KR20210068641A - Method for preparation of thermoplastic polymer/cellulose nanofiber nanocomposite comprising suspension process and melt process using co-solvent system - Google Patents

Abstract

The present invention relates to a method for producing a thermoplastic resin/cellulose nanofiber nanocomposite, which comprises: a first step of preparing a suspension by dispersing a cellulose nanofiber (CNF) in a mixed solvent of a plasticizer and ethanol; and a second step of mixing the suspension and a thermoplastic resin through a melting process. The present invention also relates to an oxygen barrier membrane made of a nanocomposite produced by the method, and a pharmaceutical or food packaging material containing the same.

Description

Method for preparation of thermoplastic polymer/cellulose nanofiber nanocomposite comprising suspension process and melt process using co-solvent system

The present invention provides a first step of preparing a suspension by dispersing cellulose nanofiber (CNF) in a mixed solvent of a plasticizer and ethanol; and a second step of mixing the suspension with a thermoplastic resin through a melting process; a method for producing a thermoplastic resin / cellulose nanofiber nanocomposite, an oxygen barrier film made of the nanocomposite prepared accordingly, and a drug or It relates to packaging materials for food.

Unlike thermosetting resins, thermoplastic resins do not have bonds between chains (there is no crosslinking), so molding and processing are advantageous. The easiest way to mold and process such a thermoplastic resin is to use the thermal properties of the polymer. A thermoplastic polymer changes from a solid to a liquid at a temperature above its melting point, and is easily molded into a desired shape. In the industrial field, an extruder is often used for molding such polymers. Specifically, the solid thermoplastic resin is injected into a high-temperature injection machine in the form of pellets or powder, melted, and then injected and spun into fibers through a die. It plays an important role in plastic molding. Materials such as PET (polyethylene terephthalate), PE (polyethylene), and PP (polypropylene) have been mainly used as such thermoplastic resins. However, these days, environmentally friendly and biodegradable materials such as PLA (polylactic acid) and PGA (polyglycolic acid) ), PLGA (polylactic-co-glycolic acid), PCL (polycaprolactone), PBAT (polybutylene adipate terephthalate), and PA (polyamide) have become a major issue for industrial application. These thermoplastic resins are mainly _{synthesized using monomers having functional groups such as -OH, -NH 2} , -COOH, and -NCO at both ends, and have long chains with functional groups such as esters, carbonates, urethanes, or amides. Therefore, in general, the thermoplastic resin has a reactive functional group (-OH, -NH ₂ , -COOH, etc.) at the terminal portion.

Among the thermoplastic resins, PLA and the like have a problem of being very hard and brittle compared to conventional petroleum-based plastics, which limits their application in various industrial fields. Accordingly, a method of changing the physical properties of a material by blending a softer and more flexible polymer or a method of imparting ductility by putting a nanocomposite in a thermoplastic resin is mainly used. However, in the former case, high ductility can be imparted by mixing and injection molding polymers such as PEG, PEO, and PU having excellent ductility, but a polymer with different properties and a chain extender are mixed during injection. There are difficulties in the process, such as having to consider compatibility and thermal properties, and the biodegradability and biocompatibility of the original thermoplastic polymer may be lowered by the physical properties of the polymer mixed together. On the other hand, in the latter case, a plasticizer or a composite such as nanoparticles, clay, graphene, and an acrylate impact modifier is mixed during injection molding to improve the ductility and/or physical properties of the thermoplastic resin. As a change method, a small amount of additive can cause a change in physical properties, and it has the advantage that it is based on a target material, a thermoplastic resin, but most additives are difficult to commercialize and require an additional process, and due to the additives, the polymer itself There is a limit that colors other than the color of the color can be developed. However, the PLA is not used as an oxygen barrier film or packaging material for medicines or food due to its inherent hard and brittle properties and/or poor oxygen barrier properties.

On the other hand, a gas barrier film designed to block active gas is one of the most important topics in food packaging as well as many applications such as solar cells and electronic devices. In general, in order to prepare a gas barrier film, vacuum deposition of aluminum on a polymer film substrate (PET, OPP, CPP, LDPE, etc.) or a method of depositing or coating an inorganic material such as silica or alumina, EVOH (ethylene vinyl alcohol copolymer) , nylon, polyacrylonitrile, PVDC (polyvinyliolene chloride), such as a polymer film with excellent gas barrier properties is laminated and used. However, in the case of an aluminum deposition film, it becomes opaque, and when an inorganic material is deposited, the production cost increases due to high deposition cost, and in the case of a gas barrier polymer film, it is difficult to form a thin film.

Accordingly, the present inventors have made intensive research efforts to discover a method for manufacturing a flexible packaging material having oxygen barrier ability based on a thermoplastic resin, and as a result, a composite is prepared by mixing cellulose nanofibers with a thermoplastic resin, but to improve miscibility. To this end, by performing a suspension process of dispersing the cellulose nanofibers in a mixed solvent of a plasticizer and ethanol of a predetermined amount, and then melt-mixing the obtained suspension and a thermoplastic resin to prepare a composite, strength as well as elasticity and/or elongation This remarkably improved, it was confirmed that it is possible to provide a composite material with improved oxygen barrier ability, and completed the present invention.

One object of the present invention is a plasticizer (plasticizer) and (15 to 25) wt% of ethanol: 0.3 to 3 parts by weight of cellulose nanofiber (cellulose nanofiber) based on 100 parts by weight of a solvent in a mixed solvent of (75 to 85) wt%; A first step of dispersing CNF) to prepare a suspension; and a second step of mixing the suspension so that the content of the thermoplastic resin and the plasticizer is 11 to 18 phr (parts per hundred rubber) through a melting process; including, providing a method for producing a thermoplastic resin/cellulose nanofiber nanocomposite will do

Another object of the present invention is to provide an oxygen barrier film formed of the nanocomposite prepared by the above method.

Another object of the present invention is to provide a food or drug packaging material comprising the nanocomposite prepared by the above method.

Hereinafter, the present invention will be described in more detail.

On the other hand, each description and embodiment disclosed herein may be applied to each other description and embodiment. That is, all combinations of the various elements disclosed herein are within the scope of the present invention. In addition, it cannot be said that the scope of the present invention is limited by the specific descriptions described below.

In addition, those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. Also, such equivalents are intended to be encompassed by the present invention.

As one aspect for achieving the above object, the present invention is a plasticizer and (15 to 25) wt% of ethanol: (75 to 85) wt% in a mixed solvent of 0.3 to 3 parts by weight based on 100 parts by weight of the solvent. A first step of preparing a suspension by dispersing cellulose nanofiber (CNF); and a second step of mixing the suspension so that the content of the thermoplastic resin and the plasticizer is 11 to 18 phr (parts per hundred rubber) through a melting process; including, providing a method for producing a thermoplastic resin/cellulose nanofiber nanocomposite do.

