Biodegradable polyester and preparation method therefor

Abstract

The present invention relates to: a biodegradable aliphatic / aromatic polyester having a high content of aromatic dicarboxylic acid; and a preparation method therefor and, more specifically, to a biodegradable aliphatic / aromatic polyester and a preparation method therefor, the biodegradable aliphatic / aromatic polyester comprising, in specific amounts, an aliphatic dicarboxylic acid, an aromatic dicarboxylic acid, and an aliphatic diol compound having a chain length of less than 4 carbon atoms, thereby having excellent biodegradability and crystalline properties.

Description

Biodegradable polyester and method for manufacturing the same

[0001] The present invention relates to a biodegradable aliphatic / aromatic polyester containing a high content of aromatic dicarboxylic acid and a method for producing the same. More specifically, the present invention relates to a biodegradable aliphatic / aromatic polyester having excellent biodegradability and crystalline characteristics by including an aliphatic dicarboxylic acid, an aromatic dicarboxylic acid, and an aliphatic diol compound having a chain length of less than 4 carbon atoms in a specific amount, and a method for producing the same.

[0002] To address the problem of waste generation caused by the use of general-purpose plastics, it is necessary to reduce plastic consumption or recycle them. Recently, biodegradable plastic materials have emerged as an alternative to solve this issue. Biodegradable plastics can be classified into bio-derived and petroleum-derived types depending on the type of raw material; among these, petroleum-derived biodegradable plastics are easy to source and do not require a biological fermentation process, allowing for the production of products at a relatively lower cost compared to bio-derived biodegradable plastics.

[0003] Among petroleum-derived biodegradable plastics, polybutylene adipate terephthalate, an aliphatic / aromatic polyester that can be produced by reacting 1,4-butanediol with adipic acid, terephthalic acid, or dimethyl terephthalate, is currently the most widely used. The aromatic dicarboxylic acid content of commercially available polybutylene adipate terephthalate is 48 mol% to 50 mol%, and this value is known to be a condition that satisfies physical properties sufficient for the resin to possess biodegradability while being applicable to various household goods fields such as disposable films or sheets, tableware, and agricultural films or sheets. In the case of polybutylene adipate terephthalate, if the aromatic dicarboxylic acid content exceeds 50 mol%, mechanical properties may improve, but biodegradability may decrease. For example, it is reported that biodegradation hardly occurs when the aromatic dicarboxylic acid content of polybutylene adipate terephthalate exceeds 60 mol% (RJ Muller et al., 2001, "Biodegradation of polyesters containing aromatic constituents"). On the other hand, while the biodegradability of polybutylene adipate terephthalate may be improved if the aromatic dicarboxylic acid content is reduced, its mechanical properties may deteriorate. Although increasing the content of aromatic dicarboxylic acids is a simple method to improve the mechanical properties of the resin, it could not be considered due to the specific characteristics of biodegradable plastics, which must simultaneously satisfy biodegradability. In various patent literatures related to biodegradable aliphatic / aromatic polyesters, the range of aromatic dicarboxylic acid content is set as low as 60 mol% and as high as 80 mol%, but in preferred or particularly preferred embodiments, it is common to include aromatic dicarboxylic acid of 50 mol% or less (Korean Patent Registration No. 10-1543489, Korean Patent Application Publication No. 10-2020-0027926).

[0004] Meanwhile, although aliphatic diol compounds with chain lengths of less than 4 carbon atoms, particularly ethylene glycol, have superior price competitiveness compared to 1,4-butanediol, methods for manufacturing biodegradable polyesters using them are rarely reported (P Monvisade et al., 2007, "Synthesis of poly(ethylene adipate) and poly(ethylene adipate-co-terephthalate) via ring-opening polymerization", Korean Patent Application No. 10-2022-0119728). Compared to 1,4-butanediol-based polyesters, ethylene glycol-based biodegradable polyesters can exhibit relatively superior biodegradability due to a higher density of ester bonds capable of hydrolysis at the same ratio of aromatic and aliphatic dicarboxylic acids. In addition, the excellent biodegradability of ethylene glycol-based biodegradable polyesters allows for the content of aromatic dicarboxylic acids to be controlled over a wider range exceeding 50 mol%, which has the advantage of enabling the development of various products by controlling the crystal characteristics and mechanical properties of the resin.

[0005] [Prior Art Literature]

[0006] [Patent Literature]

[0007] (Patent Document 1) Republic of Korea Patent Application No. 10-2022-0119728

[0008] (Patent Document 2) Republic of Korea Patent Registration No. 10-1543489

[0009] (Patent Document 3) Republic of Korea Patent Application Publication No. 10-2020-0027926

[0010] [Non-patent literature]

[0011] (Non-patent Document 1) RJ Muller et al., 2001, “Biodegradation of polyesters containing aromatic constituents”

[0012] (Non-patent document 2) P Monvisade et al., 2007, “Synthesis of poly(ethylene adipate) and poly(ethylene adipate-co-terephthalate) via ring-opening polymerization”

[0013] (Non-patent document 3) U Witt et al., 1999, “Biodegradable polymeric materials: not the origin but the chemical structure determines biodegradability”

[0014] (Non-patent Document 4) RJ Muller, 2006, “Biological degradation of synthetic polyesters—Enzymes as potential catalysts for polyester recycling”

[0015] (Non-patent Document 5) MT Zumstein et al., 2018, “Biodegradation of synthetic polymers in soils: Tracking carbon into CO2and microbial biomass”

[0016] The object of the present invention is to provide a biodegradable aliphatic / aromatic polyester containing a high content of aromatic dicarboxylic acid.

