KR102758551B1 - Eco-friendly/non-toxic hybrid sheet with excellent tensile strength and electrical properties and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a hybrid sheet and a method for manufacturing the same, and more particularly, to an environmentally friendly/non-toxic hybrid sheet having excellent electrical/mechanical properties and a method for manufacturing the same.

Description

{Eco-friendly/non-toxic hybrid sheet with excellent tensile strength and electrical properties and manufacturing method thereof}

The present invention relates to a hybrid sheet and a method for manufacturing the same, and more particularly, to an environmentally friendly/non-toxic hybrid sheet having excellent mechanical/electrical properties and a method for manufacturing the same.

-1, 4 결합으로 다수 중합된 사슬 구조를 이루고 있다. 고등식물 이외에도 세균, 바닷말, 해산물인 멍게류의 외피에도 존재하며, 아세트산균의 균체 외분비물에도 함유되어 있고, 조개류의 점액 속에는 셀룰로오스의 황산 에스테르 형태로 존재한다. Cellulose is an organic compound that exists in large quantities in nature after coal, and is an industrially very important resource. Cellulose is a polysaccharide that is the main component of the cell walls of higher plants and makes up most of the woody part. For example, about 50% of wood and about 98% of cotton are made of cellulose. The chemical structure is D-glucose.

- It forms a chain structure with multiple polymerizations by 1, 4 bonds. In addition to higher plants, it is also present in the outer skin of bacteria, seaweed, and sea cucumbers, and is also contained in the exocrine secretion of acetic acid bacteria, and exists in the form of cellulose sulfate ester in the mucus of shellfish.

This type of cellulose is an odorless white solid, insoluble in water and quite resistant to alkali, but hydrolyzed in acid to form glucose. In addition, cellulose is decomposed by cellulase from fungi, bacteria, molluscs, etc., and ultimately forms glucose.

Because cellulose is highly resistant to chemicals and is not attacked by microorganisms, in addition to being used as a raw material for paper and clothing, cellulose derivatives are being used in a variety of fields.

That is, nanocellulose obtained from cellulose is an organic polymer material with excellent tensile strength, and since it is obtained from natural materials such as various woods and plant resources, it is an environmentally friendly renewable resource. The application of nanocellulose to polymer composites can not only significantly improve the mechanical strength of polymers, but is also widely used in food and pharmaceutical packaging materials due to its low air permeability, excellent mechanical properties, and transparent optical properties. In addition, due to its low coefficient of thermal expansion, it has a high possibility of being applied to lithium ion battery separators, displays, solar cells, electronic paper, and sensors.

Accordingly, research is actively being conducted to implement various composite materials using nanocellulose and metal nanoparticles or carbon materials, but conventional methods are mainly for manufacturing composite materials through a process of simply mixing nanocellulose and carbon materials to implement specific properties. In this case, due to the weak intermolecular adsorption between nanocellulose and carbon materials, it is difficult to form a random structure and manufacture a uniformly dispersed form (i.e., formation of a large number of aggregates), and when manufacturing a film form, there is a problem that a small concentration of carbon materials (e.g., graphene) is loaded onto the nanocellulose film, resulting in a problem of reduced physical properties of the composite. Therefore, research/methods to overcome the above-mentioned problems are urgently required in the art.

Republic of Korea registered patent 1964513 (2019.03.26)

The present invention has been made to overcome the above-described problems, and the problem to be solved by the present invention is to provide a hybrid sheet and a method for manufacturing the same, which can replace conventional expensive nano sheets by manufacturing an environmentally friendly organic-inorganic composite sheet through a relatively simple manufacturing process.

In addition, another problem to be solved by the present invention is to provide a hybrid sheet having excellent mechanical/electrical properties by evenly dispersing graphene in cellulose nanofibers (CNF) and a method for manufacturing the same.

The present invention provides a method for producing a hybrid sheet, which comprises a first step of producing a first solution containing cellulose nanofibers (CNF) to solve the above-described problem, a second step of mixing the first solution with a second solution containing graphene to produce a mixed solution, and a third step of filtering and drying the mixed solution to produce a sheet.

