A method for synthesizing flame-retardant polyurethane

Abstract

This invention relates to a method for synthesizing polyurethane, and more particularly to a method for synthesizing flame-retardant polyurethane. This invention primarily addresses the problems of high flame retardant addition levels, high cost, complex processes, and susceptibility to material mechanical properties in current flame-retardant polyurethane synthesis processes. In this invention, a prepolymer composed of polyol and isocyanate is thoroughly stirred with a flame retardant obtained through chemical extraction. A chain extender is added, and the mixture is stirred again before being pressed into tablets using a vulcanizing machine and aged in an oven to obtain flame-retardant polyurethane. This invention offers advantages such as mild reaction conditions, convenient product separation, low cost, high added value of recovered components, and excellent flame-retardant properties of the synthesized polyurethane.

Description

Technical Field

[0001] This invention relates to a method for synthesizing polyurethane, and more particularly to a method for synthesizing flame-retardant polyurethane. Background Technology

[0002] Polyurethane (PU), short for polyurethane elastomer, is an organic polymer material mainly produced by the reaction of polyols and isocyanates. It possesses characteristics such as low-temperature resistance, wear resistance, high hardness, easy molding, light weight, and low cost, and is widely used in various fields including construction, home furnishings, aerospace, transportation, and home appliances. Globally, polyurethane products are diverse and produced in vast quantities. By the end of 2016, the global total production of polyurethane had reached approximately 22 million tons, of which my country's consumption reached approximately 11 million tons, generating direct economic benefits of about 350 billion yuan. However, as a high-molecular organic compound, untreated polyurethane materials are highly flammable. Upon contact with fire, the flame spreads rapidly and is accompanied by dripping, potentially leading to uncontrollable combustion and decomposition, producing large amounts of toxic gases and fumes, thus endangering human life and property. Therefore, the research on flame-retardant polyurethane elastomer materials has always been a hot topic in polyurethane material research. In the polyurethane material manufacturing industry, modification treatment is necessary to introduce flame-retardant technology into the polyurethane to improve the material's thermal properties and reduce safety hazards. The main methods for synthesizing flame-retardant polyurethane materials are as follows: (1) Introducing additive flame retardants, that is, adding substances with flame-retardant properties but no reactive activity to the raw materials, and the flame-retardant substances will be dispersed in the molded material; (2) Introducing reactive flame retardants (also known as structural flame retardants), that is, introducing elements with flame-retardant properties into the raw materials. Common flame retardants include phosphorus-based flame retardants, halogen-based flame retardants and inorganic flame retardants. Among them, halogen-based flame retardants have the advantages of low usage, high flame-retardant efficiency, good stability and high decomposition temperature (above 300℃); (3) Introducing flame-retardant structures, that is, introducing structures with certain flame-retardant properties into the polyurethane molecular structure, such as imides and isocyanurates. Among these three methods, introducing additive flame retardants has the characteristics of wide applicability, taking into account the physical and mechanical properties of the material, and having little impact on the material formation reaction. It is the earliest applied and simpler and more economical method; reactive flame retardants will be linked to the molecular skeleton of polyurethane through participation in chemical reactions, so the flame-retardant effect of reactive flame retardants is more durable.

[0003] Patent CN 105440652B discloses a flame-retardant thermoplastic polyurethane elastomer and its preparation method. It uses ionic liquids and intumescent flame retardants (ammonium polyphosphate, aluminum hypophosphite, etc.) to modify polyurethane for flame retardancy, preparing an intumescent flame-retardant thermoplastic polyurethane elastomer composite material. A small amount of ionic liquid, or the synergistic effect of ionic liquid and intumescent flame retardant, improves the oxygen index and vertical burning performance (reflecting resistance to dripping) of the composite material, significantly reducing the heat release rate and total heat release, exhibiting good flame-retardant effects. However, the synthesis of the composite material requires the addition of a large amount of intumescent flame retardant, which negatively impacts the material's mechanical properties. Furthermore, small-molecule ionic liquids are expensive and, being liquid at room temperature, easily migrate and precipitate from the matrix, causing the composite material to lose its original flame-retardant properties. Patent CN 107988811B discloses a method for producing flame-retardant polyurethane synthetic leather. This method uses an environmentally friendly magnesium hydroxide flame retardant complexed with an intumescent flame retardant to produce the leather. Due to the poor compatibility between traditional magnesium hydroxide and organic materials, this method utilizes bis(4-carboxyphenyl)phenylphosphine oxide, o-carboxyphenylacetic acid, 4-acetylaminosalicylic acid, and hypozonotriacetic acid to complex with magnesium hydroxide and the intumescent flame retardant, thereby improving the compatibility between the environmentally friendly magnesium hydroxide flame retardant and the base fabric. The resulting polyurethane synthetic leather, after flame-retardant treatment, achieves a flame retardancy level of good or higher. However, this method suffers from problems such as the addition of a large amount of organic reagents, complex processes, and high costs. In summary, current methods for synthesizing flame-retardant polyurethane suffer from problems such as high flame retardant dosage, high cost, complex processes, and susceptibility to changes in the mechanical properties of the material. Summary of the Invention

