KR20230116655A - Method for manufacturing polylactic acid/chitin nanofiber composite, its composite manufactured thereby and film using the same - Google Patents

Abstract

The present invention relates to a method for preparing a polylactic acid (PLA)/chitin nanofiber composite, a composite prepared therefrom, and a film including the same.
The present invention utilizes chitin nanofibers as a reinforcing material and introduces a Pickering emulsion and a twin-screw extrusion process using the chitin nanofibers modified through chemical and physical methods to obtain an interface between a hydrophobic PLA solution and a hydrophilic chitin nanofiber dispersion. The chitin nanofibers act as a surfactant and are prepared as a stable emulsion solution to provide a PLA / chitin nanofiber composite in which the chitin nanofibers are evenly dispersed in the PLA matrix and composited, and have excellent mechanical properties (especially ductility) PLA composites can be applied with various film materials.

Description

Manufacturing method of PLA/chitin nanofiber composite, composite produced therefrom, and film containing the same

The present invention relates to a method for producing a polylactic acid (hereinafter referred to as "PLA")/chitin nanofiber composite, a composite prepared therefrom, and a film including the same, and more specifically, to utilizing chitin nanofiber as a reinforcing material, Method for producing a PLA/chitin nanofiber composite with significantly improved mechanical properties (particularly, ductility) by introducing surface-modified chitin nanofibers, Pickering emulsion, and twin-screw extrusion process through chemical and physical methods, and manufacturing therefrom It relates to a composite and a film comprising the same.

As the problem of environmental pollution due to synthetic plastic and petrochemical-based plastic waste increases, research on eco-friendly, recyclable and compostable biodegradable bioplastics is being actively conducted.

PLA is derived from plants such as corn starch and has attracted much attention as a material that can replace existing plastics because it has advantages such as non-toxicity and biocompatibility as well as biodegradability.

Nevertheless, PLA has its own limitations, such as low thermal stability and brittleness, so its application is very limited mainly to the medical field and filament for 3D printers.

Therefore, various attempts have been made to improve and improve the thermal stability and mechanical properties of PLA. For example, addition of plasticizers or compatibilizers, addition of nucleating agents, addition of inorganic nanoparticles, inorganic fibers (glass fibers, carbon fibers) ), various methods such as addition have been proposed [Patent Documents 1 and 2].

However, the addition of inorganic materials causes another disadvantage that recycling is difficult because decomposition by heat is very difficult.

Patent Document 3 discloses a heat-resistant polylactic acid compound that overcomes the disadvantage of polylactic acid (PLA), which lacks thermal stability, by using talc together with an organic acrylic impact modifier.

In addition, Patent Document 4 also uses a specific vegetable polyol as a plasticizer to improve the mechanical properties of tensile strength and elongation of PLA; acetyl tributyl citrate; And by including polyethylene glycol, a PLA composition with improved physical properties is disclosed.

Therefore, the application of natural polymers has been proposed as a reinforcing material to improve the mechanical properties and thermal stability of PLA.

Chitin is the most abundant natural polymer on earth next to cellulose. It is biodegradable, non-toxic and biocompatible like PLA, and has a high aspect ratio and surface area very similar to glass fibers and carbon fibers.

However, when hydrophobic PLA and hydrophilic chitin are combined, the chitin component is aggregated by the hydroxyl group of chitin, which may adversely affect the mechanical properties of the composite.

Accordingly, the inventors of the present invention, as a result of efforts to solve the conventional problems, introduced a Pickering emulsion and a twin-screw extrusion process using surface-modified chitin nanofibers as a reinforcing material through chemical and physical methods, and a hydrophobic PLA solution and At the interface of the hydrophilic chitin nanofiber dispersion, the chitin nanofibers act as a surfactant to prepare a stable emulsion solution, and evenly disperse the chitin nanofibers in the PLA matrix to provide a composite PLA / chitin nanofiber composite. By confirming the excellent mechanical properties (especially ductility) of the composite, the present invention was completed.

Patent Publication No. 2021-01106859 (2021.09.08. Publication) Patent Registration No. 10-1022786 (2011.03.17. Notice) Patent Publication No. 2014-0058652 (published on May 14, 2014) Patent Registration No. 10-1875130 (2018.08.02. Notice)

One object of the present invention is to provide a method for producing a PLA/chitin nanofiber composite.

