Recyclable polyurethane composition and preparation method thereof

Abstract

The invention relates to the technical field of polyurethane materials, in particular to a recyclable polyurethane composition and a preparation method thereof, and the recyclable polyurethane composition comprises the following components: 40-60 parts by weight of composite polycaprolactone glycol, 10-20 parts by weight of 4, 4 '-diphenyl-1, 3, 4-trimethyl-1, 3-pentanediol, 5-10 parts by weight of a The adhesive is prepared from the following components in parts by weight: 15 to 25 parts of 4, 4 '-diphenylmethane diisocyanate, 5 to 15 parts of hydroquinone dihydroxypropyl ether, 3 to 10 parts of tributyl citrate, 10 to 20 parts of cross-linking agent, 0.1 to 1 part of zinc diacetate and 0.5 to 2 parts of dilauryl thiodipropionate. The long-chain alkyl halide is added, and the polarity and intermolecular force of the mixture are changed, so that the material is easier to dissolve in some relatively mild organic solvents, and the recovery efficiency and quality are improved. A disulfide bond compound is added, and due to the fact that disulfide bonds belong to dynamic covalent bonds, the disulfide bonds can be reversibly broken under the conditions of heating, illumination or application of specific mechanical force and the like, so that macromolecular chains of polyurethane are promoted to be depolymerized into relatively small fragments which are easier for subsequent processing treatment.

Description

Technical Field

[0001] The present invention relates to the technical field of polyurethane materials, and more specifically, to a recyclable polyurethane composition and a preparation method thereof. Background Art

[0002] With the acceleration of the global industrialization and urbanization processes, the usage of plastic products has been increasing day by day. As a kind of polymer material with excellent properties, polyurethane is widely used in many fields, such as automobile manufacturing, building insulation, furniture decoration, shoe materials and clothing, as well as medical devices, etc. In the automotive industry, polyurethane foam is used for seat filling to provide a comfortable driving experience; in the construction field, polyurethane insulation materials can effectively reduce heat transfer and improve the energy efficiency of buildings; in furniture production, polyurethane coatings give products an aesthetically pleasing and durable surface; in terms of shoe materials, polyurethane elastomers have good elasticity and abrasion resistance, making shoes lighter and more comfortable.

[0003] Traditional polyurethane materials are difficult to degrade in the natural environment. Long-term existence in the environment will form "white pollution". These materials are not easily decomposed by microorganisms, resulting in their accumulation in soil and water bodies, occupying valuable land resources, and may leak harmful substances to pollute soil and water sources. In view of this, we propose a recyclable polyurethane composition and a preparation method thereof. Summary of the Invention

[0004] The purpose of the present invention is to provide a recyclable polyurethane composition and a preparation method thereof to solve the problems put forward in the above background art that traditional polyurethane materials are difficult to degrade in the natural environment, long-term existence in the environment will form "white pollution", these materials are not easily decomposed by microorganisms, resulting in their accumulation in soil and water bodies, occupying valuable land resources, and may leak harmful substances to pollute soil and water sources.

[0005] To achieve the above purpose, the present invention provides a recyclable polyurethane composition, which includes the following components: 40 - 60 parts by weight of composite polycaprolactone diol, 15 - 25 parts by weight of 4,4'-diphenylmethane diisocyanate, 5 - 15 parts by weight of hydroquinone dipropyl ether, 3 - 10 parts by weight of tributyl citrate, 10 - 20 parts by weight of crosslinking agent, 0.1 - 1 part by weight of zinc diacetate, 0.5 - 2 parts by weight of dilauryl thiodipropionate;

[0006] Among them, the composite polycaprolactone diol is obtained by blending polycaprolactone diol and polycarbonate diol to get a polyol mixture, and alkylating the polyol mixture with long-chain alkyl halides.

[0007] Preferably, the preparation method of the composite polycaprolactone diol is as follows:

[0008] S1.1. Weigh the following components by weight respectively: 50 - 80 parts by weight of polycaprolactone diol, 5 - 20 parts by weight of long-chain alkyl halide, 10 - 30 parts by weight of polycarbonate diol, 0.1 - 1 part by weight of stannous octoate, 1 - 5 parts by weight of disulfide bond compound, 20 - 30 parts by weight of tetrahydrofuran, and 20 - 30 parts by weight of n-hexane;

[0009] S1.2. Place polycaprolactone diol and polycarbonate diol in an oven and dry them at 60 - 80 °C for 3 - 4 h to remove the moisture therein; at room temperature, mix the dried polycaprolactone diol and polycarbonate diol with a stirrer at a speed of 200 - 400 rpm for 30 - 45 min to obtain a diol mixture;

[0010] S1.3. Add the long-chain alkyl halide and stannous octoate to the diol mixture, introduce nitrogen at a speed of 1 - 5 L / h, gradually raise the temperature to 100 - 120 °C at a speed of 9 - 16 °C / h, stir at a speed of 300 - 400 rpm for 6 - 8 h to carry out the alkylation reaction; after the alkylation reaction is completed, lower the temperature to 60 - 90 °C, add the disulfide bond compound, and continue to stir and react at a speed of 200 - 400 rpm for 3 - 6 h;

[0011] The introduction of the long-chain alkyl halide may change the chemical structure of the polycaprolactone diol and polycarbonate diol mixture, increase the hydrophilicity or enzymatic hydrolysis sensitivity of the material, and improve its degradation performance in the natural environment; the long-chain alkyl introduced by the alkylation reaction can change the polarity and intermolecular force of the mixture, enabling it to achieve a better dissolution effect under relatively mild solvent and lower temperature conditions, facilitating subsequent effective recovery treatment through solution methods and other means, and reprocessing it into useful products; the presence of the long-chain alkyl will affect the regularity of the molecular chain and the stability of chemical bonds to a certain extent. When recovering under the action of external factors such as heat and chemical reagents, this structural feature is more likely to break the molecular chain under specific conditions, decompose into relatively small and reusable fragments, thereby improving the efficiency and quality of recovery, enabling the recovered material to be put into production circulation again, and reducing resource waste.

