Preparation method of poly (butylene adipate-co-terephthalate) and poly (butylene adipate-co-terephthalate)

Abstract

The present invention relates to a method for preparing poly (butylene adipate-co-terephthalate) and poly (butylene adipate-co-terephthalate), the method comprising: a first step of preparing a poly (butylene adipate-co-terephthalate) prepolymer by polymerizing butylene glycol, adipic acid, and terephthalic acid in the presence of a titanium (Ti)-based polymerization catalyst; and a second step of preparing a poly (butylene adipate / terephthalate) polymer by polycondensing the poly (butylene adipate / terephthalate) prepolymer in the presence of a titanium (Ti)-based polycondensation catalyst and a phosphorus (P)-based heat stabilizer, in which the molar ratio of phosphorus (P) to titanium (Ti) used in the first step and the second step satisfies Equation 1 below. [Equation 1] 0.65 < = P / Ti < = 1.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of Korean Patent Application No. 10-2023-0023776 filed on February 22, 2023, and No. 10-2024-0024326 filed on February 20, 2024, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference in their entirety. Technical Field

[0003] The invention relates to a preparation method of polybutylene adipate terephthalate and polybutylene adipate terephthalate. Background Art

[0004] Polyester resins have excellent mechanical and chemical properties, and thus they have been used for many purposes, for example, in fields such as drinking water containers, medical products, food packaging, food containers, sheets, films, and automotive molded products.

[0005] Among them, polybutylene adipate terephthalate (PBAT) is a flexible, biodegradable polyester. As environmental regulations have become more stringent recently, PBAT has received attention as an alternative material that can replace polyolefin polymers that are mainly used in films (eg, food packaging materials).

[0006] Polybutylene adipate terephthalate is processed into films, etc. by extrusion or injection molding. If the acid value of polybutylene adipate terephthalate is too high, product quality problems may occur during processing such as extrusion or injection due to insufficient mechanical strength.

[0007] Furthermore, polybutylene adipate terephthalate is mainly used for purposes such as transparent films, but there is a problem in that discoloration to red or yellow occurs in the produced film, deteriorating the appearance of the product.

[0008] Therefore, the acid value and color characteristics of polybutylene adipate terephthalate are very important, and it can be considered that there is a trade-off relationship between the acid value and color characteristics of polybutylene adipate terephthalate. Therefore, it is necessary to develop polybutylene adipate terephthalate having an appropriate acid value that does not cause discoloration while being able to simultaneously satisfy excellent mechanical properties and appearance. Summary of the invention

[0009] [Technical issues]

[0010] In the present invention, there is provided polybutylene adipate terephthalate having mechanical properties sufficient to prevent problems during processing by having an acid value within a specific range while having excellent appearance (eg, color).

[0011] The present invention also provides a method for preparing polybutylene adipate terephthalate.

[0012] [Technical solution]

[0013] In the present invention, a method for preparing polybutylene adipate terephthalate is provided, which comprises: a first step of preparing a polybutylene adipate terephthalate prepolymer by polymerizing butanediol, adipic acid and terephthalic acid in the presence of a titanium (Ti)-based polymerization catalyst; and

[0014] The second step is to prepare a polybutylene adipate terephthalate polymer by polycondensing the polybutylene adipate terephthalate prepolymer in the presence of a titanium (Ti)-based polycondensation catalyst and a phosphorus (P)-based heat stabilizer.

[0015] Wherein, the molar ratio of phosphorus to titanium used in the first step and the second step satisfies the following equation 1:

[0016] [Equation 1]

[0017] 0.65≤P / Ti≤1

[0018] According to one embodiment of the present invention, in the above preparation method, the content of 1,4-butanediol may be about 100 parts by weight to about 250 parts by weight based on 100 parts by weight of adipic acid.

[0019] According to another embodiment of the present invention, in the above preparation method, the content of terephthalic acid may be about 50 parts by weight to about 150 parts by weight based on 100 parts by weight of adipic acid.

