thermoplastic copolyester

Abstract

The purpose of this invention is to provide a thermoplastic copolyester that possesses toughness and excellent enzymatic decomposability and heat resistance. Specifically, this invention provides a thermoplastic copolyester comprising rigid segments composed of aromatic polyester structural units and soft segments composed of aliphatic polyester structural units. In the aforementioned thermoplastic copolyester, the rigid segments constitute 35-63% by mass, the aforementioned aromatic polyester structural units contain at least 70% by mass of aromatic polyester components composed of dicarboxylic acid components with furan skeletons and aliphatic diol components, the aforementioned aliphatic polyester structural units contain at least 70% by mass of aliphatic hydroxycarboxylic acid components, and the reduced viscosity is in the range of 0.5-3.5 dl / g.

Description

Technical field

[0001] The invention relates to a thermoplastic copolyester with excellent enzymatic decomposition and heat resistance. Prior technology

[0002] In recent years, as environmentally protective or environmentally sustainable materials, resins hydrolyzed by recourse to the presence of enzymes in nature have been developed and are being put into practical use. Aliphatic polyesters, in particular, will be well hydrolyzed, however have poorer mechanical or thermal characteristics compared to aromatic-containing polyesters. Among aromatic-containing polyesters, polyadipic butyl terephthalate is known to decompose well in nature. Polyadipate butyl terephthalate is a polymer with excellent toughness like polyethylene. Other high-melting-point polymers with excellent hydrolysis, such as polyhydroxyacetic acid (melting point around 230°C) or polylactic acid (melting point around 170°C), can be cited, however, with low rupture strength and brittle texture.

[0003] In addition, in terms of polymer materials with high melting point and high toughness, block copolymer polyesters with both hard and soft segments can be enumerated. For example, in the block copolymer of polybutylene terephthalate and polycaprolactone, the polybutylene terephthalate component of the hard segment has high crystallinity and may therefore have a melting point close to 200°C. [Previous technical literature] [Patent Literature]

[0004] Patent Literature 1: Japanese Patent Bulletin No. 3411289 Patent Literature 2: Bulletin of Japanese Patent No. 5847938 Patent Literature 3: Japanese Patent Bulletin No. 3674934 Contents of the invention

[0005] [Problem to be solved by the invention]

[0006] However, in the patent literature 3, the hydrolysis (enzyme decomposition) of the enzyme reaction was poor due to the presence of polybutylene terephthalate with high crystallinity. In addition, if the hard chain segment composition ratio, chain length is reduced in order to improve enzyme decomposition, the melting point will be significantly reduced. That is, previous polyesters did not balance excellent enzyme decomposition and heat resistance.

[0007] This invention was made against the backdrop of such prior art problems. That is, the object of this invention is to provide a thermoplastic copolyester comprising rigid segments composed of crystalline aromatic polyester structural units and soft segments composed of aliphatic polyester structural units, which has excellent toughness and also has excellent enzymatic decomposability and excellent heat resistance. [Problem-solving methods]

[0008] To achieve the aforementioned objectives, the inventors focused on thermoplastic copolyesters comprising rigid and flexible segments, and investigated their composition. The results showed that specific components are required for both the rigid and flexible segments, and their amounts are also important. Furthermore, the chain length of the rigid segments was also found to be a crucial factor. These insights led to the completion of this invention.

[0009] That is, the present invention has the following structure. [1] A thermoplastic copolyester comprising rigid segments composed of aromatic polyester structural units and soft segments composed of aliphatic polyester structural units, characterized in that: In the aforementioned thermoplastic copolyester, the rigid segment is 35-63% by mass. The aforementioned aromatic polyester structural unit contains at least 70% by mass of an aromatic polyester component composed of a dicarboxylic acid component with a furan backbone and an aliphatic diol component. The aforementioned aliphatic polyester structural unit contains more than 70% by mass of aliphatic hydroxycarboxylic acid. The reduced viscosity is in the range of 0.5~3.5 dl / g. [2] For example, the average chain length of the aromatic polyester structural unit calculated by nuclear magnetic resonance (NMR) is in the range of 3 to 15 for the thermoplastic copolyester of [1]. [3] Thermoplastic copolyesters such as [1] or [2], wherein the aliphatic diol component constituting the aforementioned aromatic polyester component is 1,4-butanediol. [4] The thermoplastic copolyester of any one of [1] to [3], wherein the aforementioned aliphatic hydroxycarboxylic acid component is derived from any one of ε-caprolactone, δ-valerolactone, γ-butyrolactone, β-propiolactone, β-butyrolactone, and tervarolactone. [5] The thermoplastic copolyester of any one of [1] to [4] has a weight reduction rate of more than 70% by weight in the enzymatic decomposition test using polyester decomposition enzyme. [6] The thermoplastic copolyester of any one of [1] to [5] has a melting point in the range of 130°C to 167°C. [7] A shaped body comprising a thermoplastic copolyester such as any of [1] to [6]. ﹝Effect of Invention﹞