[0012] The disulfide bond (-S-S-) has the characteristics of dynamic covalent bonds. Under specific conditions, such as heating, light irradiation, adding reducing agents, or applying specific mechanical forces, the disulfide bond can undergo reversible cleavage. When polymer materials containing disulfide bond compounds need to be recycled, by applying these external stimuli to break the disulfide bond, the macromolecular chains of the polymer can depolymerize into relatively small fragments, facilitating subsequent reprocessing and enabling them to be put back into the production cycle again, thus effectively reducing resource waste and conforming to the concept of sustainable development. During the polymer processing of disulfide bond compounds, their presence can affect the melt viscosity of the material. In the molten state, the dynamic characteristics of the disulfide bond enable the relative sliding between molecular chains to be easier, appropriately reducing the melt viscosity and making the material have better fluidity. The disulfide bond itself is relatively flexible. After introducing disulfide bond compounds into the polymer molecular chains, the overall flexibility of the molecular chains is improved, making the material have better flexibility and elasticity.

[0013] S1.4. After the reaction is completed, degassing treatment is carried out; after the degassing treatment is completed, it is dissolved in tetrahydrofuran and precipitated in n-hexane, repeated 2 - 3 times, and then vacuum dried at 40 - 60 °C for 6 - 8 h to obtain the composite polycaprolactone diol.

[0014] Preferably, in S1.2, the molecular weight of the polycaprolactone diol is 1500 - 2000 Da, and the molecular weight of the polycarbonate diol is 1000 - 2000 Da.

[0015] Preferably, in S1.3, the disulfide bond compound is any one of bis(2-hydroxyethyl) disulfide and 3,3'-dithiodipropionic acid.

[0016] Preferably, in S1.4, the degassing temperature is 100 - 120 °C, the pressure is -0.08 - -0.1 MPa, and the degassing time is 1 - 2 h.

[0017] On the other hand, the present invention provides a preparation method of a recyclable polyurethane composition for any one of the above-mentioned recyclable polyurethane compositions, including the following steps:

[0018] S2.1. Weigh the following components in parts by weight respectively: 40 - 60 parts by weight of composite polycaprolactone diol, 15 - 25 parts by weight of 4,4'-diphenylmethane diisocyanate, 5 - 15 parts by weight of hydroquinone dipropyl ether, 3 - 10 parts by weight of tributyl citrate, 10 - 20 parts by weight of crosslinking agent, 0.1 - 1 part by weight of zinc diacetate, and 0.5 - 2 parts by weight of dilauryl thiodipropionate;

[0019] S2.2. Place the composite polycaprolactone diol and hydroquinone dipropylene glycol ether separately in a vacuum drying oven, dry them at 50 - 80 °C for 4 - 6 h, and immediately transfer them to a desiccator to cool to room temperature after drying; at room temperature, use a stirrer to mix the dried composite polycaprolactone diol and hydroquinone dipropylene glycol ether at a speed of 300 - 500 rpm for 30 - 50 min to obtain a uniform mixture;

[0020] S2.3. Slowly add 4,4'-diphenylmethane diisocyanate to the mixture in S2.2, introduce nitrogen gas, raise the temperature to 60 - 70 °C, and stir at a speed of 300 - 500 rpm for 1 - 2 h; then add zinc diacetate and continue to react at a speed of 300 - 500 rpm for 2 - 3 h to form a prepolymer;

[0021] S2.4. Add hydroquinone dipropylene glycol ether and a crosslinking agent to the prepolymer, stir and react at a speed of 200 - 300 rpm at 60 - 70 °C for 2 - 4 h; after the reaction is completed, lower the temperature to 40 - 50 °C, add tributyl citrate and dilauryl thiodipropionate, and continue to stir at a speed of 200 - 300 rpm for 30 - 60 min;

[0022] S2.5. After the reaction is completed, perform degassing treatment. The degassing temperature is 100 - 120 °C, the pressure is -0.08 to -0.1 MPa, and the time is 1 - 2 h to remove the by-products generated during the reaction; after the degassing is completed, perform curing treatment to obtain a recyclable polyurethane composition.

[0023] Preferably, in S2.3, the slow addition speed of 4,4'-diphenylmethane diisocyanate is 0.75 - 1 part by weight per minute.

[0024] Preferably, in S2.3, the nitrogen gas introduction speed is 5 - 10 L / h.

[0025] Preferably, in S2.4, the crosslinking agent is any one of isophorone diisocyanate or hexamethylene diisocyanate.

[0026] Preferably, in S2.5, the curing temperature is 80 - 100 °C and the curing time is 4 - 6 h.

[0027] Compared with the prior art, the beneficial effects of the present invention:

[0028] 1. In the recyclable polyurethane composition and its preparation method, a long-chain alkyl halide is added. Since it changes the polarity and intermolecular forces of the mixture, the material is more easily soluble in some relatively mild organic solvents; the introduction of the long-chain alkyl group makes the molecular chain of the material more likely to break under the action of external factors such as heat and chemical reagents, decomposing into relatively small and reusable fragments, thereby improving the efficiency and quality of recycling.

[0029] 2. In the recyclable polyurethane composition and its preparation method, a disulfide compound is added. Since the disulfide bond belongs to a dynamic covalent bond, under conditions such as heating, light irradiation, adding a reducing agent or applying a specific mechanical force, the disulfide bond can undergo reversible cleavage, thereby promoting the depolymerization of the macromolecular chain of the polyurethane into relatively small fragments that are more easily processed subsequently, so that the material can enter the production cycle again and achieve efficient recycling of resources. Detailed implementation mode

[0030] The following will combine the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0031] The present invention provides a recyclable polyurethane composition and its preparation method, including the following components: 40-60 parts by weight of composite polycaprolactone diol, 15-25 parts by weight of 4,4'-diphenylmethane diisocyanate, 5-15 parts by weight of hydroquinone dipropyl ether, 3-10 parts by weight of tributyl citrate, 10-20 parts by weight of crosslinking agent, 0.1-1 part by weight of zinc diacetate, 0.5-2 parts by weight of dilauryl thiodipropionate;

[0032] Among them, the composite polycaprolactone diol is prepared by blending polycaprolactone diol and polycarbonate diol and performing alkylation modification with a long-chain alkyl halide; the long-chain alkyl halide is dodecyl bromide.

[0033] The disulfide compound is any one of bis(dihydroxyethyl) disulfide and dithiodipropionic acid, and the disulfide compound is preferably bis(dihydroxyethyl) disulfide.

[0034] The crosslinking agent is any one of isophorone diisocyanate or hexamethylene diisocyanate, and the crosslinking agent is preferably isophorone diisocyanate.