[0020] According to another embodiment of the present invention, in the above preparation method, the content of the titanium (Ti)-based polymerization catalyst may be about 0.001 parts by weight to about 10 parts by weight based on 100 parts by weight of adipic acid.

[0021] According to another embodiment of the present invention, in the above preparation method, the titanium (Ti)-based polymerization catalyst may be at least one selected from the group consisting of titanium methoxide, titanium ethoxide, titanium propoxide, titanium isopropoxide, titanium butoxide, titanium isobutoxide and titanium citrate.

[0022] According to another embodiment of the present invention, in the above preparation method, the titanium (Ti)-based polycondensation catalyst may be the same as or different from the titanium (Ti)-based polymerization catalyst.

[0023] According to another embodiment of the present invention, in the above preparation method, the content of the titanium (Ti)-based polycondensation catalyst may be about 0.001 parts by weight to about 0.5 parts by weight based on 100 parts by weight of the polybutylene adipate terephthalate prepolymer.

[0024] According to another embodiment of the present invention, in the above preparation method, the phosphorus (P)-based heat stabilizer may include at least one selected from the group consisting of phosphoric acid, phosphorous acid, trialkyl phosphates and trialkyl phosphonoacetate.

[0025] According to another embodiment of the present invention, in the above preparation method, the content of the phosphorus (P)-based heat stabilizer may be about 0.001 parts by weight to about 0.1 parts by weight based on 100 parts by weight of the polybutylene adipate terephthalate prepolymer.

[0026] According to another embodiment of the present invention, the weight average molecular weight of the polybutylene adipate terephthalate polymer may be about 70,000 g / mol to about 200,000 g / mol.

[0027] According to another embodiment of the present invention, the acid value (mmol / kg) of the polybutylene adipate terephthalate polymer may be about 5 to about 30.

[0028] According to another embodiment of the present invention, the b* value of the color of the polybutylene adipate terephthalate polymer may be about 0 to about 30.

[0029] According to another embodiment of the present invention, the polybutylene adipate terephthalate polymer may satisfy the following formula 1:

[0030] [Formula 1]

[0031] Acid value + b*≤30

[0032] In Formula 1, acid value is the acid value (mmol / kg) of the polybutylene adipate terephthalate polymer, and b* is the b* value of the color of the polybutylene adipate terephthalate polymer.

[0033] In the present invention, provided is polybutylene adipate terephthalate having a weight average molecular weight of 70000 g / mol to 200000 g / mol and satisfying the following Formula 1:

[0034] [Formula 1]

[0035] Acid value + b*≤30

[0036] In Formula 1, acid value is the acid value (mmol / kg) of the polybutylene adipate terephthalate polymer, and b* is the b* value of the color of the polybutylene adipate terephthalate polymer.

[0037] In the present invention, the terms "first", "second", etc. are used to describe various components, and these terms are used only to distinguish specific components from other components.

[0038] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0039] Unless the context clearly indicates otherwise, the singular forms are intended to include the plural forms as well.

[0040] It will also be understood that when used in this specification, the terms "include", "have" or "have" specify the presence of stated features, quantities, steps, components or a combination thereof, but do not exclude the presence or addition of one or more other features, quantities, steps, components or a combination thereof.

[0041] Furthermore, as used herein, when it is mentioned that a layer or an element is formed “on” a layer or an element, the layer or element may be directly formed on the layer or element, or other layers or elements may be additionally formed between layers, on a body, or on a substrate.

[0042] Since the present invention can be modified in various ways and has various forms, its specific embodiments are shown in an illustrative manner and will be described in detail. However, it is not intended to limit the present invention to the specific forms disclosed, and it should be understood that the present invention includes all modifications, equivalents and substitutes within the concept and technical scope of the present invention.

[0043] Hereinafter, the present invention will be described in detail.

[0044] According to one embodiment of the present invention, a method for preparing polybutylene adipate terephthalate is provided, which comprises: a first step, in the presence of a titanium (Ti)-based polymerization catalyst, polymerizing butanediol, adipic acid and terephthalic acid to prepare a polybutylene adipate terephthalate prepolymer; and a second step, in the presence of a titanium (Ti)-based condensation catalyst and a phosphorus (P)-based thermal stabilizer, polycondensing the polybutylene adipate terephthalate prepolymer to prepare a polybutylene adipate terephthalate polymer.

