Method for recycling polyurethane foam for multiple times by utilizing bio-based alcoholysis agent

Abstract

The invention belongs to the technical field of polyurethane foam recovery, and particularly relates to a method for recycling polyurethane foam for multiple times by utilizing a bio-based alcoholysis agent, which comprises the following steps of: performing alcoholysis on waste polyurethane foam by adopting a one-pot method, and constructing a circulating alcoholysis path of bio-based foam-regenerated polyol-polyurethane foam; the invention also discloses a method for preparing the rigid polyurethane foam by compounding the regenerated polyol and the bio-based polyol. The prepared polyurethane foam is subjected to three times of cyclic alcoholysis foaming, and the regenerated foam has good compression performance. The polyurethane foam circulating bio-based alcoholysis system is provided for the first time, waste polyurethane foam materials generated in the processing production and using process are solved, a new thought is provided for recycling of bio-based materials, and the method has remarkable technical advantages and practical application value and can be widely applied to the fields of building, packaging and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of polyurethane foam recovery, and in particular relates to a method for recovering polyurethane foam by utilizing a bio-based alcoholysis agent for multiple cycles. Background Art

[0002] With the increasing attention paid to environmental protection and sustainable development around the world, resource recovery and reuse have become key issues. As a material widely used in various fields, the output and usage of polyurethane foam are increasing. However, polyurethane foam will inevitably produce scraps during the processing and production process, accounting for about 10% of the total foam output. This part of the foam is often discarded, which not only causes a waste of resources, but also brings great pressure to the environment. At present, the main methods for recycling polyurethane foam are mechanical recycling and chemical recycling. Although mechanical recycling is relatively simple to operate, the performance of the recycled materials is often poor and the scope of application is limited. Among the chemical recycling methods, alcoholysis has unique advantages. Polyurethane foam can be decomposed into reusable polyols and other substances through alcoholysis agents, providing a source of raw materials for the production of new polyurethane foam. However, most of the existing technologies only have a process of recycling polyurethane foam by alcoholysis and foaming once, and it is impossible to recycle waste polyurethane multiple times without reducing the performance of the recycled foam. If polyurethane foam can be recycled by alcoholysis multiple times, 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 contribute to addressing climate change. As the number of cycles increases, the cost saving effect will be more significant, driving the development of recycling and processing related industries. Summary of the invention

[0003] The purpose of the present invention is to provide a method for recycling polyurethane foam by multiple cycles of bio-based alcoholysis agent, the method adopts one-pot alcoholysis of waste bio-based polyurethane foam, constructs a cyclic alcoholysis path of bio-based foam-regenerated polyol-polyurethane foam, and also discloses a method for preparing bio-based polyurethane rigid foam with regenerated polyol. Its technical advantages include reducing resource consumption, significant environmental benefits, good performance, innovative circulation system, high economic value and simple and flexible operation. Specifically, it is manifested in reducing dependence on non-renewable resources, reducing landfill and carbon emissions, synthesizing foam insulation and stable compression performance of rigid foam after regeneration, proposing a new circulation system to lead industry development, reduce costs and create industrial opportunities, and adopting one-pot method is simple to operate, the range of raw material selection is wide, and the applicability is strong, and it has significant technical advantages and practical application value.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is: A method for recycling polyurethane foam by using a bio-based alcoholysis agent for multiple cycles, wherein the same polyurethane foam can be recycled at least three times by repeating the method, and the method comprises the following steps: S1. Preparation of regenerated polyol R-POL by alcoholysis of polyurethane foam: adding alcoholysis agent, polyurethane foam and catalytic aid into a reaction kettle in a mass ratio of 1:0.5~3:0.02~0.1, heating and stirring at 160~220 ℃ for 15~240 min, and obtaining regenerated polyol R-POL after the reaction, wherein the polyurethane foam has a particle size of 2~5 cm, and the alcoholysis agent is a compound of crude glycerol and one of xylitol, diglycerol, pentaerythritol and ethylene glycol; S2. Preparation of recycled polyurethane foam RPU: The composite polyol, catalyst, silicone oil AK8805, foaming agent, isocyanate PMDI are uniformly mixed in a mass ratio of 100:1~5:2~3:2~10:90~150 and foamed to obtain recycled polyurethane foam RPU, wherein 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 glyceryl polyol; Further, the recycled polyurethane foam RPUX is prepared by cyclic alcoholysis and foaming: the recycled polyurethane foam prepared in the previous step is used as a raw material to repeat the steps S1-S2 cyclic alcoholysis and foaming to prepare the recycled polyurethane foam RPUX, X is the number of cyclic alcoholysis and foaming, and X is 1 to 3 times; the method firstly alcoholizes the waste polyurethane foam, and then regenerates the alcoholysis product into polyurethane rigid foam, and then regenerates the regenerated rigid foam for multiple cycles according to the one-time alcoholysis process, and the compression resistance and thermal insulation performance of the regenerated foam are not reduced during the cyclic regeneration process, thereby realizing the multiple recycling of polyurethane foam-polyol-polyurethane foam, solving the scraps generated during the processing process, and the alcoholysis method can achieve 1-3 cycles, mainly from two aspects. First, as the number of cycles increases, the performance of the material will gradually decrease. After multiple alcoholysis and foaming, the structure of the regenerated polyol may change, resulting in a decrease in its reaction activity, thereby affecting the performance of the regenerated polyurethane foam. After experimental testing, it was found that when the cycle was 1-3 times, the performance of the regenerated polyurethane foam could still meet certain use requirements, but after more than 3 times, the performance decreased significantly and could not meet the standards for practical application. Second: When considering the number of recycling cycles, a cost-benefit analysis is required. Although recycling can reduce the demand for raw materials and reduce costs, as the number of cycles increases, energy consumption, catalyst usage, equipment maintenance costs, etc. in the production process may increase.

