Oligomer composition and method for producing the oligomer composition

Abstract

The present invention provides a composition obtained by separating and recovering components derived from PBT from a raw material containing PBT together with other polymers, while suppressing the inclusion of components derived from other polymers, and a method for obtaining such a composition. [Solution] The oligomer composition contains a butylene terephthalate (BT) oligomer terminated at both ends with 1,4-butanediol (14BD), and does not contain PA, PET, or their decomposition products in amounts detectable by infrared absorption spectroscopy. The manufacturing method also includes a first separation step of heating the raw material mixture in 14BD at a first temperature above the dissolution start point of PA and below the dissolution start point of PBT to separate insoluble matter; a second separation step of heating the insoluble matter obtained in the first separation step in 14BD at a second temperature above the dissolution start point of PBT and below the dissolution start point of PET to separate dissolved and separated components; and a solvent removal step of removing the solvent from the dissolved and separated components obtained in the second separation step.

Description

[Technical Field]

[0001] This disclosure relates to oligomer compositions and methods for producing oligomer compositions. [Background technology]

[0002] Wire harnesses used in automobiles and other vehicles utilize many polymers as insulation for the wires, connector housings, and outer coverings. From the perspective of a circular economy, it is desirable to recover and recycle polymers from discarded wire harnesses. However, since wire harnesses are composed of a wide variety of polymers, it is important to separate these polymers by type in order to effectively carry out recycling.

[0003] One method for separating a specific polymer from a raw material containing multiple types of polymers is to chemically decompose the polymer of interest and elute it into the liquid phase. For example, Patent Document 1 discloses a process comprising the steps of: depolymerizing a first polymer containing polyethylene terephthalate with 1,4-butanediol in the presence of at least one second polymer composed of polyvinyl chloride, polyvinylidene chloride, polyamide, polylactic acid, and combinations thereof to produce a molten mixture; and polymerizing the molten mixture under conditions sufficient for the formation of a modified polybutylene terephthalate copolymer. The resulting modified polybutylene terephthalate copolymer will contain polyethylene terephthalate component residues and residues of the second polymer or residues derived from the second polymer. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Special Publication No. 2012-514111 [Overview of the project] [Problems that the invention aims to solve]

[0005] Polybutylene terephthalate (PBT) is one of the polymer species widely used in polymer materials that make up wire harnesses and other components, and it is desirable to separate it from other polymer components for recycling. Polyesters such as polybutylene terephthalate (PBT) and polyethylene phthalate (PET) can be depolymerized and eluted into the liquid phase using polyhydric alcohols such as 1,4-butanediol or alkaline aqueous solutions, as described in Patent Document 1. However, methods for separating and recovering PBT from polymers other than polyester, such as polyamides, or from other types of polyester, such as PET, are not common. In Patent Document 1, a PBT copolymer is obtained as the recovered product, but this PBT copolymer uses PET as the ester source, not PBT itself. However, PBT accounts for a large proportion of polymer-based waste, including wire harness waste, and it is expected that being able to separate and recover PBT as is, or in the form of PBT decomposition products, would greatly contribute to the recycling of polymer materials.

[0006] Furthermore, in Patent Document 1, the PBT component is not obtained in the form of a homopolymer or other form containing only the PBT backbone unit, but rather as a copolymer containing both the PBT component and a second polymer or derivative thereof, such as polyvinyl chloride or polyamide. However, when the recovered material is reused after further polymerization, etc., it is preferable to recover the polymer component in a state containing only the backbone unit of the target polymer, from the viewpoint of ease of reuse and control of the structure of the reused product. For example, when recovering PBT from waste containing multiple polymers, it is preferable to recover PBT or its derivatives alone, by minimizing copolymerization or mixing with other polymers or their derivatives.

[0007] In view of the above, the objective is to provide a composition obtained by separating and recovering components derived from polybutylene terephthalate from a raw material containing polybutylene terephthalate together with other polymers, while suppressing the inclusion of components derived from other polymers, and a method for obtaining such a composition. [Means for solving the problem]

[0008] The oligomer composition according to this disclosure comprises a butylene terephthalate oligomer terminated at both ends with 1,4-butanediol, and does not contain polyamide, polyethylene terephthalate or its degradation products in amounts detectable by infrared absorption spectroscopy.

[0009] A method for producing an oligomer composition according to this disclosure includes: a first separation step of heating a raw material mixture containing a polyester containing polybutylene terephthalate and a polyamide in 1,4-butanediol at a first temperature above the temperature at which the polyamide begins to dissolve and below the temperature at which the polybutylene terephthalate begins to dissolve, thereby separating insoluble matter; a second separation step of heating the insoluble matter obtained in the first separation step in 1,4-butanediol at a second temperature above the temperature at which the polybutylene terephthalate begins to dissolve and below the temperature at which polyethylene terephthalate begins to dissolve, thereby separating the dissolved and separated components; and a solvent removal step of removing the solvent from the dissolved and separated components obtained in the second separation step to obtain an oligomer composition containing a butylene terephthalate oligomer. [Effects of the Invention]

[0010] The oligomer composition according to this disclosure is obtained by separating and recovering the component derived from polybutylene terephthalate from a raw material containing polybutylene terephthalate together with other polymers, while suppressing the inclusion of components derived from other polymers. Furthermore, the method for producing the oligomer composition according to this disclosure is a method for obtaining such a composition. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a flowchart illustrating a method for producing an oligomer composition according to one embodiment of the present disclosure. [Figure 2]Figures 2A and 2B are diagrams explaining the mechanism of dissolution in 1,4-butanediol for PBT and PA, respectively. [Figure 3] Figure 3 shows the DSC curves for PA6, PA66, PBT, and PET. [Figure 4] Figure 4 shows the IR spectra of the products obtained from the second dissolution isolate together with various polymers as reference samples. [Figure 5] Figure 5 shows the molecular weight distribution of the products obtained from the second dissolution isolate together with PBT. [Figure 6] Figure 6 shows and displays the IR spectra of the products obtained from the second dissolution isolate together with PBT and alkali depolymerized oligomers as reference samples. [Figure 7] Figures 7A and 7B are micrographs of the gel状物 obtained in the second separation step, observing different regions respectively. Figure 7C is a micrograph of carbon coloring agent added PBT as a reference sample. [Figure 8] Figure 8A shows the IR spectra of the dissolution isolates obtained in various dissolution separation steps together with reference samples. Figure 8B shows the IR spectra of various components of the second insoluble matter together with reference samples. [Figure 9] Figure 9 shows the DSC curves of the dissolution isolates obtained in various dissolution separation steps together with various reference samples.