[0017] Another objective of the present invention is to provide a method for producing a biodegradable aliphatic / aromatic polyester containing a high content of aromatic dicarboxylic acid.

[0018] According to one aspect of the present invention, a biodegradable aliphatic / aromatic polyester is provided, comprising a dicarboxylic acid component (a) derived from an aliphatic dicarboxylic acid and an aromatic dicarboxylic acid, and a diol component (b) derived from an aliphatic diol having a chain length of less than 4 carbon atoms, wherein the content of the aromatic dicarboxylic acid is greater than 56 mol% and less than 62.5 mol% based on the total molar amount of the dicarboxylic acid component (a), and the content of the aliphatic dicarboxylic acid is greater than 37.5 mol% and less than 44 mol% based on the total molar amount of the dicarboxylic acid component (a).

[0019] In a specific embodiment of the present invention, the aromatic dicarboxylic acid may include at least one selected from the group consisting of terephthalic acid, isophthalic acid, orthophthalic acid, naphthalene dicarboxylic acid, dimethyl terephthalate, dimethyl isophthalate, dimethyl phthalate, and dimethyl naphthalene dicarboxylic acid.

[0020] In a specific embodiment of the present invention, the aliphatic dicarboxylic acid may include at least one selected from the group consisting of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimery acid, suberic acid, azelaic acid, sebacic acid and their ester compounds.

[0021] In a preferred embodiment of the present invention, the aromatic dicarboxylic acid may include terephthalic acid, and the aliphatic dicarboxylic acid may include adipic acid.

[0022] In a specific embodiment of the present invention, the diol component (b) may include at least one selected from the group consisting of ethylene glycol, 1,2-propanediol and 1,3-propanediol.

[0023] In a preferred embodiment of the present invention, the diol component (b) may include ethylene glycol.

[0024] In a specific embodiment of the present invention, the molar ratio of the diol component (b) to the dicarboxylic acid component (a) may be 1.1:1 to 1.5:1.

[0025] In a specific embodiment of the present invention, based on the total moles of the dicarboxylic acid component (a), 0.8 to 3.5 mol% of a discoloration inhibitor (c) represented by the following chemical formula 1 may be additionally included.

[0026] [Chemical Formula 1]

[0027]

[0028] In the above chemical formula, m, n ≥ 1, l, k ≥ 0, and Y is hydrogen, a hydroxyl group, or a methyl group.

[0029] In a specific embodiment of the present invention, the discoloration inhibitor (c) may include at least one selected from the group consisting of glycerol, trimethylolpropane, and pentaerythritol.

[0030] In a specific embodiment of the present invention, based on 1 mole of dicarboxylic acid component (a), 0.01 to 5.0 g of stabilizer (d) may be additionally included.

[0031] In a specific embodiment of the present invention, the stabilizer (d) may include at least one selected from the group consisting of phosphoric acid, triphenyl phosphate, trimethyl phosphonoacetate, triethyl phosphonoacetate, tripropyl phosphonoacetate, and tributyl phosphonoacetate.

[0032] In a specific embodiment of the present invention, the catalyst may comprise at least one selected from the group consisting of tetrabutyl titanate, tetraisopropyl titanate, zinc acetate, and antimony oxide, and the content of the catalyst may be 0.01 to 5.0 g based on 1 mole of dicarboxylic acid component (a).

[0033] In a specific embodiment of the present invention, the biodegradable aliphatic / aromatic polyester of the present invention has a melt flow index of 100 g / 10 min or less when measured at 190°C with a 2.16 kg load, a melt temperature peak is observed, and can have a relative biodegradability of 60% or more compared to cellulose, a standard material, within 45 days under industrial composting conditions (58±2°C).

[0034] In a specific embodiment of the present invention, a biodegradable aliphatic / aromatic polyester may be used for an application selected from the group consisting of disposable films or sheets, tableware, fishing nets, and agricultural films or sheets.

[0035] According to another aspect of the present invention, as a method for producing a biodegradable aliphatic / aromatic polyester,

[0036] (1) A step of obtaining a prepolymer by esterifying or transesterifying a reaction mixture comprising a dicarboxylic acid component (a) derived from an aliphatic dicarboxylic acid and an aromatic dicarboxylic acid and a diol component (b) derived from an aliphatic diol having a chain length of less than 4 carbon atoms, in the presence of a catalyst; and

[0037] (2) A step of obtaining a biodegradable aliphatic / aromatic polyester by condensing the prepolymer obtained in step (1), and

[0038] A method for manufacturing a biodegradable aliphatic / aromatic polyester is provided, wherein the biodegradable aliphatic / aromatic polyester has a melt flow index of 100 g / 10 min or less when measured at 190°C with a 2.16 kg load, has crystalline characteristics, and has a relative biodegradability of 60% or more compared to cellulose, a standard material, within 45 days under industrial composting conditions (58±2°C).