[0010] By the present invention, thermoplastic copolyesters with excellent enzyme decomposition and heat resistance and toughness can be obtained. By means that the aromatic polyester structural unit of the hard segment contains an established amount of an aromatic polyester component composed of a dicarboxylic acid component with a furan skeleton and an aliphatic glycol component, The mass ratio with soft chain segments in the established range can yield thermoplastic copolyesters with excellent enzyme decomposition and heat resistance, and even, by having an average chain length above the established amount of aromatic polyester structural units, thermoplastic copolyesters with even better heat resistance can be obtained. Implementation

[0011] The present invention is described in detail below. The thermoplastic copolyester used in the present invention is a copolyester comprising a hard segment constructed of an aromatic polyester structural unit and a soft segment constructed of an aliphatic polyester structural unit as a constituent component, a so-called block copolymer. Like this, toughness can be imparted by having hard and soft chain segments. Hard and soft segments can be bonded directly through an ester bond or can be bonded through a chain extender.

[0012] In thermoplastic copolyesters, the hard segment content is 35~63 mass% and the soft segment content is 37~65 mass%. In the case where the thermoplastic copolyester is composed of a hard segment constructed of aromatic polyester structural units only and a soft segment constructed of aliphatic polyester structural units, the sum of the two would be 100% by mass. If the hard chain segment exceeds 63% by mass, adequate enzyme decomposition cannot be obtained. In addition, if the soft chain segment exceeds 65% by mass, the melting point is significantly reduced, thus the heat resistance is problematic. Therefore, in order to balance enzyme decomposition and heat resistance, it is advisable to have hard chain segments of 40~63 mass% and soft chain segments of 37~60 mass%.

[0013] The aromatic polyester structural unit of the hard segment contains more than 70% by mass of the aromatic polyester component composed of a dicarboxylic acid component having a furan skeleton and an aliphatic glycol component. The hard segment is a polyester segment with crystallinity with a high melting point. The aliphatic polyester structural unit of the soft chain segment contains more than 70% by mass of aliphatic hydroxycarboxylic acid components.

[0014] When expressing the ratio of hard segments to soft segments, because the molecular weights of the units of the two types of segments are significantly different, or because calculating the actual molecular weight of a block copolymer according to the type of soft segment becomes difficult, it is not possible to use moles (%), but rather mass (%). Therefore, the ratio of hard segments or soft segments is expressed as mass (%). The proportions of each segment are calculated as follows. When the hard segment is polybutylene terephthalate and the soft segment is polycaprolactone, the hard segment is the sum of the mass percentages of terephthalic acid residues (-COC 6H 4CO-) and 1,4-butanediol residues (-OC 4H 8O-), and the soft segment is the mass of ε-caprolactone residues (-OC 5H 10CO-).

[0015] Dicarboxylic acid components with a furan backbone that form the structural units of aromatic polyesters with rigid chains include 2,5-furandicarboxylic acid, 2,3-furandicarboxylic acid, 2,4-furandicarboxylic acid, and 3,4-furandicarboxylic acid. These components have aromatic ring structures. 2,5-furandicarboxylic acid is particularly preferred for obtaining a high melting point. Other aromatic dicarboxylic acid components besides those containing a furan backbone include terephthalic acid, isophthalic acid, and sodium 5-sulfonyl isophthalate; however, alicyclic dicarboxylic acid components such as 1,4-cyclohexanedicarboxylic acid can also be used without impairing the effects of this invention. In addition to the aforementioned dicarboxylic acids, derivatives (e.g., dimethyl esters) can also be used as raw material monomers in the manufacture of thermoplastic copolyesters.

[0016] The aliphatic diols that constitute the rigid aromatic polyester structural units can specifically include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, neopentanediol, and diethylene glycol. The type of aliphatic diol used can be only one or more. Among these, ethylene glycol or 1,4-butanediol are preferred due to their versatility and linear aliphatic nature. Especially to ensure that the average chain length of the aromatic polyester structural units described later is above a predetermined value, a higher content of 1,4-butanediol is preferable.

[0017] For example, in the condensation polymerization of aromatic dicarboxylic acids, such as furanyl dicarboxylic acid, or their dimethyl esters, with 1,4-butanediol, the terminal 1,4-butanediol residues or unreacted 1,4-butanediol tend to cyclize into THF (tetrahydrofuran), which readily flows out of the system. As a result, the aliphatic diol content decreases, leading to a polymer with more acid terminals and fewer hydroxyl terminals. The presence of hydroxyl groups promotes transesterification in the synthesis of thermoplastic copolyesters, thus reducing the average chain length of aromatic polyester structural units. Therefore, 1,4-butanediol is preferred as the aliphatic diol component in aromatic polyesters.