Embodiments for Carrying Out the Invention

[0012] [Description of Embodiments of the Present Disclosure] First, the embodiments of the present disclosure will be listed and described. The oligomer composition and the method for producing the oligomer composition according to the present disclosure have the following configurations.

[0013] [1] The oligomer composition according to the present disclosure comprises a butylene terephthalate oligomer terminated at both ends with 1,4-butanediol, and does not contain polyamide, polyethylene terephthalate or its degradation products in amounts detectable by infrared absorption spectroscopy.

[0014] The oligomer composition according to this disclosure contains a butylene terephthalate oligomer terminated at both ends with 1,4-butanediol, and does not contain polyamide, polyethylene terephthalate or its decomposition products. Therefore, it can be easily used as a well-controlled butylene terephthalate (BT) oligomer source with minimal contamination from other components. For example, PBT can be obtained by homopolymerizing the oligomer composition using it as a polymerization raw material. This oligomer composition can be easily obtained by separating PBT from other polymers by performing a two-step heat treatment using 1,4-butanediol on a raw material containing PBT together with other polymers, such as waste, at a predetermined temperature, as described in the method for producing the oligomer composition according to this disclosure. Therefore, the oligomer composition according to this disclosure allows for the easy separation and recovery of PBT-derived components from a raw material containing multiple types of polymers, while suppressing contamination from components derived from other polymers, and can be used for PBT recycling.

[0015] [2] In the embodiment of [1] above, the butylene terephthalate oligomer preferably has a number average molecular weight of 1000 or less and a molecular weight polydispersity of 1.5 or less. When the oligomer composition according to this embodiment is produced by heat treatment with 1,4-butanediol on a raw material containing PBT, a BT oligomer with a low degree of polymerization and a well-uniform degree of polymerization is obtained as the depolymerization product of PBT. In other words, a BT oligomer with a low number average molecular weight and a low molecular weight polydispersity is easily obtained as described above. Thus, an oligomer composition containing a BT oligomer with a low degree of polymerization and a well-uniform degree of polymerization is easily usable as a polymerization raw material for PBT, etc.

[0016] [3] In the embodiments of [1] or [2] above, the oligomer composition may further contain at least one of a colorant and glass fibers. Colorants and glass fibers are additives that are often added to polymer materials that constitute wire harnesses, and are readily incorporated into the oligomer composition when it is produced from wire harness waste as a raw material through heat treatment with 1,4-butanediol. Therefore, the presence of at least one of a colorant and glass fibers in the oligomer composition indicates that the oligomer composition was obtained from wire harness waste as a raw material.

[0017] [4] In any of the embodiments described in [1] to [3] above, the butylene terephthalate oligomer may be obtained by depolymerizing polybutylene terephthalate with 1,4-butanediol. By heating and depolymerizing PBT in 1,4-butanediol, an oligomer composition containing a BT oligomer can be easily obtained. By appropriately setting the heating temperature, even if a raw material containing other polymers in addition to PBT is used, the PBT can be separated from the other polymer components, selectively depolymerized, and recovered. The BT oligomer obtained by depolymerizing PBT using 1,4-butanediol is terminated at both ends with 1,4-butanediol, and tends to have a relatively low degree of polymerization and a narrow distribution of the degree of polymerization.

[0018] [5] In the embodiment described in [4] above, the oligomer composition may be obtained by heating a raw material derived from wire harness waste containing polybutylene terephthalate in 1,4-butanediol at a temperature above the temperature at which polyamide begins to dissolve and below the temperature at which polybutylene terephthalate begins to dissolve, separating the insoluble material, and then heating the insoluble material in 1,4-butanediol at a temperature above the temperature at which polybutylene terephthalate begins to dissolve and below the temperature at which polyethylene terephthalate begins to dissolve, separating the dissolved components, and then removing the solvent. Wire harness waste often contains polyethylene terephthalate (PET) and polyamide (PA) in addition to PBT. However, as will be explained in detail later, in relation to the dissolution mechanisms and molecular structures of PBT, PET, and PA, the temperatures at which dissolution in 1,4-butanediol begins are, from lowest to highest, PA, PBT, and then PET. Therefore, by setting the heating temperature as described above and performing a two-stage heat treatment with 1,4-butanediol on the raw material derived from wire harness waste, the BT oligomer can be separated and recovered from PA and PET as a component dissolved and separated in the second stage. The fact that the oligomer composition obtained in this way is derived from raw material derived from wire harness waste can be confirmed, for example, by the presence of additives added to the polymer material constituting the wire harness, such as colorants and glass fibers.

[0019] [6] A method for producing an oligomer composition according to the present disclosure includes: a first separation step of heating a raw material mixture containing a polyester containing polybutylene terephthalate and a polyamide in 1,4-butanediol at a first temperature above the temperature at which the polyamide begins to dissolve and below the temperature at which the polybutylene terephthalate begins to dissolve, thereby separating insoluble matter; a second separation step of heating the insoluble matter obtained in the first separation step in 1,4-butanediol at a second temperature above the temperature at which the polybutylene terephthalate begins to dissolve and below the temperature at which polyethylene terephthalate begins to dissolve, thereby separating dissolved and separated components; and a solvent removal step of removing the solvent from the dissolved and separated components obtained in the second separation step to obtain an oligomer composition containing a butylene terephthalate oligomer.

[0020] In the method for producing the oligomer composition according to this disclosure, due to differences in dissolution mechanisms, PA dissolves in 1,4-butanediol at a lower temperature than PBT. Therefore, by going through the first separation step, a composition containing PBT as an insoluble substance but not PA can be obtained. Furthermore, due to differences in molecular structure, PBT dissolves in 1,4-butanediol at a lower temperature than PET. Therefore, by performing the second separation step at a second temperature on the insoluble substance obtained in the first separation step, even if PET is contained in the raw material mixture, a composition can be obtained that contains PBT as a component dissolved and separated in 1,4-butanediol, but not PET or other components that do not dissolve in 1,4-butanediol at the second temperature. In this way, by performing the treatment with 1,4-butanediol in two stages, even if PA or PET is contained in the raw material mixture, an oligomer composition containing BT oligomers can be easily obtained while suppressing the inclusion of polymer components other than PBT.

