Preparation method of polyurethane foam

Abstract

The invention provides a preparation method of polyurethane foam, which comprises the following steps: S10, preparing modified epoxy resin: polymerizing N-isopropylacrylamide and a cross-linking agent to form a temperature-sensitive network, and compounding the temperature-sensitive network with epoxy resin, polyvinyl alcohol and nano-zinc oxide; s20, preparing modified isooctane: forming a shell by using an acrylonitrile and methyl methacrylate copolymer through suspension polymerization, and wrapping the core substance dimethyl carbonate to obtain a core-shell structure microcapsule; and S30: mixing the two modifiers with additives such as polyol and a catalyst to form a component A, then impacting and mixing the component A with a polyisocyanate component B under high pressure, and injecting the mixture into a preheating mold for foaming and curing to finally obtain the polyurethane foam. The polyurethane foam prepared by the method is good in toughness, and is not easy to deform or break when being subjected to external tension or shear stress.

Description

Technical Field

[0001] This invention relates to the field of polyurethane foam preparation technology, and specifically to a method for preparing polyurethane foam. Background Technology

[0002] The molecular structure of polyurethane foam in the prior art is not tough enough. When subjected to external tensile or shear stress, the molecular structure of the foam is not enough to support macroscopic elastic deformation, and it is prone to deformation or breakage. Summary of the Invention

[0003] The purpose of this invention is to overcome the above-mentioned defects or problems in the prior art and provide a method for preparing polyurethane foam. The polyurethane foam prepared by this method has good toughness and is not easily deformed or broken when subjected to external tensile or shear stress.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: Technical Solution 1: A method for preparing polyurethane foam, comprising the following steps: S10: Preparation of modified epoxy resin: 15-25% N-isopropylacrylamide, 15-25% N,N'-methylenebisacrylamide, 8-12% ammonium persulfate, and 35-45% tetramethylethylenediamine aqueous solution (70-80% by mass) are mixed and reacted at 45-55°C for 10-14 hours under stirring at 250-350 rpm; after cooling, bisphenol A type epoxy resin E-51 is added. 35–45%, polyvinyl alcohol 25–35%, and nano zinc oxide 8–12% were stirred and reacted at room temperature for 10–14 hours to obtain modified epoxy resin; S20: Preparation of modified isooctane: 8–12% acrylonitrile, 8–12% methyl methacrylate, 8–12% benzoyl peroxide, 15–25% isooctane, and 8–12% dimethyl carbonate were stirred and reacted at 1–5 °C for 1.5–2.5 hours to obtain an oil phase intermediate; then the intermediate was mixed with a 2–4% magnesium chloride aqueous solution at a mass ratio of 1:(5–7), and the mixture was heated to 48–52 °C under nitrogen protection. The reaction is carried out at constant temperature for 0.8–1.2 hours, at 58–62℃ for 9–11 hours, and at 63–67℃ for 0.8–1.2 hours. After the reaction is completed, the mixture is cooled, filtered, washed, and vacuum dried to obtain modified isooctane. S30: 30–40 parts by weight of the modified epoxy resin, 7–10 parts by weight of the modified isooctane, 1–5 parts by weight of the catalyst, 3–5 parts by weight of the foam stabilizer, and 3–6 parts by weight of the anti-hydrolysis agent are added to the polyol component and mixed evenly to form component A. 40–50 parts by weight of polyisocyanate are used as component B. Subsequently, component A and component B are mixed by impact mixing head at a weight ratio of (1.05–1.15):1 under a mixing pressure of 12–18 MPa. The mixture is then injected into a mold preheated to 80–90℃ for foaming and molding. After curing in the mold for 15–25 minutes, the mixture is demolded to obtain polyurethane foam.

[0005] Technical Solution 2 based on Technical Solution 1: In step S30, the catalyst is selected from at least one of ethylenediamine, N,N-dimethylhexadecanamine, trimethylenediamine, bismuth isooctanoate, bismuth neodecanoate, stannous octoate, and dibutyltin dilaurate.

[0006] Technical Solution 3 based on Technical Solution 1: In step S30, the polyisocyanate is selected from at least one of toluene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, and naphthalene-1,5-diisocyanate.

[0007] Technical Solution 4 based on Technical Solution 1: In step S10, the weight ratio of N-isopropylacrylamide, N,N'-methylenebisacrylamide, ammonium persulfate, tetramethylethylenediamine aqueous solution, bisphenol A type epoxy resin E-51, polyvinyl alcohol and nano zinc oxide is 2:2:1:4:4:3:1.

[0008] Technical Solution 5 based on Technical Solution 1: In step S20, the weight ratio of acrylonitrile, methyl methacrylate, benzoyl peroxide, isooctane and dimethyl carbonate used to prepare the oil phase intermediate is 1:1:1:2:1.

[0009] Technical Solution Six based on Technical Solution One: In step S20, the temperatures of the three constant temperature stages of the programmed heating are 50℃, 60℃ and 65℃, respectively.

[0010] Technical solution seven based on technical solution one: In step S30, the mixing pressure is 14–16 MPa.

[0011] Technical solution eight based on technical solution one: In step S30, the curing time is 18–22 minutes.

[0012] Technical Solution Nine based on Technical Solution One: In step S10, the particle size of the nano zinc oxide is 20-40 nm.

