KR20230043744A - Method for manufacturing polylactic acid/nano cellulose composite, its composite manufactured thereby and film using the same - Google Patents

Abstract

The present invention relates to a method for manufacturing a polylactic acid (PLA)/nanocellulose composite, a composite manufactured therefrom, and a film containing the same. The PLA/nanocellulose composite of the present invention can stably and evenly disperse nanocellulose to a PLA matrix to form a composite and control the mechanical characteristics of the PLA according to the content of the nanocellulose through Pickering emulsion and a twin-screw extrusion process by utilizing nanocellulose as a reinforcing material and using the nanocellulose modified through chemical and physical methods.

Description

Manufacturing method of PLA/nano cellulose 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")/nanocellulose composite, a composite prepared therefrom, and a film including the same, and more specifically, to utilizing nanocellulose as a reinforcing material and chemical And a method for producing a PLA / nanocellulose composite in which nanocellulose is stably dispersed in a PLA matrix through a Pickering emulsion and a twin-screw extrusion process using the nanocellulose modified through a physical method, and a composite of PLA / nanocellulose composite prepared therefrom It relates to composites and films containing them.

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, because of its brittleness and low thermal stability, its application range is limited, mainly in the medical field, packaging film, and filament for 3D printers.

In order to improve the mechanical properties and thermal stability of PLA, there are many methods such as addition of plasticizers, grafting of other polymers, addition of inorganic nanoparticles as reinforcing materials, and fabrication of fiber-reinforced composites by adding glass fibers and carbon fibers. plan was presented.

In particular, since inorganic nanoparticles and fibers have very excellent thermal properties, they are difficult to decompose by heat after use and, therefore, difficult to recycle.

Recently, studies on combining cellulose nanofiber (CNF), a natural polymer, with PLA as a reinforcing material have been reported.

As an example, Patent Document 1 proposes to provide a PLA nanocomposite material having improved physical properties without requiring a pretreatment process for hydrophobicity on the surface of cellulose, a melt kneading process, a solution mixing process, and the like.

In addition, in Non-Patent Document 1, there is a report on the physical properties of the PLA/cellulose nanocrystal nanocomposite.

Cellulose is the most abundant natural polymer on earth. It has characteristics such as biodegradability and biocompatibility, and its tensile strength is very similar to that of glass fiber and carbon fiber. It has a high aspect ratio and surface area. of the external force can be effectively dispersed.

However, when CNF is dispersed in the hydrophobic PLA matrix, CNF is aggregated due to the hydrophilicity of the hydroxyl group (-OH) of CNF, and mechanical properties and thermal stability may rather deteriorate.

Therefore, after surface modification through acetylation, esterification, silylation, etc. to modify the hydroxyl group on the surface of CNF, research on the preparation of composites with PLA is in progress. While such surface modification of CNFs can make the dispersibility of CNFs uniform in the PLA matrix, the strength of hydrogen bonds between CNFs may be weakened, so that a significant improvement in mechanical properties of the final composite may not be obtained.

Methods for producing composites include a method of dispersing a reinforcing material in a matrix using a solvent and a method through extrusion. Since it is not soluble, the method through extrusion is mainly used to manufacture a composite composed of PLA and CNF.

However, when the composite is manufactured through extrusion, phase separation occurs due to the difference in polarity between PLA and CNF, which causes a decrease in mechanical properties.

Accordingly, the inventors of the present invention have made efforts to solve the conventional problems, and as a result, by adding a nanocellulose aqueous dispersion to a PLA solution dissolved in an organic solvent to stabilize the droplets containing nanocellulose in the PLA matrix as an emulsion solution, at least the PLA surface The present invention was completed by providing a composite PLA/nanocellulose composite in which nanocellulose is uniformly dispersed in part or all without phase separation, and mechanical properties such as tensile strength and elongation of the composite prepared above are confirmed.

Patent Registration No. 10-1946042 (Announced on April 17, 2019)

Polymer (Korea), Vol. 42, no. 4, p. 649-653 (2018)

One object of the present invention is to provide a method for preparing a PLA/nanocellulose composite based on a Pickering emulsion method and a twin screw extrusion process to combine hydrophobic PLA and hydrophilic cellulose nanofibers.