[0021] By performing the heat treatment involving the depolymerization of PBT using 1,4-butanediol, unlike when using alkaline aqueous solutions or other alcohols, the BT oligomers formed by the depolymerization of PBT are terminated at both ends with 1,4-butanediol, a component of PBT, and the BT oligomers are composed only of the same unit structures as those contained in PBT. Therefore, the obtained oligomer composition can be suitably used as a polymerization raw material for newly constructing PBT through polymerization. Furthermore, the BT oligomers obtained by the depolymerization of PBT using 1,4-butanediol tend to have a relatively low degree of polymerization and a narrow distribution of the degree of polymerization, which also enhances the suitability of the obtained oligomer composition when used as a new polymerization raw material. Compared to solvents that cause PBT depolymerization by hydrolysis, such as alkaline aqueous solutions, 1,4-butanediol is also superior in that it is easy to remove in the solvent removal process and is highly safe.

[0022] [7] In the embodiment of [6] above, the raw material mixture may further contain polyethylene terephthalate as the polyester. As described above, in the method for producing the oligomer composition according to the present disclosure, by performing the second step on the composition from which PA has been removed in the first separation step, the BT oligomer can be recovered by separating it from PET using the difference in the dissolution start temperatures of PBT and PET. In this way, even when a raw material mixture containing both esters, PBT and PET, is used, the two esters can be easily separated.

[0023] [8] In the embodiments of [6] or [7] above, the raw material mixture may be derived from wire harness waste. Wire harness waste contains a large amount of PBT, and by separating and recovering PBT in the form of oligomers, the recycling of wire harness waste can be efficiently promoted. Wire harness waste often contains PA and PET in addition to PBT, but as described above, by performing heat treatment in 1,4-butanediol in two stages, the first separation step and the second separation step, BT oligomers can be separated and recovered from PA and PET.

[0024] [9] In any of the embodiments described in [6] to [8] above, the first temperature is preferably 160°C or more and less than 185°C, and the second temperature is preferably 185°C or more and less than 205°C. Then, after the first and second separation steps, the BT oligomer is separated from PA and PET with high efficiency, and an oligomer composition with reduced contamination of components derived from PA and PET can be easily obtained.

[0025] [Details of the embodiments of this disclosure] An oligomer composition and a method for producing the oligomer composition according to embodiments of this disclosure will be described below with reference to the drawings.

[0026] [1] Outline of the oligomer composition An oligomer composition according to one embodiment of the present disclosure contains a butylene terephthalate oligomer. A butylene terephthalate (BT) oligomer is an oligomer having a structure in which multiple butylene terephthalate units, that is, structural units in which 1,4-butanediol and terephthalic acid are ester-bonded, are linked together via ester bonds. Here, the number of repeating units in the oligomer, i.e., the degree of polymerization, is generally recognized as being between 2 and 100 or less. However, as will be explained in detail later, the degree of polymerization corresponding to a preferred molecular weight range is small within that range, generally between 25 and 100.

[0027] The BT oligomer constituting the oligomer composition according to this embodiment is terminated at both ends by alcohols. That is, alcohol molecules are bonded to both ends. Preferably, both ends are terminated with 1,4-butanediol. In this case, the structure of the BT oligomer, in which 1,4-butanediol and terephthalic acid are alternately bonded via ester bonds, is closed at both ends by 1,4-butanediol. That is, the functional groups at both ends are 4-hydroxybutoxy groups.

[0028] The oligomer composition according to this embodiment may consist solely of BT oligomers, excluding unavoidable impurities, but may also contain components other than BT oligomers. However, it is preferable that the oligomer composition does not contain polyamide (PA), excluding unavoidable impurities. Furthermore, it is preferable that the oligomer composition does not contain polyethylene terephthalate (PET) and its decomposition products, excluding unavoidable impurities. The absence of a certain polymer species or component derived from a polymer species, excluding unavoidable impurities, means, for example, that it is not present in an amount detectable by infrared absorption spectroscopy (IR). IR measurement is performed, for example, using powder total reflection attenuation (ATR method) at 4 cm². -1 This resolution should be sufficient.

[0029] It is preferable that the oligomer composition does not contain components derived from PA and PET, except for unavoidable impurities, whether as components mixed with BT oligomers or as components that bind to BT oligomers, such as through copolymerization or side chain formation. Similarly, it is preferable that the oligomer composition does not contain components derived from polyvinyl chloride (PVC), or from polyolefins such as polyethylene (PE) and polypropylene (PP), except for unavoidable impurities. On the other hand, the oligomer composition often contains at least one of a colorant and glass fibers, as derived from the manufacturing method described below. Further details of the oligomer composition's composition will be explained after the manufacturing method.

[0030] [2] Method for producing oligomer composition The above-mentioned oligomer composition can be suitably produced by the method for producing the oligomer composition according to the embodiment of this disclosure. The method for producing the oligomer composition according to one embodiment of this disclosure will be described below.

[0031] The flowchart in Figure 1 outlines the method for producing the oligomer composition according to this embodiment. In this production method, as shown in Figure 1, the first separation step, the second separation step, and the solvent removal step are carried out in that order on the raw material mixture to obtain the oligomer composition.

[0032] The raw material mixture used as a raw material for the oligomer composition is composed of a material containing polyester including PBT and PA. The polyester may consist solely of PBT, or PBT plus other polyesters; however, it is preferable that polyethylene terephthalate (PET) is included in addition to PBT. A raw material mixture derived from wire harness waste can be suitably used as a polymer mixture containing PBT, PA, and often PET. Wire harnesses consist of electric wires, connectors, and accessories such as tape. During the disposal process, metal materials such as wire conductors and connector terminals are removed, and the material is discharged as a mixture of various polymers. It is preferable to crush the discharged material into nugget-like shapes as appropriate and utilize it as a raw material mixture. In wire harnesses, PBT is widely used in connector housings, PA in clamps, and PET in nonwoven fabrics as outer coverings. Wire harness waste often contains PVC and polyolefins such as PE and PP, in addition to PBT, PA, and PE as polymers.

[0033] In the manufacturing method according to this embodiment, a first separation step and a second separation step are performed on the above raw material mixture. In both of these separation steps, the materials are heated in a polyhydric alcohol such as 1,4-butanediol (14BD), but this heating treatment is carried out in two stages at different heating temperatures. In relation to these heating temperatures, the dissolution of each polymer in 14BD will first be explained.

