Method for preparing regenerated product based on waste polyurethane rigid foam grinding powder

Abstract

The invention provides a method for preparing a regenerated product on the basis of waste polyurethane rigid foam milled powder, which comprises the following steps: firstly, recycling waste polyurethane rigid foam on the basis of a solid shearing and milling technology to realize ultrafine crushing and uniform dispersion of the polyurethane rigid foam at room temperature, and controlling the particle size and particle size distribution of the powder; then taking the obtained superfine polyurethane powder, a silane coupling agent and polyether polyol as a material A, blending the material A with isocyanate as a material B, and foaming according to a conventional polyurethane rigid foam one-step method to prepare a polyurethane rigid foam regenerated product. The invention accidentally finds that the mechanical property of the prepared regenerated polyurethane rigid foam can be obviously improved after modification; besides, tests prove that the powder obtained through grinding can replace part of polyether polyol raw materials on the premise that the performance of the regenerated product is not degraded, so that the production cost of the regenerated product is reduced, and the value of the recycled material is maximized. The method shows the potential of industrial production application.

Description

Technical Field

[0001] This invention belongs to the technical field of waste rigid polyurethane foam recycling and preparation. It relates to a method for preparing recycled products based on the grinding of waste rigid polyurethane foam into powder. Specifically, it involves using waste rigid polyurethane foam, after solid-phase shear grinding, as a reinforcing filler, and blending it with polyether polyols, isocyanates, silane coupling agents, etc., to prepare recycled rigid polyurethane foam products with superior performance. Particularly, it addresses the use of an industrial grinding disc-shaped solid-phase mechanochemical reactor disclosed in Chinese invention patent CN114534660B for the treatment of waste rigid polyurethane foam. Background Technology

[0002] Since the 20th century, polymer materials have developed rapidly, and polyurethane foam has taken a leading position among polymer materials due to its excellent mechanical properties. Polyurethane is one of the most widely used polymers, with applications in foams, coatings, elastomers, adhesives, and more. Currently, the global annual production and volume of polyurethane foam exceed 12 million tons and 400 billion cubic meters, respectively. Due to the widespread use of polyurethane materials, its waste volume has also increased, posing a potential threat to the environment and human health. Because polyurethane foam is mostly a thermosetting polymer and an internally cross-linked polymer, it can be preserved for hundreds of years or even longer under natural conditions. Currently, polyurethane disposal methods include landfill, incineration, and recycling. However, traditional landfill and incineration can damage the ecosystem, while recycling and reusing waste polyurethane is a more environmentally friendly treatment method than these traditional waste disposal methods.

[0003] The recycling and reuse of waste polyurethane mainly includes crushing, thermal decomposition, physical recycling, chemical recycling, and energy recovery. However, thermosetting polyurethane foam is difficult to recycle economically and efficiently due to its cross-linked structure. It is estimated that approximately 91% of polyurethane foam waste is disposed of through landfill or incineration, with only 9% being mechanically recycled and chemically degraded. However, incineration produces harmful gases such as isocyanate fumes, hydrogen cyanide, or nitrogen oxides, which have a significant impact on the ecological environment. Therefore, recycling polyurethane waste is beneficial for reducing the consumption of fossil resources at the source, thereby achieving carbon emission reduction and lowering production costs. Crushing is one of the most promising methods for recycling polyurethane waste.

[0004] Through research, Li et al. successfully pulverized commercially available polyurethane foam into powder with a particle size of 74.5 μm and a specific surface area as high as 2991.0 m² using an innovative ball milling pretreatment method. 2 / kg; This superior powder significantly enhances the exchange reaction of polyurethane when in close contact with the catalyst, providing new opportunities for further research and development (Li, J.; Zhu, H.; Fang, D.; Huang, X.; Zhang, C.; Luo, Y., Mechanochemistry recycling of polyurethane foam using urethane exchange reaction. Journal of Environmental Chemical Engineering 2023, 11(3).).

[0005] However, conventional crushing and recycling methods struggle to achieve ultra-fine crushing and uniform dispersion of polyurethane foam, resulting in low recycling rates for waste polyurethane materials and hindering large-scale industrial production. Solid-state shear milling technology (S...) 3 M) combines the physicochemical structure and mechanochemical mechanism of polymers to form a unique three-dimensional shear structure, possessing multiple functions such as crushing, dispersing, mixing, and mechanochemical reactions. By utilizing the powerful three-dimensional shear force of solid-state shear milling technology, waste cross-linked polymers can achieve molecular chain recombination at room temperature. This process partially restores the thermoplasticity of the material, making it thermally reprocessable. This method effectively solves the challenge of recycling and reusing waste cross-linked polymer materials.

[0006] For example, in the use of solid shear milling technology, Lu et al. from Sichuan University successfully achieved selective cleavage of Si-O and OO bonds in cross-linked polyethylene (XLPE), which destroyed the cross-linked structure, enhanced melt flowability and plasticity, and produced a product with excellent appearance and mechanical properties, with a tensile strength of 18.6 MPa and an elongation at break of 350%. Phase domain modulation through solid-state shear milling technology has successfully enabled the high-value recycling and reuse of multiple components of complex mixed waste polymer materials (Zhang, XX; Lu, CH; Liang, M., Devulcanisation of natural rubber vulcanisate through solid state mechanochemical milling at ambient temperature. Plastics Rubber & Composites 2013, 36(7-8), 370-376.; Wu, H.; Liang, M.; Lu, C., Morphological and structural development of recycled crosslinked polyethylene during solid-state mechanochemical milling. Journal of Applied Polymer Science 2011, 122(1), 257-264.).