[0039] In a specific embodiment of the present invention, the esterification or transesterification reaction of the reaction mixture in step (1) may be carried out in a single reactor with different temperature ranges, the first esterification or transesterification reaction may be carried out at a temperature in the range of 180 to 200°C, and the second esterification or transesterification reaction may be carried out at a temperature in the range of 220 to 265°C.

[0040] In a specific embodiment of the present invention, the reaction mixture of step (1) may further include a discoloration inhibitor (c) and a stabilizer (d).

[0041] In a specific embodiment of the present invention, the condensation reaction of the prepolymer in step (2) can be carried out at a temperature in the range of 220 to 265°C and at a vacuum of less than 1 torr.

[0042] In a specific embodiment of the present invention, (3) the biodegradable aliphatic / aromatic polyester may further include the step of performing heat treatment at a temperature below the melting temperature.

[0043] A biodegradable aliphatic / aromatic polyester produced by a manufacturing method according to one embodiment of the present invention has an aromatic dicarboxylic acid content exceeding 56 mol% based on the total molar amount of the dicarboxylic acid component, and has excellent biodegradability and crystal properties.

[0044] The biodegradable aliphatic / aromatic polyester of the present invention can be utilized in various fields such as disposable films or sheets, tableware, fishing nets, and agricultural films or sheets.

[0045] Figure 1 is a photograph of the aliphatic / aromatic polyester obtained in Example 1 before and after heat treatment.

[0046] The present invention will be described in more detail below.

[0047] The biodegradable aliphatic / aromatic polyester according to the present invention comprises a dicarboxylic acid component (a) derived from an aliphatic dicarboxylic acid and an aromatic dicarboxylic acid, and a diol component (b) derived from an aliphatic diol having a chain length of less than 4 carbon atoms, wherein the content of the aromatic dicarboxylic acid is greater than 56 mol% and less than 62.5 mol% based on the total molar amount of the dicarboxylic acid component (a), and the content of the aliphatic dicarboxylic acid is greater than 37.5 mol% and less than 44 mol% based on the total molar amount of the dicarboxylic acid component (a).

[0048] The content of aromatic dicarboxylic acid may be greater than 56 mol%, 56.5 mol% or more, 57 mol% or more, 57.5 mol% or more, or 58 mol% or more, based on the total number of moles of the dicarboxylic acid components, and may be less than 62.5 mol%, 62 mol% or less, 61.5 mol% or less, 61 mol% or less, 60.5 mol% or less, or 60 mol% or less, for example, greater than 56 mol% to less than 62.5 mol%, 57 mol% to 62 mol%, or 58 mol% to 62 mol%.

[0049] The aliphatic dicarboxylic acid content may be greater than 37.5 mol%, 38 mol% or more, 38.5 mol% or more, 39 mol% or more, 39.5 mol% or more, or 40 mol% or more, based on the total number of moles of the dicarboxylic acid component (a), less than 44 mol%, 43.5 mol% or less, 43 mol% or less, 42.5 mol% or less, or 42 mol% or less, for example, greater than 37.5 mol% to less than 44 mol%, 38 mol% to 43 mol%, or 40 mol% to 42 mol%.

[0050] If the content of aromatic dicarboxylic acid exceeds the above range based on the total moles of the dicarboxylic acid component (a), the biodegradability of the resulting biodegradable aliphatic / aromatic polyester may rapidly decrease. In general, the biodegradability of biodegradable aliphatic / aromatic polyester tends to decrease as the content of aromatic dicarboxylic acid increases. For example, the effect of aromatic dicarboxylic acid content on biodegradability has been reported in the literature Witt, U. et al., 1999, "Biodegradable polymeric materials: not the origin but the chemical structure determines biodegradability", and Mueller, R.-J., 2006, "Biological degradation of synthetic polyesters—Enzymes as potential catalysts for polyester recycling".

[0051] In addition, the study Zumstein, MT et al., 2018, "Biodegradation of synthetic polymers in soils: Tracking carbon into CO2 and microbial biomass" reported that the rate of biodegradation by microbial enzymatic action of aromatic dicarboxylic acids is slower than that of aliphatic dicarboxylic acids.

[0052] In addition to chemical structural factors, the effect of aromatic dicarboxylic acid content on biodegradability can be attributed to the simultaneous increase in crystallinity and melting temperature caused by π-π stacking of the aromatic structure as the content of aromatic dicarboxylic acids increases; for these reasons, it is understood that biodegradability may rapidly decrease when the content of aromatic dicarboxylic acids exceeds a certain level.

[0053] Meanwhile, if the content of the aliphatic dicarboxylic acid exceeds the above range based on the total moles of the dicarboxylic acid component (a), the biodegradability of the biodegradable aliphatic / aromatic polyester is excellent, but the mechanical properties may be relatively degraded. In particular, if the content of the aliphatic dicarboxylic acid increases, the crystallinity of the biodegradable aliphatic / aromatic polyester decreases and it becomes amorphous, which may lead to a deterioration in mechanical properties. Additionally, the crystallization rate becomes very slow, causing stickiness of the molten resin, which may cause problems during the processing stage.

[0054] In the present invention, a biodegradable aliphatic / aromatic polyester having a high aromatic dicarboxylic acid content exceeding 56 mol%, excellent biodegradability, and crystalline properties is provided by the following composition and method.

