A recycled polycarbonate polyol, and a method of making and using the same

Abstract

The application belongs to the technical field of polymer material recycling and polyurethane synthesis, and relates to a regenerated polycarbonate polyol as well as a preparation method and application thereof. The method comprises the following steps: depolymerizing waste polyethylene terephthalate with dimethyl carbonate, adding methanol to perform an ester exchange reaction, separating unreacted methanol, and then performing ester exchange, separating unreacted dimethyl carbonate and polycondensation reaction to obtain the regenerated polycarbonate polyol. The polyol contains polyester and polycarbonate segments and is prepared by the above method. The polyol can be reacted with diisocyanate, substance X and catalyst IV to prepare a regenerated polyurethane material, wherein the substance X is a small molecule chain extender; or the substance X is a mixture of a small molecule chain extender and water. The application realizes short-process upgrading and recycling of waste polyethylene terephthalate, reduces the cost, and the obtained product can be directly used for polyurethane synthesis, and has environmental protection and economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of polymer material recycling and polyurethane synthesis technology, and relates to a recycled polycarbonate polyol, its preparation method and application. Background Technology

[0002] Polyurethane materials are widely used in foams, coatings, elastomers, and other fields due to their excellent comprehensive properties. Polycarbonate polyols, because their molecular chains contain carbonate groups, produce polyurethanes with these groups as the soft segment that outperform conventional polyether and polyester polyols in terms of hydrolysis resistance, heat resistance, and mechanical properties, making them a core raw material for high-end polyurethanes. However, the traditional preparation of polycarbonate polyols mostly relies on the transesterification method between petroleum-based small-molecule diols and dialkyl carbonates. This method not only limits the raw materials to non-renewable petroleum resources but also results in complex synthesis processes and high production costs, severely restricting their large-scale industrial application. Therefore, the industry urgently needs to find low-cost, non-petroleum-based raw materials and processes for preparing polycarbonate polyols.

[0003] Polyethylene terephthalate (PET), as the world's most produced packaging plastic, faces significant challenges in recycling its waste, making it a key focus of environmental protection and crucial for resource circularity. Notably, the PET molecular chain contains ethylene glycol and terephthalate segments, which are the core structural units required for the synthesis of polyols. Therefore, waste PET represents a potentially high-quality raw material for the preparation of non-petroleum-based polyols.

[0004] Currently, existing chemical recycling methods for polyethylene terephthalate mainly include hydrolysis, enzymatic hydrolysis, and alcoholysis. Their core purpose is to depolymerize waste polyethylene terephthalate into monomers or oligomers such as dimethyl terephthalate and ethylene glycol, thereby achieving basic resource recovery.

[0005] Patent CN120119454B and patent application CN118666683A utilize decolorization and depolymerization with carbonate solvents, followed by distillation, crystallization, and solidification to purify and recycle waste polyethylene terephthalate (PET) to produce recycled dimethyl terephthalate (DMT) and recycled PET. However, this recycling technology has significant drawbacks: the depolymerization products require multiple separation and purification steps before they can be used as repolymerization raw materials, resulting in a lengthy process with high energy and material losses. Furthermore, it can only achieve the downgrading or closed-loop recovery of PET, and cannot directly convert it into high-value-added polycarbonate polyol products that meet the requirements of polyurethane synthesis.

[0006] Therefore, it is necessary to provide a method for preparing recycled polycarbonate polyols, using waste polyethylene terephthalate as raw material, and directly converting it into qualified polycarbonate polyols through a simple and efficient process. This not only solves the problems of traditional polycarbonate polyol preparation relying on petroleum and high cost, but also overcomes the shortcomings of existing polyethylene terephthalate chemical recycling processes, which are long, can only be downgraded and reused, and cannot be adapted to the needs of polycarbonate polyol synthesis. This achieves the upgraded recycling of waste resources and the low-cost preparation of polycarbonate polyols. Summary of the Invention

[0007] The purpose of this invention is to solve the problems existing in the prior art and to provide a recycled polycarbonate polyol, its preparation method and application.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A method for preparing recycled polycarbonate polyols includes the following steps:

[0010] (a) Waste polyethylene terephthalate is depolymerized using dimethyl carbonate to obtain a mixture A containing dimethyl terephthalate, ethylene carbonate and dimethyl carbonate, wherein the total mass percentage of dimethyl terephthalate, ethylene carbonate and dimethyl carbonate in mixture A is more than 50%.

[0011] (b) Add methanol to allow it to undergo transesterification with ethylene carbonate in mixture A to produce dimethyl carbonate and ethylene glycol. Then, separate the unreacted methanol until the amount of methanol distilled is more than 90.2% of the theoretical value, to obtain mixture B containing dimethyl terephthalate, dimethyl carbonate and ethylene glycol. The total mass percentage of dimethyl terephthalate, dimethyl carbonate and ethylene glycol in mixture B is more than 50%.

[0012] (c) After the transesterification reaction of mixture B is controlled, the unreacted dimethyl carbonate is separated until the distillation amount of dimethyl carbonate is more than 90.5% of the theoretical value. Then, a polycondensation reaction is carried out to remove by-products and small molecules, and the recycled polycarbonate polyol is obtained.

[0013] This invention employs a one-pot reaction process to achieve the chemical depolymerization and upgraded recycling of waste polyethylene terephthalate (PET). First, waste PET is used as a raw material and undergoes a depolymerization reaction with dimethyl carbonate, causing the large molecular chains of PET to break down and generate oligomers (dimethyl terephthalate and ethylene carbonate). Simultaneously, dimethyl carbonate and ethylene glycol are prepared through a transesterification reaction between methanol and ethylene carbonate. Then, through transesterification and polycondensation reactions, the carbonate segments in the dimethyl carbonate molecular structure are introduced as chain extenders into the molecular chains of the depolymerized products, ultimately yielding a recycled polycarbonate polyol whose molecular chains simultaneously contain polyester segments (derived from waste PET) and polycarbonate segments (derived from dimethyl carbonate).

[0014] As a preferred technical solution:

[0015] In the above-described method for preparing a recycled polycarbonate polyol, the total mass percentage of dimethyl terephthalate, ethylene carbonate, and dimethyl carbonate in mixture A is 95% to 99%, and the total mass percentage of dimethyl terephthalate, dimethyl carbonate, and ethylene glycol in mixture B is 95% to 99%.

[0016] In the method for preparing a recycled polycarbonate polyol as described above, in step (a), the intrinsic viscosity of the waste polyethylene terephthalate is 0.70~0.78 dL / g; the molar ratio of the structural unit of the waste polyethylene terephthalate (the relative molecular mass of the structural unit of polyethylene terephthalate is 192.0 g / mol, and the molar amount is obtained by dividing the mass of polyethylene terephthalate by the relative molecular mass) to the molar amount of dimethyl carbonate is 1:5~10; depolymerization is carried out under nitrogen or an inert atmosphere, the depolymerization temperature is 160~200℃, and the time is 30~200 min.

[0017] In the above-described method for preparing a recycled polycarbonate polyol, the molar ratio of the waste polyethylene terephthalate structural unit in step (a) to the molar ratio of methanol in step (b) is 1:2.05~2.15.

[0018] In the preparation method of the above-mentioned recycled polycarbonate polyol, in step (b), the temperature of the transesterification reaction is 80~160℃ and the time is 60~120min.

[0019] In the preparation method of the recycled polycarbonate polyol described above, in step (c), the temperature of the transesterification reaction is 160~200℃ and the time is 60~120min; the temperature of the polycondensation reaction is 200~220℃, the vacuum degree is 100~1000Pa, and the time is 30~60min.

[0020] In the above-described method for preparing a recycled polycarbonate polyol, catalyst I is added during depolymerization in step (a); catalyst II is added during transesterification in step (b); and catalyst III is added during transesterification in step (c).

[0021] In the method for preparing a recycled polycarbonate polyol as described above, catalyst I is one or more of zinc acetate, zinc oxide, sodium acetate, sodium carbonate, potassium carbonate, potassium bicarbonate, potassium chloride, and lithium chloride; catalyst II is sodium methoxide; and catalyst III is one or more of tetrabutyl titanate, antimony trioxide, antimony acetate, dibutyltin dilaurate, and antimony glycolate.

[0022] In the above-described method for preparing a recycled polycarbonate polyol, in step (a), the mass addition amount of catalyst I is 300-1000 ppm of the mass addition amount of waste polyethylene terephthalate; in step (b), the mass ratio of catalyst II to catalyst III in step (c) is 1:1-3; in step (c), the mass addition amount of catalyst III is 300-1000 ppm of the mass addition amount of waste polyethylene terephthalate in step (a).

