Biodegradable polyester resin and preparation method thereof

Abstract

The present invention provides a biodegradable polyester resin composition, a method for preparing the same, and a biodegradable polyester film prepared from the same, the composition comprising a resin including a residue of a dicarboxylic acid component and a residue of a diol component, and satisfying formula 1. By satisfying Formula 1, the productivity and processability of the biodegradable polyester resin composition are improved, thereby enhancing the tensile strength, elongation, and tear strength of the biodegradable polyester film. [Formula 1]: In Formula 1, G'is the storage modulus at a temperature of 190 DEG C and a frequency of 10 radian / sec to 100 radian / sec in dynamic viscoelasticity measurement, and G ''is the loss modulus at a temperature of 190 DEG C and a frequency of 10 radian / sec to 100 radian / sec in dynamic viscoelasticity measurement.

Description

Technical Field

[0001] This invention relates to a biodegradable polyester resin and its preparation method. Background Technology

[0002] Polyester resins are polymer resins with ester (RO-C(=O)-R') functional groups on their main chain, and are used in a wide range of industrial applications, such as packaging materials, display materials, and insulating materials. In recent years, considering environmental protection issues, research has been conducted on biodegradable polyester compositions.

[0003] Biodegradable polyester compositions are typically prepared using aliphatic dicarboxylic acids, aromatic dicarboxylic acids, and aliphatic diols as the main raw materials, and branching agents, catalysts, and heat stabilizers as auxiliary raw materials.

[0004] Specifically, biodegradable polyester compositions are prepared by subjecting the main raw materials to esterification and polycondensation reactions in the presence of auxiliary raw materials. In some cases, chain extension reactions are carried out after polycondensation to enhance the mechanical properties of the biodegradable polyester resin. Furthermore, the physical properties of the final biodegradable polyester resin can vary depending on the characteristics of the raw material mixture used to prepare the biodegradable polyester. Summary of the Invention

[0005] Technical issues According to one embodiment, a biodegradable polyester resin composition with excellent processing and mechanical properties is provided.

[0006] According to another embodiment, a method for preparing a biodegradable polyester resin composition is provided, the method being able to improve the productivity and processing performance of the biodegradable polyester resin composition.

[0007] Technical solution In one general aspect, a biodegradable polyester resin composition comprises a resin containing residues of a dicarboxylic acid component and residues of a diol component, the biodegradable polyester resin composition satisfying the following formula 1: [Formula 1] , Where G' represents the storage modulus measured at 190°C within a frequency range of 10 radians / second to 100 radians / second in dynamic viscoelasticity measurement, and G'' represents the loss modulus measured at 190°C within a frequency range of 10 radians / second to 100 radians / second in dynamic viscoelasticity measurement.

[0008] The dicarboxylic acid component may include aromatic dicarboxylic acids having 6 to 12 carbon atoms and aliphatic dicarboxylic acids having 4 to 10 carbon atoms. Aromatic dicarboxylic acids having 6 to 12 carbon atoms may include terephthalic acid, isophthalic acid, furanyldicarboxylic acid, naphthalenedicarboxylic acid, their diester derivatives, their anhydrides, or mixtures thereof. Aliphatic dicarboxylic acids having 4 to 10 carbon atoms may include adipic acid, succinic acid, glutaric acid, azelaic acid, sebacic acid, cyclic fatty acids, their diester derivatives, their anhydrides, or mixtures thereof.

[0009] Based on the total amount of the dicarboxylic acid component, the dicarboxylic acid component may include 30 mol% to 70 mol% of aromatic dicarboxylic acids having 6 to 12 carbon atoms and 30 mol% to 70 mol% of aliphatic dicarboxylic acids having 4 to 10 carbon atoms.

[0010] Diols may include aliphatic diols having 2 to 10 carbon atoms, and aliphatic diols having 2 to 10 carbon atoms may include 1,4-butanediol, 1,2-butanediol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-dimethyl-1,3-propanediol, cyclic aliphatic diols, or mixtures thereof.

[0011] The molar ratio of the dicarboxylic acid component to the diol component is 1.0:0.8 to 1.0:1.2.

[0012] Before and after a 10-minute oscillation time scan at 190℃ and 20 radians / second, the change rate of complex viscosity was less than 15%.

[0013] The biodegradable polyester resin composition has a melt flow index (MI) of less than 10 g / 10 minutes, which is measured at 190°C under a load of 2.16 kg according to ASTM D1238.

[0014] In another general aspect, a method for preparing a biodegradable polyester resin composition includes a first step of preparing a mixture of raw materials containing an aromatic dicarboxylic acid, an aliphatic dicarboxylic acid, and an aliphatic diol; a second step of reacting the raw material mixture to prepare an oligomer; a third step of polycondensing the oligomer to prepare a prepolymer; and a fourth step of adding a chain extender to the prepolymer to obtain a biodegradable polyester resin composition, wherein the water content of the raw material mixture in the first step is less than 3000 ppm, and the biodegradable polyester resin composition prepared in the fourth step satisfies Formula 1.

