PLA-based composite plastic and use thereof

Abstract

The present invention relates to a polylactic acid (PLA)-based composite plastic and a use thereof. In order to reduce the inherent brittleness of a PLA material, the present invention can provide a PLA-based composite plastic in which a reinforcing material is mixed, the reinforcing material is dispersed and composited in a biodegradable polymer matrix containing PLA so as to prepare a composite filler, the composite filler is mixed with a pure PLA material and molded so that mechanical integrity satisfying both tensile strength and toughness is ensured while the amount of the reinforcing material is lowered to be less than the total weight of PLA, and transparency equivalent to that of the inherent physical property of PLA is implemented. Provided is the PLA-based transparent film, which can be applied to industrial packaging containers, food containers and food packaging applications that require the physical property.

Description

PLA-based composite plastics and their uses

[0001] The present invention relates to a polylactic acid (PLA)-based composite plastic and uses thereof, and more specifically, to a PLA-based composite plastic and uses thereof, which mixes a reinforcing material to improve the inherent brittleness of PLA materials, manufactures a composite filler in which the reinforcing material is dispersed in a biodegradable polymer matrix including PLA, and mixes the composite filler into a pure PLA raw material and molds it, thereby securing mechanical soundness that satisfies both tensile strength and toughness while lowering the reinforcing material content relative to the total PLA weight, and implements transparency equivalent to the inherent properties of PLA.

[0002] As environmental pollution caused by synthetic plastics and petrochemical-based plastic waste increases, research is actively being conducted on eco-friendly, recyclable, and compostable biodegradable bioplastics.

[0003] PLA, derived from plants like cornstarch, is biodegradable, non-toxic, and biocompatible, attracting significant attention as a potential replacement for conventional plastics. However, its brittleness and low thermal stability limit its applications, primarily in the medical field, packaging films, and filament for 3D printers.

[0004] Many methods have been proposed to improve the mechanical properties and thermal stability of PLA, including adding plasticizers, grafting other polymers, adding inorganic nanoparticles as reinforcing materials, and producing fiber-reinforced composite materials by adding glass fibers, carbon fibers, etc.

[0005] In particular, inorganic nanoparticles and fibers have the disadvantage of being difficult to decompose by heat after use of the composite due to their excellent thermal properties, making recycling difficult.

[0006] Recently, studies have been reported on composites of cellulose nanofibers (CNF), a natural polymer, with PLA as a reinforcing material.

[0007] As an example, Patent Document 1 proposes providing a PLA nanocomposite material with improved physical properties without requiring a surface hydrophobic pretreatment process of cellulose, melt mixing, solution mixing process, etc.

[0008] Additionally, non-patent literature 1 reports on the properties of PLA / cellulose nanocrystal nanocomposites.

[0009] Cellulose is the most abundant natural polymer on Earth, and not only does it have properties such as biodegradability and biocompatibility, but its tensile strength is very similar to that of glass fiber and carbon fiber, and when CNF is used as a reinforcing material, it can effectively disperse the external force of the composite.

[0010] In addition, chitin, which is another candidate for natural polymer and is the second most abundant material on Earth after cellulose, is biodegradable, non-toxic, and biocompatible like PLA, and has a high aspect ratio and surface area very similar to glass fiber and carbon fiber.

[0011] However, when hydrophilic cellulose or chitin is complexed within a hydrophobic PLA matrix, the cellulose or chitin component may aggregate due to the hydroxyl group (-OH) of the cellulose or chitin, which may have a negative effect on the mechanical properties.

[0012] Therefore, research is being conducted on the production of composites with PLA after surface modification through acetylation, esterification, silylation, etc., which modify the hydroxyl groups on the surface of cellulose or chitin. While the above surface modification methods can uniformly disperse cellulose or chitin within the PLA matrix, they may not have a significant effect on improving the mechanical properties of the final composite due to the weakening of the hydrogen bonding between cellulose or chitin.

[0013] There are several methods for producing composites, including a method of dispersing reinforcing materials within a matrix using a solvent and a method using extrusion. However, PLA is hydrophobic and therefore does not dissolve in water, making it impossible to apply a water-dispersed system. In addition, since PLA does not dissolve in general organic solvents, a method using extrusion is mainly used to produce composites containing PLA and cellulose or chitin as components.

[0014] However, when producing a composite through extrusion, the polarity difference between hydrophobic PLA and hydrophilic cellulose or chitin causes interfacial separation, which causes a deterioration in mechanical properties.

[0015] Patent Document 2 is a prior art document of the present invention, which provides a PLA-based composite plastic based on a Pickering emulsion method and a twin-screw extrusion process to composite hydrophobic PLA with hydrophilic cellulose or chitin nanofibers, and reports excellent mechanical strength (particularly, improved elongation and toughness) properties of the PLA-based composite plastic.

[0016] Accordingly, the inventors of the present invention have made efforts to improve the physical properties and process compared to the conventional ones, and as a result, by introducing Pickering emulsion and twin-screw extrusion processes using cellulose or chitin surface-modified through chemical and physical methods as a reinforcing material, and uniformly dispersing the cellulose or chitin in a PLA matrix to provide a composite filler, and mixing the composite filler with a pure PLA raw material to provide a PLA-based composite plastic with a low content of reinforcing material relative to the total PLA weight, and confirming mechanical soundness that satisfies both tensile strength and toughness and transparency equivalent to the inherent physical properties of PLA, thereby completing the present invention.

