Polyurethane foam and method for preparing same

Abstract

A polyurethane foam, according to the technical idea of the present disclosure, comprises a polyol, a foaming agent, an isocyanate, and cellulose nanofibers (CNFs) surface-modified with a silane coupling agent, thereby exhibiting the effects of enhancing thermal insulation performance, reducing thermal conductivity, and improving mechanical strength such as compressive strength and tensile strength.

Description

Polyurethane foam and its manufacturing method

[0001] The present disclosure relates to polyurethane foam and a method for producing the same.

[0002] Cellulose, an eco-friendly material used as a filler and reinforcing agent in polymer composites, is a fiber material made by mechanically or chemically nano-sizing cellulose, a plant-based component. Its surface contains numerous hydroxyl (OH) groups, and the coexistence of crystalline and amorphous regions enhances the strength and flexibility of plastics. It also possesses low density but high mechanical strength relative to its density. Nanocellulose, at its nanoscale size, can act as a nucleating agent in polyurethane composite foams, reducing pore size, which is expected to reduce thermal conductivity. It is expected that the hydroxyl groups on the surface of nanocellulose will interact with isocyanate, a raw material for polyurethane composite foams, to form bonds, thereby increasing mechanical strength.

[0003] Rigid polyurethane foam is used as an insulator in refrigerators, providing them with high insulation and rigidity. Therefore, to reduce refrigerator power consumption and achieve superior physical properties, a method for manufacturing rigid polyurethane foam with improved insulation and mechanical strength is needed.

[0004] Polyurethane resin is hydrophobic, whereas nanocellulose possesses numerous hydroxyl groups, making it hydrophilic. Consequently, compatibility between nanocellulose and polyurethane resin is reduced. Consequently, nanocellulose self-aggregates within the polyurethane resin, interfering with pore formation in the polyurethane foam, weakening its mechanical properties and causing uneven pore size. This, in turn, reduces the insulating properties of polyurethane foam.

[0005] Therefore, research is needed to improve compatibility and interfacial adhesion with polyurethane by imparting appropriate hydrophobicity through surface modification of nanocellulose.

[0006] One aspect of the present disclosure provides a polyurethane foam having excellent mechanical strength and improved insulation performance, including cellulose nanofibers surface-modified with a silane coupling agent, and a method for producing the same.

[0007] The technical problems to be achieved in this document are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by a person having ordinary skill in the technical field to which the present invention belongs from the description below.

[0008] A polyurethane foam according to one embodiment of the present disclosure includes cellulose nanofibers (CNF) surface-modified with a polyol, an isocyanate, a blowing agent, and a silane coupling agent.

[0009] In addition, the cellulose nanofibers may include those having an average diameter of 10 nm to 100 nm and an aspect ratio of 100 to 500.

[0010] Additionally, the silane coupling agent may include a compound represented by the following chemical formula 1.

[0011] [Chemical Formula 1]

[0012]

[0013] In the above chemical formula 1,

[0014] R is a C2-C8 mercaptoalkyl group, a C2-C8 aminoalkyl group, or a C2-C8 epoxyalkyl group,

[0015] n is an integer from 1 to 5.

[0016] Additionally, the silane coupling agent may include at least one selected from 3-glycidoxyalkyl trialkoxysilane, 3-aminoalkyl trialkoxysilane, and 3-mercaptoalkyl trialkoxysilane.

[0017] In addition, the alkyl may be at least one selected from 2 to 8 carbon atoms, or the alkoxy may be at least one selected from 1 to 5 carbon atoms.

[0018] Additionally, the silane coupling agent may be included in the cellulose nanofibers in an amount of 0.1 to 10.0 wt%.

[0019] Additionally, the polyurethane foam may include 10 to 40 wt% of polyol, 20 to 60 wt% of isocyanate, 1 to 25 wt% of blowing agent, and 0.1 to 10.0 wt% of cellulose nanofibers surface-modified with a silane coupling agent.

[0020] Additionally, the overall density of the polyurethane foam may be 22 kg / ㎥ to 40 kg / ㎥, and the center density may be 20 kg / ㎥ to 35 kg / ㎥.

[0021] A method for producing a polyurethane foam according to one embodiment of the present disclosure includes surface-modifying cellulose nanofibers with a silane coupling agent, dispersing the surface-modified cellulose nanofibers in a polyol, mixing the polyol in which the surface-modified cellulose nanofibers are dispersed, an isocyanate, and a blowing agent, and foaming the mixture to produce a polyurethane foam.

[0022] In addition, prior to surface modification of the cellulose nanofibers, the method may further include mixing a silane coupling agent with a solvent at a concentration of 0.1 to 30.0 wt% and hydrolyzing the mixture.

[0023] Additionally, the solvent may include one or more of distilled water, methanol, ethanol, propanol, and butanol.

[0024] In addition, the surface-modified cellulose nanofibers may be dispersed in polyol by a mechanical dispersion method or an ultrasonic dispersion method.

[0025] Additionally, the overall density of the polyurethane foam may be 22 kg / ㎥ to 40 kg / ㎥, and the center density may be 20 kg / ㎥ to 35 kg / ㎥.

[0026] A refrigerator according to one embodiment of the present disclosure includes a cabinet, a door for opening and closing the cabinet, and an insulating material provided on at least one of the cabinet and the door, wherein the insulating material includes cellulose nanofibers (CNF) surface-modified with polyol, isocyanate, a blowing agent, and a silane coupling agent.

[0027] Additionally, the cellulose nanofibers may include those having an average diameter of 10 nm to 100 nm and an aspect ratio of 100 to 500.

[0028] According to the present disclosure, by including cellulose nanofibers surface-modified with a silane coupling agent in polyurethane, the mechanical strength such as compressive strength and tensile strength of the polyurethane foam can be improved, and the cellulose nanofibers surface-modified with the silane coupling agent can act as a nucleating agent during the formation of the polyurethane foam, thereby forming a polyurethane foam having a smaller pore size. In addition, the cellulose nanofibers surface-modified with the silane coupling agent can act as a barrier to prevent the growth of pores in the polyurethane foam, thereby causing a uniform pore distribution, thereby improving the insulation performance and further reducing the thermal conductivity of the polyurethane foam. Furthermore, due to the increased hydrophobicity caused by surface modification with the silane coupling agent, compatibility with a polyurethane resin and interfacial adhesion are improved, thereby improving the mechanical strength such as compressive strength and tensile strength of the final manufactured polyurethane foam.