[0035] Example 1: A recyclable polyurethane composition and its preparation method, including the following steps:

[0036] S2.1. Weigh the following components by weight respectively: 50 parts by weight of composite polycaprolactone diol, 20 parts by weight of 4,4'-diphenylmethane diisocyanate, 10 parts by weight of hydroquinone dipropylene ether, 6 parts by weight of tributyl citrate, 15 parts by weight of isophorone diisocyanate, 0.5 part by weight of zinc diacetate, and 1 part by weight of dilauryl thiodipropionate;

[0037] S2.2. Place the composite polycaprolactone diol and hydroquinone dipropylene ether in a vacuum drying oven respectively, dry at 60 °C for 5 h, and immediately transfer to a desiccator to cool to room temperature after drying; at room temperature, mix the dried composite polycaprolactone diol and hydroquinone dipropylene ether with a stirrer at a speed of 300 rpm for 30 min to obtain a homogeneous mixture;

[0038] S2.3. Slowly add 4,4'-diphenylmethane diisocyanate to the mixture in S2.2 at a rate of 0.8 part by weight per minute, introduce nitrogen at a rate of 6 L / h, raise the temperature to 65 °C, and stir at a speed of 500 rpm for 2 h; then add zinc diacetate and continue to react at a speed of 500 rpm for 3 h to form a prepolymer;

[0039] S2.4. Add hydroquinone dipropylene ether and a crosslinking agent to the prepolymer, stir and react at 65 °C at a speed of 200 rpm for 4 h; after the reaction is completed, lower the temperature to 40 °C, add tributyl citrate and dilauryl thiodipropionate, and continue to stir at a speed of 200 rpm for 40 min;

[0040] S2.5. After the reaction is completed, perform degassing treatment. The degassing temperature is 100 °C, the pressure is -0.08 MPa, and the time is 2 h to remove the by-products generated during the reaction; after degassing is completed, perform curing treatment. The curing temperature is 80 °C and the curing time is 6 h to obtain a recyclable polyurethane composition.

[0041] The preparation method of the composite polycaprolactone diol is as follows:

[0042] S1.1. Weigh the following components by weight respectively: 65 parts by weight of polycaprolactone diol, 7 parts by weight of dodecyl bromide, 20 parts by weight of polycarbonate diol, 0.5 part by weight of stannous octoate, 3 parts by weight of bis(dihydroxyethyl) disulfide, 25 parts by weight of tetrahydrofuran, and 25 parts by weight of n-hexane;

[0043] S1.2. Place the polycaprolactone diol with a molecular weight of 1500 Da and the polycarbonate diol with a molecular weight of 1000 Da in an oven respectively and dry at 60 °C for 3 h to remove the moisture therein; at room temperature, mix the dried polycaprolactone diol and polycarbonate diol with a stirrer at a speed of 400 rpm for 30 min to obtain a diol mixture;

[0044] S1.3. Add long-chain alkyl halide and stannous octoate to the diol mixture, introduce nitrogen at a rate of 3 L / h, gradually raise the temperature to 110 °C at a rate of 10 °C / h, stir at a speed of 300 rpm for 6 h to carry out the alkylation reaction; after the alkylation reaction is completed, lower the temperature to 90 °C, add the disulfide compound, and continue to stir and react at a speed of 300 rpm for 6 h;

[0045] S1.4. After the reaction is completed, carry out degassing treatment. The degassing temperature is 100 °C, the pressure is -0.08 MPa, and the degassing time is 2 h; after the degassing treatment is completed, dissolve with tetrahydrofuran and precipitate in n-hexane, repeat 3 times, and then carry out vacuum drying at 60 °C for 8 h to obtain the composite polycaprolactone diol.

[0046] Example 2: A recyclable polyurethane composition and its preparation method, including the following steps:

[0047] S2.1. Weigh the following components by weight: 50 parts by weight of composite polycaprolactone diol, 20 parts by weight of 4,4'-diphenylmethane diisocyanate, 10 parts by weight of hydroquinone dipropyl ether, 6 parts by weight of tributyl citrate, 15 parts by weight of isophorone diisocyanate, 0.5 part by weight of zinc diacetate, 1 part by weight of dilauryl thiodipropionate;

[0048] S2.2. Place the composite polycaprolactone diol and hydroquinone dipropyl ether in a vacuum drying oven respectively, dry at 60 °C for 5 h, and immediately transfer to a dryer to cool to room temperature after drying; at room temperature, use a stirrer to mix the dried composite polycaprolactone diol and hydroquinone dipropyl ether at a speed of 300 rpm for 30 min to obtain a uniform mixture;

[0049] S2.3. Slowly add 4,4'-diphenylmethane diisocyanate to the mixture in S2.2 at a rate of 0.8 part by weight per minute, introduce nitrogen at a rate of 6 L / h, raise the temperature to 65 °C, and stir at a speed of 500 rpm for 2 h; then add zinc diacetate and continue to react at a speed of 500 rpm for 3 h to form a prepolymer;

[0050] S2.4. Add hydroquinone dipropyl ether and a crosslinking agent to the prepolymer, stir and react at 65 °C at a speed of 200 rpm for 4 h; after the reaction is completed, lower the temperature to 40 °C, add tributyl citrate and dilauryl thiodipropionate, and continue to stir at a speed of 200 rpm for 40 min;

[0051] S2.5. After the reaction is completed, degassing treatment is carried out. The degassing temperature is 100 °C, the pressure is -0.08 MPa, and the time is 2 h to remove the by-products generated during the reaction. After the degassing is completed, curing treatment is carried out. The curing temperature is 80 °C and the curing time is 6 h to obtain a recyclable polyurethane composition.

[0052] The preparation method of the composite polycaprolactone diol is as follows:

[0053] S1.1. Weigh the following components in parts by weight respectively: 65 parts by weight of polycaprolactone diol, 13 parts by weight of dodecyl bromide, 20 parts by weight of polycarbonate diol, 0.5 part by weight of stannous octoate, 3 parts by weight of bis(dihydroxyethyl) disulfide, 25 parts by weight of tetrahydrofuran, and 25 parts by weight of n-hexane;

[0054] S1.2. Place the polycaprolactone diol with a molecular weight of 1500 Da and the polycarbonate diol with a molecular weight of 1000 Da in an oven and dry them at 60 °C for 3 h to remove the moisture therein. At room temperature, use a stirrer to mix the dried polycaprolactone diol and polycarbonate diol at a speed of 400 rpm for 30 min to obtain a diol mixture;

[0055] S1.3. Add the long-chain alkyl halide and stannous octoate to the diol mixture, introduce nitrogen at a speed of 3 L / h, and gradually raise the temperature to 110 °C at a speed of 10 °C / h, and stir at a speed of 300 rpm for 6 h to carry out the alkylation reaction. After the alkylation reaction is completed, lower the temperature to 90 °C, add the disulfide compound, and continue to stir and react at a speed of 300 rpm for 6 h;

[0056] S1.4. After the reaction is completed, carry out degassing treatment. The degassing temperature is 100 °C, the pressure is -0.08 MPa, and the degassing time is 2 h. After the degassing treatment is completed, dissolve it with tetrahydrofuran and precipitate it in n-hexane, repeat 3 times, and then carry out vacuum drying at 60 °C for 8 h to obtain the composite polycaprolactone diol.

