Pet discrimination method

Abstract

To provide a PET discrimination method that is an objective method in which discrimination operation is comparatively simple and that can discriminate homogeneous polyester resins (including fiber).SOLUTION: The discrimination method includes: obtaining infrared or near-infrared absorption spectra of respective comparison resins of a group A of a plurality of comparison resins that are recycled PET resins and a group B of a plurality of comparison resins that are virgin PET resins; extracting spectral data in a predetermined wavenumber range from the absorption spectra to accumulate an analysis data group obtained by multivariate analysis of the spectral data as a database; and taking an unknown resin to be a resin under test, obtaining test data obtained by extracting spectral data in the predetermined wavenumber range from the obtained absorption spectra, collating with the analysis data group of the database by the multivariate analysis to discriminate whether the resin under test is recycled PET resin or virgin PET resin.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a PET discrimination method for discriminating the type of polyethylene terephthalate resin (PET resin) used in fibers, films, and other resin molded products. In particular, the present invention relates to a PET discrimination method for discriminating between PET fibers made of PET resin synthesized by a conventional method and PET fibers recycled from used PET bottles. [Background technology]

[0002] There are many resin products on the market for a wide range of applications. For example, synthetic resins such as nylon, polyester, and acrylic are used for textile products and films. Among these, polyester resins are widely used for clothing fibers, films, PET bottles, and the like. Moreover, polyester fibers are the most widely produced clothing fibers. Generally, polyester fibers used for clothing are made of polyethylene terephthalate (PET), and have been widely used since the past due to their physical properties suitable for clothing.

[0003] In addition to PET, polyester resins include polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), and polyethylene naphthalate (PEN). PBT and PTT are also used as fibers, and PTT is an environmentally friendly material derived from plants. PET, PBT, and PEN are also used as engineering plastics.

[0004] With the growing interest in environmental issues in recent years, environmentally conscious materials are now being desired for clothing fibers. However, there is still a large demand for chemical fibers, and among them, polyester fiber (PET fiber) is an essential fiber for clothing. On the other hand, PTT, an environmentally friendly material, is also used as a fiber due to its good stretchability. However, PTT fiber cannot replace PET fiber as a clothing material due to its basic physical properties and cost.

[0005] On the other hand, PET is recycled and reused as PET resin. There are two methods for recycling PET and using it again as PET resin: chemical recycling and material recycling. Chemical recycling of PET is a method in which PET products collected after use are returned to the synthetic raw materials terephthalic acid or dimethyl terephthalate (DMT), which are then polycondensed with ethylene glycol again to synthesize PET. This method has the advantage that PET products that have been used once can be reused even if they contain other components such as dyes and pigments. However, there are problems in terms of equipment and costs involved in depolymerization and repolycondensation.

[0006] In addition, PET material recycling involves using PET products collected after use as PET. PET is a thermoplastic resin that is heated and melted to make pellets of plastic raw material. These pellets are then made into PET fiber or PET film using standard methods. This method does not require depolymerization and re-polycondensation, so there are fewer problems in terms of equipment and costs. However, there is an issue that use is limited when other components such as dyes and pigments are mixed into PET products that have been used.

[0007] Therefore, in the material recycling of PET, the raw material is collected and reused from PET bottles, which are widely distributed on the market among PET products that have been used once. Collected PET bottles are made of PET resin and do not contain other components such as dyes and pigments. In addition, a collection system for PET bottles has been established in the market. Currently, recycled PET is being promoted from both chemical recycling and material recycling perspectives, but in the future, it is expected that the circulation of recycled PET made from PET material recycled from collected PET bottles will increase.

[0008] Therefore, in this invention, the terms "recycled PET resin" and "recycled PET fiber" are used to refer only to PET that is material recycled from collected PET bottles and does not include chemically recycled PET. In contrast, the terms "virgin PET resin" and "virgin PET fiber" are used to refer to normal PET that is newly polycondensed from monomers. Hereafter, the present invention will be explained using the terms "recycled PET resin" and "virgin PET resin", or "recycled PET fiber" and "virgin PET fiber".

[0009] In the following, PET resin will be explained using PET fiber as an example for clothing fibers. In recent years, as interest in sustainability has increased in the textile and apparel industry, the keywords traceability and transparency have become important. This is not limited to natural fibers, but will also be an important element for chemical fibers in the future.

