A method for preparing a regenerated polyol from a schiff base polyurethane

Abstract

The present application belongs to the technical field of polyurethane material recycling, and particularly relates to a method for preparing regenerated polyols from Schiff base polyurethane. The Schiff base polyurethane has an imine structure, and the preparation of regenerated polyols from amino alcohols and cyclic aliphatic carbonates is prone to metathesis reaction. The depolymerization can be performed at a temperature below 100 DEG C, thereby reducing the occurrence of side reactions such as oxidation and achieving energy-saving effects. Moreover, the obtained regenerated polyols can be fully reused as raw materials for preparing polyurethane foams or non-foam materials. Test data show that the rigid polyurethane foam prepared from the regenerated polyols obtained from the Schiff base polyurethane waste has improved thermal insulation performance and good compressive strength.

Description

Technical Field

[0001] This invention belongs to the field of polyurethane material recycling technology, specifically relating to a method for preparing recycled polyols from Schiff base polyurethane. Background Technology

[0002] Most polyurethane foam and non-foam products are thermosetting with a cross-linked structure, making physical recycling through grinding or mixing with new materials extremely difficult. Therefore, chemical recycling processes are needed to convert them back into raw materials. In the chemical recycling of polyurethane waste, processes for liquefying solid waste include alcoholysis, hydrolysis, ammonolysis using amines, and acidolysis.

[0003] In these chemical recycling processes, alcoholysis commonly uses ethylene glycol, diethylene glycol, propylene glycol, or dipropylene glycol. Through modification reactions following alcoholysis, recycled polyols suitable for polyurethane production can be obtained. The depolymerization reactions in these processes mostly occur at high temperatures ranging from 180 to 220°C, inevitably accompanied by degradation due to oxidation, resulting in a dark black product. Summary of the Invention

[0004] In view of this, the object of the present invention is to provide a method for preparing regenerated polyols from Schiff base polyurethane. The present invention regenerates Schiff base polyurethane using amino alcohols and cyclic aliphatic carbonates. The Schiff base polyurethane includes an imine structure, and depolymerization can be carried out at temperatures below 100°C, reducing the occurrence of side reactions.

[0005] This invention provides a method for preparing recycled polyols from Schiff base polyurethane, comprising the following steps:

[0006] Schiff base polyurethane and amino alcohol are mixed and depolymerized to obtain a liquefied liquid; the Schiff base polyurethane has an imine structure; the depolymerization temperature is 90-110℃ and the time is 5-7 hours.

[0007] The liquefied liquid and cyclic aliphatic carbonate are mixed and subjected to a ring-opening addition reaction to obtain a regenerated polyol;

[0008] The recycled polyols include recovered imine glycols and recovered glycols containing carbamate structures.

[0009] Preferably, the ring-opening addition reaction is carried out at a temperature of 90–110°C for 1–3 hours.

[0010] Preferably, the recovered imine glycols include imine glycols, and the recovered glycols containing urethane structures include urethane glycols.

[0011] Preferably, the Schiff base polyurethane is obtained by polymerization of raw materials comprising the following parts by mass:

[0012] The composition includes 90-110 parts of polyol, 1-3 parts of catalyst, 2-4 parts of surfactant, 14-16 parts of foaming agent, and diisocyanate, wherein the molar ratio of isocyanate group in the diisocyanate to hydroxyl group in the polyol is (0.9-1.4):1; the polyol includes iminoglycol.

[0013] Preferably, the chemical formula of the iminoglycol is HO-Rˊ-N=CH-R-CH=N-Rˊ-OH, where R and Rˊ are imino groups.

[0014] Preferably, R and Rˊ are alkylene groups.

[0015] Preferably, the chemical formula of the iminoglycol is HO-CH2-CH2-N=CH-CH2-CH2-CH2-CH=N-CH2-CH2-OH.

[0016] Preferably, the method for preparing the imine glycol includes the following steps:

[0017] A mixture of dialdehyde compounds, alcohol amine compounds, and water is subjected to an aldehyde-amine condensation reaction to yield imine glycol;

[0018] The chemical formula of the dialdehyde compound is OHC-R-CHO, and the chemical formula of the alcoholamine compound is NH2-Rˊ-OH.

