A method for recycling polyurethane foam multiple times using a bio-based alcoholysis agent

Abstract

The present application belongs to the technical field of polyurethane foam recycling, and particularly relates to a method for recycling polyurethane foam multiple times by using bio-based alcoholysis agent, which adopts one-pot method to alcoholize waste polyurethane foam, and constructs a cyclic alcoholysis path of bio-based foam-regenerated polyol-polyurethane foam. The method for preparing polyurethane rigid foam by compounding regenerated polyol with bio-based polyol is also disclosed. The prepared polyurethane foam is subjected to three cyclic alcoholization foaming, and the regenerated foams all have good compression performance. The present application first proposes a cyclic bio-based alcoholysis system of polyurethane foam, solves the problem of waste polyurethane foam material generated in the process of production and use, provides a new idea for recycling and reusing bio-based materials, has significant technical advantages and practical application value, and can be widely applied in the fields of building and packaging.

Description

Technical Field

[0001] This invention belongs to the field of polyurethane foam recycling technology, and particularly relates to a method for recycling polyurethane foam multiple times using a bio-based alcoholysis agent. Background Technology

[0002] With increasing global emphasis on environmental protection and sustainable development, resource recycling and reuse have become crucial issues. Polyurethane foam, a material widely used in various fields, is experiencing continuous growth in both production and usage. However, the processing of polyurethane foam inevitably generates scraps, accounting for approximately 10% of the total foam production. This scrap is often discarded, not only wasting resources but also placing significant pressure on the environment. Currently, the main methods for recycling polyurethane foam include mechanical recycling and chemical recycling. While mechanical recycling is relatively simple to operate, the recovered materials often have poor properties and limited applicability. Among chemical recycling methods, alcoholysis has unique advantages. Using alcoholysis agents, polyurethane foam can be decomposed into reusable polyols and other substances, providing a raw material source for the production of new polyurethane foam. However, most existing technologies only involve a single process of recycling polyurethane foam through alcoholysis and foaming. This process cannot recycle waste polyurethane multiple times while ensuring that the performance of the recycled foam is not reduced. If polyurethane foam can be recycled multiple times through alcoholysis, it will not only reduce the dependence on non-renewable resources, but also build a polyurethane recycling system. Compared with the production of new polyurethane foam, the recycling process has lower energy consumption, which helps to reduce energy consumption and carbon emissions, and contributes to addressing climate change. As the number of recycling cycles increases, the cost savings will be more significant, driving the development of related recycling industries. Summary of the Invention

[0003] The purpose of this invention is to provide a method for the multiple recycling of polyurethane foam using a bio-based alcoholysis agent. This method employs a one-pot alcoholysis process to recover waste bio-based polyurethane foam, constructing a cyclic alcoholysis pathway of bio-based foam – recycled polyol – polyurethane foam. It also discloses a method for preparing bio-based rigid polyurethane foam using recycled polyol. Its technical advantages include reduced resource consumption, significant environmental benefits, good performance, an innovative recycling system, high economic value, and simple and flexible operation. Specifically, it reduces dependence on non-renewable resources, reduces landfill and carbon emissions, provides thermal insulation to the synthesized foam, and ensures stable compression performance of the recycled rigid foam. It proposes a new recycling system to lead industry development, reduces costs, and creates industrial opportunities. Furthermore, the one-pot method is simple to operate, has a wide range of raw material selection, and strong applicability, demonstrating significant technical advantages and practical application value.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A method for recycling polyurethane foam using a bio-based alcoholysis agent, wherein the same polyurethane foam can be recycled at least three times by repeating the method, includes the following steps:

[0006] S1. Preparation of Regenerated Polyol R-POL by Alcohololysis of Polyurethane Foam: Alcohololysis agent, polyurethane foam, and catalyst are added to a reaction vessel in a mass ratio of 1:0.5~3:0.02~0.1, and heated and stirred at 160~220 ℃ for 15~240 min. After the reaction is completed, regenerated polyol R-POL is obtained. The polyurethane foam particle size is 2~5 cm. The alcohololysis agent is a compound of crude glycerol and one of xylitol, diglycerol, pentaerythritol, and ethylene glycol.