[0018] Regarding the aromatic polyester structural unit of the hard chain segment, the aromatic polyester component composed of a dicarboxylic acid component with a furan backbone and an aliphatic diol component, when accounting for 70% or more by mass, exhibits high enzymatic decomposition properties and also contributes to high heat resistance. This aromatic polyester component is preferably 80% or more by mass, more preferably 90% or more by mass, and even more preferably 95% or more by mass. An aromatic polyester component composed of a dicarboxylic acid component with a furan backbone and an aliphatic diol component accounting for 100% by mass is also a suitable state.

[0019] The aliphatic hydroxycarboxylic acid component in the aliphatic polyester structural unit of the soft chain segment can be a single component or composed of multiple components. Considering the raw material monomers used in the manufacture of thermoplastic copolyesters, the aliphatic hydroxycarboxylic acid component can be an aliphatic hydroxycarboxylic acid compound or a cyclic aliphatic lactone compound. Specifically, examples include β-propiolactone, γ-butyrolactone, δ-valerolactone, ε-caprolactone, δ-caprolactone, β-butyrolactone, p-valerolactone, p-dioxanone, lactic acid, and glycolic acid. Any one of ε-caprolactone, δ-valerolactone, γ-butyrolactone, β-propiolactone, β-butyrolactone, and p-valerolactone is particularly preferred. From the viewpoint that it yields a linear aliphatic polyester easily identifiable by enzymes and is a widely used monomer, ε-caprolactone is preferred.

[0020] In addition to aliphatic hydroxycarboxylic acid components, the soft-chain aliphatic polyester structural units can also be copolymerized from aliphatic polyester components composed of aliphatic dicarboxylic acids and aliphatic diols. For aliphatic polyester structural units with soft chain segments, aliphatic hydroxycarboxylic acid components comprising 70% or more by mass exhibit high enzymatic decomposition properties. The aliphatic hydroxycarboxylic acid component is preferably 80% or more by mass, more preferably 90% or more by mass, and even more preferably 95% or more by mass. A 100% by mass aliphatic hydroxycarboxylic acid component is also suitable.

[0021] The thermoplastic copolyester of this invention may also contain soft segments other than those composed of aliphatic polyester structural units, within a range that does not impair the effects of this invention (e.g., preferably 20% by mass or less, more preferably 10% by mass or less). Examples of such soft segments include aliphatic polyether structural units and aliphatic polycarbonate structural units. Furthermore, it is also suitable for the thermoplastic copolyester of this invention to not contain soft segments other than those composed of aliphatic polyester structural units.

[0022] The reduced viscosity of the thermoplastic copolyester in this invention is 0.5~3.5 dl / g. If it is less than 0.5 dl / g, the mechanical strength is significantly reduced, thus lacking practicality. If it exceeds 3.5 dl / g, in addition to reduced enzymatic decomposition, the polymerization time will be longer, which may adversely affect productivity. It is preferably 0.7~3.0 dl / g, and more preferably 1.0~2.5 dl / g.

[0023] In thermoplastic copolyesters possessing both rigid and flexible segments, to obtain a high melting point, it is preferable that the block copolymers, i.e., both the rigid aromatic polyester structural units and the flexible aliphatic polyester structural units, have chain lengths of a predetermined amount or more. In particular, the average chain length of the rigid segments composed of crystalline aromatic polyester structural units is preferably 3 to 15. In this case, superior enzymatic decomposition and heat resistance can be achieved. The average chain length of the aromatic polyester structural unit, in the case where the aromatic polyester structural unit is polybutylene terephthalate, refers to the average number of consecutive polybutylene terephthalate units in the thermoplastic copolyester. The average chain length is calculated using the nuclear magnetic resonance (NMR) method disclosed in the examples described later, and rounded to the nearest whole number. The average chain length of the aromatic polyester structural unit is preferably 5 or more, and more preferably 8 or more. The upper limit of the average chain length of the aromatic polyester structural unit is preferably below 12, and more preferably below 10.

[0024] The method for manufacturing the thermoplastic copolyester of the present invention can employ well-known methods. For example, after esterification of the aforementioned dicarboxylic acid component with a furan backbone and the aliphatic diol component at 150°C to 250°C, condensation polymerization is carried out under reduced pressure at 200°C to 280°C to synthesize an aromatic polyester. The lactone compound, which is the aforementioned aliphatic hydroxycarboxylic acid component, is then melted at 150°C to 250°C, and an aliphatic polyester is formed through ring-opening polymerization of the lactone compound. Simultaneously, this aliphatic polyester is copolymerized with the aromatic polyester, and then reduced pressure is applied to allow the remaining monomer to flow out of the system, thus obtaining the target thermoplastic copolyester. In the synthesis of the aromatic polyester, the aforementioned dimethyl ester of the dicarboxylic acid component with a furan backbone can also be used. The dimethyl ester of the dicarboxylic acid component and the aliphatic diol component undergo transesterification at 150°C to 250°C, followed by condensation polymerization under reduced pressure at 200°C to 280°C to obtain the aromatic polyester. In addition, when synthesizing thermoplastic copolyesters, aliphatic polyesters constituting soft segments are polymerized by a well-known method, and aromatic polyesters constituting hard segments are added. The mixture is then melted and stirred under reduced pressure at 150°C to 250°C to obtain the target thermoplastic copolyester.

