WO2024187296A1 - Degradation method for polyurethane foam - Google Patents

Abstract

A degradation method for polyurethane foam, comprising a first mixing step, a first degradation step, a second mixing step, a second degradation step and a pressure relief step. The first mixing step is to mix polyurethane foam with a first degradation liquid to form a first degradation system; the first degradation step is to degrade the first degradation system to obtain an insoluble substance; the second mixing step is to mix the insoluble substance with a second degradation liquid to form a second degradation system; the second degradation step is to degrade the second degradation system to obtain an intermediate product; and the pressure relief step is to remove the remaining first degradation liquid from the intermediate product so as to obtain a polyol. Thus, the polyurethane foam is degraded in a two-stage degradation mode, thereby increasing the polyol recovery ratio and further lowering the production cost so as to improve commercial value.

Description

Degradation methods of polyurethane foam Technical Field

The invention relates to a method for degrading polyurethane foam, in particular to a method for degrading polyurethane foam in a segmented manner.

Background Art

With the increase in the annual production and consumption of polyurethane materials worldwide, the amount of waste polyurethane materials is also increasing. Although polyurethane materials can be naturally degraded by sunlight and water vapor in the environment, their degradation rate is slow and the time is long, which still causes environmental damage. The key raw materials of polyurethane materials mostly come from petrochemical raw materials. Therefore, it is impossible to recycle waste polyurethane materials, and it will inevitably cause excessive waste of petrochemical resources.

However, among polyurethane foam materials, soft polyurethane foam will produce a large amount of insoluble matter during the degradation process, and the polyol obtained after degradation will have foreign matter precipitation after being left for a long time, which will affect the recovery rate of the polyol and the quality stability of the recycled application.

In addition, there have been related studies using a mixture of polyols and sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, triethylamine, citrate, acetate, and phosphate as a degradation liquid. Although this can ultimately be used together with the polyols obtained after degradation in the synthesis of polyurethane materials, the existing degradation liquid cannot be recycled and reused, which will directly increase the production cost of the degraded polyols and affect the economic benefits of the product.

In view of this, how to find appropriate degradation liquid and provide an efficient degradation method for polyurethane foam so that polyurethane foam and its degradation liquid can be recycled has become the goal of relevant industries.

Summary of the invention

An object of the present invention is to provide a polyurethane foam degradation method, which reduces the generation of insoluble matter through two-stage degradation and improves the recovery ratio of polyol after degradation.

One embodiment of the present invention provides a polyurethane foam degradation method, comprising a first mixing step, a first degradation step, a second mixing step, a second degradation step, and a decompression step. The first mixing step is to mix a polyurethane foam with a first degradation liquid to form a first degradation system, and the first degradation liquid has a structure as shown in formula (I) or formula (II):

Wherein, R is an alkylene with 2 to 6 carbon atoms or its structural isomers, phenyl and its derivatives. The first degradation step is to degrade the first degradation system at a first reaction temperature to form a liquid degradation solution mixture and an insoluble substance, and remove the liquid degradation solution mixture. The second mixing step is to mix the insoluble substance with a second degradation solution to form a second degradation solution. The second degradation step is to degrade the second degradation system at a second reaction temperature, cool it down and stand it for stratification to obtain an intermediate product in the upper layer. The decompression step is to remove the remaining first degradation liquid from the intermediate product at a reaction pressure to obtain a polyol.

The polyurethane foam degradation method described in the previous paragraph may further include a crushing step. The crushing step is to crush the polyurethane foam to form a plurality of polyurethane foam fragments before the first mixing step.

According to the polyurethane foam degradation method described in the previous paragraph, the polyurethane foam is obtained through a polymerization reaction, and the reactive monomers of the polymerization reaction may include an isocyanate component and an isocyanate reactive component.

According to the polyurethane foam degradation method described in the preceding paragraph, the isocyanate component can be aromatic diisocyanate, aliphatic diisocyanate, aromatic diisocyanate derivatives, aliphatic diisocyanate derivatives, polymethylene polyphenyl isocyanate or a mixture thereof.

According to the polyurethane foam degradation method described in the preceding paragraph, the isocyanate reactive component may be polyester polyol, polyether polyol, small molecule multifunctional compound or a mixture thereof.

According to the polyurethane foam degradation method described in the preceding paragraph, the mass ratio of the polyurethane foam to the first degradation liquid may be 1:0.9 to 1:3.