[0007] S2. Preparation of recycled polyurethane foam (RPU): The composite polyol, catalyst, silicone oil AK8805, foaming agent, and isocyanate PMDI are mixed evenly in a mass ratio of 100:1~5:2~3:2~10:90~150 and then foamed to obtain recycled polyurethane foam (RPU). The composite polyol is a compound of the recycled polyol prepared in the previous step and one of castor oil polyol, soybean oil polyol, xylitol polyol, and crude glycerol-based polyol.

[0008] Further, recycled polyurethane foam (RPUX) is prepared by cyclic alcoholysis foaming: Using the recycled polyurethane foam obtained in the previous step as raw material, steps S1-S2 are repeated for cyclic alcoholysis foaming to prepare recycled polyurethane foam (RPUX), where X represents the number of cyclic alcoholysis foaming cycles, ranging from 1 to 3 times. This method first alcoholyzes the waste polyurethane foam, then regenerates the alcoholysis product into rigid polyurethane foam. The regenerated rigid foam is then repeatedly recycled using a single alcoholysis process, without reducing the compressive strength and thermal insulation properties of the recycled foam during the recycling process. This achieves multiple recycling cycles of polyurethane foam-polyol-polyurethane foam, solving the problem of scrap materials generated during processing. This alcoholysis method can achieve 1-3 cycles, mainly considering two aspects: First, as the number of cycles increases, the material's performance gradually declines. After multiple alcoholysis and foaming cycles, the structure of the recycled polyol may change, leading to a decrease in its reactivity, thus affecting the performance of the recycled polyurethane foam. Experimental tests showed that the performance of the recycled polyurethane foam can still meet certain usage requirements when 1-3 cycles are performed, but after more than 3 cycles, the performance declines significantly and fails to meet the standards for practical applications. Second, a cost-benefit analysis is necessary when considering the number of recycling cycles. Although recycling can reduce the demand for raw materials and lower costs, the energy consumption, catalyst usage, and equipment maintenance costs in the production process may increase with the number of cycles.

[0009] Furthermore, the polyurethane foam is waste rigid polyurethane foam.

[0010] Furthermore, the catalyst in step S1 is a mixture of sodium hydroxide and ethanolamine, sodium hydroxide and diethylamine, potassium hydroxide and ethanolamine, or potassium hydroxide and diethylamine.

[0011] Furthermore, the foaming agent is one or two of n-pentane, isopentane, cyclopentane, and water.

[0012] Furthermore, in step S2, the catalyst is triethylenediamine A33 and stannous octoate T9, with a mass ratio of 1:1 to 3.

[0013] The advantages of this invention are:

[0014] 1. This invention utilizes multiple recycling processes to convert foam scraps and waste foam generated during processing into recycled polyols, which are then used to prepare bio-based rigid polyurethane foam. This reduces the generation of industrial waste, improves resource utilization, and the lifespan of the same polyurethane foam is already long enough for a single use. After three recycling cycles, its lifespan can achieve a qualitative leap.

[0015] 2. The hydroxyl groups contained in the alcoholysis agent of this invention can react with the chemical bonds in polyurethane molecules, causing the urethane groups in the polyurethane to break. At the same time, the compounded alcoholysis agent can achieve thermal conversion and graft onto the recycled polyol during the alcoholysis process, thereby transforming into a bio-based polyol containing active hydroxyl groups, and further transforming into renewable bio-based polyurethane foam. With the help of the dual role of the alcoholysis agent in the use process, the recycling of waste polyurethane foam is successfully achieved.