[0055] According to another aspect of the present invention, (1) a reaction mixture comprising a dicarboxylic acid component (a) derived from an aliphatic dicarboxylic acid and an aromatic dicarboxylic acid and a diol component (b) derived from an aliphatic diol having a chain length of less than 4 carbon atoms is subjected to an esterification reaction or a transesterification reaction in the presence of a catalyst to obtain a prepolymer; and

[0056] (2) A method for producing a biodegradable aliphatic / aromatic polyester is provided, comprising the step of polycondensing the prepolymer obtained in step (1) in the presence of the remaining portion of the catalyst and stabilizer or without additional catalyst and stabilizer to obtain a biodegradable aliphatic / aromatic polyester.

[0057] Step (1)

[0058] In step (1) of the method for producing a biodegradable aliphatic / aromatic polyester according to an embodiment of the present invention, a reaction mixture comprising a dicarboxylic acid component (a) derived from an aliphatic dicarboxylic acid and an aromatic dicarboxylic acid, and a diol component (b) derived from an aliphatic diol having a chain length of less than 4 carbon atoms, is subjected to an esterification reaction or a transesterification reaction in the presence of a catalyst to obtain a prepolymer.

[0059] In step (1) above, the reaction mixture comprises a dicarboxylic acid component (a) derived from an aliphatic dicarboxylic acid and an aromatic dicarboxylic acid, and a diol component (b) derived from an aliphatic diol having a chain length of less than 4 carbon atoms. In one embodiment, the reaction mixture may further comprise a discoloration inhibitor (c) and a stabilizer (d), and all or part of the stabilizer (d) used in the present manufacturing method may be included in the reaction mixture.

[0060] In a specific embodiment of the present invention, a dicarboxylic acid component (a), which is one component of the reaction mixture, may be derived from an aromatic dicarboxylic acid and an aliphatic dicarboxylic acid. Here, the aromatic dicarboxylic acid may include its ester compound, and the aliphatic dicarboxylic acid may include its ester compound. Specifically, the ester compound of the dicarboxylic acid may refer to an ester compound in which the hydrogens at both ends of the dicarboxylic acid are substituted with alkyl groups having 1 to 6 carbon atoms.

[0061] In a specific embodiment of the present invention, the aromatic dicarboxylic acid may include at least one selected from the group consisting of terephthalic acid, isophthalic acid, orthophthalic acid, naphthalene dicarboxylic acid, dimethyl terephthalate, dimethyl isophthalate, dimethyl phthalate, and dimethyl naphthalene dicarboxylic acid, but is not particularly limited thereto. In a preferred embodiment of the present invention, the aromatic dicarboxylic acid may include terephthalic acid.

[0062] In a specific embodiment of the present invention, the aliphatic dicarboxylic acid may include at least one selected from the group consisting of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimery acid, suberic acid, azelaic acid, sebacic acid, and ester compounds thereof, but is not particularly limited thereto. In a preferred embodiment of the present invention, the aliphatic dicarboxylic acid may include adipic acid.

[0063] In a preferred embodiment of the present invention, the aromatic dicarboxylic acid may include terephthalic acid, and the aliphatic dicarboxylic acid may include adipic acid.

[0064] In a specific embodiment of the present invention, the diol component (b), which is another component of the reaction mixture, may be derived from an aliphatic diol having a chain length of less than 4 carbon atoms.

[0065] In a specific embodiment of the present invention, the diol component (b) may comprise at least one selected from the group consisting of ethylene glycol, 1,2-propanediol, and 1,3-propanediol. In a preferred embodiment of the present invention, the diol component (b) may comprise ethylene glycol.

[0066] In a specific embodiment of the present invention, the molar ratio of the diol component (b) to the dicarboxylic acid component (a) may be 1.1:1 to 1.5:1. A smaller molar ratio is advantageous in terms of economic efficiency, but if it is too small, the polymerization rate may decrease due to an imbalance in the equivalent ratio of the diol and the dicarboxylic acid.

[0067] In one embodiment, the molar ratio of the diol component (b) to the dicarboxylic acid component (a) may preferably be 1.1:1 to 1.5:1, but depending on the type of reactor, i.e., a continuous reactor or a batch reactor or other types of reactors, the molar ratio is not particularly limited as long as there is no problem with the polymerization rate decreasing during the polymerization reaction.

[0068] In a specific embodiment of the present invention, the discoloration inhibitor (c) may include a compound represented by the following chemical formula 1.

[0069] [Chemical Formula 1]

[0070]

[0071] In the above chemical formula, m, n ≥ 1, l, k ≥ 0, and Y is hydrogen, a hydroxyl group, or a methyl group.

[0072] In a specific embodiment of the present invention, the compound represented by Formula 1 may include at least one selected from the group consisting of glycerol, trimethylolpropane, and pentaerythritol, but is not particularly limited to these.

[0073] The compound represented by Chemical Formula 1, exemplified above, is known as a branching agent because it can form a branched structure in three or more directions during the manufacture of polyester, and is generally used as a means to increase the molecular weight of polyester or to improve the shear thinning effect. However, in the present invention, as described in Korean Patent Application No. 10-2022-0119728, it acts as a discoloration inhibitor to effectively solve the discoloration phenomenon that may occur during the manufacture of biodegradable aliphatic / aromatic polyester using an aliphatic diol with a chain length of less than 4 carbon atoms.

