KR20180108270A - Method of preparing nanocellulose and silica aerogel composite material comprising nanocellulose - Google Patents

Abstract

The present invention relates to a method for producing a nanocellulose and to a silica aerogel composite material comprising the nanocellulose. The method for producing the nanocellulose of the present invention minimizes cost and damage to a fiber itself to prevent shortening of fiber formation, thereby providing an effect of providing a nano-cellulose of high quality. In addition, a nanofiber reinforced silica aerogel composite material according to the present invention exhibits excellent heat insulating properties as most of the total volume is composed of silica aerogel, and nano-cellulose fibers capable of self-assembly by hydrogen bonding act as a binder and a reinforcing agent to exhibit excellent heat insulating properties, density, and high mechanical properties.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for producing a nanocellulose and a nanocellulose-containing silica airgel composite material,

The present invention relates to a method for producing a nanocellulose having a sulfate function.

The present invention also relates to a composite material of silica-airgel composite containing nanocellulose fibers. More particularly, the present invention relates to a silica airgel composite material that is hydrophilized by a surfactant containing nanocellulose fibers.

Since most of the domestic energy fuel consumption depends on imports, there is a need to develop efficient energy saving technologies. Therefore, it is necessary to develop a heat insulating material in order to block heat transfer from the outside or to prevent internal heat from being discharged to the outside. Various types of organic insulation materials such as mineral wool, expanded polystyrene, cellulose, cork, and polyurethane have been commercialized, but their thermal conductivities are 0.03 to 0.05 W / mK higher than air (thermal conductivity: 0.025 W / mK) . The existing organic insulation materials are made of the principle of increasing the ratio of air with low thermal conductivity in the insulation by forming a micro-sized pore structure. It is difficult to maintain the existing thermal conductivity value when the thickness of the insulation decreases. Do. To develop innovative energy saving technologies, it is necessary to develop insulation materials with low thermal conductivity.

According to the Knudsen diffusion effect, in which diffusion of air and heat conduction is suppressed when the gas is trapped in a space smaller than the average free movement distance, the pore size in the insulation should be lower than the average free movement distance of air (less than 68 nm) A thermal conductivity lower than air can be realized. An airgel is a nano-porous structure in which a silicon dioxide (SiO ₂ ) chain has a three-dimensional network structure, and at least 90% of the total volume of the material is filled with air to be.

The thermal conductivity of the airgel is 0.018 W / mK or less, which is excellent in the heat insulating property, but it is manufactured by an expensive supercritical drying method and is difficult to mass-produce. The supercritical drying method is a high pressure reactor (50,000,000 W / L) using a drying technique that removes solvents while retaining at least 90% pore structure of silica wet gel using liquid carbon dioxide (CO ₂ ) gas (annual consumption: 75,555,000 / ) And the difficulty of high pressure operation. In addition, although aerogels are widely regarded as the next generation of insulation due to their excellent thermal insulation properties, they are easily destroyed. In order to overcome the brittleness, the development of strengthened aerogels is in full swing. However, there is still a problem that aerogels are scattered because of the use of the supercritical system, which is expensive and difficult to mass-produce.

On the other hand, nanocellulose is a nanometer-diameter crystalline fiber extracted from cellulose, which is a major component of plant cell walls. It is an inter-molecular hydrogen bond and is a carbon-neutral material that is excellent in mechanical properties and environmentally friendly as a plant-derived material. Nanocellulose is an environmentally friendly biomass material, and when it is nanoized, it has transparency and high mechanical properties. Therefore, the demand for nanocellulose is increasing due to attempts to apply it to industries such as transparent high-strength materials. Nano-cellulose can be applied mainly as a filler of eco-friendly composite material, porous material, transparent film and the like. Conventional nanocellulose production methods include extraction from wood or biomass, pulverization through mechanical and chemical treatment, and production through biological culture from bacteria.

Mechanical grinding is a method of cutting / grinding by using repetitive force, such as grinding, water jet, homogenization, solid solution, extrusion, ball milling, etc. The fibers thus produced are uneven in shape and have a high energy cost But the aspect ratio is so large that it is used as a reinforcing material.

