Biodegradable polymer dispersion, process for preparing the same, and biodegradable article using the same

Abstract

This disclosure relates to a biodegradable polymer dispersion, a method for preparing the same, and a biodegradable article using the same. The method for preparing the biodegradable polymer dispersion comprises: (1) preparing a biodegradable suspension comprising a polyhydroxyalkanoate (PHA); and (2) filtering the biodegradable suspension using rotor separation, wherein the solids content of the biodegradable polymer dispersion is from 10% to 60% by weight, and the polyhydroxyalkanoate (PHA) comprises a repeating unit derived from 4-hydroxybutyrate in an amount from 0.1% to 60% by weight based on the total weight of the polyhydroxyalkanoate (PHA).

Description

Biodegradable Polymer Dispersion, Method for Preparing the Same, and Biodegradable Articles Using the Same Field of the Invention The present disclosure relates to a biodegradable polymer dispersion, a method for preparing the same, and a biodegradable article using the same. Background of the Invention Due to the increasing environmental problems caused by the abuse of synthetic plastics, there is a growing interest in biodegradable polymers that have physical properties similar to synthetic plastics and can be naturally decomposed by microorganisms in soil or the ocean. Such biodegradable polymers are also widely used as dispersions to form coating layers to increase the service life and recyclability of various products. Generally, however, when a coating layer is formed only with a dispersion containing a biodegradable polymer, due to the high melting temperature (Tm) of the material itself, the processability and productivity are low when the coating layer is formed, making it difficult to be used in a large-scale production system. At the same time, in order to improve the service life and recyclability of various products such as paper, films, fibers, packaging materials, metals, various containers (such as bottles) and the like, it is important to improve mechanical properties such as oil resistance and water resistance. In particular, a food packaging material for packaging foods rich in moisture or oil may have the problem that the packaging material is torn by the moisture or oil from the food, thereby contaminating the food or having a short service life. To improve mechanical properties, water resistance, oil resistance and the like, a method of forming a coating layer on the surface of a product is used; however, there is a problem that biodegradability and recyclability deteriorate due to the coating layer. For example, the biodegradability of a coating layer component that can improve water resistance and oil resistance is low, or even if the biodegradability of the coating layer is excellent, but due to low antibacterial stability, the service life of a product may be poor. Moreover, once used, an additional method may be required to remove the coating layer from the surface of a product. In addition, since it is difficult to achieve the desired concentration and viscosity of a coating solution, the coating properties are reduced, resulting in low productivity and process efficiency. As a result, it is difficult to ensure the desired physical properties; therefore, there are still limitations in using it for various purposes. Technical Problem According to one aspect, a technical problem to be solved is to provide a biodegradable polymer dispersion and a method for preparing the same, which are environmentally friendly due to excellent biodegradability and biocompatibility, can improve coatability, water resistance and oil resistance, and can improve productivity and efficiency. In addition, according to another aspect to be solved, a technical problem is to provide a biodegradable object that uses the biodegradable polymer dispersion and has improved service life, quality, and recyclability. Solution to the problem One embodiment provides a method for preparing a biodegradable polymer dispersion, which includes (1) preparing a biodegradable suspension containing a polyhydroxyalkanoate (PHA); and (2) filtering the biodegradable suspension using rotor separation, wherein the solid content of the biodegradable polymer dispersion is 10% by weight to 60% by weight, and the polyhydroxyalkanoate (PHA) contains a repeating unit derived from 4-hydroxybutyrate in an amount of 0.1% by weight to 60% by weight based on the total weight of the polyhydroxyalkanoate (PHA). According to another embodiment, the rotor separation method in step (2) can be carried out with a rotational force of G' greater than 900 g. According to another embodiment, the rotor separation method in step (2) can be carried out with a rotational force of G' greater than 900 g to less than 35,000 g. According to another embodiment, the rotor separation method in step (2) can be carried out using a centrifugal filter. According to another embodiment, after step (2), a step of heating the filtered product at a temperature of 50°C to 80°C for at least 10 minutes can be further carried out. According to another embodiment, after the heat treatment step, a step of adding an additive can be further carried out, and the additive includes at least one selected from the group consisting of a thickener, wax, a pH adjuster, an antifoaming agent, and an antibacterial agent. According to another embodiment, step (1) can include mixing the polyhydroxyalkanoate (PHA) with a dispersant for dispersion treatment. According to another embodiment, the dispersant can include at least one selected from the group consisting of: polyvinyl alcohol, polyvinylpyrrolidone, methyl polyvinyl alkyl ether, sodium dodecylbenzenesulfonate, alkylbenzenesulfonate, nonylphenol ether sulfate, sodium lauryl sulfate, lithium dodecyl sulfate, alkyl phosphate, polypropylene glycol ester, cocoamidopropyl betaine, and lecithin. According to another embodiment, the dispersion treatment can be carried out at a rotational speed of 500 rpm to 30,000 rpm. According to another embodiment, the polyhydroxyalkanoate (PHA) comprises a poly(3-hydroxybutyrate-co-4-hydroxybutyrate) copolymer, and the poly(3-hydroxybutyrate-co-4-hydroxybutyrate) copolymer may comprise a repeating unit derived from 4-hydroxybutyrate in an amount of 18 wt% to 60 wt% based on the total weight of the poly(3-hydroxybutyrate-co-4-hydroxybutyrate) copolymer. According to another embodiment, the polyhydroxyalkanoate (PHA) may have a weight average molecular weight of 550,000 g / mol to 1,000,000 g / mol. In addition, another embodiment provides a biodegradable polymer dispersion prepared by the above preparation method. According to another embodiment, the viscosity measured using a Brookfield viscometer at 25 °C may be greater than 10 cPs to 10,000 cPs. According to another embodiment, when a coating layer is formed on a substrate from the biodegradable polymer dispersion at a coating amount of 15 g / m 2 and when the Cobb water absorption test is carried out according to the TAPPI T441 standard, the water resistance may be 3 g / m 2 to 50 g / m 2 . According to another embodiment, when a coating layer is formed on a substrate from the biodegradable polymer dispersion at a coating amount of 15 g / m 2 and it is evaluated according to the TAPPI T559 standard, the oil resistance set rating may be 5 or higher. Another embodiment provides a biodegradable article comprising a substrate; and a biodegradable coating layer formed on at least one side of the substrate using the biodegradable polymer dispersion. Advantageous effects of the invention The method for preparing a biodegradable polymer dispersion includes filtering a biodegradable suspension using a rotor separation method, where the biodegradable suspension contains a polyhydroxyalkanoate (PHA) that includes a repeating unit derived from a specific amount of 4-hydroxybutyrate (4-HB). As a result, a dispersion with appropriate viscosity, high purity, and high concentration can be obtained. When a coating layer is formed using the dispersion, the particles to be coated can be surface-coated with low thermal energy, thereby accelerating the production speed and ensuring process efficiency, as well as enhancing dispersibility, coatability, and antibacterial stability. In addition, a dispersion prepared according to the above method for preparing a biodegradable polymer dispersion has excellent dispersibility and coatability. A