[0007] However, in applying solid-state shear milling technology to the recycling and reuse of other thermosetting plastics, we have noticed that some waste polymer materials, after being processed by solid-state shear milling, still exhibit a problem where the added powder, when used as a filler, leads to a deterioration in the mechanical properties of the recycled products compared to conventional products without the powder. This deterioration trend is observed even with small amounts added. Furthermore, replacing the raw materials of recycled products with the milled powder results in a significant deterioration in the mechanical properties of the recycled products. These shortcomings clearly limit the application avenues and recycling capacity of this type of solid waste polymer recycling and reuse, and fail to highlight the cost advantages of recycling and reuse. Summary of the Invention

[0008] To address the problems in the prior art, this invention provides a method for preparing recycled products based on waste rigid polyurethane foam powder. This method first utilizes solid-state shear milling technology to recycle waste rigid polyurethane foam, achieving ultrafine grinding and uniform dispersion of the foam at room temperature, and controlling the particle size and distribution, thereby improving grinding efficiency, optimizing powder morphology, and refining surface functional groups. Then, a silane coupling agent is used for modification, unexpectedly revealing a significant improvement in the mechanical properties of the prepared recycled rigid polyurethane foam after modification. Furthermore, experiments demonstrate that the milled powder can replace a portion of the polyether polyol raw materials without degrading the performance of the recycled products, thereby reducing the production cost of the recycled products and maximizing the value of the recycled materials. This method demonstrates its potential for industrial application.

[0009] To achieve the above-mentioned objectives, the present invention adopts a technical solution consisting of the following technical measures.

[0010] This invention provides a method for preparing recycled products based on waste rigid polyurethane foam powder, mainly including the following steps:

[0011] (1) After pretreatment including washing, the waste rigid polyurethane foam is crushed into polyurethane crushed material with an average particle size of no more than 100 μm.

[0012] (2) The polyurethane crushed material obtained in step (1) is added to a grinding disc-shaped solid-phase mechanical chemical reactor for grinding and pulverizing. After grinding is completed, polyurethane ultrafine powder is collected. The process parameters of the grinding disc-shaped solid-phase mechanical chemical reactor are: grinding pressure of 2-4 MPa, circulating cooling liquid at 10-20℃ is introduced to control the temperature of the grinding disc surface, the grinding is at least 3 times, and the grinding disc speed is 40-50 rpm.

[0013] (3) Using the polyurethane ultrafine powder obtained in step (2) as raw material, prepare material A and material B by weight according to the conventional one-step foaming method for rigid polyurethane foam. Material A and material B respectively include the following components:

[0014] Material A:

[0015]

[0016] Material B:

[0017] 150 parts isocyanate;

[0018] (4) Mix A and B materials evenly to form a mixture. Inject the mixture into a mold according to the conventional one-step foaming method for rigid polyurethane foam. After curing at room temperature, a recycled rigid polyurethane foam product is obtained.

[0019] In this article, step (1) includes a pretreatment of washing, which mainly involves cleaning the surface of the waste rigid polyurethane foam and removing impurities. Those skilled in the art can carry out specific treatment based on the actual condition of the waste rigid polyurethane foam that needs to be recycled, according to existing technologies.

[0020] Typically, the waste rigid polyurethane foam mentioned in step (1) can be rigid polyurethane foam material or products made of rigid polyurethane foam material that has been recycled and collected after being discarded, or it can be waste scraps generated during the production process of rigid polyurethane foam.

[0021] In this article, the polyurethane crushed material with an average particle size of no more than 100 μm as described in step (1) can be crushed using conventional tearing or crushing methods, such as by using existing conventional tearing or crushing equipment such as single-shaft and bi-shaft tearing machines and jaw crushers.

[0022] The millstone-shaped solid-phase mechanochemical reactor mentioned in step (2) is the industrial millstone-shaped solid-phase mechanochemical reactor disclosed in the prior invention patent CN114534660B of the applicant of this invention.

[0023] It should be noted that this industrial millstone-shaped solid-phase mechanochemical reactor is an industrial device that is an improvement on the mechanochemical reactor disclosed in the prior authorized patent ZL95111258.9. It is significantly different from the structure of the laboratory prototype machine when ZL95111258.9 was applied for. It has designed a brand-new millstone structure for industrial high-efficiency mechanochemical grinding, which has been improved from the previous vertical millstone setting to a horizontal setting, and the size of the millstone has been greatly increased. Based on the horizontal setting and large size of the millstone, related fixed millstone components and hydraulic lifting system have been innovatively designed, which greatly improves its three-dimensional shear force.

[0024] Typically, the number of grinding cycles in step (2) is at least 3, which is essentially a cyclic grinding process; for example, after the material is ground in a disc-shaped solid-state chemical reactor, the product at the discharge end is collected and then placed in a disc-shaped solid-state chemical reactor for grinding again. The above process is considered to be 2 grinding cycles.

[0025] Typically, in step (2), the temperature of the grinding disc surface is controlled by circulating a cooling liquid at 10-20°C. The cooling liquid is water, ethylene glycol, or glycerin.

[0026] It should be noted that the applicant's prior published papers and patents have provided substantial experimental evidence and analytical research on the outstanding contributions of the disc-shaped solid-phase chemical reactor to solid waste recycling. However, it must be pointed out and emphasized that the solid-phase shear grinding technology used in the disc-shaped solid-phase chemical reactor is a purely physical and mechanical grinding and pulverizing method. Currently, there is no direct evidence to prove that it is applicable to all polymer solid wastes. For example, the applicant's prior patent application "A waste cross-linked polyethylene recycling material and its recycling method" (CN104385485A) discloses a waste cross-linked polyethylene recycling material and its recycling method. This method can grind waste cross-linked polyethylene (XLPE) into powder using solid-phase shear grinding technology. However, low-density polyethylene (LDPE), which has higher toughness, cannot be ground into powder using solid-phase shear grinding technology without grinding aids. In addition, depending on the degree of cross-linking of polymer materials and other objective factors, when the collected powder is directly used as filler after grinding and pulverizing some polymer materials in the disc-shaped solid-phase chemical reactor, there is an objective phenomenon that it may lead to the deterioration of the performance of recycled products.

[0027] In the experimental phase of this invention, we first studied the particle size, particle size distribution, and microstructure of polyurethane ultrafine powder under different milling cycles. Then, we directly used polyurethane ultrafine powder as a filler to prepare recycled rigid polyurethane foam products and compared the mechanical properties of the recycled products prepared with different filler contents. The results showed that when the amount of polyurethane ultrafine powder added was 1.5 to 4.5 parts (based on a 1:1 ratio of polyether polyol to isocyanate, the amount of polyurethane ultrafine powder added was 1 to 3 wt% of the polyether polyol), the compressive strength of the prepared recycled products was better than that of the control sample without polyurethane ultrafine powder. However, when the amount of polyurethane ultrafine powder added exceeded 7.5 parts (5 wt%), the compressive strength of the recycled products showed a very obvious deterioration trend, and in a certain batch of recycled product samples, it was found that its compressive strength was lower than that of the control sample without polyurethane ultrafine powder.