As used herein, the term "plasticizer" is an additive, also called dispersants, for increasing plasticity or reducing viscosity of a material, which changes the physical properties of a material. It is a substance added for It may be a low volatility liquid or a solid. It reduces the interaction between polymer chains and makes them more flexible. Tens of thousands of substances have been tested for their properties as plasticizers over decades, but only a handful of about 50 of them are commercially available. Its main use is plastics, but it is also used to change the properties of materials such as concrete or clay.

For example, the plasticizer may be bio-based plasticizers. These biobased plasticizers have better biodegradability and have been developed to have low environmental toxicity, and non-limiting examples thereof include alkyl citrates, which are used in food packaging, medical products, cosmetics and toys. may include For example, the alkyl citrate is triethyl citrate (TEC), acetyl triethyl citrate (ATEC), tributyl citrate (TBC), acetyl tributyl citrate (acetyl tributyl citrate) citrate; ATBC), trioctyl citrate (TOC), acetyl trioctyl citrate (ATOC), trihexyl citrate (THC), acetyl trihexyl citrate; ATHC), butyryl trihexyl citrate (BTHC, trihexyl o-butyryl citrate), and trimethyl citrate (TMC). Specifically, the plasticizer may be triethyl citrate (TEC), but is not limited thereto.

As used herein, the term "triethyl citrate" is an ester of citric acid, which is a colorless, odorless liquid. In addition to its use as a plasticizer for polymer resins, it is also used as a food additive to stabilize the foam as a foaming aid for egg white. It is also used in pharmaceutical coatings and plastics.

The plasticizer may be contained in 11 to 18 phr of the total nanocomposite, specifically 12 to 17 phr, more specifically 12.5 to 15 phr, but is not limited thereto.

In a specific embodiment of the present invention, TEC is used as a plasticizer, but the tensile strength and elongation are measured while changing the content, and as the content of the plasticizer increases, the tensile strength decreases while the elongation increases rapidly. Accordingly, while maintaining a predetermined tensile strength, the content of the plasticizer was selected in a range capable of achieving significantly improved elongation.

As used herein, the term "thermoplastic resin" refers to a polymer that melts when heat is applied and returns to a solid state when the temperature is sufficiently lowered. is created by Unlike thermosetting plastics, it melts and returns to its original state when heated, so it can be recycled. The general molecular structure is a linear structure where only weak interactions between molecules are possible.

Non-limiting examples of the thermoplastic resin include polycarbonate, polyanhydride, ABS resin (acrylonitrile butadiene styrene copolymer), AS resin (acrylonitrile-styrene copolymer), acrylic resin, polyamide, polyphenylene sulfide, polyether ether ketone , polyester, polyacetal, polysulfone, polyphenylene oxide, polyimide, polyetherimide, etc., or ethylene/glycidyl methacrylate copolymer, polyester elastomer, polyamide elastomer, ethylene/propylene terpolymer, ethylene / Polymers such as butene-1 copolymer, polyethylene glycol, polypropylene glycol, ethylene glycol, copolymers of ethylene glycol and propylene glycol, polyoxyethylated polyols, polyvinyl alcohol, polysaccharides, dextran, polyvinyl ethyl ether , polylactic acid (PLA), polylactic-glycolic acid copolymer (poly(lactic-co-glycolic acid) copolymer; PLGA). Specifically, it may be polylactic acid, but is not limited thereto.

As used herein, the term "cellulose nanofiber (CNF)" refers to nano-sized cellulose, in particular, a fiber having a large aspect ratio, for example, a width of several to several tens of nm and a width of several μm. It means cellulose in the form of having a length. As a pseudo-plastic material by itself, it exhibits thixotropy, a viscous gel or fluid state under normal conditions.

In the nanocomposite of the present invention, the CNF may be contained in an amount of 0.1 to 30% by weight. Specifically, it may be contained in an amount of 0.1 to 20% by weight, more specifically 0.2 to 10% by weight, and more specifically 0.25 to 5% by weight, but it is miscible with the thermoplastic resin, which is the basic substrate of the nanocomposite, and has the desired physical properties. As long as it can be achieved, it is not limited thereto.

For example, the nanocomposite prepared according to the manufacturing method of the present invention has improved dispersibility of CNF in the thermoplastic resin compared to the nanocomposite prepared under the same conditions using only ethanol as a solvent in the first step.

Specifically, in the nanocomposite prepared according to the method of the present invention, the total area of CNF aggregates dispersed in the thermoplastic resin is reduced by 150 to 250% compared to the nanocomposite prepared under the same conditions using only ethanol as a solvent in the first step. can be

In a specific embodiment of the present invention, by measuring and comparing the zeta potential of the suspension according to a method using only ethanol as a solvent in the first step and a method using a cosolvent system using a mixed solvent of TEC and ethanol as a plasticizer, The latter showed a significantly increased negative zeta potential, indicating that it was more uniformly distributed in the suspension of cellulose nanofibers (CNF). This difference in distribution is due to the high interfacial tension between the plasticizer TEC and CNF, and it can be expected to affect the dispersion in the nanocomposite formed after melt mixing with the thermoplastic resin using these suspensions.

On the other hand, the nanocomposite prepared according to the manufacturing method of the present invention is characterized in that it has a tensile strength increased by 10 to 25% compared to a resin prepared by mixing only the same amount of a plasticizer in the second step without the first step.

As used herein, the term “tensile strength” refers to a structural ability to support a load without collapse due to excessive stress or deformation.

In addition, the nanocomposite manufactured according to the manufacturing method of the present invention is characterized in that it has a Young's modulus increased by 10 to 70% compared to a resin prepared by mixing only the same amount of a plasticizer in the second step without the first step.

As used herein, the term "Young's modulus" is a constant named after Thomas Young, an 18th century British physicist, and a solid that experiences tension or compression applied only on one side. represents the elasticity of Young's modulus is a measure of a material's ability to withstand a change in length under tension or compression in the major axis direction. Young's modulus is meaningful only in the region where stress is proportional to strain, and when the external force is removed, the material returns to its original scale. When the stress increases, the material may flow, undergo permanent deformation, or eventually crack.

For example, the nanocomposite prepared according to the manufacturing method of the present invention has an elongation value of 300% or more. This high elongation indicates that the nanocomposite prepared according to the present invention is a material having considerable flexibility, and thus it is easy to form, so it is suggested that it can be used as an oxygen barrier film or packaging material by thinning it.

As another aspect, the present invention provides an oxygen barrier film formed of the nanocomposite prepared by the above method.

The nanocomposite prepared according to the manufacturing method of the present invention has an oxygen permeability level of 70 to 45% compared to an oxygen barrier film formed of a pure thermoplastic resin prepared to the same thickness or a thermoplastic resin composite containing the same amount of plasticizer but not containing cellulose nanofibers It is characterized by a reduction in In general, a disadvantage of a thermoplastic resin such as polylactic acid is that it has low barrier properties against gases including oxygen.