[0057] Example 3: A recyclable polyurethane composition and its preparation method, including the following steps:

[0058] S2.1. Weigh the following components in parts by weight respectively: 50 parts by weight of composite polycaprolactone diol, 20 parts by weight of 4,4'-diphenylmethane diisocyanate, 10 parts by weight of hydroquinone dipropyl ether, 6 parts by weight of tributyl citrate, 15 parts by weight of isophorone diisocyanate, 0.5 part by weight of zinc diacetate, and 1 part by weight of dilauryl thiodipropionate;

[0059] S2.2. Place the composite polycaprolactone diol and hydroquinone dipropylene glycol in a vacuum drying oven and dry at 60 °C for 5 h. Immediately transfer them to a desiccator after drying and cool to room temperature. At room temperature, use a stirrer to mix the dried composite polycaprolactone diol and hydroquinone dipropylene glycol at a speed of 300 rpm for 30 min to obtain a homogeneous mixture.

[0060] S2.3. Slowly add 4,4'-diphenylmethane diisocyanate to the mixture in S2.2 at a rate of 0.8 parts by weight per minute, introduce nitrogen at a rate of 6 L / h, raise the temperature to 65 °C, and stir at a speed of 500 rpm for 2 h. Then add zinc diacetate and continue to react at a speed of 500 rpm for 3 h to form a prepolymer.

[0061] S2.4. Add hydroquinone dipropylene glycol and a crosslinking agent to the prepolymer, and stir and react at 65 °C at a speed of 200 rpm for 4 h. After the reaction is completed, lower the temperature to 40 °C, add tributyl citrate and dilauryl thiodipropionate, and continue to stir at a speed of 200 rpm for 40 min.

[0062] S2.5. After the reaction is completed, perform degassing treatment. The degassing temperature is 100 °C, the pressure is -0.08 MPa, and the time is 2 h to remove the by-products generated during the reaction. After degassing is completed, perform curing treatment. The curing temperature is 80 °C and the curing time is 6 h to obtain a recyclable polyurethane composition.

[0063] The preparation method of the composite polycaprolactone diol is as follows:

[0064] S1.1. Weigh the following components by weight: 65 parts by weight of polycaprolactone diol, 17 parts by weight of dodecyl bromide, 20 parts by weight of polycarbonate diol, 0.5 parts by weight of stannous octoate, 3 parts by weight of bis(dihydroxyethyl) disulfide, 25 parts by weight of tetrahydrofuran, and 25 parts by weight of n-hexane.

[0065] S1.2. Place the polycaprolactone diol with a molecular weight of 1500 Da and the polycarbonate diol with a molecular weight of 1000 Da in an oven and dry at 60 °C for 3 h to remove the moisture therein. At room temperature, use a stirrer to mix the dried polycaprolactone diol and polycarbonate diol at a speed of 400 rpm for 30 min to obtain a diol mixture.

[0066] S1.3. Add the long-chain alkyl halide and stannous octoate to the diol mixture, introduce nitrogen at a rate of 3 L / h, gradually raise the temperature to 110 °C at a rate of 10 °C / h, and stir at a speed of 300 rpm for 6 h to carry out the alkylation reaction. After the alkylation reaction is completed, lower the temperature to 90 °C, add the disulfide compound, and continue to stir and react at a speed of 300 rpm for 6 h.

[0067] S1.4. After the reaction is completed, degassing treatment is carried out. The degassing temperature is 100 °C, the pressure is -0.08 MPa, and the degassing time is 2 h. After the degassing treatment is completed, it is dissolved in tetrahydrofuran and precipitated in n-hexane, repeated 3 times, and then vacuum dried at 60 °C for 8 h to obtain the composite polycaprolactone diol.

[0068] Example 4: A recyclable polyurethane composition and its preparation method, comprising the following steps:

[0069] S2.1. Weigh the following components by weight: 50 parts by weight of composite polycaprolactone diol, 20 parts by weight of 4,4'-diphenylmethane diisocyanate, 10 parts by weight of hydroquinone dipropyl ether, 6 parts by weight of tributyl citrate, 15 parts by weight of isophorone diisocyanate, 0.5 parts by weight of zinc diacetate, and 1 part by weight of dilauryl thiodipropionate;

[0070] S2.2. Place the composite polycaprolactone diol and hydroquinone dipropyl ether in a vacuum drying oven respectively, dry at 60 °C for 5 h, and immediately transfer to a dryer to cool to room temperature after drying. At room temperature, mix the dried composite polycaprolactone diol and hydroquinone dipropyl ether with a stirrer at a speed of 300 rpm for 30 min to obtain a uniform mixture;

[0071] S2.3. Slowly add 4,4'-diphenylmethane diisocyanate to the mixture in S2.2 at a rate of 0.8 parts by weight per minute, introduce nitrogen at a rate of 6 L / h, raise the temperature to 65 °C, and stir at a speed of 500 rpm for 2 h; then add zinc diacetate and continue to react at a speed of 500 rpm for 3 h to form a prepolymer;

[0072] S2.4. Add hydroquinone dipropyl ether and a crosslinking agent to the prepolymer, stir and react at 65 °C at a speed of 200 rpm for 4 h; after the reaction is completed, lower the temperature to 40 °C, add tributyl citrate and dilauryl thiodipropionate, and continue to stir at a speed of 200 rpm for 40 min;

[0073] S2.5. After the reaction is completed, degassing treatment is carried out. The degassing temperature is 100 °C, the pressure is -0.08 MPa, and the time is 2 h to remove the by-products generated during the reaction; after the degassing is completed, then carry out curing treatment, the curing temperature is 80 °C, and the curing time is 6 h to obtain the recyclable polyurethane composition.