[0019] The present invention also provides a method for preparing regenerated polyols from Schiff base polyurethane as described in the above technical solution, wherein the regenerated polyols include recovered imine glycols and recovered glycols containing urethane structures.

[0020] The present invention also provides the application of the recycled polyol described in the above technical solution in the preparation of polyurethane.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] This invention provides a method for preparing recycled polyols from Schiff base polyurethane, comprising the following steps: mixing Schiff base polyurethane and amino alcohol for depolymerization to obtain a liquefied liquid; wherein the Schiff base polyurethane has an imine structure; the depolymerization temperature is 90–110°C and the time is 5–7 hours; mixing the liquefied liquid and cyclic aliphatic carbonate for a ring-opening addition reaction to obtain a recycled polyol; wherein the recycled polyol includes recovered imine glycol and recovered glycol containing a urethane structure.

[0023] This invention regenerates Schiff base polyurethane using amino alcohols and cyclic aliphatic carbonates. Schiff base polyurethane includes an imine structure, which is prone to metathesis reactions. Depolymerization can be carried out at temperatures below 100°C, reducing side reactions such as oxidation and bringing energy-saving effects.

[0024] This invention involves alcoholystothening Schiff base polyurethane at 90–110°C to regenerate polyols. The regenerated polyols obtained can be reused as raw materials for preparing polyurethane foams or non-foam products.

[0025] The examples and test data show that rigid polyurethane foam prepared using recycled polyols obtained from Schiff base polyurethane waste has improved thermal insulation properties and better compressive strength. Detailed Implementation

[0026] This invention provides a method for preparing recycled polyols from Schiff base polyurethane, comprising the following steps:

[0027] Schiff base polyurethane and amino alcohol are mixed and depolymerized to obtain a liquefied liquid; the Schiff base polyurethane has an imine structure; the depolymerization temperature is 90-110℃ and the time is 5-7 hours.

[0028] The liquefied liquid and cyclic aliphatic carbonate are mixed and subjected to a ring-opening addition reaction to obtain a regenerated polyol;

[0029] The recycled polyols include recovered imine glycols and recovered glycols containing carbamate structures.

[0030] Unless otherwise specified, all materials and equipment used in this invention are commercially available products in the field.

[0031] In this invention, the Schiff base polyurethane is preferably obtained by polymerization of raw materials comprising the following parts by mass:

[0032] The composition includes 90-110 parts of polyol, 1-3 parts of catalyst, 2-4 parts of surfactant, 14-16 parts of foaming agent, and diisocyanate, wherein the molar ratio of isocyanate group in the diisocyanate to hydroxyl group in the polyol is (0.9-1.4):1; the polyol includes iminoglycol.

[0033] In this invention, the chemical formula of the iminoglycol is preferably HO-R′-N=CH-R-CH=NR′-OH, where R and R′ are imino groups.

[0034] In this invention, R is preferably an alkylene group, and the alkylene group preferably includes propyl.

[0035] In this invention, R′ is preferably an alkylene group, and the alkylene group preferably includes an ethyl group.

[0036] In this invention, the chemical formula of the iminoglycol is preferably HO-CH2-CH2-N=CH-CH2-CH2-CH2-CH=N-CH2-CH2-OH.

[0037] The imine glycol described in this invention exhibits dynamic covalent bond characteristics in its imine structure, making it prone to translocation reactions.

[0038] In this invention, the method for preparing the imine glycol preferably includes the following steps:

[0039] A mixture of dialdehyde compounds, alcohol amine compounds, and water is subjected to an aldehyde-amine condensation reaction to yield imine glycol;

[0040] The chemical formula of the dialdehyde compound is OHC-R-CHO, and the chemical formula of the alcoholamine compound is NH2-R′-OH.

[0041] In this invention, the dialdehyde compound is preferably an alkyl dialdehyde, and the hydrocarbon dialdehyde preferably includes glutaraldehyde.

[0042] In this invention, the alkanolamine compound is preferably a hydrocarbon alkanolamine, and the hydrocarbon alkanolamine preferably includes ethanolamine.

