KR102156238B1 - Boron nitride nanosheet-cellulosic nanofiber composite film having excellent oxygen barrier, and method for producing the same - Google Patents

Abstract

The boron nitride nanosheet-cellulose nanofiber composite film according to the present invention has a role as an excellent oxygen barrier film that is sustainable even when manufactured by a simple and mild manufacturing method that can be commercially used, as well as elastic modulus and tensile strength without a substantial decrease in elongation properties. It has an effect of improving properties such as, 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 of manufacturing the same.

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

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

In order to improve the oxygen barrier properties of synthetic polymers, halogenated or metallized polymer films have been studied, and it has been reported that a low oxygen permeability of 0.1-10 cc/m ² /day can be achieved. However, such a polymer film has a problem that causes a significant environmental and health threat. For example, aluminum-coated polyethylene terephthalate film and 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 when incinerated. Therefore, such a halogenated or metallized polymer film cannot be recycled, and there is a problem that enormous cost is required during processing.

On the other hand, cellulose nanofiber (CNF) is a sustainable and biocompatible nanomaterial and is used as a packaging material for foods and pharmaceuticals, which mechanically decomposes highly crystalline nanofibers in cellulose bulk, which is an abundant biomass. Is produced.

However, when cellulose nanofiber films are manufactured under highly controlled conditions, they have an ideal oxygen barrier performance with low oxygen permeability, but cellulose nanofiber films manufactured in actual manufacturing and use environments such as industrial sites exhibit their oxygen barrier performance properly. There is a fatal drawback that cannot be done. Specifically, there is a disadvantage of having a high oxygen permeability of 19 cc/m ² /day or more when actually manufactured and commercialized because capillary force creates a heterogeneous surface upon drying in the film manufacturing process.

Therefore, it is necessary to study an excellent cellulose-based composite film that can exhibit high oxygen barrier properties even if it is manufactured by a simple manufacturing method at a level that can be used commercially, and furthermore, performances such as optical properties, mechanical properties, and biocompatibility. There is also a need for research on excellent composite films.

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

An object of the present invention is to provide a polymer film capable of exhibiting high oxygen barrier performance even when manufactured by a simple commercially available manufacturing method.

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 includes: a) mixing and dispersing a boron nitride nanosheet and a cellulose nanofiber in an aqueous phase to prepare a dispersion; and b) drying the dispersion to form a composite. It includes the step of preparing a film.

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

In an example of the present invention, the dispersion may include 0.05 to 1 parts by weight of boron nitride nanosheets and 0.1 to 5 parts by weight of cellulose nanofibers based on 100 parts by weight of water.

The method of manufacturing a boron nitride nanosheet-cellulose nanofiber composite film according to an exemplary embodiment of the present invention includes, before step a), dispersing and reacting boron nitride powder in a dispersion medium containing an ionic liquid to react 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 0.1:99.9-10:90.

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 purposes for blocking oxygen such as food or medicine.

The boron nitride nanosheet-cellulose nanofiber composite film according to the present invention has a role as an excellent oxygen barrier film that is sustainable even when manufactured by a simple and mild manufacturing method that can be commercially used, as well as elastic modulus and tensile strength without a substantial decrease in elongation properties. It has an effect of improving properties such as, has an effect of having excellent optical properties with high light transmittance, and has an 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.
FIG. 2 shows the results of measuring the average size and polydispersity of the boron nitride nanosheets prepared in Example 1 using a zeta sizer, a scanning electron microscope, and a transmission electron microscope.
3 is an image of the boron nitride nanosheet dispersion and cellulose nanofiber dispersion prepared in Example 1.
4 shows the results of measuring the oxygen transmission rate (OTR) of the films prepared in Examples 1 to 3 and Comparative Example 1 through an oxygen permeability tester.
5 shows the results of measuring Young's modulus, tensile strengths, and elongations of 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 films prepared in Example 1 and Comparative Example 1.
Figure 8 shows the results of testing the cytotoxicity of 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 method of manufacturing the same will be described in detail with reference to the accompanying drawings.

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

Unless otherwise defined, technical terms and scientific terms used in the present specification have the meanings commonly understood by those of ordinary skill in the art to which this invention belongs, and the gist of the present invention in the following description and accompanying drawings A description of known functions and configurations that may unnecessarily obscure will be omitted.

The singular form of terms used in the present specification may be interpreted as including the plural form unless otherwise indicated.

Unless otherwise defined, the unit of% used in the present specification means% by weight.