In addition, according to one embodiment of the present invention, the first step may be characterized by being a step of preparing a first solution in which cellulose nanofiber (CNF) powder is homogeneously dispersed by stirring a suspension containing cellulose nanofiber (CNF) powder at 30 to 150 rpm for 10 to 20 minutes.

In addition, the mixed solution of the second step may be characterized by the first solution and the second solution being mixed in a volume ratio of 1:0.01 to 0.05.

In addition, it may be characterized by further including a step of stirring the mixed solution at 30 to 150 rpm for 10 to 20 minutes after the second step and before performing the third step.

In addition, the third step may be characterized as a step of mixing the mixed solution prepared in the second step with a solvent and filtering it through a hydrophilic nylon filter having a thickness of 0.3 to 0.6 ㎛.

In addition, it can be characterized that in the third step, the mixed solution and the solvent are mixed in a volume ratio of 1:0.2 to 2 and then filtered.

In addition, it may be characterized by further including a step of drying at 100 to 150°C for 8 to 15 hours after the third step.

In addition, the present invention provides an eco-friendly/non-toxic organic-inorganic composite hybrid sheet having excellent tensile strength and electrical properties, which comprises graphene evenly dispersed between cellulose nanofibers (CNF), and has an average pore size of 5 to 20 nm and a BET specific surface area of 2 m ² /g or more.

In addition, according to one embodiment of the present invention, the Young's Modulus of the hybrid sheet may be characterized as being 10 GPa or more.

In addition, the tensile strength of the hybrid sheet may be characterized as being 70 MPa or more.

The present invention enables the production of an eco-friendly organic-inorganic composite sheet through a relatively simple manufacturing process, in which graphene is evenly dispersed between cellulose nanofibers (CNF) without aggregation between the cellulose nanofibers and graphene, thereby exhibiting uniform and excellent mechanical/electrical properties, thereby greatly increasing the usability in various industrial groups.

FIG. 1 is an image showing a mixed solution in which a second solution containing graphene is mixed with a first solution containing cellulose nanofibers (CNF) according to comparative examples or embodiments of the present invention.
Figure 2 is a schematic diagram showing a filtration process according to comparative examples and embodiments of the present invention.
FIG. 3 is an image showing a drying step of a cellulose nanofiber sheet and hybrid sheet according to comparative examples and embodiments of the present invention.
FIG. 4 is an image showing a cellulose nanofiber sheet and hybrid sheet according to comparative examples and embodiments of the present invention.
FIG. 5 is an image of a cellulose nanofiber sheet and hybrid sheet having flexibility and handling stability according to comparative examples and embodiments of the present invention.
FIG. 6 is an AFM and SEM analysis image evaluating the surface characteristics of cellulose nanofiber sheets and hybrid sheets according to comparative examples and embodiments of the present invention.
Figure 7a is a graph showing the BET surface area of a cellulose nanofiber sheet according to a comparative example of the present invention.
FIG. 7b is a graph showing the BET surface area of a hybrid sheet according to an embodiment of the present invention.
FIG. 8 is a graph showing the Young's Modulus of hybrid sheets according to comparative examples and embodiments of the present invention.
Figure 9 is a graph showing the tensile strength of hybrid sheets according to comparative examples and embodiments of the present invention.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. The present invention may be implemented in various different forms and is not limited to the embodiments described herein.

As described above, the environmental friendliness and the inherent mechanical, electrical, and chemical properties of nanocellulose have not been fully utilized, which limits the ability to meet the needs of various industries.

Accordingly, the present invention seeks to solve the above-described problem by providing a method for producing a hybrid sheet, which comprises a first step of producing a first solution containing cellulose nanofibers (CNF), a second step of producing a mixed solution by mixing a second solution containing graphene with the first solution, and a third step of producing a sheet by filtering and drying the mixed solution.

Through this, the present invention can overcome the above-mentioned problems and increase the usability in various industrial fields by manufacturing an eco-friendly/non-toxic hybrid sheet with excellent mechanical/electrical properties.

The present invention will be described in detail with reference to the drawings below.