[0034] As will be shown in detail in later examples, Figure 3 shows the DSC curves obtained when differential scanning calorimetry (DSC) was performed on two types of PA, nylon 6 (PA6) and nylon 6,6 (PA66), PBT, and PET in a sealed aluminum pan while heating in 14BD. In the DSC curve, the peak appearing in the negative direction represents endothermic activity, which corresponds to the dissolution of the polymer in 14BD. In Figure 3, the temperature at which dissolution begins (dissolution initiation point) is indicated by arrows. According to Figure 3, the dissolution initiation point differs depending on the polymer type: 125°C for PA6, 158°C for PA66, 185°C for PBT, and 205°C for PET. The two types of PA begin to dissolve at relatively low temperatures, and then gradually dissolve as the temperature rises, while the polyesters PBT and PET begin to dissolve at higher temperatures than the PAs, and dissolution proceeds rapidly as the temperature rises.

[0035] These differences in the dissolution initiation point and subsequent dissolution progression are due to differences in the dissolution mechanism. Figure 2A schematically shows the dissolution mechanism for PBT, and Figure 2B shows the dissolution mechanism for PA. First, for PA shown in Figure 2B, dissolution in alcohols such as 14BD proceeds by solvation without decomposition (depolymerization) of the polymer chains. In the solvation process, hydrogen bonds formed between polymer chains are replaced by hydrogen bonds between the amide bond portion of each polymer chain and the alcohol molecule, and the crystalline structure of the polymer chain is resolved. Thus, dissolution without depolymerization proceeds from relatively low temperatures. It also proceeds slowly over a wide temperature range. On the other hand, for PBT shown in Figure 2A, dissolution in alcohols such as 14BD proceeds with decomposition of the polymer chains by depolymerization. Depolymerization occurs through transesterification between ester bonds in the polymer chain and alcohol molecules. Depolymerization leads to the depolymerization of PBT, and BT oligomers are generated. The generated BT oligomers dissolve in alcohol. Thus, dissolution accompanied by depolymerization does not begin until heated to relatively high temperatures, and proceeds rapidly within a narrow temperature range. PET also dissolves through a mechanism involving depolymerization similar to that of PBT. However, the dissolution initiation points of PBT and PET differ, corresponding to differences in their molecular structures. Specifically, PET has a higher glass transition temperature than PBT, and its dissolution initiation point due to depolymerization is also higher.

[0036] As described above, the dissolution initiation temperatures when heated in polyhydric alcohols are in the order of PA, PBT, and PET, from lowest to highest. PVC and polyolefins such as PP and PE are almost insoluble in polyhydric alcohols at temperatures at which PET dissolves. By utilizing these differences in dissolution initiation points, polymers can be separated by type.

[0037] As shown in Figure 1, in the first separation step, the raw material mixture is heated in a polyhydric alcohol at a first temperature. The first temperature is set to be above the dissolution point of PA and below the dissolution point of PBT. When 14BD is used as the polyhydric alcohol, the first temperature should be 160°C or higher and less than 185°C. More preferably, it should be 170°C or higher and less than 180°C. Because the first temperature is above the dissolution point of PA, in the first separation step, the PA in the raw material mixture dissolves in the polyhydric alcohol and is incorporated into the liquid phase. On the other hand, because the first temperature is below the dissolution point of PBT, the PBT and PET in the raw material mixture do not dissolve in the polyhydric alcohol and remain as insoluble matter. Therefore, in the first separation step, after sufficient dissolution of PA has occurred, the insoluble matter is separated from the liquid phase (which may be gel-like) and separated. This allows us to obtain a material containing PBT from which PA has been separated and removed. This insoluble matter is referred to as the first insoluble matter.

[0038] The specific operation in the first separation step involves mixing the raw material mixture with the polyhydric alcohol and heating and stirring at the first temperature. The heating and stirring time can be exemplified as 5 to 30 minutes. After heating and stirring, water or other liquid can be added as needed, and then the mixture can be filtered to separate the insoluble matter. The first dissolved and separated product, which is the liquid phase component separated from the insoluble matter, is not used in the subsequent production of the oligomer composition, but it contains PA at a high concentration.

[0039] Next, in the second separation step, the first insoluble material obtained in the first separation step is heated in a polyhydric alcohol at a second temperature higher than the first temperature. The second temperature is set to be above the dissolution start point of PBT and below the dissolution start point of PET. When 14BD is used as the polyhydric alcohol, the second temperature should be 185°C or higher and less than 205°C. More preferably, it should be 190°C or higher and less than 200°C. Because the second temperature is above the dissolution start point of PBT, in the second separation step, the PBT in the first insoluble material dissolves in the polyhydric alcohol and is incorporated into the liquid phase. On the other hand, because the second temperature is below the dissolution start point of PET, the PET in the first insoluble material does not dissolve in the polyhydric alcohol and remains as an insoluble material. Therefore, in the second separation step, after sufficient dissolution of PBT has occurred, it is separated from the insoluble material, and the dissolved and separated components of the liquid phase (which may also be gel-like) are separated. This allows us to obtain a dissolved and separated product in which PET has been separated and PBT has dissolved. This dissolved and separated product is called the second separation step product.

[0040] In the second separation step, the specific procedure is the same as in the first separation step: the first insoluble substance and the polyhydric alcohol are mixed and heated and stirred at the second temperature. The heating and stirring time can be exemplified as 5 to 30 minutes. After heating and stirring, water or other liquid can be added as needed, and the dissolved separated product can be separated by filtration.

[0041] As shown in Figure 2A, the PBT component dissolved in the polyhydric alcohol as the second dissolution separation product undergoes depolymerization, i.e., transesterification and depolymerization, upon dissolution, resulting in a BT oligomer. In this process, the BT oligomer produced by depolymerization in the polyhydric alcohol has alcohol termini at both ends and, excluding unavoidable impurities, does not have carboxylic acid termini. When 14BD is used as the polyhydric alcohol, both ends are terminated with 14BD. In other words, the functional groups at both ends are 4-hydroxybutoxy groups. The second insoluble product, which is the insoluble material separated from the second dissolution separation product, is not used in the subsequent production of the oligomer composition, but it contains components that do not dissolve at least at the second temperature, such as PVC and polyolefins, in addition to PET.

[0042] In the manufacturing method according to this embodiment, a solvent removal step is performed last. In the solvent removal step, the solvent is removed from the second dissolved separated product obtained in the second separation step. The solvent can be removed, for example, by vacuum distillation. By removing the solvent, the BT oligomer that was separated as the second dissolved separated product is recovered as a solid (powdered) oligomer composition.