[0017] (Patent Document 1) Republic of Korea Patent No. 10-1946042 (Published on April 17, 2019)

[0018] (Patent Document 2) Republic of Korea Patent Publication No. 2023-0043745 (Published on March 31, 2023)

[0019] (Non-patent literature 1) Polymer (Korea), Vol. 42, No. 4, pp. 649-653 (2018)

[0020] An object of the present invention is to provide a PLA-based composite plastic having excellent mechanical soundness and transparency while reducing the content of reinforcing material relative to the total PLA weight.

[0021] Another object of the present invention is to provide a use using a PLA-based composite plastic.

[0022] In order to achieve the above purpose, a molded body is provided, which is a mixture of 50 to 99 wt% of pure PLA raw material and 1.0 to 50 wt% of composite filler in which a reinforcing material is dispersed and composited in a biodegradable polymer matrix including PLA, wherein the composite filler is a composite in which 1 to 3 wt% of reinforcing material is dispersed and composited in a biodegradable polymer matrix including PLA, and the reinforcing material content in the composite filler is 0.01 to 1.0 wt% of reinforcing material based on the total PLA weight.

[0023] The above PLA-based composite plastic has a tensile strength of 50 to 70 MPa and a toughness of 50 to 100 MJ / m. 3 It simultaneously satisfies the requirements and has a high visible light transmittance of 89% or more (550 nm).

[0024] In the PLA-based composite plastic of the present invention, the biodegradable polymer matrix is ​​polylactic acid (PLA) alone or polyhydroxyalkanoates (PHA), polybutylene terephthalate (PBAT), polybutylenesuccinate-coadipate (PBAT), polybutylene succinate-coadipate (PBAT), polybutylene succinate-terephthalate (PBAT), aliphatic polyester (AP), polyethylene succinate (PES), polybutylene succinate (PBS), polyvinyl alcohol (PVA), polyglycolic acid (PGA), It is a mixture of one or two or more selected from the group consisting of polylactic-co-glycolic acid (PLGA), polycaprolactone (PCL), modified starch resin, and thermoplastic starch (TPS).

[0025] In the above, the reinforcing material is any one natural polymer selected from the group consisting of cellulose, chitin, chitosan, dextrin, dextran, glycogen, pullulan, gelatin, and pectin, and preferably includes a nanofiber or nanocrystal form of the natural polymer.

[0026] More preferably, cellulose or chitin that has been surface-modified by succinylation or carboxylation and then converted into nanofibers is used as a reinforcing material contained in the composite filler used in the present invention.

[0027] The composite filler, in which a reinforcing material is dispersed in a biodegradable polymer matrix including PLA of the present invention, is characterized by mixing an aqueous dispersion of a reinforcing material dispersed in a biodegradable polymer solution including PLA dissolved in an organic solvent, stabilizing it with a water-in-oil (W / O) formulation-based Pickering emulsion solution, and then drying it.

[0028] In the present invention, the molded article in which a composite filler is mixed with a reinforcing material dispersed in a biodegradable polymer matrix including PLA in the pure PLA is one selected from the group consisting of an injection molded article; a heat-processed article; and a film for extrusion molding or blow molding.

[0029] Furthermore, the present invention provides a PLA-based transparent film that is used as an industrial packaging material, a food container, and especially a food packaging material, since the mechanical properties and transparency of a PLA-based composite plastic are simultaneously satisfied.

[0030] The present invention provides a PLA-based composite plastic that achieves mechanical soundness satisfying both tensile strength and toughness and higher visible light transmittance while significantly reducing the content of reinforcing material relative to the total PLA weight by mixing reinforcing material to improve the inherent brittleness of PLA material, and manufacturing a composite filler in which the reinforcing material is dispersed in a biodegradable polymer matrix including PLA, and mixing and molding the composite filler into a pure PLA raw material.

[0031] The PLA-based composite plastic of the present invention is manufactured in the form of a masterbatch by mixing a composite filler in which a reinforcing material is dispersed in a biodegradable polymer matrix including PLA and then extruding it into a pure PLA raw material, thereby significantly reducing the amount of organic solvent (Dichloromethane, DCM) used.

[0032] In addition, the PLA-based composite plastic of the present invention provides a PLA-based transparent film that can be used as an industrial packaging material, a food container, and especially a food packaging material by utilizing mechanical soundness and excellent permeability.

[0033] Figure 1 is a schematic diagram for manufacturing a PLA-based composite plastic of the present invention.

[0034] Figure 2 is a drawing explaining the manufacture of a PLA-based composite plastic based on an embodiment of the present invention.

[0035] Figure 3 is a confocal microscope image on the top and a SEM image on the bottom of a cross-section of a sheet completely dried from the solvent for a PLA / chitin (PLA / SChNF 2 wt%) composite filler in the PLA-based composite plastic of the present invention.

[0036] Figure 4 is a confocal microscope image on the top and a SEM image of a cross-section of a sheet completely dried from solvent for a PLA / cellulose (PLA / SCNF 2 wt%) composite filler in the PLA-based composite plastic of the present invention.

[0037] Figure 5 is the mechanical property result of the PLA / chitin (PLA / SChNF) composite filler of Figure 3.