biodegradable article prepared using it has excellent water resistance, oil resistance, and antibacterial stability, thereby achieving a long service life and high quality. Correspondingly, the biodegradable polymer dispersion according to one embodiment can be advantageously used as a coating solution to increase the service life, quality, and recyclability of various products such as paper, films, fibers, packaging materials, metals, and various containers, and it is also advantageous in expanding its uses because it can be advantageously used as an additive for improving various formulations and physical properties. Best Mode for Carrying Out the Invention Hereinafter, the present disclosure will be described in detail. The present disclosure is not limited to the disclosure given below, but it can be modified into various forms as long as the gist of the present invention remains unchanged. In this specification, the term "comprising" is intended to specify a particular feature, region, step, method, element, and / or component. It does not exclude the presence or addition of any other feature, region, step, method, element, and / or component, unless specifically stated otherwise. All numbers and expressions related to the amounts of components, reaction conditions, and the like used herein should be understood to be modified by the term "about" unless otherwise specified. The terms first, second, and the like in this specification are used to describe various components. However, these components should not be limited by these terms. These terms are only used for the purpose of distinguishing one component from another. Method for Preparing a Biodegradable Polymer Dispersion In one embodiment, the method for preparing a biodegradable polymer dispersion comprises (1) preparing a biodegradable suspension comprising a polyhydroxyalkanoate (PHA); and (2) filtering the biodegradable suspension using a rotor separation method, wherein the solid content of the biodegradable polymer dispersion is 10 wt% to 60 wt%, and the polyhydroxyalkanoate (PHA) comprises a repeating unit derived from 4-hydroxybutyrate in an amount of 0.1 wt% to 60 wt% based on the total weight of the polyhydroxyalkanoate (PHA). The method for preparing a biodegradable polymer dispersion uses a filtration method of precipitation caused by a rotational force by using a rotor separation method, which is different from the conventional physical emulsification methods using high-temperature sterilization, homogenizers, high pressure, high shear, colloid mills, and the like. As a result, a stable biodegradable polymer dispersion having appropriate viscosity, high purity, and high concentration can be obtained. In addition, the biodegradable polymer dispersion thus obtained can have excellent dispersibility, coatability, antibacterial stability, water resistance, and oil resistance. Further, when a coating layer is formed on a substrate using the biodegradable polymer dispersion, the particles to be coated can be surface-coated with low thermal energy; thus, it has great technical significance because it can speed up the production speed and ensure process simplification. Hereinafter, with reference to FIG. 1, each step of the method (S100) for preparing a biodegradable polymer dispersion according to one embodiment will be described in detail. Step (1): Prepare a biodegradable suspension (S110) comprising a polyhydroxyalkanoate (PHA) The method for preparing a biodegradable polymer dispersion according to one embodiment comprises preparing a biodegradable suspension comprising a polyhydroxyalkanoate (PHA). Polyhydroxyalkanoate (PHA) is a natural thermoplastic polyester polymer that accumulates in microbial cells. Since it is a biodegradable material, it can be composted and ultimately decomposed into carbon dioxide, water, and organic waste without generating toxic waste. The polyhydroxyalkanoate (PHA) has physical properties similar to those of conventional petroleum-derived synthetic polymers such as poly(butylene adipate-co-terephthalate) (PBAT), poly(butylene succinate) (PBS), poly(butylene succinate terephthalate) (PBST), and poly(butylene succinate adipate) (PBSA), exhibits complete biodegradability, and is excellent in biocompatibility. Specifically, different from other environmentally friendly plastic materials such as PBS, PLA, and PTT, polyhydroxyalkanoates (PHA) can be synthesized from more than 150 monomers. Therefore, depending on the type of monomers, hundreds of PHAs can be prepared. Hundreds of different PHAs depending on the type of monomers have completely different structures and properties. The polyhydroxyalkanoate (PHA) can be composed of a single monomer repeating unit in living cells and can be formed by polymerizing one or more monomer repeating units. Specifically, the polyhydroxyalkanoate (PHA) can be a homo-polyhydroxyalkanoate or a polyhydroxyalkanoate copolymer, that is, a copolymer in which different repeating units are randomly distributed in the polymer chain. The polyhydroxyalkanoate (PHA) can be obtained by breaking the cells of microorganisms using a mechanical method or a physical method during water purification, or it can be obtained by using a non-mechanical method or a chemical method to break the cells of microorganisms. The polyhydroxyalkanoate (PHA) can have a weight average molecular weight of 10,000 g / mol to 1,000,000 g / mol, 30,000 g / mol to 1,000,000 g / mol, 50,000 g / mol to 1,000,000 g / mol, 70,000 g / mol to 1,000,000 g / mol, 100,000 g / mol to 1,000,000 g / mol, 100,000 g / mol to 800,000 g / mol, 200,000 g / mol to 1,000,000 g / mol, 200,000 g / mol to 800,000 g / mol, 300,000 g / mol to 1,000,000 g / mol, 300,000 g / mol to 800,000 g / mol, 400,000 g / mol to 1,000,000 g / mol, 500,000 g / mol to 1,000,000 g / mol, 500,000 g / mol to 800,000 g / mol, 550,000 g / mol to 1,000,000 g / mol, 550,000 g / mol to 800,000 g / mol, 600,000 g / mol to 1,000,000 g / mol, or 600,000 g / mol to 800,000 g / mol, but not limited thereto. The polyhydroxyalkanoate (PHA) can be a copolymer comprising a repeating unit derived from at least one (at least a monomer) selected from the group consisting of: 3-hydroxybutyrate (3-HB), 3-hydroxypropionate (3-HP), 3-hydroxyvalerate (3-HV), 3-hydroxyhexanoate (3-HH), 4-hydroxybutyrate (4-HB), 4-hydroxyvalerate (4-HV), 4-hydroxyhexanoate (4-HH), 5-hydroxyvalerate (5-HV), and 6-hydroxyhexanoate (6-HH), but not limited thereto. The polyhydroxyalkanoate (PHA) can be a crystalline polyhydroxyalkanoate (cPHA), a semi-crystalline polyhydroxyalkanoate (scPHA), or an amorphous polyhydroxyalkanoate (aPHA), depending on the type of monomer and the content of the repeating unit derived therefrom. For example, the polyhydroxyalkanoate can be classified as cPHA, scPHA, or aPHA because its crystallinity is controlled depending on the content of a repeating unit derived from 4-hydroxybutyrate (4-HB). Specifically, the polyhydroxyalkanoate (PHA) can comprise a poly(3-hydroxybutyrate-co-4-hydroxybutyrate) copolymer comprising a repeating unit derived from 3-hydroxybutyrate (3-HB); and a repeating unit derived from 4-hydroxybutyrate (4-HB). The poly(3-hydroxybutyrate-co-4-hydroxybutyrate) copolymer may comprise a repeating unit derived from 4-hydroxybutyrate (4-HB) (repeating unit derived from 4-HB) in an amount of 0.1 wt% to 60 wt% based on the total weight of the poly(3-hydroxybutyrate-co-4-hydroxybutyrate) copolymer. Specifically, the content of a repeating unit derived from the 4-HB may be 0.5 wt% to 60 wt%, 1 wt% to 60 wt%, 5 wt% to 60 wt%, 10 wt% to 60 wt%, 10 wt% to 55 wt%, 10 wt% to 50 wt%, 10 wt% to 45 wt%, 10 wt% to 40 wt%, 15 wt% to 60 wt%, 15 wt% to 55 wt%, 15 wt% to 50 wt%, 15 wt% to 45 wt%, 15 wt% to 40 wt%, 17 wt% to 60 wt%, 17 wt% to 55 wt%, 17 wt% to 50 wt%, 17 wt% to 45 wt%, 17 wt% to 40 wt%, 18 wt% to 60 wt%, 18 wt% to 55 wt%, 18 wt% to 50 wt%, 18 wt% to 45 wt%, 18 wt% to 40 wt%, 20 wt% to 60 wt%, 20 wt% to 55 wt%, 20 wt% to 50 wt%, 20 wt% to 45 wt%, 20 wt% to 40 wt%, 25 wt% to 60 wt%, 25 wt% to 55 wt%, 25 wt% to 50 wt%, 25 wt% to 45 wt%, 25 wt% to 40 wt%, 28 wt% to 60 wt%, 28 wt% to 50 wt%, 28 wt% to 45 wt%, 28 wt% to 40 wt%, 30 wt% to 60 wt%, 30 wt% to 55 wt%, 30 wt% to 50 wt%, 30 wt% to 45 wt%, 30 wt% to 40 wt%, 20 wt% to 38 wt%, or 30 wt% to 38 wt% based on the total weight of the copolymer. For example, the polyhydroxyalkanoate (PHA) comprises a poly(3-hydroxybutyrate-co-4-hydroxybutyrate) copolymer, and