[0016] 3. The hydroxyl value of the alcoholysis-regenerated polyol obtained by this invention is flexibly adjustable and can be adjusted by changing the ratio of polyurethane foam and alcoholysis agent;

[0017] 4. The alcoholysis process of this invention is simple, the reaction conditions are mild, and it can be carried out under normal pressure. The regenerated polyol can be used to prepare regenerated polyurethane foam without purification and separation.

[0018] 5. The method of the present invention does not reduce the compressive strength and thermal insulation performance of foam after multiple cycles of regeneration, ensuring product quality, reducing environmental pollution caused by waste foam, and reducing the product cost of foam production. Attached Figure Description

[0019] Figure 1 This is the infrared spectrum of the regenerated polyol prepared in Example 1 of this invention.

[0020] Figure 2 This is a thermogravimetric analysis diagram of the bio-based polyurethane foam prepared in Example 1 of the present invention.

[0021] Figure 3These are the physical specimen and electron microscope image of the bio-based polyurethane foam prepared in Example 1 of this invention. Detailed Implementation

[0022] Example 1

[0023] like Figure 1-3 As shown, a method for recycling polyurethane foam using a bio-based alcoholysis agent involves pulverizing waste rigid polyurethane foam to 4-5 cm, and then heating and stirring the alcoholysis agent (crude glycerol and xylitol in a 3:1 mass ratio), polyurethane foam, and a co-catalyst (sodium hydroxide and ethanolamine in a 4:1 mass ratio) at 220 °C for 240 min to obtain recycled polyol R-POL. The foaming formulation is then mixed with polyol (recycled polyol R-POL and castor oil polyol in a 1:1 mass ratio), catalyst (triethylenediamine A33 and stannous octoate T9 in a 1:3 mass ratio), silicone oil AK8805, foaming agent (water), and isocyanate PMDI in a mass ratio of 100:5:3:3:130, followed by foaming to obtain recycled polyurethane foam (RPU). The method was repeated to perform three alcoholysis and foaming processes on recycled polyurethane foam (RPU) to obtain recycled polyols R-POL1, R-POL2, and R-POL3, and recycled polyurethane foams RPU1, RPU2, and RPU3. After 24 hours of storage, the compressive strength of the recycled polyurethane foam RPU was measured to be 290 kPa, and the density was 48 kg / m³. 3 The thermal insulation performance is 36.8 mW / (m·K). The compressive strength of recycled polyurethane foam RPU1 is 285 kPa, and the density is 47 kg / m³. 3 The thermal insulation performance is 36.5 mW / (m·K). The compressive strength of recycled polyurethane foam RPU2 is 295 kPa, and the density is 49 kg / m³. 3 The thermal insulation performance is 37.0 mW / (m·K). The compressive strength of recycled polyurethane foam RPU3 is 288 kPa, and the density is 47.5 kg / m³. 3 Its thermal insulation performance is 36.6 mW / (m·K).

[0024] Example 2

[0025] Waste rigid polyurethane foam was pulverized to 3-4 cm. An alcoholysis agent (crude glycerol and diglycerol in a 2:1 mass ratio), polyurethane foam, and a co-catalyst (potassium hydroxide and ethanolamine in a 3:2 mass ratio) were selected at a mass ratio of 1:1.5:0.05. The mixture was heated and stirred at 180°C for 60 min to obtain recycled polyol R-POL. A foaming formulation of polyol (recycled polyol R-POL and soybean oil polyol in an 8:2 mass ratio), catalyst (triethylenediamine A33 and stannous octoate T9 in a 1:2 mass ratio), silicone oil AK8805, foaming agent (cyclopentane and water in an 8:2 mass ratio), and isocyanate PMDI were mixed and foamed to obtain recycled polyurethane foam RPU. This method was repeated three times for alcoholysis and foaming of the recycled polyurethane foam RPU to obtain recycled polyols R-POL1, R-POL2, R-POL3 and recycled polyurethane foams RPU1, RPU2, and RPU3. After 24 hours of storage, the compressive strength of the recycled polyurethane foam (RPU) was measured to be 220 kPa, and the density was 24 kg / m³. 3 The thermal insulation performance is 26.8 mW / (m·K); the compressive strength of recycled polyurethane foam RPU1 is 215 kPa, and the density is 23.5 kg / m³. 3 The thermal insulation performance is 26.6 mW / (m·K); the compressive strength of recycled polyurethane foam RPU2 is 225 kPa, and the density is 24.5 kg / m³. 3 The thermal insulation performance is 27.0 mW / (m·K); the compressive strength of recycled polyurethane foam RPU3 is 218 kPa, and the density is 23.8 kg / m³. 3 Its thermal insulation performance is 26.7 mW / (m·K).