[0025] A method for achieving an average chain length of 3 to 15 eq for aromatic polyester structural units is described. When copolymerizing aliphatic polyesters with soft segments and aromatic polyesters with hard segments, the number of hydroxyl terminals in the aromatic polyester is important. This is because a higher number of hydroxyl terminals in the aromatic polyester facilitates transesterification, resulting in a shorter average chain length for the aromatic polyester structural units. The hydroxyl valence of the aromatic polyester should preferably be below 150 eq / ton, and more preferably below 100 eq / ton. The hydroxyl valence of the aromatic polyester can be determined by NMR. Furthermore, the copolymerization conditions for aliphatic polyesters with soft chain segments and aromatic polyesters with hard chain segments must be carefully considered. Excessive time or temperature during copolymerization can shorten the average chain length of the aromatic polyester structural units; therefore, the most suitable conditions must be found. These conditions will vary depending on the polymerization equipment used and the production scale, and can be determined through several test experiments.

[0026] In the synthesis of thermoplastic copolyesters, the presence of metals in the raw materials can promote transesterification, potentially reducing the average chain length of aromatic polyester structural units. Lower metal content in the raw materials is desirable; however, this depends on the compound's structure and the type of metal, and cannot be generalized. Furthermore, using raw materials with reduced metal content obtained through known purification methods such as solution filtration, reprecipitation, and recrystallization to synthesize thermoplastic copolyesters is a suitable approach.

[0027] When manufacturing thermoplastic copolyesters, well-known substances can be used as catalysts. For example, acetates or carbonates of lead, zinc, manganese, calcium, cobalt, magnesium, sodium, etc., or metal oxides of magnesium, zinc, lead, antimony, germanium, iron, etc., or organometallic compounds of tin, lead, titanium, etc., can be used in one or more combinations depending on the reaction system. However, there are concerns that this may promote transesterification and significantly reduce the average chain length of aromatic polyester structural units. Therefore, it is best to set the most suitable type and amount of catalyst.

[0028] The thermoplastic copolyester of this invention exhibits a weight reduction rate of 70% by weight (wt%) or higher in an enzymatic decomposition test using polyester decomposition enzymes. The polyester decomposition enzyme test involves adding powdered and thoroughly dried thermoplastic copolyester and a keratinase solution to a phosphate buffer solution at pH 8.0, allowing the enzyme activity to reach 165 U, stirring at 50°C for 24 hours, filtering through a 10 μm filter, and measuring the weight of the solids remaining on the filter to confirm the enzymatic decomposition capability. Details are as described in the examples. A weight reduction rate of 75% by weight or higher is preferred, 80% by weight or higher is more preferred, 85% by weight or higher is particularly preferred, and 90% by weight or higher is optimal.

[0029] From a heat resistance point of view, the melting point of the thermoplastic copolyester in this invention is preferably in the range of 130°C to 167°C. A melting point of 135°C to 166°C is more preferred, and 140°C to 165°C is even more preferred. The melting point of the thermoplastic copolyester can be determined by differential scanning calorimetry, as detailed in the embodiments. The melting point of the thermoplastic copolyester is related to the average chain length of the aromatic polyester structural units; therefore, it is also considered important that the average chain length of the aromatic polyester structural units be within a predetermined range in order to achieve a melting point within the aforementioned range.

[0030] In the manufacture of thermoplastic copolyesters, phosphorus-based or thioether-based antioxidants can be used before, during, or after the reaction to inhibit thermal or oxidative degradation. These antioxidants can be used alone or in combination. The optimal addition amount is 0.1% to 5% by mass relative to the thermoplastic copolyester. If the addition is less than 0.1% by mass, the thermal degradation effect will be insufficient. If it exceeds 5% by mass, it will adversely affect other physical properties.

[0031] Furthermore, in this invention, multifunctional compounds selected from the group consisting of epoxy compounds, organic carboxylic acids and / or their anhydrides, oxazoline compounds, and isocyanate compounds having at least two reactive groups may also be added. This is also useful in terms of obtaining high molecular weight thermoplastic copolyesters in a shorter time and improving mechanical properties or thermal stability. Crosslinking structures can also adversely affect enzymatic decomposition; therefore, adding less than 5% by mass of a compound having two reactive groups is suitable.

[0032] To further improve the enzymatic decomposition properties of the thermoplastic copolyester of this invention, biological components such as starch, cellulose, sugar, and protein can be added alone or in combination. The amount added is preferably less than 10% by mass relative to the thermoplastic copolyester. If it exceeds 10% by mass, it may adversely affect the thermal or mechanical properties.