[0038] Figure 6 is the mechanical property result of the PLA / cellulose (PLA / SCNF) composite filler of Figure 4.

[0039] Figure 7 shows the results of permeability according to the content of composite filler in the PLA-based composite plastic of the present invention.

[0040] Figure 8 shows a transparent film made of PLA-based composite plastic manufactured according to the content of the composite filler of the present invention.

[0041] Figure 9 is a photograph of a prototype manufactured using Comparative Example 1 (Neat PLA) of the present invention.

[0042] Figure 10 is a photograph of a prototype manufactured using Example 3 of the present invention (PLA / PCX-MB 5%).

[0043] Figure 11 is a photograph of a prototype manufactured using Comparative Example 2 of the present invention (PCX-MB 100%).

[0044] Hereinafter, the present invention will be described in detail.

[0045] FIG. 1 is a schematic diagram for the production of a PLA-based composite plastic of the present invention, and the present invention provides a molded body in which 50 to 99 wt% of pure PLA raw material and 1.0 to 50 wt% of a composite filler in which a reinforcing material is dispersed and composited in a biodegradable polymer matrix including PLA are mixed, and the composite filler is a composite in which 1 to 3 wt% of a reinforcing material is dispersed and composited in a biodegradable polymer matrix including PLA, and the PLA-based composite plastic contains 0.01 to 1.0 wt% of the reinforcing material relative to the total PLA weight based on the reinforcing material content in the composite filler.

[0046] FIG. 2 is a drawing illustrating the production of a PLA-based composite plastic based on an embodiment of the present invention, in which a composite filler is produced by dispersing a reinforcing material in a biodegradable polymer matrix including PLA, and mixing and molding the composite filler into a pure PLA raw material.

[0047] 1. Composite filler

[0048] The composite filler, in which a reinforcing material is dispersed and complexed within a biodegradable polymer matrix including the above PLA, is stabilized in a first step by mixing a dispersion of a reinforcing material dispersed in an aqueous system with a biodegradable polymer solution including PLA dissolved in an organic solvent and a Pickering emulsion solution based on a water-in-oil (W / O) formulation.

[0049] A second step of manufacturing a composite material by drying the above emulsion solution, and

[0050] It is manufactured through the third step of crushing the above composite material.

[0051] The Pickering emulsion method of the first step described above is a method of producing a stabilized emulsion by reducing the interfacial tension at the hydrophobic / hydrophilic interface using small solid particles instead of a surfactant.

[0052] The biodegradable polymer matrix is ​​polylactic acid (PLA) alone or polylactic acid plus polyhydroxyalkanoates (PHA), polybutylene terephthalate (PBAT), polybutylenesuccinate-coadipate (PBAT), polybutylenesuccinate-coadipate (PBAT), polybutylene succinate-terephthalate (PBAT), aliphatic polyester (AP), polyethylene succinate (PES), polybutylene succinate (PBS), polyvinyl alcohol (PVA), polyglycolic acid (PGA), polylactic-co-glycolic acid-copolymer (PLA-copolymer). It is a mixture of one or two or more selected from the group consisting of poly(lactic acid, PLGA), polycaprolactone (PCL), modified starch resin, and thermoplastic starch (TPS).

[0053] The biodegradable polymer including the above PLA is hydrophobic and dissolves in an organic solvent. The organic solvent is 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, but the present invention is not limited thereto.

[0054] The above reinforcing material is any natural polymer selected from the group consisting of cellulose, chitin, chitosan, dextrin, dextran, glycogen, pullulan, gelatin, and pectin, and may be selected from a group of known materials as long as it is a polysaccharide including a water-soluble polysaccharide.

[0055] In addition, the natural polymer includes a nanofiber or nanocrystal form of the material, and preferably, the nanocellulose may be a cellulose nanofiber (CNF), a cellulose nanocrystal (CNC), a cellulose nanofiber (SCNF) surface-modified by reacting with succinic anhydride to undergo succinylation or carboxylation, or a surface-modified cellulose nanocrystal (SCNC).

[0056] In the embodiment of the present invention, chitin (SChNF) or cellulose (SCNF) that has been surface-modified by succinylation or carboxylation and then nanofiberized is used as a reinforcing material contained in the composite filler, and is described as a PLA / chitin (PLA / SChNF) composite filler or a PLA / cellulose (PLA / SCNF) composite filler, but is not limited thereto.

[0057] In the above first step, the dispersion in which natural polymers as reinforcing materials are dispersed in an aqueous system is a dispersion in which natural polymer raw materials are surface-modified by succinylation or carboxylation and then pre-treated to nanofiberize using the aqueous counter collision (ACC) method. It was observed that the nanofibers surface-modified by succinylation (SA) were uniformly dispersed but had a cloudy, translucent color due to their size, whereas after continuous ACC treatment, they were uniformly dispersed with smaller diameters and sizes, thereby obtaining a stable dispersion phase.

[0058] Therefore, a dispersion of natural polymers in an aqueous solution can be formed by surface-modifying the natural polymer nanofibers through succinylation or carboxylation and then dispersing them in water. For example, the succinylation is performed by reacting cellulose nanofibers with succinic anhydride (SA).

[0059] In addition, after surface modification by succinylation or carboxylation, it can be formed by dispersing it in water after being treated by the ACC (aqueous counter collision) method to become nanofibers.