Another object of the present invention is to provide a PLA/nanocellulose composite having improved tensile strength and elongation, and a film comprising the same.

A method for producing a PLA / nanocellulose composite to achieve the above object is to add 0.5 to 10 parts by weight of a nanocellulose aqueous dispersion based on 100 parts by weight of a PLA solution dissolved in an organic solvent to form droplets containing nanocellulose in the PLA A first step of stabilizing with an emulsion solution, a second step of drying the emulsion solution to form a composite material in which nanocellulose is dispersed in a PLA matrix, and a third step of molding the composite material.

The emulsion solution is stabilized in a water-in-oil (W/O) formulation, and the nanocellulose may be any one selected from cellulose nanofibers or cellulose nanocrystals, or a mixed form.

Preferably, the cellulose nanofibers are surface-modified cellulose nanofibers or surface-modified cellulose nanocrystals by reacting with succinic anhydride to undergo succinylation or carboxylation.

In one embodiment, the nano-cellulose aqueous dispersion may be formed by surface-modifying cellulose nanofibers by succinylation or carboxylation and then dispersing them in water.

In one embodiment, the succinylation or carboxylation may be performed by reacting the cellulose nanofibers with succinic anhydride.

In one embodiment, the nanocellulose aqueous dispersion may be formed by surface modification of cellulose nanofibers by succinylation or carboxylation, nanofiberization using an aqueous counter collision (ACC) method, and then dispersion in water.

In one embodiment, the cellulose nanofibers may have a diameter of 5 to 7 nm.

In one embodiment, the nano-cellulose content may be 1 to 3% by weight based on the total weight of PLA.

In one embodiment, the nano-cellulose content may be 1.5 to 2.5% by weight based on the total weight of PLA.

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

In addition, the present invention provides a PLA/nanocellulose composite in which nanocellulose is dispersed in a PLA matrix and composited without phase separation.

In the above, the nanocellulose is any one selected from cellulose nanofibers or cellulose nanocrystals, or a mixed form.

In one embodiment, the cellulose nanofibers are succinylated or carboxylated surface-modified cellulose nanofibers or surface-modified cellulose nanocrystals.

In one embodiment, the nano-cellulose content may be 1 to 3% by weight relative to the total weight of the PLA.

In one embodiment, the nano-cellulose content may be 1.5 to 2.5% by weight based on the total weight of the PLA.

Furthermore, the present invention provides a film including the PLA/nanocellulose composite having excellent mechanical properties prepared from the method for preparing the PLA/nanocellulose composite.

According to the present invention, the nanocellulose is evenly dispersed inside the PLA matrix to effectively disperse the tensile force applied from the outside, thereby providing a PLA/nanocellulose composite with remarkably improved mechanical properties.

Figure 1 is a result of evaluating the characteristics of cellulose nanofibers according to pretreatment by succinylation (a) pure cellulose nanofibers without pretreatment, (b) cellulose nanofibers succinylated by SA or surface by succinylation (c) a dispersion of cellulose nanofibers subjected to SA and ACC treatment;
Figure 2 is a PLA / SCNF emulsion solution according to the content of 1% by weight, 2% by weight and 3% by weight of surface-modified cellulose nanofibers (SCNF) compared to PLA,
Figure 3 is a cross-sectional SEM image of a film prepared from a PLA / CNF solution and a PLA / SCNF emulsion solution,
4 is an image of the composites of Examples 1, 3, and 5 prepared according to the content of surface-modified cellulose nanofibers (SCNF) and the composite of Example 6 prepared according to the content of cellulose nanofibers (CNF), compared to pure PLA. ego,
5 is a tensile test result for the composites of Examples 1 to 5 prepared according to the content of surface-modified cellulose nanofibers (SCNF) and the composite of Example 6 prepared according to the content of cellulose nanofibers (CNF), compared to pure PLA. ego,
6 is a tensile test result for the composites of Examples 7 to 9 prepared according to the surface-modified cellulose nanocrystal (SCNC) content,
Figure 7 is a cross-sectional SEM image of the composites of Examples 1, 3 and 5 prepared according to the cellulose nanofiber (SCNF) content before tensile testing,
8 is a SEM image of the fracture surface after the tensile test of FIG. 7;
9 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 is dried;
10 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 dried;
11 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 nanocellulose in the PLA as an emulsion solution by adding 0.5 to 10 parts by weight of a nanocellulose aqueous dispersion with respect to 100 parts by weight of the PLA solution dissolved in an organic solvent, the emulsion solution It provides a method for producing a PLA/nanocellulose composite including a second step of drying the composite material in which nanocellulose is dispersed in a PLA matrix and a third step of molding the composite material.