The chemical treatment method is a method of selectively dissolving and separating by the difference of the solubility. The hydrolysis method, the oxidation method, and the ion solvent method are used. The fiber thus produced is inevitably damaged by the fiber itself, do.

The biological culture method is obtained by sterilizing and washing the strain by inoculating and culturing the strain. The shaking culture method and the stationary culture method are also available. The fiber thus produced is advantageous in obtaining pure cellulose free of impurities such as hemicellulose and lignin, It is difficult to surface treatment and is used for expensive medical treatment such as artificial skin and drug delivery agent.

Numerous references are referenced throughout the specification and are cited therein. The disclosure of the cited document is incorporated herein by reference in its entirety to more clearly describe the state of the art to which the present invention pertains and the content of the present invention.

1. Korean Patent No. 10-0666110 2. Korean Patent Publication No. 10-2016-0019753

It is an object of the present invention to provide a method for producing nanocellulose fibers.

The present inventors have also made efforts to provide a novel silica airgel composite material manufacturing technique which has excellent thermal conductivity and exhibits no thermal dissipation phenomenon with excellent thermal conductivity and brittleness as compared with the conventional silica airgel composite material. As a result, the present inventors have completed the present invention by producing a composite material of silica-airgel composite containing nanocellulose fibers.

Accordingly, another object of the present invention is to provide a composite material comprising hydrophilic silica airgel particles and nanocellulose fibers.

It is still another object of the present invention to provide a product manufactured using the composite material.

It is still another object of the present invention to provide a method for manufacturing a composite material comprising the hydrophilic silica airgel particles and the nanocellulose fibers.

Other objects and advantages of the present invention will become more apparent from the following detailed description of the invention, claims and drawings.

One aspect of the present invention is to provide a method for producing nanocellulose fibers.

Conventional nanocellulose production has been produced by using a mechanical grinding method or a chemical dissolving method. In the case of mechanical grinding, incomplete separation of nanocellulose and excessive energy cost are problematic. In the case of the chemical dissolution method, there was a problem of fiber damage and short fiberization.

Accordingly, the present invention provides a chemical pretreatment method capable of reducing energy before mechanical pulverization, which uses a catalyst and sulfuric acid as a raw material for wood or biomass to impart sulfuric acid functional groups to the surface of fibers by using an esterification reaction. And a method of easily and efficiently producing nanocellulose by reducing energy when pulverized by a repulsive force by ionic impartation.

The manufacturing method of the present invention comprises the steps of (i) mixing a biomass with an urea, (ii) treating the mixture with sulfuric acid, and (iii) washing and pulverizing the sulfuric acid- will be. FIG. 1 shows a flow chart of a nano-cellulose production process.

Each step will be described in detail below.

(i) mixing the biomass with the element

First, add heat to the element and dissolve it, then add biomass, then stir and evenly impregnate the element with biomass. The weight ratio of biomass and urea, in which the elements can be dissolved to sufficiently adsorb the biomass, is preferably 1:10, more preferably 1:15. The stirring speed may be 100 to 500 rpm, preferably 200 to 500 rpm. Stirring is preferably carried out from the start of element dissolution to the end of the reaction. The biomass includes a fiber, a woody, a seaweed, a combination thereof, and the like, and more specifically, a coconut, a corn, a cotton, a hemp, a flax, a cotton, a jute, a manila hemp, There are mixtures and this is not limited. The biomass forms include, but are not limited to, powders, pellets, sheets, pulp, and combinations thereof. Examples of pulp include, but are not limited to, eucalyptus pulp, spruce pulp, pine pulp, beech pulp, hemp pulp, cotton pulp, bamboo pulp, recycled pulp or deinked pulp and combinations thereof.

(ii) treating the mixture with sulfuric acid

Sulfuric acid-treated pulp can be obtained by slowly adding sulfuric acid to the mixture obtained in the step (i) and then heat-treating it. The concentration of sulfuric acid may be 10 to 95% by weight, preferably 50% by weight, and more preferably 75% by weight, which is a condition that largely influences the physical properties of the nanocellulose after the reaction. The temperature at which the element is dissolved and the reaction temperature at which the pulp does not deteriorate may be 120 to 200 캜, preferably 140 캜, more preferably 150 캜. A yield loss due to pulp deterioration may occur at a temperature of 200 ° C or higher. The reaction time is preferably 30 minutes, more preferably 60 minutes.