[0074] The preparation method of the composite polycaprolactone diol is as follows:

[0075] S1.1. Weigh the following components by weight respectively: 65 parts by weight of polycaprolactone diol, 20 parts by weight of dodecyl bromide, 20 parts by weight of polycarbonate diol, 0.5 part by weight of stannous octoate, 3 parts by weight of bis(dihydroxyethyl) disulfide, 25 parts by weight of tetrahydrofuran, and 25 parts by weight of n-hexane;

[0076] S1.2. Place polycaprolactone diol with a molecular weight of 1500 Da and polycarbonate diol with a molecular weight of 1000 Da in an oven and dry them at 60 °C for 3 h to remove the moisture therein; at room temperature, mix the dried polycaprolactone diol and polycarbonate diol with a stirrer at a speed of 400 rpm for 30 min to obtain a diol mixture;

[0077] S1.3. Add long-chain alkyl halide and stannous octoate to the diol mixture, introduce nitrogen at a rate of 3 L / h, gradually raise the temperature to 110 °C at a rate of 10 °C / h, and stir at a speed of 300 rpm for 6 h to carry out an alkylation reaction; after the alkylation reaction is completed, lower the temperature to 90 °C, add a disulfide compound, and continue to stir and react at a speed of 300 rpm for 6 h;

[0078] S1.4. After the reaction is completed, carry out degassing treatment. The degassing temperature is 100 °C, the pressure is -0.08 MPa, and the degassing time is 2 h; after the degassing treatment is completed, dissolve with tetrahydrofuran and precipitate in n-hexane, repeat 3 times, and then carry out vacuum drying at 60 °C for 8 h to obtain composite polycaprolactone diol.

[0079] Example 5: A recyclable polyurethane composition and its preparation method, comprising the following steps:

[0080] S2.1. Weigh the following components by weight respectively: 40 parts by weight of composite polycaprolactone diol, 15 parts by weight of 4,4'-diphenylmethane diisocyanate, 5 parts by weight of hydroquinone dipropyl ether, 3 parts by weight of tributyl citrate, 10 parts by weight of isophorone diisocyanate, 0.1 part by weight of zinc diacetate, and 0.5 part by weight of dilauryl thiodipropionate;

[0081] S2.2. Place the composite polycaprolactone diol and hydroquinone dipropyl ether in a vacuum drying oven and dry them at 60 °C for 5 h. Immediately transfer them to a dryer and cool them to room temperature after drying; at room temperature, mix the dried composite polycaprolactone diol and hydroquinone dipropyl ether with a stirrer at a speed of 300 rpm for 30 min to obtain a uniform mixture;

[0082] S2.3. Slowly add 4,4'-diphenylmethane diisocyanate to the mixture in S2.2 at a rate of 0.8 parts by weight per minute, introduce nitrogen at a rate of 6 L / h, raise the temperature to 65 °C, and stir at a speed of 500 rpm for 2 h; then add zinc diacetate and continue to react at a speed of 500 rpm for 3 h to form a prepolymer.

[0083] S2.4. Add hydroquinone dipropyl ether and a crosslinking agent to the prepolymer, and stir and react at a speed of 200 rpm at 65 °C for 4 h; after the reaction is completed, lower the temperature to 40 °C, add tributyl citrate and dilauryl thiodipropionate, and continue to stir at a speed of 200 rpm for 40 min.

[0084] S2.5. After the reaction is completed, perform degassing treatment. The degassing temperature is 100 °C, the pressure is -0.08 MPa, and the time is 2 h to remove the by-products generated during the reaction; after the degassing is completed, perform curing treatment. The curing temperature is 80 °C and the curing time is 6 h to obtain a recyclable polyurethane composition.

[0085] The preparation method of the composite polycaprolactone diol is as follows:

[0086] S1.1. Weigh the following components by weight: 65 parts by weight of polycaprolactone diol, 17 parts by weight of dodecyl bromide, 10 parts by weight of polycarbonate diol, 0.1 part by weight of stannous octoate, 13 parts by weight of bis(dihydroxyethyl) disulfide, 20 parts by weight of tetrahydrofuran, and 20 parts by weight of n-hexane.

[0087] S1.2. Place polycaprolactone diol with a molecular weight of 1500 Da and polycarbonate diol with a molecular weight of 1000 Da in an oven and dry at 60 °C for 3 h to remove the moisture therein; at room temperature, use a stirrer to mix the dried polycaprolactone diol and polycarbonate diol at a speed of 400 rpm for 30 min to obtain a diol mixture.

[0088] S1.3. Add long-chain alkyl halide and stannous octoate to the diol mixture, introduce nitrogen at a rate of 3 L / h, gradually raise the temperature to 110 °C at a rate of 10 °C / h, and stir at a speed of 300 rpm for 6 h to carry out an alkylation reaction; after the alkylation reaction is completed, lower the temperature to 90 °C, add a disulfide compound, and continue to stir and react at a speed of 300 rpm for 6 h.

[0089] S1.4. After the reaction is completed, perform degassing treatment. The degassing temperature is 100 °C, the pressure is -0.08 MPa, and the degassing time is 2 h; after the degassing treatment is completed, dissolve with tetrahydrofuran and precipitate in n-hexane, repeat 3 times, and then perform vacuum drying at 60 °C for 8 h to obtain the composite polycaprolactone diol.

[0090] Example 6: A recyclable polyurethane composition and its preparation method, comprising the following steps:

[0091] S2.1: Weigh the following components by weight respectively: 55 parts by weight of composite polycaprolactone diol, 20 parts by weight of 4,4'-diphenylmethane diisocyanate, 10 parts by weight of hydroquinone dipropyl ether, 6 parts by weight of tributyl citrate, 15 parts by weight of isophorone diisocyanate, 0.5 parts by weight of zinc diacetate, 1 part by weight of dilauryl thiodipropionate;

[0092] S2.2: Place the composite polycaprolactone diol and hydroquinone dipropyl ether in a vacuum drying oven respectively, dry at 60 °C for 5 h, and immediately transfer to a desiccator to cool to room temperature after drying; at room temperature, mix the dried composite polycaprolactone diol and hydroquinone dipropyl ether with a stirrer at a speed of 300 rpm for 30 min to obtain a uniform mixture;

[0093] S2.3: Slowly add 4,4'-diphenylmethane diisocyanate to the mixture in S2.2 at a rate of 0.8 parts by weight per minute, introduce nitrogen at a rate of 6 L / h, raise the temperature to 65 °C, and stir at a speed of 500 rpm for 2 h; then add zinc diacetate and continue to react at a speed of 500 rpm for 3 h to form a prepolymer;

[0094] S2.4: Add hydroquinone dipropyl ether and a crosslinking agent to the prepolymer, stir and react at 65 °C at a speed of 200 rpm for 4 h; after the reaction is completed, lower the temperature to 40 °C, add tributyl citrate and dilauryl thiodipropionate, and continue to stir at a speed of 200 rpm for 40 min;

[0095] S2.5: After the reaction is completed, perform degassing treatment. The degassing temperature is 100 °C, the pressure is -0.08 MPa, and the time is 2 h to remove the by-products generated during the reaction; after degassing is completed, perform curing treatment. The curing temperature is 80 °C and the curing time is 6 h to obtain a recyclable polyurethane composition.