The inventors of the present invention have known that the cellulose nanofiber film has an ideal oxygen barrier property of low oxygen permeability (1 cc/m ² /day or less), but this is a characteristic that appears only when manufactured under highly controlled conditions. When manufactured under actual commercially available process conditions, such as, for example, a very high oxygen permeability (19 cc/m ² /day or more) and low oxygen barrier properties appear, so that the cellulose nanofiber film is actually mass-produced and commercially used. I recognized a fatal problem that was difficult to do.

Therefore, the present inventors have conducted in-depth research to solve this problem, and as a result of conducting an in-depth study, the cellulose nanofiber film has an ideal oxygen barrier property even under simple and mild process conditions that are advantageous for commercialization, and furthermore, the elastic modulus and tensile strength, etc., without a substantial decrease in elongation properties. It is intended to provide in the present invention by discovering a composite film having an effect of improving properties, having excellent optical properties having high light transmittance, and having very low cytotoxicity and a method for manufacturing the same.

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

The method of manufacturing a boron nitride nanosheet-cellulose nanofiber composite film according to the present invention is a) dispersion liquid by mixing and dispersing boron nitride nanosheet (BNNS) and cellulose nanofiber (CNF) in an aqueous phase. And b) drying the dispersion to prepare a composite film.

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

In particular, since 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 transmission rate. Specifically, the boron nitride nanosheets and cellulose nanofibers dispersed on a dispersion medium composed of water do not form a phase separation structure and pinholes even under a drying condition favorable for commercialization such as drying at room temperature and pressure, thereby producing a homogeneous composite film Is possible. When boron nitride nanosheets and cellulose nanofibers are dispersed and present together in a dispersion medium, when the dispersion medium is composed of water, they are highly compatible with water, and the formation of fine precipitates is extremely inhibited, resulting in a very uniform and stable state. Will exist in Therefore, even if the concentration of the dispersion increases as drying proceeds in step b), the formation of fine precipitates is extremely suppressed to form a homogeneous composite film having a phase separation structure and substantially no 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 or a heterogeneous solvent other than water, the above-described effect cannot be realized. In detail, when a dispersion medium composed of water contains a highly volatile dispersion medium such as isopropyl alcohol or a solvent, the dispersion stability may be deteriorated upon drying in step b), and the phase separation structure and fin during the drying process May cause the formation of holes. Therefore, the cellulose nanofiber film cannot have an ideal oxygen transmittance, and improvement in optical properties and mechanical properties cannot be expected.

As described above, in 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 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 based on 100 parts by weight of water. At this time, the mixing weight ratio of the boron nitride nanosheets and the cellulose nanofibers is 0.1:99.9-10:90, preferably 0.5:99.5-8:92, in terms of improving the above-described effects such as excellent oxygen barrier properties. Preferably it may be 1:99-5:95. However, this is only described as a preferred example, of course, the present invention is not limited thereto.

In step b), the drying process conditions are preferably natural drying performed at normal pressure. At this time, the atmospheric pressure means the pressure in a normal atmospheric state, and may mean 0.9 to 1.1 atm, specifically 1 atm corresponding to the actual atmospheric pressure. In the case of drying at a pressure lower than normal pressure including vacuum, specifically, in the case of reduced pressure drying, it may cause defects in which pinholes are formed as it is dried in an unstable state at a low pressure, and has a great influence on the dispersion stability of the dispersion. As a result, it is not possible to form a homogeneous composite film substantially free of a phase-separated structure and pinholes, and an effect of improving properties such as elastic modulus and tensile strength and a high light transmittance effect cannot be expected without a substantial decrease in elongation properties.

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

In the step b), the drying temperature is not greatly 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 prevent problems that cause phase separation structures and pinholes due to excessive temperature changes.

The method of manufacturing a boron nitride nanosheet-cellulose nanofiber composite film according to a preferred embodiment comprises dispersing boron nitride powder in a dispersion medium containing an ionic liquid and reacting to prepare a boron nitride nanosheet before step a). It may further include the step of. 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 in steps a) and b) is more increased, and the finally produced composite film It may be preferable that the oxygen transmission rate of may be further reduced.

Specifically, as the volatility of the ionic liquid decreases significantly, the surface of the boron nitride nanosheet prepared by reacting boron nitride in a dispersion medium containing the ionic liquid is described above on the surface of the boron nitride nanosheet even after a drying process. Ionic liquids may remain. Therefore, the ionic liquid may be included in the dispersion of steps a) and b), and may be contained in the final prepared 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 an ionic liquid. When the dispersion medium contains water and an ionic liquid, the weight ratio thereof may be 0.01 to 1 part by weight of the ionic liquid based on 100 parts by weight of water.