(iii) washing and grinding steps

The sulfuric acid-treated product is slowly cooled, added with NaOH, and washed after stirring. When the solid content is then pulverized, the nanocellulose functionalized with a sulfuric acid group can be obtained.

In the addition of NaOH and the stirring step, the hydrolyzed nanocellulose product is slowly cooled, and then NaOH (1 M) is added thereto. The mixture is further stirred for 1 hour and then allowed to stand at room temperature for phase separation. A basic solution such as NaOH provides an effect of suppressing hydrogen bonding by supplying positive ions to the fiber surface.

The compound having a hydroxyl group is not particularly limited and may be an inorganic alkali compound or an organic alkali compound. Inorganic alkali compounds include, but are not limited to, lithium hydroxide, sodium hydroxide, or potassium hydroxide compounds. Examples of the organic alkali compound include ammonia, hydrazine, methylamine, ethylamine, diethylamine, triethylamine, propylamine, dipropylamine, butylamine, diaminoethane, diaminopropane, diaminobutane, Cyclohexylamine, aniline, tetramethylammonium hydroxide, pyridine, ammonium carbonate, ammonium hydrogencarbonate, or ammonium dihydrogen phosphate compounds.

The solvent in the alkali solution is water or an organic solvent, and preferably an aqueous solvent containing water.

In the washing step, the supernatant is poured into the supernatant of the product, and the solid component is poured into distilled water and washed with a sieve. Repeat this process several times.

In the pulverizing step, the washed solid matter is pulverized using a pulverizer as a slurry to obtain a nanocellulose slurry. The slurry concentration at the time of milling may be 0.5 to 2% by weight, preferably 1 to 2% by weight, more preferably 2% by weight.

Examples of the grinding apparatuses include a water jet grinder, a high speed grinder, a grinder (mill type grinder), a high pressure homogenizer, an ultra high pressure homogenizer, a high pressure impact grinder, a ball mill, a bead mill, a disk type refiner, A vibrating mill, a homomixer under high speed rotation, an ultrasonic dispersing machine, or a beater.

The thermal stability of the nanocellulose treated with sulfuric acid is better than that of the conventional pulp by performing the thermal analysis of the nanocellulose according to the above production method. This is because the thermal stability of nanocelluloses is determined by the exchange of electrons of substituents. In the case of phosphorylation of nanocellulose, the intramolecular bonding is weakened due to strong electron accepting properties compared to sulfation, and the thermal stability is poor. 2 and 3 show the cellulose thermal stability according to the substituent. Therefore, high quality of nanocellulose can be achieved through high thermal stability of sulfated nanocellulose.

Another aspect of the present invention is to provide a composite material comprising hydrophilic silica airgel particles and nanocellulose fibers.

The present invention enables the mass production and commercialization of a fiber reinforced silica airgel because a hydrophilic nano-cellulose fiber is mixed with a solution in which silica airgel particles are dispersed in an aqueous solution instead of an expensive supercritical drying method, followed by heating and pressing. .

In one embodiment of the present invention, the hydrophilic silica airgel particles can be obtained by hydrophilizing the surface of the hydrophobic silica airgel. The hydrophobic silica airgel may be an aerogel imparted with hydrophilicity by silylation after acid treatment of water glass at normal pressure.

Hydrophilic silica airgel particles may be surface-treated with a surfactant to prepare hydrophilic silica airgel particles. Anionic surfactants, cationic surfactants or amphoteric surfactants are usable as the surfactant. Examples of the anionic surfactant include fatty acid sodium salt, monoalkyl sulfate, alkyl polyoxyethylene sulfate, monoalkyl phosphate, alkylbenzene sulfonate, polyoxyethylene alkyl ether, alkyl monoglyceryl ether, fatty acid sorbitan ester, polyethylene glycol hexadecyl ether But not limited to. Examples of cationic surfactants include dialkyldimethylammonium salts, alkylbenzylmethylammonium salts, and fatty acid diethanolamines. Amphoteric surfactants include, but are not limited to, alkyl sulfobetaine, alkylcarboxybetaine.