[0010] On the other hand, the textile industry has a fragmented industrial structure consisting of upstream, midstream, and downstream processes, making it difficult to track information on the manufacturing process of many clothing products. While there are hopes for the spread of recycled PET fibers, traceability is said to be difficult due to the complex manufacturing process from collection to spinning. Furthermore, under Japanese law, both recycled PET fibers and virgin PET fibers are labeled as "polyester," and there is no obligation to label them at the time of sale, making it difficult for environmentally conscious consumers to distinguish between recycled PET fibers and virgin PET fibers.

[0011] Nowadays, when textile production and consumption areas are expanding globally, textile inspection organizations in each country identify textiles to ensure safety and reliability in trade when importing and exporting textile products. In Japan, for example, these inspection organizations perform identification based on JIS L 1030-1 (Test methods for blending ratio of textile products - Part 1: Fiber identification). First, fiber identification methods include combustion tests, confirmation tests for chlorine in fibers, confirmation tests for nitrogen in fibers, microscopic tests, coloring tests using iodine-potassium iodide solutions, xanthoprotein reaction tests, and infrared absorption spectrum measurement tests.

[0012] Each of these test methods is effective, and by combining them, many fibers can be distinguished. However, among natural fibers, fibers with the same chemical composition (called "similar fibers"), such as cellulose-based fibers such as cotton, various types of hemp, various types of rayon, cuprammonium rayon, and solvent-spun cellulose fibers, and animal hair-based fibers such as cashmere, wool, yak, mohair, angora, alpaca, vicuna, camel, and llama, are distinguished as the same fiber or similar fibers by the chemical test methods among the above test methods. Therefore, these chemical test methods cannot clearly distinguish between similar fibers. The same is true for chemical fibers.

[0013] The above test method also includes a test for measuring infrared absorption spectra. However, this test is intended to distinguish fibers with different chemical compositions (these are called "different fibers"), and is not considered to be able to clearly distinguish between fibers of the same kind. It is particularly difficult to distinguish between cellulose-based fibers and animal hair-based fibers, which are natural fibers of the same kind, using infrared spectroscopy. In response to this, the present inventors have studied methods for analyzing infrared absorption spectra and have proposed a fiber identification method for natural fibers of the same kind, as described in Patent Document 1 below.

[0014] On the other hand, with regard to chemical fibers, it is easy to distinguish between different fibers such as rayon, nylon, polyester, and acrylic by measuring infrared absorption spectra. Chemical fibers have a chemical composition that is artificially reproduced and synthesized, and are highly uniform. In comparison with natural fibers, some of these fibers can be analyzed to some extent from infrared absorption spectra even when they are homogeneous fibers. For example, Non-Patent Document 1 below states that PET fibers, PBT fibers, and PEN fibers, which are homogeneous polyester fibers, can be distinguished by focusing on the infrared absorption peaks of the different monomers because they have different combinations of monomers in the ester reaction.

[0015] In contrast, recycled PET fibers and virgin PET fibers, which are both PET fibers, are the same type of fiber (called "same type and same type fibers") and therefore difficult to distinguish by infrared spectroscopy. As a method for distinguishing between the same type and type of polyester fibers, a method for distinguishing between these polyester fibers by instrumental analysis other than infrared spectroscopy has been established, for example, in the Chinese standard in Non-Patent Document 2 below. [Prior art documents] [Patent documents]

[0016] [Patent Document 1] Patent No. 6798885 [Non-patent literature]

[0017] [Non-Patent Document 1] Analysis of foreign body spectrum 7 Polyester: PerkinElmer Japan Co., Ltd. (https: / / www.perkinelmer.co.jp / tabid / 2585 / Default.aspx) [Non-Patent Document 2] Chinese standard: GB / T39026-2020 "Identification method for recycled PET fibers" Summary of the Invention [Problem to be solved by the invention]

[0018] The method described in Non-Patent Document 2 uses high performance liquid chromatography (HPLC) to analyze trace components contained in PET bottles, but has the problem that the pretreatment by transesterification reaction and the equipment used are special, making the analytical procedures complicated.