[0026] Example 3

[0027] Waste rigid polyurethane foam was crushed to 2-3 cm. An alcoholysis agent (crude glycerol and xylitol in a 5:1 mass ratio), polyurethane foam, and a co-catalyst (sodium hydroxide and diethylamine in a 1:1 mass ratio) were selected at a mass ratio of 1:0.5:0.02. The mixture was placed in a reactor and heated and stirred at 160 °C for 15 min. After the reaction, recycled polyol R-POL was obtained. A foaming formulation was then prepared by mixing polyol (recycled polyol R-POL and crude glycerol-based polyol in an 8:2 mass ratio), catalyst (triethylenediamine A33 and stannous octoate T9 in a 1:1 mass ratio), silicone oil AK8805, foaming agent (n-pentane and water in an 8:2 mass ratio), and isocyanate PMDI in a mass ratio of 100:1:2:8:90, followed by foaming to obtain recycled polyurethane foam (RPU). The method was repeated to perform three alcoholysis and foaming processes on recycled polyurethane foam (RPU) to obtain recycled polyols R-POL1, R-POL2, and R-POL3, and recycled polyurethane foams RPU1, RPU2, and RPU3. After 24 hours of storage, the compressive strength of the recycled polyurethane foam RPU was measured to be 322 kPa, and the density was 47 kg / m³. 3 The thermal insulation performance is 38.8 mW / (m·K); the compressive strength of recycled polyurethane foam RPU1 is 318 kPa, and the density is 46.5 kg / m³. 3 The thermal insulation performance is 38.5 mW / (m·K); the compressive strength of recycled polyurethane foam RPU2 is 325 kPa, and the density is 47.5 kg / m³. 3 The thermal insulation performance is 39.0 mW / (m·K); the compressive strength of recycled polyurethane foam RPU3 is 320 kPa, and the density is 47.0 kg / m³. 3 Its thermal insulation performance is 38.6 mW / (m·K).

[0028] Example 4

[0029] Waste rigid polyurethane foam was crushed to 3-4 cm. An alcoholysis agent (crude glycerol and pentaerythritol in a 2:1 mass ratio), polyurethane foam, and a co-catalyst (potassium hydroxide and ethanolamine in a 1:1 mass ratio) were selected in a mass ratio of 1:2:0.08. The mixture was heated and stirred at 190℃ for 120 min to obtain recycled polyol R-POL. The foaming formulation consisted of a polyol (recycled polyol R-POL and xylitol in a 9:1 mass ratio), a catalyst (triethylenediamine A33 and stannous octoate T9 in a 1:2.5 mass ratio), silicone oil AK8805, a foaming agent (isopentane and water in a 7:3 mass ratio), and isocyanate PMDI, all mixed evenly before foaming to obtain recycled polyurethane foam (RPU). The method was repeated to perform three alcoholysis and foaming processes on recycled polyurethane foam (RPU) to obtain recycled polyols R-POL1, R-POL2, and R-POL3, and recycled polyurethane foams RPU1, RPU2, and RPU3. After 24 hours of storage, the compressive strength of the recycled polyurethane foam RPU was measured to be 250 kPa, and the density was 35 kg / m³. 3 The thermal insulation performance is 32.8 mW / (m·K). The compressive strength of recycled polyurethane foam RPU1 is 245 kPa, and the density is 34.5 kg / m³. 3 The thermal insulation performance is 32.5 mW / (m·K). The compressive strength of recycled polyurethane foam RPU2 is 255 kPa, and the density is 36 kg / m³. 3 The thermal insulation performance is 33.0 mW / (m·K). The compressive strength of recycled polyurethane foam RPU3 is 248 kPa, and the density is 35.2 kg / m³. 3 Its thermal insulation performance is 32.6 mW / (m·K).