[0015] Aromatic dicarboxylic acids have a particle size distribution index (SPAN) of less than 5.0.

[0016] The reaction conversion rate of the oligomer in the third step is expressed by the following formula 2, with a reaction conversion rate of 90% to 100%: [Formula 2] Reaction conversion rate (%) = , in AV represents the acid value as expressed by the following formula 2-1; and SV represents the saponification value expressed by the following formula 2-2: [Formula 2-1] Acid value (AV) = , Where A represents the titration volume (ml) of the 0.1N sodium hydroxide solution, P represents the titer of the 0.1N sodium hydroxide solution, and W represents the mass of the oligomer. [Formula 2-2] Saponification value (SV) = , Where B represents the titration volume (ml) of the 0.5N hydrochloric acid (HCl) solution, C represents the titration volume (ml) of the blank solution, Q represents the titration degree of the 0.5N hydrochloric acid solution, and W' represents the mass of the oligomer.

[0017] Aromatic dicarboxylic acids are terephthalic acid, isophthalic acid, furanyl dicarboxylic acid, naphthalenedicarboxylic acid, their diester derivatives, their anhydrides, or combinations thereof, and aliphatic dicarboxylic acids are adipic acid, succinic acid, glutaric acid, azelaic acid, sebacic acid, cyclic fatty acids, their diester derivatives, their anhydrides, or combinations thereof.

[0018] Based on the total moles of the raw material mixture, the content of aromatic dicarboxylic acids can be from 20 mol% to 50 mol%, and the content of aliphatic dicarboxylic acids can be from 20 mol% to 50 mol%.

[0019] Aliphatic diols are 1,4-butanediol, 1,2-butanediol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-dimethyl-1,3-propanediol, cyclic aliphatic diols, or mixtures thereof.

[0020] Based on the total moles of the raw material mixture, the content of aliphatic diols can be from 30 mol% to 60 mol%.

[0021] The molar ratio of aromatic dicarboxylic acids and aliphatic dicarboxylic acids to aliphatic diols is 1.0:0.8 to 1.0:1.2.

[0022] On the other hand, a biodegradable polyester film is provided, which is obtained by melt extruding the above-described biodegradable polyester resin composition using a blown film extruder, or by melt extruding the biodegradable polyester resin composition prepared by the above-described preparation method using a blown film extruder.

[0023] Beneficial effects According to one embodiment, the polyester resin composition can have improved productivity and processing performance.

[0024] According to another embodiment, the method for preparing a polyester resin composition can uniformly control the reaction rate at each step and suppress side reactions.

[0025] Polyester films prepared from polyester resin compositions according to one embodiment can ensure excellent tensile strength, elongation and tear strength. Attached Figure Description

[0026] Figure 1 It is a graph showing the values ​​corresponding to the area of ​​the energy storage modulus and the loss modulus, which were measured at 10 radians / second to 100 radians / second according to the compositions of the examples and comparative examples. Specific implementation formula The advantages and features of the techniques described below, as well as the methods for implementing them, will become apparent from the embodiments described in detail with reference to the accompanying drawings. However, the forms of implementation are not limited to those disclosed below. Unless otherwise defined, all terms (including technical and scientific terms) used in this specification are to be interpreted as having the meaning commonly understood by those skilled in the art, and furthermore, unless explicitly defined otherwise, terms as defined in commonly used dictionaries should not be idealized or exaggerated.

[0027] In this specification, unless explicitly stated otherwise, "comprising" any component will be understood to mean that other components are also included, not that any other components are excluded. Furthermore, unless the context clearly indicates otherwise, the singular forms used herein are intended to include the plural forms.

[0028] Based on the above definitions, embodiments of the present invention will be described in detail. However, these embodiments are provided as examples, and the invention is not limited thereto, but is defined by the scope of the claims.

[0029] [Biodegradable polyester resin composition] According to one embodiment, the biodegradable polyester resin composition comprises a resin containing residues of a dicarboxylic acid component and residues of a diol component, and the biodegradable polyester resin composition satisfies the following formula 1.

[0030] [Formula 1] , In Formula 1, G' represents the storage modulus measured at 190°C in a frequency range of 10 radians / second to 100 radians / second in dynamic viscoelasticity measurement, and G'' represents the loss modulus measured at 190°C in a frequency range of 10 radians / second to 100 radians / second in dynamic viscoelasticity measurement.

[0031] In one implementation, a rotational rheometer (HR-2, TA Instruments) equipped with a 25 mm parallel plate is used to measure the storage modulus (G') and loss modulus (G'').

[0032] In Formula 1, It represents the integral value of the energy storage modulus measured by frequency scanning at a temperature of 190°C within a frequency range of 10 radians / second to 100 radians / second. It represents the integral value of the loss modulus measured by frequency scanning at a temperature of 190°C within a frequency range of 10 radians / second to 100 radians / second.