[0019] Therefore, the present invention aims to address the above problems and provide a PET discrimination method that is relatively simple and objective in its discrimination operations and can distinguish between polyester-based resins of the same type and composition (including fibers). [Means for solving the problem]

[0020] In order to solve the above problems, the inventors conducted extensive research and discovered that it is possible to distinguish between the same type of polyester resin (including fibers) through simple operations and analysis even using an infrared absorption spectrometer that is widely used in industry, thereby completing the present invention.

[0021] That is, the PET discrimination method according to the present invention comprises the following steps: A method for distinguishing between recycled and virgin polyethylene terephthalate resins (PET resins), comprising: A plurality of comparative resins known to be recycled PET resins were classified into group A, and a plurality of comparative resins known to be virgin PET resins were classified into group B. The comparative resins in each group were irradiated with infrared or near-infrared light to obtain their respective absorption spectra. a database creation step of extracting spectral data in a predetermined wavenumber range from these absorption spectra, and accumulating a group of analysis data obtained by multivariate analysis of the spectral data as a database; A resin, which is unknown as to whether it is a recycled PET resin or a virgin PET resin, is used as a test resin, and test data is obtained by extracting spectral data in a predetermined wavenumber range similar to that of the comparative resin to which the test resin is to be compared, from the absorption spectrum obtained from the test resin in the same manner as in the database creation step; The method includes a discrimination process in which the test data is compared with the analysis data group of the database by the multivariate analysis, and the consistency between the test data and the analysis data group of the database is used as an indicator to discriminate whether the test resin is recycled PET resin or virgin PET resin.

[0022] According to claim 2, the present invention provides a PET discrimination method according to claim 1, For the comparative resins and test resins of each group, a wave number of 4000 cm -1 ~600cm -1 and determining the absorption spectrum by irradiating infrared light within a range of extracting spectral data in the predetermined wavenumber range to obtain the database and the test data; The method is characterized in that it determines whether the test resin is a recycled PET resin or a virgin PET resin.

[0023] According to claim 3, the present invention provides a PET discrimination method according to claim 2, The predetermined wavenumber range is a wavenumber range of 1400 cm -1 ~600cm -1 Within the range or the vicinity thereof A feature of this method is that spectral data in these wavenumber ranges is used for analysis.

[0024] According to claim 4, the present invention provides a PET discrimination method according to any one of claims 1 to 3, The multivariate analysis is characterized by being partial least squares discriminant analysis (PLS-DA).

[0025] According to claim 5, the present invention provides a PET discrimination method according to claim 4, The PET resin is characterized in that it is a fibrous PET fiber.

[0026] According to claim 6, the present invention provides a PET discrimination method according to claim 4, The method for determining the absorption spectra of the comparative resin and the test resin is characterized by being an ATR method (attenuated total reflection method).

[0027] According to claim 7, the present invention provides a PET discrimination method according to claim 6, The PET resin is characterized in that it is a fibrous PET fiber. Effect of the Invention

[0028] According to the above configuration, the present invention is a PET discrimination method for discriminating between recycled PET resin and virgin PET resin in polyethylene terephthalate resin (PET resin), which is a type of polyester resin. Resins of the same type and system having the same chemical composition can be discriminated from each other by infrared or near-infrared absorption spectrum. According to the above configuration, the present invention has a database creation step and a discrimination step.

[0029] In the database creation process, a plurality of comparative resins known to be recycled PET resins are grouped as group A, and a plurality of comparative resins known to be virgin PET resins are grouped as group B. Next, the comparative resins in each group are irradiated with infrared or near-infrared light to obtain their respective absorption spectra. Spectral data in a specified wavenumber range is extracted from these absorption spectra, and the spectral data is subjected to multivariate analysis to obtain a group of analysis data, which is stored as a database.

[0030] Next, in the discrimination step, a resin that is unknown as to whether it is a recycled PET resin or a virgin PET resin is used as a test resin, and test data is obtained by extracting spectral data in a predetermined wavenumber range similar to that of a comparison resin to which the test resin is to be compared from the absorption spectrum obtained from the test resin in the same manner as in the database creation step. Next, the test data is collated with the analysis data group of the database by multivariate analysis, and whether the test resin is a recycled PET resin or a virgin PET resin is discriminated based on the agreement between the test data and the analysis data group of the database as an index.