[0030] Example 5

[0031] Waste rigid polyurethane foam was pulverized to 2-3 cm. An alcoholysis agent (crude glycerol and diglycerol in a 3:1 mass ratio), polyurethane foam, and a co-catalyst (sodium hydroxide and ethanolamine in a 5:1 mass ratio) were selected at a mass ratio of 1:1:0.06. The mixture was heated and stirred at 170 °C for 45 min to obtain recycled polyol R-POL. The foaming formulation consisted of a polyol (recycled polyol R-POL and castor oil polyol in a 9:1 mass ratio), a catalyst (triethylenediamine A33 and stannous octoate T9 in a 1:1.5 mass ratio), silicone oil AK8805, a foaming agent (cyclopentane and water in a 6:4 mass ratio), and isocyanate PMDI, mixed and foamed to obtain recycled polyurethane foam RPU. This method was repeated three times to perform alcoholysis and foaming on the recycled polyurethane foam RPU to obtain recycled polyols R-POL1, R-POL2, R-POL3 and recycled polyurethane foams RPU1, RPU2, and RPU3. After 24 hours of storage, the compressive strength of the recycled polyurethane foam (RPU) was measured to be 280 kPa, and the density was 40 kg / m³. 3 The thermal insulation performance is 35.8 mW / (m·K); the compressive strength of recycled polyurethane foam RPU1 is 275 kPa, and the density is 39.5 kg / m³. 3 The thermal insulation performance is 35.5 mW / (m·K); the compressive strength of recycled polyurethane foam RPU2 is 285 kPa, and the density is 41 kg / m³. 3 The thermal insulation performance is 36.0 mW / (m·K); the compressive strength of recycled polyurethane foam RPU3 is 278 kPa, and the density is 40.2 kg / m³. 3 Its thermal insulation performance is 35.6 mW / (m·K).

[0032] Example 6

[0033] Waste rigid polyurethane foam was crushed to 3-4 cm. An alcoholysis agent (crude glycerol and ethylene glycol in a 2:1 mass ratio), polyurethane foam, and a co-catalyst (potassium hydroxide and diethylamine in a 2:1 mass ratio) were selected at a mass ratio of 1:2.5:0.09. The mixture was placed in a reactor and heated and stirred at 200 °C for 180 min. After the reaction, recycled polyol R-POL was obtained. A foaming formulation was prepared by mixing polyol (recycled polyol R-POL and soybean oil polyol in an 8:2 mass ratio), catalyst (triethylenediamine A33 and stannous octoate T9 in a 1:2.8 mass ratio), silicone oil AK8805, foaming agent (n-pentane and water in a 7:3 mass ratio), and isocyanate PMDI in a mass ratio of 100:4.5:3:9:140, and then foaming to obtain recycled polyurethane foam (RPU). The method was repeated to perform three alcoholysis and foaming processes on recycled polyurethane foam (RPU) to obtain recycled polyols R-POL1, R-POL2, and R-POL3, and recycled polyurethane foams RPU1, RPU2, and RPU3. After 24 hours of storage, the compressive strength of the recycled polyurethane foam RPU was measured to be 260 kPa, and the density was 38 kg / m³. 3 The thermal insulation performance is 34.8 mW / (m·K); the compressive strength of recycled polyurethane foam RPU1 is 255 kPa, and the density is 37.5 kg / m³. 3 The thermal insulation performance is 34.5 mW / (m·K); the compressive strength of recycled polyurethane foam RPU2 is 265 kPa, and the density is 39 kg / m³. 3 The thermal insulation performance is 35.0 mW / (m·K); the compressive strength of recycled polyurethane foam RPU3 is 258 kPa, and the density is 38.2 kg / m³. 3 Its thermal insulation performance is 34.6 mW / (m·K).