Method for manufacturing hybrid sheets

The first step of the method for manufacturing a hybrid sheet according to the present invention is a step of manufacturing a first solution containing cellulose nanofibers (CNF), and according to one embodiment of the present invention, the first step may be a step of stirring a suspension containing cellulose nanofiber (CNF) powder at 30 to 150 rpm for 10 to 20 minutes to manufacture a first solution in which cellulose nanofiber powder is homogeneously dispersed.

The above cellulose nanofiber powder may be a fiber powder containing cellulose including both crystalline and amorphous regions, and may include, for example, a cellulose-based biomass such as wood or pulp. The cellulose-based biomass may be primary and secondary biomass, and may include, for example, a cellulose-based biomass, a wood-based biomass, an algae-based biomass, or a mixture thereof, and any material containing cellulose may be applied as the cellulose-based material without any particular limitation. As another example, the cellulose-based nanofiber powder may be derived from natural products such as wood, bamboo, hemp, rice straw, and Kenyan paper core, commercial products, agricultural by-products such as banana leaves, regenerated pulp or used paper, fibers, etc.

The above extracted cellulose nanofiber powder can be mixed with a known and common solvent used in the general production of cellulose to prepare a suspension, for example, it can be mixed with DI water. At this time, the cellulose nanofiber powder included in the suspension can be composed of 1 to 50 parts by weight based on the total weight of the suspension. At this time, if the weight of the cellulose nanofiber powder exceeds 50 parts by weight, the viscosity of the suspension may increase, which may make it difficult to subsequently produce a sheet form. However, this is only one embodiment and may be appropriately changed depending on the type of stirrer or solvent used and is not limited thereto. Thereafter, the suspension can be prepared into a first solution by stirring at 30 to 150 rpm for 10 to 20 minutes to uniformly disperse the cellulose nanofiber powder.

Next, the second step of the method for manufacturing a hybrid sheet according to the present invention is a step of manufacturing a mixed solution by mixing a second solution containing graphene into the first solution.

In general, cellulose nanofibers are organic polymer materials with excellent tensile strength, and their application to polymer composites can not only significantly improve the mechanical strength of the polymer, but also have high applicability to lithium ion battery separators, displays, solar cells, electronic paper, sensors, etc. due to their low air permeability, excellent mechanical properties, transparent optical properties, and low coefficient of thermal expansion. Accordingly, research is being actively conducted to implement various composite materials using nanocellulose and metal nanoparticles or carbon materials, but when manufacturing a composite material through a process of simply mixing nanocellulose and polymer composite materials to implement specific properties, it is difficult to form a random structure and manufacture a uniformly dispersed form due to the weak intermolecular adsorption between nanocellulose and carbon materials, making it difficult to exhibit uniform properties.

In particular, when manufacturing a sheet-shaped product like the present invention, there is a problem that a small concentration of polymer composite is loaded onto the cellulose nanofiber sheet, making it difficult to obtain the desired mechanical/electrical/chemical properties.

Accordingly, the present invention solves the above-described conventional problems and obtains the desired uniform and excellent mechanical/chemical/electrical properties by performing the second step such that the second solution containing graphene is mixed in the first solution prepared in the first step at a volume ratio of 1:0.01 to 0.05, as illustrated in FIG. 1.

More specifically, referring to FIG. 6, which is an AFM and SEM image of a hybrid sheet manufactured with the above-described volume ratio according to an embodiment of the present invention, it can be confirmed that graphene is evenly dispersed between cellulose nanofibers in all embodiments. At this time, if the first solution and the second solution are mixed at a volume ratio of less than 1: 0.01, the content of graphene may be too low to obtain the desired electrical properties, and there may be a problem that the dispersion of graphene is reduced. In addition, if the first solution and the second solution are mixed at a volume ratio exceeding 1: 0.05, the content of graphene may be too high to make it difficult to manufacture a sheet form or there may be a problem that an agglomeration phenomenon occurs.

To this end, according to one embodiment of the present invention, after the second step, before performing the third step, a step of stirring the mixed solution at 30 to 150 rpm for 10 to 20 minutes may be further included. At this time, if the stirring speed or stirring time is below the numerical range, there may be a problem in that the mixed solution is not formed uniformly.