[0033] Specifically, the value obtained by dividing the integral value of the energy storage modulus at a temperature of 190°C within a frequency range of 10 radians / second to 100 radians / second by the integral value of the loss modulus under the same conditions is 0.1 to 2.0, for example, 0.1 to 1.75, 0.1 to 1.50, 0.15 to 1.5, 0.20 to 1.5, 0.25 to 1.5, 0.3 to 1.5, 0.4 to 1.5, 0.50 to 1.5, 0.50 to 1.3 or 0.50 to 1.0, but not limited thereto.

[0034] When the biodegradable polyester resin composition satisfies Formula 1, the productivity and processing properties of the composition can be improved, and the biodegradable polyester film prepared therefrom can have improved tensile strength, elongation and tear strength.

[0035] In one embodiment, the dicarboxylic acid component included in the biodegradable polyester resin composition comprises aromatic dicarboxylic acids having 6 to 12 carbon atoms and aliphatic dicarboxylic acids having 4 to 10 carbon atoms.

[0036] Aromatic dicarboxylic acids are terephthalic acid, isophthalic acid, furanyl dicarboxylic acid, naphthalic acid, their diester derivatives, their anhydrides, or combinations thereof, such as terephthalic acid, isophthalic acid, their diester derivatives, or combinations thereof, but are not limited thereto.

[0037] Aliphatic dicarboxylic acids are adipic acid, succinic acid, glutaric acid, azelaic acid, sebacic acid, cyclic fatty acids, their diester derivatives, their anhydrides, or combinations thereof, such as adipic acid, succinic acid, their diester derivatives, or combinations thereof, but not limited thereto.

[0038] In one embodiment, based on the total amount of the dicarboxylic acid component, the dicarboxylic acid component may include 30 mol% to 70 mol% of an aromatic dicarboxylic acid having 6 to 12 carbon atoms and 30 mol% to 70 mol% of an aliphatic dicarboxylic acid having 4 to 10 carbon atoms.

[0039] In one embodiment, the aliphatic diol is 1,4-butanediol, 1,2-butanediol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-dimethyl-1,3-propanediol, cyclic aliphatic diols, or mixtures thereof, but is not limited thereto.

[0040] In one embodiment, the molar ratio of aromatic dicarboxylic acids and aliphatic dicarboxylic acids to aliphatic diols contained in the biodegradable polyester resin composition is from 1.0:0.8 to 1.0:1.2, for example from 1.0:0.8 to 1.0:1.15 or 1.0:1.1, but is not limited thereto.

[0041] According to one embodiment, the biodegradable polyester resin composition exhibits a change in complex viscosity of less than 15% before and after a 10-minute oscillation time scan at a temperature of 190°C and a frequency of 20 radians / second.

[0042] Complex viscosity can be measured using a rotational rheometer (HR-2, TA Instruments), and the rate of change of complex viscosity can be calculated by measuring the complex viscosity before and after a 10-minute oscillation time scan at an angular frequency of 20 radians / second. Specifically, the rate of change of complex viscosity can be calculated as [(complex viscosity value after 10 minutes - initial complex viscosity value) / initial complex viscosity value] x 100 (%).

[0043] In one embodiment, the rate of change of complex viscosity is less than 15%, such as less than 13%, less than 11%, less than 9%, or less than 6%, but not limited thereto. Furthermore, the rate of change of complex viscosity is greater than 0.5%, such as greater than 1.0% or greater than 1.5%, but not limited thereto.

[0044] When the rate of change of the complex viscosity of the biodegradable polyester resin composition is within the above range, the productivity and processing performance of the composition can be improved, and the biodegradable polyester film produced therefrom can have improved tensile strength, elongation and tear strength.

[0045] In one embodiment, the biodegradable polyester resin composition has a melt flow index (MI) of less than 10 g / 10 minutes, which is measured at 190°C under a load of 2.16 kg according to ASTM D1238. A melt flow index of less than 10 g / 10 minutes is, for example, less than 8 g / 10 minutes, less than 6 g / 10 minutes, or less than 5 g / 10 minutes, but is not limited thereto. When the melt flow index meets the above range, the productivity and processability of the composition can be improved, and the biodegradable polyester film thus produced can have improved tensile strength, elongation, and tear strength.

[0046] [Method for preparing biodegradable polyester compositions] According to another embodiment, a method for preparing a biodegradable polyester resin composition includes: a first step of preparing a raw material mixture containing an aromatic dicarboxylic acid, an aliphatic dicarboxylic acid, and an aliphatic diol; a second step of reacting the raw material mixture to prepare an oligomer; a third step of polycondensing the oligomer to prepare a prepolymer; and a fourth step of adding a chain extender to the prepolymer to obtain a biodegradable polyester resin composition, wherein the water content of the raw material mixture in the first step is less than 3000 ppm, and the biodegradable polyester resin composition prepared in the fourth step satisfies Formula 1.

[0047] The biodegradable polyester resin composition prepared by the above preparation method can be the same as that in the above embodiments. Therefore, the above description will not be repeated below, and the preparation method of one embodiment will be described step by step.