[0005] Furthermore, the polyurethane foam is waste polyurethane rigid foam.

[0006] Furthermore, the catalyst aid in step S1 is a compound of sodium hydroxide and ethanolamine, sodium hydroxide and diethylamine, potassium hydroxide and ethanolamine, or potassium hydroxide and diethylamine.

[0007] Furthermore, the foaming agent is one or two of n-pentane, isopentane, cyclopentane and water.

[0008] Furthermore, in step S2, the catalyst is triethylenediamine A33 and stannous octoate T9, and the mass ratio of the two is 1:1-3.

[0009] The present invention has the advantages that: 1. The present invention utilizes multiple recycling to convert the foam scraps and waste foam generated in the processing process into recycled polyols and then prepare bio-based polyurethane rigid foam, thereby reducing the generation of industrial waste and improving resource utilization. The same polyurethane foam itself has a sufficiently long service life once, and its service life can be substantially extended after three cycles of recycling. 2. The hydroxyl groups contained in the alcoholysis agent of the present invention can react with the chemical bonds in the polyurethane molecules to cause the carbamate groups in the polyurethane to break. At the same time, the compound alcoholysis agent can achieve thermal conversion and grafting onto the regenerated polyol during the alcoholysis process, thereby being converted into a bio-based polyol containing active hydroxyl groups, and further converted into a renewable bio-based polyurethane foam. With the dual effects of the alcoholysis agent during use, the recycling of waste polyurethane foam is successfully achieved; 3. The hydroxyl value of the alcoholysis regenerated polyol obtained by the present invention is flexibly adjustable and can be flexibly adjusted by changing the ratio of the polyurethane foam and the alcoholysis agent; 4. The alcoholysis process of the present 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 the regenerated polyurethane foam without purification and separation; 5. The compression resistance and thermal insulation properties of the foam are not reduced after multiple cycles of regeneration according to the method of the present invention, thereby ensuring product quality, reducing environmental pollution caused by waste foam, and reducing the product cost of producing the foam. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is the infrared spectrum of the regenerated polyol prepared in Example 1 of the present invention.

[0011] Figure 2 3 is a thermogravimetric analysis diagram of the bio-based polyurethane foam prepared in Example 1 of the present invention.