[0074] Discoloration problems occurring during the production of biodegradable aliphatic / aromatic polyesters using aliphatic diols with chain lengths of less than 4 carbon atoms may be caused by changes in the chemical structure of the ester bond between the aliphatic diol and the aliphatic dicarboxylic acid due to heat-induced side reactions or depolymerization. The compound represented by Chemical Formula 1 is understood to inhibit the breakdown of the ester bond between the aliphatic diol and the aliphatic dicarboxylic acid.

[0075] In the present invention, it is preferable that the discoloration inhibitor (c) be included in the reaction mixture, but the invention does not exclude the addition of the discoloration inhibitor separately during the esterification reaction or transesterification reaction.

[0076] In the present invention, the discoloration inhibitor represented by Formula 1 is included in an amount of 0.8 to 3.5 mol% based on the total molar amount of the dicarboxylic acid component (a). If the discoloration inhibitor represented by Formula 1 is used in an amount less than the above range, there is a possibility that the discoloration of the reactant may occur rapidly within tens of minutes after the start of the condensation reaction or that the polymerization reaction rate may be slowed down, and if it is used in an amount exceeding the above range, there is a possibility that the reactant may gel.

[0077] In step (1) above, it is preferable that the stabilizer (d) be included in the reaction mixture, but the invention does not exclude the separate addition of the stabilizer during the esterification reaction or transesterification reaction and / or condensation reaction.

[0078] The stabilizer (d) can be used in an amount of 0.01 to 5.0 g based on 1 mole of the dicarboxylic acid component (a). Preferably, the stabilizer (d) can be used in an amount of 0.1 to 4.0 g based on 1 mole of the dicarboxylic acid component (a).

[0079] If the content of the stabilizer (d) is below the above range, discoloration of the reactant may occur rapidly within tens of minutes after the start of the condensation reaction, and if used in excess of the above range, the polymerization reaction rate may be slowed down.

[0080] In step (1) above, the reaction mixture is subjected to an esterification reaction or a transesterification reaction in the presence of all or part of the catalyst to obtain a prepolymer.

[0081] In a specific embodiment of the present invention, the catalyst may comprise at least one selected from the group consisting of tetrabutyl titanate, tetraisopropyl titanate, zinc acetate, and antimony oxide, but is not particularly limited to these.

[0082] The catalyst can be used in an amount of 0.01 to 5.0 g based on 1 mole of the dicarboxylic acid component (a). Preferably, the catalyst can be used in an amount of 0.1 to 1.0 g based on 1 mole of the dicarboxylic acid component (a).

[0083] In step (1) above, the reaction mixture can be subjected to an esterification reaction or a transesterification reaction in the presence of the entire amount of catalyst to obtain a prepolymer. In this case, without additional catalyst, the catalyst remaining in the prepolymer can be used in the condensation reaction described later. Alternatively, the reaction mixture can be subjected to an esterification reaction or a transesterification reaction in the presence of a portion of the catalyst to obtain a prepolymer. In this case, the prepolymer can be subjected to a condensation reaction in the presence of the remaining portion of the catalyst.

[0084] In a specific embodiment of the present invention, the esterification or transesterification reaction of the reaction mixture may be carried out in a single reactor with different temperature ranges. For example, the first esterification or transesterification reaction involves forming an oligomer through a condensation reaction between an aliphatic dicarboxylic acid and an aliphatic diol at a temperature in the range of 180 to 200°C for 60 to 180 minutes. The second esterification or transesterification reaction involves randomly condensing an aromatic dicarboxylic acid, an aliphatic diol, and the oligomer formed in the first esterification or transesterification reaction at a temperature in the range of 220 to 265°C for 60 to 180 minutes to form a polyester prepolymer.

[0085] The primary esterification or transesterification and secondary esterification or transesterification reactions of step (1) described in the embodiments of the present invention are merely classified according to the temperature range, and the order thereof is not particularly limited. For example, the primary esterification or transesterification reaction may be performed to form an oligomer through a condensation reaction between an aromatic dicarboxylic acid and an aliphatic diol at a temperature in the range of 220 to 265°C for 60 to 180 minutes, and the secondary esterification or transesterification reaction may be performed at a temperature in the range of 180 to 200°C for 60 to 180 minutes to form a polyester prepolymer.

[0086] In addition, in step (1) described in the embodiment of the present invention, the number of reactors for reacting the reaction mixture is not particularly limited. For example, the primary esterification or transesterification reaction and the secondary esterification or transesterification reaction may be carried out in different reactors, and the oligomer formed in the primary esterification or transesterification reaction may be included in or excluded from the secondary esterification or transesterification reaction. The prepolymers formed in each step (2) may be mixed and the degree of polymerization may be increased through a condensation reaction.

[0087] Step (2)

[0088] In step (2) of the method for producing a biodegradable aliphatic / aromatic polyester according to an embodiment of the present invention, the prepolymer obtained in step (1) is subjected to a condensation reaction to obtain a biodegradable aliphatic / aromatic polyester. Specific details regarding the catalyst and stabilizer (d) are as described in step (1) above. Step (2) may be performed in the presence of the remaining portion of the catalyst and stabilizer (d) or without additional catalyst and stabilizer (d).

