Biodegradable composition and biodegradable film

Abstract

The present invention provides: a biodegradable composition comprising polybutylene adipate terephthalate and thermoplastic starch and having a predetermined specific recovery area; and a biodegradable film.

Description

Biodegradable compositions and biodegradable films Cross-citation with related application(s) This application claims the benefit of priority to Korean Patent Application No. 10-2023-0177651, filed December 8, 2023, and Korean Patent Application No. 10-2024-0179460, filed December 5, 2024, the entire contents of which are incorporated herein by reference. The present invention relates to a biodegradable composition and a biodegradable film. Recently, as interest in environmental protection and eco-friendliness has increased, the need for methods of cultivating eco-friendly agricultural products has increased. One of these eco-friendly farming methods is known as mulching farming, which is a method of covering the surface of the soil with mulching film when cultivating crops to prevent the growth of weeds, prevent diseases and pests, maintain soil moisture or control soil temperature, prevent soil erosion by rainwater during rainy weather, and reduce the use of pesticides. Mulching films used in this mulching method greatly contribute to the productivity of agricultural products, but there are difficulties in collecting and recycling them after use. Usually, synthetic resins such as polypropylene and polyethylene are used and biodegradable ingredients are added as additives to provide biodegradability, but biodegradation of the synthetic resin itself is impossible. In addition, synthetic resins that are not biodegraded and remain have the problem of contaminating the soil. There have been attempts to manufacture mulching films using polybutylene adipate terephthalate (PBAT), a biodegradable plastic; however, while the elongation of PBAT is high, its mechanical properties, such as Young's modulus, are lower than those of conventional films such as polyethylene. In addition, since PBAT is a 100% petroleum-based material, its bio-based raw material content is low. Accordingly, attempts have been made to improve the physical properties and increase the bio-raw material content by compounding various biodegradable materials into polybutylene adipate terephthalate (PBAT), but there is a problem that the tensile properties are low due to low compatibility between polybutylene adipate terephthalate and other biodegradable materials. The present invention provides a biodegradable composition having excellent biodegradability, compatibility and thermal diffusivity, and a biodegradable film manufactured by the composition having excellent biodegradability and mechanical properties such as tensile strength and an increased content of bio-raw materials. According to one embodiment of the present invention, a biodegradable composition comprising polybutylene adipate terephthalate and thermoplastic starch and having a non-recoverable surface area of ​​1,000 to 10,000 according to the following formula 1 is provided. In addition, according to another embodiment of the present invention, a biodegradable film is provided, which comprises a biodegradable composition comprising polybutylene adipate terephthalate and thermoplastic starch, and has a non-recoverable area of ​​1,000 to 10,000 according to the following formula 1. Hereinafter, a biodegradable composition and a biodegradable film according to specific embodiments of the invention will be described in more detail. Unless otherwise specified throughout this specification, the terms “include” or “comprising” refer to the inclusion of any component (or component) without limitation, and cannot be construed as excluding the addition of other components (or components). In addition, unless otherwise stated herein, the weight average molecular weight of polybutylene adipate terephthalate, polybutylene adipate terephthalate in which maleic acid is ester-bonded to the terminal hydroxy group, etc. can be measured using gel permeation chromatography (GPC). Specifically, the prepolymer or copolymer is dissolved in chloroform to a concentration of 2 mg / mL, 20 μL is injected into GPC, and GPC analysis is performed at 40°C. At this time, chloroform is used as the mobile phase of GPC, and the flow rate is 1.0 mL / min. Two Agilent Mixed-B columns are connected in series and used, and an RI Detector is used as the detector. The Mw value is derived using a calibration curve formed using a polystyrene standard specimen. The weight-average molecular weights of the polystyrene standard specimens were 2,000 g / mol, 10,000 g / mol, 30,000 g / mol, 70,000 g / mol, 200,000 g / mol, 700,000 g / mol, 2,000,000 g / mol, 4,000,000 g / mol, and 10,000,000 g / mol, nine types. In order to produce a composition for producing a biodegradable film, another biodegradable material, such as thermoplastic starch, can be compounded into polybutylene adipate terephthalate. However, since polybutylene adipate terephthalate is hydrophobic, whereas thermoplastic starch is hydrophilic, there is a problem that polybutylene adipate terephthalate and thermoplastic starch do not mix well, resulting in poor compatibility. Accordingly, the inventors of the present invention have found that when a biodegradable composition has a non-recoverable surface area of ​​1,000 or more and 10,000 or less according to the following formula 1, compatibility is