[0033] The thermoplastic copolyester of this invention possesses excellent enzymatic decomposition properties, heat resistance, and toughness, making it suitable for various molded applications. These molded applications include fibers, films, and sheets. Particularly promising applications are in agricultural mulch films, garbage bags, plastic tote bags, biodegradable plastic bags, beverage labels, food trays, food packaging films, straws, cutlery, medical fibers, resin modifiers, and coatings. [Example]

[0034] The following describes the specific embodiments and analysis methods; however, the present invention is not limited to the embodiments. The thermoplastic copolyesters disclosed in the examples are all polybutylene furanate-polycaprolactone block copolymers (PBFCL). In this embodiment, PBFCL is synthesized through the following three steps. (i) Oligopolymer synthesis via transesterification of dimethyl 2,5-furandicarboxylate (DMFD) and 1,4-butanol (1,4-BD), (ii) Synthesis of polybutylene furanate (PBF) by oligomer condensation polymerization (iii) Synthesis of PBFCL by ring-opening polymerization of ε-caprolactone (ε-CL) and copolymerization of PBF.

[0035] (Example 1) (i) In a 2L reactor equipped with a stirrer, thermometer, and distillation condenser, 51% by mass of DMFD (containing 43ppm Fe and 53ppm Na), 49% by mass of 1,4-BD, and a 1-butanol dilution of tetrabutyl titanate (TBT) as a catalyst (68.1 g / L) were added, ensuring that the Ti atoms relative to the mass of the obtained PBF were 150 ppm. The transesterification reaction was carried out at 170°C–190°C for 1 hour, confirming the outflow of methanol exceeding 90% by mass (theoretical value). Next, the temperature was increased from 190°C to 240°C over 1 hour with stirring at 80 rpm, while simultaneously undergoing a slow decompression and a polymerization reaction at below 10 Pa for 20 minutes. Approximately 500 g of PBF with a reduced viscosity of 1.0 dl / g, a melting point of 171°C, and a hydroxyl valence of 45 eq / ton was obtained. (iii) In a 0.1L reactor equipped with a stirrer, thermometer, and distillation condenser, 57% by mass of PBF and 43% by mass of ε-CL were added. The PBF was melted at 200°C for 15 minutes (stirring at 20 rpm for 5 minutes, then at 100 rpm for 10 minutes). Next, the ε-CL was subjected to ring-opening polymerization for 60 minutes, followed by a slow decompression for 30 minutes, and the reaction was carried out at below 500 Pa for 130 minutes. Approximately 20g of PBFCL with a reduced viscosity of 1.1 dl / g was obtained. The physical properties, such as melting point and enzymatic decomposition, are shown in Table 2 below.

[0036] (Example 2) Except for the composition ratio, it was synthesized using the same method as in Example 1. The feed composition of step (iii) was 51% by mass of PBF and 49% by mass of ε-CL. PBFCL with a reduced viscosity of 1.4 dl / g was obtained.

[0037] (Example 3) Except for the composition ratio, it was synthesized in the same manner as in Example 1. The feed composition of step (iii) was 40% by mass of PBF and 60% by mass of ε-CL. PBFCL with a reduced viscosity of 1.5 dl / g was obtained.

[0038] (Example 4) (i) In a 0.3L reactor equipped with a stirrer, thermometer, and distillation condenser, 51% by mass of DMFD (Fe and Na contents both below 1 ppm), 49% by mass of 1,4-BD, and a 1-butanol dilution of TBT (68.1 g / L) as a catalyst were added, ensuring that the Ti atom mass relative to the obtained PBF was 150 ppm. The mixture was stirred at 150°C to 180°C for 3 hours, while simultaneously undergoing transesterification, yielding approximately 80 g of oligomer. It was confirmed that more than 90% by mass of methanol, as theoretically expected, flowed out. After removing the oligomer, it was allowed to stand at room temperature overnight. (ii) In a 0.1 L reactor equipped with a stirrer, thermometer, and distillation condenser, the oligomer from (i) was added, followed by a 1-butanol dilution of TBT (68.1 g / L) as a catalyst, ensuring that the Ti atoms relative to the mass of the obtained PBF were 150 ppm. The mixture was melted at 180 °C for 10 minutes, then stirred at 100 rpm for 60 minutes, and the temperature was gradually increased to 240 °C with a slow depressurization for the first 30 minutes. The polymerization reaction was carried out at 500 Pa for 2 hours to obtain approximately 30 g of PBF with a reduced viscosity of 0.5 dl / g, a melting point of 172 °C, and a hydroxyl valence of 53 eq / ton. (iii) In a 0.1L reactor equipped with a stirrer, thermometer, and distillation condenser, 57% by mass of PBF and 43% by mass of ε-CL were added. The PBF was melted at 200°C for 10 minutes (stirring at 20 rpm for 5 minutes, then at 100 rpm for 10 minutes). Next, the ε-CL underwent ring-opening polymerization for 80 minutes, followed by a slow decompression for 30 minutes, and the reaction was carried out at below 500 Pa for 60 minutes. Approximately 20g of PBFCL with a reduced viscosity of 0.7 dl / g was obtained. Furthermore, the physical properties such as melting point and enzymatic decomposition are shown in Table 2 below.