According to the polyurethane foam degradation method described in the previous paragraph, the first reaction temperature may be 110°C to 170°C.

According to the polyurethane foam degradation method described in the previous paragraph, in the first degradation step, the first degradation system is maintained at a first reaction temperature for a first degradation time, and the first degradation time can be 30 minutes to 3 hours.

According to the polyurethane foam degradation method described in the previous paragraph, the amount of the liquid degradation solution mixture removed can be 40% to 100% of the amount of the first degradation solution added.

According to the polyurethane foam degradation method described in the previous paragraph, the second degradation liquid can be polyester polyol, polyether polyol, small molecule multifunctional compound or a mixture thereof.

According to the polyurethane foam degradation method described in the preceding paragraph, the mass ratio of the polyurethane foam to the second degradation liquid may be 1:0.1 to 1:3.

According to the polyurethane foam degradation method described in the previous paragraph, the second reaction temperature may be 110°C to 170°C.

According to the polyurethane foam degradation method described in the previous paragraph, in the second degradation step, the second degradation system is maintained at a second reaction temperature for a second degradation time, and the second degradation time can be 30 minutes to 4 hours.

According to the polyurethane foam degradation method described in the preceding paragraph, the reaction pressure may be 1 mbar to 1000 mbar.

Thus, the polyurethane foam degradation method of the present invention reduces the output of insoluble matter during the degradation process through segmented degradation, improves the recovery rate of the polyol after degradation, and the first degradation liquid can be completely recovered and reused, while the use of the second degradation liquid can be minimized, so as to reduce the production cost of the polyol obtained after degradation, improve the commercial value, and promote the recycling of polyurethane foam.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to make the above and other objects, features, advantages and embodiments of the present invention more clearly understood, the following are the descriptions of the accompanying drawings:

FIG. 1 is a flow chart showing the steps of a method for degrading polyurethane foam according to one embodiment of the present invention.

【Explanation of symbols】

100:Degradation method of polyurethane foam

110,120,130,140,150: Steps

DETAILED DESCRIPTION

The following will discuss various embodiments of the present invention in more detail. However, this embodiment can be an application of various inventive concepts and can be specifically implemented in various specific scopes. The specific embodiments are for illustrative purposes only and are not limited to the scope of the disclosure.

In the present invention, the structure of a compound is sometimes represented by a skeleton formula, which may omit carbon atoms, hydrogen atoms, and carbon-hydrogen bonds. If a functional group is clearly drawn in the structural formula, the one shown shall prevail.

In the present invention, "the first degradation solution has a structure as shown in formula (I)", for the sake of simplicity and fluency, it is sometimes expressed as the first degradation solution shown in formula (I) or the first degradation solution (I), and the representation of other compounds or groups is similar.

<Degradation Method of Polyurethane Foam>

Please refer to FIG1 , which is a flowchart showing a polyurethane foam degradation method 100 according to an embodiment of the present invention. In FIG1 , the polyurethane foam degradation method 100 includes steps 110 , 120 , 130 , 140 , and 150 .

Step 110 is to perform a first mixing step, which is to mix a polyurethane foam with a first degradation liquid to form a first degradation system, and the first degradation liquid has a structure as shown in formula (I) or formula (II):

Wherein, R is an alkylene group or its structural isomers, phenyl group and its derivatives having 2 to 6 carbon atoms. Specifically, the present invention uses an alcoholamine compound having active hydrogen on the amine group as the first degradation liquid, which can directionally open the carbamate bond and the urea bond in the polyurethane foam structure, and the mass ratio of the polyurethane foam to the first degradation liquid can be 1:0.9 to 1:3.

