Composite foamed material, method for producing the same, and refrigerator

Abstract

The application discloses a composite foaming material and a preparation method thereof and a refrigerator, and relates to the technical field of foaming materials. The preparation method of the composite foaming material comprises the following steps: mixing plant-based waste, a polyhydroxy alcohol and a composite acid catalyst, performing microwave depolymerization treatment, and obtaining plant-based polyol, wherein the composite acid catalyst comprises a strong acid and a medium-strong acid; providing bio-based polyether polyol, a cross-linking catalyst and an isocyanate compound, mixing the plant-based polyol, and performing foaming treatment to obtain the composite foaming material. The preparation method of the composite foaming material provided in the application can prepare the composite foaming material with low thermal conductivity, high low-temperature compressive strength and excellent dimensional stability by controlling the microwave-assisted acid catalytic depolymerization process, matching the plant-based polyol with the bio-based polyether polyol and regulating the foaming forming process without foaming agent, and the composite foaming material can be directly applied to the refrigerator and can adapt to the working temperature range of the refrigerator, i.e. 40 DEG C to 60 DEG C, and long-term use requirements.

Description

Technical Field

[0001] This application relates to the field of foamed materials technology, and in particular to a composite foamed material and its preparation method, and a refrigerator. Background Technology

[0002] A refrigerator is a refrigeration device that maintains a constant low temperature, and it is also a product that keeps food or other items at a constant low temperature. Foamed material is a closed-cell rigid foam that is chemically foamed and cured in the space between the refrigerator's outer shell and inner liner. The core function of foamed material is to create a continuous and uniform thermal insulation layer, minimizing the transfer of heat from the external environment to the refrigerator's interior, thereby maintaining a low-temperature environment and reducing energy consumption.

[0003] The performance of rigid polyurethane foam in refrigerators directly affects the refrigerator's performance and lifespan: for example, a high thermal conductivity will increase the refrigerator's energy consumption, insufficient low-temperature compressive strength will cause the cabinet to deform, and poor dimensional stability will cause the door seal to fail.

[0004] Therefore, developing rigid polyurethane foam for refrigerators with high bio-based content, low thermal conductivity, excellent low-temperature performance, and efficient processing is a key issue that the industry urgently needs to address. Summary of the Invention

[0005] In view of this, this application provides a composite foaming material and its preparation method, as well as a refrigerator, to solve at least one of the above problems.

[0006] The embodiments of this application are implemented as follows: A method for preparing a composite foamed material includes the following steps:

[0007] Plant-based waste, polyhydroxy alcohol and composite acid catalyst are mixed and microwave depolymerized to obtain plant-based polyol, wherein the composite acid catalyst includes strong acid and medium strong acid. A bio-based polyether polyol, a crosslinking catalyst, and an isocyanate compound are provided and mixed with the plant-based polyol, and then subjected to a foaming treatment to obtain a composite foam material.

[0008] Optionally, in some embodiments of this application, before mixing the plant-based waste with the polyhydroxy alcohol, the process further includes: pretreatment; the pretreatment includes sequentially performing crushing, sieving, drying, silane coupling agent treatment, and cellulase treatment; wherein, The average particle size of the crushed and screened plant-based waste is 330μm~370μm; the specific surface area of ​​the crushed and screened plant-based waste is 1m² / g~1.5m² / g. The moisture content of the dried plant-based waste is less than or equal to 4 wt%. The silane coupling agent used in the silane coupling agent treatment includes one or more of KH-560, KH-550, KH-570, and A-171; the mass ratio of the plant-based waste to the silane coupling agent is 100:(0.1~0.5); the temperature of the silane coupling agent treatment is 50℃~80℃, and the treatment time is 20min~40min; The mass ratio of the plant-based waste to the cellulase is 100:(8~12); the temperature of the cellulase treatment is 45℃~55℃, the pH of the cellulase treatment is 4.5~5.2, and the treatment time is 20min~40min.

[0009] Optionally, in some embodiments of this application, the plant-based waste includes one or more of corn cobs, corn stalks, wheat stalks, rice husks, and sugarcane bagasse; The polyhydroxy alcohols include one or more of glycerol, 1,2-propanediol, a mixture of glycerol and PEG400, xylitol, and sorbitol. The strong acid includes one or more of hydrochloric acid, p-toluenesulfonic acid, methanesulfonic acid, and sulfuric acid; The moderately strong acid includes one or more of phosphoric acid, aminosulfonic acid, and citric acid; The molar ratio of the strong acid to the moderately strong acid is (1~2):(1~2). The mass ratio of the plant-based waste to the polyhydroxy alcohol is 1: (8~12); The mass ratio of the plant-based waste and the polyhydroxy alcohol to the composite acid catalyst is 100:(1.5~2.5).

[0010] Optionally, in some embodiments of this application, the microwave depolymerization process is carried out in an inert atmosphere; The conditions for the microwave depolymerization process are as follows: microwave power of 1000W~1400W, temperature of 185℃~195℃, and time of 1.5h~3h. After the microwave depolymerization treatment, the process further includes: adding an alkali to neutralize to a neutral pH; the neutralization with an alkali ensures that no acidic substances remain; the alkali includes one or more of sodium hydroxide, sodium carbonate, and sodium bicarbonate; After alkali neutralization, the process further includes: filtration, taking the filtrate, removing water, and obtaining the plant-based polyol; The plant-based polyol has a hydroxyl value of 255 mg KOH / g to 265 mg KOH / g and a viscosity of 3000 mPa·s to 4000 mPa·sm.

[0011] Optionally, in some embodiments of this application, the hydroxyl value of the bio-based polyether polyol is 190 mg KOH / g to 220 mg KOH / g lower than that of the plant-based polyol; the hydroxyl value of the bio-based polyether polyol is 50 mg KOH / g to 65 mg KOH / g, and the viscosity of the bio-based polyether polyol is 800 mPa·s to 1200 mPa·sm; The bio-based polyether polyols include one or more of castor oil-derived polyether polyols and soybean oil-modified polyether polyols. The crosslinking catalyst includes one or more of amine catalysts and metal catalysts; the amine catalyst includes one or more of triethanolamine, diethanolamine, triethylamine, dimethylethanolamine, dimethylcyclohexylamine, triethylenediamine, tetramethylethylenediamine, tetramethylpropylenediamine, pentamethyldiethylenetriamine, N,N-dimethylbenzylamine, N,N-dimethylaniline, and triisopropanolamine; the metal catalyst includes one or more of stannous octoate, dibutyltin dilaurate, bismuth isooctanoate, bismuth neodecanoate, zinc naphthenate, zinc isooctanoate, cobalt isooctanoate, zirconium naphthenate, zirconium acetylacetonate, titanium acetylacetonate, organotin catalysts, and organobismuth catalysts. The isocyanate compounds include one or more of the following: isocyanate, 4,4'-diphenylmethane diisocyanate, 2,6-toluene diisocyanate, naphthalene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, hydrogenated diphenylmethane diisocyanate, and phenylmethylene diisocyanate.

