanate index of 1:0.5 and foamed. The foam is then cured at 100°C for 2 hours and allowed to stand at room temperature for 24 hours to obtain the target foam. Tests showed that after hot-pressing the sponge and white PVC leather together at 130℃ for 30 seconds, and then aging at 70℃ for 72 hours, the color difference value ΔE of the white PVC leather surface was 0.8, the yellowness change value Δb was 0.3, and the odor level met the relevant standards for automotive interior materials. The following details the specific implementation.

[0031] The preparation of supramolecular functional precursors is as follows:

[0032] In some alternative implementations, the core-shell structure of the supramolecular functional precursor is the key to achieving the synergistic effect of resistance to yellowing and low odor. The amine recognition group in the core needs to accurately capture amines generated by pyrolysis, and the hindered phenolic unit in the shell needs to be released at high temperature and exert an antioxidant effect. Therefore, the synthesis process requires strict control of reaction conditions to ensure structural integrity.

[0033] Specifically, the first step involves the preparation of the modified cyclodextrin intermediate through a first reaction: 50.0 g of β-cyclodextrin is selected. The secondary hydroxyl group in its molecular structure is a key site for grafting amine recognition groups. The cavity size of β-cyclodextrin exhibits better compatibility with amine molecules than α-cyclodextrin, and its synthesis cost is lower than that of γ-cyclodextrin; therefore, it is the preferred formulation in this embodiment. β-cyclodextrin is added to a 1000 mL four-necked flask, along with 500 mL of deionized water. A JJ-1B electric stirrer is turned on at a speed of 300 r / min, and the system temperature is simultaneously raised to 60 °C using a constant temperature water bath. Stirring continues for 30 minutes to completely dissolve the β-cyclodextrin, forming a transparent solution.

[0034] Subsequently, 12.5 g of the modifier containing crown ether units was weighed out. The hollow structure of the crown ether units can form stable complexes with amines through hydrogen bonding, serving as highly efficient amine recognition groups. The modifier was dissolved in 100 mL of anhydrous ethanol, stirred thoroughly, and then slowly added dropwise to a four-necked flask through a constant-pressure dropping funnel at a rate of 1 drop / second for 30 minutes to avoid uneven grafting due to excessively high local concentrations. After the addition was complete, 2.5 g of the alkaline catalyst potassium hydroxide was added. Potassium hydroxide can activate the secondary hydroxyl group of β-cyclodextrin, promoting the chemical bonding reaction with the crown ether units. The system temperature was raised to 80 °C and maintained at this temperature for 6 hours. The reaction progress was monitored by thin-layer chromatography (TLC) with methanol:dichloromethane (1:5, volume ratio) as the developing solvent. The reaction endpoint was considered reached when the starting material spot disappeared.

[0035] After the reaction was complete, the system was cooled to room temperature, and the pH was adjusted to neutral (pH=7.0) with 1 mol / L hydrochloric acid solution. The solution was then placed in a rotary evaporator and the solvent was removed by vacuum distillation at 60℃ and -0.09 MPa, yielding a pale yellow crude solid. The crude product was added to 300 mL of anhydrous ethanol and heated under reflux for 30 minutes. Insoluble impurities were removed by hot filtration. The filtrate was cooled to room temperature and then refrigerated at 4℃ for 12 hours, precipitating white crystals. The crystals were collected by filtration and dried in a vacuum drying oven at 80℃ for 4 hours to obtain the modified cyclodextrin intermediate. High-performance liquid chromatography (HPLC) analysis showed its purity to be 97.8%.

[0036] The second step involves the synthesis of the supramolecular functional precursor: 30.0 g of the modified cyclodextrin intermediate prepared above was weighed and added to an 800 mL four-necked flask. 400 mL of N,N-dimethylformamide was added, and stirring was started. The temperature was raised to 70 °C to completely dissolve the intermediate. A compound containing a long alkyl chain and a hindered phenolic structure was selected. In this example, 2,6-di-tert-butyl-4-methylphenol-ω-mercaptododecane was chosen. The thiol group at the molecule's end can form a corresponding functional group with a disulfide bond. The long alkyl chain is a C12 straight-chain alkyl group. This length of alkyl chain can improve the compatibility of the hindered phenolic unit in the polyurethane matrix, preventing aggregation, and can also rapidly migrate to the reaction interface at high temperatures to play a role. The hindered phenolic unit with the 2,6-di-tert-butyl-4-methylphenol structure has excellent resistance to thermal oxidation and can effectively inhibit the formation of oxidized chromophores.