[0004] To address the problems of high flame retardant dosage, high cost, complex processes, and susceptibility to material mechanical properties in current flame-retardant polyurethane preparation methods, this invention provides a synthesis method for flame-retardant polyurethane that features mild reaction conditions, simple process, low cost, and significant flame retardant effect.

[0005] To achieve the above objectives, the present invention employs the following technical solutions:

[0006] A method for synthesizing flame-retardant polyurethane involves thoroughly mixing a prepolymer composed of polyol and isocyanate with a flame retardant obtained by chemical extraction, adding a chain extender and mixing again, then pressing the mixture into tablets using a vulcanizing machine and aging it in an oven to obtain flame-retardant polyurethane.

[0007] Furthermore, the flame retardant obtained by chemical extraction includes the following steps:

[0008] Step 1: Prepare an extraction solution by mixing solvent and acid, and then soak the waste circuit boards in the extraction solution to carry out the reaction.

[0009] Step 2: After the reaction is complete, the product is separated and recovered. The recovered product is then processed to prepare a flame retardant.

[0010] Furthermore, in step 1, the solvent is one or a mixture of two solvents in any proportion, namely glacial acetic acid and water. Preferably, the solvent is glacial acetic acid, which can swell the waste circuit board in a short time. After swelling, the metal layer and glass fiber layer of the circuit board can be effectively separated from the resin, and the resin is more likely to come into contact with acid and water molecules, thereby increasing the reaction rate.

[0011] Furthermore, the acid in step 1 is one or a mixture of several of the following in any proportion: methanesulfonic acid, trifluoromethanesulfonic acid, dodecylbenzenesulfonic acid, trichloromethanesulfonic acid, trifluoroacetic acid, trichloroacetic acid, benzenesulfonic acid, p-toluenesulfonic acid, and squaric acid. The hydrogen ions provided by the acid interact with nitrogen atoms during extraction, thereby breaking the CN bonds in the resin. Moreover, these acid molecules are relatively small, making it easier for them to access the internal structure of the resin and improving reaction efficiency.

[0012] Brominated epoxy resin in waste circuit boards exhibits high combustion delay. The three-dimensional network of highly functionalized resin formed through curing possesses excellent mechanical properties and chemical stability, acting as an adhesive between the layers of the waste circuit board. Waste circuit boards are immersed in an extraction solution prepared from a solvent with swelling properties and an acid with catalytic effects. Under specific temperature and time conditions, glacial acetic acid in the extraction solution swells the resin in the waste circuit board. After swelling, the green oil layer, metal layer, glass fiber, and resin layer of the circuit board are effectively separated. The hydrogen ions provided by the catalytic acid diffuse into the resin's internal structure and interact with the N atoms near the CN bonds, causing the CN bonds in the resin to break. The main carbon skeleton of the resin and the bromine element are retained, and the effective flame-retardant components in the non-metallic components are extracted and processed to prepare a flame retardant. A prepolymer composed of polyols and isocyanates is thoroughly mixed with the flame retardant and chain extender, then pressed into sheets using a vulcanizing machine and aged in an oven to synthesize flame-retardant polyurethane.