Another object of the present invention is to provide a PLA/chitin nanofiber composite having improved mechanical properties prepared from the manufacturing method of the PLA/chitin nanofiber composite of the present invention and a film including the same.

The present invention is a first step of stabilizing droplets containing chitin nanofibers in the PLA as an emulsion solution by adding a chitin nanofiber dispersion in which chitin nanofibers are dispersed in water to a PLA solution dissolved in an organic solvent, the emulsion A method for producing a PLA/chitin nanofiber composite comprising a second step of drying the solution to form a composite material in which chitin nanofibers are dispersed in a PLA matrix and a third step of molding the composite material is provided.

More specifically, based on 100 parts by weight of the PLA solution dissolved in the organic solvent, 0.5 to 10 parts by weight of a chitin nanofiber dispersion in which chitin nanofibers are dispersed in water is added to stabilize the emulsion solution, and the emulsion solution is water- It is a water-in-oil (W/O) formulation.

In the first step, chitin nanofibers are preferably surface-modified chitin nanofibers by succinylation or carboxylation.

In one embodiment, in the first step, the chitin nanofiber dispersion may be formed by surface-modifying the chitin nanofibers by succinylation or carboxylation and then dispersing them in water.

In addition, in the first step, the chitin nanofiber dispersion may be formed by surface-modifying the chitin nanofibers by succinylation or carboxylation, converting them into nanofibers using an aqueous counter collision (ACC) method, and then dispersing in water.

The chitin nanofibers may have a diameter of 5 to 50 nm.

The content of the chitin nanofibers is to include 1 to 3% by weight, more preferably 1.5 to 2.5% by weight based on the total weight of the PLA.

In the first step, the organic solvent may be any one selected from the group consisting of dichloromethane (DCM), chloroform, ethyl acetate, tetrahydrofuran, and acetone.

The present invention provides a PLA/chitin nanofiber composite based on a water-in-oil (W/O) formulation in which chitin nanofibers are dispersed in a PLA matrix.

The chitin nanofibers may be surface-modified chitin nanofibers by succinylation or carboxylation.

The content of the chitin nanofibers is to include 1 to 3% by weight, more preferably 1.5 to 2.5% by weight based on the total weight of the PLA.

Furthermore, the present invention provides a film comprising a PLA/chitin nanofiber composite having improved mechanical strength.

According to the present invention, chitin nanofibers are used as a reinforcing material, and chitin nanofibers are uniformly applied to the PLA matrix through a Pickering emulsion and a twin-screw extrusion process using the chitin nanofibers modified through chemical and physical methods. can provide a dispersed PLA/chitin nanofiber composite.

In addition, by controlling the mechanical properties of PLA according to the content of the chitin nanofibers, it is possible to provide a PLA/chitin nanofiber composite that solves the problem of brittleness of the PLA material.

Figure 1 is a scanning electron microscope (Scanning electron microscope) image according to the pretreatment of chitin, (a) raw material ChNF, (b) SChNF subjected to succinylation or carboxylation, (c) nano through ACC finally It is SChNF with advanced fibrosis.
2 is a PLA/chitin nanofiber emulsion solution of the present invention;
Figure 3 is a tensile test result for the PLA / SChNF composite according to the content of the chitin nanofibers of the present invention,
4 is an image of a specimen subjected to a tensile test on the PLA/SChNF composite according to the content of the chitin nanofibers of the present invention;
5 is a SEM image of the fracture surface after a tensile test for the PLA / SChNF composite according to the content of the chitin nanofibers of the present invention,
6 is a melt flow index evaluation result for the PLA / SChNF composite of the present invention,
Figure 7 shows the fluorescence characteristics according to the dissolution of each solvent of the staining agent for confocal microscopy of the emulsion solution,
8 is a confocal microscope image of the emulsion solution of Example 3 and a SEM image of a cross-section of a sheet in which the solvent was completely dried;
9 is a confocal microscope image of the emulsion solution of Comparative Example 2 and a SEM image of a cross-section of a sheet in which the solvent is completely dried;
10 is a result of the mechanical properties of the composite according to the emulsion formulation.

Hereinafter, the present invention will be described in detail.

The present invention is a first step of stabilizing droplets containing chitin nanofibers in the PLA as an emulsion solution by adding a chitin nanofiber dispersion in which chitin nanofibers are dispersed in water to a PLA solution dissolved in an organic solvent, the emulsion A method for producing a PLA/chitin nanofiber composite comprising a second step of drying the solution to form a composite material in which chitin nanofibers are dispersed in a PLA matrix and a third step of molding the composite material is provided.