However, in a specific embodiment of the present invention, in the case of a membrane formed of a nanocomposite prepared using a cosolvent system of ethanol and a plasticizer prepared according to the present invention, compared to pure PLA, as well as simple mixing with TEC, a plasticizer It was confirmed that it exhibits significantly improved oxygen barrier properties compared to the composite, specifically, reduced oxygen permeability from 70% to a maximum of 45%, thereby demonstrating that it can be used as an oxygen barrier membrane.

For example, since most electronic devices contain metals with high electron conductivity and are sensitive to oxidation, that is, reaction with oxygen, it is preferable to coat them with a film or the like capable of blocking oxygen. The oxygen barrier film according to the present invention can be applied to electronic devices requiring such an oxygen barrier film. For example, non-limiting examples of electronic devices to which this can be applied may include batteries, organic light emitting devices, display devices, photovoltaic devices, integrated circuits, pressure sensors, chemical sensors, biosensors, solar devices, and lighting devices. have.

Another aspect of the present invention provides a food or drug packaging material comprising the nanocomposite prepared by the above method.

For example, the nanocomposite is characterized in that the migration rate of the plasticizer is within 5% by weight up to 100 minutes, and the migration rate is reduced by 20% compared to the nanocomposite containing no cellulose nanofibers.

In addition, as described above, the nanocomposite membrane of the present invention is a flexible material that has improved oxygen barrier properties, as well as increased strength, elasticity, and/or excellent elongation.

On the other hand, metallic substances, foods, nutrients, etc. may react with oxygen in the air to be oxidized. Therefore, currently, in order to increase the shelf life, a film deposited with aluminum or inorganic material is used, or a composite film laminated with a gas barrier resin, etc., are used, but the packaging material including them may become opaque, and the production cost increases and The thickness may be increased.

Therefore, it can be usefully used as a packaging material for the above-mentioned oxidation-sensitive food and/or medicine. In this case, the packaging material may be formed by additionally including a base layer, a printing layer, and a sealing layer for water vapor barrier and/or heat sealing to maintain the strength of the film of the present invention, or may be used by additionally coating the existing packaging material. .

The method for manufacturing a thermoplastic resin/cellulose nanofiber nanocomposite using a cosolvent system of a plasticizer and ethanol of the present invention is an eco-friendly material using a biological material and has an improved oxygen barrier ability, so it is suitable for various biodegradable packaging materials for medicine or food. It can be useful.

1 is a diagram showing the zeta potential of TEC-CNF and ethanol-CNF suspension.
Figure 2 shows the results of chemical characterization of the TEC-CNF suspension; (a) FT-IR spectra, (b) schematic diagrams of CNF and TEC interactions, (c) SEM images of TEC-CNF suspensions evaporated in ethanol at 180°C.
3 is a diagram showing the storage modulus (storage modulus, G' ) of (a) f-CNF/PLA, (b) e-CNF/PLA, and (c) t-CNF/PLA nanocomposites.
4 shows (a) storage modulus for CNF/PLA nanocomposites as a function of CNF loading at each frequency of 0.1 /s and (b) Van Gurp-Palmen plots for CNF/PLA nanocomposites. It is also
5 is a diagram showing an SEM photograph of the CNF in the nanocomposite and the measured width of the CNF.
6 is a diagram showing SEM images of the fractured surface of the CNF/PLA nanocomposite: (a) 0.25 wt% f-CNF/PLA, (b) 0.5 wt% f-CNF/PLA, (c) 1 wt% f-CNF/PLA, (d) 0.25 wt% e-CNF/PLA, (e) 0.5 wt% e-CNF/PLA, (f) 1 wt% e-CNF/PLA, (g) 0.25 wt % t-CNF/PLA, (h) 0.5 wt% t-CNF/PLA, and (i) 1 wt% t-CNF/PLA.
Figure 7 is a diagram showing the size distribution of CNF agglomerates and binarized microscopic images of CNF/PLA nanocomposites: (a) 0.25 wt% f-CNF/PLA, (b) 0.5 wt% f- CNF/PLA, (c) 1 wt% f-CNF/PLA, (d) 0.25 wt% e-CNF/PLA, (e) 0.5 wt% e-CNF/PLA, (f) 1 wt% e-CNF/ PLA, (g) 0.25 wt% t-CNF/PLA, (h) 0.5 wt% t-CNF/PLA, and (i) 1 wt% t-CNF/PLA.
8 is a diagram showing the total area of CNF aggregates for the CNF/PLA nanocomposite as a function of CNF wt%.
9 is a view showing the experimentally measured tensile modulus of the CNF/PLA nanocomposite compared with the theoretical calculated value by Cox-Krenchel: (a) f-CNF/PLA and e-CNF/PLA nanocomposites, and (b) t-CNF/PLA nanocomposites.
10 shows (a) f-CNF/PLA, (c) e-CNF/PLA, and (e) t-CNF/PLA nanocomposites elastic modulus ( E' ), and (b) f-CNF. It is a diagram showing the tan delta of /PLA, (d) e-CNF/PLA, and (f) t-CNF/PLA nanocomposite.
11 is a diagram showing the weight variation of t-PLA and t-CNF/PLA nanocomposites at 110°C.
12 is a mechanical property of t-PLA and t-CNF/PLA nanocomposite after drying at 110° C. in a vacuum oven; It is a diagram showing (a) tensile strength and (b) elongation at break.

Hereinafter, the present invention will be described in more detail through examples. However, these examples are for illustrative purposes only, and the scope of the present invention is not limited to these examples.

<substance>

Polylactic acid (PLA, Ingeo Biopolymer 2003D grade, melt flow index: 6 g/10 min, 210° C., 2.16 kg ASTM D1238) was purchased from NatureWorks (USA), and lyophilized CNF (cellulose nanofibers) was cellulose nanofibers. It was purchased from Lab (Canada). The CNFs had a width ranging from 20 to 60 nm and reached several micrometers in length. Triethyl citrate (TEC, ≥98.0%) and ethanol (≥99.5%) were purchased from Sigma Aldrich (USA) and used as such. PLA and CNF were vacuum dried at 80° C. for 12 hours to remove residual moisture prior to use.

Example 1: ethanol- CNF and TEC - CNF Preparation of suspensions

An ethanol-CNF suspension containing 0.125, 0.25, and 0.5 g of lyophilized CNF was added to 30 g of ethanol and mixed vigorously with a homogenizer (Model: T10 basic ULTA-TURRAX®, IKA, Germany). did. Using a dispersing element for mixing, not for crushing, homogenization was performed at 6000 rpm for 0.5 hours. The optimal TEC content for manufacturing flexible PLA was determined through the following experimental examples, and a mixed solvent was prepared from 6.25 g TEC and 23.75 g ethanol. A TEC-CNF suspension of each CNF content was prepared under the same conditions as above.