[0023] The present invention also provides a recycled polycarbonate polyol, which is prepared by a method for preparing recycled polycarbonate polyol as described in any of the preceding claims; the molecular chain of the recycled polycarbonate polyol contains both polyester segments introduced by waste polyethylene terephthalate and polycarbonate segments introduced by dimethyl carbonate; the recycled polycarbonate polyol has an acid value of 0.5~2.0 mgKOH / g, a hydroxyl value of 30~300 mgKOH / g, a number average molecular weight of 500~4000 g / mol, a molecular weight distribution index of 1.5~1.95, a moisture content of 0.03~0.05 wt%, and a viscosity of 500~5000 mPa·s at 25°C.

[0024] This invention achieves the orderly growth of molecular chain segments and the suppression of side reactions through controlled depolymerization in step (a), precise conversion of methanol dosage to ethylene carbonate in step (b), and gradient heating and vacuum polycondensation in step (c), thereby obtaining a stable recycled polycarbonate polyol. By precisely controlling the reaction progress of each step in the "one-pot" process, the number-average molecular weight, acid value, and hydroxyl value of the product are accurately controlled, meeting the requirements of polyurethane synthesis for soft segment raw materials. Simultaneously, because the high-temperature, high-vacuum polycondensation reaction in step (c) fully removes small molecule byproducts and unreacted monomers, the acid value of the product is controlled at 0.5~2.0 mgKOH / g, avoiding side reactions such as thermal degradation caused by excessively high acid values ​​in polyurethane synthesis. In addition, the hydroxyl value ranges from 30 to 300 mg KOH / g to meet the requirements of different soft segment lengths. Meanwhile, the molecular weight distribution index (1.5 to 1.95) and low moisture content (0.03 wt% to 0.05 wt%) ensure that the molecular weight of polyurethane is controllable and that there are few bubbles. Furthermore, the moderate viscosity (500 to 5000 mPa·s) at 25°C is conducive to processing. Finally, the presence of both polyester and polycarbonate segments in the chain, along with the uniform length of the polyol segments, endows the polyurethane material with stable mechanical properties.

[0025] The present invention also provides a recycled polyurethane material, which is prepared by reacting a recycled polycarbonate polyol, diisocyanate, substance X and catalyst IV as described above, wherein substance X is a small molecule chain extender; or, substance X is a mixture of a small molecule chain extender and water.

[0026] As a preferred technical solution:

[0027] In the recycled polyurethane material described above, the diisocyanate is one or more of toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), dicyclohexylmethane diisocyanate (HMDI), and isophorone diisocyanate (IPDI).

[0028] The small molecule chain extender is one or more of ethylene glycol, 1,3-propanediol, 1,4-butanediol, diethylene glycol, dipropylene glycol, and 1,6-hexanediol;

[0029] Catalyst IV is one or more of dibutyltin dilaurate, stannous octoate, triethylenediamine, triethanolamine, N,N-dimethylcyclohexylamine, and triethylamine; wherein, the mass addition amount of catalyst IV is 300~1000 ppm of the mass addition amount of recycled polycarbonate polyol, the molar amount of small molecule chain extender is 10%~30% of the total molar amount of hydroxyl groups of recycled polycarbonate polyol, and the mass addition amount of water is 5%~7% of the mass addition amount of recycled polycarbonate polyol.

[0030] The specific process of the recycled polyurethane material described above is as follows: Under the action of catalyst IV, diisocyanate with a molar ratio of -NCO to -OH of 1.0~1.2:1 and recycled polycarbonate polyol are reacted at 70~90℃ for 1~3h to obtain polyurethane prepolymer. Then, substance X is added and the chain extension reaction is carried out for 1min~2h. The prepolymer is then poured into a mold or coated on the substrate surface and cured at 80~100℃ for 12~24h to obtain the recycled polyurethane material.

[0031] The recycled polyurethane material described above is a polyurethane elastomer, polyurethane foam, polyurethane coating, or polyurethane adhesive. The polyurethane foam has a tensile strength of 5-10 MPa, an elongation at break of 150%-300%, and a tensile strength retention rate of 80%-85% after being placed at 70°C and 95% relative humidity for 7 days. The polyurethane elastomer has a tensile strength of 25-40 MPa and an elongation at break of 300%-600%. The polyurethane coating has a Shore hardness of D65-D85 and a cross-cut adhesion grade of 0-1. The polyurethane adhesive has a single-lap tensile shear strength of 10-15 MPa and a 180° peel strength of 20-30 kN / m.

[0032] Beneficial effects:

[0033] (1) The present invention uses a one-pot method to prepare recycled polycarbonate polyols, integrating the three-step reaction of polyethylene terephthalate depolymerization, in-situ conversion of ethylene carbonate, and transesterification / condensation into a continuous process, avoiding the separation and purification of intermediate products, effectively solving the compatibility problem of multiple steps in the same reactor, significantly shortening the process flow, reducing the preparation cost, realizing the chemical depolymerization and upgrading of waste polyethylene terephthalate, and getting rid of dependence on petroleum-based raw materials.

[0034] (2) The recycled polycarbonate polyol prepared by this invention has stable performance and contains both polyester and polycarbonate segments in its molecular chain. It has a unique structure and can be directly used as a soft segment component in polyurethane synthesis, which meets the raw material requirements for polyurethane synthesis. At the same time, it effectively solves the problems of complex sources of recycled polyol, many types of impurities, wide distribution of molecular weight and functionality, and large fluctuations in hydroxyl value and viscosity. It successfully achieves stable and controllable preparation of recycled polyurethane with qualified performance and overcomes the core technical problem in this field.

[0035] (3) The recycled polyurethane material prepared by the present invention using recycled polycarbonate polyol has both excellent mechanical properties and hydrolysis resistance. The synergistic effect of its structure and performance cannot be simply superimposed by a single polyester or polycarbonate polyol. It has unexpected technical effects, significantly improves the application performance of polyurethane material, and broadens the application range of polyurethane material.

[0036] (4) This invention realizes the direct conversion of waste polyethylene terephthalate into high value-added polycarbonate polyol, shortens the conversion path from waste to high-performance products, eliminates the need to separate and purify the depolymerization products before repolymerization, further reduces production energy consumption and material loss, and has both good environmental and economic benefits. Attached Figure Description

[0037] Figure 1 The infrared spectrum of the recycled polycarbonate polyol prepared in Example 1;

[0038] Figure 2 The infrared spectrum of the recycled polyurethane material prepared in Example 1;

[0039] Figure 3 Here is a photograph of the recycled polyurethane material prepared in Example 4;

[0040] Figure 4 Here is a photograph of the recycled polyurethane material prepared in Example 7;

[0041] Figure 5 The image shows the single-lap tensile shear strength test result of the recycled polyurethane material prepared in Example 10. Detailed Implementation

[0042] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0043] The following are the test methods or calculation formulas for the relevant performance indicators in each embodiment:

[0044] Intrinsic viscosity: Tested in accordance with GB / T 14190-2017 "Test Method for Fiber Grade Polyester (PET) Chips".

[0045] Acid value: The acid value was determined by acid-base titration according to HG / T 2708-1995 "Determination of Acid Value in Polyester Polyols".

[0046] Hydroxyl value: Tested according to Method A (acetic anhydride-pyridine method) in HG / T 2709-2022 "Determination of hydroxyl value of polyester polyols used in the production of polyurethane".

[0047] Number-average molecular weight and molecular weight distribution index: tested according to GB / T 21863-2008 "Gel permeation chromatography (GPC) using tetrahydrofuran as eluent".

[0048] Moisture content: Tested in accordance with GB / T 22313-2008 "Determination of water content of polyols used in polyurethane production of plastics".

[0049] Viscosity: The test was conducted in accordance with GB / T 21059-2007 "Determination of viscosity of polymers / resins in liquid, emulsion or dispersion systems of plastics using a rotational viscometer at a specified shear rate".

[0050] Tensile strength and elongation at break: Tested in accordance with GB / T 1040.1-2025 "Determination of tensile properties of plastics - Part 1: General", with a test speed of 50 mm / min.

[0051] Shore hardness: The test was conducted in accordance with GB / T 39693.4-2025 "Determination of hardness of vulcanized rubber or thermoplastic rubber - Part 4: Determination of indentation hardness by Shore hardness tester (Shore hardness)".

[0052] Cross-cut adhesion test: The test was conducted in accordance with GB / T 9286-2021 "Cross-cut test for paints and varnishes".

[0053] Single lap tensile shear strength: Tested in accordance with GB / T 33334-2016 "Test method for single lap tensile shear strength of adhesives (composite to composite material)".

[0054] 180° peel strength: Tested in accordance with GB / T 2790-1995 "Test method for 180° peel strength of adhesives, flexible materials vs. rigid materials".

[0055] Tensile strength retention rate: Tested in accordance with GB / T 9640-2008 "Accelerated aging test method for flexible and rigid foam polymer materials".