[0037] Weigh 22.5 g of the above compound and add it to a four-necked flask. Stir for 10 minutes to ensure homogeneity. Then add 1.5 g of the condensation catalyst dibutyltin dilaurate. This catalyst promotes the condensation reaction between the modified cyclodextrin intermediate and the compound containing the hindered phenolic structure, forming a disulfide bond. Raise the temperature to 90 °C and react for 8 hours. Monitor the reaction process using Fourier transform infrared spectroscopy (FT-IR) (characteristic peak: disulfide bond at 500-550 cm⁻¹). - The absorption peak at ¹ is considered the reaction endpoint when the intensity of the characteristic peak is stable.

[0038] After the reaction was complete, the system was cooled to room temperature, and the reaction solution was slowly poured into 800 mL of deionized water. The mixture was stirred for 30 minutes, resulting in the precipitation of a large amount of white solid. The solid product was collected by filtration. The solid product was washed three times with deionized water to remove unreacted raw materials and catalyst. The product was then dissolved in 200 mL of chloroform, and 50 g of neutral alumina was added for column chromatography purification. The eluent was chloroform:ethyl acetate = 10:1 (volume ratio). The target eluent was collected, and the solvent was removed by vacuum distillation at 60 °C and -0.09 MPa in a rotary evaporator to obtain a white powdery supramolecular functional precursor. HPLC analysis showed a purity of 98.2%, and infrared spectroscopy confirmed the successful grafting of disulfide bonds, crown ether units, and hindered phenolic structures.

[0039] The preparation of polyol mixtures is as follows:

[0040] It is understandable that the proportions of each component in a polyol mixture directly affect the foaming effect, mechanical properties, and final resistance to yellowing and low odor of polyurethane foam. Therefore, it is necessary to precisely control the amount of each component added and the mixing conditions.

[0041] Specifically, 100.0g of polypropylene oxide polyol is weighed out. The functionality and molecular weight of this polyol ensure that the sponge has good resilience and structural stability, making it a commonly used and preferred type of polyurethane sponge for automotive interiors. 1.5g of supramolecular functional precursor is added to this polypropylene oxide polyol (calculated to be 1.0% of the total mass of the subsequent polyurethane sponge; this amount ensures synergistic protective effects without causing a decrease in the sponge's mechanical properties due to excessive addition). Subsequently, 0.3g of a propylene glycol solution of bis(dimethylaminoethyl) ether (an amine catalyst) and 0.2g of a stannous octoate (a metal catalyst) are added sequentially. The amine catalyst promotes the foaming reaction, while the metal catalyst accelerates the gelation reaction; their synergistic effect ensures a stable foaming process.

[0042] Next, add 1.0g of foam stabilizer. This foam stabilizer reduces the surface tension of the system, making the foam pore size uniform and avoiding defects such as large pores and collapsed pores. Finally, add 2.8g of deionized water (calculated to be 2.5% of the total mass of the polyol mixture; water is a physical foaming agent, and too much will lead to low foam density and poor mechanical properties, while too little will result in insufficient foaming; this amount is the optimal value for balancing foaming effect and performance).

[0043] Place the above mixture in a high-speed disperser of model SDF-10L and stir at 800 r / min for 20 minutes at room temperature (25℃). During the stirring process, the container must be sealed to avoid moisture evaporation and excessive air mixing. After stirring, a uniform, transparent, and sediment-free polyol mixture is obtained. Let it stand for 5 minutes to eliminate the air bubbles generated during the stirring process.

[0044] The mixing and foaming process is as follows:

[0045] In related technologies, the isocyanate index is a key parameter affecting the degree of polyurethane reaction and product performance. An index that is too high will cause the sponge to be too hard and brittle, while an index that is too low will result in incomplete reaction, and residual isocyanate will increase odor and affect yellowing resistance. Therefore, this embodiment uses an optimized isocyanate index.

[0046] Specifically, 48.5g of diphenylmethane diisocyanate was weighed out. This isocyanate has moderate reactivity and good compatibility with polypropylene oxide polyol, resulting in sponges with excellent mechanical properties and aging resistance. The polyol mixture and diphenylmethane diisocyanate were rapidly added to the mixing head of a GH-10 polyurethane foaming machine. The mixing head speed was set to 3000 r / min, and the mixing time was controlled to 10 seconds to ensure sufficient contact and reaction between the two.