In the manufacturing method of the present invention, the chitin nanofiber used in the first step is one of natural polymers, and is used as a reinforcing material to improve the mechanical properties of PLA in the present invention, depending on the content of the chitin nanofiber. characteristics can be controlled.

The chitin nanofibers of the present invention may use chitin nanofibers (ChNF) of the material itself, which are not surface-modified, or chitin nanofibers surface-modified by succinylation or carboxylation.

Preferably, chitin nanofibers surface-modified by succinylation or carboxylation are used. In an embodiment of the present invention, chitin nanofibers are reacted with succinic anhydride to use succinylated surface-modified chitin nanofibers (SChNF). However, it will not be limited to this.

More specifically, in the first step, the chitin nanofiber dispersion may be formed by surface-modifying the chitin nanofibers by succinylation or carboxylation and then dispersing them in water. In one example, the succinylation is performed by reacting chitin nanofibers with succinic anhydride (SA).

In addition, in the first step, the chitin nanofiber dispersion may be formed by surface-modifying the chitin nanofibers by succinylation or carboxylation, converting them into nanofibers using an aqueous counter collision (ACC) method, and then dispersing in water.

Surface modification of chitin nanofibers can create an electrostatic repulsive force between the nanofibers, enabling a high degree of nanofibrillation during ACC treatment.

In the first step, the emulsion solution may be prepared through a Pickering emulsion method.

The Pickering emulsion method is a method of preparing a stabilized emulsion by reducing interfacial tension at a hydrophobic/hydrophilic interface using small solid particles instead of a surfactant.

In the present invention, the chitin nanofibers act as a surfactant at the interface between the hydrophobic PLA solution and the hydrophilic chitin nanofiber dispersion during the first step, so that a stable emulsion solution can be prepared, and thus the PLA and chitin nanofibers Fibers can be composited.

Figure 1 is a scanning electron microscope (Scanning electron microscope) image results according to the pretreatment of chitin, (a) is the raw material ChNF, (b) is SChNF subjected to succinylation or carboxylation, (c) is the final ACC 2 is the PLA/chitin nanofiber emulsion solution of the present invention.

From the above results, chitin nanofibers treated with surface modification and aqueous counter collision (ACC) can have lower turbidity and smaller nanofiber diameter compared to chitin nanofibers treated only with surface modification.

The chitin nanofibers may be nanofibers having a diameter of about 5 to 50 nm. At this time, when the diameter of the chitin nanofibers exceeds about 50 nm, it is difficult to effectively suppress the phase separation of the emulsion solution, which may cause problems in preparing a stabilized emulsion solution.

The emulsion solution stabilized in the first step of the present invention is stabilized as an emulsion solution by adding 0.5 to 10 parts by weight of a chitin nanofiber dispersion in which chitin nanofibers are dispersed in water, based on 100 parts by weight of the PLA solution dissolved in the organic solvent, , The emulsion solution is a water-in-oil (W/O) formulation.

The organic solvent may be any one selected from the group consisting of dichloromethane (DCM), chloroform, ethyl acetate, tetrahydrofuran, and acetone. In the embodiment of the present invention, dichloromethane (DCM) is used as a preferred organic solvent, but it will not be limited thereto.

In the first step, the content of chitin nanofibers may be 1 to 3% by weight based on the total weight of PLA. At this time, if the chitin nanofibers exceed 3% by weight, there is a problem in that the chitin nanofibers in the PLA matrix are excessively added and not evenly dispersed, which can rather deteriorate the mechanical properties.

More preferably, the content of the chitin nanofibers in the nanofiber dispersion is about 1.5 to 2.5% by weight based on the total weight of PLA.

In the manufacturing method of the present invention, the drying performed in the second step may be performed through natural drying, freeze drying, hot air drying, vacuum drying, etc., and if the composite material is not damaged, the drying method in the present invention is not particularly limited. Preferably, the drying may be performed by casting the emulsion solution on a substrate and drying.

After the second step and before performing the third step, the composite material may be additionally subjected to a crushing step to facilitate the twin-screw extrusion process. For example, the composite material may be ground into pieces less than about 5 mm in length.