[0056] Example 1

[0057] A method for preparing a polyurethane elastomer, comprising the following specific steps:

[0058] (1) Preparation of materials;

[0059] Catalyst I: Zinc acetate;

[0060] Dimethyl carbonate;

[0061] Waste polyethylene terephthalate: intrinsic viscosity is 0.7 dL / g;

[0062] Methanol;

[0063] Catalyst II: Sodium methoxide;

[0064] Catalyst III: Tetrabutyl titanate;

[0065] Diisocyanate: TDI;

[0066] Small molecule chain extender: ethylene glycol;

[0067] Catalyst IV: Dibutyltin dilaurate;

[0068] (2) Preparation of recycled polycarbonate polyols;

[0069] (a) Under nitrogen or inert atmosphere, and with the action of catalyst I, waste polyethylene terephthalate is depolymerized using dimethyl carbonate to obtain mixture A containing dimethyl terephthalate, ethylene carbonate and dimethyl carbonate, wherein the total mass percentage of dimethyl terephthalate, ethylene carbonate and dimethyl carbonate in mixture A is 95%;

[0070] (b) Add methanol and catalyst II to allow it to undergo transesterification with ethylene carbonate in mixture A, producing dimethyl carbonate and ethylene glycol. Then, separate the unreacted methanol until the methanol distillation amount is 94.3% of the theoretical value, to obtain mixture B containing dimethyl terephthalate, dimethyl carbonate and ethylene glycol. The total mass percentage of dimethyl terephthalate, dimethyl carbonate and ethylene glycol in mixture B is 97%.

[0071] (c) After adding catalyst III and controlling the transesterification reaction of mixture B, unreacted dimethyl carbonate is separated until the distillation amount of dimethyl carbonate is 92.8% of the theoretical value. Then, polycondensation reaction is carried out to obtain recycled polycarbonate polyol.

[0072] In step (a), the molar ratio of the structural unit of waste polyethylene terephthalate to the molar ratio of dimethyl carbonate is 1:7, the mass addition amount of catalyst I is 500 ppm of the mass addition amount of waste polyethylene terephthalate, the depolymerization temperature is 180℃, and the depolymerization time is 150 min.

[0073] The molar ratio of the waste polyethylene terephthalate structural unit in step (a) to the molar ratio of methanol in step (b) is 1:2.09.

[0074] In step (b), the transesterification reaction is carried out at a temperature of 140°C for 70 minutes.

[0075] The mass ratio of catalyst II in step (b) to catalyst III in step (c) is 1:1.8;

[0076] In step (c), the mass addition amount of catalyst III is 500 ppm of the mass addition amount of waste polyethylene terephthalate in step (a), the temperature of the transesterification reaction is 200℃, the time of the transesterification reaction is 60 min, the temperature of the polycondensation reaction is 220℃, the vacuum degree of the polycondensation reaction is 200 Pa, and the time of the polycondensation reaction is 30 min.

[0077] The obtained recycled polycarbonate polyol has an acid value of 0.7 mgKOH / g, a hydroxyl value of 50 mgKOH / g, a number-average molecular weight of 3800 g / mol, a molecular weight distribution index of 1.85, a moisture content of 0.032 wt%, and a viscosity of 4600 mPa·s at 25℃.

[0078] (3) Preparation of polyurethane elastomer;

[0079] Under the action of catalyst IV, diisocyanate with a molar ratio of -NCO to -OH of 1.1:1 and recycled polycarbonate polyol are reacted at 75°C for 2 hours to obtain polyurethane prepolymer. After adding a small molecule chain extender and reacting for 1.5 hours, it is poured into a mold and cured at 85°C for 18 hours to obtain polyurethane elastomer.

[0080] The catalyst IV was added at a mass of 800 ppm of the recycled polycarbonate polyol, and the small molecule chain extender was added at a molar amount of 20% of the total hydroxyl molar amount of the recycled polycarbonate polyol.

[0081] The final polyurethane elastomer had a tensile strength of 34 MPa and an elongation at break of 440%.

[0082] Depend on Figure 1 As can be seen in the spectrum, 2957cm -1 2877cm -1 The methylene CH symmetric / antisymmetric stretching vibration double peak at 1714 cm⁻¹ -1 A strong characteristic peak at the carbonyl C=O group of the ester bond at 1500 cm⁻¹ -1 The nearby aromatic ring skeleton vibration triplet, and 1216 cm⁻¹ -1 1065cm -1 The absorption bands of the COC stretching vibrations of the ether oxygen bond at the ether oxygen bond were clearly observed, and all characteristic peaks perfectly matched the target structure of the recycled polycarbonate polyol, confirming the successful preparation of the product. Figure 2 As can be seen, in addition to retaining the characteristic structural peaks of polyols, the spectrum also shows a peak at 3336 cm⁻¹. -1 The stretching vibration peak of amino NH appeared at 2952 cm⁻¹. -1 CH stretching vibration peak at 1712 cm⁻¹ -1 The C=O stretching vibration peak of the ester group at 1597 cm⁻¹-1 1527cm -1 1449cm -1 The triplet of the C=C vibration of the benzene ring skeleton at 1216 cm⁻¹, and the 1216 cm⁻¹ peak. -1 1065cm -1 The COC absorption peaks at the point are clearly identifiable, and all characteristic peaks correspond perfectly to the structure of the recycled polyurethane elastomer, proving that the material has been successfully synthesized.

[0083] Example 2

[0084] A method for preparing a polyurethane elastomer, comprising the following specific steps:

[0085] (1) Preparation of materials;

[0086] Catalyst I: Zinc oxide;

[0087] Dimethyl carbonate;

[0088] Waste polyethylene terephthalate: intrinsic viscosity is 0.78 dL / g;

[0089] Methanol;

[0090] Catalyst II: Sodium methoxide;

[0091] Catalyst III: Antimony trioxide;

[0092] Diisocyanate: MDI;

[0093] Small molecule chain extender: 1,3-propanediol;

[0094] Catalyst IV: Dibutyltin dilaurate;

[0095] (2) Preparation of recycled polycarbonate polyols;

[0096] (a) Under nitrogen or inert atmosphere, and with the action of catalyst I, waste polyethylene terephthalate is depolymerized using dimethyl carbonate to obtain mixture A containing dimethyl terephthalate, ethylene carbonate and dimethyl carbonate, wherein the total mass percentage of dimethyl terephthalate, ethylene carbonate and dimethyl carbonate in mixture A is 98%;

[0097] (b) Add methanol and catalyst II to allow it to undergo transesterification with ethylene carbonate in mixture A to produce dimethyl carbonate and ethylene glycol. Then, separate the unreacted methanol until the methanol distillation amount is 91.7% of the theoretical value, and obtain mixture B containing dimethyl terephthalate, dimethyl carbonate and ethylene glycol. The total mass percentage of dimethyl terephthalate, dimethyl carbonate and ethylene glycol in mixture B is 98%.

[0098] (c) After adding catalyst III and controlling the transesterification reaction of mixture B, unreacted dimethyl carbonate is separated until the distillation amount of dimethyl carbonate is 97.4% of the theoretical value. Then, polycondensation reaction is carried out to obtain recycled polycarbonate polyol.

[0099] In step (a), the molar ratio of the structural unit of waste polyethylene terephthalate to the molar ratio of dimethyl carbonate is 1:9, the mass addition amount of catalyst I is 800 ppm of the mass addition amount of waste polyethylene terephthalate, the depolymerization temperature is 200℃, and the depolymerization time is 30 min.

[0100] The molar ratio of the waste polyethylene terephthalate structural unit in step (a) to the molar ratio of methanol in step (b) is 1:2.13.

[0101] In step (b), the transesterification reaction is carried out at a temperature of 90°C for 110 min.

[0102] The mass ratio of catalyst II in step (b) to catalyst III in step (c) is 1:2.5;

[0103] In step (c), the mass addition amount of catalyst III is 800 ppm of the mass addition amount of waste polyethylene terephthalate in step (a), the temperature of the transesterification reaction is 170°C, the time of the transesterification reaction is 100 min, the temperature of the polycondensation reaction is 205°C, the vacuum degree of the polycondensation reaction is 700 Pa, and the time of the polycondensation reaction is 55 min.

[0104] The obtained recycled polycarbonate polyol has an acid value of 1.6 mgKOH / g, a hydroxyl value of 200 mgKOH / g, a number-average molecular weight of 1500 g / mol, a molecular weight distribution index of 1.6, a moisture content of 0.044 wt%, and a viscosity of 1700 mPa·s at 25℃.

[0105] (3) Preparation of polyurethane elastomer;

[0106] Under the action of catalyst IV, diisocyanate with a molar ratio of -NCO to -OH of 1.05:1 and recycled polycarbonate polyol are reacted at 90°C for 1.5 h to obtain polyurethane prepolymer. After adding a small molecule chain extender and reacting for 1 h, it is poured into a mold and cured at 100°C for 12 h to obtain polyurethane elastomer.

[0107] The mass addition amount of catalyst IV is 300 ppm of the mass addition amount of recycled polycarbonate polyol, and the molar amount of small molecule chain extender is 15% of the total molar amount of hydroxyl groups in recycled polycarbonate polyol.

[0108] The final polyurethane elastomer had a tensile strength of 25 MPa and an elongation at break of 600%.

