KR20200073189A - Boron nitride nanosheet-cellulosic nanofiber composite film having excellent oxygen barrier, and method for producing the same - Google Patents

Abstract

A boron nitride nanosheet-cellulose nanofiber composite film according to the present invention, even when manufactured by a simple and mild manufacturing method that can be commercially used, has a role as an excellent oxygen barrier film that is sustainable, has an effect of improving properties such as elastic modulus and tensile strength without a substantial decrease in elongation properties, has an effect of having excellent optical properties with high light transmittance, and has an effect of having very low cytotoxicity.

Description

Boron nitride nanosheet-cellulosic nanofiber composite film having excellent oxygen barrier, and method for producing the same}

The present invention relates to a polymer composite film having excellent oxygen barrier properties and a method for manufacturing the same.

Universal synthetic polymers such as polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET) are packaging materials for food and pharmaceuticals, and have excellent strength, viscoelasticity, and chemical resistance. And has been widely used due to its low cost.

In particular, when these materials are used as packaging films for foods and medicines, oxygen barrier properties are essential for preventing oxidation of foods and medicines. However, most polymer films have high oxygen permeability, and for example, have a high oxygen transmission rate (OTR) of about 40 to 1000 cc/m ² /day. Specifically, the polyethylene film and the polypropylene film are 1,000 cc/m ² /day or more, and the polyethylene terephthalate film is known to have an oxygen transmission rate of about 60 cc/m ² /day.

Halogenated or metallized polymer films have been studied to improve the oxygen barrier properties of synthetic polymers, which have been reported to achieve low oxygen transmission rates of 0.1 to 10 cc/m ² /day. However, such a polymer film has a problem that greatly causes an environmental and health threat. For example, an aluminum-coated polyethylene terephthalate film and a polymer film such as polyvinylidene chloride (PVDC) have a fatal problem of generating substances harmful to the human body such as fine dust and dioxins during incineration. Therefore, such a halogenated or metallized polymer film cannot be recycled, and there is a problem in that a huge cost is required during treatment.

On the other hand, cellulose nanofibers (CNFs) are sustainable and biocompatible nanomaterials that are used as packaging materials for food and pharmaceuticals, which mechanically decompose highly crystalline nanofibers in cellulose bulk, a rich biomass. Is produced.

However, when the cellulose nanofiber film is manufactured under highly controlled conditions, it has an ideal oxygen blocking performance with low oxygen permeability, but the cellulose nanofiber film manufactured in an actual manufacturing and use environment such as an industrial site exhibits its oxygen blocking performance properly. There are deadly drawbacks that cannot be. Specifically, when the film is manufactured, since the capillary force creates a heterogeneous surface during drying, it has a disadvantage of having a high oxygen permeability of 19 cc/m ² /day or more when actually manufactured and commercialized.

Therefore, research into an excellent cellulose-based composite film capable of exerting a high level of oxygen blocking properties, even when manufactured with a simple manufacturing method that is actually commercially available, furthermore, performance of optical properties, mechanical properties, biocompatibility, etc. Even excellent composite films need to be studied.

Korean Registered Patent Publication No. 10-1721753 (2017.03.24)

An object of the present invention is to provide a polymer film capable of exerting high oxygen blocking performance even when manufactured by a simple production method that is actually commercially available.

In addition, another object of the present invention is to provide a polymer film excellent in optical properties, mechanical properties, biocompatibility, and the like.

The method of manufacturing a boron nitride nanosheet-cellulose nanofiber composite film according to the present invention comprises: a) mixing and dispersing boron nitride nanosheets and cellulose nanofibers in a water phase to prepare a dispersion, and b) drying the dispersion to form a composite And producing a film.

In an example of the present invention, in step a), the dispersion may include water, boron nitride nanosheets, and cellulose nanofibers.

In one example of the present invention, the dispersion may include 0.05 to 1 part by weight of boron nitride nanosheets and 0.1 to 5 parts by weight of cellulose nanofibers with respect to 100 parts by weight of water.

A method of manufacturing a boron nitride nanosheet-cellulose nanofiber composite film according to an example of the present invention, prior to the step a), after dispersing the boron nitride powder in a dispersion medium containing an ionic liquid and reacting it, the boron nitride nanosheet It may further include the step of manufacturing.

In an example of the present invention, in step b), drying may be natural drying performed at normal pressure.

In an example of the present invention, in step b), drying may be performed at 5 to 35°C.

In one example of the present invention, the boron nitride nanosheet may have a thickness of 0.2 to 50 nm and a long axis of 300 to 1,000 nm.