[0048] first step In the first step, a mixture of raw materials containing aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and aliphatic diols is prepared.

[0049] The water content in the raw material mixture is measured using a Karl Fischer titrator. Specifically, the water content (%) is calculated by titration with Karl Fischer reagent (KFR) according to the following formula 3.

[0050] [Formula 3] , In Formula 3, T represents the volume (ml) of Karl Fischer reagent consumed for sample titration, S represents the volume (ml) of Karl Fischer reagent consumed for blank titration, R represents the titer of Karl Fischer reagent (mg / ml), and M represents the mass of the sample (mg).

[0051] In one embodiment, the water content in the feedstock mixture is less than 3000 ppm, such as less than 2900 ppm, less than 2800 ppm, less than 2600 ppm, or less than 2200 ppm, but not limited thereto. Furthermore, the water content in the feedstock mixture is more than 1400 ppm, such as more than 1500 ppm, but not limited thereto.

[0052] When the moisture content of the raw material mixture does not meet the above range, the catalyst activity may be reduced during the preparation of the resin composition, and the resin composition may be hydrolyzed, resulting in the deterioration of the physical properties of the biodegradable polyester resin film formed therefrom. When the moisture content of the raw material mixture meets the above range, the biodegradable polyester resin composition can be homogeneous.

[0053] In one embodiment, the aromatic dicarboxylic acid contained in the feedstock mixture has a particle size distribution index (SPAN) of 5.0 or less, such as 4.5 or less, 4.0 or less, or 3.5, but is not limited thereto. Furthermore, the aromatic dicarboxylic acid has a particle size distribution index of 0.5 or more, such as 1.0 or more, or 1.5 or more, but is not limited thereto.

[0054] The particle size distribution index (SPAN) of aromatic dicarboxylic acids can be measured using a particle size analyzer (LS13320 XR, dry powder module, Beckman Coulter).

[0055] When the particle size distribution index of aromatic dicarboxylic acids is within the above range, the biodegradable polyester resin composition can be homogeneous.

[0056] In one embodiment, the aromatic dicarboxylic acid is terephthalic acid, isophthalic acid, furanyl dicarboxylic acid, naphthalic acid, their diester derivatives, their anhydrides, or combinations thereof, such as terephthalic acid, isophthalic acid, their diester derivatives, or combinations thereof, but not limited thereto.

[0057] In one embodiment, the aliphatic dicarboxylic acid is adipic acid, succinic acid, glutaric acid, azelaic acid, sebacic acid, cyclic fatty acids, their diester derivatives, their anhydrides, or combinations thereof, such as adipic acid, succinic acid, their diester derivatives, or combinations thereof, but not limited thereto.

[0058] In one embodiment, the content of aromatic dicarboxylic acid is 20 mol% to 50 mol% based on the total moles of the raw material mixture, for example, 20 mol% to 45 mol%, 20 mol% to 40 mol%, 20 mol% to 35 mol%, or 20 mol% to 30 mol%, but not limited thereto.

[0059] In one embodiment, the content of aliphatic dicarboxylic acid is 20 mol% to 50 mol% based on the total moles of the raw material mixture, for example, 20 mol% to 45 mol%, 20 mol% to 40 mol%, 20 mol% to 35 mol%, or 20 mol% to 30 mol%, but not limited thereto.

[0060] In one embodiment, the aliphatic diol may be 1,4-butanediol, 1,2-butanediol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-dimethyl-1,3-propanediol, cyclic aliphatic diols, or mixtures thereof, but is not limited thereto.

[0061] In one embodiment, the aliphatic diol content is 30 mol% to 60 mol% based on the total moles of the feed mixture, for example, 30 mol% to 55 mol%, 35 mol% to 55 mol%, 40 mol% to 60 mol%, 40 mol% to 55 mol% or 50 mol%, but not limited thereto.

[0062] In one embodiment, the molar ratio of aromatic dicarboxylic acid and aliphatic dicarboxylic acid to aliphatic diol is from 1.0:0.8 to 1.0:1.2, for example from 1.0:0.8 to 1.0:1.15 or 1.0:1.1, but is not limited thereto.

[0063] In another embodiment, the raw material mixture may also contain compounds, such as branching agents or catalysts, to improve the physical properties of the biodegradable polyester resin composition.

[0064] For example, branching agents can have hydroxyl (-OH), carboxyl (-COOH), or acid anhydride as crosslinkable functional groups. Specifically, examples of branching agents include glycerol, trimethylolpropane, and pentaerythritol. Branching agents can be added not only in the first step but also later in the second or third step.

[0065] For example, the catalyst can be a titanium (Ti)-based catalyst, which may include titanium (Ti)-based esterification catalysts, titanium (Ti)-based polycondensation catalysts, or combinations thereof. Titanium (Ti)-based esterification catalysts may include organic acid chelate titanium compounds and inorganic titanium compounds. Titanium (Ti)-based polycondensation catalysts may include tetraalkoxy titanium compounds or combinations thereof.