[0096] The preparation method of the composite polycaprolactone diol is as follows:

[0097] S1.1: Weigh the following components by weight respectively: 65 parts by weight of polycaprolactone diol, 17 parts by weight of dodecyl bromide, 20 parts by weight of polycarbonate diol, 0.5 parts by weight of stannous octoate, 3 parts by weight of bis(dihydroxyethyl) disulfide, 25 parts by weight of tetrahydrofuran, 25 parts by weight of n-hexane; 7 13 17 20

[0098] S1.2. Place the polycaprolactone diol with a molecular weight of 1500 Da and the polycarbonate diol with a molecular weight of 1000 Da in an oven and dry them at 60 °C for 3 h to remove the moisture therein; at room temperature, use a stirrer to mix the dried polycaprolactone diol and polycarbonate diol at a speed of 400 rpm for 30 min to obtain a diol mixture;

[0099] S1.3. Add the long-chain alkyl halide and stannous octoate to the diol mixture, introduce nitrogen at a speed of 3 L / h, gradually raise the temperature to 110 °C at a speed of 10 °C / h, and stir at a speed of 300 rpm for 6 h to carry out the alkylation reaction; after the alkylation reaction is completed, lower the temperature to 90 °C, add the disulfide compound, and continue to stir and react at a speed of 300 rpm for 6 h;

[0100] S1.4. After the reaction is completed, carry out degassing treatment. The degassing temperature is 100 °C, the pressure is -0.08 MPa, and the degassing time is 2 h; after the degassing treatment is completed, dissolve it with tetrahydrofuran and precipitate it in n-hexane, repeat 3 times, and then carry out vacuum drying at 60 °C for 8 h to obtain the composite polycaprolactone diol.

[0101] Example 7: A recyclable polyurethane composition and a preparation method thereof, comprising the following steps:

[0102] S2.1. Weigh the following components by weight: 60 parts by weight of composite polycaprolactone diol, 15 parts by weight of 4,4'-diphenylmethane diisocyanate, 5 parts by weight of hydroquinone dipropyl ether, 3 parts by weight of tributyl citrate, 10 parts by weight of isophorone diisocyanate, 0.1 part by weight of zinc diacetate, and 0.5 part by weight of dilauryl thiodipropionate;

[0103] S2.2. Place the composite polycaprolactone diol and hydroquinone dipropyl ether in a vacuum drying oven and dry them at 60 °C for 5 h. Immediately transfer them to a dryer and cool them to room temperature after drying; at room temperature, use a stirrer to mix the dried composite polycaprolactone diol and hydroquinone dipropyl ether at a speed of 300 rpm for 30 min to obtain a uniform mixture;

[0104] S2.3. Slowly add 4,4'-diphenylmethane diisocyanate to the mixture in S2.2 at a speed of 0.8 part by weight per minute, introduce nitrogen at a speed of 6 L / h, raise the temperature to 65 °C, and stir at a speed of 500 rpm for 2 h; then add zinc diacetate and continue to react at a speed of 500 rpm for 3 h to form a prepolymer;

[0105] S2.4. Add hydroquinone dipropylene glycol and a crosslinking agent to the prepolymer, and stir and react at 65 °C at a speed of 200 rpm for 4 h; after the reaction is completed, lower the temperature to 40 °C, add tributyl citrate and dilauryl thiodipropionate, and continue to stir at a speed of 200 rpm for 40 min;

[0106] S2.5. After the reaction is completed, perform degassing treatment. The degassing temperature is 100 °C, the pressure is -0.08 MPa, and the time is 2 h to remove the by-products generated during the reaction; after the degassing is completed, perform curing treatment. The curing temperature is 80 °C and the curing time is 6 h to obtain a recyclable polyurethane composition.

[0107] The preparation method of the composite polycaprolactone diol is as follows:

[0108] S1.1. Weigh the following components by weight: 65 parts by weight of polycaprolactone diol, 17 parts by weight of dodecyl bromide, 10 parts by weight of polycarbonate diol, 0.1 part by weight of stannous octoate, 13 parts by weight of bis(dihydroxyethyl) disulfide, 20 parts by weight of tetrahydrofuran, and 20 parts by weight of n-hexane;

[0109] S1.2. Place the polycaprolactone diol with a molecular weight of 1500 Da and the polycarbonate diol with a molecular weight of 1000 Da in an oven and dry at 60 °C for 3 h to remove the moisture therein; at room temperature, use a stirrer to mix the dried polycaprolactone diol and polycarbonate diol at a speed of 400 rpm for 30 min to obtain a diol mixture;

[0110] S1.3. Add the long-chain alkyl halide and stannous octoate to the diol mixture, introduce nitrogen at a rate of 3 L / h, gradually raise the temperature to 110 °C at a rate of 10 °C / h, stir at a speed of 300 rpm for 6 h to carry out the alkylation reaction; after the alkylation reaction is completed, lower the temperature to 90 °C, add the disulfide compound, and continue to stir and react at a speed of 300 rpm for 6 h;

[0111] S1.4. After the reaction is completed, perform degassing treatment. The degassing temperature is 100 °C, the pressure is -0.08 MPa, and the degassing time is 2 h; after the degassing treatment is completed, dissolve with tetrahydrofuran and precipitate in n-hexane, repeat 3 times, and then perform vacuum drying at 60 °C for 8 h to obtain the composite polycaprolactone diol.

[0112] Comparative Example 1: Using the method of Example 6, without using the composite polycaprolactone diol, directly using polycaprolactone diol to prepare a recyclable polyurethane composition.

[0113] Comparative Example 2: Using the method of Example 6, in the preparation method of the composite polycaprolactone diol, remove the disulfide compound.

[0114] Comparative Example 3: Using the method of Example 6, the composite polycaprolactone diol was replaced with polytetrahydrofuran diol.

[0115] A recyclable polyurethane composition prepared by the composite polycaprolactone diol of the present invention, wherein the performance index test items and test standards of the recyclable polyurethane composition are as follows:

[0116] Accurately measure the mass, volume or amount of substance of the original polyurethane composition, etc., process the original polyurethane composition according to the established recycling method and process, measure the mass, volume or amount of substance of the recovered polyurethane composition, etc., and calculate the recovery rate; the large accumulation of polyurethane waste will cause environmental pollution, such as occupying land, polluting soil and water bodies, etc. A higher recovery rate can reduce the emissions of waste and reduce the pressure on the environment.