the poly(3-hydroxybutyrate-co-4-hydroxybutyrate) copolymer may comprise a repeating unit derived from 4-hydroxybutyrate (4-HB) in an amount of 18 wt% to 60 wt%, 26 wt% to 60 wt%, or 30 wt% to 60 wt% based on the total weight of the poly(3-hydroxybutyrate-co-4-hydroxybutyrate) copolymer. When the content of the repeating unit derived from 4-HB is within the above range, the poly(3-hydroxybutyrate-co-4-hydroxybutyrate) copolymer can be an amorphous PHA (aPHA). According to one embodiment, the biodegradable polymer dispersion in which this amorphous PHA is dispersed can form a coating layer having excellent mechanical properties, oil resistance, water resistance, heat resistance, and the like. The polyhydroxyalkanoate (PHA) can have a particle shape controlled to a predetermined size. Specifically, the polyhydroxyalkanoate (PHA) particles can be biodegradable polymer particles and can have an average particle diameter (D 50 ) of 0.5 μm to 5 μm. Specifically, the polyhydroxyalkanoate (PHA) can have an average particle diameter (D 50 ) of 0.6 μm or greater, 0.8 μm or greater, or 1.0 μm or greater, and 5 μm or less, 4.5 μm or less, 4 μm or less, 3.5 μm or less, 3 μm or less, 2.5 μm or less, or 2 μm or less. When the average particle diameter (D 50 ) of the polyhydroxyalkanoate (PHA) particles is within the above range, a biodegradable polymer dispersion having excellent dispersibility can be obtained. When it is used to form a coating layer on a substrate (e.g., paper, fiber, metal, and the like), a coating layer having excellent mechanical properties, oil resistance, water resistance, heat resistance, and the like can be formed. According to one embodiment, step (1) can include mixing the polyhydroxyalkanoate (PHA) with a dispersant and performing a dispersion treatment. Specifically, step (1) can include preparing a crude dispersion containing the polyhydroxyalkanoate (PHA); and mixing the crude dispersion containing the polyhydroxyalkanoate (PHA) with a dispersant and performing a dispersion treatment. That is, the polyhydroxyalkanoate (PHA) in the form of a crude dispersion containing the polyhydroxyalkanoate (PHA) can be mixed with a dispersant. In this case, the crude dispersion containing the polyhydroxyalkanoate (PHA) may contain the polyhydroxyalkanoate (PHA) with a solid content of 20% by weight or less, 15% by weight or less, or 10% by weight or less based on the total weight of the crude dispersion. Specifically, the crude dispersion containing the polyhydroxyalkanoate (PHA) may be a crude dispersion containing the polyhydroxyalkanoate (PHA) with a solid content of 1% to 20% by weight, 1% to 15% by weight, 1% to 10% by weight, 3% to 15% by weight, 3% to 10% by weight, 5% to 15% by weight, or 5% to 10% by weight. In addition, the crude dispersion containing the polyhydroxyalkanoate (PHA) may be a solution in which the polyhydroxyalkanoate (PHA) is dispersed in an aqueous solvent (such as water). According to one embodiment, the crude dispersion containing the polyhydroxyalkanoate (PHA) may be a crude dispersion of an amorphous PHA having a low solid content of 5% to 15% by weight, such as 5% to 10% by weight. Meanwhile, the dispersant is not particularly limited as long as it is a material that can uniformly disperse the polyhydroxyalkanoate (PHA). Specifically, the dispersant may include at least one selected from the group consisting of polyvinyl alcohol, polyvinylpyrrolidone, methyl polyvinyl alkyl ether, sodium dodecylbenzenesulfonate, alkylbenzenesulfonate, nonylphenol ether sulfate, sodium lauryl sulfate, lithium dodecyl sulfate, alkyl phosphate, polypropylene glycol ester, coconut betaine, and lecithin. Specifically, the dispersant can be used by being dispersed in a solvent. More specifically, the dispersant may be a PVA dispersant in which polyvinyl alcohol (PVA) is dispersed in an aqueous solvent (such as water). By using the PVA dispersant, a suspension can be obtained in which the polyhydroxyalkanoate (PHA) is homogeneously and uniformly dispersed. The content of the polyvinyl alcohol (PVA) contained in the PVA dispersant may be 1% to 50% by weight, 1% to 40% by weight, 2% to 30% by weight, 3% to 20% by weight, or 3% to 10% by weight based on the total weight of the PVA dispersant, but is not limited thereto. The polyvinyl alcohol (PVA) may have a saponification value of 1 mol% to 99 mol%, 5 mol% to 99 mol%, 10 mol% to 99 mol%, 20 mol% to 99 mol%, 30 mol% to 99 mol%, 40 mol% to 99 mol%, 45 mol% to 99 mol%, 48 mol% to 99 mol%, 50 mol% to 99 mol%, 60 mol% to 99 mol%, or 70 mol% to 98 mol%, but is not limited thereto. The content of the dispersant may be 0.01 wt% to 30 wt% based on the solid content of the PHA. For example, the solid content of the dispersant may be 0.01 wt% to 20 wt%, 0.01 wt% to 15 wt%, 0.01 wt% to 12 wt%, 0.02 wt% to 8 wt%, 0.05 wt% to 6 wt%, 0.1 wt% to 5 wt%, 0.2 wt% to 7 wt%, 0.3 wt% to 7 wt%, 0.5 wt% to 7 wt%, or 1 wt% to 7 wt%, but is not limited thereto. According to one embodiment, the dispersion treatment may be carried out at a rotational speed of 500 rpm to 30,000 rpm. The mixing of the polyhydroxyalkanoate (PHA) and the dispersant can be carried out using a commonly known mixer (such as a homogenizer or the like). When the polyhydroxyalkanoate (PHA) and the dispersant are mixed (stirred) through the mixer, the rotational speed of the mixer can be 500 rpm to 30,000 rpm, 1,000 rpm to 30,000 rpm, 1,500 rpm to 30,000 rpm, 2,000 rpm to 30,000 rpm, 2,000 rpm to 25,000 rpm, 2,000 rpm to 20,000 rpm, 2,000 rpm to 15,000 rpm, 3,000 rpm to 15,000 rpm, 4,000 rpm to 10,000 rpm, 5,000 rpm to 8,500 rpm, 5,300 rpm to 8,300 rpm, or 5,500 rpm to 8,200 rpm. The rotational speed can be adjusted depending on the type and size of the equipment, but is not limited thereto. For example, the rotational speed can be selected according to the linear speed of the homogenizer of 150 cm / s to 2,000 cm / s based on the impeller diameter size of the equipment. Step (2): Filter the biodegradable suspension (S120) using the rotor separation method The method for preparing a biodegradable polymer dispersion according to one embodiment includes filtering the biodegradable suspension obtained in step (1) using the rotor separation method. Since the method for preparing a biodegradable polymer dispersion involves filtration using a rotor separation method, a dispersion with high viscosity, high concentration, and high purity can be obtained, in which a polyhydroxyalkanoate (PHA) with a fine particle size is homogeneously dispersed. In particular, since the occurrence of aggregation or precipitation can be minimized, the production speed can be increased, and process simplification and process efficiency can be ensured. Specifically, step (2) is a filtration method for precipitation caused by the rotational force using a rotor separation method. For example, a centrifugal filter, preferably a high-speed centrifugal filter, can be used. For example, the biodegradable suspension is placed in the container (drum) of the high-speed centrifugal filter, which is a rotor separator and rotates at a high speed to homogeneously and finely separate and filter the substances in the biodegradable suspension according to the density and size of the substances. When using the rotor separation method, the degree of aggregation, fineness of particles, solid content, viscosity, coating amount, antibacterial stability, water resistance, and oil resistance of the final biodegradable polymer dispersion may vary depending on the relative centrifugal force (RCF). The relative centrifugal force refers to the ratio of gravity to the centrifugal force acting on the particles in the biodegradable suspension, which can be expressed as G' force. According to one embodiment, the rotational force of the rotor separation method can further increase the productivity while minimizing the occurrence of aggregation or precipitation, thereby obtaining a dispersion with high purity, high concentration, and optimal viscosity. It may be an important factor in enhancing antibacterial stability, oil resistance, and water resistance. Specifically, the rotor separation method in step (2) can be carried out with a rotational force of G' force greater than 900 g. For example, the rotor separation method in step (2) can be carried out with a G' force of 1,000 g or greater, 1,500 g or greater, 2,000 g or greater, 3,000 g or greater, 4,000 g or greater, 5,000 g or greater, 