[0028] This experimental evidence clearly shows that when waste rigid polyurethane foam is milled in a solid-state mechanical chemical reactor, the resulting ultrafine polyurethane powder is used as a filler to prepare recycled rigid polyurethane foam products. However, the amount of filler added is very limited without deteriorating the mechanical properties. This is obviously not conducive to the current recycling and processing of waste rigid polyurethane foam, and it fails to highlight the cost advantage of recycling and reuse.

[0029] Based on the aforementioned experimental evidence, the inventors, while attempting to change their approach, accidentally discovered that adding silane coupling agent KH-550 and polyurethane ultrafine powder together to component A in the preparation of rigid polyurethane foam significantly enhanced the mechanical properties of the resulting recycled rigid polyurethane foam. Furthermore, when the amount of polyurethane ultrafine powder added reached 5–9 wt% of the polyether polyol, the compressive strength reached its optimal level. Building upon this, and considering that the preparation of rigid polyurethane foam from waste polyurethane foam can be viewed as using homologous raw materials, they attempted to reduce the amount of polyether polyol added to component A. They found that by using polyurethane ultrafine powder as a reinforcing filler while partially replacing the polyether polyol, the resulting recycled products still exhibited significant advantages in mechanical properties, thereby reducing the production cost of recycled products and maximizing the value of recycled materials.

[0030] It should be noted that rigid polyurethane foam is a common industrial material on the market. Its preparation method usually involves foaming polyol and isocyanate as A / B materials (or white / black materials) in one step. The generally accepted mass ratio of polyol to isocyanate is 1:1.

[0031] In this document, the polyether polyol mentioned in step (3) is a conventional polyether polyol selection for preparing rigid polyurethane foam. Those skilled in the art can refer to the polyether polyol selection that can be used as raw material for rigid polyurethane foam as described in the prior art.

[0032] In this document, the isocyanate mentioned in step (3) is a conventional isocyanate selection for preparing rigid polyurethane foam. Those skilled in the art can refer to the isocyanate selections that can be used as raw materials for rigid polyurethane foam as described in the prior art.

[0033] In this paper, the raw material components in materials A and B mentioned in step (3) also include conventional catalysts / stabilizers / functional additives used in the preparation of rigid polyurethane foam in the prior art, such as triethylenediamine, diethanolamine, divalent tin, silicone oil, etc. However, it should be noted that those skilled in the art, based on the preparation principle of rigid polyurethane foam, know that the above-mentioned conventional catalysts / stabilizers / functional additives are not essential components.

[0034] In this article, step (4) describes mixing material A and material B evenly as a mixture, injecting the mixture into a mold according to the conventional one-step foaming method for rigid polyurethane foam, and preparing a recycled rigid polyurethane foam product after curing at room temperature. Those skilled in the art can know the specific process flow and operation based on the existing one-step foaming preparation process for rigid polyurethane foam or existing technical literature.

[0035] To better illustrate the present invention and provide a technical solution for reference, in step (4), material A and material B are mixed evenly as a mixture. The mixture is injected into a mold according to the conventional one-step foaming method for rigid polyurethane foam. After curing at room temperature, a recycled rigid polyurethane foam product is prepared. Specifically, material A and material B are mixed evenly at 40°C and 100r / min mechanical stirring conditions as a mixture. Then, the mixture is sprayed into a mold for self-foaming and cured at room temperature for 24 hours to prepare a recycled rigid polyurethane foam product.

[0036] In this document, the mixing and maturation processes described follow conventional principles in chemical processes, and those skilled in the art can perform the specific operations based on common knowledge.

[0037] The present invention has the following beneficial effects:

[0038] (1) This invention provides a method for preparing recycled products based on waste rigid polyurethane foam powder. The method first recycles and processes waste rigid polyurethane foam based on solid shear milling technology, realizing ultrafine grinding and uniform dispersion of rigid polyurethane foam at room temperature, and controlling the particle size and particle size distribution of the powder, thereby improving the grinding efficiency, optimizing the powder morphology, and refining the surface functional groups.

[0039] (2) The technical solution of the present invention uses silane coupling agent for modification, and it was unexpectedly found that the mechanical properties of the prepared recycled polyurethane rigid foam can be significantly improved after modification. In addition, the test proved that the powder obtained by milling can replace part of the polyether polyol raw material without deteriorating the performance of the recycled product, thereby reducing the production cost of the recycled product and maximizing the value of the recycled material.

[0040] (3) The process of this invention is simple to operate and can be continuously produced using existing industrial equipment, and has the potential for industrial production applications. Attached Figure Description

[0041] Figure 1 Figure 2 shows the particle size distribution of the polyurethane ultrafine powder obtained in Verification Examples 2 and 5 of this invention. Figure 3 shows the particle size distribution of the polyurethane ultrafine powder obtained in Verification Example 2, and Figure 4 shows the particle size distribution of the polyurethane ultrafine powder obtained in Verification Example 5.

[0042] Figure 2These are electron microscope (EM) images of the polyurethane ultrafine powder and the polyurethane crushed material before grinding obtained in Verification Examples 2 and 5 of this invention. Figures (a) and (b) are 150x and 1000x magnified EEM images of the polyurethane ultrafine powder obtained in Verification Example 2, respectively; Figures (c) and (d) are 1200x and 2400x magnified EEM images of the polyurethane ultrafine powder obtained in Verification Example 5, respectively; and Figures (e) and (f) are 150x and 500x magnified EEM images of the polyurethane crushed material before grinding, respectively.

[0043] Figure 3 The infrared spectra of the polyurethane ultrafine powders obtained in Examples 1-5 of this invention are shown. Among them, R-PUF Powder with S 3 The number following M indicates the number of grinding cycles.

[0044] Figure 4 The image shows a line graph comparing the compressive strength of the samples prepared in Examples 1-3 and Comparative Examples 1-8 of this invention.