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

In addition, after the step of preparing the boron nitride nanosheets, the step of removing the unreleased boron nitride nanosheets 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. Specifically, the boron nitride dispersion prepared by mixing the boron nitride powder with the dispersion medium is reacted in the reactor to peel and functionalize the boron nitride, and then the unreleased boron nitride nanosheet and the dispersion medium are removed to prepare a boron nitride nanosheet can do. At this time, the concentration of the boron nitride dispersion may be appropriately adjusted, and may be, for example, 5 to 100 mg/ml. The mixture solution containing the boron nitride nanosheets thus obtained may be freeze-dried for 5 to 30 hours to prepare a powdery boron nitride nanosheet.

However, in addition to this, the method of manufacturing the boron nitride nanosheet may refer to various 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 thereto.

The size of the boron nitride nanosheet used in the present invention is not largely 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 thereto.

The cellulose nanofibers used in the present invention may be any conventionally used, for example, the width may be 1 to 50 nm, the length may be 1 to 100 μm, more specifically the width may be 5 to 40 nm, and It may have a length of 5 to 50 μm.

As a specific example, the cellulose nanofibers may be manufactured by crushing from wood or non-wood biomass to smaller and smaller sizes, and for example, may be manufactured through a grinder or a high-pressure homogenizer. . In the method of manufacturing cellulose nanofibers using a grinder, a cellulose raw material or a mixed suspension containing the same is put between a fixed ceramic disk and a ceramic disk rotating at a high speed, and is compressed to both sides in the disk by eccentric force. A method of producing cellulose nanofibers by performing nanoization while receiving shear and frictional forces by rapidly rotating grinding stones on both sides of the disk may be exemplified. The method of manufacturing cellulose nanofibers using a high-pressure homogenizer is to homogenize the cellulose raw material or a mixed suspension containing the same in a high-pressure homogenizer, and at this time, the fibers pass through the thin slit at high speed due to high pressure and receive strong shear and impact force. A method of nano-ization to produce cellulose nanofibers may be illustrated. In addition, a super mass collider, air-jet mill, ultrasonic homogenizer, etc. are used to apply strong shear and impact forces to the cellulose raw material or the cellulose of the mixed suspension containing the same. A method of manufacturing cellulose nanofibers may be illustrated.

The mixed suspension includes a cellulose raw material and a solvent, and the solvent may include any one or more selected from water and an ionic liquid. At this time, the solvent may be included in an amount of 60 to 90% by weight based on the total weight of the mixed suspension, and more specifically, may be included in an amount of 70 to 80% by weight, and the remaining amount is a cellulose raw material or content of cellulose. The ionic liquid is not largely limited, for example, any 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 a mixture of two or more.

The mixed suspension is performed by immersing the cellulose raw material or cellulose in the solvent and then passing through a stirring process or agitation and pulverization process at 50 to 100°C for 3 to 24 hours, more preferably at 60 to 90°C for 4 to 10 hours. Can be. The mixed suspension containing the cellulose nanofibers thus prepared may be dried and subjected to a solvent removal process through a filter, etc. to prepare cellulose nanofibers.

The specific manufacturing method of the cellulose nanofibers is not limited because various known documents may be referred to, and as an example, Japanese Laid-Open Patent Publication No. 2010-235679, Japanese Laid-Open Patent Publication No. 2012-214717, etc. may be referred to, It goes without saying that the present invention is not limited thereto.

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

In an example of the present invention, the dispersion may further contain methyl cellulose or a derivative thereof, for example, carboxymethyl cellulose, etc., and if further included, 0.5 to 5 parts by weight per 100 parts by weight of water may be included. have. In the case of further comprising methylcellulose or a derivative thereof, the methylcellulose is dried together with the boron nitride nanosheets and cellulose nanofibers dispersed in water in a state dissolved in water, thereby increasing the concentration in the drying process of step b). By further minimizing the possible deterioration in dispersion stability, it is possible to manufacture a composite film having a lower oxygen transmittance.

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 is not largely 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 ~ 8:92, more preferably 1:99 ~ 5:95. However, this is only described as a preferred example, of course, the present invention is not limited thereto.

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 without a substantial decrease in elongation properties, and a high light transmittance effect. The composite film 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, specifically, an elongation of 4 to 15%, a Young's modulus of 4.8 to 15.0 GPa, and 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 high oxygen barrier properties, and specifically, the oxygen permeability may be 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 ㎖ / m ² /day, more specifically 1 to 12 ㎖ /m ² /day may be a composite film.