[0045] Wherein, the molar ratio of phosphorus to titanium used in the first step and the second step satisfies the following equation 1:

[0046] [Equation 1]

[0047] 0.65≤P / Ti≤1

[0048] The present inventors have found that when the ratio of phosphorus to titanium used in the polycondensation step is adjusted to a specific range in a method for preparing a polybutylene adipate terephthalate polymer (including a step of preparing a polybutylene adipate terephthalate prepolymer by polymerizing butanediol, adipic acid and terephthalic acid, and a step of preparing a polybutylene adipate terephthalate polymer by polycondensing the prepolymer), a polybutylene adipate terephthalate polymer having an appropriate acid value can be produced without causing discoloration while satisfying excellent mechanical properties and appearance, thereby completing the present invention.

[0049] Generally, high molecular weight polyester is produced by forming an ester bond through an esterification reaction of a diol compound with a dicarboxylic acid compound in the presence of a catalyst to prepare a prepolymer, transferring the prepolymer to a separate reactor, and then performing a polycondensation reaction by adding a polycondensation catalyst.

[0050] Preparation of prepolymer

[0051] A prepolymer is a polymer with a lower degree of polymerization in which the polymerization reaction has been stopped in the middle stage.

[0052] In one embodiment, the prepolymer refers to a polymer having a relatively low degree of polymerization obtained by esterifying a monomer mixture containing 1,4-butanediol, adipic acid, and terephthalic acid in the presence of a titanium (Ti)-based polymerization catalyst.

[0053] In the preparation of the prepolymer, initial polymer chains may be formed around the catalyst.

[0054] According to one embodiment of the present invention, in the preparation method, the content of 1,4-butanediol may be about 100 parts by weight to about 250 parts by weight based on 100 parts by weight of adipic acid.

[0055] This is the total amount of 1,4-butanediol required for PBAT synthesis. 1,4-Butanediol is a reactant and can also play the role of a solvent or dispersant for dispersing the catalyst. Generally, for the uniformity and stability of the catalyst, only a portion of the 1,4-butanediol to be reacted is supplied during the polymerization process, and the remaining amount can be supplied in the subsequent reaction process.

[0056] In this regard, the 1,4-butanediol may be included in an amount of about 150 parts by weight to about 250 parts by weight, or about 180 parts by weight to 220 parts by weight, based on 100 parts by weight of adipic acid in the monomer mixture.

[0057] According to another embodiment of the present invention, in the preparation method, the content of terephthalic acid may be about 50 parts by weight to about 150 parts by weight, or about 80 parts by weight to about 120 parts by weight, based on 100 parts by weight of adipic acid.

[0058] Due to its aromatic ring structure, terephthalic acid may affect the crystallinity of the polymer. However, the polymer produced within the above range may have excellent mechanical properties and biodegradability.

[0059] According to another embodiment of the present invention, in the preparation method, the titanium (Ti)-based polymerization catalyst may be included in an amount of about 0.001 parts by weight to about 10 parts by weight based on 100 parts by weight of adipic acid.

[0060] Within the above range, the esterification reaction of the monomer mixture can be appropriately mediated.

[0061] If the input amount of the catalyst is too small, the polymerization time may be extended and the productivity may be reduced. If the input amount of the catalyst is too large, the polymerization time may be shortened, but the possibility of the final PBAT discoloration increases, so the amount of the heat stabilizer must be increased in proportion to the input amount of the catalyst, and the manufacturing cost increases.

[0062] Taking this tendency into consideration, the input amount of the catalyst in the catalyst mixture can be adjusted. For example, based on 100 parts by weight of adipic acid in the monomer mixture, the amount of the catalyst that can be used in the catalyst mixture is 0.001 parts by weight or more, 0.005 parts by weight or more, or 0.01 parts by weight or more, and 10 parts by weight or less, 5 parts by weight or less, or 0.1 parts by weight or less.