[0117] Conduct performance tests on the original polyurethane composition, record its tensile strength, elongation at break and hardness, etc., and then measure the tensile strength, elongation at break and hardness of the recovered polyurethane composition, and calculate the recovery performance retention rate; a high recovery performance retention rate indicates that the recovered polyurethane material can well retain the performance of the original material, and its quality stability is good, and it can be applied in more fields and products.

[0118] Through the above standards, the recyclable polyurethane compositions prepared in Examples 1-7 and Comparative Examples 1-3 were tested, and the obtained data are shown in Table 1:

[0119] Table 1 Performance data of the recyclable polyurethane compositions of Examples 1-7 and Comparative Examples 1-3

[0120]

[0121] It can be seen from Examples 1-4 that when the mass ratio of the long-chain alkyl halide to the polycaprolactone diol in the composite polycaprolactone diol gradually increases, the recovery rate and the recovery performance retention rate of the polyurethane composition gradually increase, but when the mass ratio of the long-chain alkyl halide to the polycaprolactone diol reaches a certain value, the recovery rate and the recovery performance retention rate of the polyurethane composition gradually decrease. It can be seen that with the increase of the mass ratio of the long-chain alkyl halide, both the recovery rate and the recovery performance retention rate of the polyurethane composition are improved, but excessive increase may reduce the recovery rate and the recovery performance retention rate of the polyurethane composition;

[0122] Specifically, long-chain alkyl groups have hydrophobicity and relatively unique chemical structural characteristics. When more long-chain alkyl groups are introduced into the polyurethane molecular chain, the overall polarity and solubility of the material will change. The solubility of the material in some organic solvents is often improved, making it easier to dissolve in specific organic solvents, achieving efficient depolymerization and decomposing into recyclable small molecules or fragments, thereby increasing the recovery rate. Long-chain alkyl groups have a relatively large volume and strong van der Waals forces. As their content in the polyurethane molecular chain increases (i.e., the mass ratio increases), the van der Waals interactions between the molecular chains are enhanced. During the recycling process, this strong intermolecular force helps maintain the relatively ordered arrangement and interconnected state of the molecular chains. When remanufactured into products, this ordered and well-interacting molecular chain structure can better play a synergistic role, enabling the material to still possess good properties such as tensile strength and hardness, thereby increasing the retention rate of the properties after recycling.

[0123] The introduction of more long-chain alkyl groups can, to a certain extent, stabilize the structure of the polyurethane molecular chain, making it less likely to undergo excessive chain segment breakage or structural disorder when experiencing various physical and chemical changes (such as heating, dissolution, repolymerization, etc.) during the recycling process. When remolded after recycling, the molecular chains can be reconstructed relatively intact and orderly, closer to the molecular structure state of the original material, thereby ensuring that the recycled product can better maintain its original properties and gradually increasing the retention rate of the recycling performance.

[0124] Furthermore, by comparing Examples 5 - 7, it can be seen that: when other components remain unchanged, only when the proportion of the composite polycaprolactone diol gradually increases, the recovery rate and the retention rate of the recycling performance of the polyurethane composition increase significantly. It can be known from this that the ester bonds and other structures in the molecular chain of polycaprolactone diol make it have good solubility in some organic solvents. When its proportion increases, the material is more likely to dissolve in certain suitable organic solvents, decompose into recyclable small molecules or fragments, thereby increasing the recovery rate of the entire polyurethane composition. Polyurethane is a multiphase system composed of soft segments and hard segments. The composite polycaprolactone diol is usually used as the soft segment part. As its proportion gradually increases, the phase separation structure between the soft and hard segments becomes more perfect, with the soft segment forming a continuous phase and the hard segment being reasonably dispersed therein. During the recycling and reprocessing process, this optimized phase separation structure helps the molecular chains to better reconstruct and return to a state close to the original material, enabling the material to better maintain its original properties after remolding, thereby increasing the retention rate of the properties after recycling. In addition, it may also have certain crystalline regions (under specific conditions). During the recycling process, the crystalline regions can play a certain role in stabilizing and supporting the molecular chains, assisting in maintaining the mechanical properties, thermal properties, etc. of the material, enabling the recycled product to better maintain its original properties, and further increasing the retention rate of the recycling performance.

[0125] Comparing Example 6 with Comparative Example 1, it can be seen that when preparing the recyclable polyurethane composition directly using polycaprolactone diol without using the composite polycaprolactone diol, the recovery rate and the retention rate of the recycling performance of the polyurethane composition are significantly reduced.

[0126] Taking Example 6 as the optimal example and combining with Comparative Example 2, it can be known that in the preparation method of the composite polycaprolactone diol, when removing the disulfide compound, the recovery rate and the retention rate of the recycling performance of the polyurethane composition are significantly reduced;

[0127] The disulfide bond (-S-S-) is a kind of dynamic covalent bond with the characteristic of reversible cleavage under specific conditions (such as heating, light, adding reducing agent, etc.). In the polyurethane composition containing the disulfide compound, by applying appropriate external stimuli to break the disulfide bond, the macromolecular chains are depolymerized into relatively small fragments that are convenient for subsequent reprocessing and utilization, thereby increasing the recovery rate; during the use and recycling reprocessing of the material, the molecular chains will be damaged to varying degrees. The disulfide bond can play a role similar to a crosslinking point, transmitting stress through dynamic cleavage and recombination. And when there are local damages in the molecular chains, it can also rely on the dynamic exchange reaction of the disulfide bond for a certain degree of self-repair to keep the material in a relatively good performance state as much as possible; in addition, the disulfide bond also helps to stabilize the structure of the polyurethane molecular chain. Its existence can, to a certain extent, limit the excessive movement, deformation of the molecular chain under the influence of external factors, as well as the unreasonable cleavage of chemical bonds, etc., and can improve the retention rate of the recycling performance.