[0089] In step (2) above, the degree of polymerization of the prepolymer can be increased through a condensation reaction. The condensation reaction can generally be carried out for 60 to 420 minutes at a temperature in the range of 220 to 265°C and a vacuum of less than 1 torr. At this time, if the temperature of the condensation reaction exceeds 265°C, the biodegradable aliphatic / aromatic polyester may rapidly discolor within tens of minutes, so it is desirable to control the temperature of the condensation reaction so that it does not exceed 265°C. On the other hand, if the temperature of the condensation reaction is below 220°C, the polymerization rate becomes very slow, and the polymerization time may exceed 420 minutes. When the polymerization time is delayed in this way, not only productivity but also the color characteristics of the resin may be reduced.

[0090] The biodegradable aliphatic / aromatic polyester obtained in step (2) above has a melt flow index of 100 g / 10 min or less when measured with a 2.16 kg load at 190°C, a melt temperature peak is observed, and there is no stickiness when melted, and it can have a relative biodegradability of 60% or more compared to standard material cellulose within 45 days under industrial composting conditions (58±2°C).

[0091] The method for manufacturing a biodegradable aliphatic / aromatic polyester according to the present invention may further include the step of (3) performing heat treatment on the biodegradable aliphatic / aromatic polyester at a temperature below its melting temperature. By performing the heat treatment, the crystallization characteristics of the biodegradable aliphatic / aromatic polyester may be further increased. Specifically, if dehumidifying drying is performed at a temperature in the range of 40 to 100°C, the crystallization of the biodegradable aliphatic / aromatic polyester may be further increased, resulting in an opaque characteristic. The crystallization further increased through dehumidifying drying in this manner may also help improve the mechanical properties of the resin.

[0092] The biodegradable aliphatic / aromatic polyester according to an embodiment of the present invention can be manufactured by the above manufacturing method and has a melt flow index of 100 g / 10 min or less when measured with a 2.16 kg load at 190°C, a melt temperature peak is observed, there is no stickiness when melted, and it can have a relative biodegradability of 60% or more compared to cellulose, a standard material, within 45 days under industrial composting conditions (58±2°C).

[0093] A biodegradable aliphatic / aromatic polyester according to an embodiment of the present invention may include a dicarboxylic acid residue derived from an aliphatic dicarboxylic acid and an aromatic dicarboxylic acid, and a diol residue derived from an aliphatic diol having a chain length of less than 4 carbon atoms.

[0094] An aliphatic / aromatic polyester according to one embodiment of the present invention can be biodegraded under test conditions in accordance with ISO 14855-1, the international standard for biodegradability evaluation. In the present invention, "biodegradability" is defined as when a substance or mixture of substances (test substance) exhibits a relative "biodegradability" value of 90% or more relative to a standard substance within a period of 180 days, or a relative "biodegradability" value of 60% or more relative to a standard substance during an initial period of 45 days. The compost (inoculum) used in the biodegradability test must satisfy the characteristics of compost required by ISO 14855-1. The compost used as an inoculum is produced by deriving from municipal solid waste, farm waste, garden waste, etc., undergoing a composting process, and maturing it into a soil-like substance containing a mixture of plant residues, other organic matter, and specific inorganic components. When the test substance is mixed with the stabilized compost used as an inoculum, the "biodegradability" of the substance or mixture of substances can be measured from the amount of carbon dioxide generated under appropriate temperature, humidity, and moisture conditions. In the present invention, "biodegradability" can be calculated using values ​​such as the cumulative amount of carbon dioxide generated from a composting container containing a test substance or a standard substance, the average of the cumulative amount of carbon dioxide generated from a composting container containing only an inoculum, and the theoretical amount of carbon dioxide generated by the test substance and the standard substance.

[0095] Since various methods for evaluating "biodegradability" are introduced depending on the test environment, including the origin of the compost and the types of microorganisms within the compost, a standard is needed to determine the validity of the "biodegradability" result. In the present invention, the validity of the "biodegradability" result was determined based on the following criteria: first, the biodegradability of the standard substance is 70% or more over 45 days; second, the difference in biodegradability between each container holding the standard substance is within 20% until the end of the test; and third, the generation of (50~150) mg of carbon dioxide per gram of volatile solids for 10 days after inoculum culture.

[0096] The biodegradable aliphatic / aromatic polyester according to an embodiment of the present invention can be applied in various fields of daily life, such as disposable films or sheets, tableware, fishing nets, agricultural films or sheets, etc.

[0097] Examples

[0098] The present invention will be explained in more detail below through examples and comparative examples. However, the following examples are merely illustrative of the present invention, and the scope of the present invention is not limited thereto.

[0099] Example 1

[0100] 8.38 moles of ethylene glycol, 2.40 moles of adipic acid, and 3.61 moles of terephthalic acid were injected into a reactor equipped with a condenser. 1.50 g of tetrabutyl titanate and 6.01 g of glycerol were added to this mixture, and a first esterification reaction was carried out at 190–200°C. When the temperature at the top of the condenser fell below 90°C, it was assumed that the water generated as a byproduct had been completely discharged, and the reactor temperature was raised to 235–240°C to carry out a second esterification reaction. Likewise, when the temperature at the top of the condenser fell below 90°C, it was assumed that the water generated as a byproduct had been completely discharged, and the second esterification reaction was terminated.