[0063] According to another embodiment of the present invention, the titanium (Ti)-based polymerization catalyst may be at least one selected from the group consisting of titanium methoxide, titanium ethoxide, titanium propoxide, titanium isopropoxide, titanium butoxide, titanium isobutoxide, and titanium citrate.

[0064] The step of preparing the prepolymer may be performed at a temperature of about 150° C. to about 350° C. for about 10 minutes to about 240 minutes.

[0065] For example, the step of preparing the prepolymer may be performed at about 150° C. or more, about 170° C. or more, about 190° C. or more, or about 210° C. or more, and about 350° C. or less, about 320° C. or less, about 290° C. or less, or about 250° C. or less. In addition, the step of preparing the prepolymer may be performed for 10 minutes or more, 15 minutes or more, 20 minutes or more, or 25 minutes or more, and may be performed for about 240 minutes or less, about 120 minutes or less, about 90 minutes or less, about 60 minutes or less, or about 40 minutes or less.

[0066] In the step of preparing the prepolymer, nitrogen can be injected into the reactor. Specifically, when nitrogen is injected, water produced as a by-product is quickly removed, thereby suppressing the reverse reaction caused by water. Therefore, the polymerization conversion rate of the monomer can be improved, and the molecular weight of the polymer can be increased.

[0067] For example, the injection rate of nitrogen can be about 0.001 ml / min or more, about 0.01 ml / min or more, 0.02 ml / min or more, or about 0.05 ml / min or more, and about 100 ml / min or less, about 50 ml / min or less, about 10 ml / min or less, or about 5 ml / min or less.

[0068] In the step of preparing the prepolymer, about 0.1 parts by weight to about 1 parts by weight of a crosslinking agent or a branching agent may be added based on 100 parts by weight of adipic acid in the monomer mixture.

[0069] When the esterification reaction is performed by adding a crosslinking agent, an internally crosslinked prepolymer can be generated, and the mechanical properties in the final polymer PBAT after polycondensation can be improved.

[0070] The cross-linking agent is a low molecular weight compound containing more than 3 hydroxyl groups or more than 3 carboxyl groups in the molecule, for example, it can be an erythritol compound, a glycerol compound or citric acid.

[0071] Polycondensation

[0072] Then, the polybutylene adipate terephthalate prepolymer prepared in the above process is polycondensed to produce a polybutylene adipate terephthalate polymer.

[0073] In the case of continuous production, the polybutylene adipate terephthalate prepolymer is transferred to a separate polycondensation reactor and then polycondensation can be performed. In the case of batch production, the polybutylene adipate terephthalate prepolymer can be transferred to another location, or polycondensation can be performed by controlling the reaction conditions in the original reactor only.

[0074] According to another embodiment of the present invention, the titanium (Ti)-based polycondensation catalyst may be the same as or different from the titanium (Ti)-based polymerization catalyst in the above preparation method.

[0075] In the polycondensation reaction, the polymer chains are connected by an esterification reaction between the hydroxyl and carboxyl groups at the ends of the polybutylene adipate terephthalate prepolymer. Therefore, the catalyst used in the polycondensation process (i.e., the titanium (Ti)-based polycondensation catalyst) may be the same as or different from the catalyst used in the esterification reaction for producing the prepolymer (i.e., the above-mentioned titanium (Ti)-based polymerization catalyst).

[0076] However, even if the same kind of catalyst is used, another catalyst is added in the polycondensation reaction of the prepolymer in addition to the amount of the catalyst used in the step of preparing the prepolymer.

[0077] During the prepolymer production step, the activity of the initially added catalyst (i.e., titanium (Ti)-based polymerization catalyst) will most likely decrease. For example, titanium as the central metal component of the catalyst may react with water as a by-product of the esterification reaction to form titanium oxide, and other functional groups may replace the alkoxy sites of the alkoxy titanium.

[0078] Therefore, during the polycondensation reaction, a separate catalyst must be added prior to the polycondensation reaction.