Example 2: f- CNF / PLA , e- CNF / PLA , t- PLA , and t- CNF / PLA Preparation of Nanocomposites

Small scale internal mixer with a counter-rotating twin-screw with a barrel capacity of 50 g (Model: W50 Plastograph®Lab-Station, Brabender Gmb & Co KG, Germany) was used to prepare three kinds of CNF/PLA nanocomposites having various CNF compositions (0.25, 0.5, 1 wt%). Based on the specifications of PLA provided by the manufacturer and preliminary experiments, PLA was dried in a vacuum oven at 80° C. for 12 hours prior to melt mixing. Freeze-dried CNF/PLA nanocomposites (f-CNF/PLA ), ethanol-CNF suspension/PLA nanocomposites ( e- CNF / PLA ) under 180°C barrel temperature conditions with a rotation speed of 50 rpm and mixing time of 7 minutes , and TEC-CNF suspension/PLA nanocomposites ( t- CNF / PLA ) were prepared. First, PLA was melted in a mixer for 1 minute, then freeze-dried CNF or two solvent/CNF suspensions were added and mixed for another 6 minutes. In the meantime, the ethanol contained in the solvent-CNF suspension was evaporated during the process. In addition, t-PLA was prepared by adding TEC at a content of 12.5 phr (parts per hundred rubber) to PLA granules under the same temperature, screw speed, and mixing time conditions.

After the bulk-shaped composite sample was ground and dried at 80° C. for 12 hours, the composite granules were compression molded into a film to measure oxygen barrier properties, and also morphologically It was molded to measure morphological, rheological and mechanical properties.

Compression molding was performed using a hot press system (Model: QM900A, Quality & Measurement System, Korea), and the molding process consisted of preheating for 4 minutes, pressing for 1 minute, and cooling for 4 minutes. was carried out at 180 °C. In addition, the composite granules were prepared using a micro injection molding machine (Model: Xplore Micro 10 cc Injection Molding Machine, Xplore Instruments, Netherlands) at 180° C. in a disc shape with a diameter of 25.4 mm and a thickness of 1 mm and a length of 50 mm, 4 It was injection molded into a dumbbell-shaped test specimen with a width of mm and a thickness of 2 mm.

Example 3: Characterization

According to ISO 304, a surface tension analysis of the solvent was performed by a Pt ring desorption method using a tension meter (tension meter, Model: Surface Tension Analyzer, SEO, Korea). The interfacial tension between a solid and a liquid and between two liquids, γ _12, was calculated via the Girifalco-Good equation:

(1)

(One)

(2)

(2)

Here, γ ₁ is the surface tension of the solid or liquid. Φ and V are the interaction parameter and molar volume of the solid or liquid, respectively.

Zeta potential was measured with a zeta potential analyzer (Model: Zetasizer Nano ZS, Malvern, UK). After homogenization, the CNF-solvent sample was injected into the measuring cell through a syringe, and the zeta potential value, ζ , was calculated according to the Smoluchowski equation:

(3)

(3)

In this case, U _E is the electrophoretic mobility. η and ε are the viscosity and dielectric constant of the dispersion medium, respectively. f( κα ) is Henry's function.

Fourier transform infrared (FT-IR) spectroscopic analysis was performed using an FT-IR spectrophotometer (Model: Frontier, PerkinElmer, USA). A total of 20 scans and percentage transmission mode were performed in the 4000-500 ^{cm -1 wavenumber range.}

The morphology of the CNF and PLA composites was observed with a field emission scanning electron microscope (Model: SU8020, Hitachi, Japan). The solvent-CNF suspension was added dropwise onto a hotplate at 180° C. to evaporate the ethanol. Injection molded samples were cryo-fractured using liquid nitrogen to prevent deformation during the fracture process. All samples were coated with Pt/Pd alloy using ion sputtering (Model: E-1045, Hitachi, Japan). The tests were performed under high vacuum with an accelerating voltage of 3 to 8 kV.

A 3D laser scanning microscopy (Model: VK-X200K, KEYENCE, Japan) was applied using an optical laser equipped with 10× magnification and 408 nm purple laser. Particle area, A _A , of undispersed primary CNF aggregates was quantified according to Equation 4 using particle analysis using incorporated software developed by KEYENCE:

(4)

(4)

where d _i is the i- th diameter of the primary CNF aggregate. According to ISO 18553, agglomerates with a diameter of less than 3 μm were ignored.

Measurement of oscillatory shear stress in the linear viscoelastic region on a rheometer (Model: Physica MCR302, Anton Paar GmbH, Austria) using a parallel-plate geometry (25 mm diameter and 1 mm spacing) at 180 °C ( Oscillatory shear measurement and stress relaxation were performed. A frequency sweep was performed after 3 minutes temperature equilibration with a reduction in frequency from 100 rad/s to 0.1 rad/s and a strain of 1%. All samples were measured under atmospheric conditions.

Tensile strength with a universal testing machine (Model: INSTRON 3367, INSTRON, USA) equipped with a 30kN cell force that measures the force against displacement of each sample at 10 mm/min ) and mechanical properties such as elongation at break were measured. The gauge length was fixed at 19 mm.

Oxygen permeability measurements of PLA and CNF composite films were performed according to ASTM 3985 with an oxygen transmission rate analyzer, Model: 702, MOCON, USA; A sample was prepared using an aluminum mask (5 cm ² ), and a permeation test was performed under conditions of 0% relative humidity at 23° C. and 100% oxygen atmosphere. Oxygen permeability was measured over 24 to 48 hours until the steady state was reached.

Dynamic mechanical properties were measured in a forced flexural oscillation mode. Dynamic mechanical properties (dynamic mechanical properties) using a dynamic mechanical analyzer (Model: RSA-G2, TA instruments, USA) with a previously injection-molded sample in the form of a bar (dual cantilever geometry, width 40 mm) and a thickness of 2 mm) in a forced flexural oscillation mode. A temperature sweep was applied increasing from 20°C to 90°C with a heating rate of 3°C/min at a fixed frequency of 1 Hz.

The migration behavior of plasticizers from t-PLA and t-CNF/PLA nanocomposites was evaluated using a thermogravimetric analyzer (Model: Q500, TA Instruments, USA). The test was performed under a nitrogen atmosphere at an isothermal temperature of 110° C. to confirm the degree of thermally induced plasticizer migration. Dumbbell-shaped specimens of t-PLA and t-CNF/PLA nanocomposites were stored in a vacuum oven at 110° C., and tensile tests were performed according to specific storage times.

Multiple comparisons of each set of experimental values were analyzed by one-way ANOVA from IBM SPSS Statistics version 23 (IBM SPSS) and Tukey's honestly significant differences (HSD) test (α = 0.05).

Experimental example One: TEC according to the content PLA the tensile strength of the resin and elongation change

In order to confirm the effect of the plasticizer content on the physical properties of the PLA resin, tensile strength and elongation were measured while increasing the TEC content from 5 phr to 20 phr, and the results are shown in Table 1 below.

TEC content (phr) Tensile strength (MPa) Elongation (%) 5 62.37±1.51 7.19±0.35 10 47.40±0.87 12.34±3.28 12.5 35.75±0.75 323.62±37.87 15 29.01±0.96 378.14±22.54 20 23.27±1.53 510.14±13.91

As shown in Table 1, the tensile strength decreased as the TEC content increased, while the elongation increased rapidly. Therefore, based on this, 12.5 phr, which maintains appropriate tensile strength but exhibits significantly increased elongation, was selected as the optimal content and used in the following experimental examples.