[0034] Comparative Example 1

[0035] Waste rigid polyurethane foam was crushed to 3-4 cm. An alcoholysis agent (crude glycerol), polyurethane foam, and a co-catalyst (sodium hydroxide) were selected in a mass ratio of 1:1:0.09. The mixture was placed in a reactor and heated and stirred at 200 °C for 180 min. After the reaction, recycled polyol R-POL was obtained. A foaming formulation was prepared by mixing recycled polyol R-POL, a catalyst (triethylenediamine A33 and stannous octoate T9 in a mass ratio of 1:3), silicone oil AK8805, a foaming agent (n-pentane and water in a mass ratio of 7:3), and isocyanate PMDI in a mass ratio of 100:4:3:9:110, and foaming to obtain recycled polyurethane foam RPU. The recycled polyurethane foam RPU was then subjected to further alcoholysis and foaming to obtain recycled polyol R-POL1 and recycled polyurethane foam RPU1. RPU1 was further alcoholyzed according to the alcoholysis formulation to obtain recycled polyol R-POL2. Recycled polyurethane foam RPU2 suffered from severe shrinkage and could not be molded. After 24 hours of storage, the compressive strength of the recycled polyurethane foam (RPU) was measured to be 180 kPa, and the density was 54 kg / m³. 3 Its thermal insulation performance is 46.7 mW / (m·K).

[0036] Comparative Example 2

[0037] Waste rigid polyurethane foam was crushed to 3-4 cm. An alcoholysis agent (ethylene glycol), polyurethane foam, and a co-catalyst (sodium hydroxide) were selected in a mass ratio of 1:1:0.09. The mixture was placed in a reactor and heated and stirred at 190 °C for 180 min. After the reaction, recycled polyol R-POL was obtained. A foaming formulation was prepared by mixing recycled polyol R-POL, a catalyst (triethylenediamine A33 and stannous octoate T9 in a mass ratio of 1:3), silicone oil AK8805, a foaming agent (n-pentane and water in a mass ratio of 7:3), and isocyanate PMDI in a mass ratio of 100:4:3:9:110, and foaming to obtain recycled polyurethane foam RPU. The recycled polyurethane foam RPU was then subjected to further alcoholysis and foaming to obtain recycled polyol R-POL1 and recycled polyurethane foam RPU1. RPU1 was further alcoholyzed according to the alcoholysis formulation to obtain recycled polyol R-POL2. Recycled polyurethane foam RPU2 suffered from severe shrinkage and could not be molded. After 24 hours of storage, the compressive strength of the recycled polyurethane foam (RPU) was measured to be 145 kPa, and the density was 61 kg / m³. 3 Its thermal insulation performance is 48.7 mW / (m·K).