[0066] When a titanium (Ti)-based catalyst is also included in the feed mixture, oligomers with uniform size can be prepared, and the generation of unreacted substances can be prevented.

[0067] Step 2 In the second step, the raw material mixture is reacted to prepare the oligomer. To prevent thermal decomposition during this step, the reaction should be carried out efficiently within a short time. If the reaction temperature in the second step is too low, the residence time increases, which may result in unreacted products; conversely, if the reaction temperature is too high, the diols in the reactants, especially 1,4-butanediol, will decompose to form THF, preventing 1,4-butanediol from fully participating in the reaction, which may also lead to the formation of unreacted products.

[0068] The second step can be carried out in a temperature range of 190°C to 230°C to minimize macromolecules or aggregates in the final biodegradable polyester composition. Specifically, in the second step, the esterification reaction of the raw material mixture can be carried out under low vacuum in a temperature range of 190°C to 230°C, and water (H2O) (byproduct) and by-reaction products can be removed from the system by a distillation column to obtain oligomers.

[0069] In one implementation, the reaction conversion rate of the oligomer in the second step is represented by the following formula 2, where the reaction conversion rate is 90% to 100%.

[0070] [Formula 2] Reaction conversion rate (%) = In Formula 2, AV (acid value) represents the acid value expressed by Formula 2-1 below; SV (saponification value) represents the saponification value expressed by Formula 2-2 below.

[0071] [Formula 2-1] Acid value (AV) = In Formula 2-1, A represents the titration volume (ml) of the 0.1N sodium hydroxide solution, P represents the titer of the 0.1N sodium hydroxide solution, and W represents the mass (g) of the oligomer.

[0072] [Formula 2-2] Saponification value (SV) = In Formula 2-2, B represents the titration volume (ml) of the 0.5N hydrochloric acid (HCl) solution, C represents the titration volume (ml) of the blank solution, Q represents the titration degree of the 0.5N hydrochloric acid solution, and W' represents the mass (g) of the oligomer.

[0073] The reaction conversion rate of the oligomer is 90% to 100%, such as 91% to 100%, 93% to 100%, 95% to 100%, 96% to 100%, but not limited to this.

[0074] When the reaction conversion rate of the oligomer meets the above range, the reaction rate of the preparation process can be uniformly controlled, and side reactions can be suppressed, so that the biodegradable polyester resin composition can be uniform.

[0075] Step 3 In the third step, the oligomers can be polycondensed to prepare the prepolymer. To prevent thermal decomposition during this step, the reaction should be carried out efficiently within a short time. If the reaction temperature in the third step is too high, the thermal decomposition reaction may exceed the polycondensation reaction, leading not only to the formation of decomposition products but also to an increased residence time.

[0076] In this regard, the third step can be carried out in a temperature range of 210°C to 250°C under a vacuum of less than 1 Torr, so that byproducts generated by thermal decomposition in the final biodegradable polyester composition can be minimized.

[0077] Therefore, prepolymers with melt flow index (MI) of 5 g / 10 min to 60 g / 10 min, measured at 190 °C under a load of 2.16 kg according to ASTM D1238 standard, can be obtained.

[0078] In one implementation, a heat stabilizer may also be added in the third step of the reaction.

[0079] For example, the heat stabilizer can be a phosphorus (P)-based heat stabilizer, and can be, for example, trimethylphosphonic acid acetate, triethylphosphonic acid acetate, phosphoric acid, phosphorous acid, polyphosphoric acid, trimethyl phosphate (TMP), triethyl phosphate, trimethylphosphine, triphenylphosphine, or combinations thereof.

[0080] By adding phosphorus (P)-based heat stabilizers, thermal decomposition can be prevented without reducing catalyst activity.

[0081] Step 4 In the fourth step, a chain extender can be added to the prepolymer to further increase the viscosity, thereby obtaining a polyester resin composition.

[0082] In the fourth step, when the prepolymer and chain extender are mixed at high speed or under high shear to promote a smooth reaction between them, decomposition may occur due to increased shear stress, and thermal decomposition may also occur when the reaction is carried out at high temperature, resulting in a sharp increase in the molecular weight distribution of the final biodegradable polyester.

[0083] Therefore, it is preferable to use a static mixer or a dynamic mixer to perform the fourth step for 0 to 30 minutes at a temperature range of 120°C to 250°C.

[0084] [Biodegradable polyester film] According to another embodiment, a biodegradable polyester film can be obtained by melt extruding the above-described biodegradable polyester resin composition using a blown film extruder. Furthermore, according to another embodiment, a biodegradable polyester film can be obtained by melt extruding the biodegradable polyester resin composition prepared by the above-described preparation method using a blown film extruder. The method for manufacturing the biodegradable polyester film is not limited to these methods.

[0085] The thickness of the obtained biodegradable polyester film is 30µm to 70µm, for example, 30µm to 60µm, 40µm to 70µm, 40µm to 60µm or 50µm, but not limited thereto.

[0086] The invention will be described below with reference to embodiments. However, the following embodiments are provided by way of example only, and the scope of the invention is not limited thereto.