Molding in the third step may be performed as a twin-screw extrusion process through a twin-screw extruder. Twin-screw extrusion is a method of forming a product by continuously extruding a material by heating and fluidizing it using two screws, and has the advantage of stably extruding heat-sensitive materials because extrusion is possible even at a low temperature.

In addition, the twin-screw extrusion process has the advantage of obtaining a PLA/chitin nanofiber composite in which the chitin nanoparticles are uniformly dispersed because the residence time of the composite material is relatively uniform in the twin-screw extrusion apparatus.

The present invention provides a water-in-oil (W/O) formulation-based PLA/chitin nanofiber composite in which chitin nanofibers are dispersed in a PLA matrix, prepared from the above preparation method.

As the chitin nanofibers, chitin nanofibers (ChNF) of the material itself, which are not surface-modified, or chitin nanofibers surface-modified by succinylation or carboxylation may be used.

More preferably, chitin nanofibers surface-modified by succinylation or carboxylation are used. In an embodiment of the present invention, chitin nanofibers are reacted with succinic anhydride to obtain surface-modified chitin nanofibers (SChNF) through succinylation. It will be used to explain, but will not be limited thereto.

Figure 3 is the result of the tensile test for the PLA / SChNF composite according to the content of the chitin nanofibers of the present invention, pure PLA (NEAT PLA) has an elongation of about 4.8% due to the inherent brittleness of the material, whereas the chitin of the present invention In all PLA/SChNF composites prepared according to the content of nanofibers of 1 to 3% by weight, the elongation rate was increased by about 6 times and about 74 times at most. In particular, the composite containing 2% by weight of SChNF showed a significantly higher elongation than other composites, supporting that it was most evenly dispersed in PLA.

In addition, when the content of SChNF is 3% by weight, it is difficult to disperse in the matrix resin, resulting in a decrease in mechanical properties (particularly, ductility). More preferably, the content of SChNF is optimized to 1.5 to 2.5% by weight. do.

4 shows images of specimens subjected to tensile tests on PLA/SChNF composites according to the content of chitin nanofibers. In the case of composites containing 2% by weight of SChNF, the elongation rate is significantly higher than that of composites containing 1% by weight and 3% by weight of SChNF. It can be visually confirmed that this is a high quality material.

Figure 5 is a SEM image of the fracture surface after a tensile test for the PLA / SChNF composite according to the content of chitin nanofibers of the present invention. Pure PLA has a relatively clean fracture surface, which is a characteristic of brittleness, while the fracture surface of the PLA / ShCNF composite is A very rough surface can be seen.

In addition, in the PLA / SChNF composite of the present invention, Figure 6 is the result of melt flow index evaluation for the PLA / SChNF 2% by weight composite, and the MFI of polymers used as blown film products is usually 1 to 10, since the MFI value of the 2% by weight PLA/SChNF composite of the present invention satisfies 1.66, the PLA/chitin nanofiber composite of the present invention can be used as a blown film.

In the PLA/chitin nanofiber composite of the present invention, the chitin nanofibers act as a surfactant at the interface between the hydrophobic PLA solution and the hydrophilic chitin nanofiber dispersion through the Pickering emulsion method, resulting in a stable emulsion solution can be prepared, and thus the PLA and chitin nanofibers can be composited.

At this time, the PLA/chitin nanofiber composite of the present invention can stably and uniformly disperse the chitin nanofibers in the PLA matrix from the water-in-oil (W/O) formulation base.

Figure 7 shows the fluorescence characteristics according to the solvent-specific dissolution of the dye for confocal microscopy of the emulsion solution. It is insoluble and therefore does not fluoresce.

8 shows a confocal microscope image of an emulsion solution of a water-in-oil (W/O) formulation of the present invention and a SEM image of a cross-section of a sheet in which the solvent is completely dried. On the other hand, FIG. 9 contrasts the same experimental results for emulsion solutions of oil-in-water (O/W) formulations.

The water-in-oil (W/O) formulation is a PLA/DCM solution wrapped around a spherical fluorescent SChNF dispersion, whereas an oil-in-water (oil-in-water) formulation water, O/W) formulation is an inverted structure in which a fluorescent SChNF dispersion (suspension) surrounds a black spherical PLA/DCM solution.

This inverted structure shows a stark difference even in the SEM image of the cross section of the sheet where the organic solvent and distilled water are completely dried in the emulsion state. From the emulsion solution of the water-in-oil (W/O) formulation of the present invention The prepared composite shows a form in which fine spherical chitin nanofibers are dispersed in the PLA matrix, and uniformly dispersed on at least a part or the entire surface of the PLA matrix.