[0047] After mixing, the mixture is quickly poured into a pre-cleaned mold coated with a release agent. The mold is made of stainless steel. The release agent prevents the sponge from sticking to the mold, ensuring the integrity of the product molding. The mold is then placed in an environment with room temperature and 50% relative humidity for free foaming. The foaming process lasts for 3 minutes, during which the foaming height and surface condition of the sponge are observed to ensure that there are no collapsed bubbles or cracks. After foaming, a preliminary polyurethane sponge blank is obtained.

[0048] The maturation process is as follows:

[0049] Specifically, the foamed polyurethane sponge preform, along with the mold, is placed into a curing chamber. The curing temperature is set at 100℃. This temperature promotes further cross-linking of the polyurethane molecular chains, improving the structural stability and performance consistency of the sponge. Excessive temperature can lead to thermal aging of the sponge, while insufficient temperature results in incomplete cross-linking. The curing time is controlled at 2 hours, with temperature fluctuations within the curing chamber not exceeding ±2℃ and relative humidity controlled below 30%.

[0050] After curing, turn off the heating device in the curing room and wait for the temperature in the curing room to drop to room temperature naturally. Then, take out the sponge blank and place it in a well-ventilated indoor environment without direct sunlight for 24 hours at room temperature. During the resting process, avoid squeezing or colliding with the sponge so that the small molecules remaining inside the sponge can fully volatilize and further stabilize the molecular structure, ultimately obtaining flame-resistant composite yellowing and low-odor polyurethane sponge.

[0051] In this embodiment, the performance of the prepared polyurethane foam was tested according to the following standards:

[0052] Flame-resistant composite yellowing performance: Sponge and white PVC leather were cut into 10cm×10cm samples and hot-pressed together at 130℃ and 0.3MPa for 30 seconds. After lamination, the samples were placed in a constant temperature aging chamber and aged at 70℃ for 72 hours. The color difference value ΔE and yellowness change value Δb of the white PVC leather surface were measured using a colorimeter. Three different positions were tested for each sample, and the average value was taken.

[0053] Odor performance: In accordance with GB / T27630-2011 "Guidelines for Air Quality Evaluation in Passenger Cars", 50g of sponge sample was placed in a 1L sealed glass bottle and kept at 80℃ for 2 hours. Then, 5 professional odor evaluators evaluated the odor level (Level 1: No odor; Level 2: Slight odor but no discomfort; Level 3: Obvious odor but no discomfort; Level 4: Strong odor and discomfort; Level 5: Unbearable odor). The average level of the evaluators was taken.

[0054] Test results: The color difference value of the white PVC leather surface ΔE=0.8, the yellowness change value Δb=0.3; the odor level is 3.0, which meets the odor requirements for automotive interior materials.

[0055] In summary, this embodiment ensured the integrity of the core-shell structure and the effective grafting of each functional unit by precisely controlling the synthesis process of the supramolecular functional precursor. The combination of the β-cyclodextrin core and crown ether unit achieved efficient capture of amines. The disulfide bond broke under the instantaneous high temperature of flame lamination, releasing hindered phenolic units containing C12 long alkyl chains, effectively inhibiting the formation of oxidized chromophores. The optimized component ratios and mixing conditions of the polyol mixture ensured the stability of the foaming process and the molding quality of the sponge. Controlled curing process parameters promoted full cross-linking of molecular chains, improving the structural stability of the sponge. The entire implementation process was clear in steps and parameters, and the resulting polyurethane sponge exhibited excellent resistance to flame lamination yellowing and low odor, meeting the application requirements of automotive interiors and other fields.

[0056] Example 2

[0057] like Figures 1 to 2 As shown, this embodiment provides another method for preparing flame-resistant, yellowing-resistant, and low-odor polyurethane foam. A supramolecular functional precursor is used, comprising γ-cyclodextrin as the core, azacrown ether units as amine recognition groups, thermally unstable diethyl adipate bonds as thermosensitive linkages, and β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate containing C16 linear alkyl groups as hindered phenolic units. The amount added is 1.5% of the total mass of the polyurethane foam. A polymeric polyol with a functionality of 4 and a molecular weight of 4000 is selected and compounded with polyoxypropylene polyol as the polyol component. The amount of water added is 3.0% of the total mass of the polyol mixture. The polyol mixture is mixed with toluene diisocyanate at an isocyanate index of 1:0.55 and foamed. The foam is then cured at 110°C for 1.5 hours and allowed to stand at room temperature for 36 hours to obtain the target foam. Test results show that after the sponge and white PVC leather were heat-pressed and aged, the color difference value ΔE=1.0, the yellowness change value Δb=0.35, and the odor level was 3.0. The implementation process parameters were clear and the operation was highly feasible. The following is a detailed explanation of the specific implementation content.