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

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

To a Taylor-Couette (TC) reactor consisting of two concentric inner and outer stainless steel cylinders with a radius ratio (η=R _i /R _o =0.92) and aspect ratio (Γ=L/d=2.3). Boron nitride was added and reacted to prepare boron nitride powder by peeling and functionalizing boron nitride. (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 and 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 by volume) to prepare a boron nitride dispersion (30 mg/ml). The boron nitride dispersion was injected into a Taylor-Kuet 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 boron nitride nanosheet mixture thus obtained was freeze-dried for 24 hours to prepare a powdery boron nitride nanosheet (BNNS).

And the dispersibility of the boron nitride nanosheet dispersion and the aqueous cellulose nanofiber dispersion, and the average size and polydispersity of the boron nitride nanosheets were evaluated through an experimental method described below.

Preparation of boron nitride nanosheet-cellulose nanofiber composite film

As in the process diagram of FIG. 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 powdery 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 length of 50 nm or less and several μm, obtained from Maine University in the United States, was prepared.

The boron nitride nanosheet dispersion (BNNS dispersion) is added dropwise to the cellulose nanofiber aqueous dispersion (CNF dispersion) at a content ratio of the appropriate dispersion so that the weight ratio of the boron nitride nanosheet and the cellulose nanofiber is 5:95, and a high-speed stirrer ( Ultraturrax T25, IKA, USA) was mixed for 10 minutes at 12,000 rpm. Subsequently, degassing 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) and dried at room temperature for 6 days, and then the film was peeled off the Petri dish, and the boron nitride nanosheet was added by 5 weight. A uniform boron nitride nanosheet containing%-cellulose nanofiber composite film (BNNS/CNF composite film) was prepared.

And after storing the film in a dryer (desiccator), oxygen barrier properties, tensile properties, optical properties, morphological properties, and cytotoxic properties were evaluated through an experimental method described later.

Uniform boron nitride nanosheets containing 3% by weight of boron nitride nanosheets by making the boron nitride nanosheet dispersion in the aqueous dispersion of cellulose nanofibers in Example 1 so that the weight ratio of the boron nitride nanosheets and the cellulose nanofibers is 3:97 -Except for preparing a cellulose nanofiber composite film, it was carried out in the same manner as in Example 1.

In Example 1, a uniform boron nitride nanosheet containing 1% by weight of boron nitride nanosheets by making the boron nitride nanosheet dispersion in the aqueous dispersion of cellulose nanofibers in a weight ratio of 1:99 between the boron nitride nanosheets and the cellulose nanofibers -Except for preparing a cellulose nanofiber composite film, it was carried out in the same manner as in Example 1.

Except for the use of sodium dodecyl sulfate (SDS) as a surfactant instead of 1-ethyl-3-methylimidazolium tetrafluoroborate, an ionic liquid, when preparing boron nitride nanosheets in Example 1 It was carried out in the same manner as in Example 1.

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

[Comparative Example 1]

100 g of the aqueous dispersion of cellulose nanofibers of Example 1 was poured into a polystyrene Petri dish (150 mm in diameter), dried for 6 days under room temperature and pressure conditions, and then peeled off the film from the Petri dish to obtain a cellulose nanofiber film (CNF film). 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, a dispersion of boron nitride nanosheets prepared by dispersing a powdery boron nitride nanosheet in isopropyl alcohol instead of deionized water through ultrasonic treatment was used, and a boron nitride nanosheet-cellulose nanofiber suspension was dried under reduced pressure instead of room temperature drying. And it was carried out in the same manner as in Example 1, except that the nanosheet-cellulose nanofiber composite film was prepared by filtration.

As a result, it was confirmed that the composite film of Comparative Example 2 had a remarkably high oxygen transmittance compared to the case of Example 1. This is believed to be due to the formation of a phase-separated 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. 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 size of a particle 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 nanosheets, the relatively low polydispersity can be interpreted as the separation through the Taylor-Kuet reactor to produce boron nitride nanosheet particles of uniform size. In addition, in the case of an aqueous solution containing boron nitride nanosheets having a particle length exceeding 1,000 nm, this is the main cause of a translucent color.

From the scanning electron microscope image of FIG. 2B, it can be seen that the boron nitride nanosheet particles have a size of 1 μm or less. In addition, (c) of FIG. 2 is an enlarged transmission electron microscope image of a single boron nitride nanosheet particle, and it can be seen that it is translucent, and it means that the electron beam is transmitted through the boron nitride nanosheet particles due to the particle thickness in the nanoscale. .

<Dispersibility evaluation of boron nitride nanosheet dispersion and aqueous cellulose nanofiber 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 white and opaque as in FIG. 3(B). In addition, in the case of the boron nitride nanosheet dispersion, the boron nitride nanosheet particles and the cellulose nanofiber particles did not precipitate even after 1 year, indicating that the two particles were stably dispersed in the aqueous solution. In the case of the cellulose nanofiber dispersion, the reason for being opaque is due to the fact that the cellulose nanofibers do not have a surface charge and are partially agglomerated in an aqueous solution to cause opaque dispersion.