The weight ratio of the boron nitride nanosheet and the cellulose nanofiber of the boron nitride nanosheet-cellulose nanofiber composite film according to the present invention may be 0.1:99.9 to 10:90.

The boron nitride nanosheet-cellulose nanofiber composite film according to the present invention may have an elongation of 4% or more, a Young's modulus of 4.8 GPa or more, and a tensile strength of 90 MPa or more.

The oxygen transmittance of the boron nitride nanosheet-cellulose nanofiber composite film according to the present invention may be 15 ml/m ² /day or less.

The boron nitride nanosheet-cellulose nanofiber composite film according to the present invention may be used for packaging for blocking oxygen in food or pharmaceuticals.

The boron nitride nanosheet-cellulose nanofiber composite film according to the present invention has a role as an excellent oxygen barrier film that can be sustained even when manufactured by a simple and mild manufacturing method that is practically commercially available, as well as elastic modulus and tensile strength without substantially reducing elongation properties. It has the effect of improving the properties of the back, has the effect of having excellent optical properties with high light transmittance, and has the effect of having very low cytotoxicity.

Even if the effects are not explicitly mentioned in the present invention, the effects described in the specification expected by the technical features of the present invention and the inherent effects thereof are treated as described in the specification of the present invention.

1 is a process chart for a method of manufacturing a boron nitride nanosheet-cellulose nanofiber composite film according to the present invention.
Figure 2 shows the results of measuring the average size and polydispersity of the boron nitride nanosheet prepared in Example 1 using a zeta sizer, a scanning electron microscope and a transmission electron microscope.
3 is an image of a dispersion of boron nitride nanosheets and cellulose nanofibers prepared in Example 1.
Figure 4 shows the results of measuring the oxygen transmission rate (Oxygen transmission rate, OTR) of the films prepared in Examples 1 to 3 and Comparative Example 1 through an oxygen permeability tester.
Figure 5 shows the results of measuring the Young's modulus, tensile strengths and elongations of the films prepared in Examples 1 to 3 and Comparative Example 1.
6 shows the results of measuring the light transmittance of the films prepared in Example 1 and Comparative Example 1 through a UV-vis spectrophotometer.
7 is a field emission scanning electron microscope image of the film prepared in Example 1 and Comparative Example 1.
Figure 8 shows the results of testing the cytotoxicity for the films prepared in Example 1 and Comparative Example 1.

Hereinafter, a boron nitride nanosheet-cellulose nanofiber composite film having excellent oxygen barrier properties according to the present invention and a manufacturing method thereof will be described in detail with reference to the accompanying drawings.

The drawings described in this specification are provided as examples in order to sufficiently convey the spirit of the present invention to those skilled in the art. Therefore, the present invention is not limited to the presented drawings and may be embodied in other forms, and the drawings may be exaggerated to clarify the spirit of the present invention.

Unless otherwise defined in technical terms and scientific terms used in the present specification, those skilled in the art to which the present invention pertains have the meanings commonly understood, and the subject matter of the present invention in the following description and the accompanying drawings. Descriptions of well-known functions and configurations that may unnecessarily obscure are omitted.

As used herein, the singular form of the term may be interpreted to include the plural form unless otherwise specified.

Units of% used in the present specification without specific mention mean% by weight, unless otherwise defined.

The present inventors are known to have an ideal oxygen barrier property of a cellulose nanofiber film having a low oxygen permeability (1 cc/m ² /day or less), but this is a property that appears only when manufactured under highly controlled conditions, at room temperature and normal pressure. Cellulose nanofiber films are used in actual mass production and commercialization when they are manufactured under actual commercially available process conditions such as, for example, a very high oxygen permeability (above 19 cc/m ² /day) and low oxygen barrier properties. Recognized a fatal problem that is difficult to do.

Therefore, as a result of conducting an in-depth study to solve this problem, the present inventor has the ideal oxygen barrier property of the cellulose nanofiber film even in simple and mild process conditions favorable for commercialization, and furthermore, it has elasticity and tensile strength, etc. without substantially reducing elongation properties. The present invention is to find a composite film having an effect of improving properties, an effect of having excellent optical properties with high light transmittance, and having a very low cytotoxicity and a method of manufacturing the same, in the present invention.

Hereinafter, a boron nitride nanosheet-cellulose nanofiber (BNNS-CNF) composite film according to the present invention will be described in detail.

Method for producing a boron nitride nanosheet-cellulose nanofiber composite film according to the present invention, a) a dispersion by mixing and dispersing boron nitride nanosheets (BNNS) and cellulose nanofibers (CNF) in a water phase And b) drying the dispersion to produce a composite film.