[0058] The preparation of supramolecular functional precursors is as follows:

[0059] In some alternative embodiments, γ-cyclodextrin has a larger cavity size than β-cyclodextrin, resulting in a stronger ability to capture macromolecular amines. Compared to ordinary crown ethers, aza-crown ether units exhibit higher binding stability with amines. Therefore, this embodiment selects this combination to further optimize the amine capture effect. The cleavage efficiency of thermally unstable ester bonds at flame bonding temperatures is controllable, and hindered phenolic units containing C16 long alkyl chains exhibit better dispersibility in polyurethane matrices. These choices are all based on considerations of functional synergy.

[0060] Specifically, the first step is to carry out the first reaction and prepare the modified cyclodextrin intermediate: weigh 60.0g of γ-cyclodextrin, add it to a 1200mL four-necked flask, add 600mL of deionized water, turn on the JJ-1B electric stirrer, heat the constant temperature water bath to 65℃, and stir for 40 minutes to completely dissolve the γ-cyclodextrin and form a transparent and homogeneous solution.

[0061] Weigh 18.0 g of the modifier containing a nitrogen-containing crown ether unit. The nitrogen atom in the crown ether unit can form stronger hydrogen bonds with amines, improving recognition and capture efficiency. Dissolve the modifier in 150 mL of anhydrous ethanol, stir well, and then add it dropwise to a four-necked flask at a rate of 1 drop / second using a constant pressure dropping funnel over 40 minutes. After the addition is complete, add 3.0 g of basic catalyst sodium hydroxide. Sodium hydroxide has moderate catalytic activity, effectively promoting the grafting reaction between the secondary hydroxyl group of γ-cyclodextrin and the crown ether unit, and is easily removed subsequently.

[0062] The system temperature was raised to 85℃ and maintained at this temperature for 7 hours. The reaction progress was monitored by TLC, and the reaction was stopped when the starting material completely disappeared. After the reaction was completed, the mixture was cooled to room temperature, and the pH was adjusted to 7.0 with 1 mol / L hydrochloric acid solution. The solution was then placed in a RE-52AA rotary evaporator and the solvent was removed by vacuum distillation at 65℃ and -0.09 MPa to obtain a pale yellow viscous crude product.

[0063] Add 400 mL of anhydrous ethanol to the crude product, heat under reflux for 40 minutes, filter while hot to remove insoluble impurities, cool the filtrate to room temperature and refrigerate at 4°C for 16 hours to precipitate white crystals, filter and collect the crystals, wash twice with anhydrous ethanol, and then place in a DZF-6050 vacuum drying oven and dry at 85°C for 5 hours to obtain the modified cyclodextrin intermediate, the purity of which was 97.5% as determined by HPLC.

[0064] The second step involves the synthesis of the supramolecular functional precursor: 35.0 g of the modified cyclodextrin intermediate was weighed and added to a 1000 mL four-necked flask. 500 mL of N,N-dimethylformamide (DMF) was added, and stirring was started. The temperature was raised to 75 °C to completely dissolve the intermediate. A compound containing a long alkyl chain and a hindered phenolic structure was selected. In this example, β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate-ω-hydroxyhexadecyl ester was chosen. The hydroxyl group at the end of the molecule can form a corresponding functional group with the diethyl adipate bond. The long alkyl chain is a C16 straight-chain alkyl group. This length of alkyl chain can further improve the compatibility of the hindered phenolic unit in the polyurethane matrix and reduce aggregation. The hindered phenolic unit with the β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate structure has superior resistance to thermal oxidation and can inhibit the oxidation reaction for a long time.

[0065] Weigh 30.0 g of the above compound and add it to a four-necked flask. Stir for 15 minutes to ensure homogeneity. Then add 2.0 g of the condensation catalyst p-toluenesulfonic acid. This catalyst efficiently promotes the condensation reaction between the modified cyclodextrin intermediate and the compound containing the hindered phenolic structure, forming a thermally unstable diethyl adipate bond. Raise the system temperature to 95 °C and react for 9 hours. Monitor the reaction progress by FT-IR (characteristic peak: ester bond at 1735 cm⁻¹). - The absorption peak at ¹ is considered the reaction endpoint when the intensity of the characteristic peak is stable.