[0013] Furthermore, in step 1, the waste circuit boards can be any one of the following: waste copper-clad laminates, waste printed circuit boards, waste circuit board scraps, waste mobile phone boards, and waste computer boards. These waste circuit boards have a high metal content and high recycling value, while the flame-retardant components in the non-metallic layers have high added value and high reuse value.

[0014] Furthermore, in step 1, the mass ratio of waste circuit boards to extractant is 1:2 to 20. Within this mass range, the extraction of flame-retardant components from waste circuit boards is highly economical and effective. If the extractant content is too low, the waste circuit boards cannot be completely submerged, and the brominated epoxy resin cannot be depolymerized; if the extractant content is too high, the cost is high and the economic efficiency is poor.

[0015] Furthermore, the reaction temperature in step 1 is 130℃~200℃, and the time is 1h~18h. This temperature and time range provides mild conditions, which are conducive to the depolymerization of brominated epoxy resin, resulting in good performance. Short reaction times and low temperatures prevent the brominated epoxy resin from depolymerizing; long reaction times and high temperatures lead to excessive depolymerization, easy resin carbonization, numerous side reactions, and complex products.

[0016] Furthermore, the specific method for separation and recovery in step 2 is as follows: the copper foil, glass fiber, and extract are directly filtered and separated; the copper foil and glass fiber are washed, filtered, and dried using an organic solvent; water is added to the separated extract to wash until the substance precipitates; after centrifugation, filtration, and drying, the recovered product is obtained. This separation method is simple and convenient, the organic solvent used can be reused, and the washing agent is water, making it low-cost and environmentally friendly.

[0017] Furthermore, the organic solvent is any one of halogenated hydrocarbons, ethers, alcohols, and ketones. The aforementioned organic solvents have good treatment effects on copper foil and glass fiber; the recovered copper foil and glass fiber retain good strength, have clean surfaces without residue, and are recyclable.

[0018] Furthermore, the specific method for processing in step 2 is to grind the recycled product into powder and prepare it as a flame retardant. This processing method is simple and convenient, and the prepared flame retardant can be used directly with good flame retardant effect.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] (1) The solvent is glacial acetic acid aqueous solution, which is green and environmentally friendly and can be reused; the acid is Brønsted acid, which has a small molecular size and high reaction efficiency. (2) The reaction conditions are mild, the separation is simple and convenient, and the organic solvent used for washing can be recycled; the surface of the obtained metal layer and glass fiber layer is clean and undamaged, and the strength is well maintained, and the product is easy to recycle. (3) Under this system, the main structure of brominated epoxy resin in waste circuit boards remains stable, the bromine element is retained, the flame retardant component is easy to extract, and the synthesized flame retardant polyurethane has good flame retardant properties. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of a discarded circuit board;

[0022] Figure 2 This is a schematic diagram of the layered structure of a waste circuit board;

[0023] Figure 3 A schematic diagram of flame retardants prepared from waste circuit boards;

[0024] Figure 4 NMR spectrum of tetrabromobisphenol A, a model compound of brominated epoxy resin, for stability testing;

[0025] Figure 5 This is a schematic diagram comparing non-flame-retardant polyurethane and flame-retardant polyurethane.

[0026] Figure 6 This is a schematic diagram comparing polyurethane with physical filler and polyurethane with chemical filler.

[0027] Figure 7 This is a schematic diagram of a vertical combustion experiment on a flame-retardant polyurethane sample. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] Figure 1 Schematic diagram of waste circuit boards Figure 2 A schematic diagram of the layered structure of waste circuit boards. Figure 3 A schematic diagram of flame retardants extracted and prepared from waste circuit boards. Figure 4 NMR spectrum for stability testing of tetrabromobisphenol A, a model compound of brominated epoxy resin. Figure 5 This is a schematic diagram comparing non-flame-retardant polyurethane and flame-retardant polyurethane. Figure 6 A comparative diagram of physical filler polyurethane and chemical filler polyurethane. Figure 7 This is a schematic diagram of a vertical combustion experiment on a flame-retardant polyurethane sample.