[0013] Technical solution ten based on technical solution one: In step S30, the foam stabilizer is a double-ended hydroxypropyl silicone oil, and the anti-hydrolysis agent is a polycarbodiimide.

[0014] As can be seen from the above description of the present invention, compared with the prior art, the present invention has the following beneficial effects: In traditional polyurethane foam manufacturing, those skilled in the art typically increase the content of hard segments or add inorganic fillers to improve foam density and strength. While increasing the content of hard segments can improve the rigidity of the material, it leads to a decrease in the flexibility of the molecular chains, making the foam prone to brittle fracture under tensile or shear stress. Adding inorganic fillers such as calcium carbonate and talc can increase density, but the poor interfacial bonding between the filler and the polyurethane matrix can easily cause interfacial debonding under stress, thus reducing the overall mechanical properties of the material. Simultaneously, the addition of inorganic fillers increases the viscosity of the system, affecting the uniform dispersion of gas during foaming and resulting in uneven cell size distribution.

[0015] This invention modifies epoxy resin by combining N-isopropylacrylamide and N,N'-methylenebisacrylamide with epoxy resin, polyvinyl alcohol, and nano-zinc oxide to form a modified system with temperature sensitivity and a cross-linked structure. Specifically, poly(N-isopropylacrylamide) undergoes a phase transition at the foaming temperature, its molecular chains changing from an extended state to a contracted state; this phase transition provides additional driving force for cell nucleation. The long-chain flexible structure of polyvinyl alcohol and the rigid aromatic ring structure of epoxy resin form an interpenetrating network, providing flexibility to the molecular chains while maintaining material strength. Nano-zinc oxide, with its high specific surface area, forms a large number of nucleation sites in the system, far exceeding the nucleation site density in traditional foaming systems.

[0016] The modified isooctane was prepared using a core-shell structure design. The dimethyl carbonate in the core layer gradually vaporizes at the foaming temperature, with a boiling point of 90°C, which falls within the temperature range of polyurethane foaming, providing a continuous and stable gas release. The shell layer is composed of an acrylonitrile-methyl methacrylate copolymer and Mg... 2+ Coordination crosslinking hinders gas diffusion, allowing for precise control of the gas release rate. By adjusting the shell thickness and crosslinking density, the gas release rate can be controlled within a suitable range, avoiding the problem of cell wall rupture caused by the instantaneous large-scale gas production of traditional chemical foaming agents.

[0017] The two modified components produce a synergistic effect during the foaming process. The nucleation sites provided by the modified epoxy resin, combined with the controlled-release gas source of the modified isooctane, ensure a stable gas supply to each nucleation site, resulting in uniformly sized cells. Simultaneously, the cross-linked structure in the modified epoxy resin forms chemical bonds with the polyurethane molecular chains, enhancing the mechanical strength of the cell walls, while the flexible segments of the polyvinyl alcohol ensure the material's toughness during deformation.

[0018] Regarding process parameters, a mixing pressure of 12-18 MPa ensures uniform dispersion of the two modified components in the polyurethane matrix. This pressure range overcomes the interfacial tension between the modified components and the matrix, achieving molecular-level mixing. A mold preheating temperature of 80-90°C matches the gas release temperature of the modified isooctane, ensuring the synchronicity of the foaming process. A curing time of 15-25 minutes allows sufficient time for the polyurethane molecular chains to form a cross-linked network, while the epoxy groups in the modified epoxy resin undergo a ring-opening reaction with the isocyanate, further enhancing the cross-linking density of the molecular chains.

[0019] Through the synergistic effect of the above-mentioned technical means, the polyurethane foam prepared by this invention maintains high density while achieving microporous and uniform cell size, with the pore diameter controlled within the range of 80-110 μm and the pore diameter difference less than 30 μm. The molecular structure toughness of the material is improved, and under external tensile or shear stress, it can disperse stress through coordinated deformation of the molecular chains, avoiding localized damage caused by stress concentration. Simultaneously, the chemical bonds formed between the modified components and the polyurethane matrix ensure the strong interfacial bonding, eliminating the interfacial debonding problem in traditional filler modification methods.

[0020] In technical solution two, the combined use of amine catalysts and organometallic catalysts achieves more precise reaction rate control compared to using a single catalyst. Amine catalysts, such as ethylenediamine and trimethylenediamine, primarily promote the reaction between isocyanates and water, accelerating the foaming process, while organometallic catalysts, such as bismuth isooctanoate and stannous octoate, primarily promote the reaction between isocyanates and hydroxyl groups, accelerating the gelation process. This combination optimizes the matching of foaming and gelation reactions, avoiding the problems of excessively rapid foaming leading to cell wall rupture or excessively slow gelation leading to cell collapse, which are common in traditional single-catalyst systems.

[0021] In technical solution three, by selecting a combination of isocyanates with different molecular structures and reactivity, a better control of the hard-to-soft segment ratio can be achieved compared to using a single isocyanate. Toluene diisocyanate has high reactivity and can quickly form an initial cross-linked structure; diphenylmethane diisocyanate has high rigidity and can provide material strength; isophorone diisocyanate has moderate reactivity and good flexibility, which can balance the strength and toughness of the material. The synergistic effect of different isocyanates avoids the problem of uneven cell structure caused by the mismatch of reaction rates during the foaming process of a single isocyanate system.