The aqueous phase of the step a) may preferably mean a dispersion medium phase composed of water, and may substantially mean that it does not contain a dispersion medium other than water, that is, does not include a heterogeneous dispersion medium other than water. Therefore, the dispersion in step b) means that boron nitride nanosheets and cellulose nanofibers are dispersed in a dispersion medium composed of water.

In particular, as the dispersion medium is composed of water, the composite film prepared by drying the dispersion in step b) has an effect of having a very low oxygen permeability. Specifically, the boron nitride nanosheets and cellulose nanofibers dispersed on a dispersion medium composed of water are not formed of a phase separation structure and pinholes even under drying conditions favorable for commercialization such as drying at room temperature and pressure, thereby producing a homogeneous composite film Is possible. When the boron nitride nanosheets and cellulose nanofibers are dispersed in a dispersion medium with each other, and when the dispersion medium is composed of water, they are highly miscible with water, and the formation of fine precipitates is extremely suppressed, resulting in a very uniform and stable state. Will exist in Therefore, even if the concentration increases as the drying proceeds in step b), the formation of a fine precipitate is extremely suppressed to form a homogeneous composite film having substantially no phase separation structure and pinholes. Accordingly, it is possible to have a very low ideal oxygen transmission rate of the cellulose nanofiber film.

However, when the dispersion medium contains a heterogeneous dispersion medium other than water or a heterogeneous solvent, the above-described effect cannot be realized. In detail, when a dispersion medium composed of water includes a highly volatile dispersion medium such as isopropyl alcohol or a solvent, when drying in step b), dispersion stability may be reduced, and the phase separation structure and pins during drying It may cause the formation of holes. Therefore, it is not possible to have a very low ideal oxygen transmittance of the cellulose nanofiber film, and improvement in optical properties, mechanical properties, and the like cannot be expected.

As described above, in the step a), the dispersion may include water, boron nitride nanosheets, and cellulose nanofibers. As a specific example, the composition ratio of the dispersion is not particularly limited, but may include 0.05 to 1 part by weight of boron nitride nanosheets and 0.1 to 5 parts by weight of cellulose nanofibers per 100 parts by weight of water. At this time, in terms of further improving the above-described effects such as excellent oxygen blocking properties, the mixed weight ratio of boron nitride nanosheets and cellulose nanofibers is 0.1:99.9 to 10:90, preferably 0.5:99.5 to 8:92, more Preferably it may be 1:99 to 5:95. However, this is only described as a preferred example, of course, the present invention is not limited to this.

In step b), it is preferable that the process conditions during drying are natural drying performed at normal pressure. At this time, the normal pressure means a pressure in a normal atmospheric state, and may mean 0.9 to 1.1 atm, specifically, 1 atm corresponding to the actual normal pressure. When dried at a pressure lower than normal pressure, including vacuum, specifically, under reduced pressure drying, pinholes may be generated as a result of drying under an unstable condition at a low pressure, which may greatly affect dispersion stability of the dispersion. As a result, it is impossible to form a homogeneous composite film having substantially no phase separation structure and pinholes, and it is not possible to expect improved effects such as elastic modulus and tensile strength and high light transmittance effect without substantially reducing elongation properties.

That is, when the drying of step b) is natural drying performed at normal pressure, a homogeneous composite film having substantially no phase separation structure and pinholes can be formed, and properties such as modulus of elasticity and tensile strength are not substantially reduced. An improved effect and a high light transmittance effect can be realized.

In step b), the drying temperature is not particularly limited as long as the dispersion is capable of forming a film, but may be preferably 5 to 35°C, more specifically, room temperature. If this is satisfied, it is advantageous for mass-production and commercialization, and it may be good to be able to prevent the problem of causing the phase separation structure and pinholes due to excessive temperature change.

A method of manufacturing a boron nitride nanosheet-cellulose nanofiber composite film according to a preferred embodiment, prior to step a), disperses the boron nitride powder in a dispersion medium containing an ionic liquid and reacts to prepare a boron nitride nanosheet It may further include a step. If this is satisfied, as the ionic liquid may remain on the surface of the boron nitride nanosheet, the dispersion stability of the boron nitride nanosheet in the dispersion medium is further increased in steps a) and b), resulting in the final composite film Oxygen permeability of can be further reduced, which may be desirable.

Specifically, as the volatility of the ionic liquid is significantly reduced, the surface of the boron nitride nanosheet prepared by reacting in a dispersion medium containing boron nitride in the dispersion medium containing the ionic liquid is on the surface of the boron nitride nanosheet even though it undergoes a drying process. Ionic liquids may remain. Therefore, the ionic liquid may be included in the dispersions of steps a) and b), and may also be contained in the final manufactured boron nitride nanosheet-cellulose nanofiber composite film. In this case, the ionic liquid contained in the boron nitride nanosheet-cellulose nanofiber composite film may be contained in an amount of 0.05 to 1 part by weight based on 100 parts by weight of the boron nitride nanosheet.