Specifically, the polyurethane foam of the present invention is obtained through a polymerization reaction, and the reactive monomers of the polymerization reaction include an isocyanate component and an isocyanate reactive component. The isocyanate component can be an aromatic diisocyanate, an aliphatic diisocyanate, an aromatic diisocyanate derivative, an aliphatic diisocyanate derivative, a polymethylene polyphenyl isocyanate or a mixture thereof. For example, the aromatic diisocyanate can be but not limited to toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), naphthalene diisocyanate (NDI), p-phenylene diisocyanate (PPDI), xylylene diisocyanate (XDI), dimethyl diphenyl diisocyanate (TODI), dimethyl diphenylmethane diisocyanate (DMMDI) or a mixture of more than one thereof; the aliphatic diisocyanate can be but not limited to isophorone isocyanate (IPDI), hexamethylene diisocyanate (HDI), dicyclohexylmethane diisocyanate (H ₁₂ The aromatic diisocyanate derivative may be, but is not limited to, toluene diisocyanate dimer (TDI-dimer), toluene diisocyanate trimer (TDI-trimer) or a mixture thereof; the aliphatic diisocyanate derivative may be, but is not limited to, toluene diisocyanate dimer (TDI-dimer), toluene diisocyanate trimer (TDI-trimer) or a mixture thereof; the The cyanate derivative may be, but is not limited to, one of hexamethylene diisocyanate dimer (HDI-dimer), hexamethylene diisocyanate trimer (HDI-trimer), hexamethylene diisocyanate biuret (HDI Biuret), isophorone isocyanate trimer (IPDI-trimer), or a mixture of more than one of them.

In addition, the isocyanate reactive component may be a polyester polyol, a polyether polyol, a small molecule multifunctional compound or a mixture thereof. For example, the polyester polyol may be, but not limited to, a mixture of one or more of adipic acid polyester polyol, aromatic polyester polyol, polycaprolactone diol, and polycarbonate diol; the polyether polyol may be, but not limited to, a mixture of one or more of polyoxypropylene polyol, polyoxyethylene polyol, and polytetrahydrofuran polyol; the small molecule multifunctional compound may be, but not limited to, a mixture of one or more of water, diols, polyols, alcohol amines, and diamine compounds.

Specifically, the diol may be, but is not limited to, ethylene glycol, 1,4-butanediol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, neopentyl glycol, methyl propylene glycol, 1,6-hexanediol, 1,3-propylene glycol, dipropylene glycol, tripropylene glycol, butyl ethyl propylene glycol, diethyl pentanediol, 3-methyl-1,5-pentanediol, 1,3-butanediol, 1,2-butanediol, 2,3- Butanediol, trimethylpentanediol, cyclohexanediol or 1,4-dihydroxymethylcyclohexane; the polyol may be but not limited to trimethylolpropane, glycerol, trimethylolethane, 1,2,6-hexanetriol, trihydroxyethyl isocyanurate, pentaerythritol, xylitol or sorbitol; the amine may be but not limited to triethanolamine, diethanolamine, triisopropanolamine, methyldiethanolamine, dihydroxyisopropylaniline, dihydroxyisopropylparatoluene The diamine compound may be, but is not limited to, 3,3'-dichloro-4,4'-diphenylmethanediamine, 3,5-dimethylthiotoluenediamine, 3,5-diethyltoluenediamine, 4,4'-methylenebis(3-chloro-2,6-diethylaniline), 4,4'-methylenebis(2,6-diethylaniline), 4,4'-methylenebis(2,6-diisopropylaniline), 4,4'-methylenebis(2-isopropyl-6-methylaniline), 4,4'-methylenebis(2-isopropyl-6-diethylaniline), 4,4'-methylenebis(2-ethylaniline), toluenediamine, 4,4'-diaminodiphenylmethane, isophoronediamine, diaminodicyclohexylmethane, trimethylhexanediamine, or dimethyldiaminodicyclohexylmethane.

Furthermore, the polyurethane foam degradation method 100 of the present invention may further include a crushing step, which is to crush the polyurethane foam to form a plurality of polyurethane foam fragments before the first mixing step, and then subject the polyurethane foam fragments to the first mixing step, wherein the size of the polyurethane foam fragments may be 30×30×500 mm, but the present invention is not limited thereto.

Step 120 is to perform a first degradation step, which is to degrade the first degradation system at a first reaction temperature to form a liquid degradation liquid mixture and an insoluble matter, and remove the liquid degradation liquid mixture, wherein the amount (weight) of the liquid degradation liquid mixture removed is 40% to 100% of the amount (weight) of the first degradation liquid added, and the first reaction temperature may be 110° C. to 170° C. In detail, in the first degradation step, the first degradation system may be maintained at the first reaction temperature for a first degradation time, which may be 30 minutes to 3 hours, and the insoluble matter refers to undegraded polyurethane foam or polyurethane foam fragments. It should be understood that the morphology of the polyurethane foam or polyurethane foam fragments may change before and after the execution of step 120. Specifically, in this embodiment, the undegraded polyurethane foam or polyurethane foam fragments after the execution of step 120 may be in a paste state, and in other embodiments, the undegraded polyurethane foam fragments may be a mixture of fragments and paste, but the present invention is not limited thereto.