In the manufacturing method of the present invention, nanocellulose used in the first step is one of the most abundant natural polymers on earth, and in the present invention, it is used as a reinforcing material to improve the mechanical properties of PLA, and the content of nanocellulose According to this, the mechanical properties of PLA can be controlled.

The nanocellulose may be used in any one selected from cellulose nanofiber (CNF) or cellulose nanocrystal (CNC), or in a mixed form.

Preferably, surface-modified cellulose nanofibers or surface-modified cellulose nanocrystals (CNC) may be used as the nano-cellulose. Specifically, cellulose nanofibers or surface-modified cellulose nanocrystals surface-modified by succinylation or carboxylation may be obtained by reacting with succinic anhydride.

In the embodiment of the present invention, cellulose nanofibers (CNF), succinylated cellulose nanofibers (SCNF) and succinylated cellulose nanocrystals (SCNC) will be described as examples, but will not be limited thereto.

More preferably, in the first step, the nano-cellulose aqueous dispersion may be formed by surface-modifying the cellulose nanofibers by succinylation or carboxylation and then dispersing them in water. For example, the succinylation may be performed by reacting cellulose nanofibers with succinic anhydride (SA).

In one embodiment, the nanocellulose aqueous dispersion may be formed by surface-modifying cellulose nanofibers by succinylation or carboxylation, and then dispersing in water to form nanofibers by treating them with an aqueous counter collision (ACC) method.

In one embodiment, the cellulose nanofibers may be nanofibers having a diameter of about 1 to 10 nm. At this time, when the diameter of the cellulose nanofibers exceeds 10 nm, it is difficult to effectively inhibit phase separation of the emulsion solution, which may cause problems in preparing a stabilized emulsion solution. Preferably, the cellulose nanofibers surface-modified by the above method may have a diameter of about 5 to 7 nm.

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, in the first step, at the interface between the hydrophobic PLA solution and the hydrophilic nanocellulose aqueous dispersion, the nanocellulose serves as a surfactant to prepare a stable emulsion solution, and thus the PLA and cellulose nanofibers can be compounded.

Figure 1 is a dispersion according to the pretreatment of cellulose nanofibers by succinylation, (a) is a cellulose nanofiber (pulp) that has not been pretreated by SA, and is not evenly dispersed in the dispersion and precipitates, (b) As a dispersion of cellulose nanofibers pretreated by SA, a hazy translucent color can be observed. On the other hand, (c) has a uniform and smaller diameter by pretreatment by SA and physical nanofibrous formation by ACC, so that a transparent dispersion can be confirmed through uniform dispersion of cellulose nanofibers.

Figure 2 is an observation of PLA / SCNF emulsion solutions according to 1% by weight, 2% by weight and 3% by weight of surface-modified cellulose nanofibers (SCNF) compared to PLA. If the content of SCNF compared to PLA is 3% by weight, Due to the difference in polarity between PLA and SCNF, miscibility between the two materials is reduced, resulting in phase separation.

Surface modification of cellulose nanofibers can create an electrostatic repulsive force between cellulose nanofibers, enabling a high degree of nanofibrillation during ACC treatment. Cellulose nanofibers subjected to ACC treatment after succinylation or carboxylation of the surface may have lower turbidity and smaller size compared to the case of ACC treatment of cellulose nanofibers without succinylation or carboxylation.

In one embodiment, in the first step of the present invention, the nanocellulose is preferably surface-modified cellulose nanofibers prepared through chemical modification of succinic anhydride and aqueous counter collision.