7,000 g or greater, 8,000 g or greater, 10,000 g or greater, 12,000 g or greater, 15,000 g or greater, 17,000 g or greater, 18,000 g or greater, or 20,000 g or greater, and less than 35,000 g, 30,000 g or less, 29,000 g or less, 28,000 g or less, 25,000 g or less, 23,000 g or less, 22,000 g or less, or 21,000 g or less of rotational force. For example, the rotor separation method in step (2) can be carried out with a G' force greater than 900 g to less than 35,000 g, 1,000 g to 30,000 g, 3,000 g to 30,000 g, 5,000 g to 30,000 g, 7,000 g to 30,000 g, 10,000 g to 30,000 g, 15,000 g to 30,000 g, 15,000 g to 25,000 g, 18,000 g to 30,000 g, 18,000 g to 25,000 g, or 18,000 g to 22,000 g of rotational force. When the rotational force of the rotor separation method satisfies the above range, aggregation can be minimized, a dispersion with high viscosity, high concentration and high purity can be obtained, the coatability, antibacterial stability, water resistance and oil resistance can be improved, and the productivity and process efficiency can be improved. Specifically, based on a cylindrical drum with a diameter of about 45 cm in a high-speed centrifuge, it can be rotated at a speed of about 2,000 to 15,000 rpm, greater than 3,000 to less than 15,000 rpm, 3,500 to 14,000 rpm, or 5,000 to 13,000 rpm to generate a rotational force with a G' force greater than 900 g. The rotational speed of the G' force may vary depending on the diameter of the centrifugal equipment, such as a high-speed centrifuge. Meanwhile, according to one embodiment, an additive can be added to the biodegradable suspension before using the rotor separation method. The additive is not particularly limited as long as it is a commonly known additive. Specifically, the additive can include at least one selected from the group consisting of a thickener, wax, a pH adjuster, an antifoaming agent, and an antibacterial agent. More specifically, the additive can include an antifoaming agent. The antifoaming agent is not particularly limited as long as it is a commonly known substance. Specifically, the antifoaming agent may include at least one selected from the group consisting of an inorganic particle antifoaming agent, an oil-type antifoaming agent, and a polymer antifoaming agent. More specifically, the antifoaming agent may include at least one selected from the group consisting of a silicone antifoaming agent, a mineral oil antifoaming agent, and a polysiloxane antifoaming agent. The pH adjuster, thickener, wax, and antibacterial agent are not particularly limited as long as they are commonly known substances. For example, they may include the additives listed in step (3). According to one embodiment, once the antifoaming agent is added to the suspension, high-speed dispersion treatment is performed, and filtration is carried out using a rotary separation method to obtain a PHA suspension (e.g., an amorphous PHA suspension) having high viscosity, high concentration, and high purity. In this case, the high-speed dispersion treatment is the same as that described in step (1) (the dispersion treatment in step (1)). Step (3): Subject the filtered product to heat treatment (S130) The method for preparing a biodegradable polymer dispersion according to one embodiment may further include subjecting the filtered product obtained in step (2) to heat treatment. Specifically, step (3) is a step of heating the suspension at a temperature significantly lower than the conventional high-temperature sterilization temperature (e.g., 145 °C or higher) to sterilize the suspension. More specifically, after step (2), a further step of subjecting the filtered product to heat treatment at 50 °C to 80 °C for 10 minutes or longer may be performed. For example, the heat treatment may be carried out at 50 °C to 75 °C, 50 °C to 70 °C, or 60 °C to 70 °C for 15 minutes to 60 minutes, 15 minutes to 50 minutes, 15 minutes to 40 minutes, 20 minutes to 60 minutes, 20 minutes to 50 minutes, or 20 minutes to 40 minutes. When the suspension is subjected to heat treatment, sterilization treatment can be effectively carried out while minimizing changes in the physical properties of the biodegradable polymer (e.g., polyhydroxyalkanoate (PHA)) contained in the suspension. When the suspension subjected to the heat treatment is used to prepare the biodegradable polymer dispersion according to one embodiment, a biodegradable polymer dispersion having excellent antibacterial stability and dispersion stability can be provided. Meanwhile, after the heat treatment step, a further step of adding an additive to the suspension subjected to heat treatment may be performed. The additive is not particularly limited as long as it is a commonly known additive. Specifically, the suspension subjected to heat treatment may be mixed with an additive to be formulated. More specifically, after the heat treatment step, a step of adding an additive may be further performed. The additive includes at least one selected from the group consisting of a thickening agent, wax, a pH adjuster, an antifoaming agent, and an antibacterial agent. The additive may include two or more selected from the group consisting of a thickening agent, wax, a pH adjuster, an antifoaming agent, and an antibacterial agent. These additives can be selected depending on the desired physical properties and uses. In addition, these additives can be added simultaneously or stepwise. According to one embodiment, these additives can be added simultaneously. According to another embodiment, these additives can be added stepwise. When these additives are added stepwise, a bio-degradable polymer dispersion that has been effectively formulated can be prepared from the suspension. There is no particular limitation on the thickening agent as long as it is a substance that can control the viscosity of the suspension. Specifically, the thickening agent may include at least one selected from the group consisting of starch, xanthan gum, guar gum, carboxymethyl cellulose (CMC), and carrageenan. There is no particular limitation on the wax as long as it is a commonly known substance. Specifically, the wax may include at least one selected from the group consisting of beeswax, soy wax, and carnauba wax. There is no particular limitation on the antifoaming agent as long as it is a commonly known substance. Specifically, it may include at least one selected from the group consisting of an inorganic particle antifoaming agent, an oil-type antifoaming agent, and a polymer antifoaming agent. For example, the antifoaming agent may include at least one selected from the group consisting of a silicone antifoaming agent, a mineral oil antifoaming agent, and a polysiloxane antifoaming agent. There is no particular limitation on the antibacterial agent as long as it is a commonly known substance. Specifically, the antibacterial agent may include at least one selected from the group consisting of alcohol, salicylic acid, benzoic acid, licorice extract, yucca extract, chitooligosaccharide, chitosan, 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT), octyl isothiazolinone (OIT), and benzisothiazolinone (BIT). The pH adjuster refers to a substance added to a solution to adjust the pH. It may include both a pH reducer for reducing the pH and a pH increaser for increasing the pH. Specifically, the pH reducer may be a strong acidic substance such as sulfuric acid and hydrochloric acid or an aqueous ammonium salt solution, and the pH increaser may be a basic substance such as ammonia water, sodium hydroxide, lithium hydroxide, and potassium hydroxide or an aqueous acetate solution, but is not limited thereto. For example, the pH adjuster may be selected from at least one of the group consisting of acetic acid, lactic acid, hydrochloric acid, phosphoric acid, sodium hydroxide, citric acid, malic acid, fumaric acid, potassium phosphate, sodium bicarbonate, and sodium phosphate. The amounts of the thickener, wax, pH adjuster, defoamer, and antibacterial agent added (used) may each be based on the total weight of the solid content of the biodegradable polymer dispersion, ranging from 0.001 wt% to 20 wt%, 0.005 wt% to 20 wt%, 0.01 wt% to 15 wt%, 0.01 wt% to 12 wt%, 0.01 wt% to 10 wt%, 0.01 wt% to 8 wt%, 0.01 wt% to 5 wt%, 0.2 wt% to 4.5 wt%, 0.2 wt% to 4 wt%, or 0.5 wt% to 3 wt%. The solid content of the biodegradable polymer dispersion prepared according to the above preparation method may be 10 wt% to 60 