In the step of preparing the boron nitride nanosheet, the dispersion medium may include any one or more selected from water and ionic liquid. When the dispersion medium contains water and an ionic liquid, their weight ratio may be 0.01 to 1 part by weight of ionic liquid with respect to 100 parts by weight of water.

The ionic liquid is not particularly limited, for example, 1-butyl-3-methylimidazolium, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium bromide, 1-ethyl It may include any one or two or more selected from -3-methylimidazolium tetrafluoroborate. However, this is only described as a preferred example, of course, the present invention is not limited to this.

In addition, after the step of preparing the boron nitride nanosheet, the step of removing the unreleased boron nitride nanosheet and/or the dispersion medium (including the ionic liquid) may be further performed.

As a specific example, the boron nitride nanosheet may be prepared by peeling and functionalizing boron nitride using a Taylor-Couette (TC) reactor. In detail, the boron nitride dispersion prepared by mixing boron nitride powder with the dispersion medium is reacted in the reactor to remove and functionalize boron nitride, and then remove the unpeeled boron nitride nanosheet and dispersion medium to prepare boron nitride nanosheet. can do. At this time, the concentration of the boron nitride dispersion may be appropriately adjusted, for example, 5 to 100 mg/ml. The mixed solution containing the boron nitride nanosheet thus obtained can be freeze-dried for 5 to 30 hours to prepare a powdery boron nitride nanosheet.

However, in addition to this, the method for manufacturing the boron nitride nanosheet may refer to various well-known documents, for example, Korean Patent Publication No. 10-1721753, etc., but this is only described as a preferred example. It goes without saying that the invention is not limited to this.

The size of the boron nitride nanosheet used in the present invention is not particularly limited, for example, the thickness may be 0.2 to 50 nm, the long axis may be 300 to 1,000 nm, and more specifically, the thickness may be 1 to 30 nm, The major axis may be 400 to 800 nm. However, this is only described as a specific example, of course, the present invention is not limited to this.

The cellulose nanofibers used in the present invention may be used as long as they are commonly used, for example, the width may be 1 to 50 nm, the length may be 1 to 100 μm, and more specifically, the width may be 5 to 40 nm. The length can be 5 to 50 μm.

As a specific example, the cellulose nanofibers may be manufactured by crushing the wood or non-wood biomass to an increasingly small size, for example, a grinder or a high-pressure homogenizer. . In the method of manufacturing cellulose nanofibers using a grinder, the cellulose raw material or a mixed suspension containing the same is placed between a fixed ceramic disk and a ceramic disk rotating at high speed, and compressed at both sides in the disk by eccentric force. A method of producing cellulose nanofibers may be exemplified by being nanoized while being subjected to shearing force and frictional force by a rapidly rotating grinding stone hanging on both sides of the disk. In the method of manufacturing cellulose nanofibers using a high pressure homogenizer, the cellulose raw material or a mixed suspension containing the same is homogenized by putting it in a high pressure homogenizer. A method of producing nanocellulose cellulose nanofibers may be exemplified. In addition to this, a strong shear force and impact force are applied to the cellulose of the cellulose raw material or a mixed suspension containing the same by using a super mass collider, an air-jet mill, or an ultrasonic homogenizer. A method of manufacturing cellulose nanofibers can be exemplified.

The mixed suspension includes a cellulose raw material and a solvent, and the solvent may include any one or more selected from water and ionic liquids. At this time, the solvent may be 60 to 90% by weight based on the total weight of the mixed suspension, and more specifically, may include 70 to 80% by weight, and the residual amount is the content of the cellulose raw material or cellulose. The ionic liquid is not particularly limited, for example, any one selected from 1-butyl-3-methyl imidazolium, 1-butyl-3-methyl imidazolium chloride and 1-butyl-3-methyl imidazolium bromide Cellulose nanofibers can be produced more efficiently by using one or more mixtures.

The mixed suspension is carried out by immersing a cellulose raw material or cellulose in the solvent for 3 to 24 hours at 50 to 100°C, more preferably for 4 to 10 hours at 60 to 90°C, or through agitation and crushing processes. May be The mixed suspension containing the cellulose nanofibers thus prepared may be dried, and the cellulose nanofibers may be manufactured through a solvent removal process through a filter.