[0012] Optionally, in some embodiments of this application, mixing the bio-based polyether polyol, the crosslinking catalyst, the isocyanate compound, and the plant-based polyol comprises: mixing the bio-based polyether polyol, the crosslinking catalyst, and the plant-based polyol to obtain component A; mixing component A and component B, wherein component B includes the isocyanate compound; wherein, The bio-based polyether polyol and the plant-based polyol are mixed to obtain a polyol mixture, wherein the hydroxyl value of the polyol mixture is 80 mg KOH / g to 120 mg KOH / g; The mass ratio of the plant-based polyol to the bio-based polyether polyol is (3~11):(3~7). The mass ratio of the plant-based polyol and the bio-based polyether polyol to the crosslinking catalyst is 100:(0.3~0.5). The isocyanate index of the mixture of component A and component B is 1.0 to 1.4.

[0013] Optionally, in some embodiments of this application, the preparation of component A further includes: adding a flame-retardant material; wherein, The flame-retardant material includes one or more of intercalation compounds and metal hydroxides; The intercalation complex comprises organic acidic compounds and layered silicate clay minerals; The organic acidic compounds include one or more of phytic acid, tannic acid, gallic acid, humic acid, 2-hydroxyphosphonoacetic acid, hydroxyethylidene diphosphonic acid, aminotrimethylene phosphonic acid, and 2-phosphonobutane-1,2,4-tricarboxylic acid. The layered silicate clay minerals include one or more of montmorillonite, rettoite, and bentonite. The mass ratio of the organic acid compound to the layered silicate clay mineral is (1~3):1; The mass ratio of the plant-based polyol and the bio-based polyether polyol to the intercalation complex is 100:(0.5~1.2). The metal hydroxide includes one or more of magnesium hydroxide and aluminum hydroxide; The mass ratio of the plant-based polyol and the bio-based polyether polyol to the metal hydroxide is 100:(0.8~1.8).

[0014] Optionally, in some embodiments of this application, the preparation of component A further includes: adding a nucleating agent; wherein, The nucleating agent includes lignin derivatives modified with unsaturated dicarboxylic acids and their anhydride derivatives. The unsaturated dicarboxylic acids and their anhydride derivatives include one or more of maleic anhydride, fumaric acid, maleic acid, citraconic acid, citraconic anhydride, itaconic acid, and medoconic acid. The mass ratio of the lignin derivative to the unsaturated dicarboxylic acid and its anhydride derivative is 1:(0.3~0.8). The conditions for modifying the lignin derivative with the unsaturated dicarboxylic acid and its anhydride derivatives are: temperature of 100℃~140℃ and time of 2h~4h. The mass ratio of the plant-based polyol and the bio-based polyether polyol to the nucleating agent is 100:(0.5~1.2).

[0015] Optionally, in some embodiments of this application, the foaming process includes a foaming stage and a curing stage performed sequentially; wherein, The conditions for the foaming stage are: temperature 40℃~50℃, time 1min~3min; The conditions for the curing stage are: temperature of 50℃~80℃ and time of 30min~60min.

[0016] Accordingly, this application also provides a composite foaming material prepared by the above-described preparation method.

[0017] The method for preparing composite foamed materials provided in this application uses plant-based waste as raw material to prepare plant-based polyols, which is green and environmentally friendly. By controlling the microwave-assisted acid-catalyzed depolymerization process, combining plant-based polyols with bio-based polyether polyols, and regulating the foaming molding process without foaming agents, composite foamed materials with low thermal conductivity, high low-temperature compressive strength, and excellent dimensional stability can be prepared. These materials can be directly applied to the insulation and structural layers of refrigerator bodies, doors, and partitions, and are suitable for the working temperature range of -40℃ to 60℃ and long-term use requirements of refrigerators.

[0018] In the microwave depolymerization process, a composite acid catalyst combining strong and medium-strength acids was selected. This composite acid catalyst can exert a synergistic catalytic effect: the strong acid can quickly break the glycosidic bonds of cellulose in plant-based waste, while the medium-strength acid can slowly break the lignin ether bonds. The two complement each other in time, resulting in more thorough depolymerization and reducing residual solid impurities. The medium-strength acid has a large molecular weight and low ionization degree, which can be adsorbed on the equipment surface to form a "corrosion inhibitor film" to reduce the corrosion of metal reaction equipment (reactor) by the strong acid. The medium-strength acid can also inhibit the oxidation of hydroxyl groups in plant-based waste, reduce the formation of aldehyde groups, reduce the fluctuation of hydroxyl value, and improve the stability of subsequent foaming treatment. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart of a method for preparing a composite foamed material provided in an embodiment of this application. Detailed Implementation

[0021] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. Furthermore, it should be understood that the specific embodiments described herein are only for illustration and explanation of this application and are not intended to limit this application.

[0022] In this application, unless otherwise stated, directional terms such as "upper" and "lower" generally refer to the upper and lower positions of the device in its actual use or operating state, specifically the orientation shown in the accompanying drawings; while "inner" and "outer" refer to the outline of the device. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". The terms first, second, third, etc., are used merely as illustrative purposes and do not impose numerical requirements or establish a numerical order.

[0023] In this application, "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural.

[0024] In this application, "at least one" means one or more, and "more than one" means two or more. "One or more", "at least one of the following", or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0025] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0026] Polyurethane rigid foam is used in refrigerators as a core insulation and structural material, and the demand is relatively high. Current rigid polyurethane foams for refrigerators mainly rely on the reaction of fossil-based polyols (such as glycerol-derived polyether polyols) with diisocyanates (MDI / TDI) for preparation. This type of rigid foam has two major problems: First, the raw materials depend on non-renewable fossil fuels, resulting in high energy consumption and large carbon emissions during production, which contradicts the current trend of environmental protection and circular economy development. Second, existing bio-based modified rigid foams generally have performance shortcomings, including low bio-based content, high thermal conductivity, insufficient compressive strength at low temperatures, and poor dimensional stability. Furthermore, the preparation process often uses traditional heating depolymerization, which is inefficient.

[0027] Some studies have attempted to prepare bio-polyols using agricultural waste, but problems such as incomplete depolymerization, large fluctuations in the hydroxyl value of polyols, and uneven foam pores exist, making it difficult to balance the thermal insulation performance and mechanical strength of rigid foam, and failing to meet the stringent requirements of refrigerator cabinets for long-term low-temperature stability, low thermal conductivity, and structural support.

[0028] This application aims to address at least one of the following technical defects in existing rigid polyurethane foam for refrigerators: reliance on fossil-based raw materials, high thermal conductivity, poor low-temperature mechanical properties, insufficient dimensional stability, and low efficiency, large performance fluctuations, and poor controllability of bio-based rigid foam preparation processes.

[0029] The technical solution of this application is as follows: Firstly, please refer to Figure 1 This application provides a method for preparing a composite foamed material, comprising the following steps: Step S11: Provide plant-based waste, polyhydroxy alcohol and composite acid catalyst mixed, and perform microwave depolymerization treatment to obtain plant-based polyol, wherein the composite acid catalyst includes strong acid and medium strong acid; Step S12: Provide bio-based polyether polyol, crosslinking catalyst, isocyanate compound, mix with the plant-based polyol, and perform foaming treatment to obtain composite foam material.

[0030] It should be noted that plant-based waste refers to organic waste generated during the production, processing, consumption, or utilization of plants. It is rich in cellulose and falls under the category of renewable biomass resources. Bio-based polyether polyols refer to polyether-type polyols containing multiple hydroxyl functional groups, produced by partially or completely replacing petroleum-based raw materials with renewable bio-based raw materials through ring-opening polymerization or condensation polymerization. They belong to bio-based, low-carbon emission polyurethane raw materials.