In another embodiment according to the present invention The nanocellulose may be a nanocellulose fiber having a diameter of 20 to 100 nm and a length of at least 2 [mu] m to at least 5 [mu] m.

The hydrophilic silica aerogels and the nanocellulose fibers are mixed and densified and then dried to obtain the nanocellulose fiber-reinforced silica airgel composite material according to the present invention. The densified aerogel composite material is excellent in mechanical strength because all the pores outside the nano pores in the aerogel particle are removed. In addition, due to the high density, most of the total volume is composed of aerogels, which leads to excellent thermal insulation properties.

The silica airgel insulator reinforced with the nanocellulose fibers according to the present invention uses fibrous nanocellulose and may not contain a separate binder component such as molecular scale ethylcellulose. Since the nanocellulose fibers can be self-assembled by hydrogen bonding, the nanocellulose fibers themselves can act as a binder and a reinforcing agent without a separate binder, thereby solving the scattering problem of the airgel composite material. The density of the airgel composite material of the present invention may be 0.3 to 1.0 g / cm ³ days, may be an indication of the flexural strength and / or flexural modulus of 10 to 100 MPa for 0.5 to 3 MPa.

The airgel composite material may have a thermal conductivity of 0.01 to 0.05 W / mK.

Another aspect of the present invention is to produce a product manufactured using the aerogel composite material.

In one embodiment, the product may be, but is not necessarily limited to, thermal insulation materials, building materials, electrical materials, insulation materials, catalyst carriers, heat resistant materials, soundproofing materials, spacesuits, spacecraft, aircraft and automotive materials.

Another aspect of the present invention is to provide a method for producing a composite material comprising hydrophilic silica airgel particles and nanocellulose fibers. Fig. 4 shows a flow chart of the production of the nanocellulose fiber-reinforced silica airgel composite material.

In one embodiment, the hydrophilic silica airgel particles can be obtained by hydrophilizing the surface of the hydrophobic silica airgel, and therefore, a method for obtaining a hydrophobic silica airgel is first disclosed.

In the present invention, a low-cost silica airgel produced by atmospheric pressure drying may be used instead of the supercritical drying method. For example, acid treatment of water glass (NaSiO ₃ ), which is an inexpensive raw material at normal pressure, causes gelation to form silica airgel. Thereafter, the water in the wet gel is removed by washing and filtration, and the silica airgel surface is modified by silylation. Thereafter, the solvent and the silylating agent are recovered and dried to obtain a silica airgel having a hydrophobic surface. Acids treated in the water glass include, but are not limited to, hydrochloric acid, sulfuric acid, nitric acid and the like .

The hydrophobic silica aerogels obtained by the above-described production process may be surface-treated with a surfactant to prepare hydrophilic silica aerogels. The above-mentioned surfactants are as described above.

Thereafter, the hydrophilic silica airgel is dispersed in water to form an aqueous dispersion, and the pulp is pulverized to prepare a nanocellulose water dispersion. The volume ratio of nanocellulose fibers: hydrophilic silica aerogel particles in the mixture can be from 1: 9 to 1:99, preferably from 1:19 to 1:99, based on the composite material produced. The stirring speed at the time of mixing may be 100 to 1000 rpm, preferably 500 to 1000 rpm. The stirring time may be 5 minutes to 2 hours, preferably 20 minutes to 1 hour.

The hydrophilic silica airgel water dispersion and the nanocellulose fiber water dispersion are mixed and stirred, and then the mixed solution is filtered and mold-dried. Preforms can be formed by hydrogen bonding through mold drying at room temperature. The filtering time may be from 1 to 240 hours, preferably from 24 to 240 hours.

After the filtering process, the hot press process (densification) process is performed. The temperature condition for densification may be 30 to 300 캜, and preferably 120 to 300 캜. The densification pressure conditions can be from 5 to 70 MPa, and preferably from 30 to 70 MPa. The time period of densification may be from 30 minutes to 12 hours, and preferably from 2 hours to 12 hours. FIG. 5 shows a concept of high density.