[0029] The effects that can be obtained from the present disclosure are not limited to the effects mentioned above, and other effects that are not mentioned can be clearly understood by a person having ordinary skill in the art to which the present disclosure belongs from the description below.

[0030] FIG. 1 is a diagram illustrating a process for surface-modifying cellulose nanofibers with a silane coupling agent according to one embodiment. FIG. 1a is a diagram illustrating a step of hydrolyzing a silane coupling agent, FIG. 1b is a diagram illustrating a step of hydrogen-bonding the hydrolyzed silane coupling agent and cellulose nanofibers, and FIG. 1c is a diagram illustrating a step of performing a dehydration condensation reaction between the hydrogen-bonded silane coupling agent and cellulose nanofibers so that the cellulose nanofibers form a covalent bond with the silane coupling agent.

[0031] FIG. 2 is a perspective view illustrating the exterior of a refrigerator according to one embodiment.

[0032] Figure 3 is a drawing showing the inside of the refrigerator shown in Figure 2.

[0033] Fig. 4 is a side cross-sectional view of the refrigerator shown in Fig. 2 taken along the line AA'.

[0034] Figure 5 is a cross-sectional view showing the structure of the freezer door of the refrigerator shown in Figure 2.

[0035] Fig. 6 is a partial cutaway perspective view illustrating the structure of the freezer door of Fig. 2.

[0036] Figure 7 is an exploded perspective view showing the structure of the freezer door of Figure 2.

[0037] Fig. 8 is a drawing showing a structure in which the freezer door handle of Fig. 5 is connected to the freezer door.

[0038] FIG. 9 is a drawing showing the results of measuring the compatibility between cellulose nanofibers surface-modified with a silane coupling agent and non-surface-modified cellulose nanofibers and a polyurethane resin using a scanning electron microscope (SEM) according to one embodiment.

[0039] FIG. 10 is a drawing showing the results of measuring the pore size and uniformity of a polyurethane foam without added cellulose nanofibers, a polyurethane foam including cellulose nanofibers that are not surface-modified, and a polyurethane foam surface-modified with a silane coupling agent using a scanning electron microscope (SEM) according to one embodiment.

[0040] Preferred embodiments of the present invention are described below. However, the embodiments of the present invention may be modified in various ways, and the technical concept of the present invention is not limited to the embodiments described below. Furthermore, the embodiments of the present invention are provided to more fully explain the present invention to those of ordinary skill in the art.

[0041] The terminology used in this application is solely for the purpose of describing specific examples. Therefore, for example, singular expressions include plural expressions unless the context clearly dictates otherwise. Additionally, it should be noted that terms such as "comprise" or "have" used in this application are used to clearly indicate the presence of features, steps, functions, components, or combinations thereof described in the specification, and are not used to preliminarily exclude the presence of other features, steps, functions, components, or combinations thereof.

[0042] Meanwhile, unless otherwise defined, all terms used herein should be considered to have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Therefore, unless explicitly defined herein, specific terms should not be interpreted in an overly idealistic or formal sense. For example, singular expressions herein include plural expressions unless the context clearly indicates otherwise.

[0043] In addition, the terms "about", "substantially", etc. in this specification are used in the sense of or close to the numerical value when manufacturing and material tolerances inherent to the meanings mentioned are presented, and are used to prevent unscrupulous infringers from unfairly using the disclosure contents in which exact or absolute numerical values ​​are mentioned to aid in the understanding of the present invention.

[0044] When surface-modifying nanocellulose using a silane coupling agent for compatibility with polyurethane, the silane coupling agent can mask the hydroxyl groups on the surface of nanocellulose, and the hydrophobicity of nanocellulose can be improved through the hydrophobic functional group of the silane coupling agent. In the case of polyurethane resin, it has a small amount of hydrophilicity rather than complete hydrophobicity. Therefore, nanocellulose surface-modified with a silane coupling agent can impart appropriate hydrophobicity to polyurethane resin with a small amount of hydrophilicity, and hydrophilicity can react with hydrophilicity and hydrophobicity with hydrophobicity, thereby improving the interfacial adhesion and compatibility between nanocellulose and polyurethane resin.

[0045] Accordingly, in the present disclosure, an optimal nanocellulose capable of improving the compatibility and interfacial adhesion between nanocellulose and polyurethane resin was derived, and a silane coupling agent suitable for surface modification of the nanocellulose was derived. By controlling the concentration of the silane coupling agent, the dispersion method with polyurethane, etc. during surface modification of the derived nanocellulose, the mechanical properties as well as the insulation performance of the polyurethane foam can be maximized.

[0046] The polyurethane foam of the present disclosure includes cellulose nanofibers (CNF) to impart mechanical properties to the polyurethane resin, and the cellulose nanofibers can be surface-modified with an optimal silane coupling agent to improve compatibility and interfacial adhesion between the polyurethane resin and the cellulose nanofibers.

[0047] Hereinafter, a polyurethane foam according to one embodiment of the present disclosure will be described in detail.

[0048] In the present disclosure, 'surface modification' means that the hydroxyl group on the surface of cellulose nanofibers is covered and replaced by a silane coupling agent.

[0049] The polyurethane foam of the present disclosure comprises cellulose nanofibers (CNF) surface-modified with a silane coupling agent, a polyol, a blowing agent, and an isocyanate.

[0050] The present disclosure includes cellulose nanofibers to improve the mechanical properties and insulation performance of polyurethane foam, and the cellulose nanofibers are surface-modified with a silane coupling agent.

[0051] The above cellulose nanofibers act as a nucleating agent when forming polyurethane foam. In polyurethane foam, a nucleating agent acts as a nucleus that allows bubbles to grow. By acting as a nucleating agent, the cellulose nanofibers can make the pores of the polyurethane foam more uniform and smaller, thereby reducing the thermal conductivity of the polyurethane foam. In addition, the cellulose nanofibers impart mechanical strength properties such as compressive strength and tensile strength to the polyurethane foam, resulting in excellent mechanical properties while also improving insulation performance due to the uniform distribution of small pores.