[0043] In the manufacturing method according to this embodiment, as described above, by utilizing the difference in the dissolution start temperature of each polymer species in polyhydric alcohol, PBT can be separated and recovered from a raw material mixture containing multiple polymer species, separate from other polymers such as PA and PET. This allows PBT to be recovered from a raw material mixture derived from wire harness waste and used for recycling. In this case, since PBT is recovered in the form of BT oligomers, it can be reused by, for example, polymerizing it again to produce PBT. In the manufacturing method according to this embodiment, the separation and recovery of PBT can be performed in just two steps: heating the material in a polyhydric alcohol and separating the product. After removing the solvent, an oligomer composition containing BT oligomers can be easily obtained while suppressing the contamination of components derived from polymer species other than PBT. Polyhydric alcohols such as 14BD are also excellent in terms of handling safety and ease of removal from the product. Depolymerization of PBT can also be performed by hydrolysis using an alkaline aqueous solution, but in that case, handling the alkaline aqueous solution may be dangerous, and separation from the product is also time-consuming. Furthermore, the polyhydric alcohols used in the two separation steps can be reused by recovering them through distillation as needed.

[0044] [Details of the oligomer composition to be manufactured] As already stated, the oligomer composition according to one embodiment of this disclosure contains a BT oligomer and has a distinctive structure because it is obtained by a manufacturing method that includes a first separation step and a second separation step by heating in a polyhydric alcohol. First, since the PBT in the mixed raw materials is recovered in the form of a BT oligomer directly formed by depolymerization using a polyhydric alcohol, the PBT-derived recovered product does not contain unit structures derived from components other than PBT, except for the bonding of the polyhydric alcohol to the terminal part of the oligomer. Therefore, the recovered BT oligomer composition can be used simply and with high controllability as a raw material for a new product containing BT units. In particular, when 14BD is used as the polyhydric alcohol, both ends of the BT oligomer are terminated with 14BD, and the oligomer chain does not contain any elements other than the same unit structures that constitute PBT. Therefore, the obtained oligomer composition can be suitably used for the regeneration of PBT by polymerization.

[0045] Furthermore, the BT oligomers constituting the oligomer composition according to this embodiment are obtained by the depolymerization of PBT with polyhydric alcohols, and are therefore relatively low molecular weight oligomers. Specifically, the number-average molecular weight (Mn) tends to be 5000 or less, and particularly 1000 or less. The formula weight of the structural unit in PBT, i.e., the BT unit, is 220, and the above number-average molecular weight corresponds to a degree of polymerization of approximately 22 or less, and particularly approximately 5 or less. There is no particular lower limit set for the number-average molecular weight, but it is generally 400 or more. In addition, the obtained BT oligomers have a narrow molecular weight distribution. Specifically, the polydispersity of molecular weight (Mw / Mn) tends to be 2.0 or less, and particularly 1.5 or less. Here, the polydispersity (Mw / Mn) is determined as the ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn), and a larger value indicates a wider molecular weight distribution. There is no particular lower limit set for the polydispersity, but a value closer to 1.0 is preferable. Thus, the relatively low molecular weight of the resulting BT oligomers increases their convenience when used as raw materials for repolymerization. Furthermore, the narrow molecular weight distribution enhances the uniformity of the oligomer composition's physical properties and reactivity, making it easier to control the structure of recycled products obtained through repolymerization. Polymeric waste, such as that derived from wire harnesses, may contain various PBT materials with different degrees of polymerization. Even in such cases, a BT oligomer with a narrow molecular weight distribution can be obtained as an oligomer composition, thereby significantly increasing its suitability as a raw material for repolymerization.

[0046] Furthermore, in the above manufacturing method, PBT is selectively dissolved and separated by utilizing the differences in the dissolution initiation points of each polymer species in polyhydric alcohol. Therefore, the resulting oligomer composition can minimize the inclusion of other polymers, including PA and PET, as well as components derived from these other polymers, such as decomposition products, into the BT oligomer. As shown in later examples, it is also possible to obtain a BT oligomer that does not contain PA, PET, or PET decomposition products, except for unavoidable impurities. In this way, by suppressing the inclusion of components derived from polymers other than PBT, when the obtained oligomer composition is recycled by repolymerization or the like, the influence of components derived from other polymers can be suppressed, and a well-controlled product can be obtained.

[0047] When materials derived from wire harness waste are used as raw materials for the production of oligomer compositions, fine solid additives that were added to the constituent materials of the wire harness may be incorporated into the oligomer composition without being completely separated or removed. Examples of such additives include colorants (pigments) such as carbon colorants, reinforcing fillers such as glass fibers, and stabilizers such as hydrotalcite. Reinforcing fillers such as glass fibers are large in size and can be easily removed as needed, but colorants such as carbon are small in particle size and are difficult to remove, and tend to remain in the oligomer composition. If additives such as colorants remain in the oligomer composition, the oligomer composition may appear colored rather than white. However, the effects of these components are limited, especially when the oligomer composition is reused as a raw material for wire harnesses. [Examples]

[0048] Examples are shown below. The present invention is not limited to these examples. Unless otherwise specified, sample preparation and evaluation were carried out at room temperature in air.

[0049] [1] Confirmation of the dissolution initiation point of various polymer components First, as basic information for setting the manufacturing conditions for BT oligomers, we confirmed the dissolution initiation point for various polymers when they dissolve in 14BD.

[0050] <Testing Method> Four types of polymers—PA6, PA66, PBT, and PET—were prepared in the form of resin pieces (5 mg each). These were sealed in a lidded aluminum pan with 5 μL of 14BD (a type of nitrate) and heated. Differential scanning calorimetry (DSC) was performed using a differential scanning calorimeter while heating. The heating rate was set to 10°C / min.

[0051] <Test Results> Figure 3 shows the DSC curves obtained for each polymer. Endothermic peaks appear for all polymers, and these peaks correspond to dissolution in 14BD. The dissolution initiation point is indicated by an arrow in the figure, representing the temperature at which the endothermic peak begins to appear (the temperature at which the DSC curve begins to rise in the endothermic direction).