Step 130 is a second mixing step, which is to mix the insoluble matter with a second degradation liquid to form a second degradation system. In detail, the second degradation liquid can be a polyester polyol, a polyether polyol, a small molecule multifunctional compound or a mixture thereof of an isocyanate reactive component, and in this embodiment, the second degradation liquid and the first degradation liquid have different hydrophilicity and hydrophobicity, wherein the molecular characteristics of the second degradation liquid are closer to those of the polyol, thereby performing a second degradation of the insoluble matter in step 120, wherein the amount of the second degradation liquid added is based on the polyurethane foam added in step 110, and the mass ratio of the polyurethane foam to the second degradation liquid can be 1:0.1 to 1:3, that is, the amount of the second degradation liquid added can be 0.1 to 3 times the mass of the polyurethane foam added in step 110. The types of polyester polyols, polyether polyols and small molecule multifunctional compounds can be referred to the above description, and will not be repeated here.

Step 140 is to perform a second degradation step, which is to degrade the second degradation system at a second reaction temperature, cool it down and stand it for stratification to obtain an intermediate product in the upper layer, wherein the second reaction temperature can be 110°C to 170°C. In detail, in the second degradation step, the second degradation body can be maintained at the second reaction temperature for a second degradation time, which can be 30 minutes to 4 hours. After the degradation is completed, the temperature is reduced to 50°C to 100°C and stirred for 30 minutes to 2 hours, and the degradation of the polyurethane foam is completed. Furthermore, the degradation solution after the degradation is allowed to stand for stratification, and the intermediate product in the upper layer can include the first degradation solution, the second degradation solution and a polyol mixture, and the lower layer can include amine products, wherein the amine products will be different according to the type of isocyanate used in the synthesis of the polyurethane foam. For example, when the polyurethane foam is synthesized with toluene diisocyanate, toluene diamine, i.e. the aforementioned amine products, will be produced during its degradation.

Step 150 is to perform a decompression step, which is to remove the remaining first degradation liquid from the intermediate product under a reaction pressure to obtain a polyol, wherein the reaction pressure can be 1 mbar to 1000 mbar. In detail, since there may still be remaining first degradation liquid after the first degradation step and the second degradation step, the first degradation liquid is distilled and separated in a low-pressure environment by virtue of its low boiling point. Therefore, the intermediate product can be removed from the excess first degradation liquid at a high temperature of 110° C. to 160° C. and a pressure of 1 mbar to 1000 mbar to obtain a degraded polyol, which can be reused in the synthesis of polyurethane foam, and the functionality of the degradation product can be calculated by the hydrogen oxygen value, the change in the viscosity of the prepolymerization reaction, etc., and the degradation product can be reused in the fields of polyurethane rigid foam, soft foam, polyurethane adhesive or thermoplastic polyurethane, and the first degradation liquid removed by high temperature and decompression can be repeatedly used as the degradation liquid of polyurethane foam.

Thus, the present invention can further promote the degradation of polyurethane foam and reduce the generation of insoluble matter through two-stage degradation, so as to improve the recovery ratio of degraded polyols. Finally, stirring at 50°C to 100°C can promote the precipitation of insoluble matter, so as to improve the efficiency of stratified sampling and reduce the precipitate generated after long-term storage of the recovered degraded polyols, thereby improving the quality stability of the degraded polyols.

The present invention is further illustrated by the following specific embodiments, which are used to facilitate those skilled in the art to which the present invention belongs, so that they can fully utilize and practice the present invention without excessive interpretation. These embodiments should not be regarded as limiting the scope of the present invention, but are used to illustrate how to implement the materials and methods of the present invention.

<Example/Comparative Example>

<Degradable polyurethane foam>

Example 1: 200 g of the first degradation solution of diethanolamine was placed in a 500 mL glass reactor and heated to 150°C, then 100 g of polyurethane foam was added and reacted for 1.5 hours until the solution became transparent and clear. When there are floating insolubles, remove 160 grams of the first degradation solution. Then, add 50 grams of the second degradation solution of polyether polyol (molecular weight 2000), heat to 165 ° C and react for 3 hours. After the reaction is completed, start cooling to 60 ° C and continue stirring for 1.5 hours. After the stirring is completed, the degradation solution is allowed to stand to separate, and then the upper layer is taken and distilled under reduced pressure at a temperature of 130 ° C and a pressure of 10 mbar for 1.5 hours to obtain liquefied polyether polyol. It was determined that the OH value of the liquefied polyether polyol prepared in Example 1 was 100, the viscosity was 1200 cps, and the recovery rate of polyurethane foam was 75%.