[0031] In addition, according to the above configuration, the comparative resin and the test resin of each group are measured at a wave number of 4000 cm -1 ~600cm -1 The absorption spectrum may be obtained by irradiating infrared light in the range of 1400 cm. -1 ~600cm -1 or a range close thereto. According to the above configuration, the multivariate analysis is preferably partial least squares discriminant analysis (PLS-DA). The method for determining the absorption spectra of the comparative resin and the test resin may be an ATR method (attenuated total reflection method). The PET resin may be a fibrous PET fiber.

[0032] Therefore, according to the present invention, a PET discrimination method can be provided that is capable of discriminating between polyester-based resins of the same type and composition (including fibers) using a relatively simple and objective discrimination operation. [Brief description of the drawings]

[0033] [Figure 1] This is a graph showing the overlay of infrared absorption spectra of recycled PET fibers and virgin PET fibers. [Diagram 2] FIG. 2 is a diagram showing a spectrum (differential spectrum) obtained by second-order differentiation of the infrared absorption spectrum of FIG. 1. [Diagram 3] FIG. 3 is a diagram showing the differential spectrum of FIG. 2 at selected wavenumbers. [Figure 4] This is a diagram showing the SNV transformation of the wavenumber-selected differential spectrum of FIG. [Diagram 5] FIG. 5 is a diagram showing the centered SNV transformed differential spectrum of FIG. 4. [Figure 6] FIG. 1 is a diagram showing a discriminant model obtained by PLS-DA. [Figure 7] This is a diagram showing the discrimination of recycled PET fibers using the discrimination model obtained in Figure 6. [Figure 8] FIG. 7 is a diagram showing the discrimination of virgin PET fibers using the discrimination model obtained in FIG. 6. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] In explaining the present invention, PET fiber is specifically used as an example of PET resin. Therefore, in the following explanation, PET resin is referred to as PET fiber, recycled PET resin is referred to as recycled PET fiber, and virgin PET resin is referred to as virgin PET fiber. Note that, although PET resin in a fibrous form is explained as PET fiber here, the present invention is not limited to fibers, and also covers films and other resin molded products.

[0035] In the present invention, polyester fibers are targeted among the fibers generally used in various textile products such as clothing and industrial materials. Polyester fibers include polyethylene terephthalate fibers (PET fibers), polybutylene terephthalate fibers (PBT fibers), polytrimethylene terephthalate fibers (PTT fibers), etc., which are defined as "similar fibers." However, the present invention is not targeted at distinguishing between these similar fibers.

[0036] The present invention is aimed at distinguishing between PET fibers, and defines them as "similar fibers of the same kind." It is said that distinguishing between similar fibers of the same kind is very difficult. In the present invention, the same fibers of PET fibers are limited to PET fibers that are material recycled from recovered PET bottles, as described above, and are called "recycled PET fibers." In contrast, normal PET fibers newly polycondensed from monomers are called "virgin PET fibers."

[0037] Here, we will explain virgin PET fiber and recycled PET fiber. Virgin PET fiber is made by spinning PET resin synthesized by polycondensation of dimethyl terephthalate (DMT) and ethylene glycol (DMT method) or polycondensation of terephthalic acid and ethylene glycol (direct polymerization method). In contrast, recycled PET fiber is made by spinning PET resin that has been recycled from recovered PET bottles. It is said that in the PET resin used in recovered PET bottles, about 2% of the terephthalic acid used in polycondensing the PET resin has been replaced with isophthalic acid to improve the bottle's appearance.

[0038] Even if a small amount of isophthalic acid is added to terephthalic acid, which is a polymerization monomer of PET fiber, it is difficult to distinguish it as a homogeneous polyester fiber by infrared spectroscopy, and it must be considered as a homogeneous fiber. In reality, beverage bottles using polyester resin to which a small amount of isophthalic acid has been added are distributed as PET bottles. Therefore, in order to distinguish PET resin recycled from recovered PET bottles from conventional PET resin, a complicated analysis by HPLC is required, as in the method of Non-Patent Document 2 mentioned above.

[0039] In contrast, in the present invention, the polyester fibers of the same type and different types are distinguished by infrared spectroscopy, which is a relatively simple and objective method. In the present invention, the fibers can be distinguished not only by infrared spectroscopy but also by near-infrared spectroscopy. The present invention will be described below using infrared spectroscopy.