[0022] In technical solution four, by precisely controlling the ratio of N-isopropylacrylamide to crosslinking agent and initiator, a more stable synthesis of temperature-sensitive polymers can be achieved compared to solutions without strict ratio control. The 2:2:1 mass ratio ensures a more uniform molecular weight distribution of poly(N-isopropylacrylamide), avoiding problems such as poor solubility due to excessively large molecular weight or insufficient temperature sensitivity due to excessively small molecular weight. The 4:4:3:1 ratio of epoxy resin, polyvinyl alcohol, and nano-zinc oxide ensures a moderate viscosity of the modified system, guaranteeing both uniform dispersion of nano-zinc oxide and preventing excessively high system viscosity from affecting the foaming effect.

[0023] In technical solution five, by precisely controlling the ratio of acrylonitrile to methyl methacrylate, a more stable core-shell structure can be achieved compared to solutions without strict ratio control. A 1:1 mass ratio ensures a suitable glass transition temperature for the copolymer, avoiding the problems of an overly hard shell due to excessive acrylonitrile content or an overly soft shell due to excessive methyl methacrylate content. The 1:2:1 ratio of benzoyl peroxide, isooctane, and dimethyl carbonate ensures the stability of the oil phase and the continuity of gas release.

[0024] In technical solution six, by precisely controlling the temperature of the three isothermal stages, a more uniform Mg curing can be achieved compared to solutions that do not employ stepped heating or have imprecise temperature control. 2+ Coordination crosslinking process. The first stage at 50℃ ensures Mg 2+ Sufficient diffusion to the oil phase interface avoids problems such as insufficient diffusion due to excessively low temperature or uneven rapid crosslinking due to excessively high temperature. The second stage at 60℃ is the critical coordination crosslinking temperature, at which temperature Mg... 2+ The coordination reaction rate with nitrile and ester groups is moderate, enabling the formation of a uniform shell structure. The third stage at 65°C further solidifies the shell, avoiding structural instability caused by insufficient cross-linking.

[0025] In technical solution seven, by precisely controlling the mixing pressure within the range of 14-16 MPa, the optimal component dispersion effect can be achieved compared to solutions with inaccurate pressure control or excessively high or low pressure. This pressure range is determined based on fluid mechanics principles, which can overcome the interfacial tension between the modified component and the polyurethane matrix, achieving uniform dispersion of nano-zinc oxide and modified isooctane, while avoiding the problems of shear overheating caused by excessively high pressure or uneven dispersion caused by excessively low pressure.

[0026] In technical solution eight, by controlling the curing time within the range of 18-22 minutes, the optimal molecular chain crosslinking effect can be achieved compared to solutions with excessively long or short curing times. This time range ensures that the polyurethane molecular chains have sufficient time to form a complete three-dimensional network structure, while avoiding the problems of excessive crosslinking due to excessive curing time causing the material to become brittle, or insufficient crosslinking due to insufficient curing time causing a decrease in strength.

[0027] In technical solution nine, by precisely controlling the particle size within the 20-40 nm range, optimal nucleation effects can be achieved compared to solutions with excessively large or small particle sizes. This particle size range ensures that the nano-zinc oxide has a sufficiently high specific surface area to provide nucleation sites, while avoiding the problems of severe agglomeration due to excessively small particle sizes or decreased nucleation efficiency due to excessively large particle sizes. The 20-40 nm particle size allows the nano-zinc oxide to form a uniformly distributed nucleation network in the polyurethane matrix, with the spacing between nucleation sites controlled within the range of 10-50 μm.

[0028] In technical solution ten, by using a combination of double-terminated hydroxypropyl silicone oil and polycarbodiimide, a more stable foaming process and superior material properties can be achieved compared to solutions using other types of stabilizers or anti-hydrolysis agents. The two hydroxyl groups at both ends of the double-terminated hydroxypropyl silicone oil can react with isocyanates, acting as flexible chain extenders in molecular chain construction. Simultaneously, its siloxane backbone effectively reduces surface tension and stabilizes the cell wall structure. Polycarbodiimide can react with isocyanates to form urethane, increasing the hard segment content. Furthermore, its multifunctional structure promotes molecular chain crosslinking, improving material strength. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are preferred embodiments of the present invention and should not be considered as excluding other embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0030] In the claims and description of this invention, the terms "comprising," "having," and variations thereof are used to mean "including but not limited to."