[0109] Example 3

[0110] A method for preparing a polyurethane elastomer, comprising the following specific steps:

[0111] (1) Preparation of materials;

[0112] Catalyst I: Sodium acetate;

[0113] Dimethyl carbonate;

[0114] Waste polyethylene terephthalate: intrinsic viscosity is 0.72 dL / g;

[0115] Methanol;

[0116] Catalyst II: Sodium methoxide;

[0117] Catalyst III: Antimony acetate;

[0118] Diisocyanate: HMDI;

[0119] Small molecule chain extender: 1,4-butanediol;

[0120] Catalyst IV: Stannous octoate;

[0121] (2) Preparation of recycled polycarbonate polyols;

[0122] (a) Under nitrogen or inert atmosphere, and with the action of catalyst I, waste polyethylene terephthalate is depolymerized using dimethyl carbonate to obtain mixture A containing dimethyl terephthalate, ethylene carbonate and dimethyl carbonate, wherein the total mass percentage of dimethyl terephthalate, ethylene carbonate and dimethyl carbonate in mixture A is 97%;

[0123] (b) Add methanol and catalyst II to allow it to undergo transesterification with ethylene carbonate in mixture A to produce dimethyl carbonate and ethylene glycol. Then, separate the unreacted methanol until the methanol distillation amount is 96.2% of the theoretical value, and obtain mixture B containing dimethyl terephthalate, dimethyl carbonate and ethylene glycol. The total mass percentage of dimethyl terephthalate, dimethyl carbonate and ethylene glycol in mixture B is 95%.

[0124] (c) After adding catalyst III and controlling the transesterification reaction of mixture B, unreacted dimethyl carbonate is separated until the distillation amount of dimethyl carbonate is 91.2% of the theoretical value. Then, polycondensation reaction is carried out to obtain recycled polycarbonate polyol.

[0125] In step (a), the molar ratio of the structural unit of waste polyethylene terephthalate to the molar ratio of dimethyl carbonate is 1:5, the mass addition amount of catalyst I is 300 ppm of the mass addition amount of waste polyethylene terephthalate, the depolymerization temperature is 170℃, and the depolymerization time is 200 min.

[0126] The molar ratio of the waste polyethylene terephthalate structural unit in step (a) to the molar ratio of methanol in step (b) is 1:2.07.

[0127] In step (b), the transesterification reaction is carried out at a temperature of 160°C for 60 min.

[0128] The mass ratio of catalyst II in step (b) to catalyst III in step (c) is 1:1.2;

[0129] In step (c), the mass addition amount of catalyst III is 300 ppm of the mass addition amount of waste polyethylene terephthalate in step (a), the temperature of the transesterification reaction is 180°C, the time of the transesterification reaction is 80 min, the temperature of the polycondensation reaction is 215°C, the vacuum degree of the polycondensation reaction is 400 Pa, and the time of the polycondensation reaction is 40 min.

[0130] The obtained recycled polycarbonate polyol has an acid value of 1.1 mgKOH / g, a hydroxyl value of 110 mgKOH / g, a number-average molecular weight of 3000 g / mol, a molecular weight distribution index of 1.75, a moisture content of 0.036 wt%, and a viscosity of 3600 mPa·s at 25℃.

[0131] (3) Preparation of polyurethane elastomer;

[0132] Under the action of catalyst IV, diisocyanate with a molar ratio of -NCO to -OH of 1.18:1 and recycled polycarbonate polyol are reacted at 80°C for 2.5 h to obtain polyurethane prepolymer. After adding a small molecule chain extender and reacting for 2 h, it is poured into a mold and cured at 90°C for 20 h to obtain polyurethane elastomer.

[0133] The catalyst IV was added at a mass of 600 ppm of the recycled polycarbonate polyol, and the small molecule chain extender was added at a molar amount of 30% of the total molar amount of hydroxyl groups in the recycled polycarbonate polyol.

[0134] The final polyurethane elastomer had a tensile strength of 40 MPa and an elongation at break of 300%.

[0135] Example 4

[0136] A method for preparing polyurethane foam, comprising the following specific steps:

[0137] (1) Preparation of materials;

[0138] Catalyst I: Sodium carbonate;

[0139] Dimethyl carbonate;

[0140] Waste polyethylene terephthalate: intrinsic viscosity is 0.73 dL / g;

[0141] Methanol;

[0142] Catalyst II: Sodium methoxide;

[0143] Catalyst III: Dibutyltin dilaurate;

[0144] Diisocyanate: composed of TDI and MDI in a molar ratio of 1:1;

[0145] Small molecule chain extender: diethylene glycol;

[0146] Catalyst IV: Composed of stannous octoate and triethanolamine in a mass ratio of 1:1;

[0147] water;

[0148] (2) Preparation of recycled polycarbonate polyols;

[0149] (a) Under nitrogen or inert atmosphere, and with the action of catalyst I, waste polyethylene terephthalate is depolymerized using dimethyl carbonate to obtain mixture A containing dimethyl terephthalate, ethylene carbonate and dimethyl carbonate, wherein the total mass percentage of dimethyl terephthalate, ethylene carbonate and dimethyl carbonate in mixture A is 97%;

[0150] (b) Add methanol and catalyst II to allow it to undergo transesterification with ethylene carbonate in mixture A, producing dimethyl carbonate and ethylene glycol. Then, separate the unreacted methanol until the methanol distillation amount is 93.5% of the theoretical value, to obtain mixture B containing dimethyl terephthalate, dimethyl carbonate and ethylene glycol. The total mass percentage of dimethyl terephthalate, dimethyl carbonate and ethylene glycol in mixture B is 98%.

[0151] (c) After adding catalyst III and controlling the transesterification reaction of mixture B, unreacted dimethyl carbonate is separated until the distillation amount of dimethyl carbonate is 95.1% of the theoretical value. Then, polycondensation reaction is carried out to obtain recycled polycarbonate polyol.

[0152] In step (a), the molar ratio of the structural unit of waste polyethylene terephthalate to the molar ratio of dimethyl carbonate is 1:10, the mass addition amount of catalyst I is 900 ppm of the mass addition amount of waste polyethylene terephthalate, the depolymerization temperature is 190℃, and the depolymerization time is 50 min.

[0153] The molar ratio of the waste polyethylene terephthalate structural unit in step (a) to the molar ratio of methanol in step (b) is 1:2.11;

[0154] In step (b), the transesterification reaction is carried out at a temperature of 110°C for 90 min.

[0155] The mass ratio of catalyst II in step (b) to catalyst III in step (c) is 1:2.9;

[0156] In step (c), the mass addition amount of catalyst III is 900 ppm of the mass addition amount of waste polyethylene terephthalate in step (a), the temperature of the transesterification reaction is 160°C, the time of the transesterification reaction is 120 min, the temperature of the polycondensation reaction is 200°C, the vacuum degree of the polycondensation reaction is 900 Pa, and the time of the polycondensation reaction is 60 min.

[0157] The obtained recycled polycarbonate polyol has an acid value of 1.9 mgKOH / g, a hydroxyl value of 260 mgKOH / g, a number-average molecular weight of 600 g / mol, a molecular weight distribution index of 1.52, a moisture content of 0.048 wt%, and a viscosity of 650 mPa·s at 25 °C.

[0158] (3) Preparation of polyurethane foam;

[0159] Under the action of catalyst IV, diisocyanate with a molar ratio of -NCO to -OH of 1.02:1 and recycled polycarbonate polyol are reacted at 70°C for 2.5 h to obtain polyurethane prepolymer. After adding small molecule chain extender and water for chain extension reaction for 3 min, it is poured into a mold and cured at 80°C for 24 h to obtain polyurethane foam.

[0160] The catalyst IV is added at a mass of 1000 ppm of the recycled polycarbonate polyol, the small molecule chain extender is added at a molar amount of 15% of the total hydroxyl molar amount of the recycled polycarbonate polyol, and the water is added at a mass of 5% of the recycled polycarbonate polyol.

[0161] The final polyurethane foam (as shown in the image) Figure 3 The tensile strength of the sample (as shown) is 10 MPa, the elongation at break is 150%, and the tensile strength retention rate is 85% after being placed for 7 days at a temperature of 70℃ and a relative humidity of 95%.