Experimental example 2: CNF and solvent/ PLA interfacial tension

The affinity between CNF and solvent/polymer was tested through interfacial tension analysis during suspension and melting process. The surface tensions of TEC, CNF, ethanol and PLA were 34.1, 44.3, 21.9 and 35.5 mN/m, respectively. Table 2 shows the surface tension values calculated using the Kirifalco-Good equation of Equation 2.

suspension process melting process substance pair Interfacial tension, γ (mN/m) substance pair Interfacial tension, γ (mN/m) TEC-CNF 59.33 PLA-CNF 60.18 Ethanol-CNF 50.8 TEC-CNF 59.33 TEC-ethanol 43.1 PLA-TEC 53.17

In the suspension process, the interfacial tension of TEC-CNF was found to be higher than that of ethanol-CNF and TEC-ethanol. Therefore, it can be assumed that CNF selectively binds to TEC during the TEC-CNF suspension process, indicating that CNF is evenly dispersed due to TEC dispersion in TEC-ethanol mixed solvent. The interfacial tensions of PLA-CNF and TEC-CNF were 60.18 and 59.33 mN/m, respectively. Due to these high and similar values, CNF could be evenly dispersed in the PLA matrix by using TEC as a dispersant during the melting process.

Experimental example 3: TEC - CNF Chemical characterization of suspensions

The zeta potential results shown in FIG. 1 were analyzed using 1.67 wt% CNF in ethanol or a TEC/ethanol mixture suspension. The dispersion stability was predicted and controlled by comparing them using the zeta potential value. It was confirmed that the zeta potential value of the TEC-CNF suspension (-29.3 mV) had a higher negative value than that of the ethanol-CNF suspension (-17.45 mV). The solid-liquid interface in suspension is affected by dispersion stability, which is dependent on interfacial adhesion. The high interfacial tension between TEC and CNF in the miscible TEC/ethanol mixed solvent shown in Table 2 indicates a high negative zeta potential value. In addition, since a dispersion difference due to a difference in the zeta potential value is expected, a difference in dispersion is expected as the CNF suspension according to the solvent type is injected into the molten PLA matrix in the internal mixer.

FT-IR spectra of CNF, TEC, and TEC-CNF suspensions in which ethanol was evaporated at 180° C. are shown in FIG. 2(a). The FT-IR spectrum of the TEC showed a ^{typical OH stretching band at 3700-3584 cm -1} , which was sharp due to the alcohol compound. In the case of CNF, a broad FT-IR spectrum due to intermolecular bonding between cellulose monomers showed OH stretching at ^{3550-3200 cm -1 .} As shown in Fig. 2(a), in the case of the TEC-CNF suspension in which ethanol was evaporated at 180 °C, a wider OH stretching band than that of TEC was shown at ^{3550-3200 cm -1 , which is a chemical interaction such as hydrogen bonding.} indicating that it exists. Fig. 2(b) shows the interaction between cellulose and TEC, and the morphology of wetted TECs on CNFs from the presence of chemical bonds between CNFs and TECs was observed by the SEM microscopy image of Fig. 2(c). As a plasticizer, TEC can be uniformly distributed in the PLA matrix, as a result of which CNF can be evenly dispersed in the PLA matrix during the melting process. Also, Oksman et al. confirmed that the presence of TEC enhances the hydrogen bonding between PLA and chitin nanocrystals. Likewise, it can be expected that TEC will increase the interfacial adhesion between PLA and CNF.

Experimental example 4: CNF / PLA of nanocomposites rheological Rheological properties

One method to evaluate the change in viscoelastic behavior with filler dispersion in nanocomposites is rheological measurement. 3 shows the storage modulus ( G' ) of all CNF/PLA nanocomposites. In the low frequency region, pure PLA and t-PLA exhibit typical homopolymer-like terminal behavior, indicating full relaxation of the polymer chain. As shown in Fig. (c), t-PLA was plasticized by TEC, a plasticizer that showed a lower storage modulus compared to pure PLA in all frequency domains.

However, all CNF/PLA nanocomposites exhibited a plateau phenomenon at low frequency G'. This phenomenon occurs when the filler forms a network structure within the polymer matrix. The network formation of these fillers makes the end behavior due to complete relaxation of the polymer chains less affected. This may be indirectly involved in the dispersion of the filler, and it means that the network structure is well formed. 3 also shows the difference in the degree of plateau according to the feeding method of CNF. The G' plot of the CNF/PLA nanocomposite starts to show plateaus at angular frequencies on the order of 1 1/s. The slope of the plot in each frequency range of 0.25 to 1 1/s was calculated by first-order linear regression, and the degree of network formation of CNFs in the PLA matrix was compared through the magnitude of the slope. The e-CNF/PLA sample group showed a lower slope compared to the f-CNF/PLA sample group, and it was confirmed that the supply in the form of a suspension was more efficient than the direct supply of lyophilized CNF to the PLA matrix. However, in the t-CNF/PLA sample group fed CNF as a PLA matrix using TEC as a plasticizer, the slope was significantly lower than that of the ethanol-based suspension feeding method. This can be supported by the zeta potential results as confirmed in FIG. 1 .

In Fig. 4 (a), the storage modulus value of the CNF/PLA composite at each frequency of 0.1 /s was compared with the CNF content according to the CNF supply method. Nano-sized fillers act as physical cross-linking points, and above a critical filler content known as the rheological filtration threshold concentration, all polymer chains are linked, limiting the movement of individual chains under shear forces. These percolation phenomena were confirmed between 0 and 0.25 wt% in two types of CNF/PLA complexes (e-CNF/PLA and t-CNF/PLA) except for f-CNF/PLA. On the other hand, f-CNF/PLA showed a tendency to continuously increase the storage modulus value as the CNF content increased, indicating that CNF at low content (0.25, 0.5 wt%) did not form a sufficient network in the PLA matrix. proved. When the CNF content was less than 1 wt%, e-CNF/PLA exhibited a relatively higher storage modulus than f-CNF/PLA. These differences can be inferred from the different process techniques for feeding CNF into the internal mixer in the formation of suspensions or powders. In addition, these results can be supported by the fact that the already agglomerated lyophilized CNFs were not sufficiently mixed under the shear force in the extruder, and the solvent could adequately help the supply of CNFs to induce uniform dispersion of CNFs in the polymer matrix. . When CNF dries, intermolecular hydrogen bonding occurs. During the feeding of the CNF suspension to the extruder, the solvent can be evaporated in a short time, so that the intramolecular hydrogen bonding of CNF can be relatively small. CNF distribution could be improved due to blow-up phenomena caused by pressurized liquid evaporation from molten PLA. Similar results were also observed in Van Gurp-Palmen plots (Fig. 4(b)). For pure PLA and t-PLA, the curve approaches a phase angle of 90° indicating viscous behavior, while the curve of the CNF-loaded CNF/PLA composite decreases with a lower phase angle, which is the viscous behavior. It represents the change in rheological behavior from liquid to more elastic. A more notable curve change was observed when e-CNF/PLA and t-CNF/PLA had the same CNF composition compared to f-CNF/PLA. In addition, the curve of the t-CNF/PLA sample showed a more remarkable change, from which it could be assumed that the feeding method using the TEC-CNF suspension provided the highest dispersion effect in the PLA matrix.