Example 2: After 300 grams of the first degradation solution of isopropanolamine is placed in a 500mL glass reactor and heated to 130°C, 100 grams of polyurethane foam fragments (waste polyurethane foam) are continuously and slowly added and reacted for 2 hours. When the solution becomes transparent and clear, 150 grams of the first degradation solution are removed. Then, 50 grams of the second degradation solution of 1,4-butanediol is added, heated to 165°C and reacted for 2 hours. After the reaction is completed, the temperature is lowered to 70°C and stirred for 1 hour. After the stirring is completed, the degradation solution is allowed to stand to separate, and the upper layer liquid is taken and distilled under reduced pressure at a temperature of 100°C and a pressure of 10mbar for 2 hours to obtain a liquefied polyether polyol. It was determined that the OH value of the liquefied polyether polyol prepared in Example 2 was 750, the viscosity was 600cps, and the recovery rate of polyurethane foam fragments (waste polyurethane foam) was 85%.

Example 3: 300 grams of the first degradation solution of diethanolamine was placed in a 500 mL glass reactor and heated to 110°C, then 100 grams of polyurethane foam fragments (waste polyurethane foam) were slowly added continuously and reacted for 3 hours, and then 200 grams of the first degradation solution were removed. Then, 50 grams of the second degradation solution of ethylene glycol was added, heated to 165°C and reacted for 4 hours. After the reaction was completed, the temperature was lowered to 100°C and stirred for 1 hour. After the stirring was completed, the degradation solution was allowed to stand to separate, and the upper layer was taken and distilled under reduced pressure at a temperature of 100°C and a pressure of 10 mbar for 2 hours to obtain liquefied polyether polyol. It was determined that the OH value of the liquefied polyether polyol prepared in Example 3 was 850, the viscosity was 800 cps, and the recovery rate of polyurethane foam fragments (waste polyurethane foam) was 72%.

Example 4: After 300 grams of the first degradation solution of diisopropanolamine was placed in a 500 mL glass reactor and heated to 160°C, 100 grams of polyurethane foam fragments (waste polyurethane foam) were continuously and slowly added and reacted for 1 hour, and then 260 grams of the first degradation solution were removed. Then, 100 grams of the second degradation solution of ethylene glycol was added, heated to 160°C and reacted for 2 hours. After the reaction was completed, the temperature was lowered to 80°C and stirred for 2 hours. After the stirring was completed, the degradation solution was allowed to stand to separate, and the upper layer liquid was taken and distilled under reduced pressure at a temperature of 100°C and a pressure of 10mbar for 2 hours to obtain a liquefied polyether polyol. The liquefied polyether polyol prepared in Example 4 was measured by OH value, and the recovery rate of the polyurethane foam fragments (waste polyurethane foam) was 60%.

In the above-mentioned embodiments 1 to 4, the polyurethane foam or polyurethane foam fragments can be mixed with the first degradation liquid and then heated, or the first degradation liquid can be heated first and then mixed with the polyurethane foam or polyurethane foam fragments. For example, the first degradation liquid is heated to a temperature lower than the first reaction temperature and then mixed with the polyurethane foam or polyurethane foam fragments. Preferably, the first degradation liquid is heated to the first reaction temperature and then mixed with the polyurethane foam or polyurethane foam fragments, which can shorten the degradation time, but the present invention is not limited thereto.

<Polyurethane foam degradation cost>

In order to compare the degradation cost between the present invention and the known degradation technology, 2000 grams of polyurethane foam were also taken for degradation, and the substances added during the degradation process are shown in Table 1 below, where Example 5 is the technology of the present invention, and Comparative Example 1 is the known degradation technology. In addition, in Table 1, the degradation liquid used in Example 5 is an alcohol amine compound, that is, the present invention The first degradation solution of the comparative example 1 is potassium hydroxide and sodium carbonate in the first stage of degradation, and sulfuric acid and benzenesulfonic acid in the second stage of degradation.