improved, and the mechanical properties, such as tensile strength, of a biodegradable film manufactured with such a composition are improved, thereby completing the present invention. [Formula 1] Non-recovered area = A - B In the above equation 1, A is the area of ​​storage elastic modulus measured after increasing the strain from 0.01% to 75% at a temperature of 150°C and a frequency of 1 Hz for the biodegradable composition, B is the area of ​​storage modulus measured after the strain for the biodegradable composition is lowered again to 0.01%. The above non-recoverable area may be, for example, 2,000 or more, 5,000 or more, 10,000 or more, 15,000 or more, 20,000 or more, 25,000 or more, 30,000 or more, 35,000 or more, and may be 9,500 or less, 9,000 or less, 8,500 or less, 8,000 or less, 7,500 or less, 7,000 or less, 6,500 or less. The above non-recoverable area is a factor regarding the extent to which the composition recovers when the strain is increased and then decreased again, and the area of ​​the storage elastic modulus means the area under a line graph with the strain as the x-axis and the storage elastic modulus as the y-axis. The more the non-recoverable area satisfies the above-described range, the better the distribution of the dispersed phase to the continuous phase included in the composition, and thus the better the compatibility. The above non-recoverable area may be controlled depending on the composition of the biodegradable composition, the type of compatibilizer, and particularly, whether or not the 'polybutylene adipate terephthalate in which maleic acid is ester-bonded to a terminal hydroxyl group' described below is included, the content thereof, or the content of maleic acid included therein, but is not limited thereto. Meanwhile, if the non-recoverable area has an excessively high value, the compatibility of the biodegradable composition may be reduced, and if the non-recoverable area has an excessively low value, the thermal diffusivity may be reduced, which may result in poor formability and / or processability, and high process operation costs. In a process of manufacturing a film by reactive extrusion of a biodegradable composition, the compound discharged from the extruder is cooled by passing through a cooling tank and then cut (pelletized), but if the thermal diffusivity is low, the cooling speed of the compound discharged from the extruder is slow, which makes cutting difficult. Accordingly, the formability and / or processability may be reduced, or the process operation cost may be increased because additional cooling equipment is required. The biodegradable composition according to the above embodiment may further include polybutylene adipate terephthalate in which maleic acid is ester-bonded to a terminal hydroxyl group. When the biodegradable composition includes 'polybutylene adipate terephthalate in which maleic acid is ester-bonded to a terminal hydroxyl group', the compatibility between polybutylene adipate terephthalate, which is a resin material, and thermoplastic starch, etc., can be improved. In addition, as the content of thermoplastic starch in the biodegradable composition increases, the price is lowered and thus it is economical, biodegradability is improved, and the content of bio-based carbon is increased. By using 'polybutylene adipate terephthalate in which maleic acid is ester-bonded to a terminal hydroxyl group' as a compatibilizer in the biodegradable composition, the above-described effects can be exhibited by including a large amount of the thermoplastic starch. Furthermore, 'polybutylene adipate terephthalate with maleic acid ester-bonded to the terminal hydroxyl group' can act as a chain extender to increase molecular weight, increase melt viscosity, and improve formability such as extensibility. The above 'polybutylene adipate terephthalate having maleic acid ester-bonded to the hydroxyl group at the terminal' can be produced by an ester reaction of maleic acid to the hydroxyl group at the terminal of polybutylene adipate terephthalate. For example, the polybutylene adipate terephthalate having maleic acid ester-bonded to the hydroxyl group at the terminal can be represented by the following chemical formula 1 or 2. [Chemical Formula 1] [Chemical formula 2] In the above chemical formulas 1 and 2, a to d can each independently be an integer from 1 to 500, 5 to 450, 10 to 400, or 20 to 300. The 'polybutylene adipate terephthalate having maleic acid ester-bonded to a hydroxyl group at the terminal' represented by the above chemical formula 1 may be an ester-bonded product through an ester reaction between one carboxyl group contained in maleic acid and a hydroxyl group at the terminal of polybutylene adipate terephthalate. In addition, the 'polybutylene adipate terephthalate having maleic acid ester-bonded to a hydroxyl group at the terminal of polybutylene adipate terephthalate' represented by the above chemical formula 2 may be an ester-bonded product through an ester reaction between each of two carboxyl groups contained in maleic acid and a hydroxyl group at the terminal of another polybutylene adipate terephthalate. Polybutylene adipate terephthalate having maleic acid ester-bonded to the hydroxyl group at the terminal can be produced by esterifying maleic acid and polybutylene adipate terephthalate as described above. By controlling the content of maleic acid, the content of polybutylene adipate terephthalate, the reaction temperature, the reaction time, the type