[0045] The red line segments correspond to the compressive strength of the samples prepared in Examples 1-3 and Comparative Examples 1-2 with the addition of silane coupling agent KH-550; the black line segments correspond to the compressive strength of the samples prepared in Comparative Examples 3-8 without the addition of silane coupling agent KH-550.

[0046] Figure 5 This is a bar chart comparing the compressive strength of samples prepared in Examples 4-8 and Comparative Examples 9-18 of the present invention. The orange column (Original PU) corresponds to the samples prepared in Examples 9-13; the green column (5 wt.% Powder Addition) corresponds to the samples prepared in Examples 14-18; and the purple column (Coupling Agent Modified PU) corresponds to the samples prepared in Examples 4-8. Detailed Implementation

[0047] To further understand the present invention, preferred embodiments are described below with reference to examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims. Those skilled in the art can refer to the content of this document to appropriately improve the process parameters. In particular, it should be noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included within the scope of the present invention. The methods and applications of the present invention have been described through preferred embodiments, and those skilled in the art can obviously make modifications or appropriate changes and combinations to the methods and applications described herein without departing from the content, spirit and scope of the present invention to realize and apply the technology of the present invention. Although it is believed that those skilled in the art will fully understand the following terms, the following definitions are set forth to help illustrate the subject matter disclosed in the present invention.

[0048] This invention provides a method for preparing recycled products based on waste rigid polyurethane foam powder, mainly including the following steps:

[0049] (1) After pretreatment including washing, the waste rigid polyurethane foam is crushed into polyurethane crushed material with an average particle size of no more than 100 μm.

[0050] (2) The polyurethane crushed material obtained in step (1) is added to a grinding disc-shaped solid-phase mechanical chemical reactor for grinding and pulverizing. After grinding is completed, polyurethane ultrafine powder is collected. The process parameters of the grinding disc-shaped solid-phase mechanical chemical reactor are: grinding pressure of 2-4 MPa, circulating cooling liquid at 10-20℃ is introduced to control the temperature of the grinding disc surface, the grinding is at least 3 times, and the grinding disc speed is 40-50 rpm.

[0051] (3) Using the polyurethane ultrafine powder obtained in step (2) as raw material, prepare material A and material B by weight according to the conventional one-step foaming method for rigid polyurethane foam. Material A and material B respectively include the following components:

[0052] Material A:

[0053]

[0054] Material B:

[0055] 150 parts isocyanate;

[0056] (4) Mix A and B materials evenly to form a mixture. Inject the mixture into a mold according to the conventional one-step foaming method for rigid polyurethane foam. After curing at room temperature, a recycled rigid polyurethane foam product is obtained.

[0057] In this article, step (1) includes a pretreatment of washing, which mainly involves cleaning the surface of the waste rigid polyurethane foam and removing impurities. Those skilled in the art can carry out specific treatment based on the actual condition of the waste rigid polyurethane foam that needs to be recycled, according to existing technologies.

[0058] Typically, the waste rigid polyurethane foam mentioned in step (1) can be rigid polyurethane foam material or products made of rigid polyurethane foam material that has been recycled and collected after being discarded, or it can be waste scraps generated during the production process of rigid polyurethane foam.

[0059] In this article, the polyurethane crushed material with an average particle size of no more than 100 μm described in step (1) can be crushed using conventional tearing or crushing methods to facilitate its placement into a grinding disc-shaped solid-phase chemical reactor for grinding. In one embodiment, it can be processed by existing conventional tearing or crushing equipment such as uniaxial and biaxial tearing machines or jaw crushers.

[0060] The millstone-shaped solid-phase mechanochemical reactor mentioned in step (2) is the industrial millstone-shaped solid-phase mechanochemical reactor disclosed in the prior invention patent CN114534660B of the applicant of this invention.

[0061] It should be noted that this industrial millstone-shaped solid-phase mechanochemical reactor is an industrial device that is an improvement on the mechanochemical reactor disclosed in the prior authorized patent ZL95111258.9. It is significantly different from the structure of the laboratory prototype machine when ZL95111258.9 was applied for. It has designed a brand-new millstone structure for industrial high-efficiency mechanochemical grinding, which has been improved from the previous vertical millstone setting to a horizontal setting, and the size of the millstone has been greatly increased. Based on the horizontal setting and large size of the millstone, related fixed millstone components and hydraulic lifting system have been innovatively designed, which greatly improves its three-dimensional shear force.

[0062] Typically, the number of grinding cycles in step (2) is at least 3, which is essentially a cyclic grinding process; for example, after the material is ground in a disc-shaped solid-state chemical reactor, the product at the discharge end is collected and then placed in a disc-shaped solid-state chemical reactor for grinding again. The above process is considered to be 2 grinding cycles.

[0063] Typically, the temperature of the grinding disc surface is controlled by circulating a cooling liquid at 10-20°C in step (2). In one embodiment, the cooling liquid is water, ethylene glycol, or glycerin.

[0064] In one embodiment, the process parameters of the millstone-shaped solid-phase mechanochemical reactor in step (2) are as follows: the milling pressure is 2 to 4 MPa, for example, 2 MPa, 2.5 MPa, 3 MPa, 3.5 MPa, 4 MPa or any range or point value between them; a circulating cooling liquid at 10 to 20°C is introduced to control the temperature of the millstone surface, for example, 10°C, 15°C, 20°C or any range or point value between them; the number of milling cycles is at least 3, for example, 3, 4, 5, 6, 7, 8, 9 or 10 times; the millstone rotation speed is 40 to 50 rpm, for example, 40 rpm, 45 rpm, 50 rpm or any range or integer between them.