Therefore, the composite of the water-in-oil (W/O) formulation of the present invention makes the dispersion of chitin nanofibers uniform in the PLA matrix and serves as a reinforcement or nanofiller. or through hydrogen bonding with PLA, the mechanical properties of the composite can be significantly improved.

Figure 10 compares the mechanical properties of the composites according to the emulsion formulation, and it can be seen that the composites of the O / W formulation have significantly lower mechanical properties than the composites of the W / O formulation. On the other hand, in the case of the W / O formulation, the toughness dramatically increases with the increase in elongation, and this improvement in mechanical properties is due to the increased dispersion of SChNF inside the PLA matrix.

Furthermore, the present invention provides a film including a PLA/chitin nanofiber composite having excellent mechanical properties.

The above composite has the advantage of being easily applicable to the fields of packaging, 3D printing materials, structural lightweight composite materials, and medical technology.

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

These examples are intended to explain the present invention in more detail, and the scope of the present invention is not limited to these examples.

<Examples 1 to 5>

① Reagents and Materials

Products from NatureWorks (USA) were used for PLA, and chitin, pyridine, and sodium hydroxide (NaOH) were purchased from Sigma-Aldrich. Succinic anhydride (SA) was from Daejung Chemical, and dimethylformamide (DMF), pyridine, sodium hydroxide (NaOH), and dichloromethane (DCM) were from Sigma-aldrich. Purchased. A Homogenizer (IKA, T25) and an Ultrasonicator (SONICS, vibra cell VCX 500) were used for complexation through the formation of a Pickering emulsion of PLA and ChNF. A twin screw extruder (TSE) and an injection molding machine were used to manufacture composites using composite materials. The heater of the twin-screw extruder is divided into 4 sections from the sample hopper to the final extrusion port, and was set at 180-185-190-195 ° C, respectively.

② Surface modification and nanofiberization of chitin nanofibers (SChNF production)

After adding chitin and pyridine to DMF in which succinic anhydride (SA) was dissolved, the mixture was reacted while heating at 120° C. for 6 hours. Thereafter, chitin was completely washed with deionized water and ethanol using a centrifuge, and the chitin dispersion was neutralized with NaOH solution to prepare a surface-modified chitin dispersion. The surface-modified chitin was finally nanofibrous (SChNF) by the ACC system (CNNT CO., Ltd., Korea).

③ Preparation of PLA/chitin nanofiber composite (PLA/SChNF)

The PLA/SChNF composite was prepared using a combination of the Pickering emulsion method and TSE equipment. A PLA solution in which 5% by weight of PLA was dissolved in DCM and a dispersion of SChNF at a concentration of 1% by weight were prepared. The SChNF dispersion was mixed to be 1% by weight, 2% by weight, and 3% by weight, respectively, based on the total PLA of the PLA solution and stabilized as an emulsion solution. After that, the emulsion solution was prepared by treating with a homogenizer and an ultrasonicator for 2 minutes and 1 minute, respectively. The emulsion solution was cast in a glass Petri dish, and both the organic solvent (DCM) and water present in the emulsion solution were dried to prepare a composite material. The dried composite material was pulverized into a size of about 3 to 5 mm using a hand blender, and final composite was performed using TSE equipment.

<Example 6> Preparation of PLA/ChNF complex

A PLA / ChNF complex was prepared in the same manner as in Example 1 except for using a PLA solution in which 5% by weight of PLA was dissolved in DCM and a dispersion containing 2% by weight of ChNF relative to the total PLA. .

<Comparative Example 1>

Pure PLA (Neat PLA) was prepared.

<Comparative Example 2>

In the PLA/SChNF composite manufacturing step of Example 1, a PLA solution in which 5% by weight of PLA was dissolved in DCM and an SCNF dispersion containing 2% by weight of SChNF relative to the total PLA were prepared, and the SChNF dispersion was added to 100 ml of the PLA solution It was carried out in the same manner as in Example 1, except that 200 ml was mixed and stabilized with an emulsion solution.

<Experimental Example 1> Evaluation of nanofibrillation and emulsion

Figure 1 is a scanning electron microscope (Scanning electron microscope) image according to the pretreatment of chitin, (a) raw material ChNF, (b) SChNF subjected to succinylation or carboxylation, (c) nano through ACC finally SChNF with advanced fibrosis.