[0066] After the reaction was completed, the mixture was cooled to room temperature, and the reaction solution was slowly poured into 1000 mL of deionized water. The mixture was stirred for 40 minutes, resulting in the precipitation of a large amount of white solid. The solid product was collected by filtration. The product was washed four times with deionized water to remove unreacted raw materials and catalyst. The product was then dissolved in 250 mL of ethyl acetate, and 60 g of neutral alumina was added for column chromatography purification. The eluent was ethyl acetate:petroleum ether = 3:1 (volume ratio). The target eluent was collected, and the solvent was removed by vacuum distillation at 65 °C and -0.09 MPa in a rotary evaporator, yielding a white powdery supramolecular functional precursor with a purity of 98.0% as determined by HPLC. Infrared spectroscopy confirmed the successful grafting of ester bonds, azacrown ether units, and hindered phenolic structures.

[0067] The preparation of polyol mixtures is as follows:

[0068] It is understandable that using a blend of polymer polyols and polyoxypropylene polyols can balance the resilience and mechanical strength of the sponge, making it suitable for scenarios with higher requirements for the structural stability of the sponge. The amount of each component added needs to be adjusted according to the blending system to ensure foaming effect and functional synergy.

[0069] Specifically, weigh 70.0g of polyoxypropylene polyol and 30.0g of polymer polyol, and mix them evenly. This compounding ratio allows the sponge to have both good softness and compressive strength. Add 2.8g of supramolecular functional precursor to the mixed polyol (calculated to be 1.5% of the total mass of the subsequent polyurethane sponge; this addition can further improve the yellowing resistance and low odor effect without having a significant negative impact on the mechanical properties of the sponge).

[0070] Subsequently, 0.4g of a propylene glycol solution of triethylenediamine, an amine catalyst, and 0.3g of dibutyltin dilaurate, a metal catalyst, were added sequentially. The catalytic efficiency of this catalyst combination is well-suited to the complex polyol system, ensuring the simultaneous occurrence of foaming and gelation reactions.

[0071] Add 1.2g of foam stabilizer, which is optimized for the surface tension characteristics of the compound polyol system, resulting in more uniform foam pore size. Finally, add 3.4g of deionized water (calculated to be 3.0% of the total mass of the polyol mixture; the amount of water is appropriately increased to ensure the foaming ratio, considering the reactivity of the compound polyol).

[0072] Place the above mixture in an SDF-10L high-speed disperser and stir at 900 r / min for 25 minutes at room temperature. Keep the container sealed during stirring. After stirring, a uniform polyol mixture without precipitate is obtained. Let it stand for 8 minutes to eliminate air bubbles.

[0073] The mixing and foaming process is as follows:

[0074] Specifically, 62.0g of toluene diisocyanate was weighed out. This isocyanate has a high reaction rate matching degree with the compound polyol system, which can produce a sponge with a uniform structure. The polyol mixture and toluene diisocyanate were quickly added to the mixing head of a GH-10 polyurethane foaming machine. The mixing head speed was set to 3500r / min, and the mixing time was controlled to 12 seconds to ensure that the two were fully mixed and reacted.

[0075] After mixing, the mixture was quickly injected into a stainless steel mold coated with KD-801 release agent and placed in an environment with room temperature and 55% relative humidity for free foaming. The foaming process lasted for 3.5 minutes. It was observed that the foaming height of the sponge was stable and the surface was free of defects. After foaming, a polyurethane sponge blank was obtained.

[0076] The maturation process is as follows:

[0077] Specifically, the sponge preform, along with the mold, is placed into an SR-80 curing chamber. The curing temperature is set at 110℃, which is adjusted to accommodate the cross-linking characteristics of the compound polyol system, promoting more complete cross-linking of molecular chains and improving the sponge's aging resistance. The curing time is controlled at 1.5 hours, with temperature fluctuations within the curing chamber not exceeding ±2℃ and relative humidity controlled below 30%.

[0078] After curing, the curing room temperature is allowed to drop naturally to room temperature. The sponge blank is then removed and placed in a well-ventilated indoor environment without direct sunlight for 36 hours at room temperature to ensure that the small molecules remaining inside the sponge are fully volatilized and the molecular structure is further stabilized, ultimately resulting in a flame-resistant, composite yellowing-resistant, low-odor polyurethane sponge.

[0079] This embodiment performs performance testing according to the same standards and methods as in Embodiment 1:

[0080] Test results: The color difference value of the white PVC leather surface is ΔE=1.0, and the yellowness change value is Δb=0.35; the odor level is 3.0, which meets the odor requirements of automotive interiors and home furnishings.