[0060] In the first step of the present invention, 5 to 15 parts by weight of a dispersion of a natural polymer as a reinforcing material dispersed in an aqueous system is added to 100 parts by weight of a biodegradable polymer solution including PLA dissolved in the organic solvent, thereby stabilizing the solution into a water-in-oil (W / O) formulation-based emulsion solution.

[0061] FIG. 3 shows a confocal microscope image at the top and an SEM image at the bottom of a cross-section of a sheet in which the solvent has been completely dried for a PLA / chitin (PLA / SChNF 2 wt%) composite filler in the PLA-based composite plastic of the present invention, while FIG. 4 shows a confocal microscope image at the top and an SEM image at the bottom of a cross-section of a sheet in which the solvent has been completely dried for a PLA / cellulose (PLA / SCNF 2 wt%) composite filler in the PLA-based composite plastic of the present invention.

[0062] As a result, in the case of the water-in-oil (W / O) emulsion solutions of Examples 1 and 8, the PLA / DCM solution is observed to have a shape in which the spherical fluorescent SCNF dispersion or SChNF dispersion is wrapped, whereas in the case of the oil-in-water (O / W) formulations of Comparative Examples 1 and 2, the fluorescent SChNF dispersion or SCNF dispersion is observed to have an inverted shape in which the black spherical PLA / DCM solution is wrapped.

[0063] This structure is observed in the SEM images of the cross-sections of the sheets in which the organic solvent and water are completely dried. The composite plastics prepared from the emulsion solutions of Examples 1 and 6 (W / O formulations) have a form in which fine spherical chitin nanofibers are uniformly dispersed within the PLA matrix, whereas in the case of Comparative Examples 1 and 2 (O / W formulations), the water and DCM are dried and the cellulose or chitin reinforcing material is observed to have a form in which the spherical PLA is wrapped.

[0064] Figure 5 shows the mechanical property results of the PLA / chitin (PLA / SChNF) composite filler of Figure 3, and Figure 6 shows the mechanical property results of the PLA / cellulose (PLA / SCNF) composite filler of Figure 4, showing a significant difference in mechanical properties depending on the emulsion formulation.

[0065] Specifically, the composite filler obtained from the water-in-oil (W / O) formulation-based emulsion solution of the present invention can be confirmed to have significantly improved mechanical properties of the composite filler by uniformly dispersing chitin nanofibers or cellulose nanofibers in the PLA matrix and complexing them through hydrogen bonding with PLA.

[0066] At this time, in the composite filler in which the reinforcing material is dispersed and composited within the biodegradable polymer matrix including the PLA of the present invention, the content of the natural polymer (cellulose nanofiber or chitin nanofiber) as the reinforcing material is preferably 1 to 3 wt%, more preferably 1.5 to 2.5 wt%, and most preferably 2.0 wt%. At this time, when the content of the reinforcing material exceeds 3 wt%, dispersion within the matrix resin is difficult, resulting in a decrease in mechanical properties, whereas when it is 2 wt%, the best mechanical properties are exhibited, thereby producing a material with remarkably high elongation, whereby the mechanical properties of the PLA can be controlled depending on the content of the reinforcing material (chitin nanofiber or cellulose nanofiber).

[0067] In the second step of manufacturing a composite filler in which a reinforcing material is dispersed and composited within a biodegradable polymer matrix including PLA of the present invention, any drying method, such as natural drying, hot air drying, and freeze drying, may be used, and the present invention does not specifically limit the drying method. Preferably, the drying may be performed by casting the emulsion solution onto a substrate and drying it.

[0068] After the second step, the third step involves a crushing step to facilitate the twin-screw extrusion process. For example, the composite material may be crushed into pieces less than about 5 mm in length.

[0069] 2. PLA-based composite plastics

[0070] The present invention provides a PLA-based composite plastic by mixing and molding a composite filler prepared from the W / O formulation into a pure PLA raw material, preferably a molded body in which 50 to 99 wt% of the pure PLA raw material and 1.0 to 50 wt% of the composite filler are mixed, in which a reinforcing material is dispersed and composited in a biodegradable polymer matrix including PLA, and the composite filler is dispersed and composited in a biodegradable polymer matrix including PLA, in which 1 to 3 wt% of the reinforcing material is dispersed and composited in the biodegradable polymer matrix including PLA, and the reinforcing material is contained in an amount of 0.01 to 1.0 wt% based on the reinforcing material content in the composite filler relative to the total PLA weight.

[0071] The above pure PLA refers to the raw material itself without any processing.

[0072] The present invention is a composite in which 1 to 3 wt% of a reinforcing material is dispersed in a biodegradable polymer matrix including PLA, and at this time, a composite filler (Pre-complexation, PCX-MB) having a content of 1 to 3 wt% of PLA is manufactured as a masterbatch (MB), and then pure PLA and the PCX-MB are simply mixed and compression-molded to manufacture a PLA-based composite plastic, thereby significantly reducing the amount of organic solvent (Dichloromethane, DCM) required to manufacture a PLA organic solvent.

[0073] That is, in the embodiment of the present invention, when a composite filler in which 2 wt% of a reinforcing material is dispersed and complexed in PLA is used, the reinforcing material content in the composite filler can be reduced to 0.01 to 1.0 wt% of the reinforcing material relative to the total PLA weight, and since an organic solvent (DCM) is used only when manufacturing PCX-MB, the overall amount of organic solvent (Dichloromethane, DCM) used can be reduced.