[0065] It should be noted that the applicant's prior published papers and patents have provided substantial experimental evidence and analytical research on the outstanding contributions of the disc-shaped solid-phase chemical reactor to solid waste recycling. However, it must be pointed out and emphasized that the solid-phase shear grinding technology used in the disc-shaped solid-phase chemical reactor is a purely physical and mechanical grinding and pulverizing method. Currently, there is no direct evidence to prove that it is applicable to all polymer solid wastes. For example, the applicant's prior patent application "A waste cross-linked polyethylene recycling material and its recycling method" (CN104385485A) discloses a waste cross-linked polyethylene recycling material and its recycling method. This method can grind waste cross-linked polyethylene (XLPE) into powder using solid-phase shear grinding technology. However, low-density polyethylene (LDPE), which has higher toughness, cannot be ground into powder using solid-phase shear grinding technology without grinding aids. In addition, depending on the degree of cross-linking of polymer materials and other objective factors, when the collected powder is directly used as filler after grinding and pulverizing some polymer materials in the disc-shaped solid-phase chemical reactor, there is an objective phenomenon that it may lead to the deterioration of the performance of recycled products.

[0066] In the experimental phase of this invention, we first studied the particle size, particle size distribution, and microstructure of polyurethane ultrafine powder under different milling cycles. Then, we directly used polyurethane ultrafine powder as a filler to prepare recycled rigid polyurethane foam products and compared the mechanical properties of the recycled products prepared with different filler contents. The results showed that when the amount of polyurethane ultrafine powder added was 1.5 to 4.5 parts (based on a 1:1 ratio of polyether polyol to isocyanate, the amount of polyurethane ultrafine powder added was 1 to 3 wt% of the polyether polyol), the compressive strength of the prepared recycled products was better than that of the control sample without polyurethane ultrafine powder. However, when the amount of polyurethane ultrafine powder added exceeded 7.5 parts (5 wt%), the compressive strength of the recycled products showed a very obvious deterioration trend, and in a certain batch of recycled product samples, it was found that its compressive strength was lower than that of the control sample without polyurethane ultrafine powder.

[0067] This experimental evidence clearly shows that when waste rigid polyurethane foam is milled in a solid-state mechanical chemical reactor, the resulting ultrafine polyurethane powder is used as a filler to prepare recycled rigid polyurethane foam products. However, the amount of filler added is very limited without deteriorating the mechanical properties. This is obviously not conducive to the current recycling and processing of waste rigid polyurethane foam, and it fails to highlight the cost advantage of recycling and reuse.

[0068] Based on the aforementioned experimental evidence, the inventors, while attempting to change their approach, accidentally discovered that adding silane coupling agent KH-550 and polyurethane ultrafine powder together to component A in the preparation of rigid polyurethane foam significantly enhanced the mechanical properties of the resulting recycled rigid polyurethane foam. Furthermore, when the amount of polyurethane ultrafine powder added reached 5–9 wt% of the polyether polyol, the compressive strength reached its optimal level. Building upon this, and considering that the preparation of rigid polyurethane foam from waste polyurethane foam can be viewed as using homologous raw materials, they attempted to reduce the amount of polyether polyol added to component A. They found that by using polyurethane ultrafine powder as a reinforcing filler while partially replacing the polyether polyol, the resulting recycled products still exhibited significant advantages in mechanical properties, thereby reducing the production cost of recycled products and maximizing the value of recycled materials.

[0069] It should be noted that rigid polyurethane foam is a common industrial material on the market. Its preparation method usually involves foaming polyol and isocyanate as A / B materials (or white / black materials) in one step. The generally accepted mass ratio of polyol to isocyanate is 1:1.

[0070] In this document, the polyether polyol mentioned in step (3) is a conventional polyether polyol selection for preparing rigid polyurethane foam. Those skilled in the art can refer to the polyether polyol selection that can be used as raw material for rigid polyurethane foam as described in the prior art.

[0071] In this document, the isocyanate mentioned in step (3) is a conventional isocyanate selection for preparing rigid polyurethane foam. Those skilled in the art can refer to the isocyanate selections that can be used as raw materials for rigid polyurethane foam as described in the prior art.

[0072] In this paper, the raw material components in materials A and B mentioned in step (3) also include conventional catalysts / stabilizers / functional additives used in the preparation of rigid polyurethane foam in the prior art. In one embodiment, for example, triethylenediamine, diethanolamine, divalent tin, silicone oil, etc. However, it should be noted that those skilled in the art, based on the preparation principle of rigid polyurethane foam, know that the above-mentioned conventional catalysts / stabilizers / functional additives are not essential components.

[0073] In one embodiment, the polyether polyol in step (3) is 116 to 184 parts, for example, 116 parts, 117 parts, 118 parts, 119 parts, 120 parts, 121 parts, 122 parts, 123 parts, 124 parts, 125 parts, 126 parts, 127 parts, 128 parts, 129 parts, 130 parts, 131 parts, 132 parts, 133 parts, 134 parts, 135 parts, 136 parts, 137 parts, 138 parts, 1 39, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169 170 parts, 171 parts, 172 parts, 173 parts, 174 parts, 175 parts, 176 parts, 177 parts, 178 parts, 179 parts, 180 parts, 181 parts, 182 parts, 183 parts, 184 parts, or any range or point value between them; the deionized water is 0.5 to 1.5 parts, for example 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, 1 part, 1.1 parts, 1.2 parts, 1.3 parts, 1. The amount of the silane coupling agent KH-550 is 1.8 to 2.2 parts, for example, 1.8, 1.9, 2, 2.1, 2.2 parts, or any range or value between them; the amount of the polyurethane ultrafine powder is 6 to 16 parts, for example, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 parts, or any range or value between them.

[0074] In this article, step (4) describes mixing material A and material B evenly as a mixture, injecting the mixture into a mold according to the conventional one-step foaming method for rigid polyurethane foam, and preparing a recycled rigid polyurethane foam product after curing at room temperature. Those skilled in the art can know the specific process flow and operation based on the existing one-step foaming preparation process for rigid polyurethane foam or existing technical literature.

[0075] To better illustrate the present invention and provide a reference embodiment, in step (4), material A and material B are mixed evenly as a mixture. The mixture is injected into a mold according to the conventional one-step foaming method for rigid polyurethane foam. After curing at room temperature, a recycled rigid polyurethane foam product is prepared. Specifically, material A and material B are mixed evenly at 40°C and 100 r / min mechanical stirring as a mixture. Then, the mixture is sprayed into a mold for self-foaming and cured at room temperature for 24 h to prepare a recycled rigid polyurethane foam product.

[0076] In this document, the mixing and maturation processes described follow conventional principles in chemical processes, and those skilled in the art can perform the specific operations based on common knowledge.