wt%. Specifically, the solid content of the biodegradable polymer dispersion may be 20 wt% to 60 wt%, 20 wt% to 50 wt%, 30 wt% to 60 wt%, 30 wt% to 50 wt%, or 35 wt% to 45 wt%. For example, according to one embodiment, a crude amorphous PHA dispersion having a low solid content, such as 10 wt% or less, can be used to obtain an amorphous biodegradable polymer dispersion having a high solid content, such as 20 wt% to 50 wt%. Specifically, a crude amorphous PHA dispersion having a low solid content, such as 10 wt% or less, can be used to obtain an amorphous biodegradable polymer dispersion having a high solid content, such as 20 wt% to 50 wt%, and an optimal viscosity of 20 cPs to 10,000 cPs. As described above, the method for preparing a biodegradable polymer dispersion filters a biodegradable suspension by using precipitation caused by the rotational force of the rotor separation method, wherein the biodegradable suspension contains a polyhydroxyalkanoate (PHA) that includes a repeating unit derived from a specific amount of 4-hydroxybutyrate (4-HB). Thus, a stable dispersion with appropriate viscosity, high purity, and high concentration can be obtained. Further, when a coating layer is formed using the dispersion, the particles to be coated can be surface-coated with low thermal energy; thus, an accelerated production speed and simplified process can be ensured. Biodegradable polymer dispersion According to one embodiment, there is provided a biodegradable polymer dispersion prepared by the above preparation method. Specifically, the biodegradable polymer dispersion is prepared by the method for preparing a biodegradable polymer dispersion and has a solid content of 10 wt% to 60 wt%. The solid content of the biodegradable polymer dispersion is as described above. The biodegradable polymer dispersion prepared by the method for preparing a biodegradable polymer dispersion has high viscosity, high concentration and high purity. Due to its excellent dispersibility and coatability, it can be advantageously used as a coating solution to increase the service life and recyclability of various products such as paper, films, fibers, packaging materials, metals and various containers. In addition, the biodegradable polymer dispersion has excellent antibacterial stability (bacterial stability) and can improve the service life and quality of biodegradable products. A coating layer formed using it can have excellent water resistance and oil resistance. Since the biodegradable polymer dispersion having the above characteristics can be advantageously used as an additive for various formulations and improvement of physical properties, it is advantageous in expanding its uses. The biodegradable polymer dispersion according to one embodiment includes the above-mentioned polyhydroxyalkanoate (PHA) particles as biodegradable polymer particles; the above-mentioned dispersant; the above-mentioned additives; and a dispersion solvent (such as water or the like). In addition, the biodegradable polymer dispersion may include an additive, which includes at least one selected from the group consisting of a thickener, wax, a pH adjuster, an antifoaming agent and an antibacterial agent. The additive is not particularly limited, and its specific types are as described above. The biodegradable polymer dispersion according to one embodiment may have a viscosity that ensures coatability, processability, and the like. Specifically, when measured using a Brookfield viscometer at 25 °C, the biodegradable polymer dispersion according to one embodiment may have a viscosity greater than 10 cPs to 10,000 cPs. Specifically, the viscosity of the biodegradable polymer dispersion at 25 °C may be 20 cPs to 10,000 cPs, 30 cPs to 10,000 cPs, 50 cPs to 10,000 cPs, 100 cPs to 10,000 cPs, 200 cPs to 10,000 cPs, 300 cPs to 10,000 cPs, 400 cps to 10,000 cps, 500 cps to 10,000 cps, 300 cps to 8,000 cps, 300 cps to 6,000 cps, 300 cps to 5,000 cps, 300 cps to 4,000 cps, 300 cps to 3,000 cps, 300 cps to 2,000 cps, 300 cps to 1,000 cps, 200 cps to 2,000 cps, 300 cps to 1,500 cps, 350 cps to 1,200 cps, 400 cps to 1,000 cps, 400 cps to 900 cps, 400 cps to 800 cps, 400 cps to 700 cps, 500 cPs to 700 cPs, or 500 cPs to 600 cPs. When the biodegradable polymer dispersion has a viscosity that meets the above range, it can be advantageously used to achieve the desired effect. The biodegradable polymer dispersion according to one embodiment may have a pH that ensures long-term storage stability and the like. Specifically, the biodegradable polymer dispersion according to one embodiment may have a pH of 5 to 11, more specifically, 6 to 11, 6 to 10, or 8 to 10, but is not limited thereto. At the same time, when a coating layer is formed on a substrate from the biodegradable polymer dispersion at a coating amount of 15 g / m 2 and when the Cobb water absorption test is carried out according to the TAPPI T441 standard, the water resistance may be 3 g / m 2 to 50 g / m 2 . Specifically, the water resistance of the coating layer may be 3 g / m 2 to 40 g / m 2 and 3 g / m 2 to 30 g / m 2 and 3 g / m 2 to less than 30 g / m 2 and 3 g / m 2 to 25 g / m 2 and 3 g / m 2 to 20 g / m 2 and 3 g / m 2 to 15 g / m 2 and 5 g / m 2 to 18 g / m 2 or 5 g / m 2 to 15 g / m 2 . The water resistance can be measured according to the TAPPI T441 standard through the Cobb water absorption test (test conditions: 25 ml and 10 minutes). In addition, when a coating layer is formed on a substrate with a coating amount of 15 g / m of the biodegradable polymer dispersion, it is evaluated according to the TAPPI T559 standard, and the oil resistance set rating can be 5 or higher. 2 Specifically, a set of rating test reagents is dropped from a specific height onto the surface of a biodegradable object (width 5 cm and length 15 cm) prepared from the biodegradable polymer dispersion, specifically, on the coating layer formed on one side of the biodegradable object. Then, after a specific time (for example, about 15 seconds), the excess set rating test reagents are wiped off with a clean paper towel or cotton cloth, and the surface is immediately visually inspected to determine the oil resistance set rating. Specifically, a set of rating test reagents is dropped from a specific height onto the surface of a biodegradable object (width 5 cm and length 15 cm) prepared from the biodegradable polymer dispersion, specifically, on the coating layer formed on one side of the biodegradable object. Then, after a specific time (for example, about 15 seconds), the excess set rating test reagents are wiped off with a clean paper towel or cotton cloth, and the surface is immediately visually inspected to determine the oil resistance set rating. In this test, if it becomes significantly darker compared to the surface where the test reagent has not been dropped, it is determined as a failure; and if not, it is determined as a pass. Repeat the above test using higher-order kit rating test reagents until a failed kit rating test reagent is observed. The oil resistance kit rating can be determined as the average value of the highest-order kit rating reagents that can be determined as passing. The oil resistance kit rating is classified into grades from 1 to 12. The larger the number, the better the oil resistance. Since the biodegradable polymer dispersion according to one embodiment has excellent antibacterial stability, it has excellent long-term storage stability. Since it has excellent coatability, it can be advantageously used as a coating solution to increase the service life and recyclability of various products such as paper, films, fibers, packaging materials, metals, and various containers. Biodegradable objects According to one embodiment, there is provided a biodegradable object, which includes a substrate; and a biodegradable coating layer formed on at least one side of the substrate using the biodegradable polymer dispersion. The substrate is not particularly limited as long as a biodegradable coating layer can be formed on the surface of the substrate using the biodegradable polymer dispersion. For example, the substrate can be selected from at least one of the group consisting of: paper, kraft paper, a fabric, a knitted fabric, a non-woven fabric, a polyester film such as polyethylene terephthalate (PET), polybutylene succinate (PBS), polybutylene adipate (PBA), polybutylene adipate terephthalate (PBAT), and polybutylene succinate terephthalate (PBST), and a polyimide (PI) film. Specifically, from the viewpoint of improving the coatability of the substrate, the substrate is preferably a substrate of a single material. The substrate can be paper, kraft paper, fabric, or non-woven fabric, but is not limited thereto. In addition, when the substrate includes paper or kraft paper, since it has better biodegradability than other plastic materials, it is more beneficial to provide an environmentally friendly packaging material. The substrate can have a thickness of 15 μm or more. For example, the thickness of the substrate can be 15 μm or more, 20 μm or more, 50 μm or more, 70 μm or more, 100 μm or more, 130 μm or more, 150 μm or more, 200 μm or more, 300 μm or more, or 500 μm or more. In addition, the substrate can have 30 g / m 2 to 500 g / m 2The basis weight. For example, when the substrate is paper, kraft paper, fabric, knitted fabric or non-woven fabric, the basis weight of the substrate can be 30 g / m 2 to 500 g / m 2 、30 g / m 2 to 350 g / m 2 、30 g / m 2 to 200 g / m 2 、50 g / m 2 to 200 g / m 2 、80 g / m 2 to 200 g / m 2 、100 g / m 2 to 200 g / m 2 、130 g / m 2 to 190 g / m 2 、150 g / m 2 to 185 g / m 2 ,or 120 g / m 2 to 320 g / m 2 。 