[0043] In this invention, the molar ratio of the dialdehyde compound and the alkanolamine compound is preferably 0.9-1.1:1.9-2.1, and more preferably 1:2.

[0044] In this invention, the preferred ratio of the dialdehyde compound to water is 0.1 mol: 90-110 mL, more preferably 0.1 mol: 100 mL.

[0045] In this invention, the preferred temperature for the aldehyde-amine condensation reaction is room temperature, and the preferred time is 5–15 min, more preferably 10 min. The reaction formula for the aldehyde-amine condensation reaction is as follows:

[0046]

[0047] In this invention, the aldehyde-amine condensation reaction preferably includes water removal, which is preferably carried out by vacuum distillation, and the temperature of the vacuum distillation is preferably 70°C.

[0048] In this invention, the imine glycol can also be obtained by alcoholysis of Schiff base polyurethane.

[0049] In this invention, the Schiff base polyurethane is preferably a rigid polyurethane foam.

[0050] In this invention, the Schiff base polyurethane is preferably obtained by polymerization of the following raw materials comprising the following parts by mass: 100 parts polyol, 2 parts catalyst, 3 parts surfactant, 15 parts foaming agent, and diisocyanate, wherein the molar ratio of isocyanate groups in the diisocyanate to hydroxyl groups in the polyol is 1.2; the mass fraction of imine glycol in the polyol is 20% to 80%, specifically 20%, 40%, 60%, or 80%.

[0051] In this invention, the polyol preferably further includes ether alcohols, ester alcohols, or carbonate alcohols. The ether alcohols preferably include one or more of poly(tetramethylene ether glycol), poly(propylene glycol ether glycol), and poly(ethylene glycol). The ester alcohols preferably include one or more of poly(ethylene glycol adipate), poly(ethylene glycol succinate), poly(butylene glycol adipate), poly(butylene glycol succinate), poly(diethylene glycol adipate), and poly(diethylene glycol succinate). The carbonate alcohols preferably include one or more of poly(ethylene glycol carbonate), poly(propylene glycol carbonate), and poly(butylene glycol carbonate).

[0052] In this invention, the polyol preferably further includes polypropylene glycol, which preferably includes PPG-400, and the hydroxyl value is preferably 400 mg KOH / g. The mass ratio of the polypropylene glycol to imino glycol is preferably 4:1, 3:2, 2:3, or 1:4.

[0053] In this invention, the catalyst preferably comprises an amine catalyst, and the amine catalyst is preferably dimethylcyclohexylamine.

[0054] In this invention, the surfactant is preferably a silicone surfactant, and the silicone surfactant is preferably Evonik's B-8462.

[0055] In this invention, the foaming agent preferably comprises water and cyclopentane, and the mass ratio of water to cyclopentane is preferably 2:13.

[0056] In this invention, the diisocyanate preferably comprises aromatic diisocyanate, alicyclic diisocyanate, or aliphatic diisocyanate; the aromatic diisocyanate preferably comprises one or more of toluene diisocyanate, 4,4'-diphenylmethane diisocyanate (MDI), modified MDI, polymeric MDI, naphthalene diisocyanate, and xylene diisocyanate, wherein the polymeric MDI is preferably Cosmonate 200 from Kumho Mitsui Chemicals. The alicyclic diisocyanate preferably comprises isophorone diisocyanate and / or cyclohexane diisocyanate. The aliphatic diisocyanate preferably comprises hexamethylene diisocyanate and / or cyclohexane diisocyanate.

[0057] In this invention, the method for preparing the Schiff base polyurethane preferably includes the following steps:

[0058] The raw materials for preparing Schiff base polyurethane are mixed and subjected to a polymerization reaction, followed by curing to obtain Schiff base polyurethane.

[0059] In this invention, the polyol, catalyst, surfactant, and a portion of the emulsifier are first mixed, then mixed with the remaining emulsifier, and finally mixed with the isocyanate. The first mixing is preferably performed at a rotation speed of 2000 rpm for 1 minute; the second mixing is preferably performed at a rotation speed of 2000 rpm for 10 seconds; and the third mixing is preferably performed at a rotation speed of 2000 rpm for 7 seconds.