The specific method of manufacturing the cellulose nanofibers is not limited because it can refer to various well-known documents. For example, refer to Japanese Laid-Open Patent Publication No. 2010-235679, Japanese Laid-Open Patent Publication No. 2012-214717, and the like. It goes without saying that the present invention is not limited to this.

The method for producing a boron nitride nanosheet-cellulose nanofiber composite film according to the present invention may further include a step of degassing the BNNS-CNF dispersion between steps a) and b). By passing through this degassing process, it is possible to prevent the formation of pores due to micro bubbles during film formation in the drying process, thereby further improving the oxygen blocking properties.

In one example of the present invention, the dispersion may further include methyl cellulose or a derivative thereof, for example, carboxymethyl cellulose, and when further included, it may be included in 0.5 to 5 parts by weight with respect to 100 parts by weight of water. have. When prepared by further comprising methyl cellulose or a derivative thereof, methyl cellulose is dried with boron nitride nanosheets and cellulose nanofibers dispersed in water in a state dissolved in water, thereby increasing concentration in the drying process of step b). By further minimizing the dispersion stability that may occur, it is possible to manufacture a composite film having a lower oxygen permeability.

The weight ratio of boron nitride nanosheets and cellulose nanofibers of the boron nitride nanosheet-cellulose nanofiber composite film according to the present invention is not particularly limited as long as the above-described effects can be realized, for example, 0.1:99.9~10:90, Preferably it may be 0.5:99.5 to 8:92, more preferably 1:99 to 5:95. However, this is only described as a preferred example, of course, the present invention is not limited to this.

As described above, the boron nitride nanosheet-cellulose nanofiber composite film according to the present invention has an effect of improving properties such as elastic modulus and tensile strength and a high light transmittance effect without substantially reducing elongation properties. The composite film has an elongation of 4% or more, a Young's modulus of 4.8 GPa or more, a tensile strength of 90 MPa or more, and specifically, an elongation of 4 to 15%, a Young's modulus of 4.8 to 15.0 GPa, and a tensile strength. May be 90 to 130 MPa.

As described above, the boron nitride nanosheet-cellulose nanofiber composite film according to the present invention has a high oxygen blocking property, and specifically, may have an oxygen permeability of 15 ml/m ² /day or less, preferably 12 ml/ It may be a composite film of m ² /day or less, specifically 1 to 15 ml/m ² /day, and more specifically 1 to 12 ml/m ² /day.

The boron nitride nanosheet-cellulose nanofiber composite film according to the present invention has excellent mechanical properties, such as Young's modulus, elongation, and tensile strength, optical properties, and biocompatibility, and can be used for various film applications, particularly excellent in oxygen blocking properties Therefore, it may be more preferable to be used for packaging purposes for oxygen blocking of food or pharmaceutical products. As a specific example, it can be used in the case of food groups such as meat and cheese, where oxygen blocking is more important during storage.

Hereinafter, the present invention will be described in detail through examples, but these are for explaining the present invention in more detail, and the scope of the present invention is not limited by the following examples.

Preparation of boron nitride nanosheets

In a Taylor-Couette (TC) reactor consisting of two concentric inner and outer stainless steel cylinders with radius ratio (η=R _i /R _o =0.92) and aspect ratio (Γ=L/d=2.3) Boron nitride was added and reacted to remove and functionalize boron nitride to prepare boron nitride powder.(In the radius ratio, R _i is the radius of the inner cylinder, R _o is the radius of the outer cylinder, and in the aspect ratio, L Is the length of the cylinder, d is the diameter of the outer cylinder.)

The boron nitride powder was dispersed in a solution of deionized water and 1-ethyl-3-methylimidazolium tetrafluoroborate (99.85:0.15 volume ratio) to prepare a boron nitride dispersion (30 mg/ml). The boron nitride dispersion was injected into a Taylor-Cuet reactor and reacted for 1 hour. The reacted boron nitride dispersion was centrifuged for 150 minutes to remove 1-ethyl-3-methylimidazolium tetrafluoroborate and unpeeled boron nitride nanosheets. The thus obtained mixture of boron nitride nanosheets was freeze-dried for 24 hours to prepare powdery boron nitride nanosheets (BNNS).

In addition, the dispersibility of the boron nitride nanosheet dispersion and the cellulose nanofiber aqueous dispersion, and the average size and polydispersity of the boron nitride nanosheet were evaluated through experimental methods described below.

Preparation of boron nitride nanosheet-cellulose nanofiber composite film

As in the process diagram of Figure 1, a boron nitride nanosheet-cellulose nanofiber composite film was prepared, which is specifically as follows.