[0031] This invention relates to a method for preparing polyurethane foam, which includes the following steps: S10: Preparation of modified epoxy resin: By mass percentage, 15–25% N-isopropylacrylamide, 15–25% N,N'-methylenebisacrylamide, 8–12% ammonium persulfate, and 35–45% tetramethylethylenediamine aqueous solution (70–80% by mass) are mixed and reacted at 45–55°C for 10–14 hours under stirring at 250–350 rpm. After cooling, 35–45% bisphenol A type epoxy resin E-51, 25–35% polyvinyl alcohol, and 8–12% nano zinc oxide are added, and the reaction is continued to be stirred at room temperature for 10–14 hours to obtain modified epoxy resin. S20: Preparation of modified isooctane: Acrylonitrile 8–12%, methyl methacrylate 8–12%, benzoyl peroxide 8–12%, isooctane 15–25%, and dimethyl carbonate 8–12% were stirred at 1–5 °C for 1.5–2.5 hours to obtain an oil phase intermediate; then the intermediate was mixed with a magnesium chloride aqueous solution of 2–4% by mass at a mass ratio of 1:(5–7), and the mixture was heated under nitrogen protection to 48–52 °C for 0.8–1.2 hours, 58–62 °C for 9–11 hours, and 63–67 °C for 0.8–1.2 hours. After the reaction was completed, the mixture was cooled, filtered, washed, and vacuum dried to obtain modified isooctane. S30: 30–40 parts by weight of the modified epoxy resin, 7–10 parts by weight of the modified isooctane, 1–5 parts by weight of the catalyst, 3–5 parts by weight of the foam stabilizer, and 3–6 parts by weight of the anti-hydrolysis agent are added to the polyol component and mixed evenly to form component A; 40–50 parts by weight of polyisocyanate are used as component B; then, component A and component B are mixed by impact mixing with a high-pressure mixing head at a weight ratio of (1.05–1.15):1 under a mixing pressure of 12–18 MPa, and the mixture is injected into a mold preheated to 80–90°C for foaming and molding; after curing in the mold for 15–25 minutes, the mold is demolded to obtain polyurethane foam.

[0032] First, the preparation process of step S10 will be explained in detail.

[0033] This step of the preparation was carried out in a jacketed glass reactor equipped with a mechanical stirrer, reflux condenser, and precision temperature sensor. First, the temperature-sensitive polymer network was synthesized. Metered amounts of N-isopropylacrylamide, N,N'-methylenebisacrylamide, and a 70–80% (w / w) aqueous solution of tetramethylethylenediamine were added to a clean, dry reactor. Mechanical stirring was started, with a speed set between 250–350 rpm. Simultaneously, the reactor jacket was heated via a connected thermostatic circulation device to ensure a steady rise and stabilization of the material temperature within the reactor to the target range of 45–55°C. After temperature stabilization, a metered amount of ammonium persulfate initiator was slowly added to the reaction system. After the addition was complete, the set temperature and stirring rate were maintained for a isothermal reaction for 10–14 hours. The material in the reactor gradually became viscous, forming a three-dimensional cross-linked network of poly(N-isopropylacrylamide).

[0034] After the first stage of reaction is completed, heating is stopped, and cooling water is circulated into the reactor jacket to cool the product to room temperature. Then, the composite modification stage begins. While continuously stirring, metered amounts of bisphenol A type epoxy resin E-51, polyvinyl alcohol powder, and nano-zinc oxide with a particle size of 20-40 nm are slowly added to the reactor sequentially. To ensure uniform dispersion, it is recommended to thoroughly mix the epoxy resin with the product in the reactor before adding the other powders. Afterward, the system is stirred for 10–14 hours at room temperature. The prolonged mechanical shearing action ensures that each component achieves a uniform and stable microscopic dispersion in the high-viscosity system. After stirring, the resulting uniform viscous liquid is discharged from the bottom outlet of the reactor; this is the modified epoxy resin.

[0035] In one preferred embodiment, in step S10, the weight ratio of N-isopropylacrylamide, N,N'-methylenebisacrylamide, ammonium persulfate, tetramethylethylenediamine aqueous solution, bisphenol A type epoxy resin E-51, polyvinyl alcohol and nano zinc oxide is 2:2:1:4:4:3:1.

[0036] The preparation process of step S20 will be described in detail next.

[0037] This step begins with the preparation of the oil-phase intermediate. In a cryogenic reactor equipped with a jacket and stirrer, isooctane, dimethyl carbonate, acrylonitrile, methyl methacrylate, and the initiator benzoyl peroxide are added sequentially according to the formulation ratio. The connected cryogenic coolant circulation pump is started to lower and maintain the temperature of the materials in the reactor at 1–5°C. Stirring is initiated at this low temperature and the reaction is continued for 1.5–2.5 hours to form a stable oil-phase system containing the core material and monomers.

[0038] Suspension polymerization and coating followed. In a polymerization reactor equipped with programmed temperature control and gas protection, a metered-volume magnesium chloride aqueous solution (2–4% by mass) was first added as the aqueous phase. Under high-speed stirring, a pre-prepared oil phase intermediate was slowly injected into the aqueous phase via a transfer pump, dispersing it into fine oil droplets to form a stable oil-in-water suspension. The polymerization reactor was then sealed and nitrogen gas was introduced for protection before the programmed temperature control was initiated. The system was first heated to 48–52°C and held at that temperature for 0.8–1.2 hours to stabilize the oil droplets and allow the magnesium chloride to coat. 2+ Diffusion occurs at the oil-water interface; the temperature is then raised to 58–62°C and held for 9–11 hours, which is the main stage of polymerization and shell formation; finally, the temperature is raised to 63–67°C and held for 0.8–1.2 hours to solidify and shape the shell structure.

[0039] After the reaction was complete, the suspension in the reactor was cooled to room temperature and then filtered through a Buchner funnel to obtain a filter cake. The filter cake was repeatedly washed with a large amount of deionized water until no chloride ion precipitate was detected in the washing liquid using silver nitrate solution, ensuring that impurities were completely removed. Finally, the washed filter cake was placed in a vacuum drying oven and dried at 50-60°C to constant weight, and the resulting powdered solid was modified isooctane.