[0052] The dissolution initiation points are 125°C for PA6, 158°C for PA66, 185°C for PBT, and 205°C for PET, with PA6 and PA66 showing significantly lower initiation points than PBT and PET. Furthermore, in PA6 and PA66, endothermic reactions proceed gradually, whereas in PBT and PET, endothermic reactions proceed rapidly after passing the dissolution initiation point. These differences in dissolution initiation points and the shapes of the endothermic peaks corresponding to dissolution correspond, as explained above, to the fact that dissolution to 14BD proceeds by solvation without decomposition of polymer chains in the case of PA, while in the case of PBT and PET, it proceeds with depolymerization by 14BD.

[0053] Since the dissolution initiation points of PA, PBT, and PET appear at sufficiently distant temperatures in this order from low temperatures, it is shown that PBT can be separated and recovered from PA and PET by mixing a raw material mixture containing PA, PBT, and PET with 14BD and heating it under controlled temperature. Specifically, the raw material mixture is heated with 14BD at a first temperature of 160°C to less than 185°C, which is above the dissolution initiation point of PA and below the dissolution initiation point of PBT, and the insoluble material is separated. Then, this insoluble material is heated with 14BD at a second temperature of 185°C to less than 205°C, which is above the dissolution initiation point of PBT and below the dissolution initiation point of PET, and the dissolved and separated material is separated. This shows that the depolymerization product of PBT can be separated from PA and PET.

[0054] [2] Identification of product species Next, in the method for producing the oligomer composition according to the embodiment of the present disclosure described above, the product obtained from the second dissolved separation product was identified.

[0055] <Testing Method> (1) Implementation of the manufacturing process As described in detail above, a method for producing an oligomer composition according to an embodiment of the present disclosure, including a first separation step, a second separation step, and a solvent removal step, was carried out. In this case, 20 g of resin nuggets obtained by grinding wire harness waste after removing the metal material was used as the raw material mixture. The first and second separation steps were carried out using 14BD. The heating temperature in the first separation step (first temperature) was set to 175°C, and the heating temperature in the second separation step (second temperature) was set to 195°C. In both the first and second separation steps, the solid material was mixed with 60 mL of 14BD and heated and stirred at the above-specified temperatures for 15 minutes. After the heating and stirring of the second separation step was completed, a gel-like substance was obtained. This gel-like substance was added to an excess amount of pure water, stirred, and then filtered to obtain the second dissolved separation product as a filtrate. Furthermore, a solvent removal step was carried out on the filtrate by vacuum distillation to remove 14BD. The obtained product was dried to obtain a light gray powder. This powder was subjected to analysis as the product.

[0056] (2) Analysis of the product The products obtained above were measured using infrared absorption spectroscopy (IR). IR measurements were performed using powder total reflection decay (ATR) spectroscopy with Fourier transform infrared spectroscopy (FT-IR). The measurement resolution was 4 cm. -1 The same measurements were also performed on individual samples of PBT, PET, PVC, PP, and PA66 as reference samples. In subsequent tests, IR measurements were performed using the same method as described above.

[0057] The molecular weight distribution of the products obtained above and PBT as a reference sample was evaluated. The molecular weight distribution was evaluated using gel permeation chromatography (GPC).

[0058] <Test Results> Figure 4 shows the IR spectra of the product obtained from the second dissolution separation and each reference sample. The product spectrum is at 1700 cm⁻¹. -1 A clear peak (peak A) corresponding to the C=O stretching of the ester bond is shown nearby, indicating that the product has an ester as its basic structure. Furthermore, the 1270 cm² peak corresponds to the CO stretching vibration. -1 The characteristic shape of the nearby peak (peak B), as well as the overall peak positions and shapes of the spectrum, are very similar to those of PBT alone. This indicates that the product has the same basic structure as PBT. However, the spectrum of the product contains peaks between 3500 and 3100 cm, which are almost not seen in the spectrum of PBT alone. -1 A gentle peak (peak C) appears in the vicinity. This peak can be correlated with the OH stretching vibration of the alcohol. The appearance of this peak in the product is thought to be due to the depolymerization of the product by 14BD, which increased the proportion of 14BD at the ends of the molecular chains. Based on the above IR measurement results, it can be said that the product is based on the depolymerization product of PBT.

[0059] Furthermore, the 1300 cm⁻¹ spectrum, which is unique to the PET spectrum, is also present. -1The sharp peak in the vicinity (peak D) does not appear in the product spectrum. Furthermore, the product spectrum does not show a peak at 3300 cm⁻¹. -1 Nearby peaks of NH stretching vibrations, and 1650-1550 cm -1 The product spectrum does not contain any of the peaks characteristic of PA66 alone, such as the two distinctive peaks referred to as amide I and amide II. Similarly, the product spectrum does not contain any peaks characteristic of the spectra of PVC alone or PP alone. From these findings, it can be concluded that the product does not contain PET, PA, PVC, PP, or derivatives with the same basic structure, such as degradation products, at least at levels detectable by IR spectroscopy.

[0060] Next, Figure 5 shows the molecular weight distribution (differential molecular weight distribution curve) for the product and the reference sample PBT. Table 1 below shows the parameters derived from this molecular weight distribution.

[0061] [Table 1]

[0062] As shown in Figure 5, the product has a distribution in the low molecular weight region compared to PBT. Furthermore, the molecular weight distribution of the product is narrower. This is confirmed by the fact that the number-average molecular weight (Mn) and polydispersity (Mw / Mn) values ​​in Table 1 are significantly smaller in the product compared to PBT. Converting the number-average molecular weight of the product to a degree of polymerization yields approximately 2. In other words, it is confirmed that the depolymerization product of PBT takes the form of an oligomer with a low molecular weight and a small molecular weight distribution.

[0063] From the results of the above IR measurement and molecular weight distribution measurement, it can be seen that the product obtained from the second dissolution isolate mainly consists of BT oligomers produced by the depolymerization of PBT. That is, the product is an oligomer composition mainly composed of BT oligomers. Further, it is confirmed that the BT oligomers have a low degree of polymerization and a narrow distribution width of the degree of polymerization. Also, it is confirmed that the oligomer composition does not contain polymer species other than PBT, such as PET, PA, PVC, PP, etc., and derivatives having a skeleton similar to those polymer species, such as PET decomposition products, at least at a level detectable by IR spectrum.

[0064] [3] Structure of the ends of butylene terephthalate oligomers Next, regarding the BT oligomers that were confirmed to constitute the product obtained from the second dissolution isolate in the test of [2] above, the structure of the ends was further confirmed.