[0031] It should also be noted that a strong acid is one that completely ionizes in aqueous solution to release H+. + Strong acids have a degree of ionization close to 100%, and their pKa (acidity coefficient, the negative logarithm of the ionization constant) is less than 1. Moderately strong acids are those that partially ionize in aqueous solution, with acidity between that of strong and weak acids, and their pKa (acidity coefficient, the negative logarithm of the ionization constant) ranges from 1 to 4.

[0032] It should also be noted that in step S12, no foaming agent needs to be added during the foaming process of this application.

[0033] It is understood that the composite foaming material is rigid polyurethane foam.

[0034] The method for preparing composite foamed materials provided in this application uses plant-based waste as raw material to prepare plant-based polyols, which is green and environmentally friendly. By controlling the microwave-assisted acid-catalyzed depolymerization process, combining plant-based polyols with bio-based polyether polyols, and regulating the foaming molding process without foaming agents, composite foamed materials with low thermal conductivity, high low-temperature compressive strength, and excellent dimensional stability can be prepared. These materials can be directly applied to the insulation and structural layers of refrigerator bodies, doors, and partitions, and are suitable for the working temperature range of -40℃ to 60℃ and long-term use requirements of refrigerators.

[0035] In the microwave depolymerization process, a composite acid catalyst combining strong and medium-strength acids was selected. This composite acid catalyst can exert a synergistic catalytic effect: the strong acid can quickly break the glycosidic bonds of cellulose in plant-based waste, while the medium-strength acid can slowly break the lignin ether bonds. The two complement each other in time, resulting in more thorough depolymerization and reducing residual solid impurities. The medium-strength acid has a large molecular weight and low ionization degree, which can be adsorbed on the equipment surface to form a "corrosion inhibitor film" to reduce the corrosion of metal reaction equipment (reactor) by the strong acid. The medium-strength acid can also inhibit the oxidation of hydroxyl groups in plant-based waste, reduce the formation of aldehyde groups, reduce the fluctuation of hydroxyl value, and improve the stability of subsequent foaming treatment.

[0036] In step S11: In some embodiments, the plant-based waste includes one or more of corn cobs, corn stalks, wheat stalks, rice husks, and sugarcane bagasse.

[0037] In some embodiments, the plant-based waste is further subjected to pretreatment before being mixed with the polyhydroxy alcohol.

[0038] Furthermore, the pretreatment includes sequentially performing pulverization, sieving, drying, silane coupling agent treatment, and cellulase treatment.

[0039] It should be noted that crushing, sieving, and drying can be carried out using conventional techniques in this field, such as high-speed pulverizer crushing, air classifier sieving, and vacuum drying oven drying, etc., without further limitations.

[0040] In some embodiments, the average particle size of the pulverized and sieved plant-based waste is 330 μm to 370 μm, for example, it can be 330 μm, 340 μm, 350 μm, 360 μm, 370 μm, or any two of the above values; the specific surface area of ​​the pulverized and sieved plant-based waste is 1 m² / g to 1.5 m² / g, for example, it can be 1 m² / g, 1.1 m² / g, 1.2 m² / g, 1.3 m² / g, 1.4 m² / g, 1.5 m² / g, or any two of the above values. Within the above range, the particle size distribution of the plant-based waste is concentrated and it has a suitable specific surface area, which can increase the contact efficiency with the composite acid catalyst.

[0041] In some embodiments, the moisture content of the dried plant-based waste is less than or equal to 4 wt%, for example, it can be 4 wt%, 3 wt%, 2 wt%, 1 wt%, etc. Within the above range, the plant-based waste is subject to strict moisture control to ensure that the moisture does not affect the microwave depolymerization process.

[0042] It should be noted that the silane coupling agent treatment refers to mixing the silane coupling agent with plant-based waste and reacting the mixture.

[0043] In some embodiments, the silane coupling agent in the silane coupling agent treatment includes one or more of KH-560 (3-glycidoxypropyltrimethoxysilane), KH-550 (γ-aminopropyltriethoxysilane), KH-570 (γ-methacryloyloxypropyltrimethoxysilane), and A-171 (vinyltrimethoxysilane).

[0044] In some embodiments, the mass ratio of the plant-based waste to the silane coupling agent is 100:(0.1~0.5), for example, it can be 100:0.1, 100:0.2, 100:0.3, 100:0.4, 100:0.5, or any range between two of the above values. Within the above range, the silane coupling agent can bind to the cellulose in the plant-based waste, improving its compatibility with subsequent polyhydroxy alcohols, thereby increasing the efficiency of microwave depolymerization treatment.

[0045] In some embodiments, the temperature for treatment with the silane coupling agent is 50°C to 80°C, for example, 50°C, 60°C, 70°C, 80°C, or any range between two of the above values; the treatment time for the silane coupling agent is 20 min to 40 min, for example, 20 min, 25 min, 30 min, 35 min, 40 min, or any range between two of the above values. Within the above range, it is beneficial for the silane coupling agent to react and connect efficiently to the plant-based waste.

[0046] It should be noted that the cellulase treatment refers to mixing an aqueous solution of cellulase with plant-based waste and then reacting the mixture.

[0047] In some embodiments, the mass ratio of the plant-based waste to the cellulase is 100:(8~12), for example, it can be 100:8, 100:9, 100:10, 100:11, 100:12, or any range between two of the above values. Within the above range, the cellulase can effectively destroy the crystalline structure of cellulose in the plant-based waste, thereby helping to reduce the cost of subsequent microwave depolymerization treatment and improve production efficiency.

[0048] In some embodiments, the temperature of the cellulase treatment is 45℃~55℃, for example, 45℃, 48℃, 50℃, 52℃, 55℃, or any two of the above values; the pH of the cellulase treatment is 4.5~5.2, for example, 4.5, 4.6, 4.8, 5.0, 5.2, or any two of the above values; the treatment time is 20min~40min, for example, 20min, 25min, 30min, 35min, 40min, or any two of the above values. Within the above ranges, it is beneficial to perform preliminary depolymerization of plant-based waste and improve depolymerization efficiency.

[0049] In some embodiments, the polyhydroxy alcohol includes one or more of glycerol, 1,2-propanediol (PG), a glycerol-PEG400 mixture, xylitol, and sorbitol. It should be noted that the polyhydroxy alcohol can act as a solvent, a liquefying agent, and a reaction medium, undergoing alcoholysis (breaking glycosidic bonds) with cellulose in plant-based waste, directly participating in the formation of plant-based polyols (the hydroxyl portion of plant-based polyols originates from the hydroxyl group grafted from the polyhydroxy alcohol). Furthermore, the polyhydroxy alcohol provides a homogeneous reaction environment, dissolves complex acid catalysts, promotes uniform microwave energy transfer, and avoids localized overheating.

[0050] In some embodiments, the strong acid includes one or more of hydrochloric acid (pKa=-7), p-toluenesulfonic acid (pKa=-1.3), methanesulfonic acid (pKa=-0.6), and sulfuric acid (pKa=-3).

[0051] In some embodiments, the moderately strong acid includes one or more of phosphoric acid (pKa=2.12), aminosulfonic acid (pKa=1.0), and citric acid (pKa=3.13).