[0077] The present application will be further explained in detail below with reference to embodiments. However, those skilled in the art should understand that these embodiments are provided for illustrative purposes only and are not intended to limit the present application.

[0078] Example

[0079] The embodiments of this application will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be construed as limiting the scope of this application. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Where the manufacturers of reagents or instruments are not specified, they are all commercially available conventional products. This application should not be construed as being limited to the specific embodiments described.

[0080] 1. Raw materials and instruments

[0081] Diphenylmethane diisocyanate (PM-200, Jining Ribuluo Biotechnology Co., Ltd., Jinan, China);

[0082] Polyether polyol (HK-4110, hydroxyl value 450±20mg KOH / g, viscosity 5500±1000mpa-s / 25℃, Jining Ribuluo Biotechnology Co., Ltd.);

[0083] Deionized water (Guangzhou Hewei Pharmaceutical Technology Co., Ltd., Guangzhou, China);

[0084] Divalent tin (T12, Jinan Dahui Chemical Technology Co., Ltd., Jinan, China);

[0085] Triethylenediamine (A33, Guangdong Fangxin Biotechnology Co., Ltd., Guangdong, China);

[0086] Diethanolamine (Guangdong Zhongpeng Chemical Co., Ltd., Guangzhou, China);

[0087] Silicone oil (Shandong Yousuo Chemical Technology Co., Ltd., Linyi, Shandong);

[0088] Silane coupling agent (KH-550, Dongguan Kangjin New Material Technology Co., Ltd., Dongguan, China).

[0089] The waste rigid polyurethane foam used was prepared in the laboratory, and its preparation method is as follows:

[0090] By weight, materials A and B are prepared, and materials A and B are respectively composed of the following components:

[0091] Material A:

[0092]

[0093] Material B:

[0094] 150 parts of diphenylmethane diisocyanate;

[0095] Materials A and B are mixed evenly at 40℃ and 100r / min to form a mixture. The mixture is then sprayed into a mold to self-foam and cured at room temperature for 24 hours to prepare rigid polyurethane foam, which is then used as waste rigid polyurethane foam for later use.

[0096] Polyurethane low-pressure foaming machine: LIXIN-2028, Dongguan Lixin Machinery Technology Co., Ltd.; This machine consists of a high-speed rotating head, A and B material tanks, and drive pipeline.

[0097] 2. Preparation method

[0098] (1) After pretreatment including washing, the waste rigid polyurethane foam is crushed into polyurethane crushed material with an average particle size of no more than 100 μm.

[0099] (2) The polyurethane crushed material obtained in step (1) is added to a grinding disc-shaped solid-phase mechanical chemical reactor for grinding and pulverizing. After grinding is completed, polyurethane ultrafine powder is collected. The process parameters of the grinding disc-shaped solid-phase mechanical chemical reactor are: grinding pressure of 3MPa, circulating cooling liquid of 10-20℃ is introduced to control the temperature of the grinding disc surface, grinding is performed 3 times, and grinding disc speed is 50 rpm.

[0100] (3) Using the polyurethane ultrafine powder obtained in step (2) as raw material, prepare material A and material B by weight, wherein material A and material B respectively include the following components:

[0101] Material A:

[0102]

[0103] Material B:

[0104] 150 parts of diphenylmethane diisocyanate;

[0105] (4) Mix A and B materials evenly under mechanical stirring conditions of 40℃ and 100r / min to obtain a mixture. Then spray the mixture into a mold to self-foam and cure it at room temperature for 24h to obtain a recycled polyurethane rigid foam product.

[0106] 3. Testing Methods

[0107] Particle size and shape analyzer: S3500-SI, Macchiak, USA. Using ethanol as the dispersion medium, the powder was ultrasonically dispersed for 5 minutes, and then the particle size and particle size distribution of the powder were determined using the particle size and shape analyzer after different milling cycles.

[0108] Scanning electron microscope (SEM): JSM-5900LV, JEOL Ltd., Japan. Gold was sputtered onto the surface of powders after different milling cycles, and their morphology was observed using a scanning electron microscope at a voltage of 10 kV.

[0109] Fourier Transform Infrared (FTIR) spectroscopy analysis: Powders with different milling cycles were ground together with KBr (spectrally pure grade), compressed using a tablet press (compression pressure: 10 MPa, compression time: 30 seconds), and then placed in a Fourier Transform Infrared Spectrometer (Nicolet 6700, Thermo Scientific, USA) for testing. The Fourier Transform Infrared (FTIR) spectrometer (Nicolet 6700, Thermo Scientific, USA) was used to measure 4000-400 cm⁻¹. -1 The wavelength range was measured, with 32 scans and a resolution of 4 cm. -1 The test data was exported using the software OMNIC 8.0.

[0110] Thermogravimetric analysis (TGA): Weigh 6-9 mg of polyurethane ultrafine powder and place it in a heat loss analyzer (TGAQ-50, TA Instruments, USA) to test its thermal stability. The temperature range is from room temperature to 700℃. Record, save, and export the TG curve during the heating process.

[0111] Differential Scanning Calorimetry (DSC) Analysis: Weigh 6-9 mg of ultrafine polyurethane powder and place it in an aluminum crucible, then press the crucible lid firmly. Place the powder and reference sample together in a differential scanning calorimeter (DSC Q-20, TA Instruments, USA) for testing. The test atmosphere is nitrogen, the heating rate is 10℃ / min, and the temperature range is 40-300℃. Record, save, and export the DSC curves during the heating process.

[0112] Static mechanical property testing: The compressive properties of the samples were tested according to GB / T 1040-2006 standard using an electronic universal testing machine (L-10, Shenzhen Ruigeer Instrument Co., Ltd.), with a 2kN sensor. The compressive strength of the samples was determined at room temperature using a universal testing machine (Instron, USA) (test load: 2kN; test speed: 4mm / min), with the compressive strength measured parallel to the growth direction of the foam pores. The static mechanical properties were taken as the average of three groups of samples.