[0052] The above cellulose nanofibers may include those having an average diameter of 10 nm to 100 nm, preferably 10 nm to 20 nm, and an aspect ratio of 100 to 500, preferably 5 to 150. If the average diameter and aspect ratio of the cellulose nanofibers are too small, they may not be suitable for imparting mechanical strength properties such as compressive strength and tensile strength to the polyurethane foam, and if they are too large, the raw material transport filter and nozzle may be clogged, making foaming difficult. Therefore, using cellulose nanofibers that satisfy the above-described average diameter and aspect ratio can impart mechanical strength properties such as compressive strength and tensile strength to the polyurethane foam, thereby producing a polyurethane foam having excellent mechanical properties while also having improved insulation performance due to uniform distribution of small pores, and can prevent the problem of the cellulose nanofibers being caught in the filter or nozzle when using a high-pressure foaming machine, which is preferable.

[0053] The above cellulose nanofibers are surface-modified with a silane coupling agent, and the silane coupling agent combines with the hydroxyl group of the cellulose nanofibers to mask the hydrophilic group of the cellulose nanofibers, and the hydrophobicity of the cellulose nanofibers surface-modified with the silane coupling agent increases through the hydrophobic functional group of the silane coupling agent. Therefore, the cellulose nanofibers surface-modified with the silane coupling agent according to the present disclosure can have improved compatibility and interfacial adhesion with hydrophobic polyurethane, and can have improved dispersibility within a hydrophobic polyurethane resin.

[0054] The above silane coupling agent may include a compound represented by the following chemical formula 1.

[0055] [Chemical Formula 1]

[0056]

[0057] In the above chemical formula 1,

[0058] R is a C2-C8 mercaptoalkyl group, a C2-C8 aminoalkyl group, or a C2-C8 epoxyalkyl group,

[0059] n is an integer from 1 to 5.

[0060] Specifically, the silane coupling agent may include at least one selected from 3-glycidoxyalkyl trialkoxysilane, 3-aminoalkyl trialkoxysilane, and 3-mercaptoalkyl trialkoxysilane. In this case, the alkyl may be at least one selected from 2 to 8 carbon atoms, or the alkoxy may be at least one selected from 1 to 5 carbon atoms.

[0061] The above silane coupling agent may be included in the cellulose nanofibers in an amount of 0.1 to 10.0 wt%, and preferably in an amount of 0.3 to 0.7 wt%.

[0062] If the content of the silane coupling agent included in the above cellulose nanofibers is too low, the amount is not sufficient to react with the hydrophilic cellulose nanofibers, and thus the surface modification of the cellulose nanofibers cannot be sufficiently achieved. If the content of the silane coupling agent is too high, the amount is greater than the amount required to modify the cellulose nanofibers to be hydrophobic, which may be economically disadvantageous.

[0063] As described above, cellulose nanofibers surface-modified with a silane coupling agent can improve the insulating performance of polyurethane foam by acting as a barrier to prevent pore growth in the polyurethane foam and thereby enabling a small and uniform pore distribution.

[0064] The cellulose nanofibers surface-modified with the above silane coupling agent can be included in the polyurethane foam in an amount of 0.1 to 10.0 wt%, preferably 0.3 to 0.7 wt%, and more preferably 0.5 wt%.

[0065] If the content of the surface-modified cellulose nanofibers is too low, the mechanical strength properties such as compressive strength and tensile strength of the polyurethane foam may be inferior, and self-aggregation may occur due to the low compatibility of the cellulose nanofibers, which may increase stress and hinder pore formation of the polyurethane foam. In addition, if the content of the surface-modified cellulose nanofibers is too high, the improvement in mechanical properties compared to the content used and the effect of forming a uniform pore distribution of the polyurethane foam may be minimal.

[0066] As described above, the cellulose nanofibers surface-modified with a silane coupling agent improve the mechanical strength, such as the compressive strength and tensile strength, of polyurethane foam, and act as a nucleating agent during the formation of polyurethane foam, thereby forming polyurethane foam with a smaller pore size. In addition, they function as a barrier to prevent the growth of polyurethane foam pores, thereby inducing a uniform pore distribution, thereby improving insulation performance and further reducing the thermal conductivity of the polyurethane foam. In addition, due to the increased hydrophobic properties obtained by surface modification with a silane coupling agent, compatibility with the polyurethane resin and interfacial adhesion are improved, thereby improving the mechanical strength, such as the compressive strength and tensile strength, of the final polyurethane foam.

[0067] The polyol included in the polyurethane foam of the present disclosure may be an aliphatic compound having two or more hydroxyl groups (-OH) in its molecule, as a basic raw material that reacts with isocyanate to form polyurethane.

[0068] For example, the polyol may be a polyether polyol or a polyester polyol. Specifically, polyalkylene glycol polyols such as polypropylene glycol polyol and polytetramethylene ether glycol polyol; amine terminated polyether polyol; and polyester polyols such as adipic acid, phthalic acid, phthalic anhydride, terephthalic acid, and terephthalic anhydride may be used.

[0069] The isocyanate included in the polyurethane foam of the present disclosure is a basic raw material that reacts with polyol to form polyurethane, and a polyisocyanate compound for rigid polyurethane foam can be used. For example, the isocyanate may be methylene diphenyl diisocyanate (MDI) or toluene diisocyanate (TDI). The isocyanate may be methylene diphenyl diisocyanate in a liquid or solid form. When liquid methylene diphenyl diisocyanate is used, handling is easy, the reaction speed is improved, and the physical properties of the manufactured polyurethane foam can be improved.

[0070] The polyol may be included in the polyurethane foam in an amount of 10 to 40 wt%, and the isocyanate may be included in the polyurethane foam in an amount of 20 to 60 wt%. If the polyol or isocyanate is outside the above range, polyurethane formation may not be smooth.

[0071] The foaming agent included in the polyurethane foam of the present disclosure may be a physical foaming agent or a chemical foaming agent.

[0072] The above physical blowing agent refers to a blowing agent that forms bubbles by mixing gas or generating heat of reaction using a decomposition or vaporization blowing agent, and does not participate in a polymer reaction. The above chemical blowing agent refers to a blowing agent that causes foaming by gas generated through a chemical reaction.

[0073] Specifically, a hydrocarbon can be used as a physical blowing agent, such as a C3-C8 hydrocarbon (e.g., isobutane, isopentane, etc.) or a C5-C6 cycloalkane. Water can be used as a chemical blowing agent. For example, the blowing agent may include water and cyclopentane. In this case, the water reacts with an isocyanate group to produce carbon dioxide, and the cyclopentane acts to form bubbles.