[0039] (Example 5) The synthesis of PBF and PBFCL was carried out in a manner substantially the same as in Example 4, therefore only the changes are recorded. (ii) The time spent under reduced pressure was set to 70 minutes, and then condensation polymerization was carried out at 240°C for 60 minutes to obtain PBF with a reduced viscosity of 0.8 dl / g, a melting point of 170°C, and a hydroxyl valence of 77 eq / ton. (iii) Feed composition: PBF 40% by mass, ε-CL 60% by mass. PBFCL with a reduced viscosity of 1.5 dl / g was obtained.

[0040] (Comparative Example 1) Except for the composition ratio, it was synthesized in the same manner as in Example 1. The feed composition of step (iii) was 69% by mass of PBF and 31% by mass of ε-CL. PBFCL with a reduced viscosity of 1.4 dl / g was obtained.

[0041] (Comparative Example 2) Except for the composition ratio, it was synthesized in the same manner as in Example 1. The feed composition of step (iii) was 62% by mass of PBF and 38% by mass of ε-CL. PBFCL with a reduced viscosity of 1.1 dl / g was obtained.

[0042] (Comparative Example 3) An evaluation was conducted on polybutylene adipate terephthalate (product name: G-1100) manufactured by Changchun Group Corporation. The reduced viscosity was measured and the result was 0.9 dl / g.

[0043] (Comparative Example 4) The synthesis of PBF and PBFCL was carried out in a manner substantially the same as in Example 4, therefore only the changes are recorded. (iii) Feed composition: PBF 69% by mass, ε-CL 31% by mass. PBFCL with a reduced viscosity of 0.6 dl / g was obtained.

[0044] (Comparative Example 5) Using polybutylene terephthalate (PBT) (brand name: GT-430A) manufactured by Toyobo Co., Ltd., an ε-CL copolymer, PBTCL, was synthesized. GT-430A has a reducing viscosity of 1.0 dl / g and a melting point of 225°C. In a 0.1L reactor equipped with a stirrer, thermometer, and distillation condenser, 57% by mass of GT-430A and 43% by mass of ε-CL were added. PBT was melted at 225°C for 30 minutes (stirring was initiated at 20 rpm after 15 minutes and then reduced to 50 rpm after 30 minutes). ε-CL ring-opening polymerization was then carried out for 60 minutes, followed by a slow, reduced pressure reaction at below 100 Pa for another 60 minutes. Approximately 30g of a polybutylene terephthalate-polycaprolactone block copolymer (PBTCL) with a reducing viscosity of 1.6 dl / g was obtained.

[0045] (Comparative Example 6) Except for the composition, PBTCL was synthesized using the same method as Comparative Example 4. The composition of the feed was 40% by mass of GT-430A and 60% by mass of ε-CL, and the reduced viscosity of the obtained PBTCL was 1.7 dl / g.

[0046] (Comparative Example 7) The synthesis of PBF and PBFCL was carried out in a manner substantially the same as in Example 4, therefore only the changes are recorded. (iii) Feed composition: PBF 61% by mass, ε-CL 39% by mass. PBFCL with a reduced viscosity of 0.6 dl / g was obtained.

[0047] [Evaluation Methodology] The following analysis is performed on the metal content of the raw materials, the determination of the hydroxyl valence of aromatic polyesters, the determination of the composition and chain length of thermoplastic copolyesters, the reduction viscosity, melting point and heat of fusion, and the assessment of the weight loss rate caused by enzyme decomposition.

[0048] (Metal content analysis of raw material DMFD) Metal content was determined using a high-frequency inductively coupled plasma luminescence analyzer, SPECTROBLUE, manufactured by Hitachi Advanced Technology Co., Ltd. Approximately 1 g of sample was weighed and placed in a platinum crucible. Pre-carbonization was performed on a hot plate at 400°C. Then, carbonization was carried out at 550°C for 8 hours using a Yamato Scientific Inc. A small amount of 6.0N hydrochloric acid and hydrofluoric acid were added, and the acid was decomposed on the hot plate. After confirming acid volatilization, 20 mL of 1.2N hydrochloric acid was used to bring the volume to a final volume. The elemental concentration in the resulting solution was measured, and the elemental content in the sample was calculated.

[0049] (The hydroxyl valence of aromatic polyesters, the composition of copolyesters, and the chain length of aromatic polyester structural units) The determination of the hydroxyl valence of aromatic polyesters, the composition of copolyesters, and the chain length of aromatic polyester structural units was performed using a 400 MHz NMR apparatus with H-NMR. A mixed solution of dichloroform / ditrifluoroacetic acid / dipyridine (mass ratio 10 / 88 / 2) was used as the solvent. The chain length of the aromatic polyester structural units was expressed with decimals rounded to the nearest hundredth.

[0050] (Reduced viscosity) Dissolve 0.1 g of the sample in 25 mL of a mixed solvent of phenol / tetrachloroethane (mass ratio 6 / 4) and measure the viscosity at 30 °C using an Ubbelohde viscometer.