A dispersion of boron nitride nanosheets (1.79 mg/ml) prepared by dispersing the powdered boron nitride nanosheets in deionized water through ultrasonic treatment was prepared. In addition, an aqueous dispersion (0.5% by weight) of cellulose nanofibers (CNF) having a width and a length of 50 nm or less and several μm, respectively, obtained from Maine University, USA, was prepared.

The boron nitride nanosheet dispersion (BNNS dispersion) was dropped into the cellulose nanofiber aqueous dispersion (CNF dispersion) at a proper ratio of the dispersion so that the weight ratio of the boron nitride nanosheet and cellulose nanofibers was 5:95, and a high-speed stirrer ( Ultraturrax T25, IKA, USA) was mixed for 10 minutes at 12,000 rpm. Subsequently, degassing was performed for 20 minutes using an ultrasonic cleaner (SD-D400H, lklab Co., Korea) to obtain a boron nitride nanosheet-cellulose nanofiber suspension. 100 g of the boron nitride nanosheet-cellulose nanofiber suspension was poured into a polystyrene petri dish (150 mm in diameter), dried at ambient temperature for 6 days, and then peeled off the film from the petri dish to give the boron nitride nanosheet 5 weight. A uniform boron nitride nanosheet-cellulose nanofiber composite film (BNNS/CNF composite film) containing% was prepared.

Then, after the film was stored in a desiccator, oxygen blocking properties, tensile properties, optical properties, morphological properties, and cytotoxic properties were evaluated through an experimental method described later.

A uniform boron nitride nanosheet containing 3% by weight of boron nitride nanosheets in a weight ratio of boron nitride nanosheets and cellulose nanofibers to a dispersion of boron nitride nanosheets in an aqueous dispersion of cellulose nanofibers in Example 1 -It was carried out in the same manner as in Example 1, except that a cellulose nanofiber composite film was prepared.

A uniform boron nitride nanosheet containing 1% by weight of boron nitride nanosheets in a weight ratio of boron nitride nanosheets and cellulose nanofibers to a dispersion of boron nitride nanosheets in an aqueous dispersion of cellulose nanofibers in Example 1 -It was carried out in the same manner as in Example 1, except that a cellulose nanofiber composite film was prepared.

In Example 1, the preparation of boron nitride nanosheets was carried out, except that sodium dodecyl sulfate (SDS), a surfactant, was used instead of 1-ethyl-3-methylimidazolium tetrafluoroborate, an ionic liquid. It was performed in the same manner as in Example 1.

As a result, it was confirmed that the oxygen permeability of the composite film prepared in Example 4 was significantly higher than 10 ml/m ² /day compared to 4.7 ml/m ² /day in Example 1. This is considered to be due to the significantly improved peeling and dispersibility of the boron nitride nanosheet as compared to the case of using the surfactant of Example 4, as the case of Example 1 uses an ionic liquid.

[Comparative Example 1]

100 g of the cellulose nanofiber aqueous dispersion of Example 1 was poured into a polystyrene petri dish (150 mm in diameter) and dried under normal temperature and pressure conditions for 6 days, and then the film was peeled off the petri dish to make a cellulose nanofiber film (CNF film). It was prepared.

And after storing the film in a dryer (desiccator), each property was evaluated in the same manner as in Example 1.

[Comparative Example 2]

In Example 1, the boron nitride nanosheet dispersion prepared by dispersing the boron nitride nanosheet in powder form through ultrasonic treatment in isopropyl alcohol instead of deionized water, and drying the boron nitride nanosheet-cellulose nanofiber suspension under reduced pressure instead of drying at room temperature And it was carried out in the same manner as in Example 1, except that a nanosheet-cellulose nanofiber composite film was produced by filtration.

As a result, it was confirmed that the composite film of Comparative Example 2 had a significantly higher oxygen transmittance than that of Example 1. This is considered to be caused by the formation of a phase separation structure and pinholes in the drying process, as a dispersion medium other than water is further used and dried in an extremely low pressure state.

<Evaluation of average size and polydispersity of boron nitride nanosheets>

The average size and polydispersity of the boron nitride nanosheets prepared in Example 1 were measured by the following method.

Specifically, the average size and polydispersity of the boron nitride nanosheet particles having a thickness in nanometers were measured using a zeta sizer, a scanning electron microscope and a transmission electron microscope, and the results are shown in FIG. 2. It is shown.

As a result, as shown in FIG. 2(a), the average zeta size and polydispersity (PDI) of the boron nitride nanosheet particles were 1084 nm or less and 0.85 or less, respectively. The particle size can be expressed as a hydrodynamic diameter of an equivalent sphere. Therefore, since the average zeta size will be similar to the longest length of the nanosheet, the relatively low polydispersity can be interpreted as peeling through the Taylor-Cuet reactor to produce boron nitride nanosheet particles of uniform size. In addition, in the case of an aqueous solution containing a boron nitride nanosheet having a particle length exceeding 1,000 nm, this is a major cause of translucent color.