[0079] According to another embodiment of the present invention, in the above preparation method, the content of the titanium (Ti)-based polycondensation catalyst may be about 0.001 parts by weight to about 0.5 parts by weight based on 100 parts by weight of the polybutylene adipate terephthalate prepolymer.

[0080] In addition to the addition of the polycondensation catalyst, a heat stabilizer is also added. The heat stabilizer is intended to suppress discoloration of the final polybutylene adipate terephthalate polymer and can be added simultaneously with the polycondensation catalyst, or before or after the addition of the polycondensation catalyst.

[0081] According to another embodiment of the present invention, in the above preparation method, the phosphorus (P)-based heat stabilizer may include at least one selected from the group consisting of phosphoric acid, phosphorous acid, trialkyl phosphates and trialkyl phosphonoacetate.

[0082] According to another embodiment of the present invention, in the above preparation method, the content of the phosphorus (P)-based heat stabilizer may be about 0.001 parts by weight to about 0.1 parts by weight based on 100 parts by weight of the polybutylene adipate terephthalate prepolymer.

[0083] The polycondensation reaction may include the following steps: increasing the temperature of a reactor containing a prepolymer until the temperature reaches a polycondensation temperature, specifically, about 150° C. to about 350° C.; after increasing the temperature, reducing the pressure of the reactor until the pressure reaches 0.1 atm to 0.00001 atm; and terminating the reaction by confirming the degree of polycondensation while maintaining the pressure and temperature after the reduced pressure.

[0084] For example, the temperature of the reactor containing the prepolymer can be increased until the temperature reaches above about 150°C, above about 170°C, above about 190°C, or above about 210°C, and below about 350°C, below about 320°C, below about 290°C, or below about 250°C.

[0085] The pressure is reduced about 1 minute to about 10 minutes after the above temperature is reached. At this time, the pressure of the reactor can be reduced until the pressure reaches about 0.00001 atm or more, about 0.00005 atm or more, about 0.0001 atm or more, or about 0.0002 atm or more, and reaches about 0.1 atm or less, about 0.05 atm or less, about 0.03 atm or less, or about 0.01 atm or less.

[0086] After the pressure is reduced, the reaction may be carried out while maintaining the pressure and temperature. In addition, depending on the degree of polycondensation, the reaction may be terminated after confirming that the desired molecular weight has been achieved.

[0087] The molecular weight can be confirmed by collecting the product inside the reactor, but, usually, the molecular weight can be confirmed by the torque load of the stirrer installed inside the reactor.

[0088] The reaction time is not particularly limited, but the reaction can be terminated at about 2 hours or more, about 2.2 hours or more, about 2.4 hours or more, or about 3 hours or more after the start of the reaction, and at about 8 hours or less, about 7.5 hours or less, about 7 hours or less, or about 6 hours or less.

[0089] According to another embodiment of the present invention, the weight average molecular weight of the polybutylene adipate terephthalate polymer prepared by the method of the present invention can be about 70,000 g / mol to about 200,000 g / mol, preferably about 70,000 g / mol or more, or about 80,000 g / mol or more, and about 200,000 g / mol or less, or about 150,000 g / mol or less.

[0090] According to another embodiment of the present invention, the acid value (mmol / kg) of the polybutylene adipate terephthalate polymer prepared by the method of the present invention can be about 5 to about 30, preferably about 5 or more, or about 7 or more, and about 30 or less, about 25 or less, or about 20 or less.

[0091] The acid value refers to the free acid groups remaining in the polymer chain when some of the acid functional groups do not react during the esterification reaction between the dicarboxylic acid and the diol. If the acid value is too high, the free acid groups may promote hydrolysis over time, leading to various problems such as a decrease in the molecular weight of the polymer or deterioration in the mechanical properties of the polymer.

[0092] According to another embodiment of the present invention, the b* value of the color of the polybutylene adipate terephthalate polymer prepared by the method of the present invention can be about 0 to about 30, preferably about 0 or more, greater than about 0, about 3 or more, or about 5 or more, and about 30 or less, about 25 or less, or about 20 or less, so that almost no discoloration occurs, and excellent optical properties can be obtained.