[0051] (Melting point, heat of fusion) A differential scanning calorimeter (DSC7020) manufactured by Hitachi Advanced Technology Co., Ltd. was used. 5.0 mg of copolyester sample was placed in an aluminum pan, sealed with a cap, and heated from 20°C to 250°C at a rate of 20°C / min, held for 2 minutes to allow the sample to completely melt. Next, it was cooled to -50°C at a rate of 20°C / min, held for 2 minutes, and then heated again to 250°C at a rate of 20°C / min. The melting point and heat of fusion were calculated from the endothermic peak of the thermal analysis curve obtained during the second heating.

[0052] (Preparation of thin films for tensile properties) Using a benchtop hot press "SA-302" manufactured by Tester Industrial Co., Ltd., films were prepared from the copolyesters of the examples and comparative examples. A 0.3 mm thick mold frame was placed between two Teflon (registered trademark) sheets, and the sample was placed inside. Two stainless steel plates were then used to clamp the Teflon (registered trademark) sheets, and the press was placed on the hot press. The samples were melted at approximately +30°C (the melting point of each polyester) for 2 minutes (6 minutes for PBTCL only), followed by an application of a 30 MPa load and a 1-minute resting period. The films were then cooled with pure water to produce an evaluation film with a thickness of 0.2 mm.

[0053] (Tensive properties [elastic modulus, elongation at break]) A tensile testing machine "TG-2kN" manufactured by MinebeaMitsumi Co., Ltd. was used. A 0.2mm thick evaluation film was punched into 10mm x 50mm dimensions, with the 50mm length direction defined as the tensile direction. The film was placed on the tensile testing machine with a 20mm distance between the clamps, and the test was performed at a tensile speed of 300mm / min. The test was conducted three times, and the average of the modulus of elasticity and elongation at break was used.

[0054] (Enzyme activity assay) The enzyme decomposition assay used a commercially available keratinase solution, Novozym (registered trademark) 51032 (manufactured by Strem Chemicals), from Humicola insolens. Enzyme activity was determined using p-nitrophenyl butyrate (pNPB) as the matrix. The hydrolysis of pNPB produces 1-butyric acid and p-nitrophenol (pNP), and the concentration was determined by tracking the absorbance change at the maximum absorption wavelength of pNP, 400 nm. Buffer A for activity assay was a 100mM Tris-HCl buffer (pH 9.0) containing 150mM NaCl and 0.5% (v / v) Triton X-100. Matrix solution B was prepared by dissolving p-nitrobenzene butyrate (pNPB, made in Nacalai Tesque) in acetonitrile to a concentration of 50mM. Enzyme dilution solution C was prepared by diluting the aforementioned commercially available keratinase solution to the predetermined concentration using buffer A. The determination was performed at 37°C according to the composition shown in Table 1. The reaction was initiated by sequentially adding reagents and stirring in an inverted position in a 1 cm path length cuvette of a spectrophotometer (UV-2450 UV / Vis spectrophotometer, manufactured by Shimadzu Corporation), and measuring the absorbance (A 400) at 400 nm for 5 minutes. The ΔA 400 / min was calculated for both the test solution and the blank solution at the time point where the slope of the absorbance change reached its maximum. The determination was performed three times, and the average value was used to calculate the enzyme activity using Equation 1.

[0055] [Table 1] Blank Test Buffer A 3000μL 2700μL Enzyme dilution solution C - 300μL Matrix solution B 30μL 30μL total 3030μL 3030μL

[0056] [Number 1]

[0057] Here, ΔA 400 / min: absorbance difference per minute, VT: reaction volume, VE: enzyme dilution volume, ε 400: millimolecular absorptivity of pNP under the above measurement conditions (14.8 mM⁻¹ cm⁻¹, based on the literature (Biochemistry 198 2, vol. 21, pp. 6872-6879.)), l: optical path length, and df: dilution rate. Additionally, 1 U (Unit) is defined as the amount of enzyme required to hydrolyze 1 μmol of substrate (pNPB) in 1 minute.

[0058] (Enzyme decomposition test) 50 mg of the cryogenically pulverized polymer sample was weighed into a test tube, and 5 mL of 0.1 M phosphate buffer (pH 8.0, made by Fujifilm and Kodenpaku) was added. Keratinase solution was added to the test tube to achieve an enzyme concentration of 165 U, and the tube was sealed and gently stirred at 50°C for 24 hours. After the predetermined time, the reaction solution was filtered under vacuum to recover the powdered polymer. An Omnipore membrane (Merck) with a pore size of 10 μm was used as the filter. The recovered polymer was dried at room temperature to a certain weight, and the weight after decomposition was weighed. The polymer weight loss rate (wt%) was calculated using the following formula as a measure of the degree of enzyme decomposition. Weight loss rate (wt%) = [(W1 - W2) / W1] × 100 Here, W1 represents the initial weight of the polymer, and W2 represents the weight of the polymer after the enzymatic decomposition test.