[0074] The above-mentioned foaming agent may be included in the polyurethane foam at 1 to 25 wt%. When the above-mentioned foaming agent is included within the above range, the foaming reaction rate can be appropriately controlled to produce a polyurethane foam having a small pore size, the thermal conductivity of the final polyurethane foam can be controlled to be low, and a foam having sufficient strength at an optimal density can be produced.

[0075] The polyurethane foam of the present disclosure containing the above components may further contain additives such as a catalyst, a surfactant, and a flame retardant, as needed.

[0076] The above catalyst helps to actively react polyol and isocyanate, and for example, an amine catalyst or a metal catalyst can be used. Specifically, tertiary amine catalysts such as triethylenediamine, N-methylmorpholine, N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetramethylhexamethylenediamine, N,N-dimethylcyclohexylamine, etc.; metal catalysts such as potassium acetate, potassium octylate, etc. can be used.

[0077] The above surfactant helps the polyol and isocyanate to be mixed uniformly, lowers the surface tension of the polyurethane to help bubble growth, lowers the pressure difference between bubbles to prevent gas diffusion and polyurethane foam from becoming uneven, and plays a role in controlling the bubble structure. The above surfactant may be a silicone-based surfactant, and specifically, polydimethylsiloxane, or a graft copolymer or block copolymer of polydimethylsiloxane and polyalkylene oxide, etc. may be used. The polyalkylene oxide may be polyethylene oxide having a weight average molecular weight of about 5,000 to 8,000, polypropylene oxide, a random copolymer of ethylene oxide and propylene oxide, or a block copolymer.

[0078] The flame retardant may be a halogen-containing compound, an organic phosphate ester, or a metal compound such as antimony trioxide or aluminum hydroxide.

[0079] The overall density of the polyurethane foam of the present disclosure including the above components may be 22 kg / ㎥ to 40 kg / ㎥, and the center density may be 20 kg / ㎥ to 35 kg / ㎥. That is, the density may tend to appear higher the farther away from the center of the polyurethane foam.

[0080] Hereinafter, a method for manufacturing polyurethane foam according to one embodiment of the present disclosure is described in detail.

[0081] The method for producing a polyurethane foam of the present disclosure comprises surface-modifying cellulose nanofibers with a silane coupling agent, dispersing the surface-modified cellulose nanofibers in a polyol, mixing the polyol in which the surface-modified cellulose nanofibers are dispersed, an isocyanate, and a blowing agent, and foaming the mixture to produce a polyurethane foam.

[0082] First, the surface of cellulose nanofibers is modified with a silane coupling agent.

[0083] Figure 1 is a drawing illustrating a process of surface modifying cellulose nanofibers with a silane coupling agent.

[0084] Referring to FIG. 1, a method for surface-modifying cellulose nanofibers with a silane coupling agent according to one embodiment comprises: hydrolyzing a silane coupling agent (FIG. 1a), hydrogen-bonding the hydrolyzed silane coupling agent with cellulose nanofibers (FIG. 1b), and performing a dehydration condensation reaction between the hydrogen-bonded silane coupling agent and cellulose nanofibers so that the cellulose nanofibers form a covalent bond with the silane coupling agent, thereby surface-modifying the cellulose nanofibers (FIG. 1c).

[0085] Specifically, for hydrolysis of the silane coupling agent, a silane coupling agent solution is prepared by mixing the silane coupling agent with a solvent at a concentration of 0.1 to 30.0 wt%. At this time, the solvent may be distilled water or an organic solvent containing a hydroxyl group such as methanol, ethanol, propanol, or butanol.

[0086] In addition, a pH regulator may be used to control pH when preparing the above silane coupling agent solution. As the pH regulator, an acidic (pH 3-4) pH regulator such as acetic acid or hydrogen chloride, or a basic (pH 9-10) pH regulator such as sodium hydroxide or potassium hydroxide may be used.

[0087] Next, cellulose nanofibers are mixed and dispersed in the hydrolyzed silane coupling agent solution. At this time, hydrogen bonds are formed between the hydroxyl groups (-OH) of the hydrolyzed silane coupling agent and the hydroxyl groups (-OH) of the cellulose nanofibers. Next, the hydrogen-bonded silane coupling agent and cellulose nanofiber solution are subjected to dehydration condensation and drying at a temperature of 100 to 180°C. The high heat at this time causes the water connected by the hydrogen bonds to escape, resulting in a dehydration condensation reaction, which results in the formation of covalent bonds between the silane coupling agent and nanocellulose.

[0088] Afterwards, the surface-modified cellulose nanofibers are mixed with polyol, isocyanate, and a foaming agent and foamed to produce polyurethane foam.

[0089] Specifically, the surface-modified cellulose nanofibers are dispersed in polyol, and then a foaming agent and an isocyanate are added, mixed, and foamed to produce a polyurethane foam.

[0090] Methods for dispersing the surface-modified cellulose nanofibers in polyol include mechanical dispersion using physical dispersion, ultrasonic dispersion using electrochemical dispersion, and the like. In particular, when surface-modified cellulose nanofibers are dispersed in polyol by an ultrasonic dispersion method, the cellulose nanofibers are more evenly dispersed in the polyol, thereby forming smaller pore sizes in the polyurethane foam and lowering the thermal conductivity.

[0091] The polyurethane foam of the present disclosure manufactured as described above can improve the mechanical strength, such as the compressive strength and tensile strength, of the polyurethane foam by including cellulose nanofibers surface-modified with a silane coupling agent, and can form a polyurethane foam in which pores having smaller sizes are uniformly distributed, thereby reducing thermal conductivity and improving insulation performance.

[0092] Below, a refrigerator according to one embodiment of the present disclosure is described in detail.

[0093] FIG. 2 is a perspective view illustrating the exterior of a refrigerator according to one embodiment, FIG. 3 is a drawing illustrating the interior of a refrigerator according to one embodiment, and FIG. 4 is a side cross-sectional view of the refrigerator taken along line AA' according to one embodiment.

[0094] Referring to FIGS. 2 to 4, a refrigerator (100) may include a cabinet (110), a storage compartment (120, 150) formed inside the cabinet (110), a storage compartment door (130, 140, 200) that is rotatably provided on the front of the cabinet (110) to shield the storage compartment (120, 150) from the outside, and a cold air supply device (not shown) that supplies cold air to the storage compartment (120, 150).