[0040] In a preferred embodiment, in step S20, the weight ratio of acrylonitrile, methyl methacrylate, benzoyl peroxide, isooctane, and dimethyl carbonate used to prepare the oil phase intermediate is 1:1:1:2:1; and the temperatures of the three isothermal stages of the programmed temperature rise are 50°C, 60°C, and 65°C, respectively.

[0041] Finally, the preparation process of step S30 is described in detail.

[0042] This step employs a high-pressure reactive injection molding process. First, component A (polyol blend) is prepared. In the component A storage tank of the high-pressure foaming machine, the basic polyol component is added, and the tank's stirring function is activated. While stirring, the modified epoxy resin prepared in step S10 is added at a ratio of 30–40 parts by weight, and the modified isooctane powder prepared in step S20 is added at a ratio of 7–10 parts by weight. Then, metered amounts of catalyst, foam stabilizer, and anti-hydrolysis agent are added sequentially. The component A storage tank is continuously stirred until all materials are completely and uniformly dispersed, forming a stable component A without precipitation or stratification. Simultaneously, 40–50 parts by weight of polyisocyanate are added to the component B storage tank as component B for later use.

[0043] Before foaming and molding, parameters are set on the control system of the high-pressure foaming machine to precisely control the output weight ratio of the high-pressure metering pumps for components A and B within the range of (1.05–1.15):1, and the working pressure of the mixing system is set to 12–18 MPa. Simultaneously, the temperature of the sealed metal mold is preheated and maintained at 80–90℃ using a mold temperature controller. After starting the equipment, components A and B are respectively pumped to the high-pressure impact mixing head by the high-pressure pump, achieving instantaneous and intense mixing within the cavity. The mixed material is immediately injected through the nozzle into the preheated and locked mold, where foaming and gelation reactions rapidly occur at the high temperature of the mold. The material is held under pressure and cured in the mold for 15–25 minutes until the cross-linking reaction of the polyurethane is fully completed and a stable cell structure is formed. Then, the mold can be opened, and the molded polyurethane foam product can be removed.

[0044] In a preferred embodiment, in step S30, the catalyst is selected from at least one of ethylenediamine, N,N-dimethylhexadecanamine, trimethylenediamine, bismuth isooctanoate, bismuth neodecanoate, stannous octoate, and dibutyltin dilaurate; the polyisocyanate is selected from at least one of toluene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, and naphthalene-1,5-diisocyanate; the mixing pressure is 14–16 MPa; the curing time is 18–22 minutes; the foam stabilizer is hydroxypropyl silicone oil, and the anti-hydrolysis agent is polycarbodiimide.

[0045] To further illustrate the advantages of the preparation method involved in this invention, the following examples and comparative examples are provided in this specification. It should be understood that these examples are only used to more clearly illustrate the technical solutions of this invention, and are not intended to limit the scope of protection of this invention in any way.

[0046] To ensure that the technical solutions of this invention can be clearly understood and implemented, unless otherwise stated, the information on raw materials and reagents used in the embodiments and comparative examples of this invention is as follows: N-Isopropylacrylamide (NIPAM): Analytical grade, Shanghai Aladdin Biochemical Technology Co., Ltd.

[0047] N,N'-Methylenebisacrylamide (MBA): Analytical grade, Shanghai Maclean Biochemical Technology Co., Ltd.

[0048] Ammonium persulfate (APS): Analytical grade, Sinopharm Chemical Reagent Co., Ltd.

[0049] Tetramethylethylenediamine (TEMED): Analytical grade, 75% aqueous solution, Sinopharm Chemical Reagent Co., Ltd.

[0050] Bisphenol A type epoxy resin E-51: Industrial grade, brand name NPEB-441, Nan Ya Epoxy Resin (Kunshan) Co., Ltd.

[0051] Polyvinyl alcohol (PVA): Industrial grade, brand name SVP-1799, China Petroleum & Chemical Corporation.

[0052] Nano-ZnO: Industrial grade, brand name JR-ZnO-30, average particle size 30nm, Xuancheng Jingrui New Materials Co., Ltd.

[0053] Acrylonitrile (AN): Analytical grade, Sinopharm Chemical Reagent Co., Ltd.

[0054] Methyl methacrylate (MMA): Analytical grade, Sinopharm Chemical Reagent Co., Ltd.

[0055] Benzoyl peroxide (BPO): Analytical grade, Sinopharm Chemical Reagent Co., Ltd.

[0056] Dimethyl carbonate (DMC): Analytical grade, Sinopharm Chemical Reagent Co., Ltd.

[0057] Polyol: Polyether polyol, brand name Wannol-360, Yantai Wanhua Polyurethane Co., Ltd.

[0058] Polyisocyanate: Polymerized MDI, brand name Wannol PM-200, Yantai Wanhua Polyurethane Co., Ltd.

[0059] Catalyst: Amine catalyst A-33 (33% triethylenediamine in propylene glycol solution) and organotin catalyst T-9 (stannous octoate) are used in combination.

[0060] Foam stabilizer: hydroxypropyl silicone oil with two ends, grade AK-8805, Jiangsu Momentive New Material Technology Co., Ltd.