[0074] In the PLA-based composite plastic of the present invention, as a result of mechanical properties according to the content of composite filler, tensile strength of 50 to 70 MPa and toughness of 50 to 100 MJ / m 3By verifying the mechanical properties that satisfy the requirements, the brittleness problem inherent in PLA materials can be resolved.

[0075] In addition, Fig. 7 shows the results of transmittance according to the content of composite filler in the PLA-based composite plastic of the present invention, and Fig. 8 shows a transparent film made of the PLA-based composite plastic manufactured according to the content of composite filler in the present invention.

[0076] From the above, it can be confirmed that the transmittance of the PLA-based composite plastic of the present invention tends to increase as the content of the composite filler (PCX-MB) decreases, and that the PLA-based composite plastic has visible light transmittance (550 nm) 4 to 10% higher than that of the composite filler alone (PCX-MB 100%).

[0077] From the above, the PLA-based composite plastic of the present invention can reduce the amount of organic solvent used during manufacturing, and can achieve mechanical soundness satisfying both tensile strength and toughness and higher visible light transmittance while significantly lowering the reinforcing material content relative to the total PLA weight compared to the composite filler (PCX-MB) alone.

[0078] In addition, as a result of comparing the prototype photos of Figs. 9 and 11, a difference in transparency can be confirmed with the naked eye, and the PLA-based composite plastic of the present invention (PLA / PCX-MB 5% of Example 3) confirmed transparency equivalent to that of Comparative Example 1 (Neat PLA), whereas the product of Comparative Example 2 (PCX-MB 100%) showed yellowish turbidity.

[0079] From the above, the PLA-based composite plastic of the present invention implements mechanical properties and transparency equivalent to the inherent properties of PLA, and thus provides a PLA-based transparent film that can be utilized in any one selected from the group consisting of industrial packaging materials, food containers, and food packaging materials.

[0080] Hereinafter, the present invention will be described in more detail through examples.

[0081] These examples are intended to explain the present invention more specifically, and the scope of the present invention is not limited to these examples.

[0082] <Examples 1 to 7> Manufacturing of PLA-based composite plastic 1

[0083] Reagents and Materials

[0084] PLA was used as 3D870 from NatureWorks (USA) and LX175 from Totalcorbion (Netherlands). Hardwood kraft pulp was supplied as a 1 wt% dispersion from CNNT Co., Ltd. Succinic anhydride (SA) was purchased from Daejung Chemical, and chitin (chitin from shrimp shell), dimethylformamide (DMF), pyridine, sodium hydroxide (NaOH), and dichloromethane (DCM) were purchased from Sigma-Aldrich. 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. The twin-screw extruder (TSE) and injection molding machine used in the production of composite plastics using composite materials were the SJZS-10B equipment of Wuhan Ruiming, China. The twin-screw extruder has a length to diameter (L / D) ratio of 40 with a pair of rotating screws. The heater is divided into four sections from the sample hopper to the final extrusion port, and is set to 180-185-190-195℃, respectively. The injection molding machine was operated at a temperature of 195℃ and a pressure of 10 MPa.

[0085] Step 1: Surface modification and nanofiberization of chitin nanofibers (SChNF fabrication)

[0086] Chitin and pyridine were added to DMF containing succinic anhydride (SA), and the mixture was heated at 90°C for 5 hours to react. The chitin was then thoroughly washed with deionized water and ethanol using a centrifuge, and the chitin dispersion was neutralized with NaOH solution to produce a surface-modified chitin dispersion. The surface-modified chitin was finally nanofiberized (SChNF) using an ACC system (CNNT CO., Ltd., Korea).

[0087] Step 2: PLA / chitin (PLA / SChNF) composite filler manufacturing step

[0088] A PLA / chitin (PLA / SChNF) composite filler was prepared using the Pickering emulsion method. A PLA solution containing 5 wt% PLA dissolved in DCM was prepared, and 5 ml, 10 ml, and 15 ml of an SChNF dispersion were added to each 200 ml of the PLA solution so that the SChNF content was 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, and 3 wt% relative to the dissolved PLA, thereby stabilizing the solution as a water-in-oil (W / O) Pickering emulsion solution. The emulsion solution was then homogenized and ultrasonicated for 2 minutes and 1 minute, respectively, to prepare an emulsion solution. The emulsion solution was then cast onto a glass petri dish to dry both the organic solvent and water, thereby preparing a composite material. The above dried composite material was manufactured by crushing it into pieces of approximately 3 to 5 mm in length using a blender.

[0089] Step 3: Mixing molding step of composite filler into pure PLA

[0090] In pure PLA, 1.0 wt%, 2.5 wt%, 5 wt%, 7.5 wt%, 10 wt%, 30 wt%, and 50 wt% of the composite filler PLA / chitin (PLA / SChNF 2 wt%) manufactured in step 2 was mixed and extruded through a twin-screw extruder to manufacture a PLA-based composite plastic.

[0091] <Comparative Example 1>

[0092] In the PLA / chitin (PLA / SChNF) composite filler manufacturing step of Step 2 of the above Example 1, a PLA solution in which 5 wt% of PLA is dissolved in DCM and a SChNF dispersion having a concentration of 1 wt% are manufactured, and 200 ml of the SChNF dispersion is mixed with 100 ml of the PLA solution to stabilize it as an oil-in-water (O / W) emulsion solution, and the same procedure as in Example 1 was performed, except that the mixture was stabilized.