[0095] The cabinet (110) may include an inner case (111) forming a storage room, an outer case (112) coupled to the outside of the inner case (111), and an insulating material (250) disposed between the inner case (111) and the outer case (112) to prevent cold air from leaking out of the storage room (120, 150) and prevent external heat from entering the storage room.

[0096] The insulation (250) may be formed of polyurethane foam (250). Specifically, the insulation (250) may be formed of polyurethane foam (250) including cellulose nanofibers surface-modified with a silane coupling agent of the present disclosure. Hereinafter, the terms "insulation (250)" and "polyurethane foam (250)" may be used as terms referring to the same object.

[0097] This polyurethane foam (250) may have an overall density of 22 kg / ㎥ to 40 kg / ㎥, and a center density of 20 kg / ㎥ to 35 kg / ㎥. That is, the density may tend to become higher the farther away from the center of the polyurethane foam (250).

[0098] A machine room (190) may be formed at the bottom of the cabinet (110). Components such as a compressor (191) are accommodated in the machine room (190), and refrigerant is compressed at high temperature and high pressure. Accordingly, a large amount of heat is generated in the machine room (190), and a polyurethane foam (250) including cellulose nanofibers surface-modified with a silane coupling agent according to the present disclosure may be applied to block the generated heat from being supplied to the storage room (120, 150).

[0099] The storage room (120, 150) can be partitioned into a refrigerator room (120) on the upper side and a freezer room (150) on the lower side by a middle partition. The refrigerator room (150) can be maintained at a temperature of approximately 3°C, and the freezer room (150) can be maintained at a temperature of approximately -18°C.

[0100] The refrigerator (120) is provided with an open front so that food can be stored, and the open front can be opened and closed by a pair of refrigerator doors (130, 140) that are rotatably connected by a hinge member (not shown). The refrigerator doors (130, 140) include a left door (130) that opens and closes the left side of the refrigerator (120) and a right door (140) that opens and closes the right side of the refrigerator (120). A shelf (121) on which food can be placed can be provided inside the refrigerator (120).

[0101] A refrigerator door handle (131, 141) that can open and close the refrigerator door (130, 140) may be provided on the front of the refrigerator door (130, 140), and the refrigerator door handle (131, 141) may include a left door handle (131) that can open and close the left side of the refrigerator (120) and a right door handle (141) that opens and closes the right side of the refrigerator (140). In addition, a door guard (132, 142) that can place food on may be provided on the back of the refrigerator door (130, 140), and the door guard (132, 142) may include a left door guard (132) that is provided on the back of the left door (130) and a right door guard (142) that is provided on the back of the right door (140).

[0102] Meanwhile, polyurethane foam (250) according to the present disclosure may be applied to the interior of the refrigerator door (130, 140) to prevent cold air from leaking out from the interior of the refrigerator (120) and to prevent external warm air from flowing into the interior of the freezer (150).

[0103] The freezer (150) is provided with an open front to allow food storage, and can be opened and closed by a freezer door (200) that is provided to slide back and forth. A storage box (160) can be provided on the back of the freezer door (200).

[0104] A movable rail part (170) may be coupled to the freezer door (200) and the storage box (160), and the movable rail part (170) may be slidably supported by a fixed rail part (180) formed in the cabinet (110). Accordingly, the freezer door (200) and the storage box (160) may be slidably supported with respect to the cabinet (110). A freezer door handle (290) capable of opening and closing the freezer door (200) may be provided on the front of the freezer door (200).

[0105] Meanwhile, the polyurethane foam (250) according to the present disclosure may be applied to the freezer door (200) to prevent cold air from leaking inside the freezer (150) and to prevent external heat from entering inside the freezer (150).

[0106] The cold air supply device may include a compressor (191) that compresses a refrigerant, a condenser (not shown) that condenses the refrigerant, a capillary tube (not shown) that expands the refrigerant, and an evaporator (not shown) that evaporates the refrigerant to generate cold air.

[0107] Above, an example of a refrigerator structure according to one embodiment of the present disclosure has been described.

[0108] Next, an example in which the polyurethane foam (250) according to the present disclosure is applied to a refrigerator (100) will be described in detail. Hereinafter, for convenience of explanation, an example in which the polyurethane foam (250) according to the present disclosure is applied to a freezer door (200) will be described.

[0109] FIG. 5 is a cross-sectional view showing the structure of the freezer door (200) of the refrigerator (100) shown in FIG. 2, FIG. 6 is a partial cutaway perspective view showing the structure of the freezer door (200) of FIG. 2, FIG. 7 is an exploded perspective view showing the structure of the freezer door of FIG. 2, and FIG. 8 is a drawing showing the structure in which the freezer door handle (290) of FIG. 5 is coupled to the freezer door (200).

[0110] Referring to FIGS. 5 to 8, a freezer door (200) according to one embodiment may include an outer panel (210), an inner panel (220), an upper cap (230), and a lower cap (240). The outer panel (210), the inner panel (220), the upper cap (230), and the lower cap (240) may be assembled together to form an internal space.

[0111] The internal space may be a single closed space, and a polyurethane foam (250) including cellulose nanofibers surface-modified with a silane coupling agent of the present disclosure may be placed between the outer plate (210) and the inner plate (220). The polyurethane foam (250) may be prepared by filling a urethane solution between the outer plate (210) and the inner plate (220).

[0112] The outer panel (210) may include a front portion (211) forming the front of the freezer door (200), side portions (212, 213) forming both sides of the freezer door (200), and a connecting portion (214, 215) connected to the inner panel (220). The outer panel (210) may be made of a wood material or a plastic material to provide rigidity and aesthetics, or may be made of a mixed material thereof, and may be surface-treated to improve the appearance and durability. In addition, a transparent or opaque paint or varnish may be applied to the front portion (211) of the outer panel (210), and a coating material having a waterproofing function or an antibacterial function may be treated.

[0113] The inner plate (220) is joined to the back surface of the outer plate (210) and forms the back surface of the freezer door (200). The inner plate (220) may have a concave fan slot (216, 217) formed on the edge of the inner plate (220) so that a gasket (not shown) may be placed. The inner plate (220) may be made of wood or plastic, or a mixture of these, similar to the outer plate (210), and any description overlapping with the outer plate (210) will be omitted below.