Experimental example 5: CNF / PLA Morphological Properties of Nanocomposites

5 shows SEM images of CNFs measured using Hitachi FE-PC SEM software. The width of CNF appeared in the range of 15.2 to 66.8 nm (average value: 32.0 nm), and the length was estimated to be several micrometers.

SEM images of the ruptured surfaces of CNF/PLA complexes containing different amounts of CNF are shown in FIG. 6 . f-CNF/PLA, e-CNF/PLA, and t-CNF/PLA samples were observed at 200x and 500x magnifications, respectively. In the case of f-CNF/PLA, CNF was formed as a bundle of 0.25 wt% in the PLA matrix, and it was observed to grow into large aggregates with increasing CNF content. However, it was observed that CNFs exhibit a much stronger network structure within the PLA matrix with increasing CNF content in e-CNF/PLA and t-CNF/PLA. In particular, t-CNF/PLA has a CNF network already formed at a CNF content of 0.5 wt% and uniform dispersion at a relatively low content compared to e-CNF/PLA. These morphological features can be supported by rheological properties. In the case of the t-CNF/PLA nanocomposite, the degree of plateau phenomenon due to non-terminal behavior at low frequencies was most evident due to the strong network formation of CNFs in the PLA matrix. In addition, the effects of the dispersion behavior of CNF on mechanical properties such as tensile strength and tensile modulus are shown in Tables 3 and 3.

sample Tensile strength (MPa) Elongation at break (%) Young's modulus (GPa) pure PLA 71.82±0.96 9.50±0.90 1.09±0.11 f-CNF/PLA 0.25 74.66±1.28 7.63±0.79 1.29±0.08 e-CNF/PLA 0.25 77.65±0.49 7.95±0.44 1.23±0.05 f-CNF/PLA 0.5 73.31±1.01 7.66±0.81 1.29±0.05 e-CNF/PLA 0.5 78.65±0.81 8.19±0.44 1.27±0.06 f-CNF/PLA 1 71.44±0.54 8.62±1.14 1.05±0.15 e-CNF/PLA 1 80.72±0.54 8.80±0.56 1.33±0.08

sample Tensile strength (MPa) Elongation at break (%) Young's modulus (GPa) t-PLA 35.75±0.75 323.62±37.87 0.63±0.03 t-CNF/PLA 0.25 39.74±0.12 339.26±39.05 0.71±0.04 t-CNF/PLA 0.5 42.15±1.21 325.71±41.07 0.89±0.07 t-CNF/PLA 1 43.02±1.49 308.24±67.16 1.06±0.09

Images and graphs of macro-dispersion, size distribution, and total area sum of undispersed CNF aggregates were evaluated by 3D laser scanning microscopy at various CNF contents, and the results are shown in FIGS. 7 and 8 . As the CNF content in the PLA matrix increased, the total area of CNF aggregation tended to increase. The size distribution of aggregate diameters in f-CNF/PLA containing 1 wt% CNF is 3 to 250 μm, and the maximum sizes of CNF aggregates observed in e-PLA/CNF and t-PLA/CNF are 260 and 85 μm, respectively. . At a low CNF content, such as 0.25 wt%, there was no difference in the number and area of aggregation for the three samples, but a significant difference was observed as the CNF content increased. When the composite material contains about 1 wt% CNF, the total area of CNF aggregates is reduced by 448% and 211%, respectively, when t-CNF/PLA is compared with f-CNF/PLA and e-CNF/PLA did. The t-CNF/PLA complex containing 1 wt% CNF significantly reduced both CNF aggregates and total area, and this significant reduction demonstrates that the CNF dispersion method using a plasticizer is highly effective.

Experimental example 6: CNF / PLA Mechanical Properties of Nanocomposites

The measured mechanical properties are shown in Tables 3 and 3. The addition of 0.25 wt% CNF to PLA improved the tensile strength of f-CNF/PLA and e-CNF/PLA by 4% and 8%, respectively, depending on the feed method, which was the reinforcing effect of CNF on the PLA matrix. effect) can be attributed to However, in the case of f-CNF/PLA, when the CNF content exceeded 0.5 wt%, the tensile strength was rather decreased. As observed in the morphological results shown in Figures 6 and 7, the mechanical properties deteriorated due to CNF aggregation. However, in the case of the e-CNF/PLA composite prepared using the CNF-ethanol suspension, the tensile strength and Young's modulus were improved as the CNF content increased. The tensile strength of the e-CNF/PLA composite increased from 8% to 12% as the CNF content increased. The elongation at break decreased somewhat, which could be caused by the increase in stiffness and hardness due to inclusion of CNF.

Table 4 shows the mechanical properties of t-PLA and t-CNF/PLA nanocomposites. When PLA was plasticized by TEC, PLA showed a rapid change in mechanical properties dependent on the TEC content. When 12.5 phr of TEC was added, the tensile strength decreased from 71.82 MPa to 35.75 MPa, and the elongation at break increased from 9.50% to 323.62%. Similar to e-CNF/PLA, t-CNF/PLA also improved tensile strength and Young's modulus by increasing CNF content. Compared with t-PLA, the tensile strength of the nanocomposite increased by 11 to 20% and the Young's modulus by 13 to 68% with the increase in CNF content. This indicates that the mechanical properties of PLA, which were reduced by the plasticizing effect, were successfully improved due to the loading of CNFs.

Interestingly, even though the content of CNF increased up to 1 wt% in t-PLA, the elongation at break value did not decrease significantly, indicating elongation above 300%, indicating that TEC is well distributed between the interface of PLA and CNF and This may be due to the fact that the location induces a slippery effect.

To closely examine the potential reinforcement effect of CNF, the theoretical model developed by Cox and Krenchel was applied and compared with experimental values. It is well known as a reasonable model for predicting theoretical modulus data of composites through melting processes such as compounding and injection. The theoretical elongation modulus according to the fiber content was calculated through Equation 5-8.

(5)

(5)

η _l and η _o are a length correction factor and an orientation factor, respectively. When the fibers are randomly oriented in the plane, the orientation factor is 3/8. The volume fraction of CNF was calculated using Equation 6.

(6)

(6)

Here, w _CNF is the weight fraction of _CNF, and ρ CNF and ρ _matrix are the densities of CNF and the polymer matrix: ρ _CNF = 1.50 g/cm ³ and ρ _matrix = 1.24 g/cm ³ .

(7)

(7)

(8)

(8)

Here, l is the CNF length, and r is the radius or width. R/r is predicted to be (K _r / V _f ) ^1/2 , when square packing is considered, Kr is π.

