Polyurethane foam comprising nanocellulose to which inorganic nanoparticles are chemically bonded and manufacturing method thereof

Abstract

The present invention relates to a polyurethane foam comprising dispersed nanocellulose to which inorganic nanoparticles are chemically bonded and a manufacturing method thereof and, more specifically, to a polyurethane foam comprising dispersed nanoparticle-nanocellulose, and a manufacturing method thereof, wherein the nanocellulose to which inorganic nanoparticles are chemically bonded is uniformly dispersed and impregnated into polyurethane without agglomeration, thereby reducing the cell size compared to existing urethane foams and lowering the thermal conductivity, and the nanoparticle-nanocellulose is uniformly impregnated into cell walls without agglomeration, thereby increasing the compressive strength of the foam.

Description

Polyurethane foam comprising nanocellulose chemically bonded with inorganic nanoparticles and method for producing the same

[0001] The present invention relates to a polyurethane foam containing nanocellulose to which inorganic nanoparticles are chemically bonded and a method for producing the same, and more particularly, to a polyurethane foam containing nanocellulose containing inorganic nanoparticles (hereinafter, 'nanoparticle-nanocellulose') which is uniformly dispersed and impregnated into polyurethane without agglomeration, thereby reducing the cell size compared to existing urethane foams and lowering thermal conductivity, and to a polyurethane foam containing nanocellulose containing inorganic nanoparticles and a method for producing the same, wherein the nanocellulose containing inorganic nanoparticles is uniformly dispersed and impregnated into polyurethane without agglomeration, thereby increasing the compressive strength of the foam.

[0002]

[0003] Appliances like refrigerators, which require a constant temperature difference between their interior and exterior, typically utilize insulating materials to block heat transfer. A refrigerator's insulating wall structure typically consists of steel plates on the exterior, ABS (acrylonitrile-butadiene-styrene) or HIPS (high-impact polystyrene) molded parts on the interior, and insulating materials between them. Polyurethane foam and vacuum insulated panels (VIPs) are commonly used as insulation materials.

[0004] Typically, polyurethane foam uses rigid polyurethane foam, and liquid raw materials are injected under high pressure between the cabinet and cavity of the refrigerator, and then a solid foam shape is manufactured through a foaming process.

[0005] Rigid polyurethane foam offers superior insulation, can seamlessly fill complex shapes, and boasts excellent compressive strength, making it an essential insulation material for refrigerators. Vacuum insulation, which offers even better insulation than polyurethane foam, is often used attached to the sides or back of refrigerators. However, its poor formability, low strength, rapid deterioration of insulation performance upon damage, and high cost limit its use to supplement insulation performance.

[0006] Conventional polyurethane foam improves insulation performance through a number of closed cells filled with a foaming gas having low thermal conductivity, as shown in Fig. 2, and provides excellent strength characteristics by forming a chemical network structure through high cross-linking of polyol and isocyanate, which are raw materials for polyurethane.

[0007] However, with the recent strengthening of global energy consumption regulations, the demand for low-power consumption home appliances is increasing, and in home appliances such as refrigerators that require heat insulation, the demand for high-performance insulating materials with improved thermal conductivity and mechanical strength properties is also increasing significantly to improve efficiency.

[0008] In general, the insulation performance of polyurethane foam can be expressed by the following equation 1.

[0009] [Formula 1]

[0010] λ urethane = λ gas + λ solid + λ radiation + λconvection

[0011] (λ urethane : Thermal conductivity of polyurethane foam, λ gas : Thermal conductivity of the gas within the cell, λ solid : Thermal conductivity of the cell wall, λ radiation : Thermal conductivity due to radiation energy, λconvection: Convective thermal conductivity due to gas circulation within the cell)

[0012] To improve the insulation performance of polyurethane foam, the following methods are being attempted to lower each thermal conductivity.

[0013] λ gas In order to lower the thermal conductivity, there is a method of filling the inside of the cell with a gas with low thermal conductivity, and currently, the method of increasing the ratio of a foaming gas with lower thermal conductivity than air or CO2 is mainly used, and cyclopentane is a representative foaming gas. (Air 25 mW / m·K, CO2 15.7 mW / m·K, cyclopentane 12.7 mW / m·K) Recently, various foaming gases with low thermal conductivity of hydrochlorofluorocarbon and hydrofluoro-olefin series are being developed, but the market is still conservative in actively adopting them due to remaining issues such as global warming index, price, and plastic deterioration.

[0014] λ solid One way to lower the density is to reduce the thickness of the cell wall or increase the diameter of the closed cell to lower the density of the foamed polyurethane. However, refrigerator insulation materials require a certain level of mechanical strength against external impacts, which limits the ability to lower the density of polyurethane. In addition, recently, a method of lowering the thermal conductivity of the cell wall by adding porous materials such as aerogel has been studied, but there are problems such as a decrease in the chemical reaction of urethane, a phenomenon in which the effect is significantly reduced due to the original solution being impregnated into the porous material, and the mixing process is not smooth.

[0015] λ radiation This can be reduced by increasing the density of the foamed polyurethane and reducing the size of the closed cells. Methods have been applied to shorten the gelation reaction time of urethane or to reduce the size of the closed cells by adding nucleating agents, and various attempts are ongoing to form uniform and fine closed cells.

[0016] λconvection is only affected when the cell size is greater than mm, and the effect is so minimal that it can be ignored in the case of polyurethane foam for general refrigerators, which has a cell size of several hundred μm.

[0017] Recently, a method of improving the strength of polyurethane foam by adding CNF has been reported. CNF is a cellulose ((C6H)) which is a major component of plant cell walls. 10 O5) n ) is an eco-friendly nanomaterial that has a crystalline molecular structure and exhibits high mechanical properties and thermal stability. When CNF is combined with polyurethane foam, it acts as a reinforcing material to increase strength, and acts as a nucleating agent for the urethane reaction to reduce cell size and slightly improve thermal conductivity. However, CNF is a nanomaterial with a large specific surface area and countless hydroxyl groups (-OH) on the surface, so it is dispersed in small amounts in water, and this dispersion characteristic causes limitations in the amount that can be mixed into the urethane raw material. In reality, if the amount of water increases in the polyurethane raw material, the reactivity increases, causing the closed cells to grow abnormally large or burst, and the amount of CO2 generated also increases, which causes problems such as a decrease in strength and insulation properties. In addition, when the CNF dispersion is dried, the strong hydrogen bonding of the hydroxyl groups (-OH) easily causes strong aggregation between CNFs, which significantly reduces the dispersibility in the polyurethane raw material, making it impossible to proceed with the polyurethane foam manufacturing process.