[0113] Examples 1-3

[0114] Examples 1-3 are polyurethane rigid foam recycled products prepared according to the steps in "2. Preparation method" above. The polyether polyol mentioned in step (3) is 150 parts (the mass ratio of polyether polyol to diphenylmethane diisocyanate is 1:1). The amount of polyurethane ultrafine powder added in step (3) is used as a variable, and is 7.5 parts, 10.5 parts, and 13.5 parts respectively as Examples 1, Examples 2, and Examples 3. That is, the amount of polyurethane ultrafine powder added is 5 wt%, 7 wt%, and 9 wt% of polyether polyol respectively.

[0115] Comparative Examples 1-2

[0116] Comparative Examples 1 and 2 are polyurethane rigid foam recycled products prepared according to the steps of "2. Preparation Method" above. The polyether polyol mentioned in step (3) is 150 parts (the mass ratio of polyether polyol to diphenylmethane diisocyanate is 1:1). The amount of polyurethane ultrafine powder added in step (3) is used as a variable, which is 1.5 parts and 4.5 parts respectively as Comparative Examples 1 and 2. That is, the amount of polyurethane ultrafine powder added is 1 wt% and 3 wt% of polyether polyol respectively.

[0117] Comparative Examples 3-8

[0118] Comparative Examples 3-8 are polyurethane rigid foam recycled products prepared according to the above "2. Preparation Method" steps as samples. The polyether polyol mentioned in step (3) is 150 parts (the mass ratio of polyether polyol to diphenylmethane diisocyanate is 1:1), but no silane coupling agent KH-550 is added in step (i.e., the silane coupling agent KH-550 is 0 parts).

[0119] The amount of polyurethane ultrafine powder added in step (3) was used as a variable, and 0 parts, 1.5 parts, 4.5 parts, 7.5 parts, 10.5 parts, and 13.5 parts were used as comparative examples 3, 4, 5, 6, 7, and 8, respectively. That is, the amount of polyurethane ultrafine powder added was 0 wt%, 1 wt%, 3 wt%, 5 wt%, 7 wt%, and 9 wt% of polyether polyol.

[0120] The samples in Examples 1-3 and Comparative Examples 1-8 were prepared in the same batch.

[0121] Examples 4-8

[0122] Examples 4-8 are polyurethane rigid foam recycled products prepared according to the steps in "2. Preparation Method" above. The polyurethane ultrafine powder in step (3) is 7.5 parts (5 wt% of diphenylmethane diisocyanate). The amount of polyether polyol added in step (3) is used as a variable, and is 183.33 parts, 166.67 parts, 150 parts, 133.33 parts, and 116.67 parts respectively as Examples 4, 5, 6, 7, and 8. That is, the mass ratio of diphenylmethane diisocyanate to polyether polyol is 18:22, 18:20, 18:18, 18:16, and 18:14 respectively.

[0123] Comparative Examples 9–13

[0124] Comparative Examples 9-13 were prepared using rigid polyurethane foam as samples, following the steps in "2. Preparation Method" above. However, in step (3), polyurethane ultrafine powder and silane coupling agent KH-550 were not added (i.e., 0 parts of polyurethane ultrafine powder and 0 parts of silane coupling agent KH-550). The amount of polyether polyol added in step (3) was used as a variable, and was 183.33 parts, 166.67 parts, 150 parts, 133.33 parts, and 116.67 parts respectively, as Comparative Examples 9, 10, 11, 12, and 13. That is, the mass ratio of diphenylmethane diisocyanate to polyether polyol was 18:22, 18:20, 18:18, 18:16, and 18:14 respectively.

[0125] Comparative Examples 14–18

[0126] Comparative Examples 14-18 are polyurethane rigid foam recycled products prepared according to the steps in "2. Preparation Method" above. The polyurethane ultrafine powder in step (3) is 7.5 parts (5 wt% of diphenylmethane diisocyanate). However, silane coupling agent KH-550 was not added in step (i.e., silane coupling agent KH-550 is 0 parts). The amount of polyether polyol added in step (3) is used as a variable. The amounts are 183.33 parts, 166.67 parts, 150 parts, 133.33 parts, and 116.67 parts, respectively, which are used as Comparative Examples 14, 15, 16, 17, and 18. That is, the mass ratio of diphenylmethane diisocyanate to polyether polyol is 18:22, 18:20, 18:18, 18:16, and 18:14, respectively.

[0127] The samples in Examples 4-8 and Comparative Examples 9-18 were prepared from another batch.

[0128] To facilitate the study of the particle size, particle size distribution and micromorphology of polyurethane ultrafine powder under different milling times, polyurethane ultrafine powder was collected according to steps (1) to (2) of “2. Preparation Method” above. The number of milling times mentioned in step (2) was used as a variable, and 1 time, 3 times, 5 times, 7 times and 9 times were used as verification examples 1, 2, 3, 4 and 5 respectively.

[0129] 4. Test Results

[0130] Figure 1 and Figure 2 The particle size, particle size distribution, and microstructure of polyurethane ultrafine powder under different milling cycles are shown. Figure 2 As shown in (a) and (b), the application of shear force significantly reduced the particle size of the powder with increasing milling cycles. Specifically, the average particle size decreased from 93.34 μm after 3 milling cycles to 55.91 μm after 9 milling cycles, and the particle size distribution became increasingly wider. Figure 2 The results show that the milled powder exhibits an irregular and complex surface morphology, with a rough, loose texture and numerous grooves, leading to an increase in specific surface area. Particles larger than 100 μm were prevalent after three milling cycles, but this significantly decreased after nine milling cycles. This reduction in particle size is attributed to the solid-state force of the chemical shear reactor, which applies strong extrusion and shear forces to the material, effectively pulverizing it. During milling, mechanical force induces the breaking of hydrogen bonds, thereby weakening the cross-linking between polyurethane molecules and enhancing the surface activity of the powder. The finely milled powder facilitates subsequent mixing with polyol raw materials, ensuring uniform dispersion during the mixing process. This uniformity increases the contact area with the polyol, promoting subsequent reactions and enabling effective composite formation of the powder with rigid polyurethane foam. Therefore, the mechanical properties of the rigid foam material are improved.