[0052] In some embodiments, the molar ratio of the strong acid to the moderately strong acid is (1~2):(1~2), for example, it can be 1:2, 1.2:1.8, 1:1, 1.8:1.2, 2:1, or any range between two of the above ratios. Within the above range, the strong acid and the moderately strong acid work synergistically to assist microwave depolymerization, effectively control reaction efficiency, and reduce erosion.

[0053] In some embodiments, the mass ratio of the plant-based waste to the polyhydroxy alcohol is 1:(8~12), for example, it can be 1:8, 1:9, 1:10, 1:11, 1:12, or any range between two of the above ratios. The mass ratio of the plant-based waste and the polyhydroxy alcohol to the composite acid catalyst is 100:(1.5~2.5), for example, it can be 100:1.5, 100:1.8, 100:2.0, 100:2.2, 100:2.5, or any range between two of the above ratios. Within the above range, it is beneficial for the raw materials to be fully and uniformly mixed, for the depolymerization of the plant-based waste, and to avoid waste of raw materials.

[0054] In some embodiments, the microwave depolymerization process is carried out in an inert atmosphere to avoid oxidation of the raw materials. The inert gas in the inert atmosphere may be nitrogen.

[0055] In some embodiments, the microwave depolymerization process can be carried out in a microwave reactor.

[0056] In some embodiments, the conditions for the microwave depolymerization treatment are as follows: microwave power is 1000W~1400W, for example, 1000W, 1100W, 1200W, 1300W, 1400W, or any range between two of the above values; temperature is 185℃~195℃, for example, 185℃, 188℃, 190℃, 192℃, 195℃, or any range between two of the above values; time is 1.5h~3h, for example, 1.5h, 1.8h, 2h, 2.2h, 2.5h, 3h, or any range between two of the above values. Under the above conditions, it is beneficial to efficiently prepare plant-based polyols from plant-based waste.

[0057] In some embodiments, after the microwave depolymerization treatment, the process further includes adding an alkali to neutralize the pH to neutral. Neutralization with an alkali ensures that no acidic substances remain.

[0058] Furthermore, the alkali includes one or more of sodium hydroxide, sodium carbonate, and sodium bicarbonate.

[0059] It should be noted that the pH value of neutral refers to a pH value of 6.5 to 7.5.

[0060] In some embodiments, after alkali neutralization, the method further includes: filtration, taking the filtrate, removing water, and obtaining the plant-based polyol.

[0061] It should be noted that during the microwave depolymerization process, the cellulose and hemicellulose in the plant-based waste are mainly converted into plant-based polyols. However, lignin is usually present in the plant-based waste. Due to its dense structure, a small portion of the lignin degrades into low molecular weight lignin derivatives, which dissolve in the plant-based polyols. After removing the water, the product can be separated by gel permeation chromatography (GPC) to obtain plant-based polyols and lignin derivatives with higher purity. These can be used as polyols and nucleating agents in the foaming raw materials, respectively. Alternatively, the product after removing the water can be directly used as a plant-based polyol for foaming.

[0062] In some embodiments, the hydroxyl value of the plant-based polyol is 255 mg KOH / g to 265 mg KOH / g, for example, 255 mg KOH / g, 258 mg KOH / g, 260 mg KOH / g, 262 mg KOH / g, 265 mg KOH / g, or any range between two of the above values. The viscosity (25°C) of the plant-based polyol is 3000 mPa·s to 4000 mPa·s, for example, 3000 mPa·s, 3200 mPa·s, 3500 mPa·s, 3800 mPa·s, 4000 mPa·s, or any range between two of the above values. It should be noted that the hydroxyl value is obtained by testing according to ASTM D4274-2016, and the viscosity is obtained by testing at 25°C using a Brookfield DV-S viscometer, rotor No. 6, and rotation speed of 20 rpm.

[0063] Furthermore, the Fourier transform infrared (FT-IR) spectrum of the plant-based polyols provided in this application is available at 3300 cm⁻¹. - ¹(-OH)1050cm - A characteristic absorption peak was observed at ¹(CO).

[0064] In this application, plant-based polyols with high hydroxyl values ​​were prepared by microwave-assisted acid-catalyzed depolymerization of plant-based waste. When combined with bio-based polyether polyols, they can form a 100% bio-based system, achieving a balance between the environmental friendliness and low-temperature performance of rigid foam for refrigerators.

[0065] In step S12: In some embodiments, the hydroxyl value of the bio-based polyether polyol is 190 mg KOH / g to 220 mg KOH / g lower than that of the plant-based polyol. It is understood that the plant-based polyol is a highly reactive polyol, while the bio-based polyether polyol is a less reactive polyol. The significant difference in their hydroxyl values ​​leads to a substantial difference in reaction kinetics (reaction rates). The plant-based polyol with a high hydroxyl value has a high hydroxyl density, resulting in a rapid reaction rate with isocyanate compounds to form urethane bonds. Conversely, the bio-based polyether polyol with a low hydroxyl value has a low hydroxyl density, resulting in a slow reaction rate with isocyanate compounds. This difference in reaction rates is the key driving force for the "controllable nucleation and stable growth" of cells without a blowing agent. The highly reactive plant-based polyol triggers "rapid nucleation" (replacing the "bubble generation" function of the blowing agent), while the less reactive bio-based polyether polyol achieves "stable growth" (replacing the "bubble size control" function of the blowing agent). The synergistic "curing and shaping" of the two systems ensures the closed-cell rate and structural stability.

[0066] Furthermore, the hydroxyl value of the bio-based polyether polyol is 50 mg KOH / g to 65 mg KOH / g, for example, it can be 50 mg KOH / g, 52 mg KOH / g, 55 mg KOH / g, 58 mg KOH / g, 60 mg KOH / g, 65 mg KOH / g, or any range between two of the above values. The viscosity (25°C) of the bio-based polyether polyol is 800 mPa·s to 1200 mPa·sm, for example, it can be 800 mPa·s, 900 mPa·s, 1000 mPa·s, 1100 mPa·s, 1200 mPa·s, or any range between two of the above values.

[0067] In some embodiments, the bio-based polyether polyol includes one or more of castor oil-derived polyether polyol (CSP-3) and soybean oil-modified polyether polyol.

[0068] In some embodiments, the crosslinking catalyst includes one or more of amine catalysts and metal catalysts.

[0069] Furthermore, the amine catalyst includes one or more of triethanolamine (TEOA), diethanolamine (DEA), triethylamine (TEA), dimethylethanolamine, dimethylcyclohexylamine, triethylenediamine, tetramethylethylenediamine, tetramethylpropylenediamine, pentamethyldiethylenetriamine, N,N-dimethylbenzylamine, N,N-dimethylaniline, and triisopropanolamine.

[0070] The metal catalysts include one or more of the following: stannous octoate, dibutyltin dilaurate, bismuth isooctanoate, bismuth neodecanoate, zinc naphthenate, zinc isooctanoate, cobalt isooctanoate, zirconium naphthenate, zirconium acetylacetonate, titanium acetylacetonate, organotin catalysts, and organobismuth catalysts.