The elongation values of PLA were applied to the experimental values of pure PLA and t-PLA given as GPa and 0.63 GPa, respectively. The elongation modulus value of CNF was used as 107 GPa from the reference [39]. The length of CNF was predicted to be 10 μm, and its width was chosen to be 32 μm based on the results of SEM analysis. The volume percentages of CNF were determined to be about 0.21%, 0.41% and 0.83%, respectively.

FIG. 9 shows values of elongation modulus predicted as a function of an arbitrary distribution of fiber-type reinforcing fillers in a polymer matrix through the Cox-Krenzel model. f-CNF/PLA containing 1 wt% CNF shows a decrease in the elongation modulus due to the aggregation of CNF. However, the t-CNF/PLA and e-CNF/PLA nanocomposites are in good agreement with the elongation modulus predicted through the Cox-Krenzel model, indicating that CNF was successfully dispersed in the PLA matrix by using a solvent. Compared with pure PLA, the tensile strength and modulus of t-PLA were decreased due to plasticization, but these mechanical properties were improved due to the successful dispersion of CNF. Based on these results, it was confirmed that the t-CNF/PLA nanocomposite with high mechanical properties and high elongation at break has significant potential in the field of flexible packaging.

Experimental example 7: CNF / PLA of nanocomposites oxygen barrier (Oxygen Barrier Properties)

It is widely known that PLA has poor oxygen barrier properties. Table 5 shows the oxygen permeability of pure PLA, f-CNF/PLA and e-CNF/PLA nanocomposites. As a result, pure PLA exhibited an oxygen permeability value of about 32.26 ± 1.24 cc·mm/m ^{2 ·day·atm.} Several factors affecting oxygen permeability include polymer internal structure, molecular weight, polymer crystallinity, molecular chain entanglement, and processing technique. Here, the CNF/PLA nanocomposite was prepared in the form of a film over a two-step process, and thus, some thermal degradation of the polymer was expected, leading to a slight increase in oxygen permeability.

sample Oxygen permeability (cc·mm/m ² ·day·atm) pure PLA 32.26±1.24 t-PLA 34.54±2.17 f-CNF/PLA 0.25 31.55±0.08 e-CNF/PLA 0.25 32.87±0.55 t-CNF/PLA 0.25 21.23±0.40 f-CNF/PLA 0.5 22.52±0.07 e-CNF/PLA 0.5 26.43±0.24 t-CNF/PLA 0.5 18.41±0.07 f-CNF/PLA 1 29.86±0.12 e-CNF/PLA 1 15.88±1.36 t-CNF/PLA 1 16.99±0.85

Aulin et al. reported an oxygen permeability value of ^{0.00006 cc·mm/m 2} ·day·atm at 23°C and 0% RH for a 5 μm nanocellulose thin film. Cellulose, a highly oxygen-blocking material, was distributed or dispersed in the PLA matrix to form a nanocomposite, and it was confirmed that the oxygen barrier property was improved compared to pure PLA. On the other hand, f-CNF/PLA containing 1 wt% CNF showed an increase in oxygen permeability compared to f-CNF/PLA 0.5, which is CNF that forms a chin and crack at the interface between PLA and CNF. may be due to aggregation of Similar to the results for mechanical properties, it was confirmed that the uniform dispersion of CNF in the PLA matrix affects the improvement of oxygen barrier properties. On the other hand, the e-CNF/PLA sample showed a decrease in oxygen permeability consistent with an increase in CNF content.

As shown in Table 5, t-PLA containing 12.5 phr TEC exhibited increased oxygen permeability compared to pure PLA. The same trend was observed for mechanical properties in that plasticization induced a negative effect on oxygen barrier properties induced from disentanglement of PLA chains. However, the oxygen barrier performance was improved by the uniform dispersion of CNF in the PLA matrix. In addition, in the amorphous region of PLA, CNF had limited chain movement and caused entanglement of polymer chains, resulting in a decrease in oxygen permeability. This was confirmed by the results shown in FIG. 10 , which was reduced by 47.3% compared to pure PLA in the t-CNF/PLA sample containing 1 wt% CNF. Similar to the result of improving the oxygen barrier properties, it is suggested that the oxygen barrier film can be produced smoothly through the melting process method using CNF compared to the coating method.

Experimental example 8: CNF / PLA Dynamic Mechanical Properties of Nanocomposites

10 is a diagram showing the elastic modulus and tan delta as a function of temperature for pure PLA and CNF/PLA nanocomposites. In general, it is known that the presence of CNFs in a polymer matrix improves the modulus of elasticity. Similar results were also confirmed in the present invention. The modulus of elasticity of the f-CNF/PLA and e-CNF/PLA nanocomposites at 66.41°C was higher than the values for pure PLA according to the CNF content. The f-CNF/PLA nanocomposite containing 0.5 wt% CNF showed an increased tan delta peak by 3°C, and the tan delta peak intensity was decreased compared to pure PLA. From this, it can be seen that the polymer chain is not involved in this glass transition behavior. The increase in elastic modulus and shift of the tan delta peak may be due to the physical interaction between the CNF and the polymer, which limits the segmental mobility of the polymer chain adjacent to the nanofiber. However, for the f-CNF/PLA nanocomposite, the elastic modulus and tan delta peaks did not increase regularly with increasing CNF content, which can be seen as a result of the non-uniform dispersion of CNF within the PLA matrix. could The tan delta peak of the f-CNF/PLA nanocomposite containing 1 wt% CNF was reduced by 4°C compared to the f-CNF/PLA nanocomposite containing 0.5 wt%. This was confirmed by the fact that CNF aggregation was restricted in the polymer amorphous region and growth was inhibited, promoting the glass transition behavior.

In Fig. 10(d), the e-CNF/PLA nanocomposite containing 0.25 wt% CNF decreased the tan delta peak by 2.54 °C compared to pure PLA, which is attributed to the hydrolysis of PLA by non-evaporated trace amounts of ethanol. . However, due to the increase of the CNF content, the tan delta peak showed a tendency to gradually improve. In addition, the modulus of elasticity at 66.41 °C showed a gradual increase with increasing CNF content, which was significantly improved compared to that of pure PLA. PLA showed a decrease in the tan delta peak at 18.16°C at a TEC content of 12.5 phr, but this was recovered by successful dispersion of CNF. Oksman and co-workers reported that nanocomposites containing 1 wt% CNF were prepared and the tan delta peak increased from 70°C to 71°C compared to pure PLA. was reported to increase from 57.5°C to 58.9°C. However, in the present invention, it was confirmed that the tan delta peak significantly increased from 48.25 to 52.89° C. in the t-CNF/PLA nanocomposite containing 1 wt% CNF compared to plasticized PLA (t-PLA). This led to the uniform dispersion of CNF achieved by the TEC-CNF suspension technique, leading to chain entanglement as successful CNF dispersion in the amorphous region of the polymer matrix.