[0018] In order to improve the mechanical strength properties of polyurethane foam, many attempts are being made to improve the strength of polyurethane foam by mixing and dispersing various strength-reinforcing organic and inorganic fillers such as carbon nanotubes (hereinafter referred to as 'CNTs'), nano glass bubbles, nano glass fibers, and cellulose fibers into polyurethane and impregnating them into the cell walls.

[0019] However, since the cell thickness of polyurethane foam is very thin, within 1 to 2 ㎛, the use of nanoparticle-sized organic and inorganic fillers is inevitable for uniform impregnation of the organic and inorganic fillers within the cells, and this makes it difficult to achieve uniform mixing and dispersion due to strong aggregation caused by the large specific surface area of ​​the nanomaterial.

[0020]

[0021] Below, we will introduce a prior art that improves thermal conductivity and mechanical strength by compounding nano-sized organic and inorganic fillers into polyurethane foam.

[0022] First, Korean Patent No. 10-2465857 (Title of invention: Polyurethane foam, refrigerator including the same, and method for producing polyurethane foam) discloses a technology for improving the compressive strength of polyurethane foam by mixing 0.01 to 1 wt% of fibers having hydroxyl groups in a polyol system of rigid polyurethane for refrigerator insulation based on the total composition weight. The fibers having hydroxyl groups include cellulose fibers such as micro cellulose and CNF, and the polyurethane is produced by mixing and dispersing them.

[0023] However, when dispersed in a mixed manner with microcellulose and CNF in a polyol system of polyurethane as described above, when dried cellulose is added, strong aggregation occurs due to the many -OH groups on the surface of the cellulose, making uniform dispersion impossible. As a result, the foam forms open cells due to the aggregation, making it difficult to expect improvement in thermal conductivity. In addition, when cellulose containing moisture is added, the introduction of additional moisture causes excessive CO2 production with high thermal conductivity and rapid reactivity, resulting in a decrease in cell uniformity and strength of the foam, making it difficult to expect improvement in thermal conductivity and strength. In addition, when microcellulose is added, there was a limitation in that it was difficult to impregnate the thin polyurethane foam cell wall (1-2 μm) due to the large particle diameter, so there was a high possibility of forming open cells rather than closed cells, making it difficult to improve thermal conductivity.

[0024]

[0025] Another prior art document, Korean Patent No. 10-2578672 (Title of the invention: Polyurethane foam composition using methyl formate and method for producing polyurethane foam using the same), discloses a technology for improving the mechanical strength, thermal conductivity, and flame retardancy of architectural polyurethane foam by mixing nanoglass bubbles and CNTs into the polyol system of polyurethane. This technology is characterized by improving strength and thermal conductivity by mixing 5 to 10 parts by weight of glass bubbles with an average diameter of 15 to 30 nm per 100 parts by weight of polyol components, and improving flame retardancy by mixing 0.1 to 3 parts by weight of CNTs per 100 parts by weight of polyol components.

[0026] However, when glass bubbles are added and mixed, the difference in specific gravity between the polyol system of polyurethane and the glass bubbles causes the glass bubbles to float, making uniform mixing very difficult. In addition, when the manufactured glass bubble-mixed polyurethane solution is stored for a long time, there is a high possibility of phase separation of the glass bubbles. In addition, due to the rapid increase in viscosity and the formation of large-sized glass bubble aggregates with the addition of high-concentration (6-10 wt%) of glass bubbles, it is difficult to apply it to the mass production process due to the limitation of exceeding the foaming viscosity limit (1000 cps or less) of high-pressure foaming equipment for refrigerators and filter clogging. There is a problem. In addition, since nano-sized glass bubbles must be added at a high concentration of 6-10 wt%, there was also the problem of increasing the material cost for mass production application due to the high material price.

[0027]

[0028] In order to solve the above problems, the present invention aims to provide a polyurethane foam containing nanoparticles-nanocellulose dispersed therein, which can reduce the cell size compared to conventional urethane foam, thereby lowering thermal conductivity and increasing the compressive strength of the foam, and a method for producing the same.

[0029]

[0030] In order to achieve the above purpose, the present invention relates to a polyurethane having nanoparticles-nanocellulose dispersed therein, in which inorganic nanoparticles, which are metal oxides, are chemically bonded to the surface.

[0031] The metal oxide may be selected from the group consisting of Al2O3, SiO2, TiO2, and ZrO, or may be represented by the following chemical formula 1.

[0032] [Chemical Formula 1]

[0033] M2O3 (where M is a metal belonging to group 13 of the periodic table)

[0034] The above nanocellulose may be nanocellulose fibers or nanocellulose crystals. When the nanocellulose is nanocellulose fibers, the nanocellulose fibers may have a diameter of 5 to 500 nm, a length of 100 nm to 10 μm, and an aspect ratio of 5 to 1000. When the nanocellulose is nanocellulose crystals, the nanocellulose crystals may have a size of 3 nm to 50 nm.

[0035] The above nanocellulose can be chemically bonded to the surface in such a way that the inorganic nanoparticles or clusters of the inorganic nanoparticles are chemically bonded and coated, or the inorganic nanoparticles are coated by forming a layer.

[0036] Another invention relates to an insulating material for home appliances comprising the polyurethane foam, wherein the home appliances include refrigerators.

[0037] Another invention relates to a method for producing a polyurethane foam, comprising the steps of: preparing a polyol solution by adding and dispersing nanoparticle-nanocellulose having inorganic nanoparticles chemically bonded to the surface thereof into a polyol solution; preparing a polyurethane solution by adding and dispersing a catalyst, a surfactant, and a foaming agent into the polyol solution; and preparing a polyurethane solution by mixing polyisocyanate into the polyurethane solution and then molding and foaming the mixture to produce a polyurethane foam.