[0081] In summary, this embodiment improved the capture efficiency of amines by using a combination of γ-cyclodextrin and azacrown ether units; it achieved precise release of hindered phenol units by employing thermally unstable ester bonds as thermosensitive linkages; and it balanced the mechanical properties and functional characteristics of the sponge through a polyol complex system. Throughout the implementation process, the process parameters for each step were optimized based on material properties and functional requirements, and the operational details were clearly defined. The resulting polyurethane sponge maintains good flame-retardant properties and low odor characteristics while exhibiting superior mechanical strength and a wider range of applications.

[0082] Comparative Example

[0083] This comparative example aims to illustrate the advantages of the technical solution of this invention. A conventional antioxidant and light stabilizer compound system is used to replace the supramolecular functional precursor of this invention, while the remaining preparation process parameters are basically the same as in Example 1. Specifically, antioxidant 1010 and light stabilizer 770 are selected as anti-yellowing additives, with an addition amount of 1.0% of the total mass of the polyurethane sponge. The amounts and types of polyol components, catalysts, foam stabilizers, and water are the same as in Example 1. The polyol mixture is mixed with diphenylmethane diisocyanate at an isocyanate index of 1:0.5 for foaming, and then cured at 100°C for 2 hours and left to stand at room temperature for 24 hours to obtain the polyurethane sponge. Test results show that after hot-pressing and aging with white PVC leather, the color difference value ΔE=1.8, the yellowness change value Δb=1.0, and the odor level is 4, which is significantly worse than the products of Examples 1 and 2. This indicates that the conventional additive system cannot achieve effective anti-yellowing and low-odor effects under the extreme conditions of flame lamination. The following detailed description is provided in conjunction with specific implementation details.

[0084] Preparation of polyol mixtures:

[0085] In related technologies, conventional anti-yellowing solutions often employ the physical blending of antioxidants and light stabilizers. However, this method suffers from problems such as additive failure and poor compatibility under extreme high temperatures. This comparative example uses antioxidant 1010 and light stabilizer 770, both commonly used in the industry. Their combination is a typical pairing in conventional anti-yellowing systems.

[0086] Specifically, 100.0g of polyoxypropylene polyol was weighed, and 0.7g of antioxidant 1010 and 0.8g of light stabilizer 770 were added (the total amount of the two added was calculated to be 1.0% of the total mass of the subsequent polyurethane foam, which is consistent with the amount of supramolecular functional precursor added in Example 1).

[0087] Subsequently, 0.3g of a propylene glycol solution of the amine catalyst bis(dimethylaminoethyl) ether, 0.2g of the metal catalyst stannous octoate, 1.0g of foam stabilizer, and 2.8g of deionized water were added sequentially. The types and amounts of each component were exactly the same as in Example 1 to ensure the fairness of the comparison.

[0088] The above mixture was placed in an SDF-10L high-speed disperser and stirred at 800 r / min for 20 minutes at room temperature. After stirring, a polyol mixture was obtained and allowed to stand for 5 minutes to eliminate bubbles.

[0089] The mixing and foaming process is as follows:

[0090] Specifically, 48.5g of diphenylmethane diisocyanate was weighed, consistent with the type and amount of isocyanate used in Example 1. The polyol mixture and diphenylmethane diisocyanate were rapidly added to the mixing head of a GH-10 polyurethane foaming machine at a speed of 3000 r / min for 10 seconds, the same mixing conditions as in Example 1.

[0091] After mixing, the mixture was quickly injected into a stainless steel mold coated with KD-801 release agent and placed in an environment of room temperature and 50% relative humidity for free foaming. The foaming process lasted for 3 minutes, consistent with the foaming environment and time in Example 1, to obtain a polyurethane sponge blank.

[0092] The maturation process is as follows:

[0093] Specifically, the sponge blank along with the mold was sent into an SR-80 curing chamber, the curing temperature was set at 100℃, the curing time was 2 hours, the temperature fluctuation in the curing chamber was ±2℃, and the relative humidity was below 30%, which was completely consistent with the curing process in Example 1.

[0094] After curing, the curing room temperature was allowed to drop naturally to room temperature. The sponge blank was then removed and placed in a well-ventilated indoor environment without direct sunlight for 24 hours at room temperature, under the same conditions as in Example 1. This resulted in the final polyurethane sponge of the conventional anti-yellowing system.