and content of the additive, etc., polybutylene adipate terephthalate having maleic acid ester-bonded to the hydroxyl group at the terminal can be produced, and the weight average molecular weight, structure, viscosity, etc. of the polybutylene adipate terephthalate having maleic acid ester-bonded to the hydroxyl group at the terminal can be controlled. Meanwhile, in the past, there were cases where a compatibilizer was used in which maleic anhydride was graft-bonded to polybutylene adipate terephthalate, but while it is difficult for a radical to be generated in the middle of the polybutylene adipate terephthalate chain or the grafting reaction efficiency is low due to steric hindrance, polybutylene adipate terephthalate in which the maleic anhydride is ester-bonded has the advantage of significantly high reaction efficiency. In addition, in the case of using a 'compatibility agent in which maleic anhydride is graft-bonded to polybutylene adipate terephthalate' instead of 'polybutylene adipate terephthalate in which maleic acid is ester-bonded to the hydroxyl group of the terminal' in the biodegradable composition and biodegradable film, there are problems in that the manufacturing cost is high because additional process operation and long process operation time are required to manufacture a compatibilizer with low reaction efficiency, and since a highly toxic radical initiator must be used, the work must be done with care for environmental safety. The polybutylene adipate terephthalate having maleic acid ester-bonded to the hydroxyl group at the terminal may have a weight average molecular weight of 50,000 or more and 200,000 or less, 70,000 or more and 190,000 or less, 90,000 or more and 180,000 or less, 100,000 or more and 170,000 or less, or 120,000 or more and 160,000 or less. If the polybutylene adipate terephthalate having maleic acid ester-bonded to the hydroxyl group at the terminal does not satisfy the weight average molecular weight range described above, the compatibility improvement effect may not be exhibited, and thus the mechanical properties such as tensile strength of a film manufactured from the composition may deteriorate. In addition, it is preferable that the polybutylene adipate terephthalate having maleic acid ester-bonded to the hydroxy group at the terminal is smaller than the weight average molecular weight of the polybutylene adipate terephthalate included in the biodegradable composition according to the above embodiment, for example, the weight average molecular weight of the polybutylene adipate terephthalate having maleic acid ester-bonded to the hydroxy group at the terminal may be 0.9 times or less with respect to the weight average molecular weight of the polybutylene adipate terephthalate. For example, the weight average molecular weight of the polybutylene adipate terephthalate having maleic acid ester-bonded to the hydroxy group at the terminal may be 0.4 to 0.8 times, 0.5 to 0.7 times, or 0.5 to 0.6 times or less with respect to the weight average molecular weight of the polybutylene adipate terephthalate. In addition, when manufacturing a film by reaction extrusion of the biodegradable composition according to the above embodiment, it is preferable that the polybutylene adipate terephthalate in which maleic acid is ester-bonded to the terminal hydroxyl group has lower viscosity than other components, such as polybutylene adipate terephthalate and thermoplastic starch, at the process temperature. When the polybutylene adipate terephthalate in which maleic acid is ester-bonded to the terminal hydroxyl group, which is a compatibilizer, has lower viscosity than other components, the polybutylene adipate terephthalate can exhibit excellent fluidity during extrusion and be well distributed at the interface between the polybutylene adipate terephthalate and thermoplastic starch, thereby improving compatibility. For example, the polybutylene adipate terephthalate in which maleic acid is ester-bonded to the hydroxyl group of the terminal may have a viscosity of 1,000 Pa.s or more and 5,000 Pa.s or less at a temperature of 120° C. to 180° C., 130° C. to 170° C., 140° C. to 160° C., or 150° C. For example, the viscosity may be 1,300 Pa.s or more, 1,600 Pa.s or more, 1,800 Pa.s or more, 2,000 Pa.s or more, 2,100 Pa.s or more, 2,200 Pa.s or more, and may be 4,800 Pa.s or less, 4,600 Pa.s or less, or 4,400 Pa.s or less. If the viscosity of the polybutylene adipate terephthalate in which maleic acid is ester-bonded to the hydroxyl group at the terminal is too high, the effect of improving compatibility may not be achieved, and thus the mechanical properties of the film manufactured from the composition, such as the tensile strength, may deteriorate. In addition, if the viscosity of the polybutylene adipate terephthalate in which maleic acid is ester-bonded to the hydroxyl group at the terminal is too low, the thermal diffusivity of the biodegradable composition may be reduced, resulting in poor formability and / or processability and increased process operation costs. In addition, the polybutylene adipate terephthalate in which maleic acid is ester-bonded to the hydroxy group at the terminal may contain maleic acid in an amount of 2.0 wt% or more and 5.0 wt% or less, based on 100 wt% of the polybutylene adipate terephthalate contained in the polybutylene adipate terephthalate in which maleic acid is ester-bonded to the hydroxy group at the terminal, for example, may contain 2.2 wt% or more, 2.4 