[0038] The above polyol solution may be a polyol or a mixture-based solution obtained by polymerizing an alkylene oxide including ethylene oxide, propylene oxide or butylene oxide using an organic oxide including a compound having an ester group, ethylene glycol, glycerin, trimethylpropane, sorbitol, sucrose, ethylene diamine (EDA), diethylenetriamine, toluenediamine (TDA) or diphenylmethanediamine as an initiator.

[0039] The nanocellulose chemically bonded to the surface of the above-mentioned inorganic nanoparticles can be dispersed by adding 0.001 to 10 wt% compared to the polyol solution.

[0040] The catalyst may include a gelling catalyst, a trimerization catalyst or a blowing catalyst, and the blowing agent may include a chemical blowing agent selected from the group consisting of azodicarbonamide, activated azodicarbonamide, 5-phenyltetrazole, sodium bicarbonate and water (DI) or a physical blowing agent selected from the group consisting of cyclopentane and HFO, and the polyurethane solution and polyisocyanate may be mixed in a weight ratio of 1:1 to 1.3.

[0041]

[0042] 1. The conventional technology for improving the compressive strength of polyurethane foam is a structure in which nano-fillers for reinforcing strength, such as glass bubbles, glass fibers, CNTs, inorganic nanoparticles, and non-surface-treated CNFs, are added to the polyurethane solution, and the fillers are dispersed within the urethane foam cells to increase the mechanical strength. However, glass bubbles, glass fibers, and inorganic nanoparticles, etc., have a large specific surface area, which causes significant agglomeration between materials, and a strong shear force is required to crush and disperse them, which has limitations in producing a homogeneously dispersed polyurethane solution, making it difficult to expect the desired strength improvement.

[0043] On the other hand, the nanoparticle-nanocellulose according to the present invention forms inorganic nanoparticles through chemical bonding on the surface of nanocellulose that causes strong aggregation on the surface, thereby improving the aggregation between nanoparticles and nanocellulose, thereby enabling the production of polyurethane foam in which nanocellulose is uniformly dispersed on the cell wall, thereby improving the compressive strength of the polyurethane foam. In addition, since the inorganic nanoparticles are bonded to the nanocellulose, additional rigidity of the nanocellulose is imparted, thereby also improving the strength of the polyurethane foam cell.

[0044]

[0045] 2. Another conventional technology for improving the thermal conductivity of polyurethane foam is to add an F-based organic nucleating agent to the polyurethane solution to increase the number of bubble nucleation sites, thereby reducing the cell size and improving the thermal conductivity. However, F-based organic substances are currently subject to strict regulations on their use as a major culprit in global warming, which limits their practical use. Another conventional method has been proposed to improve thermal conductivity by forming nanopores inside the urethane foam cell walls by adding nanoglass bubbles, aerogels, etc. However, when nanoglass bubbles, aerogels, etc. are added, problems such as floating and sedimentation occur during mixing due to the difference in specific gravity with the polyurethane solution, making it difficult to expect the desired improvement in thermal conductivity.

[0046] On the other hand, the present invention enables the production of a homogeneously dispersed polyurethane solution by chemically bonding inorganic nanoparticles to the surface of nanocellulose, thereby enabling uniform dispersion without aggregation during mixing, and thus the nanocellulose can be expected to act as a nucleating site for bubble formation during a foam reaction, thereby reducing thermal conductivity by reducing cell size and cell size dispersion. In addition, as shown in Fig. 3, nano-sized micropores are trapped between the inorganic nanoparticles bonded to nanocellulose, thereby achieving an additional thermal conductivity reduction effect.

[0047]

[0048] 3. The nanoparticle-nanocellulose according to the present invention can prevent aggregation between nanocelluloses compared to conventional non-surface-treated nanocellulose, so that even when nanocellulose is dried and mixed into a polyurethane solution, the nanocellulose can be evenly distributed, and thus, the phenomenon of filter and discharge head clogging due to large nanocellulose aggregates can be prevented during a high-pressure foaming process for refrigerators, thereby having the advantage of ensuring mass production processability.

[0049]

[0050] Figure 1 is a flow chart showing a process for manufacturing a polyurethane foam in which nanoparticles and nanocellulose are mixed and dispersed according to the present invention.

[0051] Figure 2 is a cross-sectional schematic diagram of a conventional rigid polyurethane foam.

[0052] Figure 3(a) is a schematic diagram of a nanopore cross-section of a polyurethane foam containing nanoparticle clustered nanocellulose.

[0053] Figure 3(b) is a schematic diagram of a nanopore cross-section of a polyurethane foam containing nanocellulose coated with a nanoparticle layer.

[0054] Figure 4(a) is a conceptual diagram showing the form in which nanoparticles are chemically bonded to the CNF surface.

[0055] Figure 4(b) is a conceptual diagram showing the form in which nanoparticle clusters are chemically bonded to the surface of nanocellulose.

[0056] Figure 4(c) is a conceptual diagram showing the form in which a nanoparticle layer is coated and chemically bonded to the surface of nanocellulose.

[0057] Figure 5 is a SEM photograph (x100k) of nanocellulose fibers in which alumina nanoparticles of Example 1 according to the present invention are clustered.

[0058] Figure 6 is a SEM photograph (x100k) of nanocellulose fibers coated with an alumina nanoparticle layer of Example 2 according to the present invention.

[0059] Figure 7 is a SEM photograph (x100k) of non-surface-treated nanocellulose fibers of Comparative Example 1.

[0060] Figure 8 is an image of the EDS elemental analysis results of the alumina nanoparticle clustered nanocellulose fiber of Example 1 according to the present invention.

[0061] Figure 9 is an image of the EDS elemental analysis results of non-surface-treated nanocellulose fibers of Comparative Example 1.

[0062] Figure 10 is an image of the XPS elemental analysis results of the alumina nanoparticle clustered nanocellulose fiber of Example 1 according to the present invention.

[0063] Figure 11 is an image of the XPS elemental analysis results for the Al narrow peak of the alumina nanoparticle clustered nanocellulose fiber of Example 1 according to the present invention.

[0064] Figure 12 is an image of the XPS elemental analysis results of non-surface-treated nanocellulose fibers of Comparative Example 1.