[0101] Next, 0.75 g of tetrabutyl titanate was added to the prepolymer, and a polycondensation reaction was carried out at 250°C and a vacuum of less than 1 torr to obtain an aliphatic / aromatic polyester.

[0102] Example 2

[0103] Aliphatic / aromatic polyesters were obtained by reacting in the same manner as in Example 1, except that the amount of ethylene glycol was changed to 1.61 mol, the amount of adipic acid to 0.48 mol, the amount of terephthalic acid to 0.67 mol, the amount of glycerol to 1.72 g, and the amount of tetrabutyl titanate to 0.57 g, and the condensation reaction was performed at 225°C.

[0104] Comparative example

[0105] Comparative Example 1

[0106] Aliphatic / aromatic polyesters were obtained by reacting in the same manner as in Example 2, except that the amount of adipic acid was changed to 0.55 mol and the amount of terephthalic acid to 0.60 mol.

[0107] Comparative Example 2

[0108] Aliphatic / aromatic polyesters were obtained by reacting in the same manner as in Example 2, except that the amount of adipic acid was changed to 0.51 mol and the amount of terephthalic acid to 0.64 mol.

[0109] Comparative Example 3

[0110] Aliphatic / aromatic polyesters were obtained by reacting in the same manner as in Example 1, except that the amount of adipic acid was changed to 2.36 mol, the amount of terephthalic acid to 3.93 mol, the amount of glycerol to 6.30 g, and the amount of tetrabutyl titanate added before the esterification reaction and before the condensation reaction to 1.57 g and 0.79 g, respectively, and the condensation reaction was performed at 255°C.

[0111] Comparative Example 4

[0112] Aliphatic / aromatic polyesters were obtained by reacting in the same manner as in Example 1, except that the amount of adipic acid was changed to 2.20 mol, the amount of terephthalic acid to 4.09 mol, the amount of glycerol to 6.30 g, and the amount of tetrabutyl titanate added before the esterification reaction and before the condensation reaction to 1.57 g and 0.79 g, respectively, and the condensation reaction was performed at 255°C.

[0113] Comparative Example 5

[0114] Aliphatic / aromatic polyesters were obtained by reacting in the same manner as in Example 1, except that the amount of adipic acid was changed to 2.05 mol, the amount of terephthalic acid to 4.25 mol, the amount of glycerol to 6.30 g, and the amount of tetrabutyl titanate added before the esterification reaction and before the condensation reaction to 1.57 g and 0.79 g, respectively, and the condensation reaction was performed at 255°C.

[0115]

[0116] The aliphatic / aromatic polyesters obtained from the above examples and comparative examples were tested in the following manner, and the results are listed in Table 1 below.

[0117] Test example

[0118] (1) Melt flow index (MFI)

[0119] The melt flow index of aliphatic / aromatic polyester was measured at 190°C with a 2.16 kg load according to ASTM D1238.

[0120] (2) Color characteristics

[0121] The color characteristics of aliphatic / aromatic polyesters were measured using a spectrophotometer (spectrophotometer SE 7700, NIPPON DENSHOKU).

[0122] (3) Biodegradability

[0123] According to ISO 14855, the relative biodegradability of aliphatic / aromatic polyesters relative to cellulose, a standard material, was measured after 45 days at 58°C.

[0124] (4) Melting temperature

[0125] The melting temperatures of aliphatic / aromatic polyesters were measured using a temperature-modulated differential scanning calorimeter (DSC204 F1 Phoenix, Netzsch).

[0126] [Table 1]

[0127]

[0128]

[0129] As can be seen from Table 1 above, when comparing Examples 1 and 2, in which terephthalic acid exceeds 56 mol%, with Comparative Examples 1 and 2, in which terephthalic acid is 56 mol% or less, the melting temperature was observed in the Examples, and crystalline characteristics were exhibited as there was no stickiness upon melting. In addition, when comparing Example 1 with Comparative Examples 3 to 5, in which terephthalic acid is 62.5 mol% or more, the Examples showed excellent biodegradability with a relative biodegradability of 86% relative to cellulose, a standard material, after 45 days at 58°C, whereas the Comparative Examples showed a rapidly degraded relative biodegradability. Through the above results, it was confirmed that the ratio of aromatic dicarboxylic acid content required for an aliphatic / aromatic polyester containing an aliphatic diol with a chain length of less than 4 carbon atoms to possess excellent biodegradability and crystalline characteristics is greater than 56 mol% and less than 62.5 mol%.

[0130] In addition, photographs of the aliphatic / aromatic polyester obtained in Example 1 before and after heat treatment are shown in Fig. 1. The heat treatment was performed at a temperature of 80°C for 10 hours. As can be seen from Fig. 1, the aliphatic / aromatic polyester exhibited transparency before heat treatment, whereas after heat treatment, its crystallinity increased further, resulting in relatively opaque characteristics.

Claims

1. A dicarboxylic acid component (a) derived from an aliphatic dicarboxylic acid and an aromatic dicarboxylic acid, and a diol component (b) derived from an aliphatic diol having a chain length of less than 4 carbon atoms, comprising The content of aromatic dicarboxylic acid is greater than 56 mol% and less than 62.5 mol% based on the total moles of dicarboxylic acid component (a), and the content of aliphatic dicarboxylic acid is greater than 37.5 mol% and less than 44 mol% based on the total moles of dicarboxylic acid component (a). Biodegradable aliphatic / aromatic polyester.