[0071] In some embodiments, the isocyanate compounds include one or more of isocyanates, 4,4'-diphenylmethane diisocyanate (MDI), 2,6-toluene diisocyanate (TDI), naphthalene diisocyanate (NDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), hydrogenated diphenylmethane diisocyanate (H12MDI), and phenylmethylene diisocyanate (XDI).

[0072] In some embodiments, the mixture of the bio-based polyether polyol, the crosslinking catalyst, the isocyanate compound, and the plant-based polyol comprises: The bio-based polyether polyol, the crosslinking catalyst, and the plant-based polyol are mixed to obtain component A; The components A and B are mixed, wherein component B comprises the isocyanate compound.

[0073] In some embodiments, the bio-based polyether polyol and the plant-based polyol are mixed to obtain a polyol mixture. The hydroxyl value of the polyol mixture is 80 mg KOH / g to 120 mg KOH / g, for example, it can be 80 mg KOH / g, 90 mg KOH / g, 100 mg KOH / g, 110 mg KOH / g, 120 mg KOH / g, or any range between two of the above values. Within the above range, component A has a suitable hydroxyl value, which facilitates efficient reaction with the hydroxyl groups of isocyanate compounds to prepare rigid polyurethane foam.

[0074] In some embodiments, the mass ratio of the plant-based polyol to the bio-based polyether polyol is (3~11):(3~7), for example, it can be 3:7, 4:6, 8:5, 10:4, 11:3, or any range between the above two ratios. Within the above range, the plant-based polyol and the bio-based polyether polyol are conducive to synergistic interaction, constructing a reactivity gradient, providing the sole driving force for foam-free cell control, and achieving controllable nucleation-slow growth-stable curing of cells.

[0075] In some embodiments, the mass ratio of the plant-based polyol and the bio-based polyether polyol to the crosslinking catalyst is 100:(0.3~0.5), for example, it can be 100:0.3, 100:0.35, 100:0.4, 100:0.45, 100:0.5, or any range between two of the above ratios. Within the above range, it is beneficial for the foaming agent to regulate and accelerate the nucleation and foaming reaction of isocyanate and polyol, balance the chain growth and gas generation rate, ensure the smooth rise and normal curing of foam, and form a uniform and stable cell and crosslinking network.

[0076] In some embodiments, the isocyanate index of the mixture of component A and component B is 1.0 to 1.4, for example, it can be 1.0, 1.1, 1.2, 1.3, 1.4, or any range between two of the above values. It should be noted that the isocyanate index represents the equivalent ratio of isocyanate groups (NCO) in isocyanate compounds to hydroxyl groups (-OH) in polyols. Within a suitable range, composite foam materials with excellent mechanical properties, thermal stability, and microstructure can be prepared, while reducing raw material waste.

[0077] In some embodiments, the preparation of component A further includes adding a flame-retardant material.

[0078] In some embodiments, the flame-retardant material includes one or more of intercalation compounds and metal hydroxides.

[0079] Furthermore, the intercalation complex comprises an organic acidic compound and layered silicate clay minerals.

[0080] Furthermore, the organic acidic compound includes one or more of phytic acid, tannic acid, gallic acid, humic acid, 2-hydroxyphosphonoacetic acid, hydroxyethylidene diphosphonic acid, aminotrimethylene phosphonic acid, and 2-phosphonobutane-1,2,4-tricarboxylic acid.

[0081] The layered silicate clay minerals include one or more of montmorillonite, rettoite, and bentonite.

[0082] The mass ratio of the organic acidic compound to the layered silicate clay mineral is (1~3):1, for example, it can be 1:1, 1.5:1, 2:1, 2.5:1, 3:1, or any range between two of the above ratios. Within the above range, it is beneficial for the organic acidic compound and the layered silicate clay mineral to form an intercalation complex, effectively improving the flame retardant properties of the composite foam material.

[0083] In some embodiments, the mass ratio of the plant-based polyol and the bio-based polyether polyol to the intercalation composite is 100:(0.5~1.2), for example, it can be 100:0.5, 100:0.6, 100:0.8, 100:1, 100:1.2, or any range between two of the above ratios. Within the above range, the intercalation composite is beneficial for improving the flame retardant properties of the composite foam material.

[0084] In some embodiments, the metal hydroxide includes one or more of magnesium hydroxide and aluminum hydroxide.

[0085] In some embodiments, the mass ratio of the plant-based polyol and the bio-based polyether polyol to the metal hydroxide is 100:(0.8~1.8), for example, it can be 100:0.8, 100:1, 100:1.2, 100:1.5, 100:1.8, or any range between two of the above ratios. Within the above range, the metal hydroxide is beneficial for improving the flame retardant properties of the composite foam material.

[0086] By selecting suitable flame-retardant materials, the problems of flame retardant failure and foam embrittlement during long-term use of refrigerators can be effectively solved, while improving anti-aging performance and effectively extending the service life of refrigerators.

[0087] In some embodiments, the preparation of component A further includes adding a nucleating agent.

[0088] In some embodiments, the nucleating agent comprises lignin derivatives modified with unsaturated dicarboxylic acids and their anhydride derivatives.

[0089] It should be noted that the lignin derivative can be obtained by further separation and extraction from the filtrate after removing water during the preparation of plant-based polyols, thus achieving full utilization of beneficial components. More specifically, the components in the lignin derivative include syringylpropane units, guaiacylpropane units, and p-hydroxyphenylpropane units (the basic structural units of lignin, which retain some hydroxyl and methoxy functional groups after depolymerization), mainly providing phenolic hydroxyl (-OH), methoxy (-OCH3), and ether bonds (-O-), providing reaction sites for grafting modification of unsaturated dicarboxylic acids and their anhydride derivatives.

[0090] In some embodiments, the unsaturated dicarboxylic acids and their anhydride derivatives include one or more of maleic anhydride, fumaric acid, maleic acid, citraconic acid, citraconic anhydride, itaconic acid, and zebufenacic acid.

[0091] In some embodiments, the mass ratio of the lignin derivative to the unsaturated dicarboxylic acid and its anhydride derivative is 1:(0.3~0.8), for example, it can be 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, or any range between two of the above values. Within this mass ratio range, it is beneficial for the unsaturated dicarboxylic acid and its anhydride derivative to fully modify the lignin derivative and improve its nucleation performance.

[0092] In some embodiments, the conditions for modifying the lignin derivative with the unsaturated dicarboxylic acid and its anhydride derivative are as follows: a temperature of 100℃ to 140℃, for example, 100℃, 110℃, 120℃, 130℃, 140℃, or any range between two of the above values; and a time of 2h to 4h, for example, 2h, 2.5h, 3h, 3.5h, 4h, or any range between two of the above values. Under these conditions, efficient modification of the lignin derivative is advantageous.

[0093] In some embodiments, the mass ratio of the plant-based polyol and the bio-based polyether polyol to the nucleating agent is 100:(0.5~1.2), for example, it can be 100:0.5, 100:0.6, 100:0.8, 100:1.0, 100:1.2, or any range between two of the above ratios. Within the above range, it is beneficial for the nucleating agent to form bubble nuclei in the early stage of foaming, thereby improving the closed-cell rate of the composite foam material.

[0094] It is understandable that, under the action of the nucleating agent, this application does not require a traditional foaming agent, thus avoiding the compatibility problem between traditional foaming agents such as pentane and bio-based polyether polyols, thereby preventing cell rupture and improving the performance of the composite foam material.