[0162] Example 5

[0163] A method for preparing polyurethane foam, comprising the following specific steps:

[0164] (1) Preparation of materials;

[0165] Catalyst I: Potassium carbonate;

[0166] Dimethyl carbonate;

[0167] Waste polyethylene terephthalate: intrinsic viscosity is 0.71 dL / g;

[0168] Methanol;

[0169] Catalyst II: Sodium methoxide;

[0170] Catalyst III: Antimony Glycol;

[0171] Diisocyanate: composed of TDI and HMDI in a molar ratio of 1:1;

[0172] Small molecule chain extender: dipropylene glycol;

[0173] Catalyst IV: Composed of dibutyltin dilaurate and triethylenediamine in a mass ratio of 1:1;

[0174] water;

[0175] (2) Preparation of recycled polycarbonate polyols;

[0176] (a) Under nitrogen or inert atmosphere, and with the action of catalyst I, waste polyethylene terephthalate is depolymerized using dimethyl carbonate to obtain mixture A containing dimethyl terephthalate, ethylene carbonate and dimethyl carbonate, wherein the total mass percentage of dimethyl terephthalate, ethylene carbonate and dimethyl carbonate in mixture A is 97%;

[0177] (b) Add methanol and catalyst II to allow it to undergo transesterification with ethylene carbonate in mixture A, producing dimethyl carbonate and ethylene glycol. Then, separate the unreacted methanol until the methanol distillation amount is 97.1% of the theoretical value, to obtain mixture B containing dimethyl terephthalate, dimethyl carbonate and ethylene glycol. The total mass percentage of dimethyl terephthalate, dimethyl carbonate and ethylene glycol in mixture B is 95%.

[0178] (c) After adding catalyst III and controlling the transesterification reaction of mixture B, unreacted dimethyl carbonate is separated until the distillation amount of dimethyl carbonate is 90.5% of the theoretical value. Then, polycondensation reaction is carried out to obtain recycled polycarbonate polyol.

[0179] In step (a), the molar ratio of the structural unit of waste polyethylene terephthalate to the molar ratio of dimethyl carbonate is 1:6, the mass addition amount of catalyst I is 600 ppm of the mass addition amount of waste polyethylene terephthalate, the depolymerization temperature is 160℃, and the depolymerization time is 180 min.

[0180] The molar ratio of the waste polyethylene terephthalate structural unit in step (a) to the molar ratio of methanol in step (b) is 1:2.14.

[0181] In step (b), the transesterification reaction is carried out at a temperature of 130°C for 80 minutes.

[0182] The mass ratio of catalyst II in step (b) to catalyst III in step (c) is 1:1.4;

[0183] In step (c), the mass addition amount of catalyst III is 600 ppm of the mass addition amount of waste polyethylene terephthalate in step (a), the temperature of the transesterification reaction is 190°C, the time of the transesterification reaction is 70 min, the temperature of the polycondensation reaction is 210°C, the vacuum degree of the polycondensation reaction is 500 Pa, and the time of the polycondensation reaction is 45 min.

[0184] The obtained recycled polycarbonate polyol has an acid value of 1.3 mgKOH / g, a hydroxyl value of 140 mgKOH / g, a number-average molecular weight of 2500 g / mol, a molecular weight distribution index of 1.7, a moisture content of 0.038 wt%, and a viscosity of 2900 mPa·s at 25℃.

[0185] (3) Preparation of polyurethane foam;

[0186] Under the action of catalyst IV, diisocyanate with a molar ratio of -NCO to -OH of 1.15:1 and recycled polycarbonate polyol are reacted at 85°C for 2.0 h to obtain polyurethane prepolymer. After adding small molecule chain extender and water for chain extension reaction for 2 min, it is poured into a mold and cured at 95°C for 20 h to obtain polyurethane foam.

[0187] The catalyst IV was added at 500 ppm of the mass of the recycled polycarbonate polyol, the small molecule chain extender was added at 25% of the total hydroxyl molar amount of the recycled polycarbonate polyol, and the water was added at 6% of the mass of the recycled polycarbonate polyol.

[0188] The final polyurethane foam had a tensile strength of 8 MPa and an elongation at break of 240%. After being placed at 70°C and 95% relative humidity for 7 days, the tensile strength retention rate was 83%.

[0189] Example 6

[0190] A method for preparing polyurethane foam, comprising the following specific steps:

[0191] (1) Preparation of materials;

[0192] Catalyst I: Potassium bicarbonate;

[0193] Dimethyl carbonate;

[0194] Waste polyethylene terephthalate: intrinsic viscosity is 0.74 dL / g;

[0195] Methanol;

[0196] Catalyst II: Sodium methoxide;

[0197] Catalyst III: Composed of tetrabutyl titanate and antimony glycol in a mass ratio of 1:1;

[0198] Diisocyanate: Composed of MDI and HMDI in a molar ratio of 1:1;

[0199] Small molecule chain extender: composed of diethylene glycol and dipropylene glycol in a molar ratio of 1:1;

[0200] Catalyst IV: Triethylenediamine;

[0201] water;

[0202] (2) Preparation of recycled polycarbonate polyols;

[0203] (a) Under nitrogen or inert atmosphere, and with the action of catalyst I, waste polyethylene terephthalate is depolymerized using dimethyl carbonate to obtain mixture A containing dimethyl terephthalate, ethylene carbonate and dimethyl carbonate, wherein the total mass percentage of dimethyl terephthalate, ethylene carbonate and dimethyl carbonate in mixture A is 96%;

[0204] (b) Add methanol and catalyst II to allow it to undergo transesterification with ethylene carbonate in mixture A, producing dimethyl carbonate and ethylene glycol. Separate the unreacted methanol until the methanol distillation amount is 90.8% of the theoretical value, to obtain mixture B containing dimethyl terephthalate, dimethyl carbonate and ethylene glycol. The total mass percentage of dimethyl terephthalate, dimethyl carbonate and ethylene glycol in mixture B is 97%.

[0205] (c) After adding catalyst III and controlling the transesterification reaction of mixture B, unreacted dimethyl carbonate is separated until the distillation amount of dimethyl carbonate is 96.9% of the theoretical value. Then, polycondensation reaction is carried out to obtain recycled polycarbonate polyol.

[0206] In step (a), the molar ratio of the structural unit of waste polyethylene terephthalate to the molar ratio of dimethyl carbonate is 1:8, the mass addition amount of catalyst I is 1000 ppm of the mass addition amount of waste polyethylene terephthalate, the depolymerization temperature is 180℃, and the depolymerization time is 80 min.

[0207] The molar ratio of the waste polyethylene terephthalate structural unit in step (a) to the molar ratio of methanol in step (b) is 1:2.06.

[0208] In step (b), the transesterification reaction is carried out at a temperature of 80°C for 120 min.

[0209] The mass ratio of catalyst II in step (b) to catalyst III in step (c) is 1:2.1;

[0210] In step (c), the mass addition amount of catalyst III is 1000 ppm of the mass addition amount of waste polyethylene terephthalate in step (a), the temperature of the transesterification reaction is 200℃, the time of the transesterification reaction is 60 min, the temperature of the polycondensation reaction is 220℃, the vacuum degree of the polycondensation reaction is 100 Pa, and the time of the polycondensation reaction is 30 min.

[0211] The obtained recycled polycarbonate polyol has an acid value of 0.5 mg KOH / g, a hydroxyl value of 30 mg KOH / g, a number-average molecular weight of 4000 g / mol, a molecular weight distribution index of 1.95, a moisture content of 0.03 wt%, and a viscosity of 5000 mPa·s at 25℃.

[0212] (3) Preparation of polyurethane foam;

[0213] Under the action of catalyst IV, diisocyanate with a molar ratio of -NCO to -OH of 1.08:1 and recycled polycarbonate polyol are reacted at 75°C for 1.5 h to obtain polyurethane prepolymer. After adding small molecule chain extender and water for chain extension reaction for 1 min, it is poured into a mold and cured at 85°C for 18 h to obtain polyurethane foam.

[0214] The catalyst IV was added at 700 ppm of the mass of the recycled polycarbonate polyol, the small molecule chain extender was added at 20% of the total hydroxyl molar amount of the recycled polycarbonate polyol, and the water was added at 7% of the mass of the recycled polycarbonate polyol.

[0215] The final polyurethane foam had a tensile strength of 5 MPa and an elongation at break of 300%. After being placed at 70°C and 95% relative humidity for 7 days, the tensile strength retention rate was 80%.

[0216] Example 7

[0217] A method for preparing a polyurethane coating, comprising the following specific steps:

[0218] (1) Preparation of materials;

[0219] Catalyst I: Lithium chloride;

[0220] Dimethyl carbonate;

[0221] Waste polyethylene terephthalate: intrinsic viscosity is 0.75 dL / g;

[0222] Methanol;

[0223] Catalyst II: Sodium methoxide;

[0224] Catalyst III: Antimony Glycol;

[0225] Diisocyanate: IPDI;

[0226] Small molecule chain extender: composed of ethylene glycol and 1,3-propanediol in a molar ratio of 1:1;

[0227] Catalyst IV: Triethanolamine;

[0228] (2) Preparation of recycled polycarbonate polyols;

[0229] (a) Under nitrogen or inert atmosphere, and with the action of catalyst I, waste polyethylene terephthalate is depolymerized using dimethyl carbonate to obtain mixture A containing dimethyl terephthalate, ethylene carbonate and dimethyl carbonate, wherein the total mass percentage of dimethyl terephthalate, ethylene carbonate and dimethyl carbonate in mixture A is 97%;

[0230] (b) Add methanol and catalyst II to allow it to undergo transesterification with ethylene carbonate in mixture A to produce dimethyl carbonate and ethylene glycol. Then, separate the unreacted methanol until the methanol distillation amount is 95.6% of the theoretical value, and obtain mixture B containing dimethyl terephthalate, dimethyl carbonate and ethylene glycol. The total mass percentage of dimethyl terephthalate, dimethyl carbonate and ethylene glycol in mixture B is 98%.