[0093] When the b* value of the color is too high, the polymer appears yellow, making it difficult to use the polymer in applications requiring excellent optical properties.

[0094] According to another embodiment of the present invention, the polybutylene adipate terephthalate polymer may satisfy the following Formula 1.

[0095] [Formula 1]

[0096] Acid value + b*≤30

[0097] In Formula 1, acid value is the acid value (mmol / kg) of the polybutylene adipate terephthalate polymer, and b* is the b* value of the color of the polybutylene adipate terephthalate polymer.

[0098] As described above, the acid value and color characteristics of polybutylene adipate terephthalate are very important, and it can be considered that there is a trade-off relationship between the acid value and color characteristics of polybutylene adipate terephthalate. Therefore, it is difficult to obtain polybutylene adipate terephthalate having an appropriate acid value to ensure processability but without discoloration.

[0099] However, according to one embodiment of the present invention, when the ratio of the titanium (Ti)-based polycondensation catalyst and the phosphorus (P)-based heat stabilizer added during the polycondensation process is maintained to satisfy the P / Ti molar ratio of 0.65 to 1, polybutylene adipate terephthalate having an appropriate acid value and a low color b* value without coloring or discoloration can be provided. In other words, polybutylene adipate terephthalate can satisfy excellent mechanical properties and appearance.

[0100] Meanwhile, according to another aspect of the present invention, polybutylene adipate terephthalate having a weight average molecular weight of 70,000 g / mol to 200,000 g / mol and satisfying the following Formula 1 is provided.

[0101] [Formula 1]

[0102] Acid value + b*≤30

[0103] In Formula 1, acid value is the acid value (mmol / kg) of the polybutylene adipate terephthalate polymer, and b* is the b* value of the color of the polybutylene adipate terephthalate polymer.

[0104] [Beneficial Effects]

[0105] According to the preparation method of the present invention, polybutylene adipate terephthalate having an appropriate acid value and a low color b* value without coloration or discoloration is provided, that is, the polybutylene adipate terephthalate satisfies both excellent mechanical properties and appearance. DETAILED DESCRIPTION

[0106] Hereinafter, the functions and effects of the present invention will be described in more detail by specific examples. However, these examples are only for illustrative purposes, and the present invention is not intended to be limited by these examples.

[0107] Example

[0108] Example 1

[0109] Preparation of prepolymer

[0110] 2372 g of 1,4-butanediol, 1538 g of adipic acid and 1614 g of terephthalic acid as monomers, 0.741 g of pentaerythritol as a cross-linking agent, and 2.601 g of titanium citrate (Ti content: 4.9 wt%) as a titanium (Ti) polymerization catalyst were placed in a polymerization reactor, the temperature was raised to about 230° C., and a polymerization reaction (esterification reaction) was carried out at a pressure of 400 mbar for about 2 hours while maintaining the temperature to obtain a polybutylene adipate terephthalate prepolymer.

[0111] (Molecular weight of prepolymer: 3700 g / mol)

[0112] Polycondensation

[0113] In the reactor for obtaining the polybutylene adipate terephthalate prepolymer, 4.595 g of titanium citrate (Ti content: 4.9 wt%), which is the same as the polymerization catalyst, as a titanium (Ti)-based condensation catalyst, and 1.076 g of triethyl phosphonoacetate (based on the phosphorus atom content of about 35 ppm in the PBAT polymer to be obtained) as a phosphorus (P)-based heat stabilizer were further added, and stirred at 60 rpm for about 10 minutes.

[0114] After stirring, the temperature of the reactor was raised to about 240° C. When the temperature of the reactor reached about 240° C., the pressure was reduced so that the internal pressure of the reactor reached about 1 mbar about 5 minutes after reaching the temperature. Then, polycondensation was carried out while maintaining the reduced pressure and continuing stirring at 60 rpm.

[0115] When the torque of the stirrer reached about 0.5 ampere, the reaction was stopped to obtain polybutylene adipate terephthalate polymer.