2. In Paragraph 1, The aromatic dicarboxylic acid comprises at least one selected from the group consisting of terephthalic acid, isophthalic acid, orthophthalic acid, naphthalene dicarboxylic acid, dimethyl terephthalate, dimethyl isophthalate, dimethyl phthalate, and dimethyl naphthalene dicarboxylate. Biodegradable aliphatic / aromatic polyester.

3. In Paragraph 1, The aliphatic dicarboxylic acid comprises at least one selected from the group consisting of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimeric acid, suberic acid, azelaic acid, sebacic acid, and their ester compounds, Biodegradable aliphatic / aromatic polyester.

4. In Paragraph 1, The aromatic dicarboxylic acid includes terephthalic acid, and the aliphatic dicarboxylic acid includes adipic acid, Biodegradable aliphatic / aromatic polyester.

5. In Paragraph 1, The diol component (b) comprises at least one selected from the group consisting of ethylene glycol, 1,2-propanediol, and 1,3-propanediol, Biodegradable aliphatic / aromatic polyester.

6. In Paragraph 5, The diol component (b) is ethylene glycol, Biodegradable aliphatic / aromatic polyester.

7. In Paragraph 1, The molar ratio of the diol component (b) to the dicarboxylic acid component (a) is 1.1:1 to 1.5:1, Biodegradable aliphatic / aromatic polyester.

8. In Paragraph 1, Based on the total moles of the dicarboxylic acid component (a), the composition further comprises 0.8 to 3.5 mol% of a discoloration inhibitor (c) represented by the following chemical formula 1, Biodegradable aliphatic / aromatic polyesters: [Chemical Formula 1] In the above chemical formula, m, n ≥ 1, l, k ≥ 0, and Y is hydrogen, a hydroxyl group, or a methyl group.

9. In Paragraph 8, The above discoloration inhibitor (c) comprises at least one selected from the group consisting of glycerol, trimethylolpropane, and pentaerythritol, Biodegradable aliphatic / aromatic polyester.

10. In Paragraph 1, Based on 1 mole of dicarboxylic acid component (a), additionally comprising 0.01 to 5.0 g of stabilizer (d), Biodegradable aliphatic / aromatic polyester.

11. In Paragraph 10, The above stabilizer (d) is at least one selected from the group consisting of trimethylphosphonoacetate, triethylphosphonoacetate, tripropylphosphonoacetate, and tributylphosphonoacetate. Biodegradable aliphatic / aromatic polyester.

12. In Paragraph 1, Biodegradable aliphatic / aromatic polyester having a melt flow index of 100 g / 10 min or less when measured at 190℃ with a 2.16 kg load, and having a relative biodegradability of 60% or more compared to standard material cellulose within 45 days at 58±2℃ under industrial composting conditions.

13. In Paragraph 1, Biodegradable aliphatic / aromatic polyester used for applications selected from the group consisting of disposable films or sheets, tableware, fishing nets, and agricultural films or sheets.

14. A method for manufacturing a biodegradable aliphatic / aromatic polyester, (1) A step of obtaining a prepolymer by esterifying or transesterifying a reaction mixture comprising a dicarboxylic acid component (a) derived from an aliphatic dicarboxylic acid and an aromatic dicarboxylic acid and a diol component (b) derived from an aliphatic diol having a chain length of less than 4 carbon atoms, in the presence of a catalyst; and (2) A step of obtaining a biodegradable aliphatic / aromatic polyester by condensing the prepolymer obtained in step (1), and Biodegradable aliphatic / aromatic polyester having a melt flow index of 100 g / 10 min or less when measured at 190°C with a 2.16 kg load, crystalline characteristics, and a relative biodegradability of 60% or more compared to the standard material cellulose within 45 days under industrial composting conditions (58±2°C), Method for manufacturing biodegradable aliphatic / aromatic polyester.

15. In Paragraph 14, The catalyst comprises at least one selected from the group consisting of tetrabutyl titanate, tetraisopropyl titanate, zinc acetate, and antimony oxide, and the content of the catalyst is 0.01 to 5.0 g based on 1 mole of dicarboxylic acid component (a). Method for manufacturing biodegradable aliphatic / aromatic polyester.

16. In Paragraph 14, In step (1), the esterification or transesterification reaction of the reaction mixture is carried out in a single reactor with different temperature ranges, wherein the first esterification or transesterification reaction is carried out at a temperature in the range of 180 to 200°C and the second esterification or transesterification reaction is carried out at a temperature in the range of 220 to 265°C. Method for manufacturing biodegradable aliphatic / aromatic polyester.

17. In Paragraph 14, The reaction mixture of step (1) further comprises a discoloration inhibitor (c) and a stabilizer (d), Method for manufacturing biodegradable aliphatic / aromatic polyester.

18. In Paragraph 14, In step (2), the condensation reaction of the prepolymer proceeds at a vacuum of less than 1 torr, Method for manufacturing biodegradable aliphatic / aromatic polyester.

19. In Paragraph 14, (3) The biodegradable aliphatic / aromatic polyester further comprises the step of performing heat treatment at a temperature below the melting temperature, Method for manufacturing biodegradable aliphatic / aromatic polyester.

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