Next, the third step of the method for manufacturing a hybrid sheet according to the present invention is a step of manufacturing a sheet by filtering and drying the mixed solution.

More specifically, referring to FIG. 2 which shows a schematic diagram of a filtration process, in the third step of the present invention for manufacturing a hybrid sheet, the mixed solution manufactured in the second step is mixed with a solvent, and a cellulose ester, PTFE having a thickness of 0.1 to 1.0 ㎛ and having hydrophilicity can be used as a filtration filter, and preferably, a hydrophilic nylon filter having a thickness of 0.3 to 0.6 ㎛ can be used, which may be advantageous in terms of the filtration efficiency of DI water used as a solvent for the cellulose suspension mixed with graphene. In addition, the mixed solution and the solvent may be mixed at a volume ratio of 1: 0.2 to 2, and more preferably, may be mixed at a volume ratio of 1: 0.5 to 1.5. If the volume ratio of the mixed solution and the solvent is less than 1: 0.2, there may be a problem that it is difficult to control the circular shape because the suspension is not evenly applied to the entire surface of the filter during filtration due to the high viscosity of the suspension.

Meanwhile, the solvent mixed with the above-described mixed solution is not particularly limited as any known conventional solvent suitable for the above-described filtration filter can be used. However, in a preferred embodiment of the present invention, when a hydrophilic nylon filter is used as the filtration filter, the solvent mixed with the above-described mixed solution may be DI water.

Referring to FIG. 3, according to one embodiment of the present invention, after the third step, a step of drying the filtered sheet at 100 to 150° C. for 8 to 15 hours may be further included. At this time, if the drying temperature is lower than 100° C. or shorter than 8 hours, there may be a problem that the filtered sheet is not sufficiently dried, and if the drying temperature exceeds 150° C. or the drying time exceeds 15 hours, there may be a problem that deformation of the sheet occurs during the drying step.

Hereinafter, a hybrid sheet manufactured by the above-described method for manufacturing a hybrid sheet will be described in detail. However, in order to avoid duplication, descriptions of content that is identical in technical concept to the above-described method for manufacturing a hybrid sheet will be omitted.

Hybrid Seat

The hybrid sheet according to the present invention is an eco-friendly/non-toxic organic-inorganic composite hybrid sheet having excellent tensile strength and electrical properties, and includes graphene evenly dispersed between cellulose nanofibers (CNF). The hybrid sheet according to the present invention may have an average pore size of 5 to 20 nm and a BET specific surface area of 2 m ² /g or more.

That is, one purpose of the present invention is to manufacture a hybrid sheet having excellent mechanical/electrical properties. Referring to FIGS. 7a and 7b, it is possible to know the relationship between the specific surface area and pore size of the hybrid sheet according to the present invention manufactured through the method for manufacturing the hybrid sheet described above.

As shown in FIGS. 4 and 5, the state images of a pure cellulose nanofiber (CNF) sheet and a hybrid sheet containing graphene can be confirmed, and it can be seen that the hybrid sheet according to the present invention manufactured through the above-described method for manufacturing a hybrid sheet has excellent mechanical strength and flexibility.

Figure 6 is an image of a hybrid sheet according to the present invention manufactured through the above-described method for manufacturing a hybrid sheet, in which the morphological characteristics are analyzed using a field emission scanning electron microscope (FE-SEM) and an atomic force microscope (AFM). Through this, the surface roughness (RMS) of the hybrid sheet was observed, and it can be confirmed that the surface roughness of the hybrid sheet increases as the graphene content increases.

Meanwhile, it can be seen through FIGS. 8 and 9 that the present invention can manufacture a hybrid sheet having excellent mechanical properties as desired by the present invention. That is, referring to FIGS. 8 and 9, the Young's modulus of the hybrid sheet according to an embodiment of the present invention may be 10 GPa or more, and the tensile strength may be 70 MPa or more.