[0012] Figure 3 The figures are the physical object and electron microscope image of the bio-based polyurethane foam prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0013] Example 1 like Figure 1-3 As shown in the figure, a method for recycling polyurethane foam by multiple cycles of bio-based alcoholysis agent is provided, wherein the waste polyurethane rigid foam is crushed to 4-5 cm, and the alcoholysis agent (the mass ratio of crude glycerol and xylitol is 3:1), polyurethane foam and co-catalyst (the mass ratio of sodium hydroxide and ethanolamine is 4:1) are heated and stirred at 220 ℃ for 240 min in a mass ratio of 1:3:0.1 to obtain the regenerated polyol R-POL. The foaming formula is mixed with polyol (the mass ratio of regenerated polyol R-POL and castor oil polyol is 1:1) in a mass ratio of 100:5:3:3:130, catalyst (the mass ratio of triethylenediamine A33 and stannous octoate T9 is 1:3), silicone oil AK8805, foaming agent (water), isocyanate PMDI and then foamed to obtain the regenerated polyurethane foam RPU. The method was repeated for three times of 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, 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 / m 3 The thermal insulation performance is 36.8 mW / (m·K). The compression strength of recycled polyurethane foam RPU1 is 285kPa and the density is 47 kg / m 3 The thermal insulation performance is 36.5 mW / (m·K). The compression strength of recycled polyurethane foam RPU2 is 295kPa and the density is 49 kg / m 3 The thermal insulation performance is 37.0 mW / (m·K). The compression strength of recycled polyurethane foam RPU3 is 288 kPa and the density is 47.5 kg / m 3 , the thermal insulation performance is 36.6 mW / (m·K).

[0014] Example 2 The waste polyurethane rigid foam was crushed to 3-4 cm, and the alcoholysis agent (the mass ratio of crude glycerol and diglycerol was 2:1), polyurethane foam and co-catalyst (the mass ratio of potassium hydroxide and ethanolamine was 3:2) were selected in a mass ratio of 1:1.5:0.05. The mixture was heated and stirred at 180℃ for 60 min to obtain the regenerated polyol R-POL. The polyol (the mass ratio of regenerated polyol R-POL and soybean oil polyol was 8:2) with a foaming formula of 100:3:2.5:10:120, the catalyst (the mass ratio of triethylenediamine A33 and stannous octoate T9 was 1:2), silicone oil AK8805, the foaming agent (the mass ratio of cyclopentane and water was 8:2), and the isocyanate PMDI were mixed and foamed to obtain the regenerated polyurethane foam RPU. The method was repeated for three times of alcoholysis and foaming of the regenerated polyurethane foam RPU to obtain the regenerated polyols R-POL1, R-POL2, R-POL3 and the regenerated polyurethane foams RPU1, RPU2, 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 / m 3 The thermal insulation performance is 26.8 mW / (m·K); the compression strength of recycled polyurethane foam RPU1 is 215 kPa and the density is 23.5 kg / m 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 / m 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 / m 3 , the thermal insulation performance is 26.7mW / (m·K).

[0015] Example 3 The waste polyurethane rigid foam was crushed to 2-3 cm, and the alcoholysis agent (mass ratio of crude glycerol and xylitol was 5:1), polyurethane foam and co-catalyst (mass ratio of sodium hydroxide and diethylamine was 1:1) were selected according to the mass ratio of 1:0.5:0.02. It was placed in a reactor and heated and stirred at 160 ℃ for 15 min. After the reaction, the regenerated polyol R-POL was obtained. The foaming formula was mixed with polyol (mass ratio of regenerated polyol R-POL and crude glycerol polyol was 8:2) in a mass ratio of 100:1:2:8:90, catalyst (mass ratio of triethylenediamine A33 and stannous octoate T9 was 1:1), silicone oil AK8805, foaming agent (mass ratio of n-pentane and water was 8:2), isocyanate PMDI, and foamed to obtain recycled polyurethane foam RPU. The method was repeated to perform alcoholysis and foaming three times on the recycled polyurethane foam RPU to obtain recycled polyols R-POL1, R-POL2, R-POL3 and recycled polyurethane foams RPU1, RPU2, 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 / m 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 / m 3 The thermal insulation performance is 38.5 mW / (m·K); the compression strength of recycled polyurethane foam RPU2 is 325kPa and the density is 47.5 kg / m 3 The thermal insulation performance is 39.0 mW / (m·K); the compression strength of recycled polyurethane foam RPU3 is 320 kPa and the density is 47.0 kg / m 3 , the thermal insulation performance is 38.6 mW / (m·K).