[0040] The present inventors measured the infrared absorption spectra of recycled PET fibers and virgin PET fibers and compared them. Figure 1 shows the infrared absorption spectra of recycled PET fibers and virgin PET fibers superimposed on each other. In Figure 1, the infrared absorption spectra of recycled PET fibers and virgin PET fibers have overlapping absorption peaks in the entire wavenumber range measured, and they cannot be distinguished from the spectrum as it is. In addition, the present inventors expanded each wavenumber range and conducted a detailed study, but were unable to distinguish them.

[0041] Infrared spectroscopy provides an infrared absorption spectrum based on the molecular vibration of the substance being measured. Therefore, the infrared absorption spectrum contains information about the specific functional groups and crystal structure of the substance. Even if a very small amount of isophthalic acid is mixed into terephthalic acid, one of the polymerization monomers of the PET resin that is the subject of the present invention, these functional groups are the same. In other words, the two carboxylic acids that are the functional groups of phthalic acid (benzenedicarboxylic acid) are the same, but their positional relationship is slightly different. Terephthalic acid is a para-form of benzenedicarboxylic acid, and isophthalic acid is a meta-form of benzenedicarboxylic acid. These are structural isomers.

[0042] Therefore, the inventors of the present invention considered the following. When para- and meta-benzenedicarboxylic acids form a linear polymer, the difference in the configuration of some of the monomers would cause a difference in the conformation of the PET resin, resulting in a difference in the crystal structure. They thought that this slight difference in crystal structure could be distinguished by multivariate analysis of many infrared absorption spectra.

[0043] First, a method for obtaining infrared absorption spectra from a fiber of known fiber type (hereinafter referred to as "comparison fiber") and a fiber to be identified (hereinafter referred to as "test fiber") when creating a database in the present invention will be described. This method is generally called infrared spectroscopy, in which infrared rays are irradiated onto the substance to be measured, and the transmitted or reflected light is separated to obtain an infrared absorption spectrum and determine the characteristics of the object. Infrared spectroscopy is used to determine the molecular structure of an object, and is an extremely common method for analyzing organic matter.

[0044] In general, in infrared spectroscopy, wave numbers (also referred to as "WN" in the present invention) are often used rather than wavelengths. The wave number range used in the present invention is 4000 cm -1 ~600cm -1 On the other hand, the wave number range used in near-infrared spectroscopy is 12500 cm -1 ~4000cm -1 Within the range.

[0045] In the present invention, a commonly used Fourier transform infrared spectrophotometer (hereinafter referred to as "FT / IR spectrophotometer") can be used. Infrared absorption spectra of the comparative and test fibers can be obtained by pulverizing the fibers and forming them into tablets with potassium bromide (KBr) powder, and measuring the transmitted light by the KBr tablet method. Alternatively, the measurements can be performed by the ATR method (attenuated total reflection measurement method), which can measure the reflected light without destroying the woven or knitted fabric. In addition, it is preferable to perform atmospheric correction, baseline correction, smoothing correction, penetration depth correction, etc., by conventional methods in the infrared absorption spectra obtained by the ATR method, if necessary.

[0046] The PET discrimination method according to the present invention will be described in detail below with reference to an embodiment for PET fibers. Note that the present invention is not limited to the following embodiment. Note that the present invention is composed of a "database creation step" and a "discrimination step".

[0047] In the present invention, the infrared absorption spectra of a plurality of comparative fibers (Group A) known to be recycled PET fibers and the infrared absorption spectra of a plurality of comparative fibers (Group B) known to be virgin PET fibers are obtained. Next, spectral data in a predetermined wavenumber range important for analysis is extracted from these absorption spectra. Next, a group of analysis data obtained by multivariate analysis of these spectral data is stored as a database. This process is called the "database creation process."

[0048] Next, a fiber, which is unknown whether it is a recycled PET fiber or a virgin PET fiber, is used as a test fiber in the same manner, and its infrared absorption spectrum is obtained. Next, test data is obtained by extracting spectral data in a predetermined wavenumber range similar to that of the comparative fibers of Groups A and B from the obtained infrared absorption spectrum of the test fiber. Next, the obtained test data is compared with the analysis data group of the database by the above multivariate analysis. In this comparison, whether the test fiber is a recycled PET fiber or a virgin PET fiber is determined based on the agreement between the test data of the test fiber and the analysis data group of the comparative fiber in the database. This process is called the "discrimination process". Each process will be described below.