Meanwhile, a barrier layer can be disposed on at least one side of the substrate. A pair of environmentally friendly barrier films can be coated on the surface of the substrate to have moisture and / or oxygen barrier properties, or a functional coating layer having antistatic properties or adhesive properties can be further formed. The functional coating layer can include a primer coating layer and / or an adhesive coating layer, which can have common materials and physical properties as long as they do not damage the desired effects. For example, the substrate can include a barrier layer or a functional coating layer, and the barrier layer or the functional coating layer can be located on one side of the substrate or on one side of the biodegradable coating layer. In addition, the biodegradable coating layer can have a thickness of 5 μm to 50 μm, 5 μm to 40 μm, or 6 μm to 30 μm. The biodegradable article comprising the biodegradable coating layer can be a packaging material, a cardboard box, a shopping bag, a disposable tableware, a packaging container, or a paper straw, but is not limited thereto. The biodegradable article not only has excellent biodegradability and recyclability, but also has excellent water resistance, oil resistance, and antibacterial stability; thus, it can achieve a long service life and high quality. The water resistance, oil resistance, and antibacterial stability of the biodegradable article are as described in the biodegradable polymer dispersion. Method for preparing a biodegradable article According to one embodiment, a method for preparing the biodegradable article is provided. The method for preparing the biodegradable article includes preparing the biodegradable polymer dispersion; and forming a biodegradable coating layer on at least one side of a substrate using the biodegradable polymer dispersion. For example, the biodegradable article can be obtained in the form of a film comprising a biodegradable coating layer by the above preparation method. The method for preparing a biodegradable polymer dispersion is as described above, and the substrate is also as described above. The step of forming a biodegradable coating layer can be carried out by applying the biodegradable polymer dispersion on at least one side of a substrate and drying it. Specifically, the amount of the biodegradable polymer dispersion coated on at least one side of a substrate can be 5 g / m 2 to 100 g / m 2 、5 g / m 2 to 85 g / m 2 、5 g / m 2 to 70 g / m 2 、8 g / m 2 to 60 g / m 2 、9 g / m 2 to 50 g / m 2 、5 g / m 2 to 50 g / m 2 、6 g / m 2 to 40 g / m 2 、7 g / m 2 to 30 g / m 2 、10 g / m 2 to 40 g / m 2 ,or 10 g / m 2 to 30 g / m 2 。When the coating amount meets the above range, the coatability, productivity, and processability can be further improved. In addition, the coating can be applied once to form a single coating layer, or can be applied two or more times to form a plurality of coating layers. The coating amount can be adjusted within the above range depending on the desired number of coating layers. Specifically, the coating amount can be the total amount applied to a plurality of coating layers. Once the biodegradable polymer dispersion is applied to the substrate, it can be dried at 50°C to 200°C for 5 seconds to 30 minutes. For example, the drying can be carried out at 60°C to 200°C, 80°C to 185°C, 80°C to 150°C, or 80°C to 130°C for 5 seconds to 30 minutes, 10 seconds to 20 minutes, 10 seconds to 10 minutes, 10 seconds to 5 minutes, 10 seconds to 3 minutes, 10 seconds to 1 minute, 10 seconds to 50 seconds, or 10 seconds to 30 seconds. The formation of a biodegradable coating layer can be carried out without particular limitation as long as it is a coating method commonly used in the art. For example, the formation of a biodegradable coating layer can be carried out by gravure coating, slot coating, knife coating, spray coating, bar coating, spin coating, or in-line coating, but is not limited thereto. When the biodegradable article is prepared using the biodegradable polymer dispersion, the particles to be coated can be surface-coated with low thermal energy; thus, it can ensure an accelerated production speed and a simplified process and easily achieve the desired physical properties. Modes for the present invention Hereinafter, the present disclosure will be described in detail with reference to examples, but the scope of the present disclosure is not limited to these examples. Examples Example 1 [Preparation of a biodegradable polymer dispersion] Step (1): Prepare a biodegradable suspension containing a polyhydroxyalkanoate (PHA) Distilled water was added to polyhydroxyalkanoate (PHA) granules obtained by physical pulverization (Mw: 600,000 g / mol, content of repeating units derived from 4-HB: 34 wt%, manufacturer: CJ CheilJedang) to obtain a crude amorphous PHA dispersion with a low solid content of 8 wt%. 50 liters of the crude PHA dispersion and 5 parts by weight of a polyvinyl alcohol (PVA, saponification degree: 80 mol%, average degree of polymerization: 13,000, manufacturer: Kuraray) were charged into a homogenizer (product name: Homomixer Mark2, manufacturer: PRIMIX) relative to 100 parts by weight of the solid content of the PHA. They were subjected to high-speed dispersion treatment at a linear velocity of 1,250 cm / s to prepare a biodegradable suspension containing a low concentration of amorphous PHA. Step (2): Filtering the biodegradable suspension using the rotor separation method 0.5 wt% of a polysiloxane defoamer was added thereto, based on the solid content of the biodegradable suspension obtained in step (1), and then stirred at high speed under the same conditions as above. A high-speed centrifugal filter (product name: Clara 20, manufacturer: Alfa Laval, cylindrical drum with a diameter of approximately 45 cm) was used to filter it with a rotational force of about 20,500 g in terms of G' force to obtain an amorphous suspension with a high solid content of 40 wt%. Step (3): Heat treatment of the filtered suspension The high-concentration amorphous suspension obtained in step (2) was heated at a temperature of about 60°C for about 20 minutes while stirring at a low speed, and then cooled to room temperature. Thereafter, additives such as 0.7 wt% of carrageenan as a thickener and 0.01 wt% of polysiloxane as a defoamer were added to the high-concentration amorphous suspension, based on the solid content of the high-concentration amorphous suspension, to obtain a biodegradable polymer dispersion (PHA dispersion). [Preparation of a biodegradable object (film)] The biodegradable polymer dispersion was coated onto a substrate using a bar coater (mayer bar coater, manufacturer: RDS) at a coating amount of about 15 g / m 2 and dried at about 100°C for about 20 seconds to prepare a biodegradable object (film) formed with a biodegradable coating layer. Here, uncoated kraft paper with a basis weight of 180 g / m 2 was used as the substrate. Example 2 A PHA dispersion and a film were prepared through the same procedure as in Example 1, except that when preparing the crude PHA dispersion in step (1), the type of PHA was changed (solid content: 9 wt%, content of repeating units derived from 4-HB: 50 wt%, Mw: 800,000 g / mol, manufacturer: CJ CheilJedang). Example 3 A PHA dispersion and a film were prepared through the same procedure as in Example 1, except that when preparing the crude PHA dispersion in step (1), the type of PHA was changed (solid content: 8 wt%, content of repeating units derived from 4-HB: 25 wt%, Mw: 700,000 g / mol, manufacturer: CJ CheilJedang). Comparative Example 1 A PHA dispersion and a film were prepared through the same procedure as in Example 1, except that when preparing the crude PHA dispersion in step (1), the type of PHA was changed (solid content: 8 wt%, content of repeating units derived from 4-HB: 17 wt%, Mw: 700,000 g / mol, manufacturer: CJ CheilJedang). Comparative Example 2 A PHA dispersion and a film were prepared through the same procedure as in Example 1, except that when preparing the crude PHA dispersion in step (1), the type of PHA was changed (solid content: 8 wt%, content of repeating units derived from 4-HB: 25 wt%, Mw: 500,000 g / mol, manufacturer: CJ CheilJedang). Comparative Example 3 A PHA dispersion and a film were prepared through the same procedure as in Example 1, except that the biodegradable suspension was filtered using the high-speed centrifugal filter with a rotational force of about 900 g in terms of G' force. Comparative Example 4 A PHA dispersion and a film were prepared through the same procedure as in Example 1, except that the biodegradable suspension was filtered using the high-speed centrifugal filter with a rotational force of about 35,000 g in terms of G' force. Comparative Example 5 A PHA dispersion and a film were prepared through the same procedure as in Example 1, except that in step (2), a pressure filter (product name: F-SA-1000-40, manufacturer: APK) was used for filtration instead of the high-speed centrifugal filter. The biodegradable polymer dispersions (PHA dispersions) and films of these examples and comparative examples were evaluated as follows. Test Example Test Example 1: Preparation of an emulsion The preparation of an emulsion of the biodegradable polymer dispersion is evaluated depending on the solid content and aggregation, and the results are shown in Table 1 below. Here, aggregation is observed with the naked eye. ◎: When the solid content of the biodegradable polymer dispersion is 30% by weight or more, and an emulsion is well prepared and there is no aggregation. ○: When the solid content of the biodegradable polymer dispersion is 8% by weight or more to less than 30% by weight, and slight aggregation occurs. △: When the solid content of the biodegradable polymer dispersion is 5% by weight or more to less than 8% by weight, and aggregation may occur during preparation. ×: When the solid content of the biodegradable polymer dispersion is less than 5% by weight, and preparation or fine particle recovery is impossible due to aggregation. Test Example 2: Solid Content The biodegradable polymer dispersion is dried at a temperature of 170 °C for 10 minutes, and then the water evaporation amount is measured. The results are shown in Table 1 below. Test Example 3: Viscosity Measurement is carried out using a DV-1 viscometer (BROOKFIELD) device at 12 rpm with spindle #63. The results are shown in Table 1 below. Test Example 4: Evaluation of Antibacterial Stability Three types of dry culture media (Petrifilm from 3M) are prepared for general bacteria, fungi, and Escherichia coli. 1 ml of the PHA dispersion is diluted 10 times in 9 ml of sterilized water to prepare a diluted solution. It is subjected to vortex for 1 minute, and then 1 ml is taken out and evenly distributed in each dry culture medium. Then, the dry culture medium for general bacteria is cultured at 35 °C for 48 hours, the dry culture medium for fungi is cultured at 25 °C for 48 hours, and the dry culture medium for Escherichia coli is cultured at 35 °C for 24 hours. After the culture is completed, the number of colonies is measured and evaluated as follows. The results are shown in Table 1 below. Contamination: When the measured number of colonies is 10 or more Pass: When the measured number of colonies is less than 10 Test Example 5: Coating Amount When a film is prepared by coating each of the biodegradable polymer dispersions prepared in these examples and comparative examples onto a substrate, a Mayer rod coater #18 is used. The coating layer is dried at about 100 °C for 20 seconds, and the coating amount is measured. The results are shown in Table 1 below. Test Example 6: Measurement of Water Resistance The biodegradable objects prepared in these examples and comparative examples were each subjected to the Cobb water absorbency test according to the TAPPI T441 standard (test conditions: 25 ml and 10 minutes). The results are shown in Table 1 below. Test Example 7: Measurement of oil resistance The biodegradable objects prepared in these examples and comparative examples were each evaluated according to the oil resistance kit rating of the TAPPI T559 standard. Specifically, a set of rating test reagents of 5 drops was dropped from a height of 2.54 cm onto the surface of the biodegradable object (width 5 cm and length 15 cm) prepared from each of the biodegradable polymer dispersions in these examples and comparative examples, specifically, on the coating layer formed on one side of the biodegradable object. After 15 seconds, the excess rating test reagent was wiped off with a clean paper towel or cotton cloth, and the surface was visually inspected immediately. If it becomes significantly darker compared to the coated surface without the test reagent drop, it is judged as a failure; and if not, it is judged as a pass. The above test was repeated with higher-order rating test reagents until a failed rating test reagent was observed. The oil resistance kit rating can be determined as the average value of the highest-order rating test reagents that can be judged as passing. The oil resistance kit rating is classified into grades from 1 to 12. The larger the number, the better the oil resistance. The results are shown in Table 1 below. [Table 1] As can be seen from Table 1 above, the biodegradable polymer dispersions prepared according to these examples are each a dispersion with a high concentration and excellent viscosity, antibacterial stability (bacterial stability), coating amount, water resistance, and oil resistance. Specifically, the biodegradable polymer dispersions prepared according to Examples 1 to 3 each have a solid content of 40% by weight or higher and a viscosity of 500 to 600 cPs, indicating that a dispersion (emulsion) with a high viscosity and high concentration was prepared, and no bacterial contamination occurred, showing excellent antibacterial stability (resistance). In addition, the water resistance is 8 to 15 g / m 2 and the oil resistance kit rating is 5 or higher, all of which are excellent. Conversely, the biodegradable polymer dispersions prepared in Comparative Examples 1, 2, and 4 could not be prepared into an emulsion due to aggregation. The biodegradable polymer dispersion prepared in Comparative Example 3 could be prepared in the form of an emulsion; however, the solid content was 9 wt% and the viscosity was 20 cPs, indicating that the solid content and viscosity were significantly lower than those of the biodegradable polymer dispersions prepared in Examples 1 to 3. The oil resistance set rating was only 1. Meanwhile, the biodegradable polymer dispersion prepared in Comparative Example 5 had a low concentration and low viscosity, making it impossible to recover fine particles. The above results show that the method for preparing a biodegradable polymer dispersion according to the embodiments is excellent in terms of productivity and process efficiency, and can easily prepare a biodegradable polymer dispersion with high viscosity, high concentration, and high purity. In addition, the biodegradable polymer dispersion prepared by the above preparation method not only has antibacterial stability, but also when coated on a substrate, the water resistance and oil resistance of the coating layer are also significantly improved; therefore, it can be advantageously used as a coating solution to increase the service life, quality, and recyclability of various products. S100: Method S110, S120, S130: Steps FIG. 1 is a flowchart schematically illustrating the method for preparing a biodegradable polymer dispersion according to an embodiment of the present disclosure. S100: Method S110, S120, S130: Steps