Referring to FIG. 1, after surface modification by succinylation or carboxylation and nanofibrous formation, SChNF having a uniform diameter of about 5 to 20 nm was finally confirmed.

Figure 2 is a PLA/chitin nanofiber emulsion solution of the present invention, and no phase separation was observed.

<Experimental Example 2> Tensile test ①

A tensile test was performed on the PLA/SChNF composites prepared according to the chitin nanofiber content in Examples 1 to 6.

Tensile tests were measured using a universal testing machine (UTM) (AMETEK, LS5, USA), and specimens were prepared according to ASTM D638 standards. The results are shown in Table 1 and FIG. 3 below.

From the results of Table 1 and FIG. 3, compared to the result of pure PLA (NEAT PLA) having an elongation of only about 4.8% due to the inherent brittleness of the material, the PLA / SChNF composite prepared in Examples 1 to 5 of the present invention In this case, it was confirmed that the elongation rate increased by about 6 times at a minimum and about 74 times at a maximum.

In particular, since the composite containing 2% by weight of SChNF shows a significantly higher elongation of 351.8% than other composites, the content of SChNF in the PLA matrix is optimized to 1 to 3% by weight, more preferably 1.5 to 2.5% by weight. . At this time, when the SChNF content is 3% by weight, the mechanical properties are lowered, which supports the result that in a general composite system, as the amount of reinforcing agent increases, dispersion in the matrix resin becomes difficult, thereby reducing mechanical properties. .

In addition, the PLA/ChNF composite prepared in Example 6 also showed 6 times improved elongation compared to pure PLA.

<Experimental Example 3> Tensile test ②

4 is an image of a specimen subjected to a tensile test on the PLA/SChNF composites of Examples 1, 3, and 5 prepared according to the content of chitin nanofibers. In the case of the composite containing 2% by weight of SChNF, 1 weight and 3 weight It was confirmed that the elongation rate was significantly higher than that of the composite containing %.

5 is a SEM image of the fracture surface after a tensile test on the PLA/SChNF composite according to the content of the chitin nanofibers of the present invention.

As a result, it can be confirmed that the pure PLA has a relatively clean fracture surface, which is a characteristic of brittleness, while the surface of the fracture surface of the PLA/ShCNF composite is very rough. This can be interpreted as the fact that the evenly dispersed SChNF in the PLA matrix effectively disperses the tensile force. Among them, it was confirmed that the 2 wt% PLA/SChNF composite formed a very dense network.

<Experimental Example 4> Evaluation of melt flow index (MFI)

The melt flow index (MFI) of the PLA/SChNF composite of Example 3 was evaluated.

Melt flow index is an important evaluation factor for evaluating fairness in an extrusion process, and indicates how easily a molten polymer flows under specific conditions. If the MFI value does not reach the standard, the molded extrudate lacks the melt strength to maintain its shape, making it difficult to extrude the product.

6 is a melt flow index evaluation result for the PLA / SChNF composite of Example 3, considering that the MFI of polymers commonly used as blown film products is usually 1 to 10, the PLA / SChNF composite of Example 3 Since the MFI value of the SChNF complex is 1.66, it suggests that the PLA-based chitin complex of the present invention can be used as a blown film.

<Experimental Example 5> Evaluation of emulsion formulation

Each emulsion solution was observed using a confocal microscope in Example 3 and Comparative Example 2 for preparing the PLA/SChNF 2% by weight composite.

Figure 7 shows the fluorescence characteristics according to the solvent-specific dissolution of the dye for confocal microscopy of the emulsion solution. The dye (Fluorescein) is soluble in distilled water (DI water) and emits fluorescence, while the organic solvent (DCM) It is insoluble and therefore does not fluoresce.

8 shows a confocal microscope image of an emulsion solution of a water-in-oil (W/O) formulation of Example 3 and a SEM image of a cross-section of a sheet in which the solvent is completely dried, and FIG. This is a confocal microscope image of the emulsion solution of the oil-in-water (O/W) formulation of Comparative Example 2 and a SEM image of a cross-section of the sheet in which the solvent was completely dried.

In the confocal microscopy image results of FIGS. 9 and 10 , the fluorescently colored part is the SChNF suspension, and the colorless part is the PLA/DCM solution in which PLA is dissolved. Therefore, while the water-in-oil (W/O) formulation of Example 3 was confirmed as a shape in which the PLA/DCM solution wrapped around a spherical fluorescent SChNF dispersion, the comparative example The oil-in-water (O/W) formulation of 2 was confirmed as a shape in which a fluorescent SChNF dispersion (suspension) wrapped around a black spherical PLA/DCM solution.