[0114] The upper cap (230) is coupled to the upper ends of the outer plate (210) and the inner plate (220), and the lower cap (240) is coupled to the lower ends of the outer plate (210) and the inner plate (220). The upper cap (230) forms the upper surface of the freezer door (200), and the lower cap (240) forms the lower surface of the freezer door (200). The upper cap (230) and the lower cap (240) may be made of the same material as the outer plate (210) or the inner plate (220).

[0115] Additionally, a sealing member may be applied to each of the upper cap (230) and the lower cap (240).

[0116] The upper cap (230) may have a receiving portion (231) to which a freezer door handle (290) is coupled. The receiving portion (231) may be provided to protrude from the front side to the rear side of the freezer door (200), and an receiving space (232) may be formed inside the receiving portion (231) to accommodate a coupling portion (292) of the freezer door handle (290).

[0117] The freezer door handle (290) may include a grip portion (291) that can be held by hand, and a coupling portion (292) that can couple the freezer door handle (290) to the freezer door (200). A plurality of coupling portions (292) may be formed on both sides of the grip portion (291).

[0118] The freezer door handle (290) can be fitted to the freezer door (200) by inserting the connecting portion (292) into the receiving space (232). To strengthen the bonding strength between the freezer door handle (290) and the freezer door (200), the connecting portion (292) and the receiving portion (231) can be fastened by a separate, not-illustrated fastening member.

[0119] An opening (216) may be formed in the outer panel (210) so that the connecting portion (292) of the freezer door handle (290) passes through and is received in the receiving space (232) of the upper cap (230).

[0120] Above, an example in which a polyurethane foam (250) according to one embodiment of the present disclosure is applied to a freezer door (200) has been described. The above structure can also be applied to refrigerator doors (130, 140), cabinets (110), etc., within a range that can be easily conceived by a person having ordinary skill in the art, and the description of the freezer door (200) below may include a description of the refrigerator door (130, 140) and cabinet (110).

[0121] Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the following examples are intended only to illustrate the present invention and the scope of the present invention is not limited to these examples.

[0122] Example 1. Preparation of polyurethane foam containing cellulose nanofibers surface-modified with a silane coupling agent

[0123] A silane aqueous solution containing 1.8 wt% of 3-glycidoxypropyl trimethoxy silane was prepared, and hydrolyzed at room temperature for 1 hour. 0.9 wt% of cellulose nanofibers was added to the hydrolyzed silane aqueous solution and dispersed. Subsequently, unreacted silane was removed by vacuum filtration, and then a dehydration condensation reaction was performed at 110°C for 1 hour to obtain cellulose nanofibers surface-modified with a silane coupling agent. 0.5 wt% of the obtained cellulose nanofibers surface-modified with a silane coupling agent were added to 28.2 wt% of polyol, and ultrasonically dispersed for 1 hour. Next, 14.0 wt% of a physical blowing agent was added to 33.7 wt% of polyol in which cellulose nanofibers surface-modified with a silane coupling agent were dispersed, and the mixture was stirred at 1,500 rpm for 2 minutes. Then, 52.3 wt% of isocyanate was added and mixed at 3,000 rpm for 5 seconds to produce a polyurethane foam including cellulose nanofibers surface-modified with a silane coupling agent.

[0124] Example 2. Preparation of polyurethane foam containing cellulose nanofibers surface-modified with a silane coupling agent

[0125] The same procedure as in Example 1 was followed, except that 3-aminopropyl triethoxysilane was used as a silane coupling agent.

[0126] Example 3. Preparation of polyurethane foam containing cellulose nanofibers surface-modified with a silane coupling agent.

[0127] The same procedure as in Example 1 was followed, except that 3-mercaptopropyltrimethoxysilane was used as a silane coupling agent.

[0128] Comparative Example 1. Manufacturing of polyurethane foam

[0129] 33.7 wt% of polyol and 14.0 wt% of physical blowing agent were mixed and stirred at 1,500 rpm for 2 minutes, then 52.3 wt% of isocyanate was added and mixed for 5 seconds using a mechanical stirrer to produce a pure polyurethane foam that does not contain cellulose nanofibers.

[0130] Comparative Example 2. Preparation of polyurethane foam containing non-surface-modified cellulose nanofibers.

[0131] Cellulose nanofibers were added to distilled water without silane and dispersed, and then dried at 110°C for 1 hour. 0.5 wt% of the cellulose nanofibers, 28.2 wt% of polyol, and 14.0 wt% of a physical blowing agent were mixed and stirred at 1,500 rpm for 2 minutes, and then 52.3 wt% of isocyanate was added and mixed at 3,000 rpm for 5 seconds to produce a polyurethane foam including cellulose nanofibers.

[0132] Experimental Example 1. Evaluation of Compatibility with Polyurethane Resin Depending on Surface Modification of Cellulose Nanofibers

[0133] In order to determine the compatibility with polyurethane resin depending on whether cellulose nanofibers are surface-modified, the compatibility with polyurethane resin was measured using a scanning electron microscope (SEM) using cellulose nanofibers surface-modified with a silane coupling agent of Example 2 and cellulose nanofibers not surface-modified of Comparative Example 2, and the results are shown in Fig. 9.

[0134] As shown in Fig. 9, in the case of non-surface-modified cellulose nanofibers, the cellulose nanofibers were not uniformly dispersed due to low compatibility with the polyurethane resin (Fig. 9 (b)), but in the case of cellulose nanofibers surface-modified with a silane coupling agent, the compatibility with the polyurethane resin improved, and it was confirmed that the cellulose nanofibers were uniformly dispersed within the polyurethane resin (Fig. 9 (c)).

[0135] Experimental Example 2. Evaluation of pore size and uniformity of polyurethane foam according to surface modification of cellulose nanofibers.

[0136] The pore size and uniformity of the polyurethane foams of Example 2 and Comparative Examples 1 and 2 were measured using a scanning electron microscope (SEM), and the results are shown in Fig. 10.

[0137] As shown in Fig. 10, in the case of Comparative Example 1 without adding cellulose nanofibers, the pore size was large and non-uniform (Fig. 10 (a)), and it was confirmed that Comparative Example 2 including non-surface-modified cellulose nanofibers also had large and non-uniform pore sizes (Fig. 10 (b)). On the other hand, in the case of Example 2 including cellulose nanofibers surface-modified with a silane coupling agent according to the present disclosure, it was confirmed that the pore size was small and the pore size was uniformly distributed compared to Comparative Examples 1 and 2 (Fig. 10 (c)).