[0059] The results of each assessment are shown in Table 2.

[0060] [Table 2] thermoplastic copolyester Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Example 4 Example 5 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Polymer composition [quality%] Hard chain segment PBF 62 53 43 73 67 0 59 42 73 0 0 65 PBT 0 0 0 0 0 51 0 0 0 58 41 0 soft segments PCL 38 47 57 27 33 0 41 58 27 42 59 35 PBA 0 0 0 0 0 49 0 0 0 0 0 0 Melting point [°C] 149 137 130 148 148 126 160 143 166 200 197 163 Heat of fusion [mJ / mg] twenty four 19 16 25 25 20 27 16 34 29 twenty four 30 Chain length of aromatic polyester structural units [unit] 6 5 4 7 6 2 8 5 13 9 10 7 Elastic modulus [MPa] 75 55 33 146 95 84 95 35 192 116 41 82 Elongation at break[%] 1088 1152 1470 940 952 941 687 1315 542 1286 1549 940 Enzyme decomposition - weight loss rate [wt%] 78 87 92 49 56 83 96 92 54 5 11 56 PBF: Polybutylene furanate PBT: Polybutylene terephthalate PCL: Polycaprolactone PBA: Polybutylene adipate

[0061] Compared to copolyesters outside the scope of this invention, the thermoplastic copolyester of this invention exhibits excellent enzymatic decomposition properties by comprising specific hard and soft segments, including a predetermined amount of hard segments and an aromatic polyester component composed of a dicarboxylic acid component with a furan backbone and an aliphatic diol component within the hard segments. For example, in the cases of Example 1 (62% by mass of hard segment component in the copolyester) and Comparative Example 7 (65% by mass of hard segment component in the copolyester), Example 1 showed high enzymatic decomposition properties, while Comparative Example 7 showed significantly reduced enzymatic decomposition properties. Furthermore, comparing the weight loss rate due to enzymatic decomposition in Example 1 (where the dicarboxylic acid component of the hard segment is furanyl dicarboxylic acid) with that in Comparative Example 5 (where the dicarboxylic acid component of the hard segment is terephthalic acid), the former showed particularly high enzymatic decomposition properties. Furthermore, the enzymatic decomposition properties of the thermoplastic copolyesters of the present invention (Examples 1 to 5) are approximately equal to or greater than those of Comparative Example 3 (polybutylene adipate terephthalate), which is generally known to have excellent enzymatic decomposition properties.

[0062] The thermoplastic copolyester of this invention exhibits superior heat resistance by ensuring that the average chain length of the aromatic polyester structural units is above a predetermined amount. For example, comparing Example 2 (aromatic polyester structural unit chain length of 5) with Comparative Example 3 (aromatic polyester structural unit chain length of 2, polybutylene terephthalate adipate) with the same content of rigid segments, the former has a higher melting point. Within the scope of this invention, Example 4 (aromatic polyester structural unit chain length of 8) with approximately the same content of rigid segments has a higher melting point than Example 1 (aromatic polyester structural unit chain length of 6).

[0063] Furthermore, although the elongation at break of the thermoplastic copolyester within the scope of the present invention is slightly inferior to that of Comparative Examples 5 and 6 (the dicarboxylic acid component of the hard segment is terephthalic acid), it has an elongation at break that is not inferior to that of polybutylene adipate terephthalate of Comparative Example 3, and a thermoplastic copolyester with excellent toughness can be obtained. [Potential for industrial applications]

[0064] The thermoplastic copolyester of this invention has excellent enzyme decomposition and heat resistance, and has high industrial application value.

Claims

1. A thermoplastic copolyester comprising rigid segments composed of aromatic polyester structural units and soft segments composed of aliphatic polyester structural units, characterized in that: the rigid segments in the thermoplastic copolyester are 35-63% by mass; the aromatic polyester structural units contain more than 70% by mass of aromatic polyester components composed of dicarboxylic acid components with furan skeletons and aliphatic diol components; the aliphatic polyester structural units contain more than 70% by mass of aliphatic hydroxycarboxylic acid components; the reduced viscosity is in the range of 0.5-3.5 dl / g; and the melting point is in the range of 130℃-167℃.

2. The thermoplastic copolyester of claim 1, wherein the average chain length of the aromatic polyester structural unit calculated using nuclear magnetic resonance (NMR) is in the range of 3 to 15.

3. The thermoplastic copolyester of claim 1, wherein the aliphatic diol component constituting the aromatic polyester component is 1,4-butanediol.

4. The thermoplastic copolyester of claim 1, wherein the aliphatic hydroxycarboxylic acid component is derived from any one of ε-caprolactone, δ-valerolactone, γ-butyrolactone, β-propiolactone, β-butyrolactone, and tervarolactone.

5. The thermoplastic copolyester of Request 1, in an enzymatic decomposition test using polyester decomposition enzymes, has a weight reduction rate of 70% or more.

6. A molded article comprising a thermoplastic copolyester as claimed in any one of claims 1 to 5.