[0016] Example 4 The waste polyurethane rigid foam was crushed to 3-4 cm, and the alcoholysis agent (the mass ratio of crude glycerol and pentaerythritol was 2:1), polyurethane foam and co-catalyst (the mass ratio of potassium hydroxide and ethanolamine was 1:1) were selected according to the mass ratio of 1:2:0.08. The regenerated polyol R-POL was obtained by heating and stirring at 190℃ for 120 min. The foaming formula was a polyol with a mass ratio of 100:4:2.8:6:130 (the mass ratio of regenerated polyol R-POL and xylitol polyol was 9:1), a catalyst (the mass ratio of triethylenediamine A33 and stannous octoate T9 was 1:2.5), silicone oil AK8805, a foaming agent (the mass ratio of isopentane and water was 7:3), and isocyanate PMDI. After being evenly mixed, the regenerated polyurethane foam RPU was obtained. The method was repeated for three times of 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, 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 / m 3 The thermal insulation performance is 32.8 mW / (m·K). The compression strength of recycled polyurethane foam RPU1 is 245 kPa and the density is 34.5 kg / m 3 The thermal insulation performance is 32.5mW / (m·K). The compression strength of recycled polyurethane foam RPU2 is 255 kPa and the density is 36 kg / m 3 The thermal insulation performance is 33.0mW / (m·K). The compression strength of recycled polyurethane foam RPU3 is 248 kPa and the density is 35.2 kg / m 3 , the thermal insulation performance is 32.6 mW / (m·K).

[0017] Example 5 The waste polyurethane rigid foam was crushed to 2-3 cm, and the alcoholysis agent (mass ratio of crude glycerol and diglycerol was 3:1), polyurethane foam and co-catalyst (mass ratio of sodium hydroxide and ethanolamine was 5:1) were selected in a mass ratio of 1:1:0.06. The mixture was heated and stirred at 170 ℃ for 45 min to obtain the regenerated polyol R-POL. The foaming formula was a polyol (mass ratio of regenerated polyol R-POL and castor oil polyol was 9:1) with a mass ratio of 100:2:2.2:7:110, a catalyst (mass ratio of triethylenediamine A33 and stannous octoate T9 was 1:1.5), silicone oil AK8805, a foaming agent (mass ratio of cyclopentane and water was 6:4), and isocyanate PMDI. The regenerated polyurethane foam RPU was foamed. The method was repeated for three times of alcoholysis and foaming of the regenerated polyurethane foam RPU to obtain regenerated polyols R-POL1, R-POL2, R-POL3 and regenerated polyurethane foams RPU1, RPU2, 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 / m 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 / m 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 / m 3 The thermal insulation performance is 36.0mW / (m·K); the compressive strength of recycled polyurethane foam RPU3 is 278 kPa and the density is 40.2 kg / m 3 , the thermal insulation performance is 35.6 mW / (m·K).

[0018] Example 6 The waste polyurethane rigid foam was crushed to 3-4 cm, and the alcoholysis agent (mass ratio of crude glycerol and ethylene glycol was 2:1), polyurethane foam and co-catalyst (mass ratio of potassium hydroxide and diethylamine was 2:1) were selected according to the mass ratio of 1:2.5:0.09. It was put into a reactor and heated and stirred at 200 ℃ for 180 min. After the reaction, the regenerated polyol R-POL was obtained. The foaming formula was mixed with polyol (mass ratio of regenerated polyol R-POL and soybean oil polyol was 8:2) in a mass ratio of 100:4.5:3:9:140, catalyst (mass ratio of triethylenediamine A33 and stannous octoate T9 was 1:2.8), silicone oil AK8805, foaming agent (mass ratio of n-pentane and water was 7:3), isocyanate PMDI, and foamed to obtain recycled polyurethane foam RPU. The method was repeated to perform alcoholysis and foaming of the recycled polyurethane foam RPU three times to obtain recycled polyols R-POL1, R-POL2, R-POL3 and recycled polyurethane foams RPU1, RPU2, 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 / m 3 The thermal insulation performance is 34.8 mW / (m·K); the compression strength of recycled polyurethane foam RPU1 is 255kPa and the density is 37.5 kg / m 3 The thermal insulation performance is 34.5 mW / (m·K); the compression strength of recycled polyurethane foam RPU2 is 265 kPa and the density is 39 kg / m 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 / m 3 , the thermal insulation performance is 34.6 mW / (m·K).

[0019] Comparative Example 1 The waste polyurethane rigid foam was crushed to 3~4 cm, and the alcoholysis agent (crude glycerol), polyurethane foam and co-catalyst (sodium hydroxide) were selected according to the mass ratio of 1:1:0.09. It was put into a reactor and heated and stirred at 200 ℃ for 180 min. After the reaction, the regenerated polyol R-POL was obtained. The foaming formula was mixed with the regenerated polyol R-POL, catalyst (triethylenediamine A33 and stannous octoate T9 mass ratio of 1:3), silicone oil AK8805, foaming agent (n-pentane and water mass ratio of 7:3), and isocyanate PMDI in the mass ratio of 100:4:3:9:110, and foamed to obtain the regenerated polyurethane foam RPU. According to the above steps, the regenerated polyurethane foam RPU was alcoholyzed and foamed again to obtain the regenerated polyol R-POL1 and the regenerated polyurethane foam RPU1. RPU1 was alcoholyzed again according to the alcoholysis formula to obtain the regenerated polyol R-POL2. The regenerated polyurethane foam RPU2 had severe shrinkage and could not be formed. 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 / m 3 , the thermal insulation performance is 46.7 mW / (m·K).