wt% or more, 2.5 wt% or more, 2.7 wt% or more, 2.9 wt% or more, 3.0 wt% or more, and may contain 4.8 wt% or less, 4.6 wt% or less, 4.5 wt% or less, 4.3 wt% or less, 4.1 wt% or less, or 4.0 wt% or less. If the polybutylene adipate terephthalate in which maleic acid is ester-bonded to the hydroxyl group at the terminal contains too little maleic acid, the compatibility of the biodegradable composition may be reduced, and if the polybutylene adipate terephthalate in which maleic acid is ester-bonded to the hydroxyl group at the terminal contains too much maleic acid, the thermal diffusivity of the biodegradable composition may be reduced, resulting in poor formability and / or processability and increased process operating costs. In the biodegradable composition according to the above embodiment, the polybutylene adipate terephthalate in which maleic acid is ester-bonded to a hydroxyl group at the terminal may be included in an amount of 1.5 wt% or more and 15.0 wt% or less, based on 100 wt% of the total of the polybutylene adipate terephthalate and the thermoplastic starch. For example, the polybutylene adipate terephthalate in which maleic acid is ester-bonded to a hydroxy group at the terminal may be included in an amount of 1.7 wt% or more, 1.9 wt% or more, 2.0 wt% or more, 2.5 wt% or more, 3.0 wt% or more, 3.5 wt% or more, 4.0 wt% or more, and may be included in an amount of 13.0 wt% or less, 12.0 wt% or less, 11.0 wt% or less, 10.0 wt% or less, 9.0 wt% or less, 7.0 wt% or less, 6.0 wt% or less, 5.0 wt% or less, based on 100 wt% of the total of the polybutylene adipate terephthalate and the thermoplastic starch. If the amount of polybutylene adipate terephthalate in which maleic acid is ester-bonded to the hydroxyl group at the terminal is too small, the effect of improving compatibility may not be achieved, and thus the mechanical properties of the film manufactured from the composition, such as tensile strength and elongation at break, may deteriorate. In addition, if the amount of polybutylene adipate terephthalate in which maleic acid is ester-bonded to the hydroxyl group at the terminal is too large, the melt viscosity may become excessively high, which may deteriorate the formability and increase the cost of manufacturing the composition or film. In addition, the content of PBAT including maleic acid may also increase, which may increase the acid value of the composition and thus reduce the lifespan of the film manufactured from the composition. In the biodegradable composition according to the above embodiment, the polybutylene adipate terephthalate in which maleic acid is ester-bonded to the hydroxy group at the terminal may be included in an amount of 0.5 wt% or more and 10.0 wt% or less, based on 100 wt% of the total solid content of the biodegradable composition. For example, the polybutylene adipate terephthalate in which maleic acid is ester-bonded to the hydroxy group at the terminal may be included in an amount of 1.0 wt% or more, 1.3 wt% or more, 1.5 wt% or more, 1.8 wt% or more, 1.9 wt% or more, 2.0 wt% or more, and may be included in an amount of 9.0 wt% or less, 7.0 wt% or less, 6.0 wt% or less, or 5.0 wt% or less, based on 100 wt% of the total solid content of the biodegradable composition. The biodegradable composition according to the above embodiment may include the polybutylene adipate terephthalate (PBAT) as a biodegradable resin. The polybutylene adipate terephthalate may be included in an amount of 30 to 80 wt% based on 100 wt% of the total solid content of the biodegradable composition, and more specifically, may be included in an amount of 30 wt% or more, 35 wt% or more, 40 wt% or more, 80 wt% or less, 75 wt% or less, or 70 wt% or less. If the polybutylene adipate terephthalate (PBAT) is included in the biodegradable composition in an excessively small amount, the elongation of a film manufactured therefrom may be lowered, and if the polybutylene adipate terephthalate is included in an excessive amount in the biodegradable composition, the tensile properties such as Young's modulus and yield tensile strength of a film manufactured therefrom may be lowered. In addition, the biodegradable composition may include thermoplastic starch to increase the processability of polybutylene adipate terephthalate and to accelerate the biodegradation rate. The thermoplastic starch may be starch that is a natural polymer and to which a plasticizer is added so that it is thermoplastic and can freely change shape without being carbonized even at a certain temperature or higher, unlike conventional general-purpose resins such as polyethylene, polystyrene, and polypropylene. The thermoplastic starch may include at least one selected from the group consisting of rice starch, wheat starch, corn starch, sweet potato starch, potato starch, tapioca starch, cassava starch, and modified starches thereof. In addition, the plasticizer contained in the natural polymer starch may be at least one selected from the group consisting of isosorbide, glycerol, sorbitol, fructose, formamide, xylitol, corn oil, and edible oil. The plasticizer may be contained in an amount of 5 wt% to 50 wt%, 10 wt% to 45 wt%, or 15 wt% to 35 wt%, based on 100 wt% of the total thermoplastic starch. The biodegradable composition according to the above embodiment may contain the thermoplastic starch in an amount of 10 wt% or more and 50 wt% or less, based on 100 wt% of the total solid content of the biodegradable composition. For example, the thermoplastic