In summary, the present invention perfectly solves the problem of dispersibility due to the weak adsorption force between nanocellulose material and carbon material or polymer material so as to fully utilize the excellent intrinsic properties of cellulose nanofibers, and not only remarkably improves the mechanical strength even when manufactured in sheet form, but also exhibits excellent electrical properties that can be applied to electronic products that are in the trend of miniaturization/thinning, such as lithium ion battery separators, displays, solar cells, electronic paper, and sensors.

Hereinafter, the present invention will be described more specifically through examples, but the following examples do not limit the scope of the present invention, and should be interpreted as helping to understand the present invention.

Example 1 - Manufacturing of hybrid sheets

First, 200 ml of a suspension containing cellulose nanofiber powder (manufactured by CNNT, High Grade, crystallinity 77–80%, length 4–6 μm, width 5–70 nm) was stirred at 50 rpm for 15 minutes to prepare a first solution in which cellulose nanofibers were uniformly dispersed.

Next, 1 ml of the second solution (Graphene solution) was mixed with 100 ml of the first solution (CNF solution) to prepare a mixed solution. After stirring at 50 rpm for 15 minutes, cellulose ester having a thickness of 0.45 μm was filtered using a filter, and dried at 120° C. for 12 hours as shown in Fig. 3 to prepare a hybrid sheet having a final thickness of 1 to 100 μm as shown in Fig. 4. The thickness of the hybrid sheet can be prepared differently depending on the mixing ratio of the first solution, the second solution, and the solvent.

Examples 2 and 3 - Manufacturing of hybrid sheets

A hybrid sheet was manufactured in the same manner as in Example 1 above, but using different amounts of the second solution (graphene solution) to 2 ml and 3 ml, respectively.

Comparison Example 1

A cellulose nanofiber sheet composed only of cellulose nanofibers was manufactured in the same manner as in Example 1 above, but without mixing the second solution (graphene solution).

Test Example 1 - Structural/Electrical/Mechanical Properties Analysis of Sheets

The structural, electrical and mechanical properties of the cellulose nanofiber sheets and hybrid sheets according to the comparative examples and embodiments above were measured, and the results are shown in Table 1.

RMS
(㎛) BET specific surface area (m ² /g) BJH diameter (nm) Young’s Modulus (GPa) Tensile Strength (MPa) Comparative Example 1 (CNF) 0.216 2.045 9.4 7.2 48 Example 1 (CNF@G1) 0.237 2.345 16.4 10.1 72 Example 2 (CNF@G2) 0.259 6.694 10.3 11.3 86 Example 3 (CNF@G3) 0.282 3.616 12.7 12.7 103

Claims (10)

A first step of preparing a first solution containing cellulose nanofibers (CNF);
A second step of preparing a mixed solution by mixing a second solution containing graphene into the first solution; and
A third step of filtering and drying the above mixed solution to produce a sheet; including;
The first step is a step of preparing a first solution in which cellulose nanofiber (CNF) powder is homogeneously dispersed by stirring a suspension containing cellulose nanofiber (CNF) powder at 30 to 150 rpm for 10 to 20 minutes.
The mixed solution of the second step is a mixture of the first solution and the second solution in a volume ratio of 1:0.01 to 0.05.
After the second step, a step of stirring the mixed solution at 30 to 150 rpm for 10 to 20 minutes is further included before performing the third step.
A method for manufacturing a hybrid sheet, characterized in that the sheet has a surface roughness (RMS) of 0.259 to 0.282 ㎛, a BET specific surface area of 3.616 to 6.694 m ² /g, and an average pore size of 10.3 to 12.7 nm.
delete delete delete In paragraph 1,
The third step above mixes the mixed solution prepared in the second step above with a solvent,
A method for manufacturing a hybrid sheet, characterized in that it is a step of filtering through a hydrophilic nylon filter having a thickness of 0.3 to 0.6 ㎛.
In paragraph 5,
A method for manufacturing a hybrid sheet, characterized in that in the third step, the mixed solution and the solvent are mixed in a volume ratio of 1:0.2 to 2 and filtered.
In paragraph 1,
A method for manufacturing a hybrid sheet, characterized in that, after the third step, it further includes a step of drying at 100 to 150°C for 8 to 15 hours.
delete delete delete