[0065] FIG. 13(a) is an enlarged image (x5) showing the dispersion state of nanocellulose fibers clustered with alumina nanoparticles in a polyurethane solution of Example 3 according to the present invention.

[0066] Figure 13(b) is an enlarged image (x5) showing the dispersion state of nanocellulose fibers coated with an alumina nanoparticle layer in a polyurethane solution of Example 4 according to the present invention.

[0067] Figure 13(c) is an enlarged image (x5) showing the dispersion state of non-surface-treated nanocellulose fibers in the polyurethane solution of Comparative Example 3.

[0068] Figures 14 to 17 are SEM enlarged images (x1000K) of polyurethane foams of Examples 3 and 4 and Comparative Examples 2 and 3 according to the present invention, respectively.

[0069] Figure 18 is a comparative analysis graph of the average cell size of polyurethane foam by nanocellulose fiber type.

[0070]

[0071] Hereinafter, the present invention will be described in detail with reference to the attached drawings and examples. However, the present invention is not intended to be limited to the details disclosed in the examples; rather, the present invention includes all modifications, equivalents, and substitutions consistent with the spirit of the present invention as defined by the claims.

[0072]

[0073] The present invention relates to a polyurethane foam characterized in that the cell size of the foam is reduced, thermal conductivity is reduced, and mechanical strength is improved by dispersing nanoparticles-nanocellulose in which inorganic nanoparticles, which are metal oxides, are chemically bonded to the surface.

[0074] The polyurethane foam according to the present invention can be manufactured according to the steps illustrated in Fig. 1, and each step will be described in detail below.

[0075]

[0076] 1. Preparation of nanoparticles and nanocellulose

[0077] Nanoparticle-nanocellulose, in which inorganic nanoparticles are chemically bonded to the surface, is prepared by inducing a sol-gel reaction by mixing metal alkoxide, CNF, and a reaction catalyst in an organic solvent or water (DI) to form the nanoparticles on the surface of cellulose. The inorganic nanoparticles may be selected from the group consisting of SiO2, TiO2, and ZrO, and preferably a metal oxide represented by the following chemical formula 1, more preferably Al2O3.

[0078] [Chemical Formula 1]

[0079] M2O3 (where M is a metal belonging to group 13 of the periodic table)

[0080] The above nanocellulose may be nanocellulose fibers or nanocellulose crystals, and more preferably nanocellulose fibers.

[0081] When the above nanocellulose is a nanocellulose fiber, it may be a nanocellulose fiber having a diameter of 5 to 500 nm and a length of 100 nm to 10 μm, and an aspect ratio of 5 to 1000. In addition, when the above nanocellulose is a nanocellulose crystal, a nanocellulose crystal having a size of 3 nm to 50 nm is preferable.

[0082] In order to manufacture nanoparticle-nanocellulose according to the present invention, a reaction solution in which a precursor of a metal oxide, which is a nanoparticle, and nanocellulose are dispersed is prepared, and then a reaction catalyst is added to manufacture nanoparticle-nanocellulose.

[0083] (1) Preparation of reaction solution

[0084] To prepare the above reaction solution, nanocellulose dispersed in water is replaced with an organic solvent. The organic solvent may be, but is not necessarily limited to, methanol, ethanol, isopropyl alcohol, butanol, NMP, or acetonitrile.

[0085] Next, the substituted nanocellulose is dispersed in an organic solvent in a certain amount, preferably 0.05 to 2 wt%. Thereafter, a metal oxide precursor is added and uniformly dispersed in the solution. For example, when the nanoparticle is alumina (Al2O3), the precursor, aluminum alkoxide, may be aluminum isopropoxide, aluminum ethoxide, aluminum tri-sec-butoxide, aluminum tert-butoxide, or aluminum trimethoxide.

[0086]

[0087] (2) Nanoparticle-nanocellulose synthesis

[0088] A reaction catalyst is added to an organic solvent solution in which a metal oxide precursor and nanocellulose are dispersed, and the metal oxide nanoparticles are chemically bonded to the surface of the nanocellulose.

[0089] The above reaction catalyst not only promotes the sol-gel reaction of the metal oxide precursor but also activates the nanocellulose surface, thereby inducing the metal oxide precursor to be chemically bonded to the nanocellulose surface.

[0090] The above reaction catalyst may be an acid catalyst or a basic catalyst. As an acid catalyst, hydrochloric acid, sulfuric acid, nitric acid, or acetic acid may be used, and as a basic catalyst, sodium hydroxide, lithium hydroxide, barium hydroxide, or ammonium hydroxide may be used.

[0091] The composition and reaction conditions of the above sol-gel reaction solution can be controlled to control the shape of the nanoparticles to be combined. The amount of the metal oxide precursor added can be 0.01 to 5 wt%, preferably 0.01 to 1 wt%, based on the total reaction solution, and the amount of the catalyst added can be 1 to 30 wt%, preferably 3 to 20 wt%, based on the total reaction solution.

[0092] As shown in Fig. 4, depending on the amount of metal oxide precursor or nanocellulose input, the formed nanoparticles may be chemically bonded to the surface of nanocellulose in the form of particles, or the nanoparticles may be chemically bonded in the form of clusters, or the nanoparticles may be chemically bonded to form a layer to form a coating layer over a certain area.

[0093] When chemically bonded in the form of particles, the diameter of the nanoparticles may be 50 to 500 nm, and when the nanoparticles are chemically bonded in the form of a coating layer, the thickness of the coating layer may be 2 to 50 nm.

[0094]

[0095] (3) Nanoparticle-nanocellulose cleaning

[0096] It is preferable to remove residual reagents from nanocellulose with nanoparticles chemically bonded to the surface through a washing process. The washing process can utilize methods such as centrifugation, vacuum filtration, and osmotic filtration, and the washing solvent can be an organic solvent such as methanol, ethanol, isopropyl alcohol, butanol, N-methylpyrrolidone (NMP), acetonitrile, or water (DI).