Experimental example 9: t- PLA and t- CNF / PLA In nanocomposites, plasticizers ( plasticizer ) of Migration Properties

t-PLA and t-CNF/PLA nanocomposites can be used as food and pharmaceutical packaging materials. The issue of migration of plastics from packaging to product can be an important factor in designing packaging based on flexible materials. By returning to the brittleness of PLA itself, it can affect its mechanical properties, particularly its flexibility. 11 shows the mass loss of plasticizer in t-PLA and t-CNF/PLA nanocomposites occurring over time at a temperature of 110° C., with t-PLA showing a linear increase in mass loss of plasticizer up to 60 min. It was. The t-CNF/PLA nanocomposite also showed similar mass loss behavior, but the mass loss of the plasticizer was relatively slow compared to that of t-PLA. At the initial stage, the difference in elapsed time between t-PLA and t-CNF/PLA nanocomposites was 100 min when a mass loss of 6 wt% of the plasticizer occurred, and the difference in mass loss was , when the peak almost reached equilibrium, it was about 1 wt%. This indicates that CNF can slow the movement of plasticizers in the nanocomposite by the strong interaction between TEC and CNF. Furthermore, in the initial stage where about 65% mass loss occurs, as the content of CNF in the t-CNF/PLA nanocomposite increases, the mass loss of the plasticizer tends to decrease. These results can be supported by Fig. 1(b), which shows that TECs were coated on the surface of CNFs. It was hypothesized that the difference in the mass loss rate of the plasticizer depends on the increase in the surface area of the CNF matrix interacting with the TEC as the CNF content increases.

As shown in FIG. 12 showing the mechanical properties after drying in a vacuum oven, t-PLA showed an increase in tensile strength and a decrease in elongation at break continuously until a drying time of 400 minutes, and the t-CNF/PLA nanocomposite was 30 From the drying time of minutes, the values of tensile strength and elongation at break were almost constant, respectively. These results indicate that the CNFs contained in the t-CNF/PLA nanocomposite experience little change in mechanical properties due to the migration of the plasticizer compared to t-PLA due to the interaction with the TEC. Due to the interaction of TEC and CNF, the amount of TEC located at the interface between PLA and CNF increases with increasing CNF content. As a result, the tensile strength decreases and the elongation increases due to the slippery effect. However, the t-CNF/PLA nanocomposite containing 1 wt% CNF showed a different trend. This is presumably due to the lack of a sufficient amount of TEC to achieve a lubricating effect at the interface between PLA and CNF as the plasticizer migrates.

<Conclusion>

In the previous experiment, the optimal content of plasticizer was determined through mechanical property analysis according to the TEC content for PLA. TEC-CNF suspensions were prepared with varying CNF contents (0.25, 0.5, and 1 wt%) in a solvent mixture consisting of TEC and ethanol. CNF/PLA nanocomposites were prepared by a 7-minute melt mixing process. From the zeta potential results, it was confirmed that CNF was more uniformly dispersed in the solvent by the inclusion of TEC, and the dispersion of CNF in the PLA matrix was significantly improved during the melt mixing process. In the present invention, it was confirmed that CNF was successfully dispersed in the PLA matrix using the TEC-CNF suspension through the results of rheological and morphological properties. Compared with t-PLA, the tensile strength of the nanocomposite improved by 11 to 20% and Young's modulus by 13 to 68% as the CNF content increased. In addition, the elongation value exceeded 300%, and the flexibility was improved, so that it could be used in the field of flexible packaging. In terms of oxygen barrier properties, the t-CNF/PLA sample containing 1 wt% of CNF was reduced by 47.3% compared to pure PLA. As a result of the improvement of the oxygen barrier properties, this indicates that the oxygen barrier film can be produced by a melt process method using CNF rather than a coating method.

In the t-CNF/PLA nanocomposite containing 1 wt% CNF, it was confirmed that the tan delta peak was significantly increased from 48.25°C to 52.89°C compared to t-PLA. In addition, it was demonstrated that, due to the interaction of CNFs with TECs, the transport of plasticizers was slowed. As an eco-friendly material, the t-CNF/PLA nanocomposite prepared from a fully bio-based material has the potential to be applied to various biodegradable flexible packaging materials.

From the above description, those skilled in the art to which the present invention pertains will understand that the present invention may be embodied in other specific forms without changing the technical spirit or essential characteristics thereof. In this regard, it should be understood that the embodiments described above are illustrative in all respects and not restrictive. The scope of the present invention should be construed as being included in the scope of the present invention, rather than the above detailed description, all changes or modifications derived from the meaning and scope of the claims described below and their equivalents.

Claims (12)

0.3 to 3 parts by weight of cellulose nanofiber (CNF) based on 100 parts by weight of the solvent is dispersed in a (15 to 25) weight %: (75 to 85) weight % mixed solvent of a plasticizer and ethanol to form a suspension. the first step of preparing; and
A second step of mixing the suspension through a melting process so that the content of the thermoplastic resin and the plasticizer is 11 to 18 phr (parts per hundred rubber); including,
Method for producing a thermoplastic resin/cellulose nanofiber nanocomposite.
According to claim 1,
The method of claim 1, wherein the plasticizer is triethyl citrate (TEC).
According to claim 1,
The method of claim 1, wherein the thermoplastic resin is polylactic acid (PLA).
According to claim 1,
In the first step, the dispersibility of CNF in the thermoplastic resin is improved compared to the nanocomposite prepared under the same conditions using only ethanol as a solvent.
According to claim 1,
In the first step, the total area of the CNF aggregates dispersed in the thermoplastic resin is reduced by 150 to 250% compared to the nanocomposite prepared under the same conditions using only ethanol as a solvent.
According to claim 1,
Without the first step, to provide a thermoplastic resin / cellulose nanofiber nanocomposite having a tensile strength increased by 10 to 25% compared to the resin prepared by mixing only the same amount of the plasticizer in the second step, the manufacturing method.
According to claim 1,
Without the first step, to provide a thermoplastic resin / cellulose nanofiber nanocomposite having a Young's modulus increased by 10 to 70% compared to the resin prepared by mixing only the same amount of the plasticizer in the second step, the manufacturing method.
According to claim 1,
To provide a thermoplastic resin / cellulose nanofiber nanocomposite having an elongation value of 300% or more, a manufacturing method.
An oxygen barrier film formed of a nanocomposite prepared by the method of any one of claims 1 to 8.
10. The method of claim 9,
Compared to the oxygen barrier film formed of a pure thermoplastic resin prepared to the same thickness or a thermoplastic resin composite containing the same amount of plasticizer but not containing cellulose nanofibers, the oxygen permeability is reduced to a level of 70 to 45%, the oxygen barrier film.
A food or drug packaging material comprising a nanocomposite prepared by the method of any one of claims 1 to 8.
12. The method of claim 11,
The nanocomposite has a plasticizer migration rate of less than 5% by weight up to 100 minutes, and a packaging material that exhibits a migration rate reduced by 20% compared to a nanocomposite containing no cellulose nanofibers.

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