[0095] Performance tests are as follows:

[0096] Performance tests were performed using the same standards and methods as in Example 1:

[0097] Test results: The color difference value of the white PVC leather surface ΔE=1.8, the yellowness change value Δb=1.0; the odor level is 4.0, which does not meet the odor requirements for automotive interior materials.

[0098] In summary, this comparative example uses a static addition scheme of conventional antioxidants and light stabilizers. While it provides some anti-yellowing effect under normal temperature and conditions, antioxidant 1010 decomposes under the instantaneous high temperature of flame lamination. This not only fails to effectively inhibit the migration of amines generated by sponge pyrolysis, but its decomposition products also become new chromophores, leading to severe yellowing of the PVC leather surface. Light stabilizer 770 loses its activity at high temperatures and cannot prevent the formation of oxidized chromophores. Simultaneously, conventional additives have poor compatibility with the polyurethane matrix, and some additives volatilize or decompose at high temperatures, producing a large amount of small-molecule odorous substances, resulting in an increased odor level. The test results of this comparative example contrast sharply with those of Examples 1 and 2, fully demonstrating that the supramolecular functional precursor of this invention achieves a synergistic effect of amine capture and antioxidant protection through a dynamic response mechanism, thereby solving the yellowing and odor problems during flame lamination. Its technical effect is significantly superior to conventional technical solutions.

[0099] To more intuitively demonstrate the performance differences between the technical solution of this invention and conventional technical solutions, the key process parameters and performance test results of Examples 1, 2, and the comparative examples are summarized in the following table:

[0100] project Example 1 Example 2 Comparative Example Supramolecular functional precursor composition Core: β-cyclodextrin; Amine recognition group: crown ether unit; Thermosensitive link: disulfide bond; Hindered phenolic unit: 2,6-di-tert-butyl-4-methylphenol containing a C12 straight-chain alkyl group. Core: γ-cyclodextrin; Amine recognition group: azirconium crown ether unit; Thermosensitive link: diethyl adipate bond; Hindered phenolic unit: β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate containing a C16 straight-chain alkyl group. No, it uses a compound system of antioxidant 1010 + light stabilizer 770. Supramolecular functional precursor addition amount (total sponge mass %) 1.0 1.5 0 (Total amount of additives added: 1.0%) polyol components Polyoxypropylene polyol (GP3030, functionality 3, molecular weight 3000) Polyoxypropylene polyol (GP4000) + polymer polyol (POP-3620) = 7:3 (mass ratio) Polyoxypropylene polyol (GP3030, functionality 3, molecular weight 3000) Types and indices of isocyanates Diphenylmethane diisocyanate, 1:0.5 Toluene diisocyanate, 1:0.55 Diphenylmethane diisocyanate, 1:0.5 Curing process 100℃, 2 hours 110℃, 1.5 hours 100℃, 2 hours Color difference value ΔE 0.8 1.0 1.8 Yellowness change value Δb 0.3 0.35 1.0 Odor rating (GB / T27630-2011) Level 3.0 Level 3.0 Level 4.0

[0101] The table above clearly presents the differences between Example 1, Example 2, and the comparative example in core process parameters and key performance indicators. It can be seen that the polyurethane foam prepared by this invention, through the design of a supramolecular functional precursor with a specific structure, combined with an optimized polyol system, isocyanate index, and curing process, exhibits excellent performance in flame-bonded yellowing resistance and low odor characteristics. The color difference value ΔE and yellowness change value Δb are significantly lower than those of the comparative example, and the odor level also meets the requirements of high-end applications. In contrast, the comparative example, using a conventional additive compounding system, cannot achieve effective functional protection under the extreme conditions of flame bonding, resulting in severe yellowing and excessive odor. This comparison fully verifies the superiority of the technical solution of this invention, which solves technical problems that are difficult to overcome by conventional technologies through a dynamic synergistic mechanism, providing an effective solution for improving the performance of polyurethane foam used in flame bonding processes.