[0116] Examples 2 to 4 and Comparative Examples 1 to 6

[0117] A polybutylene adipate terephthalate polymer was obtained in the same manner as in Example 1, except that the P / Ti ratio was changed by changing the amounts of the titanium (Ti)-based polycondensation catalyst and the phosphorus (P)-based heat stabilizer in the polycondensation step.

[0118] The reaction conditions are summarized in Table 1 below.

[0119] [Table 1]

[0120]

[0121] X*: When the reaction was carried out for about 360 minutes, the torque load of the stirrer in the reactor did not reach about 0.5 ampere, and thus polycondensation did not proceed sufficiently.

[0122] The physical properties of the polybutylene adipate terephthalate polymers obtained in Examples and Comparative Examples were measured by the following methods.

[0123] Measurement of weight average molecular weight

[0124] After dissolving the polymer to be tested in chloroform at a concentration of 1 mg / ml, the solution was placed in a gel permeation chromatography (GPC, PLGPC220, Agilent Technologies) instrument to measure the molecular weight. At this time, polystyrene was used as a standard polymer.

[0125] Acid value measurement

[0126] The sample was dissolved in a mixed solution of o-cresol:chloroform (weight ratio of 1:1), and 1-2 drops of an aqueous solution containing 0.1 wt % phenol red was used as an indicator.

[0127] A 0.1 N potassium hydroxide (KOH) / ethanol solution was titrated using a micropipette, and the acid value was measured using the following Mathematical Formula 1.

[0128] [Mathematical formula 1] Acid value (mgKOH / g) = (V-V0)*M*F*1000 / W

[0129] V: Volume of KOH / ethanol solution consumed for sample titration (mL)

[0130] V0: Volume of KOH / ethanol solution consumed in blank titration (mL)

[0131] M: molar concentration of KOH / ethanol solution (0.1M / L)

[0132] W: mass of sample (g)

[0133] F: Titer of KOH / ethanol solution

[0134] The acid value is the number of milligrams (mg) of KOH required to neutralize the free fatty acids contained in 1 g of oil. RCOOH + KOH → RCOOK + H2O. In other words, the acid value measures the amount of free fatty acids that are not bound in the form of glycerides.

[0135] In particular, in the esterification reaction, the acid value is a measure of the degree of reaction and refers to the amount of KOH required to neutralize the carboxyl groups contained in 1 g of the polymer. The larger the number, the worse the reaction rate.

[0136] Measurement of b* value of color

[0137] The granulated PBAT was placed in a cylindrical transparent glass sample bottle with a diameter of 60 mm and a height of 50 mm, and the color L* / a* / b* / YI value was measured using a spectrophotometer (product name: ColorFlexEZ) according to CIE 15:2004 standard.

[0138] The measurement results are summarized in Table 2 below.

[0139] [Table 2]

[0140] Weight average molecular weight (g / mol) Acid value (mmol / kg) b* Formula 1 Example 1 106k 9 19.5 28.5 Example 2 105k 12 16.0 28 Example 3 107k 16 8.2 24.2 Example 4 110k 24 5.1 29.1 Comparative Example 1 105k 7 30.5 36.4 Comparative Example 2 103k 5 36.1 41.1 Comparative Example 3 54k 41 1.3 42.3 Comparative Example 4 34k 273 12.8 285.8 Comparative Example 5 98k 42 4.6 46.6 Comparative Example 6 106k 8 35.4 43.4

[0141] Referring to Table 2 above, the b* values ​​of the colors of Comparative Examples 1 and 2 are too high, resulting in appearance problems. In Comparative Examples 3 and 4, the molecular weight is almost half or less of that of the embodiments, polycondensation or a reaction for increasing the molecular weight is not properly performed, and it is found that the acid value is too high. In addition, Comparative Example 5 has a problem of lower molecular weight and higher acid value than the embodiments, and the b* value of the color of Comparative Example 6 is too high, resulting in appearance problems.

[0142] However, the polybutylene adipate terephthalate prepared according to one embodiment of the present invention has a relatively low acid value and a low color b* value, and thus can have excellent mechanical properties and durability, while achieving excellent optical properties.