[0093] <Examples 8-12> Manufacturing of PLA-based composite plastic 2

[0094] Step 1: Surface modification and nanofiberization of CNF (manufacture of SCNF)

[0095] Wood pulp, succinic anhydride (SA), and pyridine were added to a flask containing DMF, and the mixture was heated for 6 hours with stirring. The mixture was then thoroughly rinsed with deionized water and ethanol using a centrifuge and neutralized with NaOH solution to produce surface-modified cellulose nanofibers by succinylation. A 1 wt% dispersion of cellulose nanofibers (SCNF) was then prepared using an ACC system (CNNT Co., Ltd., Korea). The diameter of the SCNF thus prepared was approximately 5 to 7 nm.

[0096] Step 2: PLA / Cellulose (PLA / SCNF) composite filler manufacturing step

[0097] A PLA solution containing 5 wt% PLA dissolved in DCM and a SCNF dispersion were mixed to form an emulsion solution in amounts of 1 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, and 3 wt%, respectively, based on the total PLA content of the PLA solution, thereby stabilizing the emulsion. At this time, a stabilized emulsion can be prepared by reducing the interfacial tension at the hydrophobic / hydrophilic interface using small solid particles instead of a surfactant through the Pickering emulsion method. Afterwards, the emulsion solution was treated with a homogenizer and an ultrasonicator for 2 minutes and 1 minute, respectively, to prepare an emulsion solution. Then, the emulsion solution was cast on a glass petri dish to dry both the organic solvent and water, thereby preparing a composite material. The above dried composite material was crushed into pieces of approximately 3 to 5 mm in length using a blender to produce a PLA / cellulose (PLA / SCNF) composite filler.

[0098] Step 3: Mixing molding step of composite filler into pure PLA

[0099] In pure PLA, 1.0 wt%, 2.5 wt%, 5 wt%, 7.5 wt%, 10 wt%, 30 wt%, and 50 wt% of the PLA / cellulose (PLA / SCNF 2 wt%) composite filler manufactured in step 2 were mixed and extruded through a twin-screw extruder to manufacture a PLA-based composite plastic.

[0100] Comparative Example 2

[0101] In the PLA / cellulose (PLA / SCNF) composite filler manufacturing step of Step 2 of the above Example 8, an emulsion solution was manufactured by mixing a PLA solution in which 5 wt% of PLA was dissolved in DCM and a SCNF dispersion having a concentration of 1 wt% so that SCNF was 2 wt% relative to the dissolved PLA, and the same procedure as in Example 8 was performed except that 100 ml of the PLA solution and 200 ml of the SCNF dispersion were mixed and stabilized into an oil-in-water (O / W) type emulsion solution.

[0102] <Example 13> Manufacturing of PLA+PHA / SChNF composite plastic

[0103] A PLA+PHA / SChNF composite filler was manufactured and a composite plastic using the same was manufactured in the same manner as in Example 1, except that a PLA+PHA solution containing 3 wt% PLA and 2 wt% PHA dissolved in DCM and a dispersion containing 2 wt% SChNF were used.

[0104] <Example 14> Manufacturing of PLA+PHA / SCNF composite plastic

[0105] A PLA+PHA / SCNF composite filler was manufactured and a composite plastic using the same was manufactured in the same manner as in Example 8, except that a PLA+PHA solution containing 3 wt% PLA and 2 wt% PHA dissolved in DCM and a dispersion containing 2 wt% SCNF were used.

[0106] <Experimental Example 1> Image analysis and mechanical property evaluation according to the emulsion formulation of composite filler

[0107] Confocal microscopy of an emulsion solution can determine the fluorescence characteristics according to the dissolution of the dye in each solvent. The dye (Fluorescein) is soluble in distilled water (DI water) and fluoresces, whereas it is insoluble in an organic solvent (DCM) and does not fluoresce.

[0108] FIG. 3 shows the results of the confocal microscopy images on the top and the SEM images on the bottom of the cross-sections of the sheets after complete drying of the solvent for the emulsion solutions of Example 1 (W / O formulation) and Comparative Example 1 (O / W formulation) in the production of PLA / chitin (PLA / SChNF 2 wt%) composite fillers, and FIG. 4 shows the results of the emulsion solutions of Example 8 (W / O formulation) and Comparative Example 2 (O / W formulation) for the PLA / cellulose (PLA / SCNF 2 wt%) composite filler.

[0109] As a result, in the case of the water-in-oil (W / O) emulsion solutions of Examples 1 and 8, the PLA / DCM solution is observed to have a shape in which the spherical fluorescent SChNF dispersion or SCNF dispersion is wrapped, whereas in the case of the oil-in-water (O / W) formulations of Comparative Examples 1 and 2, the fluorescent SCNF dispersion or SChNF dispersion is observed to have an inverted shape in which the black spherical PLA / DCM solution is wrapped.

[0110] This structure is observed in the SEM images of the cross-sections of the sheets in which the organic solvent and water are completely dried. The composite plastics prepared from the emulsion solutions of Examples 1 and 8 (W / O formulations) have a form in which fine spherical chitin nanofibers are uniformly dispersed within the PLA matrix, whereas in the case of Comparative Examples 1 and 2 (O / W formulations), the water and DCM are dried and the chitin or cellulose reinforcing material is observed to have a form in which the spherical PLA is wrapped.