[0020] Comparative Example 2 The waste polyurethane rigid foam was crushed to 3~4 cm, and the alcoholysis agent (ethylene glycol), polyurethane foam and co-catalyst (sodium hydroxide) were selected according to the mass ratio of 1:1:0.09. It was placed in a reactor and heated and stirred at 190 ℃ for 180 min. After the reaction, the regenerated polyol R-POL was obtained. The foaming formula was mixed with the regenerated polyol R-POL, catalyst (triethylenediamine A33 and stannous octoate T9 mass ratio of 1:3), silicone oil AK8805, foaming agent (n-pentane and water mass ratio of 7:3), and isocyanate PMDI in the mass ratio of 100:4:3:9:110, and foamed to obtain the regenerated polyurethane foam RPU. According to the above steps, the regenerated polyurethane foam RPU was alcoholyzed and foamed again to obtain the regenerated polyol R-POL1 and the regenerated polyurethane foam RPU1. RPU1 was alcoholyzed again according to the alcoholysis formula to obtain the regenerated polyol R-POL2. The regenerated polyurethane foam RPU2 had severe shrinkage and could not be formed. 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 / m 3 , the thermal insulation performance is 48.7 mW / (m·K).

[0021] Comparative Example 3 The waste polyurethane rigid foam was crushed to 3~4 cm, and the alcoholysis agent (ethylene glycol), polyurethane foam and co-catalyst (sodium hydroxide) were selected according to the mass ratio of 1:1:0.09. It was placed in a reactor and heated and stirred at 190 ℃ for 180 min. After the reaction, the regenerated polyol R-POL was obtained. The foaming formula was mixed with polyols (the mass ratio of regenerated polyol R-POL and castor oil polyol was 7:3) in a mass ratio of 100:4:3:9:110, catalyst (the mass ratio of triethylenediamine A33 and stannous octoate T9 was 1:3), silicone oil AK8805, foaming agent (the mass ratio of n-pentane and water was 7:3), and isocyanate PMDI, and foamed to obtain regenerated polyurethane foam RPU. According to the above steps, the regenerated polyurethane foam RPU was alcoholyzed and foamed again to obtain regenerated polyol R-POL1 and regenerated polyurethane foam RPU1. RPU1 was alcoholyzed again according to the alcoholysis formula to obtain regenerated polyol R-POL2, and the regenerated polyurethane foam RPU2 was prepared, and the corresponding indicators were measured. RPU2 was alcoholyzed again according to the alcoholysis formula to obtain regenerated polyol R-POL3, and the regenerated polyurethane foam RPU3 was prepared. The foam cracked and became brittle during the foaming process. After being placed for 24 hours, the compressive strength of the regenerated polyurethane foam RPU was measured to be 130 kPa, and the density was 65 kg / m 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 / m 3 The thermal insulation performance is 50.8 mW / (m·K); the compression strength of recycled polyurethane foam RPU2 is 80 kPa and the density is 52.7 kg / m 3 The thermal insulation performance is 55.0 mW / (m·K); the cracking of the recycled polyurethane foam RPU3 cannot be detected.

[0022] Test example 1. Figure 1 The infrared spectrum of the regenerated polyol prepared in Example 1 of the present invention is shown in Figure 1. The FTIR spectra of the polyols regenerated multiple times are very similar, indicating that the polyols have the same groups. As the number of regenerations increases, the 3200-3450 cm -1 The vibration band at 1733 cm -1 The stretching vibration of C=O was identified at 1514 cm -1 and 1614 cm -1 Bending vibration of the NH bonds was observed at , which indicated the breaking of the CN bonds in the PU foam.

[0023] 2. Figure 2Thermogravimetric analysis of the bio-based polyurethane foam prepared in Example 1 of the present invention. The foam regenerated by multiple alcoholysis shows similar three degradation stages, indicating that the composition and structure of the foam are similar. The initial stage occurs at about 150 ° C and is attributed to the degradation of the residual monoglyceride in the regenerated polyol. The second stage occurs between about 240 and 340 ° C and involves the cleavage of the urethane bond.