[0138] Experimental Example 3. Evaluation of the physical properties of polyurethane foam

[0139] The compressive strength, tensile strength, pore size, and thermal conductivity of the polyurethane foams manufactured in Examples 1 to 3 and Comparative Examples 1 to 2 were measured, and the results are shown in Table 1 below.

[0140] Classification Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Silane coupling agent 3-Glycidoxypropyl trimethoxysilane 3-Aminopropyl triethoxysilane 3-Mercaptopropyl trimethoxysilane -- Compressive strength (Pa) 163000 176000 159000 140000 150000 Tensile strength (Pa) 91000 93000 93000 77000 87000 Pore size (㎛) 396.36 378.74 384.15 417.24 13.83 Thermal conductivity (mW / m K) 23.90 22.64 23.17 24.49 24.1

[0141] As shown in Table 1 above, it was confirmed that the polyurethane foam of Example 1 including cellulose nanofibers surface-modified using a silane coupling agent according to the present disclosure had superior compressive strength and tensile strength, and had a smaller pore size, resulting in reduced thermal conductivity and improved insulation performance compared to Comparative Examples 1 and 2. These results indicate that the cellulose nanofibers surface-modified with a silane coupling agent have excellent compatibility and interfacial adhesiveness in the polyurethane resin, thereby acting as a nucleating agent and inducing crosslinking formation in the polyurethane resin, thereby reducing the pore size and improving insulation performance and mechanical strength.

[0142] Experimental Example 4. Evaluation of the physical properties of polyurethane foam according to the dispersion method.

[0143] In order to investigate the effect of the dispersion method of cellulose nanofibers surface-modified with a silane coupling agent on the properties of polyurethane foam, 0.5 wt% of cellulose nanofibers surface-modified with a silane coupling agent of Example 2 was added to 99.5 wt% of polyol, and then dispersed by mechanical dispersion (1 hour) and ultrasonic dispersion (5 hours, 7 hours), respectively. As described above, 14.0 wt% of a physical blowing agent was added to 33.7 wt% of polyol in which cellulose nanofibers surface-modified with a silane coupling agent were dispersed, and stirred at 1,500 rpm for 2 minutes, and then 52.3 wt% of isocyanate was added and mixed at 3,000 rpm for 5 seconds to manufacture a polyurethane foam containing cellulose nanofibers surface-modified with a silane coupling agent.

[0144] The compressive strength, tensile strength, pore size, and thermal conductivity of the polyurethane foam manufactured above were measured, and the results are shown in Table 2 below.

[0145] Distinction Mechanical Dispersion Ultrasonic Dispersion Dispersion Time 1 hour 5 hours 7 hours Compressive Strength (Pa) 149000 142000 136000 Tensile Strength (Pa) 85000 85000 86000 Pore Size (㎛) 413.83 409.52 405.35 Thermal Conductivity (mW / m K) 24.1 23.8 23.7

[0146] As shown in Table 2 above, when cellulose nanofibers surface-modified with a silane coupling agent are dispersed in polyol by ultrasonic dispersion, it was confirmed that the cellulose nanofibers are more evenly dispersed and act as nuclei, resulting in small pore sizes and low thermal conductivity. However, it was found that when the dispersion time is increased, the cellulose nanofibers, which are weak to heat, are destroyed, resulting in a decrease in crystallinity and a decrease in compressive strength. Therefore, it was found that if cellulose nanofibers surface-modified with a silane coupling agent are dispersed in a polyurethane resin for an appropriate period of time by ultrasonic dispersion, a polyurethane foam with improved physical properties can be obtained.

[0147] Experimental Example 5. Evaluation of the physical properties of polyurethane foam according to the content of cellulose nanofibers.

[0148] In order to determine the effect of the content of cellulose nanofibers surface-modified with a silane coupling agent on the properties of polyurethane foam, polyurethane foams were manufactured by varying the content of nanocellulose surface-modified with 3-aminopropyl ethoxysilane in Example 2 and the content of cellulose nanofibers not surface-modified in Comparative Example 2 to 0.3 wt%, 0.5 wt%, and 0.7 wt%, respectively.

[0149] The compressive strength, tensile strength, pore size, and thermal conductivity of the polyurethane foam manufactured above were measured, and the results are shown in Table 3 below.

[0150] Classification Example 2 Comparative Example 2 Cellulose nanofiber (weight%) 0.3 0.5 0.7 0.3 0.5 0.7 Compressive strength (Pa) 15 3 000 17 6 ​​000 16 3 000 14 1 000 15 000 13 7 000 Tensile strength (Pa) 8 9 000 9 3 000 9 000 8 4 000 8 7 000 8 9 000 Pore size (㎛) 3 9 8 3 7 8 7 4 3 8 5 4 5 4 5 4 12 9 5 4 13 8 3 3 9 8 3 2 Thermal conductivity (mW / m K) 2 3 9 4 2 2 6 4 2 3 2 5 2 4 4 7 2 4 12 3 9 4

[0151] As shown in Table 3 above, in the case of Comparative Example 2 containing non-surface-modified cellulose nanofibers, self-aggregation occurred at 0.3 wt% or more due to low compatibility with the polyurethane resin, which rather concentrated stress and hindered pore formation, resulting in an increase in pore size and a decrease in mechanical properties. On the other hand, in the case of Example 2 containing cellulose nanofibers surface-modified with a silane coupling agent, it was confirmed that mechanical properties such as compressive strength and tensile strength were improved even at 0.5 wt%. These results indicate that the cellulose nanofibers were evenly dispersed without aggregation even as the content of the cellulose nanofibers increased due to improved compatibility between the cellulose nanofibers and the polyurethane resin through surface modification with a silane coupling agent.

[0152] Experimental Example 5. Evaluation of the properties of polyurethane foam according to the type of nanocellulose.

[0153] In order to determine the effect of nanocellulose types on the properties of polyurethane foam, surface modification was performed with 3-glycidoxypropyl trimethoxysilane in the same manner as in Example 2, except that cellulose nanofibers (CNF), cellulose nanocrystals (CNC), and microcrystalline cellulose (MCC) were used.