[0030] The specific implementation method is as follows:

[0031] Example 1

[0032] 2g of glacial acetic acid was added to a 10mL high-pressure polytetrafluoroethylene (PTFE) reactor. 0.5g of waste circuit boards were then immersed in the glacial acetic acid, with a mass ratio of waste circuit boards to glacial acetic acid of 1:4. The reactor was placed in an oven and reacted at 220℃ for 16 hours. After the reaction was complete, the extract and solid phase were separated by filtration. The green oil layer and copper foil layer in the solid phase were washed with distilled water and then dried in an oven at 80℃. The surface of the glass fiber was washed with anhydrous ethanol, and after evaporating the ethanol, clean glass fiber was obtained. The extract was placed in a centrifuge tube with distilled water added. After the product precipitated, it was centrifuged, the upper liquid phase was poured off, and the bottom product was washed three times with distilled water and then dried in a vacuum drying oven. Under these conditions, carbonization occurred in the resin, the product was complex, and excessive degradation occurred.

[0033] Examples 2-4

[0034] A certain amount of glacial acetic acid was added to a 10 mL polytetrafluoroethylene high-pressure reactor. 0.5 g of waste circuit boards were then immersed in the glacial acetic acid, with a mass ratio of waste circuit boards to glacial acetic acid of 1:4–10. The reactor was placed in an oven for reaction at a temperature of 120℃–220℃ for 12–16 hours. After the reaction was complete, the extract and solid phase were separated by filtration. The green oil layer and copper foil layer in the solid phase were washed with distilled water and then dried in an oven at 80℃. The surface of the glass fiber was cleaned with organic solvent, and after evaporation of the organic solvent, clean glass fiber was obtained. The extract was placed in a centrifuge tube with distilled water added. After the product precipitated, it was centrifuged, and the upper liquid phase was poured off. The bottom product was washed three times with distilled water and then placed in a vacuum drying oven for drying. The product characteristics are shown in Table 1.

[0035] Table 1 shows the products obtained after separating and recovering the extract when glacial acetic acid was used as the extraction solvent, under different masses of extraction solvent, different temperatures, and different times.

[0036]

[0037] Example 5

[0038] A glacial acetic acid aqueous solution prepared by mixing 1.5g of glacial acetic acid with 1g of water was placed in a 10mL polytetrafluoroethylene high-pressure reactor. 50µL of trifluoromethanesulfonic acid was added as the extraction solution. 0.5g of waste circuit boards were immersed in the extraction solution, with a mass ratio of waste circuit boards to extraction solution of 1:5. The reactor was placed in an oven and reacted at 170℃ for 12 hours. After the reaction was complete, the extract and solid phase were separated by filtration. The green oil layer and copper foil layer in the solid phase were washed with distilled water and then dried in an oven at 80℃. The surface of the glass fiber was washed with acetone, and after evaporating the acetone, clean glass fiber was obtained. The extract was placed in a centrifuge tube with distilled water added. After the product precipitated, it was centrifuged, and the upper liquid phase was poured off. The bottom product was washed three times with distilled water and then dried in a vacuum drying oven. The dried, blocky black asphalt product was ground into powder in a mortar. Under these conditions, the resin completely depolymerized.

[0039] Example 6

[0040] A glacial acetic acid aqueous solution prepared by mixing 1.8g of glacial acetic acid with 1.2g of water was placed in a 10mL polytetrafluoroethylene high-pressure reactor. 100µL of p-toluenesulfonic acid was added as the extraction solution. 0.6g of waste circuit boards were immersed in the extraction solution, with a mass ratio of waste circuit boards to extraction solution of 1:5. The reactor was placed in an oven and reacted at 180℃ for 12 hours. After the reaction was complete, the extract and solid phase were separated by filtration. The green oil layer and copper foil layer in the solid phase were washed with distilled water and then dried in an oven at 80℃. The surface of the glass fiber was washed with anhydrous ethanol, and after evaporating the ethanol, clean glass fiber was obtained. The extract was placed in a centrifuge tube with distilled water added. After the product precipitated, it was centrifuged, and the upper liquid phase was poured off. The bottom product was washed three times with distilled water and then dried in a vacuum drying oven. The dried, blocky black asphalt product was ground into powder in a mortar. Under these conditions, the resin completely depolymerized.

[0041] Table 2 shows the products obtained after separating and recovering the extract when the solvent and acid were used to prepare the extract under different masses of extract, different masses of waste circuit boards, and different reaction temperatures.