starch may be contained in an amount of 10 wt% or more, 15 wt% or more, 20 wt% or more, 25 wt% or more, and may be contained in an amount of 45 wt% or less, 40 wt% or less, or 35 wt% or less, based on 100 wt% of the total solid content of the biodegradable composition. As the content of thermoplastic starch in the biodegradable composition increases, the price becomes lower and thus economical, biodegradability improves, and the content of bio-based carbon can increase. However, if the thermoplastic starch is included in an excessive amount in the biodegradable composition, the elongation of the film manufactured from it may decrease, and if the thermoplastic starch is included in an excessive amount in the biodegradable composition, the biodegradation rate may be slowed and the tensile properties, such as the Young's modulus and yield tensile strength, of the film manufactured from it may deteriorate. The biodegradable composition according to the above embodiment may include hydrophobic polybutylene adipate terephthalate and hydrophilic thermoplastic starch, and whether their compatibility is improved is determined by the fact that the more densely and uniformly the thermoplastic starch dispersed in the polybutylene adipate terephthalate matrix is ​​distributed, the more the compatibility is improved. In addition, whether the compatibility is improved is determined by the fact that the stronger the adhesive force at the interface between the polybutylene adipate terephthalate and the thermoplastic starch, the more the compatibility is improved. That is, the more densely and uniformly the thermoplastic starch dispersed in the polybutylene adipate terephthalate matrix is ​​distributed, the more the compatibility is improved, and the stronger the adhesive force at the interface between the polybutylene adipate terephthalate and the thermoplastic starch, the more the compatibility is improved. In addition, whether the compatibility is improved can be numerically confirmed through analysis using a dynamic mechanical analyzer (DMA) device. For example, whether the compatibility is improved can be confirmed by measuring the glass transition temperature (Tg) of thermoplastic starch and polybutylene adipate terephthalate using a dynamic mechanical analyzer (DMA) device. Specifically, the more densely and uniformly the thermoplastic starch dispersion is distributed on the polybutylene adipate terephthalate matrix, the lower the glass transition temperature (Tg) of the thermoplastic starch. The glass transition temperature of this thermoplastic starch can be analyzed using a polymer viscoelasticity analyzer to determine whether compatibility has improved. In addition, the stronger the adhesive force at the interface between the polybutylene adipate terephthalate and the thermoplastic starch, the more effectively the thermoplastic starch dispersion transfers stress to the polybutylene adipate terephthalate, thereby increasing the glass transition temperature (Tg) of the polybutylene adipate terephthalate, especially the glass transition temperature (Tg) of the butylene-adipate repeating unit, which is the soft segment. The glass transition temperature of this polybutylene adipate terephthalate can be analyzed using a polymer viscoelasticity analyzer to determine whether compatibility has improved. Accordingly, the better the compatibility between polybutylene adipate terephthalate and thermoplastic starch, the lower the glass transition temperature (Tg) of the thermoplastic starch. For example, the thermoplastic starch may have a glass transition temperature (Tg) of 10° C. to 140° C., 15° C. to 120° C., 20° C. to 100° C., 25° C. to 80° C., 25° C. to 50° C., or 25° C. to 40° C. In addition, as the compatibility between polybutylene adipate terephthalate and thermoplastic starch becomes better, the glass transition temperature (Tg) of the polybutylene adipate terephthalate increases. For example, the glass transition temperature (Tg) of the polybutylene adipate terephthalate may be -23.0° C. or higher and -10.0° C. or lower, or -22.5° C. or higher and -15.0° C. or lower. Additionally, the absolute value of the difference in glass transition temperature (Tg) of the thermoplastic starch and polybutylene adipate terephthalate may be 20°C or more and 70°C or less, 25°C or more and 65°C or less, 30°C or more and 60°C or less, or 35°C or more and 59°C or less. According to another embodiment of the present invention, a biodegradable film is provided, which comprises a biodegradable composition comprising polybutylene adipate terephthalate and thermoplastic starch, and has a non-recoverable area of ​​1,000 to 10,000 according to the above formula 1. The above non-recoverable area is as described above in the biodegradable composition according to the above embodiment. In addition, the biodegradable film may further include polybutylene adipate terephthalate having maleic acid ester-bonded to a terminal hydroxyl group, as described above in the biodegradable composition according to the above embodiment. In addition, the maleic acid content, molecular weight, structure, etc. of the polybutylene adipate terephthalate, the thermoplastic starch, and the polybutylene adipate terephthalate having maleic acid ester-bonded to a terminal hydroxyl group are as described above. For example, the polybutylene adipate terephthalate may be included in an amount of 30 to 80 wt% based on 100 wt% of the total biodegradable film, and more specifically, may be