It can be seen from the scanning electron microscope image of FIG. 2B that the boron nitride nanosheet particles have a size of 1 μm or less. In addition, FIG. 2(c) is a more enlarged transmission electron microscope image of a single boron nitride nanosheet particle, and can be confirmed to be translucent, meaning that the electron beam was transmitted through the boron nitride nanosheet particle due to the particle thickness of the nano unit. .

<Dispersion evaluation of boron nitride nanosheet dispersion and cellulose nanofiber aqueous dispersion>

As shown in the image of FIG. 3(A), the dispersion of boron nitride nanosheets was translucent, while the aqueous dispersion of cellulose nanofibers was opaque as in FIG. 3(B). In addition, in the case of the dispersion of boron nitride nanosheets, boron nitride nanosheet particles and cellulose nanofiber particles did not precipitate even after one year had passed, which means that the two particles were stably dispersed in an aqueous solution. In the case of the cellulose nanofiber dispersion, the opaque reason is that the cellulose nanofibers do not have a surface charge and are partially agglomerated in an aqueous solution to cause an opaque dispersion.

<Evaluation of film characteristics>

1. Experiment of oxygen blocking properties

The oxygen transmission rate (OTR) of the films prepared in Examples 1 to 3 and Comparative Example 1 was measured by an automated oxygen permeability tester (Lyssy L100-5000, Systech Instruments Ltd, UK). Specifically, the measurement was performed at 23° C. and 50% relative humidity using high purity oxygen gas (99.999%) according to ASTM D3985 standard protocol, with the test area of each film being 65 cm ² .

As a result, as shown in Figure 4, the cellulose nanofiber film prepared in Comparative Example 1 exhibited an oxygen permeability of 19.08 cc/m ² /day, which is for use in packaging fields such as most foods and medicines. This is not enough. The theoretical oxygen permeability under the ideal process conditions of cellulose nanofiber films is known to be about 1 cc/m ² /day, but the induced capillary force caused by drying in the manufacturing process causes pinholes in the film, and thus the theoretical value It can be several to tens of times different.

On the other hand, the oxygen permeability of the boron nitride nanosheet-cellulose nanofiber composite film prepared in Example 1 was 4.7 cc/m ² /day, which is a value suitable for use as a packaging film for meat and cheese.

2. Experiment of tensile properties

Tensile propertiy, specifically, Young's modulus, tensile strengths and elongations were quantitatively tested for the films prepared in Examples 1 to 3 and Comparative Example 1, It was performed with a universal testing machine with 1000 N load cells (Instron 5943, Instron Corp., USA). At this time, the film was cut into a dog-bone shape, and the test area was 26.5 mm long, 3.2 mm wide, and 70.0 μm thick. The test was performed at a strain rate of 1 mm/min at room temperature, and a total of three specimens were tested.

As a result, as shown in FIG. 5, in the case of the composite films of Examples 1 to 3, as the content of the boron nitride nanosheet increases, the elongation does not change substantially, and both the Young's modulus (elastic modulus) and tensile strength Significantly increased. Specifically, the composite film of Example 1 was about 1.52 times and 1.19 times higher than the film of Comparative Example 1, respectively. These results can be seen as an improvement in mechanical properties according to the addition of boron nitride nanosheets having a two-dimensional geometric structure.

In most cases where a composite material is prepared by adding a reinforcing filler to a material, the reinforcing filler is known to improve tensile strength but decrease elongation, which means that the composite material added with a filler has high strength but is brittle. do.

That is, the boron nitride nanosheet-cellulose nanofiber composite film according to the present invention has improved strength and stiffness than the cellulose nanofiber film of Comparative Example 1 without impairing elasticity, and these effects are remarkable compared to conventional composite materials. You can see that These results are believed to be attributable to the fact that the boron nitride nanosheets and cellulose nanofibers have excellent adhesion properties to each other.

3. Optical properties

The light transmittance spectrum of the films prepared in Example 1 and Comparative Example 1 was measured at 400 to 800 nm using a UV-vis spectrophotometer (UV-2600, Shimadzu, Japan).

6 is a light transmittance spectrum of the films prepared in Example 1 and Comparative Example 1, from which the effect of the composite material on the light transmittance according to the addition of the boron nitride nanosheet is very minimal.

Therefore, it can be seen that the color change due to the addition of the boron nitride nanosheet of the boron nitride nanosheet-cellulose nanofiber composite film according to the present invention is negligible.