[0042]

[0043] Example 7

[0044] A glacial acetic acid aqueous solution prepared by mixing 40g of glacial acetic acid with 10g of water was placed in a 250mL polytetrafluoroethylene high-pressure reactor. 10g of trichloroacetic acid was added as the extraction solution. 10g of waste circuit boards were immersed in the extraction solution, with a mass ratio of waste circuit boards to extraction solution of 1:6. The reactor was placed in an oven and reacted at 160℃ for 12 hours. After the reaction was complete, the extract and solid phase were separated by filtration. The green oil layer and copper foil layer in the solid phase were washed with distilled water and then dried in an oven at 80℃. The surface of the glass fiber was washed with acetone, and after evaporating the acetone, clean glass fiber was obtained. The extract was placed in a centrifuge tube with distilled water added. After the product precipitated, it was centrifuged, and the upper liquid phase was poured off. The bottom product was washed three times with distilled water and then dried in a vacuum drying oven. The dried, blocky black asphalt product was ground into powder in a mortar to prepare a flame retardant. The prepolymer composed of polyol and isocyanate was thoroughly stirred with the obtained flame retardant, and the chain extender was added and stirred again. The mixture was then pressed into tablets using a vulcanizing machine and aged in an oven to obtain a flame-retardant polyurethane material. The oxygen index of the material was measured to be 25.

[0045] Example 8

[0046] A glacial acetic acid aqueous solution prepared by mixing 35g of glacial acetic acid with 15g of water was placed in a 250mL polytetrafluoroethylene high-pressure reactor. 10g of trifluoromethanesulfonic acid was added as the extraction solution. 5g of waste circuit boards were immersed in the extraction solution, with a mass ratio of waste circuit boards to extraction solution of 1:12. The reactor was placed in an oven and reacted at 170℃ for 12 hours. After the reaction was complete, the extract and solid phase were separated by filtration. The green oil layer and copper foil layer in the solid phase were washed with distilled water and then dried in an oven at 80℃. The surface of the glass fiber was washed with anhydrous ethanol, and after evaporating the ethanol, clean glass fiber was obtained. The extract was placed in a centrifuge tube with distilled water added. After the product precipitated, it was centrifuged, and the upper liquid phase was poured off. The bottom product was washed three times with distilled water and then dried in a vacuum drying oven. The dried, blocky black asphalt product was ground into powder in a mortar to prepare a flame retardant. The prepolymer composed of polyol and isocyanate was thoroughly stirred with the obtained flame retardant, and the chain extender was added and stirred again. The mixture was then pressed into tablets using a vulcanizing machine and aged in an oven to obtain a flame-retardant polyurethane material. The oxygen index of the material was measured to be 26.5.

[0047] Example 9

[0048] A glacial acetic acid aqueous solution prepared by mixing 40g of glacial acetic acid with 10g of water was placed in a 250mL polytetrafluoroethylene high-pressure reactor. 10g of dodecylbenzenesulfonic acid was added as the extraction solution. 10g of waste circuit boards were immersed in the extraction solution, with a mass ratio of waste circuit boards to extraction solution of 1:6. The reactor was placed in an oven and reacted at 180℃ for 12 hours. After the reaction was complete, the extract and solid phase were separated by filtration. The green oil layer and copper foil layer in the solid phase were washed with distilled water and then dried in an oven at 80℃. The surface of the glass fiber was washed with acetone, and after evaporating the acetone, clean glass fiber was obtained. The extract was placed in a centrifuge tube with distilled water added. After the product precipitated, it was centrifuged, and the upper liquid phase was poured off. The bottom product was washed three times with distilled water and then dried in a vacuum drying oven. The dried, blocky black asphalt product was ground into powder in a mortar to prepare a flame retardant. The prepolymer composed of polyol and isocyanate was thoroughly stirred with the obtained flame retardant, and the chain extender was added and stirred again. The mixture was then pressed into tablets using a vulcanizing machine and aged in an oven to obtain a flame-retardant polyurethane material. The oxygen index of the material was measured to be 27.3.