included in an amount of 30 wt% or more, 35 wt% or more, 40 wt% or more, or 80 wt% or less, 75 wt% or less, or 70 wt% or less. In addition, the polybutylene adipate terephthalate having maleic acid ester-bonded to the hydroxyl group at the terminal may be included in an amount of 1.5 wt% or more and 15.0 wt% or less, based on 100 wt% of the total of the polybutylene adipate terephthalate and the thermoplastic starch. In addition, the biodegradable film may contain 0.5 wt% or more and 10.0 wt% or less of polybutylene adipate terephthalate in which maleic acid is ester-bonded to the hydroxy group at the terminal, based on 100 wt% of the total biodegradable film. For example, the biodegradable composition may contain 1.0 wt% or more, 1.3 wt% or more, 1.5 wt% or more, 1.8 wt% or more, 1.9 wt% or more, 2.0 wt% or more of polybutylene adipate terephthalate in which maleic acid is ester-bonded to the hydroxy group at the terminal, based on 100 wt% of the total solid content, and may contain 9.0 wt% or less, 7.0 wt% or less, 6.0 wt% or less, or 5.0 wt% or less. In addition, the thermoplastic starch may be included in an amount of 10 wt% or more and 50 wt% or less based on 100 wt% of the total biodegradable film. For example, the thermoplastic starch may be included in an amount of 10 wt% or more, 15 wt% or more, 20 wt% or more, 25 wt% or more, and may be included in an amount of 45 wt% or less, 40 wt% or less, or 35 wt% or less based on 100 wt% of the total solid content of the biodegradable composition. The method for manufacturing the above biodegradable film is not particularly limited, but the biodegradable composition according to the above embodiment can be used to obtain the film by a conventional film manufacturing method such as an inflation method, a tubular method, a T-die casting method, etc., which is known. For example, the composition can be pelletized, and the pellets can be dried at 60 to 100° C. for 6 hours or more to control the moisture content to 1,200 ppm or less, 500 ppm or less, or 200 ppm or less. Thereafter, the pelletized composite can be applied to a release film, and then placed in a thermocompression machine and pressure can be applied to manufacture the film. At this time, the temperature can be 130 to 250° C., 150 to 220° C., or 160 to 200° C., and the pressure can be 5 MPa to 20 MPa, 8 MPa to 17 MPa, or 10 MPa to 15 MPa. The thickness of the above biodegradable film may be 10 to 300 ㎛, and more specifically, may be 10 ㎛ or more, 13 ㎛ or more, 15 ㎛ or more, 20 ㎛ or more, 20 ㎛ or more, 25 ㎛ or more, or 300 ㎛ or less, 200 ㎛ or less, 150 ㎛ or less, 100 ㎛ or less, 80 ㎛ or less, or 50 ㎛ or less. Since the thickness of the film is within the above-described range, the film has strong elasticity, excellent handleability, and can have a good roll take-up state or unwindability. If the film thickness is too thin, the tensile strength, tear strength and elongation may deteriorate, causing holes or tears to form in the film during use. If the film thickness is too thick, the unit price competitiveness may decrease. In addition, the biodegradable film can be used as an agricultural mulching film, disposable gloves, medical individual packaging paper, food packaging paper, garbage bags or various industrial product wrappers. The biodegradable film according to the above embodiment may have a tensile strength of 5 MPa or more, 7 MPa or more, 8 MPa or more, or 5 MPa to 30 MPa as measured according to ASTM D882. Additionally, the biodegradable film can have an elongation at break of greater than or equal to 300%, greater than or equal to 350%, greater than or equal to 400%, greater than or equal to 420%, greater than or equal to 430%, or between 300% and 700% as measured according to ASTM D882. Additionally, the biodegradable film may have a tear strength measured according to ASTM 1922 of 200 gf or more, 220 gf or more, 240 gf or more, 260 gf or more, 280 gf or more, or 285 gf or more. The maximum tensile strength, elongation at break, and tear strength of the above biodegradable film can satisfy the numerical ranges described above when measured in the MD (Machine Direction) and TD (Transverse Direction) directions, respectively. According to the present invention, a biodegradable composition having excellent biodegradability, compatibility and thermal diffusivity, and a biodegradable film manufactured by the composition having excellent mechanical properties such as biodegradability and tensile strength and having an increased content of bio-raw materials can be provided. The invention is described in more detail in the following examples. However, the following examples are only intended to illustrate the present invention, and the content of the present invention is not limited by the following examples. Manufacturing Example 1: Manufacturing of thermoplastic starch Corn starch (700 g) and glycerol (300 g) were mixed in a mixer and then placed in an extruder for compounding, based on dry weight. The temperature of the extruder was set to 120°C, the screw speed was set to 150 rpm, and the extruded strands were cut in a pelletizer to produce thermoplastic starch pellets. Manufacturing Example 2: Manufacturing of polybutylene adipate terephthalate in which maleic acid is ester-bonded to the hydroxyl group at the terminal 100 g of polybutylene adipate terephthalate (PBAT, Solpol 1000N, SOLTECH) and 5 g of maleic anhydride were placed in an internal mixer and reacted while mixing for 10 minutes at 160°C and 50 rpm