[0095] It should be noted that after the components A and B are mixed, they can be poured into a suitable mold for foaming.

[0096] In some embodiments, the foaming process includes a foaming stage and a curing stage performed sequentially.

[0097] Furthermore, the conditions for the foaming stage are as follows: the temperature is 40℃~50℃, for example, it can be 40℃, 42℃, 45℃, 48℃, 50℃ or any two of the above values; the time is 1min~3min, for example, it can be 1min, 1.5min, 2min, 2.5min, 3min or any two of the above values.

[0098] The conditions for the curing stage are as follows: the temperature is 50℃~80℃, for example, it can be 50℃, 60℃, 70℃, 80℃ or any two of the above values; the time is 30min~60min, for example, it can be 30min, 40min, 50min, 60min or any two of the above values.

[0099] Thus, under the aforementioned foaming treatment conditions, it is beneficial to prepare composite foamed materials with excellent properties.

[0100] It should be noted that after the curing stage, the product can be further placed in a constant temperature and humidity chamber for curing. During the curing period, direct sunlight and mechanical impact should be avoided. After curing, the rigid foam is cut and the edge burrs are removed to obtain a finished product that meets the assembly dimensions of the refrigerator and is then applied to the refrigerator.

[0101] Secondly, embodiments of this application also provide a composite foaming material, which is prepared by the above-described preparation method.

[0102] The composite foam material prepared using the above-mentioned method exhibits a significant reduction in thermal conductivity, meeting the first-level energy efficiency standard for refrigerators. It also boasts high room-temperature and low-temperature compressive strength, addressing the industry pain point of "low-temperature brittleness" in bio-based rigid foam. Furthermore, its structural stability indicators (size and closed-cell rate) are comprehensively optimized, with improved closed-cell rate and dimensional stability, ensuring the refrigerator remains undeformed and moisture-free under temperature cycling conditions from -40℃ to 60℃. Additionally, the composite foam material's aging resistance is upgraded, significantly extending the service life of the rigid foam in the refrigerator.

[0103] Thirdly, embodiments of this application also provide a refrigerator, which includes a cabinet, and the interlayer of the cabinet is provided with the above-mentioned composite foam material, or the composite foam material prepared by the above-mentioned preparation method.

[0104] In addition to refrigerator insulation, the composite foam material provided in this application embodiment can also be widely used in cold chain equipment such as cold chain containers and refrigerated trucks, and has broad market application prospects.

[0105] The present application will be specifically described below through specific embodiments. The following embodiments are only some embodiments of the present application and are not intended to limit the present application.

[0106] Example 1 This embodiment provides a composite foaming material, and the preparation method of the composite foaming material is as follows: Step S21: Take corn cob waste, crush it in a high-speed pulverizer (12000 rpm), and then sieve it through a classifier (0.6 MPa air pressure, 3000 rpm classifier wheel speed) to obtain corn cob waste with an average particle size of 350 μm and a specific surface area of ​​1.2 m² / g. Dry it in a vacuum drying oven at -0.09 MPa vacuum and 80℃ for 6 hours, strictly controlling the moisture content to within 3.5 wt%. After drying, add 0.3 wt% (based on the mass of corn cob waste) of KH-560 silane coupling agent and stir in a twin-screw mixer at 60℃ for 30 minutes for silane coupling agent treatment. Then mix it with cellulase solution (concentration 10 mg / mL, mass ratio of corn cob waste to cellulase 10:1) and pretreat it at 50℃ and pH=4.8 for 30 minutes. Step S22: Transfer the pretreated material into a continuous microwave reactor. Select a 10L microwave reactor (equipped with three 800W microwave generators, high-purity fused silica for the quartz window, and a maximum working pressure of 0.3MPa). Add 500g of pretreated corn cob waste and 5000g of glycerol sequentially, and stir for 10 minutes (100rpm). Introduce nitrogen (purity ≥99.99%) into the reactor at a flow rate of 0.5L / min, replacing the air in the reactor three times, and finally maintain a slight positive pressure of nitrogen. (0.03MPa); Start the microwave reactor, set the heating rate to 5℃ / min, and heat to 190℃ (using a PT100 platinum resistance thermometer, with the measuring point located at the center of the reaction system, accuracy ±0.5℃); After reaching the set temperature, slowly add 2wt% (based on the mass of corn cob waste and glycerol) of composite acid catalyst (hydrochloric acid and phosphoric acid mixed in a 1:1 molar ratio) through a constant pressure dropping funnel (volume 500mL), with a dropping rate of 10mL / min. After the dropping is completed, increase the stirring speed to 20. The reaction was carried out at 0 rpm with a microwave power of 1200W and a constant temperature of 190℃ for 2 hours. Temperature and pressure data were recorded every 15 minutes during the reaction, with temperature fluctuations controlled within ±2℃ and pressure fluctuations ≤0.05MPa. After the reaction, the microwave was turned off, and the reaction system was cooled to 90℃. While maintaining a stirring speed of 150 rpm, 5g of flake NaOH was slowly added every 5 minutes, while simultaneously monitoring the pH value of the system in real time using a precision pH meter until pH=7.0. After neutralization, stirring was continued for 30 minutes to ensure... The neutralization reaction was complete, with no localized residual acidic substances. The neutralized mixture was cooled to 40°C and filtered through a ceramic filter (5μm mesh size, 0.2MPa working pressure). The filtrate was collected and transferred to a rotary evaporator. A vacuum of 0.095MPa and a water bath temperature of 80°C were set to evaporate and remove moisture until the moisture content was ≤0.3wt% (Kal Fischer method detection). The filtrate was then separated by coagulation-permeation chromatography to obtain corn cob polyol and lignin derivatives. The corn cob polyol had a hydroxyl value of 260 mg KOH / g, a viscosity (25°C) of 3500 mPa·s, and an FT-IR reading at 3300 cm⁻¹. - ¹(-OH)1050cm - ¹A characteristic absorption peak is present at (CO); Step S23: Weigh corn cob polyol and castor oil-derived polyether polyol in a weight ratio of 7:5, add them to a stainless steel mixing tank (5L capacity, with jacket temperature control, set to 25℃), start the stirrer (anchor type, impeller type), and stir at 300 rpm for 30 minutes to ensure the polyols are mixed evenly, obtaining a polyol mixture; add 0.4wt% TEOA crosslinking catalyst (based on the mass of the polyol mixture), maintaining a stirring speed of 350 rpm. Continue stirring for 120 seconds, during which the viscosity of the system is monitored using an online viscometer. After uniform mixing, the viscosity fluctuation is ≤5%. Phytic acid and montmorillonite are ultrasonically exfoliated (20kHz, 1200W) to form an intercalation complex (PA-MMT). Flame retardant material is weighed and added to the system at a ratio of 0.8wt% PA-MMT and 1.2wt% Mg(OH)2 (based on the mass of the polyol mixture). Using the above lignin derivative as raw material, maleic anhydride grafting modification is performed (reaction at 120℃ for 3 hours) to prepare a nucleating agent. This agent is added to the system at a ratio of 0.8wt% (based on the mass of the polyol mixture) to obtain component A. Component A must be used within 1 hour after preparation. Step S24: Add 4,4'-diphenylmethane diisocyanate (component B, isocyanate index 1.3) to component A, maintain the reaction system temperature at 25℃, stir at 350 rpm for 60 s to obtain the foaming material; after stirring, immediately pour the foaming material into a refrigerator-specific sealed metal mold (material 304). Stainless steel, with cavity dimensions adapted to refrigerator side panels (600mm×400mm×50mm) and door panels (500mm×400mm×40mm). The inner wall of the mold is coated with a polyethylene coating with a thickness of 0.5mm. The mold temperature is controlled at 45℃, foaming for 3 minutes at 45℃, and then curing at 50℃ for 30 minutes. (After curing, the surface hardness of the foam is tested using a Shore D hardness tester. If the hardness is ≥60D, it is considered to be qualified for curing and can be demolded.) After demolding, the rigid foam is cured in a constant temperature and humidity chamber (temperature 25℃, relative humidity 50%) for 72 hours. During the curing period, direct sunlight and mechanical impact are avoided. After curing, the rigid foam is cut using a CNC cutting machine to remove edge burrs and obtain composite foam material.