Microwave drying is performed after high density. The electromagnetic wave drying condition may be 5 minutes to 2 hours on the basis of 1000 W, preferably 10 minutes to 2 hours. When the process of drying the electromagnetic wave is completed, a silica airgel insulator reinforced by the nanocellulose fibers can be obtained.

The method of producing nanocellulose of the present invention has the effect of reducing the cost of nanocellulose and minimizing the damage to the fiber itself, thereby preventing the monofilization and providing high quality of nanocellulose.

The nanofiber-reinforced silica airgel composite material according to the present invention is composed of silica airgel in a majority of its volume, and exhibits excellent heat insulating properties. In addition, nanocellulose fibers that can self-assemble by hydrogen bonding to a weakly brittle silica airgel can act as a binder and a reinforcing agent, so that they can be applied to a wide range of areas, from thin type insulation to thick building insulation It is expected to be.

1 is a flow chart of a process for producing nanocellulose fibers by a sulfuric acid treatment method.
2 shows the thermal stability of the polymer according to the substituent. The stronger the electron accepting property of the substituent, the lower the thermal stability.
FIG. 3 is a conceptual diagram for comparing the thermal stability of the sulfated nanocellulose and the phosphorylated nanocellulose.
Fig. 4 is a flow chart of production of a nanocellulose fiber-reinforced silica airgel composite material.
FIG. 5 shows a process of increasing the density of a composite material through heating and pressing.
6 shows a conventional method of producing nanocellulose by mechanical pulverization and hydrolysis.
7 shows a method for producing nanocellulose by the sulfuric acid treatment method.
8 shows the results of analysis of the shape of the nanocellulose prepared by the sulfuric acid pretreatment manufacturing method in the examples. The left side shows the state after the sulfuric acid pretreatment and the grinder 15 after the pass milling, and the right side shows the SEM (electron scanning microscope) analysis result.
Fig. 9 shows the results of SEM analysis of the fibrous nanocellulose prepared in the examples.
FIG. 10 shows a graph of thermal conductivity according to the density of the composite material. The lower the thermal conductivity, the better the adiabatic properties.
Fig. 11 shows the results of non-acidic comparison of the glass fiber-reinforced aerogels and the nanocellulose fiber-reinforced silica airgel composite materials.
12 shows a comparison of three-point bending strength measurement between a glass fiber-reinforced airgel and a nano-cellulose fiber-reinforced silica airgel composite material.

Hereinafter, the present invention will be described in more detail with reference to Examples. It is to be understood by those skilled in the art that these embodiments are only for describing the present invention more specifically and that the scope of the present invention is not limited by these embodiments.

Example

Example  One - Nano-cellulose  Manufacturing method

(a) Element Impregnation  The Biomass  Preparation step of reagent (A)

500 g of the component was dissolved by heating at 140 DEG C and then 50 g of pulp was added and stirred so that the pulp was evenly impregnated with the element. The agitation speed was 250 rpm and stirring was started from the beginning of urea dissolution to the end of the reaction.

(b) Sulfuric acid treatment step

Sulfuric acid was slowly added to the reagent (A) and then heat-treated to obtain a sulfuric acid-treated pulp. 150 g of 75 wt% sulfuric acid was slowly added to the above reagent (A), and then heat-treated at 150 ° C for 60 minutes to obtain a sulfuric acid-treated pulp.

(c) washing and pulverizing the sulfuric acid-treated mixture

The product of step (b) was slowly cooled, added with NaOH, and washed after stirring. Thereafter, the solid content was pulverized to obtain a nanocellulose functionalized with a sulfate group.

-NaOH addition and stirring step

After the step (b) was cooled slowly, NaOH (1 M) was added and the mixture was stirred for 1 hour and allowed to stand at room temperature for phase separation.

- washing step

The supernatant was passed through the top of the phase-separated product and the solid was added to distilled water and washed with a sieve. This procedure was repeated three times.

- grinding step

The washed solid matter was pulverized 15 times using a grinder mill (Masuko, MKCA6-2) at a speed of 1500 rpm and a grinder interval of -80 쨉 m, to obtain a nanocellulose slurry.

The nanocellulose prepared according to the above procedure was observed with a scanning electron microscope (SEM), and the results are shown in FIGS. 8 and 9. FIG. As a result of the SEM shape analysis, it was confirmed that the nanocellulose had a fiber shape having a diameter of 20 to 50 nm and a length of 2 탆 or more (see FIGS. 8 and 9).