Figure 3 is a cross-sectional SEM image of a film prepared from a PLA / CNF solution and a PLA / SCNF solution. When the content of SCNF compared to PLA is 2% by weight, the size of Pickering is generally reduced and uniform after surface modification by succinylation. one can observe. Therefore, after surface modification by SA, the size of Pickering can be formed with a finer and more uniform size as the nanofibroization of CNF proceeds.

Therefore, the content of nanocellulose relative to the total weight of PLA may be 1 to 3% by weight. At this time, if the nano-cellulose exceeds 3% by weight, there is a problem in that the mechanical properties may be deteriorated rather than being uniformly dispersed due to excessive addition in the PLA matrix. More preferably, the nano-cellulose content is included in 1.5 to 2.5% by weight relative to the total weight of PLA.

Figure 4 is an image of a composite prepared according to the content of surface-modified cellulose nanofibers (SCNF) and a composite prepared according to the content of cellulose nanofibers (CNF), compared to pure PLA. As the SCNF content increases, the color appears darker, These results are expected to be the result of deterioration of SCNF during extrusion through a twin screw extruder.

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. 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 manufacturing method of the present invention, the drying performed in the second step can be any drying method such as natural drying, hot air drying, and freeze drying, and the drying method is not particularly limited in the present invention. 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.

The present invention provides a PLA/nanocellulose composite in which nanocellulose is dispersed in a PLA matrix and composited without phase separation.

Preferably, the PLA/nanocellulose composite may be prepared according to the manufacturing method of the present invention.

In the above, the nanocellulose is any one selected from cellulose nanofibers or cellulose nanocrystals, or a mixed form.

More preferably, they are succinylated or carboxylated surface-modified cellulose nanofibers or surface-modified cellulose nanocrystals.

In this case, the nanocellulose content may be 1 to 3% by weight based on the total weight of the PLA, more preferably 1.5 to 2.5% by weight based on the total weight of the PLA.

5 is a tensile test result for the composites of Examples 1 to 5 prepared according to the content of surface-modified cellulose nanofibers (SCNF) and the composite of Example 6 prepared according to the content of cellulose nanofibers (CNF), compared to pure PLA. is shown.

6 is a tensile test result for the composites of Examples 7 to 9 prepared according to the surface-modified cellulose nanocrystal (SCNC) content.

As a result of the tensile test, when surface-modified cellulose nanofibers (SCNF), cellulose nanofibers (CNF) or surface-modified cellulose nanocrystals (SCNC) were used as reinforcing materials compared to pure PLA (NEAT PLA) elongation of 4.8%, at least By improving the elongation by about 5 times, as much as about 24 times, it can be confirmed that the mechanical properties of PLA are improved by solving the brittle problem inherent in PLA material.

In particular, most preferably, by confirming that improved mechanical properties are maximized when the content of SCNF in the PLA matrix is 2% by weight, the mechanical properties of PLA can be controlled according to the content of nanocellulose.

7 is a cross-sectional SEM image of the composites of Examples 1, 3 and 5 prepared according to the cellulose nanofiber (SCNF) content before the tensile test, and FIG. 8 is a SEM image of the fracture surface after the tensile test of FIG. 7 is shown.

From the results of the figure, it is possible to form a stable network complexed by the Pickering emulsion process, and in particular, a very dense network can be confirmed in the case of the PLA/SCNF composite having a content of 2% by weight of SCNF compared to PLA.

In addition, the fracture surface after tensile sealing confirms the rough surface compared to the clean fracture surface due to the brittle nature of pure PLA, supporting that the SCNF evenly dispersed in the PLA matrix effectively distributes the tensile force.

In the PLA/nanocellulose composite of the present invention, the physicochemically treated nanocellulose serves as a surfactant, so that a stable emulsion solution can be prepared, and thus the PLA and cellulose nanofibers can be combined. At this time, the emulsion solution is preferably stabilized in a water-in-oil (W/O) formulation.

9 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. 10 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 SCNF aqueous dispersion, while an oil-in-water (oil-in-water) formulation. -water, O/W) formulation is an inverted structure in which a fluorescent SCNF aqueous 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 cellulose is dispersed in the PLA matrix, and is 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 dispersibility of nanocellulose uniform in the PLA matrix and acts as a reinforcement or nanofiller. Alternatively, the mechanical properties of the composite can be significantly improved through hydrogen bonding with PLA.