to produce polybutylene adipate terephthalate (weight average molecular weight; 120,000) in which maleic acid is ester-bonded to the hydroxyl group at the terminal. <Examples and Comparative Examples> Example 1 A composition was prepared by hand mixing 750 g of polybutylene adipate terephthalate (PBAT, Solpol 1000N, SOLTECH Co.) based on dry weight, 250 g of the thermoplastic starch prepared in Manufacturing Example 1, and 20 g of 'polybutylene adipate terephthalate in which maleic acid is ester-bonded to a terminal hydroxyl group' prepared in Manufacturing Example 2. Afterwards, it was put into an extruder and compounded. The temperature range of the extruder was set to 150℃, the screw speed was set to 200 rpm, and the extruded strand was cut with a pelletizer to manufacture composite pellets. Example 2 A composition and pellets were prepared in the same manner as in Example 1, except that 30 g of 'polybutylene adipate terephthalate having maleic acid ester-bonded to the terminal hydroxyl group' was used instead of 20 g of 'polybutylene adipate terephthalate having maleic acid ester-bonded to the terminal hydroxyl group'. Example 3 A composition and pellets were prepared in the same manner as in Example 1, except that 40 g of 'polybutylene adipate terephthalate having maleic acid ester-bonded to the terminal hydroxyl group' was used instead of 20 g of 'polybutylene adipate terephthalate having maleic acid ester-bonded to the terminal hydroxyl group'. Example 4 A composition and pellets were prepared in the same manner as in Example 1, except that 50 g of 'polybutylene adipate terephthalate having maleic acid ester-bonded to the terminal hydroxyl group' was used instead of 20 g of 'polybutylene adipate terephthalate having maleic acid ester-bonded to the terminal hydroxyl group'. Example 5 A composition and pellets were prepared in the same manner as in Example 1, except that 110 g of the 'polybutylene adipate terephthalate having maleic acid ester-bonded to the terminal hydroxyl group' was used instead of 20 g of the 'polybutylene adipate terephthalate having maleic acid ester-bonded to the terminal hydroxyl group'. Comparative Example 1 A composition and pellets were prepared in the same manner as in Example 1, except that 10 g of the 'polybutylene adipate terephthalate in which maleic acid is ester-bonded to the hydroxyl group at the terminal' was used instead of 20 g of the 'polybutylene adipate terephthalate in which maleic acid is ester-bonded to the hydroxyl group at the terminal'. Comparative Example 2 A composition and pellets were prepared in the same manner as in Example 1, except that 20 g of 'polybutylene adipate terephthalate having maleic acid ester-bonded to the terminal hydroxyl group' was not used. evaluation 1. Evaluation of commerciality (non-recoverable area) The compatibility of the compositions of the examples and comparative examples was evaluated, and the compatibility was evaluated by measuring the specific surface area of ​​the compositions. Specifically, the compositions were placed on a parallel plate geometry of a 25 mm diameter DHR (Discovery hybrid rheometer) device of TA Instruments, melted, and loaded by pressing so that the gap became 1 mm. The storage modulus was measured while increasing the strain from 0.01% to 75% and then decreasing it to 0.01% at 150°C and a frequency of 1 Hz. The difference between the area of ​​the storage modulus from strain 0.01% to 75% and the area of ​​the storage modulus from strain 75% to 0.01% is the non-recoverable area. Here, the area of ​​the storage modulus refers to the area under the line graph with the strain as the x-axis and the storage modulus as the y-axis. In addition, the non-recoverable area is a factor of the extent to which the composition recovers when the strain is increased and then decreased again. The smaller the non-recoverable area, the better the distribution of the dispersed phase to the continuous phase included in the composition, and the better the compatibility. 2. Evaluation of tensile properties and tear strength The pellets of the examples and comparative examples were used to manufacture films having a thickness of 15 ㎛ at 150°C using a film blown unit (BL50T) of Collin, and the tensile strength and elongation at break of the films were evaluated according to ASTM D882, and the tear strength was evaluated according to ASTM D1922. In addition, the tensile strength, elongation at break, and tear strength in the MD (Machine Direction) were evaluated, and the results are shown in Table 1 below. Compatibility (non-recoverable area) Tensile strength (MPa) Elongation at break (%) Tear strength (gf) Example 1808314363287 Example 2692515376294 Example 3484920527294 Example 4447922581298 Example 5361925631300 Comparative Example 11274213330280 Comparative Example 220847 Not measurable Not measurable According to Table 1 above, Examples 1 to 5, which satisfy the non-recoverable surface area of ​​1,000 or more and 10,000 or less, have superior compatibility compared to Comparative Example 1, and thus have superior mechanical properties such as tensile strength and elongation at break. In addition, Comparative Example 2, which did not use 'polybutylene adipate terephthalate in which maleic acid is ester-bonded to the hydroxyl group at the terminal', has the disadvantage that the hydrophobic polybutylene adipate terephthalate and the hydrophilic thermoplastic starch are hardly mixed, making it difficult to measure the overall properties.