Clear distinction according to the emulsion formulation of W / O or O / W was also confirmed in the results of fluorescence microscopy images [not shown].

In addition, a clear difference between the W / O formulation and the O / W formulation can be confirmed in the results of the SEM image of the cross section of the sheet in which DCM and distilled water, which are organic solvents, are completely dried in the emulsion state.

That is, in the case of Comparative Example 2, the dispersion in which the chitin nanofibers are dispersed wraps around the spherical PLA matrix, whereas the composite of Example 3 is in the form of the PLA matrix wrapping the fine spheres of the dispersion in which the chitin nanofibers are dispersed. , It shows a uniformly dispersed form on at least a part or the entire surface of the PLA matrix.

<Experimental Example 6> Evaluation of mechanical properties of the composite according to the formulation

The results of measuring the mechanical properties of the PLA/SChNF 2% by weight composites prepared in Example 3 and Comparative Example 2 are shown in Table 2 and FIG. 10 below.

From the above results, there was no significant difference in elastic modulus and tensile strength according to the W/O formulation or O/W formulation, but in the case of the W/O formulation, the toughness increased dramatically with the increase in elongation.

This improvement in mechanical properties is due to the increased dispersion of SChNF inside the PLA matrix.

Although the present invention has been described in detail only with respect to the specific embodiments described above, it is obvious to those skilled in the art that various changes and modifications are possible within the scope of the technical idea of the present invention, and it is natural that such changes and modifications fall within the scope of the appended claims.

Claims (14)

A first step of stabilizing droplets containing chitin nanofibers in the PLA with an emulsion solution by adding a chitin nanofiber dispersion in which chitin nanofibers are dispersed in water to a PLA solution dissolved in an organic solvent,
A second step of drying the emulsion solution to form a composite material in which chitin nanofibers are dispersed in a PLA matrix; and
A method for producing a PLA/chitin nanofiber composite comprising a third step of molding the composite material. According to claim 1, based on 100 parts by weight of the PLA solution dissolved in the organic solvent, 0.5 to 10 parts by weight of chitin nanofiber dispersion in water is added to stabilize the emulsion solution PLA / Manufacturing method of chitin nanofiber composite. The method of claim 1, wherein the chitin nanofibers are surface-modified chitin nanofibers by succinylation or carboxylation. The method for preparing a PLA/chitin nanofiber composite according to claim 1, wherein the chitin nanofiber dispersion is formed by surface-modifying the chitin nanofibers by succinylation or carboxylation and then dispersing them in water. The method of claim 1, wherein the chitin nanofiber dispersion is formed by surface-modifying the chitin nanofibers by succinylation or carboxylation, converting them into nanofibers using an aqueous counter collision (ACC) method, and then dispersing them in water. A method for producing a PLA/chitin nanofiber composite. The method of claim 1, wherein the chitin nanofibers have a diameter of 5 to 50 nm. The method of claim 1, wherein the content of the chitin nanofibers is 1 to 3% by weight based on the total weight of the PLA. The method of claim 1, wherein the content of the chitin nanofibers is 1.5 to 2.5% by weight based on the total weight of the PLA. The method of claim 1, wherein the organic solvent is any one selected from the group consisting of dichloromethane (DCM), chloroform, ethyl acetate, tetrahydrofuran and acetone A method for producing a PLA/chitin nanofiber composite characterized in that It is prepared from the manufacturing method of any one of claims 1 to 9, but the chitin nanofibers are dispersed in the PLA matrix in water-in-oil (W / O) formulation-based PLA / chitin nanofibers complex. The PLA/chitin nanofiber composite according to claim 10, wherein the chitin nanofiber is a chitin nanofiber surface-modified by succinylation or carboxylation. The PLA/chitin nanofiber composite according to claim 10, wherein the amount of the chitin nanofibers is dispersed in an amount of 1 to 3% by weight based on the total weight of the PLA. 11. The PLA/chitin nanofiber composite according to claim 10, wherein the chitin nanofibers are dispersed in an amount of 1.5 to 2.5% by weight based on the total weight of the PLA. A film comprising the PLA/chitin nanofiber composite of any one of claims 10 to 13.