Figure 11 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.

From the above, the present invention provides a film comprising a PLA/nanocellulose composite having excellent mechanical properties.

The PLA/nanocellulose composite can be easily prepared as a composite by solving the conventional phase separation problem by preparing PLA and cellulose nanofibers having different polarities through a Pickering emulsion method.

In addition, the composite can be easily applied to the fields of packaging, 3D printing materials, lightweight composite materials for structure, 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> Preparation of PLA/SCNF composites

① Reagents and Materials

For PLA, 3D870 product from NatureWorks (USA) was used. Hardwood kraft pulp was supplied as a 1% by weight dispersion from CNNT Co., Ltd. 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 CNF. A twin screw extruder (TSE) and an injection molding machine (SJZS-10B, manufactured by Wuhan Ruiming, China) were used to manufacture composites using composite materials. The twin screw extruder is a corotating method in which a pair of screws rotate, and the length to diameter (L/D) is 40. The heater was divided into 4 sections from the sample hopper to the final extrusion port, and each was set at 180-185-190-195°C. The temperature of the injection molding machine was 195°C and the pressure was 10 MPa.

② Surface modification and nanofiberization of CNF (manufacture of SCNF)

By adding wood pulp, succinic anhydride (SA) and pyridine to a flask containing DMF, heating with stirring for 6 hours, rinsing thoroughly with deionized water and ethanol using a centrifuge, and neutralizing with NaOH solution, succinic acid Cellulose nanofibers surface-modified by nitration were prepared. Then, using an ACC system (CNNT Co., Ltd., Korea), a 1% by weight cellulose nanofiber (SCNF) dispersion was finally prepared. The prepared SCNF had a diameter of about 5 to 7 nm.

③ Preparation of PLA/SCNF composites

The PLA/SCNF composite was prepared by the Pickering emulsion method. A PLA solution in which 5% by weight of PLA was dissolved in DCM and a SCNF dispersion having a concentration of 1% by weight were prepared. The SCNF 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.

The emulsion solution was treated with a homogenizer and an ultrasonicator for 2 minutes and 1 minute, respectively, and then cast in a glass petri dish to dry both the organic solvent and water A composite material was prepared. The dried composite material was pulverized into pieces with a length of about 3 to 5 mm using a blender, and final composite was performed using TSE equipment to prepare a PLA/SCNF composite.

<Example 6> Preparation of PLA/CNF composite

PLA / CNF composite 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 CNF dispersion containing 2% by weight of CNF relative to the total PLA. manufactured.

<Examples 7 to 9> Preparation of PLA/SCNC composites

Prepare succinylated cellulose nanocrystal (SCNC), and use a dispersion containing a PLA solution in which 5% by weight of PLA is dissolved in DCM and SCNC to be 1, 2, and 3% by weight relative to the total PLA. A PLA/SCNC composite was prepared in the same manner as in Example 1 except for the above.

<Comparative Example 1>

Pure PLA (Neat PLA) was prepared.

<Comparative Example 2>

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

<Experimental Example 1> Evaluation of properties according to pretreatment of cellulose nanofibers

1 is a result of evaluating the characteristics according to the pretreatment by succinylation of cellulose nanofibers. Specifically, (a) is a pure cellulose nanofiber (Pulp) that has not been pretreated, and it is confirmed that it is not evenly dispersed in the solution and sinks, and (b) is a cellulose nanofiber that has been pretreated by SA and is uniformly dispersed, but is cloudy and translucent due to size It was observed to have a color of (c) is SA and ACC-treated cellulose nanofibers that are uniformly dispersed with smaller diameters and sizes to form a stable dispersed phase.

<Experimental Example 2> Characteristic evaluation according to cellulose nanofiber content

2 is a result of observing PLA / SCNF emulsion solutions according to 1% by weight, 2% by weight and 3% by weight of surface-modified cellulose nanofibers (SCNF) compared to PLA prepared in Examples 1, 3 and 5.

As a result, when the content of SCNF compared to PLA was 3% by weight, the miscibility between the two materials was reduced due to the difference in polarity between PLA and SCNF, and a phase separation phenomenon was observed.