4. Morphological characteristics

The structure and morphology of the films prepared in Example 1 and Comparative Example 1 are Field Emission Scanning Electron Microscope (FE-SEM, MIRA 3 XMU, TESCAN, Czech Republic) equipped with OIMTM technology of EDAX / TSL. The acceleration voltage was measured at 10 kV. At this time, for measurement, platinum (Pt) was tested by vacuum sputtering on each film.

As a result, as shown in Figure 7 (A), the SEM image of the film of Comparative Example 1 shows a typical surface morphology of the cellulose nanofiber film having a nanofiber (nanofibril) structure.

As in the result of the optical properties, as shown in (B) of FIG. 7, the SEM image of the composite film of Example 1 shows a similar shape to that of the film of Comparative Example 1, so that the addition of the boron nitride nanosheet is cellulose nano It can be seen that there was no significant effect on the surface morphology of the fiber film. In addition, boron nitride nanosheet particles were not observed in the SEM image of the composite film of Example 1.

<Cytotoxicity characteristics>

Cytotoxicity tests for the films of Example 1 and Comparative Example 1 were performed on the surface of each film, specifically, as follows. A fully inflated film disc having the same diameter as a 24-well plate was immersed in ethanol for 12 hours and washed with phosphate buffered saline (PBS) before cell seeding. Minimum pre-osteoblast cell line (MC3T3-E1) supplemented with 10% fetal bovine serum (Hyclone, FBS) and 1% penicillin/streptomycin (Hyclone) at 37°C. In essential medium-alpha, MEM-α; Hyclone), subconfluent cells were isolated using a humidified atmosphere of 5% CO ₂ and 95% air and 0.2% trypsin-EDTA (Hyclone) at 30°C and using trypan blue assay. The number of viable cells was counted. Cells were further seeded on films and empty wells as controls in 24-well plates at a density of about 3 x 10 ⁴ cells per well and incubated for 3 days. The number of viable cells as a function of culture time (0 to 3 days) was measured by colorimetric analysis (CCK-8, Dojindo). The number of viable cells is proportional to the absorbance value at 450 nm.

As a result, as shown in Figure 8, compared to the cellulose nanofiber film of Comparative Example 1, the boron nitride nanosheet of Example 1 is introduced, the significance of the cytotoxicity of the nanosheet-cellulose nanofiber composite film There is no difference.

Claims (11)

a) mixing and dispersing boron nitride nanosheets and cellulose nanofibers in an aqueous phase to prepare a dispersion, and
b) drying the dispersion to prepare a composite film
Method for producing a boron nitride nanosheet-cellulose nanofiber composite film comprising a. According to claim 1,
In step a), the dispersion includes water, boron nitride nanosheets, and cellulose nanofibers,
The dispersion is a method for producing a boron nitride nanosheet-cellulose nanofiber composite film comprising 0.05 to 1 part by weight of boron nitride nanosheets and 0.1 to 5 parts by weight of cellulose nanofibers with respect to 100 parts by weight of water. According to claim 1,
The method of manufacturing the boron nitride nanosheet-cellulose nanofiber composite film,
Before step a),
A method of manufacturing a boron nitride nanosheet-cellulose nanofiber composite film, further comprising dispersing the boron nitride powder in a dispersion medium containing an ionic liquid and reacting to prepare a boron nitride nanosheet. According to claim 1,
In the step b), drying is a method of manufacturing a boron nitride nanosheet-cellulose nanofiber composite film, which is natural drying performed at normal pressure. According to claim 4,
In step b), drying is carried out at 5 to 35° C., a method for producing a boron nitride nanosheet-cellulose nanofiber composite film. According to claim 1,
The method of manufacturing the boron nitride nanosheet-cellulose nanofiber composite film having a thickness of 0.2 to 50 nm and a long axis of 300 to 1,000 nm. A boron nitride nanosheet-cellulose nanofiber composite film produced by the method of any one of claims 1 to 6. The method of claim 7,
The weight ratio of boron nitride nanosheets and cellulose nanofibers of the composite film is 0.1:99.9-10:90 boron nitride nanosheet-cellulose nanofiber composite film. The method of claim 7,
The composite film is a boron nitride nanosheet-cellulose nanofiber composite film having an elongation of 4% or more, a Young's modulus of 4.8 GPa or more, and a tensile strength of 90 MPa or more. The method of claim 7,
The oxygen permeability of the composite film is 15 ml/m ² /day or less boron nitride nanosheet-cellulose nanofiber composite film. The method of claim 7,
The composite film is a boron nitride nanosheet-cellulose nanofiber composite film used for packaging for oxygen blocking of food or pharmaceuticals.

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