[0107] Example 2 Example 2 is basically the same as Example 1, except that: In step S23, castor oil-derived polyether polyol is replaced with soybean oil-modified polyether polyol.

[0108] Example 3 Example 3 is basically the same as Example 1, except that: In step S22, the amount of composite acid catalyst used is 2.5 wt%.

[0109] Example 4 Example 4 is basically the same as Example 1, except that: In step S22, the amount of composite acid catalyst used is 1.5 wt%.

[0110] Example 5 Example 5 is basically the same as Example 1, except that: In step S23, the mass ratio of corn cob polyol to castor oil-derived polyether polyol is 11:3.

[0111] Example 6 Example 6 is basically the same as Example 1, except that: In step S23, the mass ratio of corn cob polyol to castor oil-derived polyether polyol is 3:7.

[0112] Example 7 Example 7 is basically the same as Example 1, except that: In step S21, KH-560 silane coupling agent was not added.

[0113] Example 8 Example 8 is basically the same as Example 1, except that: In step S21, no cellulase solution was added.

[0114] Example 9 Example 9 is basically the same as Example 1, except that: In step S23, the flame retardant materials PA-MMT and Mg(OH)2 were not added.

[0115] Example 10 Example 10 is basically the same as Example 1, except that: In step S23, maleic anhydride-modified lignin derivatives, which are nucleating agents, were not added.

[0116] Comparative Example 1 Comparative Example 1 and Example 1 are basically the same, except that: In step S21, the composite acid catalyst is replaced with a catalyst containing only hydrochloric acid and no medium-strong acid phosphoric acid catalyst.

[0117] Comparative Example 2 Comparative Example 2 provides a composite foaming material obtained by foaming and curing petroleum-based polyether polyol, 4,4'-diphenylmethane diisocyanate, foaming agent cyclopentane, water, and catalyst triethanolamine.

[0118] The density (kg / m³), thermal conductivity (W / (m·K)), room temperature compressive strength (test conditions: 25℃, 10% strain, MPa), low temperature compressive strength (test conditions: -20℃, 10% strain, MPa), dimensional stability (test conditions: -40℃ to 60℃ for 10 cycles, %), thermal decomposition temperature (temperature at 5% weight loss, ℃), average pore size (μm), closed-cell rate (%), water absorption rate (24h, 25℃, %), flammability rating, and aging resistance (70℃, 95%RH, 1000h) of the composite foamed materials in Examples 1-10 and Comparative Examples 1-2 were tested. The test results are shown in Table 1.

[0119] The density was tested according to ASTM D7710-14 standard, using a Shimadzu AUW220D analytical balance (accuracy 0.0001g) and a 1000mL graduated cylinder.

[0120] The thermal conductivity was tested according to the GB / T 10294-2008 standard "Determination of Steady-State Thermal Resistance and Related Properties of Insulation Materials - Protective Hot Plate Method", and the testing equipment was an EKOHC-074-200 thermal conductivity meter.

[0121] The compressive strength at room temperature (25℃, 10% strain) was tested according to ASTM D695 standard, and the testing equipment was an Instron 68TM-50 universal testing machine (50kN sensor).

[0122] The low-temperature compressive strength (-20℃, 10% strain) was tested according to GB / T 20284-2006 standard. The testing equipment was an Instron 68TM-50 universal testing machine (50kN sensor) and a low-temperature environment chamber.

[0123] Dimensional stability (10 cycles at -40℃ to 60℃) was tested according to GB / T 8811-2019 standard, using a Mitutoyo digital micrometer (accuracy ±0.001mm). A lower dimensional stability value indicates greater stability.

[0124] The thermal decomposition temperature (5% weight loss) was determined by TG-DTG thermogravimetric analysis (10℃ / min, N2 atmosphere) using a Netzsch TG 209 F3 Tarsus thermogravimetric analyzer.

[0125] The average pore size was statistically analyzed using SEM, with the testing equipment being a Nova NanoSEM 630 scanning electron microscope (accelerating voltage 10kV).

[0126] The closed-cell rate was tested according to the GB / T 10799-2008 standard "Determination of Open and Closed Cell Volume Percentage of Rigid Foamed Plastics", specifically using Archimedes' displacement method and density measurement.

[0127] Water absorption (24h, 25℃) was tested according to ASTM D2842-19 standard, and the testing equipment was an electronic balance (accuracy 0.001g).

[0128] The combustion performance rating is tested according to the GB / T 8624-2012 standard, and the testing equipment is a horizontal combustion tester.

[0129] The aging resistance (70℃, 95%RH, 1000h) was tested according to GB / T 14683-2017 standard. The testing equipment was a thermal conductivity meter and a universal testing machine. The thermal conductivity change rate was represented by D, and the compressive strength retention rate was represented by K.

[0130] Table 1

[0131] From Table 1, we can obtain: The composite foam materials in Examples 1-10 of this application have a thermal conductivity of 0.015 W / (m·K) to 0.016 W / (m·K), which is lower than that of the comparative examples, thus reducing the daily power consumption of refrigerators. Their low-temperature compressive strength is ≥0.95 MPa at -20℃, making them suitable for refrigerator freezers. Their closed-cell rate is ≥98.5%, preventing moisture from affecting insulation. Their dimensional stability is ≤1.5% after 10 cycles at -40℃ to 60℃, ensuring the refrigerator door seal is not easily compromised. Their density is ≥29.5 kg / m³, meeting the lightweight requirements of refrigerators. Furthermore, the flame retardant properties, thermal decomposition temperature, and aging resistance of these examples are superior to those of the comparative examples, significantly improving the performance of the composite foam materials. This addresses the technical shortcomings of existing refrigerator polyurethane rigid foam, such as reliance on fossil-based raw materials, high thermal conductivity, poor low-temperature mechanical properties, insufficient dimensional stability, and low efficiency, large performance fluctuations, and poor controllability of the bio-based rigid foam manufacturing process.

[0132] The technical solutions provided by the embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for preparing a composite foamed material, characterized in that, Includes the following steps: Plant-based waste, polyhydroxy alcohol and composite acid catalyst are mixed and microwave depolymerized to obtain plant-based polyol, wherein the composite acid catalyst includes strong acid and medium strong acid. A bio-based polyether polyol, a crosslinking catalyst, and an isocyanate compound are provided and mixed with the plant-based polyol, and then subjected to a foaming treatment to obtain a composite foam material.