Figure 3 is a SEM image of the cross section of the film prepared from the emulsion solutions prepared in Example 6 (PLA / CNF 2% by weight) and Example 3 (PLA / SCNF 2% by weight), the content of SCNF compared to PLA is 2 In terms of weight%, it was observed that the size of Pickering generally decreased and was uniform after surface modification by SA. Therefore, it is believed that the size of Pickering was formed with a finer and more uniform size as nanofibroization of CNF progressed after surface modification by SA.

Figure 4 is an image of the composites of Examples 1, 3 and 5 prepared according to the content of surface-modified cellulose nanofibers (SCNF) and the composite of Example 6 prepared according to the content of cellulose nanofibers (CNF), compared to pure PLA. , it was confirmed that the color appeared darker as the SCNF content increased. These results can be expected to be the result of the deterioration of SCNF in the process of being extruded through a twin screw extruder.

5 is a tensile test result of composites prepared according to the content of surface-modified cellulose nanofibers (SCNF) prepared in Examples 1 to 5 and cellulose nanofibers (CNF) prepared in Example 6, compared to pure PLA.

Figure 6 shows the results of the tensile test of the composites prepared according to the surface-modified cellulose nanocrystal (SCNC) content of Examples 7 to 9, respectively, compared to pure PLA. Tensile tests were measured using a universal testing machine (UTM) (AMETEK, LS5, USA), and specimens were prepared according to ASTM D638 standards. The length was 75 mm, the width was 6 mm, and the thickness was 2 mm, and tensile strain was applied at a rate of 1 mm/min.

The results are shown in Table 1 below.

Referring to Table 1 and FIG. 5, pure PLA (NEAT PLA) has an elongation of only 4.8% due to material inherent brittleness, compared to the result of PLA / SCNF composites prepared in Examples 1 to 5 of the present invention, It was confirmed that the elongation rate increased by at least about 5 times and at most about 24 times.

At this time, the best elongation was shown when the SCNF content was 2% by weight compared to PLA, while the mechanical properties were lowered when the SCNF content was 3% by weight, compared to 2% by weight. These results support the result that, in a general composite system, as the amount of reinforcing agent increases, dispersion in the matrix resin becomes difficult, and as a result, mechanical properties decrease.

Therefore, it can be confirmed that the improved mechanical properties are maximized when the content of SCNF in the PLA matrix is 2% by weight, which means that the optimal content of SCNF that can be evenly dispersed in the PLA matrix.

Originally, PLA and SCNF have weak interfacial adhesion due to the difference in polarity, but in the present invention, since the composite was prepared based on the Pickering emulsion method, the elongation and toughness of the PLA / nanocellulose composite prepared therefrom were improved, thereby improving PLA and SCNF It was confirmed that the compatibility problem between the liver was overcome.

In addition, the PLA / CNF composite prepared in Example 6 also showed 19 times improved elongation when 2% by weight of CNF compared to pure PLA was included.

Referring to Table 1 and FIG. 6, the reinforcement effect of the PLA composite of CNC, which is generally known to have a smaller aspect ratio than that of CNF, was confirmed to be smaller than that of CNF, but all composites containing 1 to 3% by weight of SCNC compared to pure PLA were compared to pure PLA. The elongation rate was improved.

7 is a cross-section of the composites prepared according to the cellulose nanofiber (SCNF) content before the tensile test, and it was confirmed that a stable network effectively composited by the Pickering emulsion process was formed through the cross-section of the PLA / SCNF composite. In particular, The PLA/SCNF composite with 2% by weight of SCNF compared to PLA formed a very dense network.

In addition, FIG. 8 is a SEM image of the fracture surface after the tensile test, and it can be confirmed that pure PLA has a relatively clean fracture surface, which is a characteristic of brittleness, while the surface of the fracture surface of the PLA / SCNF composite is very rough.

This can be interpreted as the fact that the SCNF evenly dispersed in the PLA matrix effectively disperses the tensile force.

<Experimental Example 3> Evaluation of mechanical properties according to formulation

In the case of Example 3 and Comparative Example 2 composited with 2% by weight of SCNF compared to PLA, images were observed using a confocal microscope for each emulsion solution for preparing the composite.

9 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.