[0087] Preparation of biodegradable polyester resin compositions Example 1: first step: A feedstock mixture was prepared by stirring 24 mol% terephthalic acid (TPA), 26 mol% adipic acid (AA), and 50 mol% 1,4-butanediol (1,4-BDO). The particle size distribution index (SPAN) of terephthalic acid and the water content in the feedstock mixture are shown in Table 1.

[0088] Step Two: Tetrabutyl titanate (a titanium-based catalyst) was added to the feed mixture from the first step, and the reaction was carried out at 220°C under a low vacuum of 650 mbar. Simultaneously, wastewater was removed via a distillation column to prepare oligomers. The reaction conversion rates of the oligomers in the second step are shown in Table 1.

[0089] Step 3: The reaction mixture obtained after the second step was heated to 250°C and subjected to polycondensation below 1 Torr. The reaction was terminated when the discharge load was reached, thereby obtaining a prepolymer with a number average molecular weight of 35,000 g / mol.

[0090] Step 4: The obtained biodegradable polyester prepolymer is dried and then subjected to a chain extension process using a mixer to obtain a final biodegradable polyester resin composition with the properties shown in Table 2.

[0091] Examples 2 to 6 Biodegradable polyester resin compositions were prepared by changing the properties of the raw materials shown in Table 1.

[0092] Comparative Examples 1 to 4 Biodegradable polyester resin compositions were prepared by changing the properties of the raw materials shown in Table 1.

[0093] Experimental Example 1: Physical Properties of Raw Material Mixtures Moisture content in the raw material mixture: The moisture content (%) is calculated by titration using a Karl Fischer titrator and Karl Fischer reagent (KFR) according to the following formula 3.

[0094] [Formula 3] , In Formula 3, T represents the volume (ml) of Karl Fischer reagent consumed for sample titration, S represents the volume (ml) of Karl Fischer reagent consumed for blank titration, R represents the titer of Karl Fischer reagent (mg / ml), and M represents the mass (mg) of the raw material mixture sample.

[0095] Particle size distribution index (SPAN) of aromatic dicarboxylic acids: The measurements were performed using a particle size analyzer (LS13320 XR, dry powder module, Beckman Coulter), and the SPAN was calculated using the following formula 4.

[0096] [Formula 4] SPAN = (D90 - D10) / D50 In Formula 4, D90 refers to the particle size corresponding to 90% of the cumulative volume on the smaller particle size side of the particle size distribution curve, D10 refers to the particle size corresponding to 10% of the cumulative volume on the smaller particle size side, and D50 refers to the particle size corresponding to 50% of the cumulative volume on the smaller particle size side.

[0097] Experimental Example 2: Determination of Oligomer Reaction Conversion Rate Acid value measurement (acid value: AV) Sample solutions and blank solutions (50 ml of dimethylformamide solvent) were prepared by injecting 50 ml of dimethylformamide (DMF) into each of the oligomer samples of Examples 1 to 6 and Comparative Examples 1 to 4, using 0.2 g of each sample solution. The solutions were dissolved in an ultrasonic bath at 85°C to 90°C for 1 hour, and then cooled to room temperature. Two or three drops of 0.1% rosolic acid were added to each sample solution and blank solution, and the solutions were titrated with N / 10 NaOH methanol solution. The endpoint was defined as the point where the color changed from pale yellow to pale purple, and the acid value was calculated using Formula 2-1 below.

[0098] [Formula 2-1] Acid value (AV) = , In Formula 2-1, A represents the titration volume (ml) of the 0.1N sodium hydroxide solution, P represents the titer of the 0.1N sodium hydroxide solution, and W represents the mass (g) of the oligomer.

[0099] Determination of saponification value (SA) Sample solutions were prepared by injecting 20 ml of 0.5 N KOH ethanol solution into each of the oligomer samples from Examples 1 to 6 and Comparative Examples 1 to 4, and adding two or three zeolite particles. Blank solutions were prepared by adding two or three zeolite particles to 20 ml of 0.5 N KOH ethanol solution excluding the sample. The sample and blank solutions were hydrolyzed for 40 minutes in a 110°C oil bath equipped with a cooling condenser. 15 ml of distilled water was added and thoroughly mixed, and the mixture was then cooled to room temperature. Subsequently, three or four drops of 0.1% phenolphthalein were added to each sample and blank solution, and titration was performed with 0.5 N HCl. The endpoint was defined as the point where the color changed from pink to colorless, and the saponification value was calculated using Formula 2-2 below.

[0100] [Formula 2-2] Saponification value (SV) = , In Formula 2-2, B represents the titration volume (ml) of the 0.5N hydrochloric acid (HCl) solution, C represents the titration volume (ml) of the blank solution, Q represents the titration degree of the 0.5N hydrochloric acid solution, and W' represents the mass (g) of the oligomer.

[0101] Derivation of reaction conversion rate (%) The reaction conversion rate of the oligomers is calculated by applying the acid value (AV) and saponification value (SV) obtained above to Equation 2 below.