Example 2 - Nanocellulose thermal analysis according to the above preparation method

DSC (STA409PC, Netzch) at a heating rate of 10 占 폚 / min from 30 占 폚 to 600 占 폚 under an air atmosphere in order to evaluate the thermal stability of the reactants. The heat stability was evaluated in the 2 ^nd step in which the cellulose was substantially decomposed since a mass reduction by moisture occurred at 1 ^st step.

It was confirmed that the thermal stability of the sulfuric acid-treated nanocellulose was superior to that of the conventional pulp. Also, it was confirmed that the sulfuric acid - treated nanocellulose had better thermal stability than the case of phosphoric acid treatment.

In the case of phosphorylation, the covalent bond of the cellulose molecule is weakened due to the strong electron-receiving property compared to the sulfation, and the thermal stability is lowered. Another TGA (Thermogravimetric anaylsis) is shown in the table below. Similarly, it was confirmed that the sulfuric acid-treated nanocellulose had excellent thermal stability.

Example  3 - Nano-cellulose  Fiber reinforced silica Aerogels  Composite material manufacturing

The silica airgel produced by the acid treatment of water glass (267 won / kg), which is an inexpensive raw material at atmospheric pressure, and the hydrophilization by silylation, was made into a hydrophobic silica airgel. In this study, low cost silica airgel made by atmospheric pressure drying was used instead of supercritical drying method.

The hydrophobic silica airgel was surface-treated with a surfactant such as polyethylene glycol hexadecylether (Brij 56) to prepare a hydrophilic silica airgel.

Thereafter, the hydrophilic silica airgel aqueous dispersion (not more than 20% by weight) and the nanocellulose fiber aqueous dispersion (not more than 1% by weight) prepared by pulverizing the pulp were mixed. The volume ratio of the nanocellulose fibers: hydrophilic silica aerogels in the mixture was 1:20 based on the composite material. The stirring speed at the time of mixing was 750 rpm, and the stirring time was 40 minutes. The nanocellulose used was nanocellulose fibers having a diameter of 35 nm and a length of 3 탆.

After the hydrophilic silica airgel aqueous dispersion and the nanocellulose fiber water dispersion were mixed and stirred, the mixed solution was filtered and mold-dried. The filtering time was 1200 hours.

 After the filtering process, a hot press process was performed. The temperature condition for high density was 150 DEG C, and the pressure condition for high density was 40 MPa. The time for high density was set to 6 hours.

After the densification, microwave drying was performed. Electromagnetic wave drying was carried out for 1 hour at 1000 W standard.

After the electromagnetic wave drying step, the silica airgel insulator reinforced by the nanocellulose fibers was obtained.

The characteristics of the nanocellulose fiber-reinforced silica airgel composite obtained through high temperature and high pressure drying are shown in the following table.

Example  4 - Aerogels  Comparison of insulation properties of composite materials

The thermal insulation properties of the nanocellulose reinforced nanoparticle samples, the glass fiber reinforced silica airgel samples, and the nanocellulose fiber reinforced silica airgel samples were compared.

The nanocellulose-reinforced nanoparticle sample was obtained by mixing inorganic nano-particles with water-dispersed nanocellulose, filtering and drying the glass fiber-reinforced silica airgel sample. The glass fiber-reinforced silica airgel sample was impregnated with a silica airgel in a glass fiber blanket, I could make it. The nanocellulose fiber-reinforced silica airgel sample was prepared by mixing the nanocellulose fiber and the water-dispersed silica airgel in the same manner as in Example 1, followed by filtering and hot pressing.

In the case of nanocellulosic reinforced nanoparticle samples, the thermal conductivity increased with increasing density, but in the case of samples mixed with silica airgel, the thermal conductivity tended to decrease with increasing density. FIG. 10 shows a comparison of the heat insulating properties of each sample.

Example 5 - Comparison of scattering characteristics of fiber reinforced silica aerogel composite material

The scattering characteristics of the glass fiber reinforced silica airgel and the nanocellulose fiber reinforced silica airgel were evaluated using 3M tape.