As can be seen from Table 1 above, during the degradation process, a total of 8220 grams of additives were added in Comparative Example 1 of the known technology, and these additives could not be recycled, while only 5000 grams of additives were added in Example 5 of the present invention, and the degradation liquid could be recycled by vacuum distillation, which greatly reduced the use of additives and reduced the degradation cost in the process of degrading polyurethane foam.

In summary, the advantages of the polyurethane foam degradation method of the present invention are as follows. First, the first degradation liquid used in the present invention is a conventional compound, which is easy to be distilled and separated in a low-pressure environment, and can be reused to degrade soft polyurethane materials, which can reduce the degradation cost of soft polyurethane foam and improve the price competitiveness of the polyols obtained after degradation. Second, the structure of the first degradation liquid used in the present invention has both amines and alcohol structures containing active hydrogen, which can degrade carbamate and urea structures, and the formation of aromatic polyamine compounds can be reduced by controlling the degradation temperature. Third, the degradation method of the present invention can efficiently improve the yield of polyols obtained by degrading soft polyurethane foam.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims (14)

A method for degrading polyurethane foam, characterized by comprising: A first mixing step is performed, which is to mix a polyurethane foam with a first degradation liquid to form a first degradation system, and the first degradation liquid has a structure as shown in formula (I) or formula (II):

Wherein, R is an alkylene group having 2 to 6 carbon atoms or its structural isomers, phenyl group and its derivatives; Performing a first degradation step, which is to degrade the first degradation system at a first reaction temperature to form a liquid degradation solution mixture and an insoluble substance, and removing the liquid degradation solution mixture; Performing a second mixing step, which is to mix the insoluble matter with a second degradation liquid to form a second degradation system; Performing a second degradation step, which is to degrade the second degradation system at a second reaction temperature, cool it down and stand it for stratification to obtain an intermediate product in the upper layer; and A decompression step is performed, wherein the intermediate product is subjected to a reaction pressure to remove the remaining first degradation liquid, so as to obtain a polyol. The method for degrading polyurethane foam according to claim 1, further comprising: A crushing step is performed before the first mixing step, wherein the polyurethane foam is crushed to form a plurality of polyurethane foam fragments. The method for degrading polyurethane foam as claimed in claim 1, wherein the polyurethane foam is obtained by a polymerization reaction, and the reactive monomers of the polymerization reaction include an isocyanate component and an isocyanate reactive component. The method for degrading polyurethane foam as claimed in claim 3, characterized in that the isocyanate component is an aromatic diisocyanate, an aliphatic diisocyanate, an aromatic diisocyanate derivative, an aliphatic diisocyanate derivative, polymethylene polyphenyl isocyanate or a mixture thereof. The method for degrading polyurethane foam as claimed in claim 3, characterized in that the isocyanate reactive component is a polyester polyol, a polyether polyol, a small molecule multifunctional compound or a mixture thereof. The method for degrading polyurethane foam according to claim 1, characterized in that the mass ratio of the polyurethane foam to the first degradation liquid is 1:0.9 to 1:3. The method for degrading polyurethane foam as claimed in claim 1, characterized in that the first reaction temperature is 110°C to 170°C. The method for degrading polyurethane foam as claimed in claim 1, characterized in that in the first degradation step, the first degradation system is maintained at the first reaction temperature for a first degradation time, and the first degradation time is 30 minutes to 3 hours. The polyurethane foam degradation method according to claim 1, wherein the amount of the liquid degradation solution mixture removed is 40% to 100% of the amount of the first degradation solution added. The method for degrading polyurethane foam according to claim 1, wherein the second degradation liquid is polyester polyol, polyether polyol, small molecule multifunctional compound or a mixture thereof. The method for degrading polyurethane foam according to claim 1, characterized in that the mass ratio of the polyurethane foam to the second degradation liquid is 1:0.1 to 1:3. The method for degrading polyurethane foam according to claim 1, wherein the second reaction temperature is 110°C to 170°C. The method for degrading polyurethane foam according to claim 1, characterized in that in the second degradation step, the second degradation system is maintained at the second reaction temperature for a second degradation time, and the second degradation time is 30 minutes to 4 hours. The method for degrading polyurethane foam according to claim 1, characterized in that the reaction pressure is 1 mbar to 1000 mbar.