<Film property evaluation>

1. Oxygen barrier properties experiment

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

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

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 suitable value for use as a packaging film for meat and cheese.

2. Tensile property test

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 carried out with a universal tester (Instron 5943, Instron Corp., USA) having a 1000 N load cell. 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 room temperature at a strain rate of 1 mm/min, and a total of three samples 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 substantially change, and both Young's modulus (elastic modulus) and tensile strength Markedly increased. Specifically, the composite film of Example 1 was about 1.52 times and 1.19 times higher than that of the film of Comparative Example 1, respectively. This result can be seen as an improvement in mechanical properties by the addition of boron nitride nanosheets having a two-dimensional geometry.

In most cases where composite materials are made by adding reinforcing fillers to materials, reinforcing fillers are known to improve tensile strength but reduce elongation, meaning that composite materials added with fillers have high strength but are 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 the elasticity, and this effect is a remarkable effect compared to the conventional composite material. It can be seen that This result is considered to be due to the fact that the boron nitride nanosheets and the cellulose nanofibers have excellent adhesion properties to each other.

3. Optical properties

The light transmittance spectra of the films prepared in Example 1 and Comparative Example 1 were 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 on the light transmittance of the composite material according to the addition of the boron nitride nanosheets shows only minimal effect to a very slight extent.

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

4. Morphological characteristics

The structure and shape of the films prepared in Example 1 and Comparative Example 1 were based on a 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, platinum (Pt) was vacuum sputtered on each film for measurement.

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

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

<Cytotoxic characteristics>

The cytotoxicity test for the films of Example 1 and Comparative Example 1 was performed on the surface of each film, and specifically, it is as follows. A fully expanded film disk 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. Mouse pre-osteoblast cell line (MC3T3-E1) was added to 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 0.2% trypsin-EDTA (Hyclone) at 30°C and a humidified atmosphere of 5% CO ₂ and 95% air and used trypan blue assay. The number of viable cells was calculated. Cells were further seeded on film and empty wells as controls in 24-well plates at a density of about 3×10 ⁴ cells per well and incubated for 3 days. The number of viable cells as a function of incubation time (0 to 3 days) was measured by colorimetric analysis (CCK-8, Dojindo). At this time, 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 nanosheets introduced with the boron nitride nanosheets of Example 1-Note on the cytotoxicity of the cellulose nanofiber composite film There seems to be no difference.

Claims (11)

Dispersing and reacting boron nitride powder in a dispersion medium containing an ionic liquid to prepare a boron nitride nanosheet
Mixing and dispersing the boron nitride nanosheets and cellulose nanofibers in an aqueous phase to prepare a dispersion, and
As a method for producing a boron nitride nanosheet-cellulose nanofiber composite film comprising the step of preparing a composite film by drying the dispersion,
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 an oxygen permeability of 15 ml/m2/day or less, a method of manufacturing a boron nitride nanosheet-cellulose nanofiber composite film . The method of claim 1,
In the step of preparing the dispersion, the dispersion contains water, boron nitride nanosheets and cellulose nanofibers,
The dispersion comprises 0.05 to 1 parts by weight of boron nitride nanosheets and 0.1 to 5 parts by weight of cellulose nanofibers based on 100 parts by weight of water, boron nitride nanosheets-method for producing a cellulose nanofiber composite film. delete The method of claim 1,
In the step of preparing the composite film, the drying is carried out at normal pressure, the natural drying of boron nitride nanosheet-cellulose nanofiber composite film manufacturing method. The method of claim 1,
In the step of manufacturing the composite film and drying the boron nitride nanosheets it is performed at 5 to 35 ℃ - cellulose nanofiber production method of the composite film. The method of claim 1,
The boron nitride nanosheets have a thickness of 0.2 to 50 nm and a long axis of 300 to 1,000 nm of a boron nitride nanosheet-cellulose nanofiber composite film. The boron nitride nanosheet-cellulose nanofiber composite film prepared by the method of any one of claims 1, 2, 4 to 6. The method of claim 7,
The weight ratio of the boron nitride nanosheet and the cellulose nanofiber of the composite film is 0.1:99.9-10:90 boron nitride nanosheet-cellulose nanofiber composite film. delete delete The method of claim 7,
The composite film is a boron nitride nanosheet-cellulose nanofiber composite film used for packaging purposes for blocking oxygen in food or pharmaceutical products.

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