[0097]

[0098] 2. Preparation of polyurethane solution containing nanoparticles and nanocellulose dispersion

[0099] The above-mentioned nanoparticle-nanocellulose is concentrated and dried through filtering, then mixed with a polyol solution for polyurethane production, and a mixer such as a homomixer, homogenizer, or 3-roll mill is used to pulverize / disperse the nanoparticle-nanocellulose, thereby producing a polyurethane crude solution in which the nanoparticle-nanocellulose is evenly dispersed. This is explained in more detail as follows.

[0100]

[0101] (1) High concentration and drying of nanoparticles and nanocellulose

[0102] Nanoparticle-nanocellulose dispersed at a low concentration (1 to 2 wt%) in water or an organic solvent can be highly concentrated (> 10 wt%) using a centrifuge, filter press, etc. If necessary, highly concentrated nanoparticle-nanocellulose can be further dried through spray drying, freeze drying, oven drying, etc.

[0103]

[0104] (2) Preparation of polyurethane solution in which nanoparticles and nanocellulose are mixed and dispersed

[0105] A certain amount of the previously manufactured nanoparticle-nanocellulose is prepared, and a polyol solution of polyurethane is ground and dispersed using a homogenizer, homogenizer, 3-roll mill, etc. to prepare a polyol solution.

[0106] The above polyol solution may be a polyol or a mixture-based solution obtained by polymerizing an alkylene oxide including ethylene oxide, propylene oxide or butylene oxide using an organic oxide including a compound having an ester group, ethylene glycol, glycerin, trimethylpropane, sorbitol, sucrose, ethylene diamine (EDA), diethylenetriamine, toluenediamine (TDA) or diphenylmethanediamine as an initiator. In addition, it is preferable to disperse the nanoparticle-nanocellulose by adding it in an amount of 0.001 to 10 wt% relative to the polyol solution.

[0107] Afterwards, a certain amount of additives such as a catalyst (gelling catalyst, trimerization catalyst, blowing catalyst, etc.), surfactant, chemical blowing agent, physical blowing agent (cyclopentane, HFO, etc.) is mixed into the polyol solution in which nanoparticles-nanocellulose are dispersed to prepare a polyurethane solution.

[0108] The blowing agent may be a chemical blowing agent selected from the group consisting of azodicarbonamide, activated azodicarbonamide, 5-phenyltetrazole, sodium bicarbonate, and water (DI), or a physical blowing agent selected from the group consisting of cyclopentane and HFO.

[0109]

[0110] 3. Manufacturing of nanoparticle-nanocellulose dispersed composite polyurethane foam

[0111] The polyurethane solution in which the nanoparticles-nanocellulose are dispersed as above can be mixed with a certain amount of polyisocyanate, injected into a mold to foam, and then cured for a certain period of time to produce a polyurethane foam having evenly dispersed nanoparticles-nanocellulose fibers.

[0112] At this time, the above-mentioned composite polyurethane solution and isocyanate can be mixed in a mass ratio of 1:1 to 1.3. Afterwards, it is injected into a mold to foam, and then cured for 2 to 10 minutes to produce a polyurethane foam.

[0113]

[0114] [Example]

[0115] 1. Manufacturing of nanoparticle-nanocellulose fibers

[0116]

[0117] Example 1: Preparation of alumina nanoparticle clustered nanocellulose fibers (CNFs)

[0118] First, nanocellulose fibers dispersed in DI (water) were replaced with an alcohol-based organic solvent (isopropyl alcohol). Solvent replacement was performed by repeating centrifugation three times.

[0119] Solvent-exchanged nanocellulose fibers were dispersed in an alcohol-based organic solvent (isopropyl alcohol) with an acid concentration of 0.5 wt%. Then, aluminum alkoxide reagent was added to the solvent in which the nanocellulose fibers were dispersed to 0.5 wt% based on the total solution and dispersed for several hours. Afterwards, a basic catalyst was added to the prepared dispersion solution (7 v / v% based on the total solution) to initiate a sol-gel reaction. Afterwards, a uniform reaction was achieved by stirring, and after a certain period of time, centrifugation was performed three times using isopropyl alcohol as a washing solution, thereby removing the reaction reagent.

[0120] It was confirmed that the manufactured alumina nanocellulose fibers had alumina particles chemically bonded to the surface of the nanocellulose fibers, as shown in Fig. 5.

[0121]

[0122] Example 2: Preparation of nanocellulose fibers (CNF) coated with alumina nanoparticle layer

[0123] Except for adding 0.07 wt% of the alkoxide reagent, the reaction was carried out in the same manner as in Example 1 to manufacture nanocellulose fibers with an alumina nanoparticle layer coated on the surface, as shown in Fig. 6. It was confirmed that the manufactured nanocellulose fibers coated with an alumina nanoparticle layer existed in a chemically bonded form by forming a coating layer on the surface of the nanocellulose fibers, as shown in Fig. 6.

[0124]

[0125] Comparative Example 1: Preparation of non-surface-treated nanocellulose fibers (CNF)

[0126] In the same manner as in Example 1, nanocellulose fibers were substituted with an organic solvent, dispersed in the organic solvent, and then stirred for a certain period of time by adding a basic catalyst without adding an aluminum alkoxide reagent. Thereafter, centrifugation was performed three times in the same manner as in Example 1 to remove and wash the basic catalyst. As shown in Fig. 7, it was confirmed that the manufactured non-surface-treated nanocellulose fibers did not have alumina nanoparticles chemically bonded to the surface of the nanocellulose fibers.

[0127]

[0128] 2. Manufacturing of polyurethane foam containing nanoparticles and nanocellulose fibers

[0129]

[0130] Example 3: Preparation of alumina nanoparticle clustered nanocellulose fiber composite polyurethane foam.