[0102] [Formula 2] Reaction conversion rate (%) = , The reaction conversion rates of the oligomers obtained by the above method are shown in Table 1.

[0103] [Table 1]

[0104] Experimental Example 3: Physical Properties of Biodegradable Polyester Resin Compositions The physical properties of the biodegradable polyester resin compositions of the examples and comparative examples were evaluated using the following methods, and the results are shown in Table 2.

[0105] Melt Flow Index (MI): After the sample was loaded, the weight of polyester extruded through the orifice of the capillary rheometer was measured at 190°C for 10 minutes under a load of 2.16 kg, in accordance with ASTM D1238 standard.

[0106] Molecular weight distribution (PDI):Molecular weight distribution was measured using gel permeation chromatography (GPC, Technology 1200 Series, Agilent Technologies) with chloroform as solvent and polystyrene as standard. Measurements were performed at a column temperature and detector temperature of 40°C and a flow rate of 1 mL / min.

[0107] Zero shear viscosity (η0): Zero-shear viscosity refers to the complex viscosity value at an angular frequency of 0.1 radians per second, which is obtained by frequency scanning at a strain of 1%.

[0108] Cumulative energy storage coefficient (Cotδ): Storage modulus and loss modulus were measured by mounting a 25 mm parallel plate on a rotational rheometer (HR-2, TA Instruments) and performing frequency sweeps at 190°C in a frequency range of 10 radians / second to 100 radians / second. Figure 1 This is a graph showing the energy storage modulus and loss modulus of the embodiments and comparative examples. The cumulative energy storage coefficient is the value obtained by dividing the integral value of the energy storage modulus over a frequency range of 10 radians / second to 100 radians / second by the integral value of the loss modulus, as shown in Formula 1-1 below.

[0109] [Formula 1-1] , Complex viscosity change rate: Measurements were performed using a rotational rheometer (HR-2, TA Instruments). During a 10-minute time-scan test at a fixed angular frequency of 20 radians / second and a fixed strain of 1%, the rate of change of viscosity relative to the initial viscosity was calculated. Specifically, the rate of change of complex viscosity was calculated as [(complex viscosity value after 10 minutes - initial complex viscosity value) / initial complex viscosity value] x 100 (%).

[0110] Experimental Example 4: Physical Properties of Biodegradable Polyester Films The biodegradable polyester resin compositions obtained in the Examples and Comparative Examples were melt-extruded using a blown film extruder to prepare 50 µm biodegradable polyester films. Their physical properties were evaluated using the following methods, and the results are shown in Table 2.

[0111] Tensile strength: Tensile strength refers to the resistance of a membrane to tearing. Tensile strength is measured using a general-purpose testing machine 5965 from INSTRON, in accordance with ASTM D882 standard.

[0112] Elongation: Elongation was measured using a general-purpose testing machine 5965 from INSTRON, in accordance with ASTM D882 standard.

[0113] Tear strength: Tear strength was measured using an Elmendorf tear tester from Thwing-Albert Instruments in accordance with ASTM D1922 standard.

[0114] [Table 2]

[0115] Referring to Table 2, it can be confirmed that the biodegradable polyester resin composition according to the embodiments has a cumulative storage coefficient of 0.1 to 1.5 and a complex viscosity change rate (%) of less than 6%. It can be confirmed that the biodegradable polyester film according to the embodiments has superior tensile strength, elongation, and tear strength compared with the biodegradable polyester film according to the comparative examples.

[0116] While the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto. Various modifications and improvements made by those skilled in the art using the basic concepts of the present invention as defined in the claims also fall within the scope of the present invention.

Claims

1. A biodegradable polyester resin composition comprising a resin containing residues of a dicarboxylic acid component and residues of a diol component, the biodegradable polyester resin composition satisfying the following Equation 1: [Equation 1] G' > G'' wherein G' represents a storage modulus measured in a dynamic viscoelasticity measurement at a temperature of 190°C in a frequency range of 10 rad / sec to 100 rad / sec, and G'' represents a loss modulus measured in a dynamic viscoelasticity measurement at a temperature of 190°C in a frequency range of 10 rad / sec to 100 rad / sec.

2. The biodegradable polyester resin composition according to claim 1, wherein the dicarboxylic acid component includes an aromatic dicarboxylic acid having 6 to 12 carbon atoms and an aliphatic dicarboxylic acid having 4 to 10 carbon atoms, the aromatic dicarboxylic acid having 6 to 12 carbon atoms includes terephthalic acid, isophthalic acid, furandicarboxylic acid, naphthalene dicarboxylic acid, diester derivatives thereof, anhydrides thereof, or a mixture thereof, and the aliphatic dicarboxylic acid having 4 to 10 carbon atoms includes adipic acid, succinic acid, glutaric acid, azelaic acid, sebacic acid, cyclic aliphatic acid, diester derivatives thereof, anhydrides thereof, or a mixture thereof. ， 3. The biodegradable polyester resin composition according to claim 1, wherein the dicarboxylic acid component includes 30 to 70 mole% of an aromatic dicarboxylic acid having 6 to 12 carbon atoms and 30 to 70 mole% of an aliphatic dicarboxylic acid having 4 to 10 carbon atoms, based on the total amount of the dicarboxylic acid component.