[0049] (1) Database creation process In this embodiment, 100 samples known to be recycled PET fibers were used as comparative fibers in Group A, and 100 samples known to be virgin PET fibers were used as comparative fibers in Group B. For these comparative fibers in Group A and Group B, -1 ~600cm -1 The infrared absorption spectrum was obtained within the range of 100 nm. Figure 1 shows the infrared absorption spectra of recycled PET fibers and virgin PET fibers superimposed on each other. Note that the infrared absorption spectrum in Figure 1 has been subjected to ATR correction. As mentioned above, the infrared absorption spectra of recycled PET fibers (Group A) and virgin PET fibers (Group B) shown in Figure 1 have overlapping absorption peaks over the entire wavenumber range measured, and therefore cannot be distinguished from the spectra alone.

[0050] In this embodiment, an FT / IR spectrophotometer (FT / IR-6800 manufactured by JASCO Corporation) was used to obtain the infrared absorption spectrum of the comparative fiber. FT / IR spectrophotometers are inexpensive because they are used in many industries, and the investment in equipment and maintenance costs for identification are reduced. In this embodiment, the ATR method (attenuated total reflection measurement method) was used for the measurement. In many cases, the fibers to be identified are already in the woven or knitted state as textile products, and this has the advantage that the identification can be performed non-destructively in this woven or knitted state. The type of prism used in the ATR method is not particularly limited, but a diamond prism was used in this embodiment.

[0051] Here, when analyzing the spectral data of the comparative fiber, it is preferable to first pre-process the spectral data. For the pre-processing, it is preferable to perform, for example, first-order differentiation, second-order differentiation, or higher-order differentiation. These differentiation processes can enhance the spectral information, such as sharpening peaks buried in the spectrum and removing the effects of the background. The method and dimension used in the differentiation process are not particularly limited, but in this embodiment, it is preferable to perform second-order differentiation by the Savitzky-Golay method (SG method). Figure 2 is a diagram showing a spectrum (differential spectrum) obtained by second-order differentiation of an infrared absorption spectrum.

[0052] Next, spectral data in a predetermined wavenumber range effective for analysis is extracted from the obtained differential spectrum. The method of extracting the spectral data is not particularly limited. A wavenumber range according to a specific functional group considered necessary for analysis may be selected for the type and combination of fibers to be identified. The inventors selected a wavenumber range related to the functional group of isophthalic acid, which they believe will affect the crystallinity of PET fibers. In addition, spectral data in a wavenumber range considered to contain noise in the analysis may be actively eliminated. As a result of intensive research, the inventors have found that in order to distinguish between recycled PET fibers and virgin PET fibers, a wavenumber range of 1400 cm is the most suitable. -1 ~600cm -1It has been found that it is preferable to extract spectral data within or near the range of Fig. 3. The differential spectrum is shown in Fig. 3 with selected wave numbers.

[0053] Next, in this embodiment, the wavenumber-selected differential spectrum was converted by standard normal variation (SNV). SNV conversion is a method for normalizing each spectrum so that the average of the constituent data is 0 and the standard deviation is 1. Fig. 4 shows the wavenumber-selected differential spectrum converted by SNV conversion. Furthermore, mean centering was performed on scattering variations that cannot be eliminated experimentally. Fig. 5 shows the centered SNV-converted differential spectrum.

[0054] Next, the extracted spectral data is subjected to multivariate analysis to obtain an analysis data group. The analysis method used for the multivariate analysis is not particularly limited, and any method may be adopted as long as it is an analysis method usually used in multivariate analysis. Generally, the multivariate analysis method includes principal component analysis, multiple regression analysis, independent component analysis, factor analysis, discriminant analysis, quantification theory, cluster analysis, and multidimensional scaling method. In the present invention, among these, it is preferable to use multiple regression analysis such as principal component analysis (PCA), principal component regression (PCR), and PLS regression, and it is particularly preferable to use partial least squares discriminant analysis (PLS-DA).