Specifically, the dye (Fluorescein) is soluble in distilled water and emits a fluorescent color, whereas it does not emit a fluorescent color because it is insoluble in DCM, an organic solvent. Accordingly, in the confocal microscopy image results of FIGS. 9 and 10 , the fluorescently colored portion is the SCNF aqueous dispersion, and the colorless portion is the PLA/DCM solution in which PLA is dissolved. Therefore, through FIGS. 9 and 10, the water-in-oil (W/O) formulation of Example 3 has a shape in which the PLA/DCM solution wraps the SCNF aqueous dispersion giving off a spherical fluorescent color. On the other hand, the oil-in-water (O / W) formulation of Comparative Example 2 was confirmed in the form of a fluorescent SCNF aqueous dispersion (suspension) surrounding the black spherical PLA / DCM solution. It became.

The formulation of W/O or O/W was also clearly distinguished from the fluorescence microscopic image results [not shown].

In addition, a clear difference between the W / O formulation and the O / W formulation can be confirmed in 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 distilled water dried cellulose wrapped around the spherical PLA matrix, whereas in the composite of Example 3, the PLA matrix covered the spherical cellulose while covering at least a part or the entire surface of the PLA matrix. It shows a uniformly dispersed form.

<Experimental Example 4> Evaluation of mechanical properties of the composite according to the formulation

The results of measuring the mechanical properties of the composites prepared in Example 3 and Comparative Example 2 composited with 2% by weight of SCNF compared to PLA are shown in Table 2 and FIG. 11 below.

From the above results, it was confirmed that the composite of the O/W formulation had significantly lower mechanical properties than the composite of the W/O formulation.

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 (16)

A first step of stabilizing droplets containing nanocellulose in the PLA as an emulsion solution by adding 0.5 to 10 parts by weight of a nanocellulose aqueous dispersion with respect to 100 parts by weight of the PLA solution dissolved in an organic solvent,
A second step of drying the emulsion solution to form a composite material in which nanocellulose is dispersed in a PLA matrix; and
Method for producing a PLA / nano-cellulose composite comprising a; third step of molding the composite material. The method of claim 1, wherein the emulsion solution is stabilized in a water-in-oil (W/O) formulation. The method of claim 1, wherein the nanocellulose is any one selected from cellulose nanofibers or cellulose nanocrystals, or a mixed form. The method of claim 3, wherein the cellulose nanofibers are cellulose nanofibers or surface-modified cellulose nanocrystals surface-modified by succinylation or carboxylation by reacting with succinic anhydride. The method of claim 1, wherein the nano-cellulose aqueous dispersion is formed by surface-modifying cellulose nanofibers by succinylation or carboxylation and then dispersing them in water. The method of claim 1, wherein the nano-cellulose aqueous dispersion is formed by surface-modifying cellulose nanofibers by succinylation or carboxylation, converting them into nanofibers using an aqueous counter collision (ACC) method, and then dispersing them in water. Manufacturing method of PLA/nanocellulose composite. The method of claim 4, wherein the surface-modified cellulose nanofibers have a diameter of 5 to 7 nm. The method of claim 1, wherein the content of the nanocellulose is 1 to 3% by weight based on the total weight of the PLA. The method of claim 1, wherein the content of the nanocellulose 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 Method for producing a PLA/nanocellulose composite characterized in that A PLA/nanocellulose composite in which nanocellulose is dispersed in a PLA matrix and composited without phase separation. The PLA/nanocellulose composite according to claim 11, wherein the nanocellulose is any one selected from cellulose nanofibers or cellulose nanocrystals or a mixed form. The PLA/nanocellulose composite according to claim 11, wherein the cellulose nanofibers are cellulose nanofibers surface-modified by succinylation or carboxylation or surface-modified cellulose nanocrystals. The PLA/nanocellulose composite according to claim 11, wherein the nanocellulose is dispersed in an amount of 1 to 3% by weight based on the total weight of PLA. The PLA/nanocellulose composite according to claim 11, wherein the nanocellulose is dispersed in an amount of 1.5 to 2.5% by weight based on the total weight of PLA. A film comprising a PLA/nanocellulose composite prepared from the method of any one of claims 1 to 10.

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