4. The biodegradable polyester resin composition according to claim 1, wherein the diol includes an aliphatic diol having 2 to 10 carbon atoms, and the aliphatic diol having 2 to 10 carbon atoms includes 1,4-butanediol, 1,2-butanediol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-dimethyl-1,3-propanediol, a cyclic aliphatic diol, or a mixture thereof.

5. The biodegradable polyester resin composition according to claim 1, wherein the molar ratio of the dicarboxylic acid component to the diol component is 1.0:0.8 to 1.0:1.

2.

6. The biodegradable polyester resin composition according to claim 1, wherein the rate of change of complex viscosity before and after an oscillation time sweep at a temperature of 190°C and a frequency of 20 rad / sec for 10 minutes is less than 15%.

7. The biodegradable polyester resin composition according to claim 1, wherein the biodegradable polyester resin composition has a melt flow index (MI) of 10 g / 10 min or less, measured at 190°C under a load of 2.16 kg according to ASTM D1238.

8. A method for preparing a biodegradable polyester resin composition, the method comprising: a first step of preparing a raw material mixture containing an aromatic dicarboxylic acid, an aliphatic dicarboxylic acid, and an aliphatic diol; a second step of polymerizing the raw material mixture to prepare a polyester resin; and a third step of adding a biodegradable additive to the polyester resin. ​ ​ ​ ​ ​ ​ ​ ​ second step of reacting the raw material mixture to produce an oligomer; a third step of polycondensing the oligomer to produce a prepolymer; and a fourth step of adding a chain extender to the prepolymer to obtain a biodegradable polyester resin composition, wherein the raw material mixture in the first step has a water content of 3000 ppm or less, and the biodegradable polyester resin composition produced in the fourth step satisfies the following Formula 1: [Formula 1] ， wherein G' represents a storage modulus measured at a temperature of 190°C in a frequency range of 10 rad / sec to 100 rad / sec in a dynamic viscoelasticity measurement, and G" represents a loss modulus measured at a temperature of 190°C in a frequency range of 10 rad / sec to 100 rad / sec in a dynamic viscoelasticity measurement.

9. The method of claim 8, wherein the aromatic dicarboxylic acid has a particle size distribution index (SPAN) of 5.0 or less.

10. The method of claim 8, wherein a reaction conversion rate of the oligomer in the third step is 90% to 100%, represented by the following Formula 2: [Formula 2] Reaction conversion rate (%) = , wherein AV represents an acid value represented by the following Formula 2-1; and SV represents a saponification value represented by the following Formula 2-2: [Formula 2-1] Acidity (AV)= , wherein A represents a titration volume (ml) of a 0.1N sodium hydroxide solution, P represents a titer of the 0.1N sodium hydroxide solution, and W represents a mass of the oligomer: [Formula 2-2] Saponification value (SV) = 0.43 mg KOH / g , wherein B represents a titration volume (ml) of a 0.5N hydrochloric acid (HCl) solution, C represents a titration volume (ml) of a blank solution, Q represents a titer of the 0.5N hydrochloric acid solution, and W' represents a mass of the oligomer.

11. The method of claim 8, wherein the aromatic dicarboxylic acid is terephthalic acid, isophthalic acid, furandicarboxylic acid, naphthalene dicarboxylic acid, a diester derivative thereof, an anhydride thereof, or a combination thereof, and the aliphatic dicarboxylic acid is adipic acid, succinic acid, glutaric acid, azelaic acid, sebacic acid, a cyclic aliphatic acid, a diester derivative thereof, an anhydride thereof, or a combination thereof.

12. The method of claim 8, wherein the content of the aromatic dicarboxylic acid is 20 mol% to 50 mol% and the content of the aliphatic dicarboxylic acid is 20 mol% to 50 mol% based on the total moles of the raw material mixture.

13. The method of claim 8, wherein the aliphatic diol is 1,4-butanediol, 1,2-butanediol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-dimethyl-1,3-propanediol, a cyclic aliphatic diol, or a mixture thereof.

14. The method of claim 8, wherein the content of the aliphatic diol is 30 mol% to 60 mol% based on the total moles of the raw material mixture.

15. The method of claim 8, wherein the molar ratio of the aromatic dicarboxylic acid and the aliphatic dicarboxylic acid to the aliphatic diol is 1.0:0.8 to 1.0:1.

2.

16. A biodegradable polyester film obtained by melt-extruding the biodegradable polyester resin composition according to any one of claims 1 to 7 using a film blowing extruder.

17. A biodegradable polyester film obtained by melt-extruding a biodegradable polyester resin composition using a film blowing extruder, the biodegradable polyester resin composition being prepared by the method for preparing a biodegradable polyester resin composition according to any one of claims 8 to 15.

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