[0060] In this invention, the polymerization reaction is preferably carried out under stirring, with the stirring speed preferably being 2000 rpm and the stirring time preferably being 7 seconds. The curing temperature is preferably 25°C, the curing time is preferably 10 minutes, and the density of the Schiff base polyurethane is preferably 40 kg / m³.

[0061] In this invention, the amino alcohol preferably includes aminoethanol.

[0062] In this invention, the Schiff base polyurethane preferably includes waste material, which is preferably used in powder form.

[0063] In this invention, the mass ratio of the Schiff base polyurethane to the amino alcohol is preferably 100:20 to 400, more preferably 100:200. The amount of amino alcohol used in this invention avoids the situation where the depolymerization product has extremely high viscosity, making it difficult to use; moreover, it is economical and does not cause waste of the amino alcohol.

[0064] In this invention, the depolymerization temperature is preferably 100°C, and the depolymerization time is preferably 6 hours. During the depolymerization process, the Schiff base polyurethane undergoes transformation, ammonolysis, and alcoholysis to generate imine glycol and amine. The low depolymerization temperature of this invention reduces side reactions and is energy-saving and environmentally friendly.

[0065] In this invention, the cyclic aliphatic carbonate preferably includes monocyclic carbonate or polycyclic carbonate, wherein the monocyclic carbonate preferably includes cyclopropylene carbonate, ethylene glycol carbonate, propylene glycol carbonate, glycerol carbonate or trimethylene carbonate; and the polycyclic carbonate preferably includes trialkyl carbonate.

[0066] In this invention, the preferred temperature for the ring-opening reaction is 90–110°C, more preferably 100°C, and the preferred time is 1–3 hours, more preferably 2 hours. During the ring-opening reaction, the amine (or alkanolamine) reacts with the cyclic aliphatic carbonate to obtain glycol containing a carbamate structure, as shown in the following reaction formula:

[0067]

[0068]

[0069] In the formula, R1 and R2 represent hydrocarbon groups.

[0070] The present invention also provides a method for preparing regenerated polyols from Schiff base polyurethane as described in the above technical solution, wherein the regenerated polyols include recovered imine glycols and recovered glycols containing urethane structures.

[0071] In this invention, the recovered imine glycol preferably includes imine glycol, the recovered glycol containing a carbamate structure preferably includes carbamate glycol, and the hydroxyl value of the regenerated polyol is preferably 450 mg KOH / g.

[0072] The present invention also provides the application of the recycled polyol described in the above technical solution in the preparation of polyurethane.

[0073] Using the recycled polyol of the present invention to prepare polyurethane can improve the thermal insulation performance and compressive strength of polyurethane. The present invention does not impose any special requirements on the method for preparing polyurethane from the recycled polyol. The polyurethane comprises the following raw materials in parts by weight: 90-110 parts polyol, 1-3 parts catalyst, 2-4 parts surfactant, 14-16 parts blowing agent, and isocyanate with an isocyanate index of (0.9-1.4):1; the preferred mass fraction of the recycled polyol in the polyol is 20%-80%, specifically 20%, 40%, 60%, or 80%.

[0074] This invention helps to activate the recycling of polyurethane resources and reduce greenhouse gas emissions that contribute to climate change.

[0075] To further illustrate the present invention, the method for preparing regenerated polyols from Schiff base polyurethane provided by the present invention will be described in detail below with reference to the embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0076] Example 1: Production of imine glycol via Schiff base formation

[0077] Iminoglycol was produced by Schiff base formation by mixing 200 g of a 50 wt% aqueous solution of glutaraldehyde with 122 g of ethanolamine and stirring for 10 minutes. Subsequently, vacuum distillation was carried out at 70 °C to evaporate the water, yielding iminoglycol (iminoglycol).

[0078] The hydroxyl value of the obtained imine glycol was measured using the ASTM E 1899-08 method, and the result was 610 mg KOH / g.