Claims

1. Contains polybutylene adipate terephthalate and thermoplastic starch, A biodegradable composition having a non-recoverable surface area of ​​1,000 to 10,000 according to the following formula 1: [Formula 1] Non-recovered area = A - B In the above equation 1, A is the area of ​​storage elastic modulus measured after increasing the strain from 0.01% to 75% at a temperature of 150°C and a frequency of 1 Hz for the biodegradable composition, B is the area of ​​storage modulus measured after the strain for the biodegradable composition is lowered again to 0.01%.

2. In paragraph 1, A biodegradable composition further comprising polybutylene adipate terephthalate having maleic acid ester-bonded to a terminal hydroxyl group.

3. In paragraph 1, A biodegradable composition, wherein polybutylene adipate terephthalate having maleic acid ester-bonded to the hydroxyl group at the terminal is represented by the following chemical formula 1 or 2: [Chemical Formula 1] [Chemical formula 2] In the above chemical formulas 1 and 2, a to d are each independently integers from 1 to 500.

4. In paragraph 1, A biodegradable composition comprising 1.5 wt% or more and 15.0 wt% or less of polybutylene adipate terephthalate in which maleic acid is ester-bonded to a hydroxyl group at the terminal, based on 100 wt% of the total of the polybutylene adipate terephthalate and thermoplastic starch.

5. In paragraph 1, A biodegradable composition, wherein the thermoplastic starch comprises at least one selected from the group consisting of rice starch, wheat starch, corn starch, sweet potato starch, potato starch, tapioca starch, cassava starch, and modified starches thereof.

6. In paragraph 1, A biodegradable composition comprising 10 wt% or more and 50 wt% or less of the thermoplastic starch relative to 100 wt% of the total solid content of the biodegradable composition.

7. A biodegradable composition comprising polybutylene adipate terephthalate and thermoplastic starch, A biodegradable film having a non-recoverable surface area of ​​1,000 to 10,000 according to the following formula 1. [Formula 1] Non-recovered area = A - B In the above equation 1, A is the area of ​​storage elastic modulus measured after increasing the strain from 0.01% to 75% at a temperature of 150°C and a frequency of 1 Hz for the biodegradable composition, B is the area of ​​storage modulus measured after the strain for the biodegradable composition is lowered again to 0.01%.

8. In paragraph 7, A biodegradable film further comprising polybutylene adipate terephthalate having maleic acid ester-bonded to a terminal hydroxyl group.

9. In paragraph 7, A biodegradable film comprising 1.5 wt% or more and 15.0 wt% or less of polybutylene adipate terephthalate in which maleic acid is ester-bonded to a hydroxyl group at the terminal, based on 100 wt% of the total of the polybutylene adipate terephthalate and thermoplastic starch.

10. In paragraph 7, A biodegradable film comprising 10 wt% or more and 50 wt% or less of the thermoplastic starch relative to 100 wt% of the total biodegradable film.

11. In paragraph 7, The above biodegradable film is a biodegradable film having a tensile strength of 5 MPa or more as measured according to ASTM D882.

12. In paragraph 7, The above biodegradable film is a biodegradable film having an elongation at break of 300% or more as measured according to ASTM D882.

13. In paragraph 7, The above biodegradable film is a biodegradable film having a tear strength of 200 gf or more as measured according to ASTM 1922.

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