[0131] The alumina nanoparticle clustered nanocellulose fibers (1 wt%) of Example 1 dispersed in an organic solvent (isopropyl alcohol) were concentrated to a high concentration (>10%) using a centrifuge, and then dried with hot air at 100°C or higher to prepare the fibers. Then, 0.03 g of the dried alumina nanoparticle clustered nanocellulose fibers was mixed with 100 g of a polyol solution (a solution of ar-Methyl-1,3-benzenediamine polymer with methyloxirane and oxirane, propoxylated sugar, and sorbitol based polymer), and then ground / dispersed with a homogenizer for a certain period of time to prepare a polyol crude solution dispersed with alumina nanoparticle clustered nanocellulose fibers. Afterwards, 100 g of the prepared alumina nanoparticle clustered nanocellulose fiber dispersed polyol crude liquid was mixed with 2.5 g of a catalyst (gelling catalyst, blowing catalyst, trimerization catalyst), 3 g of a surfactant, 2 g of a chemical blowing agent (water), and 17.2 g of a physical blowing agent (cyclopentane) to prepare an alumina nanoparticle clustered nanocellulose fiber dispersed polyurethane crude liquid. Afterwards, the prepared alumina nanoparticle clustered nanocellulose fiber dispersed polyurethane crude liquid and polyisocyanate were mixed in a 1:1.15 ratio, injected into a mold, foamed, and cured for 5 minutes to prepare an alumina nanoparticle clustered nanocellulose fiber composite polyurethane foam.

[0132]

[0133] Example 4: Preparation of nanocellulose fiber composite polyurethane foam coated with an alumina nanoparticle layer.

[0134] Nanocellulose fibers (1 wt%) coated with an alumina nanoparticle layer of Example 2 dispersed in an organic solvent (isopropyl alcohol) were concentrated to a high concentration (>10%) using a centrifuge, and then dried with hot air at 100°C or higher to prepare the fibers. Then, 0.03 g of the dried nanocellulose fibers coated with an alumina nanoparticle layer was mixed with 100 g of a polyol solution (a solution of ar-Methyl-1,3-benzenediamine polymer with methyloxirane and oxirane, PROPOXYLATED SUCROSE, and SORBITOL BASED POLYETHER POLYOL), and then ground / dispersed with a homogenizer for a certain period of time to prepare a polyol crude solution dispersed with a nanoparticle layer coated on the nanocellulose fibers. Afterwards, 2.5 g of catalyst (gelling catalyst, blowing catalyst, trimerization catalyst), 3 g of surfactant, 2 g of chemical blowing agent (water), and 17.2 g of physical blowing agent (cyclopentane) were mixed with 100 g of the CNF dispersed polyol crude solution coated with the alumina nanoparticle layer manufactured above to manufacture a nanocellulose fiber dispersed polyurethane crude solution coated with an alumina nanoparticle layer. Afterwards, the nanocellulose fiber composite polyurethane crude solution coated with an alumina nanoparticle layer and polyisocyanate were mixed at a ratio of 1:1.15, and then injected into a mold, foamed, and cured for 5 minutes to manufacture a nanocellulose fiber composite polyurethane foam coated with an alumina nanoparticle layer.

[0135]

[0136] Comparative Example 2: Manufacturing of polyurethane foam without nanocellulose fiber (CNF) addition

[0137] In order to manufacture rigid polyurethane foam for refrigerators, 100 g of a polyol solution (a solution of ar-Methyl-1,3-benzenediamine polymer with methyloxirane and oxirane, a mixture of propoxylated sucrose, and sorbitol-based polymer) was mixed, 2.5 g of a catalyst (gelling catalyst, blowing catalyst, trimerization catalyst), 3 g of a surfactant, 2 g of a chemical blowing agent (water), and 17.2 g of a physical blowing agent (cyclopentane) was mixed to prepare a polyurethane solution. Thereafter, the prepared polyurethane solution and polyisocyanate were mixed in a 1:1.15 ratio, and then injected into a mold, foamed, and cured for 5 minutes to manufacture a polyurethane foam.

[0138]

[0139] Comparative Example 3: Preparation of polyurethane foam containing non-surface-treated nanocellulose fibers (CNF)

[0140] Nanocellulose fibers (1 wt%) dispersed in water were prepared by hot air drying at 100°C or higher, and 0.03 g of the dried nanocellulose fibers were mixed with 100 g of a polyol solution (a solution of ar-Methyl-1,3-benzenediamine polymer with methyloxirane and oxirane, PROPOXYLATED SUCROSE, and SORBITOL BASED POLYETHER POLYOL), and then ground / dispersed with a homogenizer for a certain period of time to prepare a polyol solution in which non-surface-treated nanocellulose fibers were dispersed.

[0141] Afterwards, 2.5 g of catalyst (gelling catalyst, blowing catalyst, trimerization catalyst), 3 g of surfactant, 2 g of chemical blowing agent (water), and 17.2 g of physical blowing agent (cyclopentane) were mixed with 100 g of the non-surface-treated nanocellulose fiber composite polyol crude liquid manufactured above to manufacture a non-surface-treated nanocellulose fiber dispersed polyurethane crude liquid.

[0142] Afterwards, the non-surface-treated nanocellulose fiber dispersed polyurethane solution and polyisocyanate were mixed in a mass ratio of 1:1.15, injected into a mold, foamed, and cured for 5 minutes to produce a non-surface-treated nanocellulose fiber composite polyurethane foam.

[0143]

[0144] [Analysis Results]

[0145]

[0146] 1. Analysis of nanocellulose fibers

[0147] The nanocellulose fibers manufactured in Examples 1 and 2 and Comparative Example 1 were analyzed as follows.

[0148]

[0149] (1) SEM image analysis

[0150] As shown in Fig. 5, the nanocellulose fiber surface of Example 1 was coated with large alumina particles (average diameter: 160 nm) and fine particles (approximately 10 nm, <20 nm or less). Furthermore, it was confirmed that the fine particles coated on the surface thickened the nanocellulose fiber. (Fiber diameter: 30.3 nm after initial non-surface treatment → 47.6 nm after alumina particle bonding)

[0151] By controlling the amount of aluminum alkoxide reagent added, fine alumina particles were coated on the surface of the nanocellulose fibers without forming large alumina particles, as shown in Fig. 6. At this time, it was confirmed that the fiber diameter had thickened to 44.1 nm. (Fiber diameter: 30.3 nm without surface treatment → 44.1 nm after alumina particle coating)

[0152] As shown in Fig. 7, the non-surface-treated nanocellulose fiber of Comparative Example 1 has no alumina particles attached to the surface, so the fiber surface is smooth in the SEM image, and the fiber diameter at this time was measured to be 30.3 nm on average.

[0153]

[0154] (2) EDS elemental analysis

[0155] EDS analysis was performed to analyze the elements of the nanocellulose fibers manufactured in Example 1 and Comparative Example 1.