[0154] Cellulose nanofibers, cellulose nanocrystals, and microcrystalline cellulose, which were surface-modified with the above silane coupling agent, were each added at 0.5 wt% to 28.2 wt% of polyol and dispersed ultrasonically for 1 hour. Subsequently, 14.0 wt% of a physical blowing agent was added to 33.7 wt% of each polyol in which cellulose nanofibers, cellulose nanocrystals, or microcrystalline cellulose, which were surface-modified with the silane coupling agent, were dispersed, stirred at 1,500 rpm for 2 minutes, and then 52.3 wt% of isocyanate was added and mixed at 3,000 rpm for 5 seconds to produce three types of polyurethane foams.

[0155] The compressive strength, tensile strength, pore size, and thermal conductivity of the three types of polyurethane foam manufactured above were measured, and the results are shown in Table 4 below.

[0156] In Table 4 below, neat PUF means a pure polyurethane foam without nanocellulose added, Si(b)-CNF / PUF means a polyurethane foam containing cellulose nanofibers surface-modified with 3-glycidoxypropyl trimethoxysilane, Si(b)-CNC / PUF means a polyurethane foam containing cellulose nanocrystals surface-modified with 3-glycidoxypropyl trimethoxysilane, and Si(b)-MCC / PUF means a polyurethane foam containing microcrystalline cellulose surface-modified with 3-glycidoxypropyl trimethoxysilane.

[0157] ClassificationSi(b)-CNF / PUFSi(b)-CNC / PUFSi(b)-MCC / PUFneat PUFAverage density (㎏ / ㎥)25.6225.4525.2725.47Compressive strength (Pa)172000162000154000155000Tensile strength (Pa)97000910008900083000Pore size (㎛)383.41389.44397.14419.95Thermal conductivity (mW / m K)25.0625.0524.5024.56Specific thermal conductivity (mW / m K)24.0824.4225.0224.67

[0158] As shown in Table 4 above, when comparing the compressive strength at the same density, Si(b)-CNF / PUF increased by 10.3%, Si(b)-CNC / PUF increased by 4.5%, and Si(b)-MCC / PUF increased by 0% compared to neat PUF. In addition, in the case of tensile strength, Si(b)-CNF / PUF increased by 15.7%, Si(b)-CNC / PUF increased by 9.6%, and Si(b)-MCC / PUF increased by 8.4% compared to neat PUF. In addition, in the case of thermal conductivity, Si(b)-CNF / PUF decreased by 2.4% compared to neat PUF, confirming that it had the most improved insulation performance. From these results, it was found that when cellulose nanofibers (CNF) surface-modified with a silane coupling agent were used in the manufacture of polyurethane foam, the best mechanical properties and insulation performance were achieved. In addition, when cellulose nanocrystals (CNC) and microcrystalline cellulose (MCC) surface-modified with a silane coupling agent were applied to polyurethane foam, they could help improve the mechanical properties, but they did not help improve the insulation performance, so they were not suitable for polyurethane foam for insulation that required insulation performance.

[0159] In conclusion, it was found that when cellulose nanofibers (CNF), which have a smaller particle size than microcrystalline cellulose (MCC) and a larger aspect ratio than cellulose nanocrystals (CNC), are surface-modified with a silane coupling agent and then applied to polyurethane foam for insulation, not only mechanical strength but also insulation performance can be improved.

Claims

1. Polyol, isocyanate, Foaming agent, and A polyurethane foam comprising cellulose nanofibers (CNF) surface-modified with a silane coupling agent.

2. In paragraph 1, A polyurethane foam comprising the above cellulose nanofibers having an average diameter of 10 nm to 100 nm and an aspect ratio of 100 to 500.

3. In paragraph 1, The above silane coupling agent is a polyurethane foam comprising a compound represented by the following chemical formula 1: [Chemical Formula 1] In the above chemical formula 1, R is a C2-C8 mercaptoalkyl group, a C2-C8 aminoalkyl group, or a C2-C8 epoxyalkyl group, n is an integer from 1 to 5.

4. In paragraph 1, A polyurethane foam comprising the silane coupling agent at least one selected from 3-glycidoxyalkyl trialkoxysilane, 3-aminoalkyl trialkoxysilane, and 3-mercaptoalkyl trialkoxysilane.

5. In paragraph 4, A polyurethane foam wherein the alkyl has at least one selected from 2 to 8 carbon atoms, or the alkoxy has at least one selected from 1 to 5 carbon atoms.

6. In paragraph 1, A polyurethane foam in which the silane coupling agent is contained in an amount of 0.1 to 10.0 wt% in cellulose nanofibers.

7. In paragraph 1, The above polyurethane foam, 10 to 40 wt% polyol, 20 to 60 wt% of isocyanate, 1 to 25 wt% of a foaming agent, and A polyurethane foam comprising 0.1 to 10.0 wt% of cellulose nanofibers surface-modified with a silane coupling agent.

8. In paragraph 1, A polyurethane foam comprising a total density of 22 kg / ㎥ to 40 kg / ㎥ and a center density of 20 kg / ㎥ to 35 kg / ㎥.

9. Surface-modify cellulose nanofibers with a silane coupling agent, Dispersing the surface-modified cellulose nanofibers in polyol, A method for producing a polyurethane foam, comprising mixing a polyol, an isocyanate and a blowing agent in which the surface-modified cellulose nanofibers are dispersed, and foaming the mixture to produce a polyurethane foam.

10. In paragraph 9, Prior to surface modification of the above cellulose nanofibers, A method for producing a polyurethane foam, further comprising mixing a silane coupling agent with a solvent at a concentration of 0.1 to 30.0 wt% and performing hydrolysis.

11. In paragraph 10, A method for producing polyurethane foam, wherein the solvent comprises at least one of distilled water, methanol, ethanol, propanol, and butanol.

12. In paragraph 9, A method for producing a polyurethane foam, comprising dispersing the surface-modified cellulose nanofibers in a polyol by a mechanical dispersion method or an ultrasonic dispersion method.

13. In paragraph 9, A method for manufacturing a polyurethane foam, wherein the overall density of the polyurethane foam is 22 kg / ㎥ to 40 kg / ㎥ and the center density is 20 kg / ㎥ to 35 kg / ㎥.

14. Cabinet, A door for opening and closing the above cabinet, and Including insulation provided in at least one of the above cabinets and doors, The above insulation material is, polyol, isocyanate, Foaming agent, and A refrigerator comprising a polyurethane foam containing cellulose nanofibers (CNF) surface-modified with a silane coupling agent.

15. In paragraph 14, A refrigerator comprising the above cellulose nanofibers having an average diameter of 10 nm to 100 nm and an aspect ratio of 100 to 500.

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