[0102] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a flame-resistant, yellowing-resistant, low-odor polyurethane foam, characterized in that, The method includes the following steps: Step 1, Preparation of supramolecular functional precursor: The supramolecular functional precursor is a core-shell structure molecule consisting of a core and a shell. The core is a cyclodextrin derivative modified with an amine recognition group, and the shell is a plurality of hindered phenol units containing long alkyl chains connected to the outer edge of the core by thermosensitive linkages. Step 2, preparation of polyol mixture: The polyether polyol, the supramolecular functional precursor prepared in Step 1, the catalyst, the foam stabilizer, and water are mixed at room temperature and stirred evenly to form a polyol mixture. The amount of supramolecular functional precursor added is 0.5% to 2.0% of the total mass of the polyurethane foam. Step 3, Mixing and foaming: The polyol mixture obtained in Step 2 is rapidly mixed with the polyisocyanate at an isocyanate index of 1:0.4 to 1:0.6, and then injected into a mold for free foaming; Step 4, Curing: Place the foamed polyurethane sponge product in a curing room at 90℃ to 120℃ for 1 to 3 hours, and then let it stand at room temperature for more than 24 hours to obtain flame-resistant, yellowing-resistant, low-odor polyurethane sponge.

2. The method for preparing a flame-resistant, yellowing-resistant, low-odor polyurethane foam according to claim 1, characterized in that, In step one, the cyclodextrin derivative modified with an amine recognition group, wherein the amine recognition group is a crown ether unit or an azacrown ether unit, and the cyclodextrin is selected from at least one of α-cyclodextrin, β-cyclodextrin or γ-cyclodextrin, and the modification refers to the amine recognition group being chemically grafted onto the secondary hydroxyl position in the cyclodextrin molecule structure.

3. The method for preparing a flame-resistant, yellowing-resistant, low-odor polyurethane foam according to claim 1, characterized in that, In step one, the thermosensitive link is selected from at least one of disulfide bonds and thermally unstable specific ester bonds, the long alkyl chain is a straight-chain alkyl chain with 8 to 18 carbon atoms, and the structure of the hindered phenolic unit is selected from at least one of 2,6-di-tert-butyl-4-methylphenol structure and β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate structure.

4. The method for preparing a flame-resistant, yellowing-resistant, low-odor polyurethane foam according to claim 1, characterized in that, In step one, the method for synthesizing supramolecular functional precursors includes the following steps: First, cyclodextrin is reacted with a modifier containing an amine recognition group under the action of an alkaline catalyst to obtain a modified cyclodextrin intermediate. Then, the modified cyclodextrin intermediate and a compound containing a long alkyl chain and a hindered phenolic structure with a terminal reactive functional group corresponding to the thermosensitive link bond are subjected to a second reaction in the presence of a condensation catalyst, and the supramolecular functional precursor is obtained after purification.

5. The method for preparing a flame-resistant, yellowing-resistant, low-odor polyurethane foam according to claim 1, characterized in that, In step two, the catalyst includes amine catalysts and metal catalysts. The amine catalyst is at least one of a propylene glycol solution of dimethylaminoethyl ether and a propylene glycol solution of triethylenediamine. The metal catalyst is at least one of stannous octoate and dibutyltin dilaurate.

6. The method for preparing a flame-resistant, yellowing-resistant, low-odor polyurethane foam according to claim 1, characterized in that, In step two, the polyether polyol is at least one of polyoxypropylene polyol and polymer polyol with a functionality of 2 to 4 and a molecular weight of 1,000 to 6,000. The foam stabilizer is a non-hydrolyzable stabilizer of polysiloxane-oxyolefin block copolymer. The amount of water added is 1.5% to 4.0% of the total mass of the polyol mixture.

7. The method for preparing a flame-resistant, yellowing-resistant, low-odor polyurethane foam according to claim 1, characterized in that, In step three, the polyisocyanate is at least one of diphenylmethane diisocyanate, toluene diisocyanate, or polymethylene polyphenyl polyisocyanate.

8. The method for preparing a flame-resistant, yellowing-resistant, low-odor polyurethane foam according to claim 1, characterized in that, In step four, the curing temperature is 100℃ and the curing time is 2 hours.

9. The method for preparing a flame-resistant, yellowing-resistant, low-odor polyurethane foam according to claim 1, characterized in that, After the polyurethane foam and white PVC leather are hot-pressed together at 130°C for 30 seconds, they are aged at 70°C for 72 hours. The color difference value ΔE on the surface of the white PVC leather is less than or equal to 0.8, and the yellowness change value Δb is less than or equal to 0.

3.

10. A flame-resistant, low-odor polyurethane foam with composite yellowing resistance, applicable to the preparation method of the flame-resistant, low-odor polyurethane foam with composite yellowing resistance according to any one of claims 1 to 9, characterized in that, The polyurethane foam is used in the preparation of composite materials by laminating it with PVC artificial leather using a flame lamination process. The flame temperature of the flame lamination process is 860°C to 980°C, and the lamination linear speed is 15 m / min to 20 m / min.

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