[0231] (c) After adding catalyst III and controlling the transesterification reaction of mixture B, unreacted dimethyl carbonate is separated until the distillation amount of dimethyl carbonate is 93.6% of the theoretical value. Then, polycondensation reaction is carried out to obtain recycled polycarbonate polyol.

[0232] In step (a), the molar ratio of the structural unit of waste polyethylene terephthalate to the molar ratio of dimethyl carbonate is 1:9, the mass addition amount of catalyst I is 400 ppm of the mass addition amount of waste polyethylene terephthalate, the depolymerization temperature is 200℃, and the depolymerization time is 50 min.

[0233] The molar ratio of the waste polyethylene terephthalate structural unit in step (a) to the molar ratio of methanol in step (b) is 1:2.1;

[0234] In step (b), the transesterification reaction is carried out at a temperature of 150°C for 70 min.

[0235] The mass ratio of catalyst II in step (b) to catalyst III in step (c) is 1:1.6;

[0236] In step (c), the mass addition amount of catalyst III is 400 ppm of the mass addition amount of waste polyethylene terephthalate in step (a), the temperature of the transesterification reaction is 170°C, the time of the transesterification reaction is 90 min, the temperature of the polycondensation reaction is 205°C, the vacuum degree of the polycondensation reaction is 800 Pa, and the time of the polycondensation reaction is 55 min.

[0237] The obtained recycled polycarbonate polyol has an acid value of 1.8 mgKOH / g, a hydroxyl value of 230 mgKOH / g, a number-average molecular weight of 1000 g / mol, a molecular weight distribution index of 1.55, a moisture content of 0.046 wt%, and a viscosity of 1100 mPa·s at 25℃.

[0238] (3) Preparation of polyurethane coatings;

[0239] Under the action of catalyst IV, diisocyanate with a molar ratio of -NCO to -OH of 1.12:1 and recycled polycarbonate polyol are reacted at 90°C for 1.5 h to obtain polyurethane prepolymer. After adding a small molecule chain extender and reacting for 1 h, it is coated on the substrate surface and cured at 100°C for 12 h to obtain polyurethane coating.

[0240] The catalyst IV was added at a mass of 400 ppm of the recycled polycarbonate polyol, and the small molecule chain extender was added at a molar amount of 25% of the total molar amount of hydroxyl groups in the recycled polycarbonate polyol.

[0241] The final polyurethane coating (actual sample as shown) Figure 4 The Shore hardness of the sample (as shown) is D65, and the cross-cut adhesion is grade 1.

[0242] Example 8

[0243] A method for preparing a polyurethane coating, comprising the following specific steps:

[0244] (1) Preparation of materials;

[0245] Catalyst I: Potassium chloride;

[0246] Dimethyl carbonate;

[0247] Waste polyethylene terephthalate: intrinsic viscosity is 0.76 dL / g;

[0248] Methanol;

[0249] Catalyst II: Sodium methoxide;

[0250] Catalyst III: Tetrabutyl titanate;

[0251] Diisocyanate: HDI;

[0252] Small molecule chain extender: ethylene glycol;

[0253] Catalyst IV: N,N-dimethylcyclohexylamine;

[0254] (2) Preparation of recycled polycarbonate polyols;

[0255] (a) Under nitrogen or inert atmosphere, and with the action of catalyst I, waste polyethylene terephthalate is depolymerized using dimethyl carbonate to obtain mixture A containing dimethyl terephthalate, ethylene carbonate and dimethyl carbonate, wherein the total mass percentage of dimethyl terephthalate, ethylene carbonate and dimethyl carbonate in mixture A is 96%;

[0256] (b) Add methanol and catalyst II to allow it to undergo transesterification with ethylene carbonate in mixture A to produce dimethyl carbonate and ethylene glycol. Then, separate the unreacted methanol until the methanol distillation amount is 92.4% of the theoretical value, and obtain mixture B containing dimethyl terephthalate, dimethyl carbonate and ethylene glycol. The total mass percentage of dimethyl terephthalate, dimethyl carbonate and ethylene glycol in mixture B is 99%.

[0257] (c) After adding catalyst III and controlling the transesterification reaction of mixture B, unreacted dimethyl carbonate is separated until the distillation amount of dimethyl carbonate is 98% of the theoretical value. Then, polycondensation reaction is carried out to obtain recycled polycarbonate polyol.

[0258] In step (a), the molar ratio of the structural unit of waste polyethylene terephthalate to the molar ratio of dimethyl carbonate is 1:5, the mass addition amount of catalyst I is 700 ppm of the mass addition amount of waste polyethylene terephthalate, the depolymerization temperature is 170℃, and the depolymerization time is 130 min.

[0259] The molar ratio of the waste polyethylene terephthalate structural unit in step (a) to the molar ratio of methanol in step (b) is 1:2.12.

[0260] In step (b), the temperature of the transesterification reaction is 100℃ and the time of the transesterification reaction is 100 min;

[0261] The mass ratio of catalyst II in step (b) to catalyst III in step (c) is 1:2.7;

[0262] In step (c), the mass addition amount of catalyst III is 700 ppm of the mass addition amount of waste polyethylene terephthalate in step (a), the temperature of the transesterification reaction is 180°C, the time of the transesterification reaction is 70 min, the temperature of the polycondensation reaction is 215°C, the vacuum degree of the polycondensation reaction is 300 Pa, and the time of the polycondensation reaction is 40 min.

[0263] The obtained recycled polycarbonate polyol has an acid value of 0.9 mgKOH / g, a hydroxyl value of 80 mgKOH / g, a number-average molecular weight of 3500 g / mol, a molecular weight distribution index of 1.8, a moisture content of 0.034 wt%, and a viscosity of 4200 mPa·s at 25℃.

[0264] (3) Preparation of polyurethane coatings;

[0265] Under the action of catalyst IV, diisocyanate and recycled polycarbonate polyol with a molar ratio of -NCO to -OH of 1.06:1 were reacted at 80°C for 2.5 h to obtain polyurethane prepolymer. After adding a small molecule chain extender and reacting for 1.5 h, it was coated on the substrate surface and cured at 90°C for 20 h to obtain polyurethane coating.

[0266] The catalyst IV is added at a mass of 500 ppm of the recycled polycarbonate polyol, and the small molecule chain extender is added at a molar amount of 20% of the total molar amount of hydroxyl groups in the recycled polycarbonate polyol.

[0267] The final polyurethane coating has a Shore hardness of D77 and a cross-cut adhesion rating of 0.

[0268] Example 9

[0269] A method for preparing a polyurethane coating, comprising the following specific steps:

[0270] (1) Preparation of materials;

[0271] Catalyst I: Composed of zinc acetate and sodium acetate in a mass ratio of 1:1;

[0272] Dimethyl carbonate;

[0273] Waste polyethylene terephthalate: intrinsic viscosity is 0.77 dL / g;

[0274] Methanol;

[0275] Catalyst II: Sodium methoxide;

[0276] Catalyst III: Tetrabutyl titanate;

[0277] Diisocyanate: IPDI;

[0278] Small molecule chain extender: 1,6-hexanediol;

[0279] Catalyst IV: Triethylamine;

[0280] (2) Preparation of recycled polycarbonate polyols;

[0281] (a) Under nitrogen or inert atmosphere, and with the action of catalyst I, waste polyethylene terephthalate is depolymerized using dimethyl carbonate to obtain mixture A containing dimethyl terephthalate, ethylene carbonate and dimethyl carbonate, wherein the total mass percentage of dimethyl terephthalate, ethylene carbonate and dimethyl carbonate in mixture A is 99%;

[0282] (b) Add methanol and catalyst II to allow it to undergo transesterification with ethylene carbonate in mixture A to produce dimethyl carbonate and ethylene glycol. Then, separate the unreacted methanol until the methanol distillation amount is 98% of the theoretical value, to obtain mixture B containing dimethyl terephthalate, dimethyl carbonate and ethylene glycol. The total mass percentage of dimethyl terephthalate, dimethyl carbonate and ethylene glycol in mixture B is 97%.

[0283] (c) After adding catalyst III and controlling the transesterification reaction of mixture B, unreacted dimethyl carbonate is separated until the distillation amount of dimethyl carbonate is 94.7% of the theoretical value. Then, polycondensation reaction is carried out to obtain recycled polycarbonate polyol.

[0284] In step (a), the molar ratio of the structural unit of waste polyethylene terephthalate to the molar ratio of dimethyl carbonate is 1:10, the mass addition amount of catalyst I is 800 ppm of the mass addition amount of waste polyethylene terephthalate, the depolymerization temperature is 190℃, and the depolymerization time is 90 min.