Claims

1. A method for preparing polybutylene adipate terephthalate, comprising: The first step is to prepare a polybutylene adipate terephthalate prepolymer by polymerizing butanediol, adipic acid and terephthalic acid in the presence of a titanium (Ti) based polymerization catalyst; as well as The second step is to prepare a polybutylene adipate terephthalate polymer by polycondensing the polybutylene adipate terephthalate prepolymer in the presence of a titanium (Ti)-based polycondensation catalyst and a phosphorus (P)-based heat stabilizer. Wherein, the molar ratio of phosphorus to titanium used in the first step and the second step satisfies the following equation 1: [Equation 1] 0.65≤P / Ti≤1.

2. The method for preparing polybutylene adipate terephthalate according to claim 1, wherein: The 1,4-butanediol may be included in an amount of 100 to 250 parts by weight based on 100 parts by weight of the adipic acid.

3. The method for preparing polybutylene adipate terephthalate according to claim 1, wherein: The terephthalic acid may be included in an amount of 50 to 150 parts by weight based on 100 parts by weight of the adipic acid.

4. The method for preparing polybutylene adipate terephthalate according to claim 1, wherein: The titanium (Ti)-based polymerization catalyst may be included in an amount of about 0.001 parts by weight to about 10 parts by weight based on about 100 parts by weight of the adipic acid.

5. The method for preparing polybutylene adipate terephthalate according to claim 1, wherein: The titanium (Ti)-based polymerization catalyst is at least one selected from the group consisting of titanium methoxide, titanium ethoxide, titanium propoxide, titanium isopropoxide, titanium butoxide, titanium isobutoxide, and titanium citrate.

6. The method for preparing polybutylene adipate terephthalate according to claim 1, wherein: The titanium (Ti)-based polycondensation catalyst is the same as or different from the titanium (Ti)-based polymerization catalyst.

7. The method for preparing polybutylene adipate terephthalate according to claim 1, wherein: The titanium (Ti)-based polycondensation catalyst may be included in an amount of about 0.001 to about 0.5 parts by weight based on 100 parts by weight of the polybutylene adipate terephthalate prepolymer.

8. The method for preparing polybutylene adipate terephthalate according to claim 1, wherein: The phosphorus (P)-based heat stabilizer includes at least one selected from the group consisting of phosphoric acid, phosphorous acid, trialkyl phosphates, and trialkyl phosphonoacetate.

9. The method for preparing polybutylene adipate terephthalate according to claim 1, wherein: The phosphorus (P)-based heat stabilizer may be included in an amount of 0.001 to 0.1 parts by weight based on 100 parts by weight of the polybutylene adipate terephthalate prepolymer.

10. The method for preparing polybutylene adipate terephthalate according to claim 1, wherein: The weight average molecular weight of the polybutylene adipate terephthalate polymer is 70000 g / mol to 200000 g / mol.

11. The method for preparing polybutylene adipate terephthalate according to claim 1, wherein: The acid value (mmol / kg) of the polybutylene adipate terephthalate polymer is 5 to 30.

12. The method for preparing polybutylene adipate terephthalate according to claim 1, wherein: The b* value of the color of the polybutylene adipate terephthalate polymer is 0 to 30.

13. The method for preparing polybutylene adipate terephthalate according to claim 1, wherein: The polybutylene adipate terephthalate polymer satisfies the following formula 1: [Formula 1] Acid value + b*≤30 In Formula 1, acid value is the acid value (mmol / kg) of the polybutylene adipate terephthalate polymer, and b* is the b* value of the color of the polybutylene adipate terephthalate polymer.

14. A polybutylene adipate terephthalate having a weight average molecular weight of 70,000 g / mol to 200,000 g / mol and satisfying the following formula 1: [Formula 1] Acid value + b*≤30 In Formula 1, acid value is the acid value (mmol / kg) of the polybutylene adipate terephthalate polymer, and b* is the b* value of the color of the polybutylene adipate terephthalate polymer.

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