Claims

1. A method for preparing a biodegradable polymer dispersion, comprising: (1) preparing a biodegradable suspension comprising a polyhydroxyalkanoate (PHA); and (2) filtering the biodegradable suspension using rotor separation to obtain the biodegradable polymer dispersion, wherein the solids content of the biodegradable polymer dispersion is from 10% to 60% by weight, and the polyhydroxyalkanoate (PHA) comprises a repeating unit derived from 4-hydroxybutyrate in an amount from 0.1% to 60% by weight based on the total weight of the polyhydroxyalkanoate (PHA), wherein the rotor separation in step (2) is performed with a rotational force of 1000 g to 30,000 g.

2. The method for preparing a biodegradable polymer dispersion as claimed in claim 1, wherein the rotor separation in step (2) is performed using a centrifugal filter.

3. The method for preparing a biodegradable polymer dispersion as claimed in claim 1, further comprising heating the filtered product at a temperature of 50°C to 80°C for at least 10 minutes after step (2).

4. The method for preparing a biodegradable polymer dispersion as claimed in claim 3, further comprising adding an additive after the heat treatment step, the additive comprising at least one selected from the group consisting of a thickener, a wax, a pH adjuster, an antifoaming agent and an antimicrobial agent.

5. The method for preparing a biodegradable polymer dispersion as claimed in claim 1, wherein step (1) comprises mixing the polyhydroxyalkanoate (PHA) with a dispersant for dispersion treatment.

6. The method of claim 5 for preparing a biodegradable polymer dispersion, wherein the dispersant comprises at least one selected from the group consisting of: polyvinyl alcohol, polyvinylpyrrolidone, methyl polyvinyl alkyl ether, sodium dodecylbenzene sulfonate, alkylbenzene sulfonate, nonylphenol ether sulfate, sodium lauryl sulfate, lithium dodecyl sulfate, alkyl phosphate, polypropylene glycol ester, cocoyl betaine, and lecithin.

7. The method of claim 1 for preparing a biodegradable polymer dispersion, wherein the polyhydroxyalkanoate (PHA) comprises a poly(3-hydroxybutyrate-co-4-hydroxybutyrate) copolymer, and the poly(3-hydroxybutyrate-co-4-hydroxybutyrate) copolymer comprises a repeating unit derived from 4-hydroxybutyrate, the amount of which is from 18% by weight to 60% by weight based on the total weight of the poly(3-hydroxybutyrate-co-4-hydroxybutyrate) copolymer.

8. The method of claim 1 for preparing a biodegradable polymer dispersion, wherein the polyhydroxyalkanoate (PHA) may have a weight average molecular weight of 550,000 g / mole to 1,000,000 g / mole.

9. A biodegradable polymer dispersion prepared by any one of claims 1 to 8.

10. The biodegradable polymer dispersion of claim 9, wherein the viscosity measured at 25°C using a Brookfield viscometer is greater than 10 cPs to 10,000 cPs.

11. The biodegradable polymer dispersion of claim 9, wherein when a coating layer is formed on a substrate by the biodegradable polymer dispersion at a coating amount of 15 g / m2, and when the Cobb water absorption test is performed according to the TAPPI T441 standard, the water resistance is from 3 g / m2 to 50 g / m2.

12. The biodegradable polymer dispersion of claim 9, wherein when a coating layer is formed on a substrate by the biodegradable polymer dispersion at a coating amount of 15 g / m2, it is evaluated according to the TAPPI T559 standard and has an oil resistance rating of 5 or higher.

13. A biodegradable article comprising a substrate; and a biodegradable coating layer formed on at least one side of the substrate using a biodegradable polymer dispersion as claimed in claim 9.

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