[0285] The molar ratio of the waste polyethylene terephthalate structural unit in step (a) to the molar ratio of methanol in step (b) is 1:2.08.

[0286] In step (b), the transesterification reaction is carried out at a temperature of 120°C for 80 minutes.

[0287] The mass ratio of catalyst II in step (b) to catalyst III in step (c) is 1:1;

[0288] In step (c), the mass addition amount of catalyst III is 800 ppm of the mass addition amount of waste polyethylene terephthalate in step (a), the temperature of the transesterification reaction is 160°C, the time of the transesterification reaction is 110 min, the temperature of the polycondensation reaction is 200°C, the vacuum degree of the polycondensation reaction is 1000 Pa, and the time of the polycondensation reaction is 60 min.

[0289] The obtained recycled polycarbonate polyol has an acid value of 2 mgKOH / g, a hydroxyl value of 300 mgKOH / g, a number-average molecular weight of 500 g / mol, a molecular weight distribution index of 1.5, a moisture content of 0.05 wt%, and a viscosity of 500 mPa·s at 25℃.

[0290] (3) Preparation of polyurethane coatings;

[0291] Under the action of catalyst IV, diisocyanate with a molar ratio of -NCO to -OH of 1.2:1 and recycled polycarbonate polyol are reacted at 70°C for 3 hours to obtain polyurethane prepolymer. After adding a small molecule chain extender and reacting for 2 hours, it is coated on the substrate surface and cured at 80°C for 24 hours to obtain polyurethane coating.

[0292] The mass addition amount of catalyst IV is 900 ppm of the mass addition amount of recycled polycarbonate polyol, and the molar amount of small molecule chain extender is 30% of the total molar amount of hydroxyl groups in recycled polycarbonate polyol.

[0293] The final polyurethane coating has a Shore hardness of D85 and a cross-cut adhesion rating of 0.

[0294] Example 10

[0295] A method for preparing a polyurethane adhesive, comprising the following specific steps:

[0296] (1) Preparation of materials;

[0297] Catalyst I: Zinc acetate;

[0298] Dimethyl carbonate;

[0299] Waste polyethylene terephthalate: intrinsic viscosity is 0.78 dL / g;

[0300] Methanol;

[0301] Catalyst II: Sodium methoxide;

[0302] Catalyst III: Antimony Glycol;

[0303] Diisocyanate: IPDI;

[0304] Small molecule chain extender: ethylene glycol;

[0305] Catalyst IV: Stannous octoate;

[0306] (2) Preparation of recycled polycarbonate polyols;

[0307] (a) Under nitrogen or inert atmosphere, and with the action of catalyst I, waste polyethylene terephthalate is depolymerized using dimethyl carbonate to obtain mixture A containing dimethyl terephthalate, ethylene carbonate and dimethyl carbonate, wherein the total mass percentage of dimethyl terephthalate, ethylene carbonate and dimethyl carbonate in mixture A is 95%;

[0308] (b) Add methanol and catalyst II to allow it to undergo transesterification with ethylene carbonate in mixture A to produce dimethyl carbonate and ethylene glycol. Then, separate the unreacted methanol until the methanol distillation amount is 90.2% of the theoretical value, and obtain mixture B containing dimethyl terephthalate, dimethyl carbonate and ethylene glycol. The total mass percentage of dimethyl terephthalate, dimethyl carbonate and ethylene glycol in mixture B is 95%.

[0309] (c) After adding catalyst III and controlling the transesterification reaction of mixture B, unreacted dimethyl carbonate is separated until the distillation amount of dimethyl carbonate is 90.9% of the theoretical value. Then, polycondensation reaction is carried out to obtain recycled polycarbonate polyol.

[0310] In step (a), the molar ratio of the structural unit of waste polyethylene terephthalate to the molar ratio of dimethyl carbonate is 1:7, the mass addition amount of catalyst I is 500 ppm of the mass addition amount of waste polyethylene terephthalate, the depolymerization temperature is 160℃, and the depolymerization time is 200 min.

[0311] The molar ratio of the waste polyethylene terephthalate structural unit in step (a) to the molar ratio of methanol in step (b) is 1:2.15.

[0312] In step (b), the transesterification reaction is carried out at a temperature of 140°C for 70 minutes.

[0313] The mass ratio of catalyst II in step (b) to catalyst III in step (c) is 1:3;

[0314] In step (c), the mass addition amount of catalyst III is 500 ppm of the mass addition amount of waste polyethylene terephthalate in step (a), the temperature of the transesterification reaction is 190°C, the time of the transesterification reaction is 70 min, the temperature of the polycondensation reaction is 210°C, the vacuum degree of the polycondensation reaction is 600 Pa, and the time of the polycondensation reaction is 45 min.

[0315] The obtained recycled polycarbonate polyol has an acid value of 1.5 mgKOH / g, a hydroxyl value of 170 mgKOH / g, a number-average molecular weight of 2000 g / mol, a molecular weight distribution index of 1.65, a moisture content of 0.042 wt%, and a viscosity of 2300 mPa·s at 25℃.

[0316] (3) Preparation of polyurethane adhesive;

[0317] Under the action of catalyst IV, diisocyanate with a molar ratio of -NCO to -OH of 1:1 and recycled polycarbonate polyol are reacted at 85°C for 1 hour to obtain polyurethane prepolymer. After adding a small molecule chain extender and reacting for 1 hour, it is coated on the substrate surface and cured at 95°C for 15 hours to obtain polyurethane adhesive.

[0318] The mass addition amount of catalyst IV is 300 ppm of the mass addition amount of recycled polycarbonate polyol, and the molar amount of small molecule chain extender is 10% of the total molar amount of hydroxyl groups in recycled polycarbonate polyol.

[0319] The final polyurethane adhesive has a single lap tensile shear strength of 10 MPa (test procedure is shown in [link]). Figure 5 The 180° peel strength is 20 kN / m.

[0320] Example 11

[0321] A method for preparing a polyurethane adhesive, comprising the following specific steps:

[0322] (1) Preparation of materials;

[0323] Catalyst I: Zinc acetate;

[0324] Dimethyl carbonate;

[0325] Waste polyethylene terephthalate: intrinsic viscosity is 0.73 dL / g;

[0326] Methanol;

[0327] Catalyst II: Sodium methoxide;

[0328] Catalyst III: Antimony Glycol;

[0329] Diisocyanate: TDI;

[0330] Small molecule chain extender: 1,3-propanediol;

[0331] Catalyst IV: Dibutyltin dilaurate;

[0332] (2) Preparation of recycled polycarbonate polyols;

[0333] (a) Under nitrogen or inert atmosphere, and with the action of catalyst I, waste polyethylene terephthalate is depolymerized using dimethyl carbonate to obtain mixture A containing dimethyl terephthalate, ethylene carbonate and dimethyl carbonate, wherein the total mass percentage of dimethyl terephthalate, ethylene carbonate and dimethyl carbonate in mixture A is 96%;

[0334] (b) Add methanol and catalyst II to allow it to undergo transesterification with ethylene carbonate in mixture A, producing dimethyl carbonate and ethylene glycol. Then, separate the unreacted methanol until the methanol distillation amount is 94.9% of the theoretical value, to obtain mixture B containing dimethyl terephthalate, dimethyl carbonate and ethylene glycol. The total mass percentage of dimethyl terephthalate, dimethyl carbonate and ethylene glycol in mixture B is 97%.

[0335] (c) After adding catalyst III and controlling the transesterification reaction of mixture B, unreacted dimethyl carbonate is separated until the distillation amount of dimethyl carbonate is 95.8% of the theoretical value. Then, polycondensation reaction is carried out to obtain recycled polycarbonate polyol.

[0336] In step (a), the molar ratio of the structural unit of waste polyethylene terephthalate to the molar ratio of dimethyl carbonate is 1:8, the mass addition amount of catalyst I is 900 ppm of the mass addition amount of waste polyethylene terephthalate, the depolymerization temperature is 180℃, and the depolymerization time is 150 min.

[0337] The molar ratio of the waste polyethylene terephthalate structural unit in step (a) to the molar ratio of methanol in step (b) is 1:2.05.

[0338] In step (b), the transesterification reaction is carried out at a temperature of 90°C for 110 min.

[0339] The mass ratio of catalyst II in step (b) to catalyst III in step (c) is 1:1.9;

[0340] In step (c), the mass addition amount of catalyst III is 600 ppm of the mass addition amount of waste polyethylene terephthalate in step (a), the temperature of the transesterification reaction is 200°C, the time of the transesterification reaction is 60 min, the temperature of the polycondensation reaction is 220°C, the vacuum degree of the polycondensation reaction is 200 Pa, and the time of the polycondensation reaction is 30 min.