2. The preparation method according to claim 1, characterized in that, Before mixing the plant-based waste with the polyhydroxy alcohol, the process further includes: pretreatment; the pretreatment includes sequential crushing, sieving, drying, silane coupling agent treatment, and cellulase treatment; wherein... The average particle size of the crushed and screened plant-based waste is 330μm~370μm; the specific surface area of ​​the crushed and screened plant-based waste is 1m² / g~1.5m² / g. The moisture content of the dried plant-based waste is less than or equal to 4 wt%. The silane coupling agent used in the silane coupling agent treatment includes one or more of KH-560, KH-550, KH-570, and A-171; the mass ratio of the plant-based waste to the silane coupling agent is 100:(0.1~0.5); the temperature of the silane coupling agent treatment is 50℃~80℃, and the treatment time is 20min~40min; The mass ratio of the plant-based waste to the cellulase is 100:(8~12); the temperature of the cellulase treatment is 45℃~55℃, the pH of the cellulase treatment is 4.5~5.2, and the treatment time is 20min~40min.

3. The preparation method according to claim 1, characterized in that, The plant-based waste includes one or more of the following: corn cobs, corn stalks, wheat straw, rice husks, and sugarcane bagasse. The polyhydroxy alcohols include one or more of glycerol, 1,2-propanediol, a mixture of glycerol and PEG400, xylitol, and sorbitol. The strong acid includes one or more of hydrochloric acid, p-toluenesulfonic acid, methanesulfonic acid, and sulfuric acid; The moderately strong acid includes one or more of phosphoric acid, aminosulfonic acid, and citric acid; The molar ratio of the strong acid to the moderately strong acid is (1~2):(1~2). The mass ratio of the plant-based waste to the polyhydroxy alcohol is 1: (8~12); The mass ratio of the plant-based waste and the polyhydroxy alcohol to the composite acid catalyst is 100:(1.5~2.5).

4. The preparation method according to claim 1, characterized in that, The microwave depolymerization process is carried out in an inert atmosphere; The conditions for the microwave depolymerization process are as follows: microwave power of 1000W~1400W, temperature of 185℃~195℃, and time of 1.5h~3h. After the microwave depolymerization treatment, the process further includes: adding an alkali to neutralize to a neutral pH; the neutralization with an alkali ensures that no acidic substances remain; the alkali includes one or more of sodium hydroxide, sodium carbonate, and sodium bicarbonate; After alkali neutralization, the process further includes: filtration, taking the filtrate, removing water, and obtaining the plant-based polyol; The plant-based polyol has a hydroxyl value of 255 mg KOH / g to 265 mg KOH / g and a viscosity of 3000 mPa·s to 4000 mPa·sm.

5. The preparation method according to claim 1, characterized in that, The hydroxyl value of the bio-based polyether polyol is 190 mg KOH / g to 220 mg KOH / g lower than that of the plant-based polyol; the hydroxyl value of the bio-based polyether polyol is 50 mg KOH / g to 65 mg KOH / g; and the viscosity of the bio-based polyether polyol is 800 mPa·s to 1200 mPa·sm. The bio-based polyether polyols include one or more of castor oil-derived polyether polyols and soybean oil-modified polyether polyols. The crosslinking catalyst includes one or more of amine catalysts and metal catalysts; the amine catalyst includes one or more of triethanolamine, diethanolamine, triethylamine, dimethylethanolamine, dimethylcyclohexylamine, triethylenediamine, tetramethylethylenediamine, tetramethylpropylenediamine, pentamethyldiethylenetriamine, N,N-dimethylbenzylamine, N,N-dimethylaniline, and triisopropanolamine; the metal catalyst includes one or more of stannous octoate, dibutyltin dilaurate, bismuth isooctanoate, bismuth neodecanoate, zinc naphthenate, zinc isooctanoate, cobalt isooctanoate, zirconium naphthenate, zirconium acetylacetonate, titanium acetylacetonate, organotin catalysts, and organobismuth catalysts. The isocyanate compounds include one or more of the following: isocyanate, 4,4'-diphenylmethane diisocyanate, 2,6-toluene diisocyanate, naphthalene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, hydrogenated diphenylmethane diisocyanate, and phenylmethylene diisocyanate.

6. The preparation method according to claim 1, characterized in that, The mixing of the bio-based polyether polyol, the crosslinking catalyst, the isocyanate compound, and the plant-based polyol comprises: mixing the bio-based polyether polyol, the crosslinking catalyst, and the plant-based polyol to obtain component A; mixing component A and component B, wherein component B includes the isocyanate compound; wherein... The bio-based polyether polyol and the plant-based polyol are mixed to obtain a polyol mixture, wherein the hydroxyl value of the polyol mixture is 80 mg KOH / g to 120 mg KOH / g; The mass ratio of the plant-based polyol to the bio-based polyether polyol is (3~11):(3~7). The mass ratio of the plant-based polyol and the bio-based polyether polyol to the crosslinking catalyst is 100:(0.3~0.5). The isocyanate index of the mixture of component A and component B is 1.0 to 1.

4.

7. The preparation method according to claim 6, characterized in that, The preparation of component A further includes: adding a flame-retardant material; wherein, The flame-retardant material includes one or more of intercalation compounds and metal hydroxides; The intercalation complex comprises organic acidic compounds and layered silicate clay minerals; The organic acidic compounds include one or more of phytic acid, tannic acid, gallic acid, humic acid, 2-hydroxyphosphonoacetic acid, hydroxyethylidene diphosphonic acid, aminotrimethylene phosphonic acid, and 2-phosphonobutane-1,2,4-tricarboxylic acid. The layered silicate clay minerals include one or more of montmorillonite, rettoite, and bentonite; The mass ratio of the organic acid compound to the layered silicate clay mineral is (1~3):1; The mass ratio of the plant-based polyol and the bio-based polyether polyol to the intercalation complex is 100:(0.5~1.2). The metal hydroxide includes one or more of magnesium hydroxide and aluminum hydroxide; The mass ratio of the plant-based polyol and the bio-based polyether polyol to the metal hydroxide is 100:(0.8~1.8).

8. The preparation method according to claim 6, characterized in that, The preparation of component A further includes: adding a nucleating agent; wherein, The nucleating agent includes lignin derivatives modified with unsaturated dicarboxylic acids and their anhydride derivatives; The unsaturated dicarboxylic acids and their anhydride derivatives include one or more of maleic anhydride, fumaric acid, maleic acid, citraconic acid, citraconic anhydride, itaconic acid, and medoconic acid. The mass ratio of the lignin derivative to the unsaturated dicarboxylic acid and its anhydride derivative is 1:(0.3~0.8). The conditions for modifying the lignin derivative with the unsaturated dicarboxylic acid and its anhydride derivatives are: temperature of 100℃~140℃ and time of 2h~4h. The mass ratio of the plant-based polyol and the bio-based polyether polyol to the nucleating agent is 100:(0.5~1.2).

9. The preparation method according to claim 1, characterized in that, The foaming process includes a foaming stage and a curing stage performed sequentially; wherein... The conditions for the foaming stage are: temperature 40℃~50℃, time 1min~3min; The conditions for the curing stage are: temperature of 50℃~80℃ and time of 30min~60min.

10. A composite foaming material, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 9.

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