[0156] The alumina nanoparticle clustered nanocellulose fibers of Example 1 were measured to contain approximately 28.7% Al element. This confirmed that the formed nanoparticles were Al2O3 nanoparticles. (See Figure 8)

[0157] On the other hand, in the case of Comparative Example 1, the Al element was not analyzed due to the non-surface-treated nanocellulose. (See Fig. 9)

[0158]

[0159] (3) XPS elemental analysis

[0160] The formation of alumina nanoparticles in Example 1 and Comparative Example was confirmed through XPS analysis.

[0161] The alumina particle-bonded clustered nanocellulose fibers of Example 1 detected 22.2 atonic % Al. (See Fig. 10) In addition, the narrow peak analysis result of Al showed that the peak was due to Al-O bonds, confirming the formation of Al2O3 particles. (See Fig. 11)

[0162] On the other hand, no Al element was detected in the non-surface-treated nanocellulose fiber of Comparative Example 1. (See Fig. 12)

[0163]

[0164] 2. Characterization of nanocellulose fibers (CNF) in polyurethane solution

[0165] The dispersion characteristics of the nanocellulose fibers of the polyurethane crude solution prepared by mixing and dispersing the alumina nanoparticle cluster nanocellulose fibers and the alumina nanoparticle layer coated nanocellulose fibers manufactured in Examples 1 and 2, respectively, and the non-surface-treated nanocellulose fibers of Comparative Example 1 into a polyol solution of polyurethane after being highly concentrated and dried were compared and analyzed using an optical microscope.

[0166] Figure 13 shows the dispersion state of nanoparticle cluster nanocellulose fibers (Example 3), nanoparticle layer-coated nanocellulose fibers (Example 4), and non-surface-treated nanocellulose fibers (Comparative Example 3) dispersed in a polyurethane solution, respectively.

[0167] In the case of each of the nanoparticle cluster nanocellulose fibers and nanoparticle layer coated nanocellulose fibers manufactured in Examples 3 and 4, it can be seen that the nanoparticle nanocellulose fibers were uniformly and stably dispersed in the polyurethane solution, as no nanocellulose fiber aggregates were observed.

[0168] On the other hand, in the case of the polyurethane solution of Comparative Example 3 in which non-surface-treated nanocellulose fibers were mixed and dispersed, strong coagulation occurred between nanocellulose fibers due to hydrogen bonding by the numerous -OH groups on the surface of the nanocellulose fibers when concentrated and dried, and many undispersed large nanocellulose fiber aggregates (tens to hundreds of μm) were observed, which means that the nanocellulose fibers were not uniformly dispersed in the polyurethane solution.

[0169]

[0170] 3. Analysis of thermal conductivity and compressive strength characteristics of polyurethane foam

[0171] Table 1 below shows the results of comparative analysis of the characteristics of polyurethane foams composited with nanoparticles and nanocellulose fibers of Examples 3 and 4 and polyurethane foams composited with non-added and non-surface-treated nanocellulose fibers of Comparative Examples 2 and 3.

[0172] ClassificationComparative Example 2Comparative Example 3Example 3Example 4Polyurethane precipitate added CNF typeNo additionNon-surface treatmentCNF nanoparticle clusterCNF nanoparticle layer coatingCNF polyol system (g)100100100100CNF added amount(g)00.030.030.03Catalyst (g)2.52.52.52.5Surfactant3333Chemical blowing agent (g)(water)2222Physical blowing agent (g)(cyclopentane)17.217.2417.217.2Viscosity (cps@25℃)500733545587Polyisocyanate(g)143.4143.4143.4143.4Foam reactivity(sec)42424141Free foam density (kg / m 3 )24.524.623.823.2Thermal Conductivity (mW / mK)20.7120.6820.5720.35Compressive Strength (kgf / cm 2 )1.111.271.381.31Cell size (um)290.6247199.4213.4

[0173] The measured viscosity of the polyurethane solution in which the nanoparticle-nanocellulose fibers of Examples 3 and 4 were dispersed was at the level of 545 to 587 cps. On the other hand, the viscosity of the polyurethane solution in which the non-surface-treated nanocellulose fibers of Comparative Example 3 were dispersed was 733 cps, which showed a high level of viscosity compared to the nanoparticle-nanocellulose fibers. Considering that the viscosity limit of a high-pressure foamer for refrigerators is 1000 cps or less, when adding and dispersing the nanoparticle-nanocellulose fibers, there is an advantage in that a higher concentration of cellulose fibers can be added.

[0174] In addition, as a result of comparative analysis of thermal conductivity characteristics, it was confirmed that the thermal conductivity of the nanocellulose fibers of Examples 3 and 4, which were mixed and dispersed with nanoparticle clusters and nanocellulose fibers coated with a nanoparticle layer, was reduced compared to the polyurethane foam of Comparative Example 2, which did not contain nanocellulose fibers, and thus the insulation characteristics were improved.

[0175] As can be seen from the cell size comparison results of the foams, the average cell size of the nanoparticle-nanocellulose fiber composite urethane foams of Examples 3 and 4 is reduced compared to Comparative Examples 2 and 3, resulting in a decrease in λ radiation It is interpreted that the thermal conductivity was improved due to the decrease. On the other hand, it was confirmed that the non-surface-treated nanocellulose fiber composite polyurethane foam of Comparative Example 3 did not show any improvement in thermal conductivity characteristics. This is because the strong aggregation of the non-surface-treated nanocellulose fibers did not allow for uniform CNF dispersion, so it could not properly play the role of a bubble nucleator during foam formation. In addition, the possibility of forming open cells increased due to the nanocellulose fiber aggregation size being larger than the thin thickness (1 to 2 um) of the urethane foam cell, so the thermal conductivity was not improved.

[0176] These nanocellulose fiber aggregates, which are several hundred micrometers in size, cause filter clogging, which makes it difficult to carry out a stable foaming process, considering that the filter size of a high-pressure foamer for refrigerators is approximately 80 micrometers.