[0079] Example 2: Production of Schiff base polyurethane using imine glycol

[0080] 80 g of polypropylene glycol (PPG-400, 400 mg KOH / g) was mixed with 20 g of imine glycol obtained in Example 1 to produce rigid polyurethane foam. The production formulation of rigid polyurethane foam is shown in Table 1:

[0081] Table 1 Formulations for manufacturing rigid polyurethane foam using Schiff base polyurethane containing imine glycol.

[0082]

[0083] Note: The amine catalyst in the table is dimethylcyclohexylamine, the silicone surfactant is B-8462 from Evonik, and the polymeric MDI is Cosmonate 200 from Kumho Mitsui Chemicals.

[0084] In a production example of rigid polyurethane foam based on Schiff base polyurethane, the polyol was maintained at 25°C, and the polyol, amine catalyst, silicone surfactant, and water were added to a 500 mL plastic cup according to the weight ratios specified in Table 1. The mixture was stirred at 2000 rpm for 1 minute. Subsequently, cyclopentane was added to the mixture, and it was stirred at 2000 rpm for 10 seconds to obtain the polyol fraction.

[0085] The polymeric MDI, maintained at 25°C, was weighed until it reached an isocyanate index of 120 (isocyanate to polyol equivalent ratio of 1.2) and mixed with the polyol portion. The mixture was then stirred at 2000 rpm for 7 seconds to obtain the final mixture.

[0086] Pour the mixture into a mold (400×400×100 mm), close the mold, and cure at 25°C for 10 minutes to obtain Schiff base polyurethane foam with a density of 40 kg / m³ at the foam center. 3 .

[0087] Example 3: Production and recovery of polyols from Schiff base polyurethane foam waste using amino alcohols

[0088] To produce recycled polyols, 200 grams of aminoethanol were added to a 1-liter reactor and the temperature was maintained at 100°C. Then, 100 grams of pulverized waste from rigid polyurethane foam (produced in Example 2) were added to the reactor in five portions.

[0089] When solid waste is added to aminoethanol, it rapidly liquefies due to Schiff base conversion and ammonolysis and alcoholysis reactions. Equilibrium is reached after 6 hours of reaction, and the amine value of the liquid product, determined by ASTM E 1899-08, is 182 mg KOH / g.

[0090] Add 100g of cyclopropylene carbonate and continue the reaction for 2 hours. Then cool to room temperature to convert the amine into a urethane polyol, yielding the recovered polyol. The hydroxyl value of the recovered polyol was determined to be 450mg KOH / g using ASTM E 1899-08 method.

[0091] Example 4: Production of rigid polyurethane foam using recycled polyols obtained from Schiff base polyurethane foam waste

[0092] To evaluate the performance of the polyurethane obtained using the recycled polyols obtained in Example 3, rigid polyurethane foam was manufactured according to the formulation ratios shown in Table 2.

[0093] Table 2 Formulations for producing rigid polyurethane foam using recycled polyols obtained from Schiff base polyurethane.

[0094]

[0095]

[0096] Note: The silicone surfactant in the table is B-8462 from EVONIK, the amine catalyst is PC-8 from EVONIK, and the polymeric MDI is Cosmonate 200 from Kumho Mitsui Chemicals. Except for polymeric MDI, all other values ​​in the table are parts by weight.

[0097] For cases involving recycled polyols, the new polyol (PPG-400) and recycled polyols were mixed at weights of 20%, 40%, 60%, and 80% (mass fraction of recycled polyols). The polyols, silicone surfactants, amine catalysts, and water were added to a 500 mL plastic cup at the weight ratios specified in Table 2 and stirred at 2000 rpm for 1 minute. Cyclopentane was then added to the mixture, and it was stirred at 2000 rpm for 10 seconds to obtain the polyol fraction.

[0098] The polymeric MDI, maintained at 25°C, was weighed until it reached an isocyanate index of 120 and mixed with the polyol portion. The mixture was then stirred at 2000 rpm for 7 seconds to obtain the final mixture.

[0099] Pour the mixture into a mold (400×400×100 mm), close the mold, and cure at 25°C for 10 minutes to obtain Schiff base polyurethane foam with a core density of 40 kg / m³. 3 .

[0100] Test Example 1: Testing the performance of rigid polyurethane foam prepared using recycled polyols obtained from Schiff base polyurethane foam waste.