[0061] Anti-hydrolysis agent: polycarbodiimide, brand name Stabaxol P, Lanxess Chemicals (China) Co., Ltd.

[0062] Nano-CaCO3: Industrial grade, brand name HN-1000, average particle size 40nm, Guangxi Huana New Materials Technology Co., Ltd. (For comparative example only) Water: Deionized water, used as a standard chemical foaming agent. (For comparative purposes only) Example 1 Step S10: Prepare the materials according to the weight ratio of N-isopropylacrylamide:N,N'-methylenebisacrylamide:ammonium persulfate:tetramethylethylenediamine aqueous solution:bisphenol A type epoxy resin E-51:polyvinyl alcohol:nano zinc oxide = 2:2:1:4:4:3:1. Specifically: Add 200g of N-isopropylacrylamide, 200g of N,N'-methylenebisacrylamide, and 400g of 75% tetramethylethylenediamine aqueous solution to the reactor. After stirring evenly, add 100g of ammonium persulfate, heat to 50℃, and react for 12 hours with stirring at 300 rpm. After cooling to room temperature, add 400g of bisphenol A type epoxy resin E-51, 300g of polyvinyl alcohol, and 100g of nano zinc oxide. Continue stirring at room temperature for 12 hours to obtain the modified epoxy resin.

[0063] Step S20: The reactants are prepared according to a weight ratio of acrylonitrile:methyl methacrylate:benzoyl peroxide:isooctane:dimethyl carbonate = 1:1:1:2:1. Specifically, 100g of acrylonitrile, 100g of methyl methacrylate, 100g of benzoyl peroxide, 200g of isooctane, and 100g of dimethyl carbonate are added to a low-temperature reactor and stirred at 3°C ​​for 2 hours to obtain an oil-phase intermediate. This intermediate is then mixed with 6000g of a 3% (w / w) magnesium chloride aqueous solution, and under nitrogen protection, the temperature is programmed to rise to 50°C and hold for 1 hour, then to 60°C and hold for 10 hours, and finally to 65°C and hold for 1 hour. After the reaction is complete, the mixture is cooled, filtered, washed, and vacuum dried to obtain modified isooctane.

[0064] Step S30: In the A material storage tank, 35 parts by weight of the modified epoxy resin prepared above, 8 parts by weight of the modified isooctane prepared above, 3 parts by weight of catalyst (A-33 to T-9 mass ratio 1:1), 4 parts by weight of foam stabilizer AK-8805, and 4 parts by weight of anti-hydrolysis agent Stabaxol P are added to 100 parts by weight of polyol Wannol-360 and mixed evenly to form component A. 45 parts by weight of polyisocyanate Wannol PM-200 are used as component B. The weight ratio of component A to component B is set to 1.1:1, the mixing pressure is 15 MPa, and the mixture is injected into a mold preheated to 85°C for foaming and molding. After curing in the mold for 20 minutes, the mixture is demolded to obtain polyurethane foam.

[0065] Example 2 Step S10: By mass percentage, 15% N-isopropylacrylamide, 15% N,N'-methylenebisacrylamide, 8% ammonium persulfate, and 35% tetramethylethylenediamine aqueous solution (70% by mass) are mixed and reacted at 45°C for 14 hours with stirring at 250 rpm. After cooling, 45% bisphenol A epoxy resin E-51, 25% polyvinyl alcohol, and 8% nano zinc oxide are added, and the reaction is continued with stirring at room temperature for 14 hours to obtain the modified epoxy resin.

[0066] Step S20: By mass percentage, 8% acrylonitrile, 8% methyl methacrylate, 8% benzoyl peroxide, 25% isooctane, and 8% dimethyl carbonate are stirred and reacted at 5°C for 2.5 hours; then, they are mixed with a 2% magnesium chloride aqueous solution at a mass ratio of 1:7, and the mixture is heated under nitrogen protection to 48°C for 1.2 hours, 58°C for 11 hours, and 63°C for 1.2 hours. After the reaction is completed, the treatment is the same as in Example 1.

[0067] Step S30: Add 30 parts by weight of modified epoxy resin, 7 parts by weight of modified isooctane, 1 part by weight of catalyst, 3 parts by weight of foam stabilizer, and 3 parts by weight of anti-hydrolysis agent to the polyol component to form component A; add 40 parts by weight of polyisocyanate as component B. Set the A:B weight ratio to 1.05:1, the mixing pressure to 12 MPa, the mold temperature to 80℃, and the curing time to 15 minutes.

[0068] Example 3 Step S10: By mass percentage, 25% N-isopropylacrylamide, 25% N,N'-methylenebisacrylamide, 12% ammonium persulfate, and 45% tetramethylethylenediamine aqueous solution (80% by mass) are mixed and reacted at 55°C for 10 hours with stirring at 350 rpm. After cooling, 35% bisphenol A epoxy resin E-51, 35% polyvinyl alcohol, and 12% nano zinc oxide are added, and the reaction is continued with stirring at room temperature for another 10 hours to obtain the modified epoxy resin.