[0038] Comparative Example 3

[0039] Waste rigid polyurethane foam was crushed to 3-4 cm. An alcoholysis agent (ethylene glycol), polyurethane foam, and a co-catalyst (sodium hydroxide) were selected in a mass ratio of 1:1:0.09. The mixture was placed in a reactor and heated and stirred at 190 °C for 180 min. After the reaction, recycled polyol R-POL was obtained. A foaming formulation was prepared by mixing polyol (recycled polyol R-POL and castor oil polyol in a mass ratio of 7:3), catalyst (triethylenediamine A33 and stannous octoate T9 in a mass ratio of 1:3), silicone oil AK8805, foaming agent (n-pentane and water in a mass ratio of 7:3), and isocyanate PMDI in a mass ratio of 100:4:3:9:110, and then foaming to obtain recycled polyurethane foam RPU. The recycled polyurethane foam RPU was then subjected to further alcoholysis and foaming following the above steps to obtain recycled polyol R-POL1 and recycled polyurethane foam RPU1. RPU1 was further alcoholyzed according to the alcoholysis formula to obtain recycled polyol R-POL2, which was used to prepare recycled polyurethane foam RPU2, and the corresponding indicators were measured. RPU2 was then alcoholyzed again according to the alcoholysis formula to obtain recycled polyol R-POL3, which was used to prepare recycled polyurethane foam RPU3. The foam cracked and became brittle during the foaming process. After 24 hours, the compressive strength of the recycled polyurethane foam RPU was measured to be 130 kPa, and the density was 65 kg / m³. 3 The thermal insulation performance is 50.6 mW / (m·K). The compressive strength of recycled polyurethane foam RPU1 is 107 kPa, and the density is 55.8 kg / m³. 3 The thermal insulation performance is 50.8 mW / (m·K); the compressive strength of recycled polyurethane foam RPU2 is 80 kPa, and the density is 52.7 kg / m³. 3 The thermal insulation performance is 55.0 mW / (m·K); cracking of the recycled polyurethane foam RPU3 could not be detected.

[0040] Test case

[0041] 1. Figure 1 The image shows the infrared spectrum of the regenerated polyol prepared in Example 1 of this invention. The polyols that underwent multiple regenerations exhibited very similar FTIR spectra, indicating that the polyols possess the same functional groups. With increasing regeneration cycles, the FTIR spectra at 3200-3450 cm⁻¹... -1 The enhanced vibrational bands at this location indicate an increase in the content of hydroxyl and amino groups. Furthermore, at 1733 cm⁻¹... -1 Tensile vibrations at C=O were identified at 1514 cm. -1 and 1614 cm -1 Bending vibrations of NH bonds were observed, indicating the breaking of CN bonds in PU foam.

[0042] 2. Figure 2This is a thermogravimetric analysis (TGA) diagram of the bio-based polyurethane foam prepared in Example 1 of this invention. The foam, after multiple alcoholysis regenerations, exhibits three similar degradation stages, indicating that the foam composition and structure are similar. The initial stage occurs at approximately 150 °C, attributed to the degradation of residual monoglycerides in the regenerated polyol. The second stage occurs between approximately 240 and 340 °C, involving the breaking of urethane bonds.

[0043] 3. Figure 3 The images show the physical specimen and SEM image of the bio-based polyurethane foam prepared in Example 1 of this invention. It can be observed that the recycled PU foam has a unique three-dimensional network closed-cell wrinkled structure; however, with increasing recycling cycles, the cell morphology becomes fragmented, indicating that repeated recycling affects the polyurethane foam structure.

[0044] The oil absorption performance results of the embodiments and comparative examples of the present invention are shown in Table 1.

[0045]