[0101] The thermal conductivity and compressive strength of the rigid polyurethane foam manufactured using recycled polyols in Example 4 were measured. Thermal conductivity (K-value) and compressive strength values ​​were measured using the KS M 3809 method. Thermal conductivity samples were cut into rectangular foam pieces of 300 × 300 × 50 mm, and compressive strength samples were cut into rectangular foam pieces of 100 × 100 × 50 mm.

[0102] Table 3 shows the performance of rigid polyurethane foam manufactured using recycled polyols obtained from Schiff base polyurethane waste.

[0103]

[0104]

[0105] According to the measurement results in Table 3, the rigid polyurethane foam manufactured using recycled polyols (IG-20, IG-40, IG-60, IG-80) obtained from Schiff base polyurethane waste exhibits lower thermal conductivity than typical polyols (comparative samples). This indicates that the rigid polyurethane foam manufactured using Schiff base conversion and ammonolysis and alcoholysis products of this invention has improved thermal insulation properties. Furthermore, the compressive strength is also increased, indicating improved rigidity.

[0106] Based on these measurements, it can be seen that the recovered polyols (iminoglycol and urethane polyols) obtained from Schiff base polyurethane waste provide better final product performance than those recovered through conventional alcoholysis.

[0107] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, not all embodiments. People can obtain other embodiments based on the present invention without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing recycled polyols from Schiff base polyurethane, characterized in that, Includes the following steps: Schiff base polyurethane and amino alcohol are mixed and depolymerized to obtain a liquefied liquid; the Schiff base polyurethane has an imine structure; the depolymerization temperature is 90-110℃ and the time is 5-7 hours. The liquefied liquid and cyclic aliphatic carbonate are mixed and subjected to a ring-opening addition reaction to obtain a regenerated polyol; The recycled polyols include recovered imine glycols and recovered glycols containing carbamate structures.

2. The method for preparing recycled polyols from Schiff base polyurethane according to claim 1, characterized in that, The ring-opening addition reaction is carried out at a temperature of 90–110°C for 1–3 hours.

3. The method for preparing recycled polyols from Schiff base polyurethane according to claim 1, wherein the recovered imine glycols include imine glycols and the recovered glycols containing urethane structures include urethane glycols.

4. The method for preparing recycled polyols from Schiff base polyurethane according to claim 1, characterized in that, The Schiff base polyurethane is obtained by polymerization of the following raw materials in parts by mass: The composition includes 90-110 parts of polyol, 1-3 parts of catalyst, 2-4 parts of surfactant, 14-16 parts of foaming agent, and diisocyanate, wherein the molar ratio of isocyanate group in the diisocyanate to hydroxyl group in the polyol is (0.9-1.4):1; the polyol includes iminoglycol.

5. The method for preparing recycled polyols from Schiff base polyurethane according to claim 4, characterized in that, The chemical formula of the iminoglycol is HO-R′-N=CH-R-CH=NR′-OH, where R and R′ are imino groups.

6. The method for preparing recycled polyols from Schiff base polyurethane according to claim 5, characterized in that, R and R′ are alkylene groups.

7. The method for preparing recycled polyols from Schiff base polyurethane according to claim 5, characterized in that, The chemical formula of the iminoglycol is HO-CH2-CH2-N=CH-CH2-CH2-CH2-CH=N-CH2-CH2-OH.

8. The method for preparing recycled polyols from Schiff base polyurethane according to claim 4, 5, or 6, characterized in that, The method for preparing the imino glycol includes the following steps: A mixture of dialdehyde compounds, alcohol amine compounds, and water is subjected to an aldehyde-amine condensation reaction to yield imine glycol; The chemical formula of the dialdehyde compound is OHC-R-CHO, and the chemical formula of the alcoholamine compound is NH2-R′-OH.

9. The regenerated polyol obtained by the method for preparing regenerated polyols from Schiff base polyurethane according to any one of claims 1 to 8, characterized in that, This includes recovered imine glycols and recovered glycols containing carbamate structures.

10. The use of the recycled polyol according to claim 9 in the preparation of polyurethane.

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