[0069] Step S20: By mass percentage, 12% acrylonitrile, 12% methyl methacrylate, 12% benzoyl peroxide, 15% isooctane and 12% dimethyl carbonate are stirred and reacted at 1°C for 1.5 hours; then mixed with a 4% magnesium chloride aqueous solution at a mass ratio of 1:5, and the mixture is heated under nitrogen protection to 52°C for 0.8 hours, 62°C for 9 hours, and 67°C for 0.8 hours. After the reaction is completed, the treatment is the same as in Example 1.

[0070] Step S30: Add 40 parts by weight of modified epoxy resin, 10 parts by weight of modified isooctane, 5 parts by weight of catalyst, 5 parts by weight of foam stabilizer, and 6 parts by weight of anti-hydrolysis agent to the polyol component to form component A; add 50 parts by weight of polyisocyanate as component B. Set the A:B weight ratio to 1.15:1, the mixing pressure to 18 MPa, the mold temperature to 90℃, and the curing time to 25 minutes.

[0071] Comparative Example 1 This comparative example is a conventional polyurethane foam preparation method that does not use any of the core additives of this invention.

[0072] Component A is a mixture of 100 parts by weight of polyol Wannol-360, 3 parts by weight of catalyst, 4 parts by weight of foam stabilizer AK-8805, and 2 parts by weight of water (as a chemical blowing agent). Component B is 45 parts by weight of polyisocyanate Wannol PM-200. The foaming process parameters are the same as in Example 1.

[0073] Comparative Example 2 This comparative example illustrates the method of using inorganic fillers to improve performance in the background technology.

[0074] Component A is a mixture of 100 parts by weight of polyol Wannol-360, 35 parts by weight of nano-calcium carbonate (replacing modified epoxy resin), 3 parts by weight of catalyst, 4 parts by weight of foam stabilizer AK-8805, and 2 parts by weight of water. Component B is 45 parts by weight of polyisocyanate Wannol PM-200. The foaming process parameters are the same as in Example 1.

[0075] Comparative Example 3 This comparative example uses only the modified epoxy resin prepared in step S10, instead of the modified isooctane prepared in step S20. Specifically, component A is a mixture of 100 parts by weight of polyol Wannol-360, 35 parts by weight of the modified epoxy resin prepared in Example 1, 3 parts by weight of catalyst, 4 parts by weight of foam stabilizer AK-8805, and 2 parts by weight of water (in place of modified isooctane as a blowing agent). Component B is 45 parts by weight of polyisocyanate Wannol PM-200. The foaming process parameters are the same as in Example 1.

[0076] Comparative Example 4 This comparative example uses only the modified isooctane prepared in step S20, instead of the modified epoxy resin prepared in step S10. Specifically, component A is a mixture of 100 parts by weight of polyol Wannol-360, 8 parts by weight of the modified isooctane prepared in Example 1, 3 parts by weight of catalyst, 4 parts by weight of foam stabilizer AK-8805, and 4 parts by weight of anti-hydrolysis agent Stabaxol P. Component B is 45 parts by weight of polyisocyanate Wannol PM-200. The foaming process parameters are the same as in Example 1.

[0077] The samples prepared in the above embodiments and comparative examples were tested using the following test methods: After the samples prepared in the above examples and comparative examples were placed in a standard environment (23±2℃, 50±5% RH) for 24 hours, they were tested using the following test methods: Apparent density: The density was determined according to GB / T 6343-2009 "Determination of density of flexible foam polymer materials". The sample was cut into regular specimens of 50mm×50mm×fixed thickness, and its mass was accurately weighed. The apparent density was obtained by calculating "mass / (length×width×thickness)".

[0078] Compressive strength: The test was conducted in accordance with GB / T 8813-2008 "Determination of compressive properties of rigid foamed plastics". A universal testing machine was used to compress the sample at a rate of 5 mm / min. The compressive stress at which the sample exhibited 25% relative deformation was recorded as the 25% compressive strength.

[0079] Cell structure analysis: Polyurethane foam samples were immersed in liquid nitrogen for 1 minute to induce brittle fracture. Fresh cross-sections were photographed and magnified using a digital microscope. Within a 2mm field of view, the cell diameter of all bubbles was measured, and this process was repeated 5 times. The maximum pore diameter (ASmax) and minimum pore diameter (ASmin) of each measurement were recorded, and the pore diameter difference (ASmax - ASmin) was calculated as the core indicator for evaluating cell uniformity.

[0080] The test results are shown in the table below:

[0081] Comparative Example 1, using a conventional chemical foaming process, exhibited low compressive strength and a pore size difference of 70 μm, indicating inconsistent pore sizes and poor structural uniformity. Comparative Example 2 simulated a conventional inorganic filler-reinforced method; although the density was significantly increased, the improvement in compressive strength was limited, and the pore size difference further increased to 80 μm, demonstrating that simple physical filling failed to improve the pore structure and may even introduce defects due to filler agglomeration. Example 1 of the present invention, while achieving higher density, increased compressive strength to 10.2 kPa and controlled the pore size difference to 25 μm, demonstrating excellent mechanical properties and a highly uniform pore structure, effectively solving the problems existing in the prior art.