[0046] This invention achieves the recycling and alcoholysis of waste polyurethane foam through the use of compound alcoholysis agents and the synergistic blending and foaming of compound polyols. Crude glycerol is particularly effective in breaking polyurethane molecular chains, while xylitol, diglycerol, and pentaerythritol play unique roles in the thermal conversion grafting process. These alcoholysis agents, combined, complement each other, working together to efficiently complete the alcoholysis and conversion of polyurethane foam. The recycled polyols, derived from the alcoholysis of waste polyurethane foam, retain specific structural characteristics and reactivity. Bio-based polyols, such as castor oil polyols, possess additional performance advantages, including better flexibility and weather resistance. The combination of these two types of polyols provides complementary advantages, ensuring reliable performance of the recycled polyurethane foam even after multiple cycles. During the foaming process, the active groups of the recycled polyols interact with the groups of the bio-based polyols, enhancing the degree of intermolecular cross-linking and thus improving the strength and stability of the foam. The bio-based polyol molecules contain long-chain fatty acid structures, giving the material good flexibility and water resistance. When recycled polyols are blended with bio-based polyols, their different molecular structures complement each other. The combination of long-chain and short-chain structures can adjust the mechanical and thermal properties of the foam, while the combination of branched and linear structures can improve cell formation and stability, resulting in a more uniform cell distribution and better compressive strength. The different active groups of the blended polyols synergistically regulate the reaction rate and extent. On the one hand, highly reactive groups promote the foaming reaction and increase the reaction rate; on the other hand, less reactive groups stabilize the network structure in the later stages of the reaction, preventing over-reaction and a decline in foam performance. For example, certain active groups of recycled polyols can form hydrogen bonds or other weak interactions with specific groups of bio-based polyols, regulating reactivity, making the foaming process smoother, and improving foam quality and stability. In the process of multiple cycles of recycling recycled polyurethane foam, it demonstrates the advantage of maintaining good compressive strength stability. Meanwhile, different combinations and proportions of co-catalysts have little impact on the compressive strength of recycled polyurethane foam within a certain range. In contrast, a single alcoholysis agent is difficult to meet the performance requirements of recycled polyurethane foam in multiple cycles, and is prone to problems such as foam shrinkage. Therefore, using a combination of multiple alcoholysis agents can achieve efficient recycling and reuse of polyurethane foam.

Claims

1. A method for repeatedly recycling polyurethane foam using a bio-based alcoholysis agent, characterized in that, The method includes the following steps: S1. Preparation of Regenerated Polyol R-POL by Alcohololysis of Polyurethane Foam: A composite alcoholysis agent, polyurethane foam, and catalyst are added to a reaction vessel at a mass ratio of 1:0.5~3:0.02~0.

1. The mixture is heated and stirred at 160~220 ℃ for 15~240 min. After the reaction is completed, regenerated polyol R-POL is obtained. The polyurethane foam particle size is 2~5 cm. The composite alcoholysis agent is a mixture of crude glycerol and one of xylitol, diglycerol, pentaerythritol, and ethylene glycol. The catalyst is a mixture of sodium hydroxide and ethanolamine, sodium hydroxide and diethylamine, potassium hydroxide and ethanolamine, or potassium hydroxide and diethylamine. S2. Preparation of recycled polyurethane foam (RPU): The composite polyol, catalyst, silicone oil AK8805, foaming agent, and isocyanate PMDI are mixed evenly in a mass ratio of 100:1~5:2~3:2~10:90~150 and then foamed to obtain recycled polyurethane foam (RPU). The composite polyol is a compound of the recycled polyol prepared in the previous step and one of castor oil polyol, soybean oil polyol, xylitol polyol, and crude glycerol-based polyol. S3. Recycling and preparing recycled polyurethane foam RPUX: Using the recycled polyurethane foam obtained in the previous step as raw material, repeat steps S1-S2 for cyclic alcoholysis foaming to prepare recycled polyurethane foam RPUX, where X is the number of cyclic alcoholysis foaming times, X is 1~3 times.

2. The method for repeatedly recycling polyurethane foam using a bio-based alcoholysis agent as described in claim 1, characterized in that: The polyurethane foam is waste rigid polyurethane foam.

3. The method for repeatedly recycling polyurethane foam using a bio-based alcoholysis agent as described in claim 1, characterized in that: The foaming agent is one or two of n-pentane, isopentane, cyclopentane, and water.

4. The method for repeatedly recycling polyurethane foam using a bio-based alcoholysis agent as described in claim 1, characterized in that: In step S2, the catalyst is triethylenediamine A33 and stannous octoate T9, with a mass ratio of 1:1 to 3.

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