[0111] Table 1

[0112] Mechanical properties of composite fillers according to emulsion formulation

[0113]

[0114] From the results in Table 1 above, in the manufacture of composite fillers, there was no significant difference in the elastic modulus and tensile strength depending on the W / O formulation or the O / W formulation, but in the case of the W / O formulation, a significant increase in elongation was confirmed, and the toughness according to elongation also increased dramatically.

[0115] Therefore, the results of improvement in mechanical properties of composite fillers prepared from emulsion solutions based on W / O formulations support the uniform dispersion of chitin nanofibers (SChNF) or cellulose nanofibers (SCNF) within the PLA matrix.

[0116] The results shown in FIGS. 5 and 6 also confirm that the composite filler manufactured from the emulsion solution based on the W / O formulation has significantly better mechanical properties than the composite filler of the O / W formulation.

[0117] Table 2 below shows the results of measuring the mechanical properties of PLA / chitin (PLA / SChNF) composite filler according to the reinforcing material content manufactured according to the W / O emulsion formulation.

[0118] Table 2

[0119] Mechanical properties of PLA / chitin (PLA / SChNF) composite fillers according to reinforcing material content

[0120]

[0121] From the results in Table 2 above, it was confirmed that, compared to the NEAT PLA, which had an elongation of only about 4.8% due to the inherent brittleness of the material, the elongation of the PLA / SChNF composite filler of the present invention increased by at least about 6 times and at most about 74 times.

[0122] In particular, since the composite filler containing 2 wt% of SChNF shows an elongation of 351.8%, which is significantly higher than that of other composite fillers, the content of SChNF in the PLA matrix is ​​optimized to 1 to 3 wt%, more preferably 1.5 to 2.5 wt%. At this time, when the SChNF content is 3 wt%, the mechanical properties are reduced, which supports the result that as the amount of reinforcing agent added in a general composite system increases, dispersion within the matrix resin becomes difficult, which in turn reduces the mechanical properties.

[0123] Table 3 below shows the results of measuring the mechanical properties of PLA / cellulose (PLA / SCNF) composite filler according to the reinforcing material content manufactured according to the W / O emulsion formulation.

[0124] Table 3

[0125] Mechanical properties of PLA / cellulose (PLA / SCNF) composite fillers according to reinforcing material content

[0126]

[0127] Referring to Table 3 above, it was confirmed that, compared to the NEAT PLA, which had an elongation of only 4.8% due to the inherent brittleness of the material, the elongation of the PLA / SCNF composite filler of the present invention increased by at least about 5 times and at most about 24 times.

[0128] At this time, the best elongation was observed when the SCNF content was 2 wt% compared to PLA, whereas when the SCNF content was 3 wt%, the mechanical properties were confirmed to be lower than 2 wt%. These results support the finding that in a general composite system, as the amount of reinforcing agent added increases, dispersion within the matrix resin becomes difficult, resulting in a decrease in mechanical properties. Therefore, it can be confirmed that the improved mechanical properties were maximized when the SCNF content within the PLA matrix was 2 wt%, which means that it is the optimal content of SCNF that can be evenly dispersed within the PLA matrix.

[0129] Originally, due to the difference in polarity between PLA and SCNF, there was weak interfacial adhesion, but in the present invention, since the composite plastic was manufactured based on the Pickering emulsion method, the mechanical strength (especially, improved elongation and toughness) of the PLA / chitin or cellulose composite filler manufactured therefrom was demonstrated, thereby confirming that the problem of miscibility with PLA was overcome.

[0130] <Experimental Example 2> Evaluation of Mechanical Properties of PLA-Based Composite Plastics

[0131] The mechanical properties of a PLA-based composite plastic manufactured by mixing a composite filler containing 2 wt% of SChNF content (PCX-MB 2 wt%), which has the best mechanical properties among the composite fillers, into pure PLA are shown in Table 4 below.

[0132] Table 4

[0133] Evaluation of mechanical properties of PLA-based composite plastics

[0134]

[0135] As confirmed in Table 4 above, PCX-MB 100% (2 wt% of reinforcement content compared to the total PLA weight) has a tensile strength of 57.55 MPa, elongation of 267.26%, and toughness of 98.61 MJ / m 3 As a result, it has low tensile strength but the highest elongation and toughness, and Neat PLA (0 wt% of reinforcement content compared to the total PLA weight) has a tensile strength of 63.64 MPa, elongation of 5.26%, and toughness of 1.97 MJ / m. 3As a result, the tensile strength was the highest, but the elongation and toughness showed the lowest values, whereas in Examples 1 to 5, the PLA-based composite plastics manufactured with 1.0 wt%, 2.5 wt%, 5 wt%, 7.5 wt%, 10 wt%, 30 wt%, and 50 wt% of composite filler (PCX-MB) in pure PLA showed results that satisfied both tensile strength and toughness, and among them, in the case of 5 wt% of PLA / PCX-MB, the tensile strength was 55 MPa, the elongation was 209.75%, and the toughness was 66.03 MJ / m. 3 showed the highest figure.