[0082] Analysis of Comparative Examples 3 and 4 shows that using modified epoxy resin alone (Comparative Example 3) or modified isooctane alone (Comparative Example 4) can improve the performance of foam to a certain extent. Specifically, both can improve the cell size difference from 70 μm to 50 μm and increase the compressive strength to varying degrees, indicating that each additive has the function of optimizing cell structure and improving mechanical properties. However, when the two additives are used in combination, as shown in Example 1, the cell size difference of the resulting foam is further significantly reduced to 25 μm, a value superior to that achieved by using either additive alone. Simultaneously, its compressive strength reaches 10.2 kPa, higher than the values ​​of the two comparative examples. This significant performance improvement is not a simple additive effect of the two additives, but rather indicates that they produce functional complementarity and synergy during the foaming process. Modified epoxy resin provides a large number of uniform nucleation sites, while modified isooctane provides a stable and controllable gas source for these sites. The combination of the two makes the cell nucleation and growth process highly matched, thus forming a more uniform and fine cell structure that cannot be obtained when used alone.

[0083] The foregoing description of the specifications and embodiments is intended to explain the scope of protection of this invention, but does not constitute a limitation on the scope of protection of this invention. Modifications, equivalent substitutions, or other improvements to the embodiments of this invention or a portion thereof that can be obtained by those skilled in the art through logical analysis, reasoning, or limited experimentation, based on the teachings of this invention or the foregoing embodiments, in conjunction with common knowledge, general technical knowledge, and / or existing technology, should all be included within the scope of protection of this invention.

Claims

1. A method for preparing polyurethane foam, characterized in that, Includes the following steps: S10: Preparation of modified epoxy resin: By mass percentage, 15–25% N-isopropylacrylamide, 15–25% N,N'-methylenebisacrylamide, 8–12% ammonium persulfate, and 35–45% tetramethylethylenediamine aqueous solution (70–80% by mass) are mixed and reacted at 45–55°C for 10–14 hours under stirring at 250–350 rpm. After cooling, 35–45% bisphenol A epoxy resin E-51, 25–35% polyvinyl alcohol, and 8–12% nano zinc oxide are added, and the reaction is continued to be stirred at room temperature for 10–14 hours to obtain modified epoxy resin. S20: Preparation of modified isooctane: Acrylonitrile 8–12%, methyl methacrylate 8–12%, benzoyl peroxide 8–12%, isooctane 15–25%, and dimethyl carbonate 8–12% were stirred at 1–5 °C for 1.5–2.5 hours to obtain an oil phase intermediate; then the intermediate was mixed with a magnesium chloride aqueous solution of 2–4% by mass at a mass ratio of 1:(5–7), and the mixture was heated under nitrogen protection to 48–52 °C for 0.8–1.2 hours, 58–62 °C for 9–11 hours, and 63–67 °C for 0.8–1.2 hours. After the reaction was completed, the mixture was cooled, filtered, washed, and vacuum dried to obtain modified isooctane. S30: 30–40 parts by weight of the modified epoxy resin, 7–10 parts by weight of the modified isooctane, 1–5 parts by weight of the catalyst, 3–5 parts by weight of the foam stabilizer, and 3–6 parts by weight of the anti-hydrolysis agent are added to the polyol component and mixed evenly to form component A; 40–50 parts by weight of polyisocyanate are used as component B; then, component A and component B are mixed by impact mixing with a high-pressure mixing head at a weight ratio of (1.05–1.15):1 under a mixing pressure of 12–18 MPa, and the mixture is injected into a mold preheated to 80–90°C for foaming and molding; after curing in the mold for 15–25 minutes, the mold is demolded to obtain polyurethane foam.

2. The method for preparing polyurethane foam as described in claim 1, characterized in that, in In step S30, the catalyst is selected from at least one of ethylenediamine, N,N-dimethylhexadecanamine, trimethylenediamine, bismuth isooctanoate, bismuth neodecanoate, stannous octoate, and dibutyltin dilaurate.

3. The method for preparing polyurethane foam as described in claim 1, characterized in that, in In step S30, the polyisocyanate is selected from at least one of toluene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, and naphthalene-1,5-diisocyanate.

4. The method for preparing polyurethane foam as described in claim 1, characterized in that, In step S10, the weight ratio of N-isopropylacrylamide, N,N'-methylenebisacrylamide, ammonium persulfate, tetramethylethylenediamine aqueous solution, bisphenol A type epoxy resin E-51, polyvinyl alcohol and nano zinc oxide is 2:2:1:4:4:3:

1.

5. The method for preparing polyurethane foam as described in claim 1, characterized in that, In step S20, the weight ratio of acrylonitrile, methyl methacrylate, benzoyl peroxide, isooctane and dimethyl carbonate used to prepare the oil phase intermediate is 1:1:1:2:

1.

6. The method for preparing polyurethane foam as described in claim 1, characterized in that, In step S20, the temperatures of the three isothermal stages of the programmed heating are 50°C, 60°C, and 65°C, respectively.

7. A method for preparing polyurethane foam as described in claim 1, characterized in that, In step S30, the mixing pressure is 14–16 MPa.

8. The method for preparing polyurethane foam as described in claim 1, characterized in that, In step S30, the curing time is 18–22 minutes.

9. The method for preparing polyurethane foam as described in claim 1, characterized in that, In step S10, the particle size of the nano zinc oxide is 20-40 nm.

10. A method for preparing polyurethane foam as described in claim 1, characterized in that, In step S30, the foam stabilizer is a double-ended hydroxypropyl silicone oil, and the anti-hydrolysis agent is a polycarbodiimide.

Images