[0049] Example 10

[0050] A glacial acetic acid aqueous solution prepared by mixing 40g of glacial acetic acid with 10g of water was placed in a 250mL polytetrafluoroethylene high-pressure reactor. 10g of methanesulfonic acid was added as the extraction solution. 10g of waste circuit boards were immersed in the extraction solution, with a mass ratio of waste circuit boards to extraction solution of 1:6. The reactor was placed in an oven and reacted at 170℃ for 12 hours. After the reaction was complete, the extract and solid phase were separated by filtration. The green oil layer and copper foil layer in the solid phase were washed with distilled water and then dried in an oven at 80℃. The surface of the glass fiber was washed with anhydrous ethanol, and after evaporating the ethanol, clean glass fiber was obtained. The extract was placed in a centrifuge tube with distilled water added. After the product precipitated, it was centrifuged, and the upper liquid phase was poured off. The bottom product was washed three times with distilled water and then dried in a vacuum drying oven. The dried, blocky black asphalt product was ground into powder in a mortar to prepare a flame retardant. The prepolymer composed of polyol and isocyanate was thoroughly stirred with the obtained flame retardant, and the chain extender was added and stirred again. The mixture was then pressed into tablets using a vulcanizing machine and aged in an oven to obtain a flame-retardant polyurethane material. The oxygen index of the material was measured to be 28.2.

[0051] Table 3 shows the process of preparing an extract using solvent and acid. Waste circuit boards are immersed in the extract for reaction. After the reaction, the extract is separated and recycled. The resulting product is then processed to prepare a flame retardant and synthesize flame-retardant polyurethane material. The oxygen index of the material is measured.

[0052]

[0053] Contents not described in detail in this specification are prior art known to those skilled in the art. Although illustrative specific embodiments of the invention have been described above to facilitate understanding by those skilled in the art, it should be understood that the invention is not limited to the scope of the specific embodiments. Various modifications are readily apparent to those skilled in the art as long as they fall within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of this invention are protected.

Claims

1. A method for synthesizing flame-retardant polyurethane, characterized in that: The prepolymer composed of polyol and isocyanate is thoroughly stirred with the flame retardant obtained by chemical extraction, and the chain extender is added and stirred again. The mixture is then pressed into tablets in a vulcanizing machine and aged in an oven to obtain flame-retardant polyurethane. The flame retardant obtained by chemical extraction includes the following steps: Step 1: Prepare an extraction solution by mixing solvent and acid, and then soak the waste circuit boards in the extraction solution to carry out the reaction. Step 2: After the reaction is complete, the product is separated and recovered. The recovered product is then processed to prepare a flame retardant. The resin used in step 1 for the waste circuit boards is brominated epoxy resin; In step 1, the waste circuit board can be any one of the following: waste copper-clad laminate, waste printed circuit board, waste circuit board scraps, waste mobile phone board, or waste computer board. In step 1, the mass ratio of waste circuit boards to extractant is 1:2 to 20. The reaction temperature in step 1 is 130℃~200℃, and the time is 1h~18h; The specific method for separation and recovery in step 2 is as follows: the copper foil, glass fiber and extract are directly filtered and separated; the copper foil and glass fiber are washed, filtered and dried using organic solvents; water is added to the separated extract and washed until the substance precipitates; the recovered product is obtained after centrifugation, filtration and drying.

2. The method for synthesizing flame-retardant polyurethane according to claim 1, characterized in that: The solvent in step 1 is one or a mixture of two solvents in any proportion, namely glacial acetic acid and water.

3. The method for synthesizing flame-retardant polyurethane according to claim 1, characterized in that: The acid in step 1 is one or a mixture of several of the following in any proportion: methanesulfonic acid, trifluoromethanesulfonic acid, dodecylbenzenesulfonic acid, chloroform sulfonic acid, trifluoroacetic acid, trichloroacetic acid, benzenesulfonic acid, p-toluenesulfonic acid, and squaric acid.

4. The method for synthesizing flame-retardant polyurethane according to claim 1, characterized in that: The organic solvent is any one of halogenated hydrocarbons, ethers, alcohols, and ketones.

5. The method for synthesizing flame-retardant polyurethane according to claim 1, characterized in that: The specific method in step 2 is to grind the recycled product into powder and prepare it as a flame retardant.

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