[0065] <Test method> IR measurement was performed on the product obtained from the second dissolution isolate in the test of [2] above, and PBT and alkali depolymerized oligomers as reference samples. The alkali depolymerized oligomers were obtained by heating and refluxing PBT in an aqueous sodium hydroxide solution with a concentration of 2.5 mol / L at 90 °C for 2 hours, neutralizing with hydrochloric acid, and then washing with water and filtering.

[0066] <Test results> Figure 6 shows the obtained IR spectra for the product and two reference samples. Here, the spectra of only the product and PBT are the same as those shown in Figure 4. In the spectrum of the alkali depolymerized oligomers, a peak (peak E) derived from the carboxyl group of associated carboxylic acid is observed in the region of approximately 2700 - 2500 cm -1 . This is associated with the fact that during the alkali depolymerization process, hydrolysis by water molecules proceeded, and BT oligomers terminated with carboxyl groups at the ends were generated.

[0067] In contrast, the spectrum of the product, as explained in the test in [2] above, corresponds to 3500-3100 cm⁻¹, which is associated with OH stretching vibrations. -1 A gentle peak (peak C) in this region is characteristically observed. This suggests that the terminal end of the BT oligomer constituting the product is an alcohol terminal. On the other hand, the 2700-2500 cm⁻¹ corresponds to the terminal carboxyl group characteristic of alkali depolymerization oligomers. -1 The peak in this region (peak E) is not observed in the product spectrum. In other words, the PBT oligomer constituting the product does not have a carboxylic acid terminus, at least at a level detectable by the IR spectrum. From these results, it is confirmed that in the product obtained from the second dissolution separation after depolymerization of PBT using the polyhydric alcohol 14BD, both ends of the BT oligomer are alcohol terminus, not carboxylic acid terminus. This corresponds to the fact that the depolymerization of PBT proceeds by transesterification with 14BT.

[0068] [4] Additives contained in the product In the above [2] test, the product obtained from the second dissolved separation was colored light gray, suggesting that the product contains additives in addition to the BT oligomer. Therefore, we attempted to identify these additives.

[0069] <Testing Method> In the test described in [2] above, the gel-like substance obtained after heating and stirring in the second separation step was collected as a sample before mixing with pure water and filtering. The gel-like substance exhibits a darker black color than the final powder product, contains higher concentrations of the additives that will be included in the final product, and is easier to identify than the final product. The collected gel-like substance was dissolved in hexafluoro-2-propanol (HFIP) and observed using a transmission light microscope. Observations were performed in multiple regions. In addition, as a reference sample, PBT was colored black by adding a carbon colorant, and similarly dissolved in HFIP and observed under a microscope.

[0070] <Test Results> Figures 7A and 7B show microscopic images of the HFIP solution of the gel-like substance obtained in the second separation step. Figures 7A and 7B show observations of different regions of the same sample. Figure 7C shows a microscopic image of the HFIP solution of the reference sample, carbon-doped PBT.

[0071] In Figure 7A, a rod-shaped substance extending horizontally is observed near the center of the image in the vertical direction. Such a rod-shaped, translucent image is characteristic of glass fibers, and it is highly likely that glass fibers are being observed here as well. In other words, the gel-like substance can be said to contain glass fibers.

[0072] Figure 7B, which shows an observation of a different region, reveals numerous tiny black dots. Comparing the observation image in Figure 7B with the observation image of carbon-doped PBT in Figure 7C, both images show scattered tiny black dots. Therefore, it is highly likely that the black dots observed in the gel-like substance of the sample in Figure 7B are due to the carbon coloring agent.

[0073] Based on the above observations, it is considered that the gel-like substance obtained in the second separation step contains glass fibers and carbon colorants. Furthermore, it is highly probable that the powdered product obtained by processing this gel-like substance also contains similar glass fibers and carbon colorants, albeit in smaller quantities than the gel-like substance. Glass fibers and carbon colorants are commonly added as additives to polymer materials that constitute wire harnesses.

[0074] [5] Identification of polymers separated in each step Up to this point, in the method for producing the oligomer composition according to the embodiments of this disclosure, it has been confirmed that the product obtained from the second dissolved separation product is an oligomer composition containing a small amount of glass fiber and carbon colorant in a BT oligomer having an alcohol terminus. Finally, it has been confirmed what polymers are contained in the components separated in each step of the above production method, in addition to the second dissolved separation product.

[0075] <Testing Method> In the test described in [2] above, the polymers contained in the substances separated at each step during the process of carrying out the method for producing oligomer materials according to the embodiments of this disclosure were identified. Specifically, in the first and second separation steps, after heating and stirring were completed, the dissolved and insoluble products were separated. In detail, the gel-like substance obtained in each separation step was added to an excess amount of pure water, stirred, and filtered to obtain the first dissolved product and the second dissolved product, respectively, as filtrates. Furthermore, a solvent removal step was performed on each filtrate by vacuum distillation to remove 14BD. The obtained products were then dried to obtain powder samples. The powder material obtained from the first dissolved product was light brown, and the powder material obtained from the second dissolved product was light gray. The powder material obtained from the second dissolved product corresponds to the "product" analyzed in steps [2] to [4] above. Furthermore, in the second separation step, the insoluble material remaining after filtration was recovered, washed with water, and dried to obtain the second insoluble material. The resulting second insoluble material contained three types of insoluble material with different morphologies. These were separated manually and labeled as Insoluble Material 1, Insoluble Material 2, and Insoluble Material 3.

[0076] IR measurements were performed on the powder materials obtained from the first and second dissolved and separated products, as well as on insoluble materials 1, 2, and 3 obtained from the second insoluble material. In addition, the same measurements were performed on individual PBT, PET, PVC, PP, and PA66 samples as reference samples. Furthermore, IR measurements were also performed on a one-step dissolved and separated product as another reference sample. Here, a one-step dissolved and separated product refers to a dissolved and separated product obtained by performing a separation process equivalent to the second separation process (heating at the second temperature in one step) on the raw material mixture without performing the first separation process. Measurements were performed on the powder material obtained by performing the same process as the first and second dissolved and separated products described above.

[0077] Furthermore, DSC measurements were performed on the powder materials obtained from the first and second dissolved and separated products described above. Specifically, 5 mg of each powder material obtained from the first and second dissolved and separated products was placed in an aluminum pan, heated in the range of 50 to 300°C, and DSC measurements were performed. The heating rate was set to 10°C / min. The endothermic peaks obtained from this DSC measurement correspond to the melting of the polymer. In addition, DSC measurements were similarly performed on the raw material mixture before treatment and the one-step dissolved and separated product described above as reference samples. From these DSC measurements, information regarding polymer mixing and the presence or absence of a low degree of polymerization can be obtained from the number and temperature of endothermic peaks.