[0136] <Experimental Example 3> Evaluation of the optical properties of PLA-based composite plastics

[0137] A PLA-based composite plastic was manufactured by mixing pure PLA with the composite filler manufactured above, which has the best mechanical properties compared to PLA, containing 2 wt% of SChNF content (PCX-MB 2 wt%), and the composite filler (PCX-MB 2 wt%) was composited with pure PLA through a twin-screw extrusion process at various contents (0 wt%, 1.0 wt%, 2.5 wt%, 5 wt%, 7.5 wt%, 10 wt%, 30 wt%, 50 wt%), and manufactured into a film through a hot press, and the results of measuring the transmittance of the manufactured film are presented in Table 5 below.

[0138] Table 5

[0139] Evaluation of optical properties of PLA-based composite plastics

[0140]

[0141] As confirmed in Table 5 above, Neat PLA (0 wt% of reinforcement content relative to the total PLA weight) showed the highest permeability at 91.3%, and when the content of composite filler (PCX-MB) was 1 wt%, 2.5 wt%, 5 wt%, 7.5 wt%, 10 wt%, 30 wt%, and 50 wt%, the permeability was 90.9%, 90.6%, 90.5%, 90.2%, 89.1%, and 86.4%, respectively, which were equivalent to or similar to that of pure PLA. On the other hand, when PCX-MB was 100% (2 wt% of reinforcement content relative to the total PLA weight), the lowest permeability was shown at 82.7%.

[0142] From the above, the transmittance of the PLA-based composite plastic of the present invention tends to increase as the content of the composite filler (PCX-MB) decreases, and in particular, as confirmed in Fig. 7, it can be confirmed that the PLA-based composite plastic has a visible light transmittance (550 nm) that is 4 to 10% higher than that of the composite filler alone (PCX-MB 100%).

[0143] FIGS. 9 to 11 are photographs of prototypes for comparing the transmittance of the PLA-based composite plastic of the present invention. The product model Neat L130 of FIG. 9 is Neat PLA of Comparative Example 1, the product model L130_V of FIG. 10 is PLA / PCX-MB 5% of Example 3, and the product model L130_O of FIG. 11 is a photograph of PCX-MB 100% as Comparative Example 2. The difference in apparent transparency can be confirmed with the naked eye through the photographs of the prototypes.

[0144] Although the present invention has been described in detail above only with respect to the described specific examples, it will be apparent to those skilled in the art that various modifications and variations are possible within the technical scope of the present invention, and it is natural that such modifications and variations fall within the scope of the appended claims.

Claims

1. 50 to 99 wt% of pure polylactic acid (PLA) raw material and A molded article in which 1.0 to 50 wt% of a composite filler is mixed with a reinforcing material dispersed in a biodegradable polymer matrix including PLA, A PLA-based composite plastic in which the above composite filler is a biodegradable polymer matrix including PLA and 1 to 3 wt% of a reinforcing material is dispersed and composited, and the reinforcing material is contained in an amount of 0.01 to 1.0 wt% based on the total PLA weight based on the reinforcing material content in the composite filler.

2. In the first paragraph, the PLA-based composite plastic has a tensile strength of 50 to 70 MPa and a toughness of 50 to 100 MJ / m. 3 A PLA-based composite plastic characterized by being satisfied with .

3. A PLA-based composite plastic according to claim 1, characterized in that the PLA-based composite plastic has a high visible light transmittance of 89% or more at a transmittance (550 nm).

4. In the first paragraph, the biodegradable polymer matrix is ​​polylactic acid (PLA) alone or polylactic acid plus polyhydroxyalkanoates (PHA), polybutylene terephthalate (PBAT), polybutylenesuccinate-coadipate (PBAT), polybutylenesuccinate-coadipate (PBAT), polybutylene succinate-terephthalate (PBAT), aliphatic polyester (AP), polyethylene succinate (PES), polybutylene succinate (PBS), polyvinyl alcohol (PVA), polyglycolic acid (PGA), polylactic acid-glycolic acid-copolymer (Poly A PLA-based composite plastic characterized by a mixture of one or two or more selected from the group consisting of polylactic-co-glycolic acid (PLGA), polycaprolactone (PCL), modified starch resin, and thermoplastic starch (TPS).

5. A PLA-based composite plastic according to claim 1, characterized in that the reinforcing material is any one natural polymer selected from the group consisting of cellulose, chitin, chitosan, dextrin, dextran, glycogen, pullulan, gelatin, and pectin.

6. A PLA-based composite plastic according to claim 5, characterized in that the natural polymer is in the form of nanofibers or nanocrystals of the natural polymer.

7. A PLA-based composite plastic characterized in that the natural polymer in paragraph 6 is surface-modified by succinylation or carboxylation and then nanofiberized.

8. A PLA-based composite plastic characterized in that, in the first paragraph, the composite filler is a biodegradable polymer solution containing PLA dissolved in an organic solvent, an aqueous dispersion in which a reinforcing material is dispersed, and the mixture is stabilized as a water-in-oil (W / O) Pickering emulsion solution and then dried.

9. A PLA-based composite plastic characterized in that the molded body in the first paragraph is one selected from the group consisting of an injection-molded product; a heat-processed product; and a film for extrusion molding or blow molding.

10. A PLA-based transparent film applicable to any one selected from the group consisting of industrial packaging materials, food containers, and food packaging materials made of PLA-based composite plastics according to any one of claims 1 to 9.

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