[0131] Fourier transform infrared (FTIR) spectra of polyurethane ultrafine powders after different milling cycles are as follows: Figure 3 As shown. 1520cm -1 1720cm -1 2271cm -1 and 3330cm -1 The peaks at 3330 cm⁻¹ correspond to the stretching vibrations of amide II, amide I, -NCO and -OH groups, and the stretching vibration of the cis-NH group in -NHCO, respectively. The FTIR spectra of powders prepared under different conditions are generally similar; however, the peaks at 3330 cm⁻¹ show a more pronounced difference. -1 The peak intensity at 3330cm increases significantly with increasing milling cycles. -1The peak at 3330 cm⁻¹ represents the stretching vibration of the -OH group and the stretching vibration of the cis--NH group in -NHCO, indicating that the hydrogen bonds formed by -NH or -OH may be broken during the milling process, thus enhancing the surface activity of the powder. With increasing milling cycles, the peak at 3330 cm⁻¹... -1 The increased peak intensity at the 1710-1750 cm⁻¹ confirms the effectiveness of solid-state shear milling in treating rigid polyurethane foam and indicates mechanochemical changes, chain reorganization and breakage, leading to better processing flowability. During solid-state shearing, mechanical forces may cause the breakage of the polyurethane backbone and the formation of new urethane end groups (-NHCOO-). The vibrational absorption peaks of the C=O bonds in these newly formed end groups are located at 1710-1750 cm⁻¹. -1 Within this range, an increase in their quantity directly leads to an increase in IR absorption intensity. 2271cm -1 The peak at this point is a characteristic peak of the -NCO group. Unlike ball milling or twin-roll milling, solid-state shear milling technology does not destroy the -NCO groups during the shearing process, but rather reduces the steric hindrance of unreacted -OH groups. This is because, although the polyurethane index is usually greater than 1, due to steric hindrance, the primary and secondary hydroxyl groups have different reactivity, resulting in the retention of many -OH groups in the polyurethane matrix. The mechanochemical effect of solid-state shearing allows more encapsulated or reaction-impeded -OH groups to participate in the reaction, thereby enhancing its reactivity. This confirms the effect of the mill disc-shaped solid-state mechanochemical reactor on molecular chain recombination at room temperature, providing more reaction sites for the subsequent reaction between the polyol solution and the isocyanate. This improves the mechanical properties of the polyurethane ultrafine powder.

[0132] Figure 4 The effects of different amounts of polyurethane ultrafine powder added on the mechanical properties of recycled products were explained. In Comparative Examples 3–8, the compressive strength first increased and then decreased with increasing amounts of polyurethane ultrafine powder added. When the amount of polyurethane ultrafine powder added was 1–3 wt% of the polyether polyol, the compressive strength of the prepared recycled products was better than that of the control sample without polyurethane ultrafine powder added. However, when the amount of polyurethane ultrafine powder added exceeded 5 wt%, the compressive strength of the recycled products showed a very obvious deterioration trend. In contrast, in Examples 1–3, when the amount of polyurethane ultrafine powder added was 5–9 wt% of the polyether polyol, the prepared recycled products were significantly better than those in Comparative Examples 3–8, and the deterioration trend only appeared after the amount of polyurethane ultrafine powder added exceeded 7 wt%, but it was still significantly better than the original rigid polyurethane foam sample (Comparative Example 3).

[0133] from Figure 5As can be seen, after milling and modification with silane coupling agents, some polyether polyol raw materials can be replaced, exhibiting higher mechanical properties than the original rigid polyurethane foam samples (Comparative Examples 9-13). However, when the replacement amount continues to increase (18:14, Example 8), it is found that the compressive strength decreases in both the original sample (Comparative Example 13) and the sample without added silane coupling agent (Comparative Example 18). Excessive reduction in the amount of polyether polyol leads to more isocyanate groups failing to participate in the reaction, resulting in reduced crosslinking and decreased mechanical strength. However, in Example 7 (18:16), it was unexpectedly found that the compressive performance of the sample further improved when the amount of polyether polyol was reduced. These results are encouraging because they indicate that the scheme of using polyurethane ultrafine powder as a raw material to replace polyol raw materials is feasible.

[0134] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing recycled products based on waste rigid polyurethane foam powder, characterized in that... The main steps include: (1) After pretreatment including washing, the waste rigid polyurethane foam is crushed into polyurethane crushed material with an average particle size of no more than 100 μm. (2) The polyurethane crushed material obtained in step (1) is added to a grinding disc-shaped solid-phase mechanical chemical reactor for grinding and pulverizing. After grinding is completed, polyurethane ultrafine powder is collected. The process parameters of the grinding disc-shaped solid-phase mechanical chemical reactor are: grinding pressure of 2-4 MPa, circulating cooling liquid at 10-20℃ is introduced to control the temperature of the grinding disc surface, the grinding is at least 3 times, and the grinding disc speed is 40-50 rpm. (3) Using the polyurethane ultrafine powder obtained in step (2) as raw material, prepare material A and material B by weight according to the conventional one-step foaming method for rigid polyurethane foam. Material A and material B respectively include the following components: Material A: Material B: 150 parts isocyanate; (4) Mix A and B materials evenly to form a mixture. Inject the mixture into a mold according to the conventional one-step foaming method for rigid polyurethane foam. After curing at room temperature, a recycled rigid polyurethane foam product is obtained.

2. The method according to claim 1, characterized in that: The raw material components in materials A and B mentioned in step (3) also include conventional catalysts / stabilizers / functional additives used in the preparation of rigid polyurethane foam in the prior art.

3. The method according to claim 1, characterized in that: The raw material components in materials A and B mentioned in step (3) also include any one or more of triethylenediamine, diethanolamine, divalent tin, and silicone oil.

4. The method according to claim 1, characterized in that: In step (4), material A and material B are mixed evenly to form a mixture. The mixture is then injected into a mold using the conventional one-step foaming method for rigid polyurethane foam. After curing at room temperature, a recycled rigid polyurethane foam product is obtained. Specifically, material A and material B are mixed evenly at 40°C and 100 r / min mechanical stirring to form a mixture. The mixture is then sprayed into a mold to self-foam and cured at room temperature for 24 hours to obtain a recycled rigid polyurethane foam product.

5. The recycled polyurethane rigid foam product prepared by the method for preparing recycled products based on the grinding powder of waste polyurethane rigid foam as described in claim 1.

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