[0078] <Test Results> Figure 8A shows the IR spectra for the first dissolved product, the second dissolved product, the one-step dissolved product, and each of the reference samples. Figure 8B shows the IR spectra for insoluble products 1, 2, and 3, and each of the reference samples.

[0079] Looking at the spectrum of the first dissolved separation in Figure 8A, it is very close to the spectrum of PA66 alone. 3300 cm⁻¹ -1 The peak of NH stretching vibration in the vicinity (peak F), and 1650~1550cm -1Characteristic peaks of PA are also observed, including two distinctive peaks (peak G) in the vicinity, referred to as amide I and amide II. This confirms that PA is separated as a dissolved product in the first separation step. The spectrum of the second dissolved product is the same as that of the test in [2] shown in Figure 4, and as explained for the test in [2], comparison with the reference spectrum shows that PBT is separated as the second dissolved product. This PBT is a BT oligomer with alcohol terminators at both ends. The one-step dissolved product shows both the characteristic peaks of PA and the characteristic peaks of PBT, indicating that it is a mixture of PA and PBT.

[0080] Next, looking at the spectra of insoluble substances 1, 2, and 3 in Figure 8B, the spectrum of insoluble substance 1 is at 600 cm⁻¹. -1 The spectrum is similar to that of PVC alone, with a peak (peak H) of C-Cl stretching vibration visible in the vicinity. The spectrum of insoluble material 2 is at 1700 cm⁻¹. -1 Nearby are the peaks of C=O stretching of ester bonds (Peak A) and 1300 cm, which corresponds to CO stretching vibrations. -1 The spectrum is similar to that of PET alone, with a sharp peak (peak D) visible in the vicinity. The spectrum of insoluble material 3 is from 3000 to 2800 cm⁻¹. -1 The peak of the CH stretching vibration is strongly visible in the vicinity, at 1470cm. -1 and 1380cm -1 The spectrum is similar to that of PP alone, as evidenced by the presence of a peak (peak I) of CH bending vibration. These results indicate that the second insoluble material contains polyolefins such as PVC, PET, and PP.

[0081] Finally, looking at the DSC curve shown in Figure 9, the first dissolved product yields only peaks of almost the same temperature and shape as the reference sample of PA66 alone. In other words, the first dissolved product can be said to contain PA as a polymer alone and without undergoing depolymerization. The second dissolved product yields a single peak in a temperature range lower than that of PBT alone and PA66 alone. This indicates that PBT has a lower melting point in the second dissolved product, which is consistent with PBT becoming an oligomer through depolymerization.

[0082] When measurements were taken directly on the raw material mixture before processing, the results showed complex peaks, reflecting the fact that the raw material mixture is a mixture of various polymers. The one-stage dissolved and separated product also showed complex peaks, although less pronounced than those of the raw material mixture. A closer examination of the measurement results for the one-stage dissolved product revealed peaks similar to those found in the case of PA66 alone, and peaks similar to those found in the second-stage dissolved and separated product, i.e., peaks corresponding to BT oligomers. This indicates that in the one-stage dissolved product, PA and BT oligomers are mixed together without being separated.

[0083] Based on the combined results of IR and DSC measurements, it can be seen that the polymer components separated in each step of the method for producing the oligomer composition according to the embodiments of this disclosure are as follows: In the first separation step, undepolymerized PA is separated as a dissolved product. In the second separation step, PBT is depolymerized and separated as a dissolved product, yielding a BT oligomer. The second insoluble product remaining after the second separation step includes polyolefins such as PVC, PET, and PP. Furthermore, if only a single separation step corresponding to the second separation step is performed without carrying out the first separation step, it is not possible to separate and recover PBT from PA. From this, it can be said that two separation steps are necessary to separate PBT from PA and other types of polymers and recover it.

[0084] Although embodiments of the present disclosure have been described in detail above, the present invention is not limited in any way to the above embodiments, and various modifications are possible without departing from the spirit of the present invention.

Claims

1. It contains a butylene terephthalate oligomer terminated at both ends with 1,4-butanediol, An oligomer composition that does not contain polyamide, polyethylene terephthalate, or its decomposition products in amounts detectable by infrared absorption spectroscopy.

2. The oligomer composition according to claim 1, wherein the butylene terephthalate oligomer has a number average molecular weight of 1000 or less and a molecular weight polydispersity of 1.5 or less.

3. The oligomer composition according to claim 1 or claim 2, further comprising at least one of a colorant and glass fibers.

4. The oligomer composition according to claim 1 or claim 2, wherein the butylene terephthalate oligomer is obtained by depolymerizing polybutylene terephthalate with 1,4-butanediol.

5. For raw materials derived from wire harness waste containing polybutylene terephthalate, the material is heated in 1,4-butanediol at a temperature above the dissolution temperature of polyamide but below the dissolution temperature of polybutylene terephthalate, and the insoluble material is separated. The oligomer composition according to claim 4, wherein the insoluble substance is heated in 1,4-butanediol at a temperature above the temperature at which polybutylene terephthalate begins to dissolve and below the temperature at which polyethylene terephthalate begins to dissolve, and the solvent is removed from the dissolved and separated components.

6. A first separation step involves heating a raw material mixture containing a polyester containing polybutylene terephthalate and a polyamide in 1,4-butanediol at a first temperature above the temperature at which the polyamide begins to dissolve and below the temperature at which the polybutylene terephthalate begins to dissolve, thereby separating the insoluble material. The insoluble material obtained in the first separation step is heated in 1,4-butanediol at a second temperature above the temperature at which polybutylene terephthalate begins to dissolve and below the temperature at which polyethylene terephthalate begins to dissolve, and the dissolved and separated components are separated in a second separation step. A method for producing an oligomer composition, comprising: a solvent removal step, which involves removing the solvent from the dissolved and separated components obtained in the second separation step to obtain an oligomer composition containing a butylene terephthalate oligomer.

7. The method for producing the oligomer composition according to claim 6, wherein the raw material mixture further comprises polyethylene terephthalate as the polyester.

8. A method for producing the oligomer composition according to claim 6 or claim 7, wherein the raw material mixture is derived from wire harness waste.

9. The first temperature is 160°C or higher and less than 185°C. A method for producing an oligomer composition according to claim 6 or claim 7, wherein the second temperature is 185°C or higher and less than 205°C.

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