[0128] Taking Example 6 as the optimal example and combining with Comparative Example 3, it can be seen that when replacing the composite polycaprolactone diol with polytetrahydrofuran diol, the recovery rate and the retention rate of the recycling performance of the polyurethane composition are significantly reduced;

[0129] The chemical bonds in the molecular chain of polycaprolactone diol have relatively appropriate stability and breakable characteristics under specific recycling conditions (such as the action of heat, chemical reagents, etc.), which is conducive to realizing a controllable depolymerization process and decomposing the macromolecular chains into units convenient for subsequent processing and utilization; while the chemical bonds in the molecular chain of polytetrahydrofuran diol are relatively more stable and are not easily broken under conventional recycling conditions, making it difficult to achieve effective depolymerization, thus resulting in a significant decrease in the overall recovery rate of the polyurethane composition; in the polyurethane system, when polycaprolactone diol is used as the soft segment component, it can form a specific phase separation structure with the hard segment, and this structure has an important impact on the material properties. When replaced with polytetrahydrofuran diol, due to the differences in its chemical structure and physical properties, the phase separation structure formed with the hard segment will change, and the interactions and arrangement patterns between the molecular chains will also be different. During the recycling reprocessing process, this new structure is not conducive to the recovery and maintenance of the material properties, resulting in the difficulty for the recycled product to maintain the original properties and reducing the retention rate of the recycling performance.

[0130] The foregoing has shown and described the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and the above embodiments and the descriptions in the specification are only preferred examples of the present invention and are not used to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. A recyclable polyurethane composition, characterized in that: The invention comprises the following components: 40-60 parts by weight of composite polycaprolactone diol, 15-25 parts by weight of 4,4'-diphenylmethane diisocyanate, 5-15 parts by weight of hydroquinone dihydroxypropyl ether, 3-10 parts by weight of tributyl citrate, 10-20 parts by weight of a crosslinking agent, 0.1-1 parts by weight of zinc diacetate, and 0.5-2 parts by weight of dilauryl thiodipropionate; The composite polycaprolactone diol is prepared by blending polycaprolactone diol and polycarbonate diol to obtain a polyol mixture, and then alkylating and modifying the polyol mixture with a long-chain alkyl halide.

2. The recyclable polyurethane composition according to claim 1, characterized in that The preparation method of the composite polycaprolactone diol is as follows: S1.

1. Weigh the following components in parts by weight respectively: 50-80 parts by weight of polycaprolactone diol, 5-20 parts by weight of long-chain alkyl halide, 10-30 parts by weight of polycarbonate diol, 0.1-1 parts by weight of stannous octoate, 1-5 parts by weight of disulfide bond compound, 20-30 parts by weight of tetrahydrofuran, and 20-30 parts by weight of n-hexane; S1.2, drying the polycaprolactone diol and the polycarbonate diol in an oven at 60-80°C for 3-4 hours to remove moisture therein; mixing the dried polycaprolactone diol and the polycarbonate diol with a stirrer at a speed of 200-400 rpm for 30-45 minutes at room temperature to obtain a diol mixture; S1.3, add the long-chain alkyl halide and stannous octoate to the diol mixture, introduce nitrogen at a rate of 1-5L / h, gradually increase the temperature to 100-120°C at a rate of 9-16°C / h, stir at a speed of 300-400rpm for 6-8h, and carry out alkylation reaction; after the alkylation reaction is completed, reduce the temperature to 60-90°C, add the disulfide bond compound, and continue to stir the reaction at a speed of 200-400rpm for 3-6h; S1.

4. After the reaction is completed, degassing is performed; after the degassing is completed, dissolving in tetrahydrofuran and precipitating in n-hexane is repeated 2-3 times, and then vacuum drying is performed at 40-60°C for 6-8h to obtain composite polycaprolactone diol.

3. The recyclable polyurethane composition according to claim 2, characterized in that In the S1.2, the molecular weight of the polycaprolactone diol is 1500-2000 Da, and the molecular weight of the polycarbonate diol is 1000-2000 Da.

4. The recyclable polyurethane composition according to claim 2, characterized in that In S1.3, the disulfide bond compound is any one of bis(dihydroxyethyl) disulfide and dithiodipropionic acid.

5. The recyclable polyurethane composition according to claim 2, characterized in that In the S1.4, the degassing temperature is 100-120°C, the pressure is -0.08-~-0.1MPa, and the degassing time is 1-2h.

6. A method for preparing a recyclable polyurethane composition, for preparing a recyclable polyurethane composition as claimed in any one of claims 1 to 5, characterized in that: The preparation method of the recyclable polyurethane composition is as follows: S2.

1. Weigh the following components in parts by weight respectively: 40-60 parts by weight of composite polycaprolactone diol, 15-25 parts by weight of 4,4'-diphenylmethane diisocyanate, 5-15 parts by weight of hydroquinone dihydroxypropyl ether, 3-10 parts by weight of tributyl citrate, 10-20 parts by weight of a crosslinking agent, 0.1-1 parts by weight of zinc diacetate, and 0.5-2 parts by weight of dilauryl thiodipropionate; S2.2, respectively place the composite polycaprolactone diol and hydroquinone dihydroxypropyl ether in a vacuum drying oven, dry at 50-80°C for 4-6h, and immediately transfer to a dryer to cool to room temperature; at room temperature, use a stirrer to mix the dried composite polycaprolactone diol and hydroquinone dihydroxypropyl ether at a speed of 300-500rpm for 30-50min to obtain a uniform mixture; S2.3, slowly add 4,4'-diphenylmethane diisocyanate to the mixture in S2.2, introduce nitrogen, raise the temperature to 60-70°C, and stir at a speed of 300-500rpm for 1-2h; then add zinc diacetate and continue to react at a speed of 300-500rpm for 2-3h to form a prepolymer; S2.4, add hydroquinone dihydroxypropyl ether and crosslinking agent to the prepolymer, stir and react at 60-70°C at a speed of 200-300rpm for 2-4h; after the reaction is completed, lower the temperature to 40-50°C, add tributyl citrate and dilauryl thiodipropionate, and continue to stir at a speed of 200-300rpm for 30-60min; S2.

5. After the reaction is completed, degassing treatment is carried out at a temperature of 100-120°C, a pressure of -0.08~-0.1MPa, and a time of 1-2h to remove by-products produced during the reaction; after degassing is completed, curing treatment is carried out to obtain a recyclable polyurethane composition.

7. The method for preparing a recyclable polyurethane composition according to claim 6, characterized in that: In the above S2.3, the speed of slowly adding 4,4'-diphenylmethane diisocyanate is 0.75-1 parts by weight per minute.

8. The method for preparing a recyclable polyurethane composition according to claim 6, characterized in that: In S2.3, the nitrogen introduction rate is 5-10 L / h.

9. The method for preparing a recyclable polyurethane composition according to claim 6, characterized in that: In the above S2.4, the cross-linking agent is any one of isophorone diisocyanate or hexamethylene diisocyanate.

10. The method for preparing a recyclable polyurethane composition according to claim 6, characterized in that: In the S2.5, the curing temperature is 80-100° C. and the curing time is 4-6 hours.

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