[0177] As a result of comparative analysis of the compressive strength, the product with non-surface-treated nanocellulose fibers of Comparative Example 3 showed some improvement in the compressive strength compared to the product without nanocellulose fibers of Comparative Example 2, but the products with nanoparticle clustered nanocellulose fibers and nanoparticle layer coated nanocellulose fibers of Examples 3 and 4 showed a higher improvement in the compressive strength. This is because the nanocellulose fibers are evenly distributed without aggregation, faithfully playing the role of reinforcing the strength of the cell walls of the foam, and in addition, it is believed that the inorganic nanoparticles chemically bonded to the nanocellulose fibers induce additional strength improvement of the cell walls.

[0178]

[0179] 4. Analysis of cell size characteristics of polyurethane foam

[0180] (1) Analysis of polyurethane foam microstructure

[0181] Figures 14 to 17 are SEM enlarged images (x100K) of polyurethane foams according to Examples 2 and 3 and Comparative Examples 2 and 3, respectively.

[0182] In the case of the nanoparticle clustered nanocellulose fibers of Example 3 and the nanoparticle layer coated nanocellulose fiber composite polyurethane foam of Example 4, it was confirmed that the cell size was small and closed cells of relatively uniform size were formed. This is believed to be because the nanoparticle-nanocellulose fibers were uniformly dispersed in the polyurethane and acted as a large amount of bubble nucleating agent during foam formation, reducing the cell size and forming uniform cells.

[0183] On the other hand, when comparing the cell images of the non-nanocellulose fiber-added polyurethane foam of Comparative Example 2 and the non-surface-treated nanocellulose fiber composite polyurethane foam of Comparative Example 3, it showed a mixed appearance of large and small cells. In the case of the non-surface-treated nanocellulose fiber of Comparative Example 3, the cell size did not decrease compared to the non-nanocellulose fiber-added polyurethane foam of Comparative Example 2 and showed a similar level image. This means that the strong aggregation of the non-surface-treated CNF did not allow for proper uniform dispersion and thus did not function as a bubble nucleating agent.

[0184]

[0185] (2) Polyurethane foam cell size analysis

[0186] Figure 18 shows the results of comparing and analyzing the average cell size by measuring various cell sizes in SEM images of polyurethane foam according to the type of added nanocellulose fiber.

[0187] As can be seen in Fig. 18, the average cell size of the nanoparticle clustered nanocellulose fibers of Example 3 and the nanoparticle layer coated nanocellulose fiber composite urethane foam of Example 4 decreased compared to Comparative Examples 2 and 3. This is believed to be because the uniformly dispersed nanoparticle-nanocellulose fibers simultaneously act as nucleation sites for a large number of bubbles during the urethane foam reaction, thereby inducing uniform cell formation and forming closed cells with small cell sizes and less size dispersion.

[0188]

[0189] The embodiments disclosed herein are merely specific examples intended to aid understanding of the invention and are not intended to limit the scope of the invention. It will be apparent to those skilled in the art that other modifications based on the technical concepts of the present invention are possible in addition to the embodiments disclosed herein.

Claims

1. Polyurethane foam characterized by containing nanocellulose chemically bonded to the surface of inorganic nanoparticles, which are metal oxides.

2. In paragraph 1, The above metal oxide is a polyurethane foam represented by the following chemical formula 1. [Chemical Formula 1] M2O3 (where M is a metal belonging to group 13 of the periodic table) 3. In paragraph 1, Polyurethane foam, wherein the metal oxide is at least one selected from the group consisting of Al2O3, SiO2, TiO2 and ZrO.

4. In paragraph 1, The above nanocellulose is a polyurethane foam which is a nanocellulose fiber or nanocellulose crystal.

5. In paragraph 4, If the above nanocellulose is a nanocellulose fiber, Polyurethane foam having nanocellulose fibers having a diameter of 5 to 500 nm, a length of 100 nm to 10 μm, and an aspect ratio of 5 to 1000.

6. In paragraph 4, If the above nanocellulose is a nanocellulose crystal, Polyurethane foam with nanocellulose crystals having a size of 3 nm to 50 nm.

7. In paragraph 1, The above nanocellulose is a polyurethane foam in which the surface is coated with the above inorganic nanoparticles or clusters of the above inorganic nanoparticles by compounding and bonding, or the above inorganic nanoparticles are coated by compounding and bonding to form a layer.

8. Insulating material for home appliances, including polyurethane foam according to Article 1; 9. In paragraph 8, The above home appliances include refrigerators, home appliance insulation materials, 10. In the method for manufacturing polyurethane foam according to Article 1, A step of preparing a polyol solution by adding and dispersing nanocellulose, the surface of which is chemically bonded to the above-mentioned inorganic nanoparticles, into a polyol solution; A step of preparing a polyurethane solution by adding and dispersing a catalyst, a surfactant, and a blowing agent into the polyol solution; and A step of manufacturing a polyurethane foam by mixing polyisocyanate into the above polyurethane solution and then molding and foaming it; A method for manufacturing polyurethane foam comprising:

11. In paragraph 10, A method for producing polyurethane foam, wherein the polyol solution is a solution of a polyol or a mixture thereof obtained by polymerizing an alkylene oxide including ethylene oxide, propylene oxide or butylene oxide using an organic oxide including a compound having an ester group, ethylene glycol, glycerin, trimethylpropane, sorbitol, sucrose, ethylene diamine (EDA), diethylene triamine, toluenediamine (TDA) or diphenylmethanediamine as an initiator.

12. In paragraph 10, A method for manufacturing polyurethane foam, wherein the nanocellulose chemically bonded to the surface of the above-mentioned inorganic nanoparticles is added and dispersed in an amount of 0.001 to 10 wt% compared to the above-mentioned polyol solution.

13. In paragraph 10, A method for producing polyurethane foam, wherein the catalyst comprises a gelling catalyst, a trimerization catalyst or a blowing catalyst.

14. In paragraph 10, A method for producing polyurethane foam, wherein the blowing agent comprises at least one chemical blowing agent selected from the group consisting of azodicarbonamide, activated azodicarbonamide, 5-phenyltetrazole sodium bicarbonate, and water (DI), or at least one physical blowing agent selected from the group consisting of cyclopentane and HFO.

15. In paragraph 10, A method for manufacturing polyurethane foam, wherein the above polyurethane solution and polyisocyanate are mixed in a weight ratio of 1:1 to 1.3.

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