In the case of glass fiber reinforced silica airgel samples with micrometer diameter, it was found that not only airgel particles but also glass fibers were scattered. On the other hand, in the case of the nanocellulose fiber-reinforced silica airgel, it was confirmed that it was hardly scattered. The nanocellulose fibers that can be self-assembled by hydrogen bonding serve as a binder and a reinforcing agent, thereby solving the problem of scattering of silica airgel after high density became possible (see FIG. 11).

Example 6 - Flexural strength comparison of fiber reinforced silica airgel composite

The flexural strengths of glass fiber reinforced silica airgel samples and nano - cellulose fiber reinforced silica airgel samples were compared by three - point flexural strength measurements. The size of each sample was 25 mm x 50 mm x 3 mm (width x length x thickness). In the case of glass fiber reinforced silica airgel, the sample was warped and the flexural strength could not be measured. The flexural strength of the nanocellulosic fiber reinforced silica airgel was 1.2 MPa. Also, it was confirmed that the flexural modulus of the nano-cellulose fiber reinforced silica airgel was 58.5 MPa. Fig. 12 shows an experiment for measuring the bending strength.

The nano-cellulose fiber-reinforced silica aerogels according to the present invention are excellent in thermal insulation properties and mechanical characteristics, and can be used in many areas, from thin insulation to thick building insulation.

Claims (17)

A composite material comprising hydrophilic silica airgel particles and nanocellulose fibers. The composite material according to claim 1, wherein the hydrophilic silica airgel particles are surface-treated with a surfactant. The composition according to claim 2, wherein the surfactant is selected from the group consisting of sodium fatty acid, monoalkyl sulfate, alkyl polyoxyethylene sulfate, alkylbenzene sulfonate, monoalkyl phosphate, dialkyldimethylammonium salt, alkylcellum methylammonium salt, alkyl sulfobetaine, A polyoxyethylene alkyl ether, a fatty acid sorbitan ester, a fatty acid diethanolamine, an alkyl monoglyceryl ether, and a polyethylene glycol hexadecyl ether. The composite material according to claim 2, wherein the hydrophobic silica airgel particles are produced by a normal-pressure drying method using water glass (NaSiO ₃ ). The composite material according to claim 1, wherein the volume ratio of the nanocellulose fibers: hydrophilic silica airgel particles contained in the composite material is 1: 9 to 1:99. The composite material of claim 1, wherein the nanocellulose fibers have a length of at least 2 microns to at least 5 microns. The composite material of claim 1, wherein the nanocellulose fibers have a diameter of from 20 to 100 nm and a length of at least 2 microns to at least 5 microns. The composite material according to claim 1, wherein the composite material does not include a separate binder component. The composite material according to claim 1, wherein the airgel particles and the nanocellulose fibers form hydrogen bonds with each other. The composite material according to claim 1, wherein the composite material has a density of 0.3 to 1.0 g / cm ³ . The composite material according to claim 1, wherein the composite material exhibits a bending strength of 0.5 to 3 MPa. The composite material according to claim 1, wherein the composite material exhibits a flexural modulus of 10 to 100 MPa. The composite material according to claim 1, wherein the composite material has a thermal conductivity of 0.01 to 0.05 W / mK. A product manufactured using the composite material of claim 1, wherein the product is selected from the group consisting of a heat insulating material, a building material, an electric material, an insulating material, a catalyst carrier, a heat resistant material, a soundproofing material, a space suit, a spacecraft, Products featured. Preparing hydrophobic silica airgel particles;
Preparing a hydrophilic silica airgel particle by surface-treating the hydrophobic silica airgel particle with a surfactant;
Mixing the hydrophilic silica airgel particles and the nanocellulose fibers; And
Drying the mixture at room temperature and applying densification at a temperature of 30 to 300 DEG C and a pressure of 5 to 70 MPa
The method of manufacturing a composite material according to claim 1, (I) mixing a biomass with an element;
(Ii) treating the mixture with sulfuric acid; And
(Iii) washing and pulverizing the sulfuric acid treated mixture
≪ / RTI > The process according to claim 16, wherein the concentration of sulfuric acid in step (ii) is 10 to 95% by weight.

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