[0341] The obtained recycled polycarbonate polyol has an acid value of 0.7 mgKOH / g, a hydroxyl value of 50 mgKOH / g, a number-average molecular weight of 3800 g / mol, a molecular weight distribution index of 1.85, a moisture content of 0.032 wt%, and a viscosity of 4600 mPa·s at 25℃.

[0342] (3) Preparation of polyurethane adhesive;

[0343] Under the action of catalyst IV, diisocyanate and recycled polycarbonate polyol with a molar ratio of -NCO to -OH of 1.14:1 were reacted at 75°C for 2.5 h to obtain polyurethane prepolymer. After adding a small molecule chain extender and reacting for 1.5 h, it was coated on the substrate surface and cured at 85°C for 18 h to obtain polyurethane adhesive.

[0344] The catalyst IV was added at a mass of 700 ppm of the recycled polycarbonate polyol, and the small molecule chain extender was added at a molar amount of 25% of the total molar amount of hydroxyl groups in the recycled polycarbonate polyol.

[0345] The final polyurethane adhesive has a single lap tensile shear strength of 15 MPa and a 180° peel strength of 30 kN / m.

[0346] Example 12

[0347] A method for preparing a polyurethane adhesive, comprising the following specific steps:

[0348] (1) Preparation of materials;

[0349] Catalyst I: Zinc acetate;

[0350] Dimethyl carbonate;

[0351] Waste polyethylene terephthalate: intrinsic viscosity is 0.72 dL / g;

[0352] Methanol;

[0353] Catalyst II: Sodium methoxide;

[0354] Catalyst III: Tetrabutyl titanate;

[0355] Diisocyanate: MDI;

[0356] Small molecule chain extender: diethylene glycol;

[0357] Catalyst IV: Composed of dibutyltin dilaurate and triethylenediamine in a mass ratio of 1:1;

[0358] (2) Preparation of recycled polycarbonate polyols;

[0359] (a) Under nitrogen or inert atmosphere, and with the action of catalyst I, waste polyethylene terephthalate is depolymerized using dimethyl carbonate to obtain mixture A containing dimethyl terephthalate, ethylene carbonate and dimethyl carbonate, wherein the total mass percentage of dimethyl terephthalate, ethylene carbonate and dimethyl carbonate in mixture A is 98%;

[0360] (b) Add methanol and catalyst II to allow it to undergo transesterification with ethylene carbonate in mixture A to produce dimethyl carbonate and ethylene glycol. Then, separate the unreacted methanol until the methanol distillation amount is 96.8% of the theoretical value, and obtain mixture B containing dimethyl terephthalate, dimethyl carbonate and ethylene glycol. The total mass percentage of dimethyl terephthalate, dimethyl carbonate and ethylene glycol in mixture B is 96%.

[0361] (c) After adding catalyst III and controlling the transesterification reaction of mixture B, unreacted dimethyl carbonate is separated until the distillation amount of dimethyl carbonate is 92.1% of the theoretical value. Then, polycondensation reaction is carried out to obtain recycled polycarbonate polyol.

[0362] In step (a), the molar ratio of the structural unit of waste polyethylene terephthalate to the molar ratio of dimethyl carbonate is 1:6, the mass addition amount of catalyst I is 600 ppm of the mass addition amount of waste polyethylene terephthalate, the depolymerization temperature is 190℃, and the depolymerization time is 90 min.

[0363] The molar ratio of the waste polyethylene terephthalate structural unit in step (a) to the molar ratio of methanol in step (b) is 1:2.09.

[0364] In step (b), the transesterification reaction is carried out at a temperature of 160°C for 60 min.

[0365] The mass ratio of catalyst II in step (b) to catalyst III in step (c) is 1:2.4;

[0366] In step (c), the mass addition amount of catalyst III is 900 ppm of the mass addition amount of waste polyethylene terephthalate in step (a), the temperature of the transesterification reaction is 170°C, the time of the transesterification reaction is 100 min, the temperature of the polycondensation reaction is 205°C, the vacuum degree of the polycondensation reaction is 700 Pa, and the time of the polycondensation reaction is 55 min.

[0367] The obtained recycled polycarbonate polyol has an acid value of 1.6 mgKOH / g, a hydroxyl value of 200 mgKOH / g, a number-average molecular weight of 1500 g / mol, a molecular weight distribution index of 1.6, a moisture content of 0.044 wt%, and a viscosity of 1700 mPa·s at 25℃.

[0368] (3) Preparation of polyurethane adhesive;

[0369] Under the action of catalyst IV, diisocyanate with a molar ratio of -NCO to -OH of 1.09:1 and recycled polycarbonate polyol are reacted at 90°C for 1.5 h to obtain polyurethane prepolymer. After adding a small molecule chain extender and reacting for 1 h, it is coated on the substrate surface and cured at 100°C for 12 h to obtain polyurethane adhesive.

[0370] The mass addition amount of catalyst IV is 400 ppm of the mass addition amount of recycled polycarbonate polyol, and the molar amount of small molecule chain extender is 20% of the total molar amount of hydroxyl groups in recycled polycarbonate polyol.

[0371] The final polyurethane adhesive has a single-lap tensile shear strength of 13 MPa and a 180° peel strength of 25 kN / m.

Claims

1. A method for preparing recycled polycarbonate polyols, characterized in that, Includes the following steps: (a) Waste polyethylene terephthalate was depolymerized using dimethyl carbonate to obtain a mixture A containing dimethyl terephthalate, ethylene carbonate and dimethyl carbonate; (b) Add methanol to allow it to undergo transesterification with ethylene carbonate in mixture A to produce dimethyl carbonate and ethylene glycol. Then, separate the unreacted methanol until the methanol distillation amount is more than 90.2% of the theoretical value, to obtain mixture B containing dimethyl terephthalate, dimethyl carbonate and ethylene glycol. (c) After the transesterification reaction of mixture B is controlled, the unreacted dimethyl carbonate is separated until the distillation amount of dimethyl carbonate is more than 90.5% of the theoretical value, and then a polycondensation reaction is carried out to obtain the recycled polycarbonate polyol.

2. The method for preparing a recycled polycarbonate polyol according to claim 1, characterized in that, In step (a), the intrinsic viscosity of the waste polyethylene terephthalate is 0.70~0.78 dL / g; the molar ratio of the structural units of the waste polyethylene terephthalate to the molar ratio of dimethyl carbonate is 1:5~10; the depolymerization is carried out under nitrogen or an inert atmosphere, the depolymerization temperature is 160~200℃, and the time is 30~200min.

3. The method for preparing a recycled polycarbonate polyol according to claim 1, characterized in that, The molar ratio of the waste polyethylene terephthalate structural unit in step (a) to the molar ratio of methanol in step (b) is 1:2.05~2.

15.

4. The method for preparing a recycled polycarbonate polyol according to claim 1, characterized in that, In step (b), the temperature of the transesterification reaction is 80~160℃ and the time is 60~120min.

5. The method for preparing a recycled polycarbonate polyol according to claim 1, characterized in that, In step (c), the temperature of the transesterification reaction is 160~200℃ and the time is 60~120min; the temperature of the polycondensation reaction is 200~220℃, the vacuum degree is 100~1000Pa, and the time is 30~60min.

6. The method for preparing a recycled polycarbonate polyol according to claim 1, characterized in that, In step (a), catalyst I is added during depolymerization; in step (b), catalyst II is added during transesterification; and in step (c), catalyst III is added during transesterification.

7. The method for preparing a recycled polycarbonate polyol according to claim 6, characterized in that, Catalyst I is one of zinc acetate, zinc oxide, sodium acetate, sodium carbonate, potassium carbonate, potassium bicarbonate, potassium chloride, and lithium chloride; Catalyst II is sodium methoxide; Catalyst III is one of tetrabutyl titanate, antimony trioxide, antimony acetate, dibutyltin dilaurate, and antimony glycolate.

8. The method for preparing a recycled polycarbonate polyol according to claim 6, characterized in that, In step (a), the mass addition amount of catalyst I is 300~1000 ppm of the mass addition amount of waste polyethylene terephthalate; the mass ratio of catalyst II in step (b) to catalyst III in step (c) is 1:1~3; in step (c), the mass addition amount of catalyst III is 300~1000 ppm of the mass addition amount of waste polyethylene terephthalate in step (a).

9. A recycled polycarbonate polyol, characterized in that, The recycled polycarbonate polyol is prepared by any one of the preparation methods described in claims 1 to 8; the recycled polycarbonate polyol has an acid value of 0.5 to 2.0 mg KOH / g, a hydroxyl value of 30 to 300 mg KOH / g, a number-average molecular weight of 500 to 4000 g / mol, a molecular weight distribution index of 1.5 to 1.95, a moisture content of 0.03 to 0.05 wt%, and a viscosity of 500 to 5000 mPa·s at 25°C.

10. A recycled polyurethane material, characterized in that, It is prepared by reacting a recycled polycarbonate polyol as described in claim 9, diisocyanate, substance X and catalyst IV, wherein substance X is a small molecule chain extender; or, substance X is a mixture of a small molecule chain extender and water.

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