[0024] 3. Figure 3 The physical picture and SEM picture of the bio-based polyurethane foam prepared in Example 1 of the present invention are shown. It can be observed that the recycled PU foam has a special three-dimensional network closed-cell pleated structure, but as the number of regenerations increases, the cell morphology becomes broken, indicating that multiple regenerations will affect the polyurethane foam structure.

[0025] The oil absorption performance results of the embodiments of the present invention and the comparative examples are shown in Table 1.

[0026] The present invention realizes the cyclic alcoholysis of waste polyurethane foam by adopting a composite alcoholysis agent and a composite polyol synergistically blended foaming method, wherein crude glycerol has an advantage in breaking the polyurethane molecular chain, while xylitol, diglycerol, pentaerythritol, etc. play a unique role in the thermal conversion grafting process. These alcoholysis agents are combined together to complement each other and effectively complete the alcoholysis and conversion of polyurethane foam. Regenerated polyols are derived from the alcoholysis of waste polyurethane foam, retaining specific structural characteristics and reaction activity. Bio-based polyols such as castor oil polyols have additional performance advantages, including better flexibility and weather resistance. The combination of the two can complement each other and ensure that the regenerated polyurethane foam still has reliable performance in multiple cycles. During the foaming process, the active groups of the regenerated polyols interact with the groups of the bio-based polyols to enhance the degree of cross-linking between molecules, thereby improving the strength and stability of the foam. The bio-based polyol molecules contain long-chain fatty acid structures, which give the material good flexibility and water resistance. When recycled polyols are compounded with bio-based polyols, 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. The combination of branched structures and linear structures can improve the formation and stability of pores, making the foam have a more uniform pore distribution and better compressive resistance. The different active groups of the compounded polyols work together to adjust the reaction rate and degree of reaction. On the one hand, the groups with high reaction activity promote the foaming reaction and increase the reaction speed; on the other hand, the groups with low reaction activity stabilize the network structure in the later stage of the reaction to prevent excessive reaction from causing the foam performance to decrease. For example, some active groups of recycled polyols can form hydrogen bonds or other weak interactions with specific groups of bio-based polyols, adjust the reaction activity, make the foaming process smoother, and improve the quality and stability of the foam. In the process of recycling recycled polyurethane foam for multiple cycles, it shows the advantage of being able to maintain good compressive strength stability. At the same time, different combinations and proportions of co-catalysts have little effect on the compressive strength of recycled polyurethane foam within a certain range. In comparison, a single alcoholysis agent is difficult to meet the performance requirements of recycled polyurethane foam during multiple cycles, and is prone to problems such as shrinkage. Therefore, the use of a combination of multiple alcoholysis agents can achieve efficient recovery and reuse of polyurethane foam.

Claims

1. A method for recycling polyurethane foam by using a bio-based alcoholysis agent for multiple cycles, characterized in that: Repeating the method to recycle the same polyurethane foam at least three times, the method comprises the following steps: S1. Preparation of regenerated polyol R-POL by alcoholysis of polyurethane foam: adding a composite alcoholysis agent, polyurethane foam and a catalytic aid into a reactor in a mass ratio of 1:0.5-3:0.02-0.1, heating and stirring at 160-220 °C for 15-240 min, and obtaining regenerated polyol R-POL after the reaction. The polyurethane foam has a particle size of 2-5 cm. The composite alcoholysis agent is a compound of crude glycerol and one of xylitol, diglycerol, pentaerythritol and ethylene glycol; S2. Preparation of recycled polyurethane foam RPU: Mix the composite polyol, catalyst, silicone oil AK8805, foaming agent and isocyanate PMDI in a mass ratio of 100:1~5:2~3:2~10:90~150 and foam 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 polyol.

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

3. The method for recycling polyurethane foam by using a bio-based alcoholysis agent for multiple cycles as claimed in claim 1, characterized in that: The catalyst aid in step S1 is a compound of sodium hydroxide and ethanolamine, a compound of sodium hydroxide and diethylamine, a compound of potassium hydroxide and ethanolamine, or a compound of potassium hydroxide and diethylamine.

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

5. The method for recycling polyurethane foam by using a bio-based alcoholysis agent for multiple cycles as claimed in claim 1, characterized in that: The catalyst in step S2 is triethylenediamine A33 and stannous octoate T9, and the mass ratio of the two is 1:1-3.

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