[0055] In this embodiment, PLS-DA was used. The creation of a discrimination model by PLS-DA will be specifically described below. The wave number of 1400 cm for the comparison fibers of 60 pieces of recycled PET fibers (Group A) and 60 pieces of virgin PET fibers (Group B) prepared as described above was 1400 cm. -1 ~600cm -1 A discrimination model was created using a database of analysis data obtained by analyzing the spectral data within the range of 1. In this discrimination model, the value 1 corresponds to group A and the value -1 corresponds to group B, and if the predicted value on the vertical axis is positive, it is determined to be recycled PET fiber, and if it is negative, it is determined to be virgin PET fiber.

[0056] Figure 6 shows the discrimination model obtained by PLS-DA. The number of factors was set to 7 to create the discrimination model. In Figure 6, the horizontal axis shows the sample number (comparative fibers 1 to 120) and the vertical axis shows the predicted value of each sample. The predicted values ​​of the comparative fibers were all positive for recycled PET fibers and all negative for virgin PET fibers, allowing for correct discrimination.

[0057] (2) Discrimination process In this discrimination process, first, an infrared absorption spectrum is obtained for a test fiber that is unknown as to whether it is a recycled PET fiber or a virgin PET fiber. In this embodiment, in order to verify the discrimination model, 18 fibers known to be recycled PET fibers and 36 fibers known to be virgin PET fibers were used as provisional test fibers for verification. In addition, two chemically recycled PET fibers were added to the provisional test fibers to verify how they were discriminated.

[0058] The methods for obtaining the infrared absorption spectrum, making various corrections to the infrared absorption spectrum, and performing preprocessing such as second derivative processing, wavenumber range extraction, SNV conversion, and centering processing are the same as those for the comparison fiber described above.

[0059] The results of the discrimination of the test fibers using the discrimination model by PLS-DA are shown in Figures 7 and 8. Figure 7 shows the discrimination of recycled PET fibers using the discrimination model. In Figure 7, 18 tentative test fibers, which are recycled PET fibers, were correctly discriminated as recycled PET fibers. Also, in Figure 7, two tentative test fibers, which are chemically recycled PET fibers, were discriminated as virgin PET fibers. Chemically recycled PET fibers are collected from recycled PET bottles, but are recycled down to polymerized monomers through depolymerization. Chemically recycled PET fibers are made by polycondensing recycled polymerized monomers with ethylene glycol, and are judged to be of the same quality as virgin PET fibers.

[0060] On the other hand, Fig. 8 is a diagram showing the discrimination of virgin PET fibers using the discrimination model. In Fig. 8, 36 tentative test fibers, which are virgin PET fibers, were correctly discriminated as virgin PET fibers. These 36 tentative test fibers were randomly selected from commercially available products, and included woven fabrics, knitted fabrics, filament yarns, staple yarns, and some dyed fibers. However, according to the discrimination model of this embodiment, all of these virgin PET fibers randomly selected from commercially available products were correctly discriminated.

[0061] As described above, the present invention provides a PET discrimination method that is relatively simple and objective in its discrimination operations, and can distinguish between polyester-based resins of the same type and composition (including fibers).

[0062] It should be noted that the present invention is not limited to the above-described embodiment, and various modifications can be made as follows. (1) In the above embodiment, the discrimination is made based on the reflection spectrum obtained by infrared spectroscopic analysis using the ATR method. However, this is not limited to this, and the discrimination may be made based on the transmission spectrum obtained by infrared spectroscopic analysis. (2) In the above embodiment, the infrared absorption spectrum is obtained by the ATR method, but this is not limited to this. Other methods may be used, for example, the comparison fiber or test fiber may be finely ground and then the infrared absorption spectrum may be obtained by the KBr pellet method. (3) In the above embodiment, the wave number is 4000 to 600 cm -1 In the present invention, the infrared absorption spectrum is measured within a range of 100 nm, and then spectral data in a predetermined wave number range to be used in the analysis is extracted from the measured spectrum. However, the present invention is not limited to this, and the infrared absorption spectrum in the predetermined wave number range to be used in the analysis may be directly measured. (4) In the above embodiment, the wave number is 1400 cm -1 ~600cm -1 However, the present invention is not limited to this, and other wavelength ranges may be extracted. (5) In the above embodiment, the spectral data is analyzed by PLS-DA. However, this is not limited to this, and the spectral data may be analyzed by principal component analysis (PCA), principal component regression (PCR), PLS regression, or other multivariate analyses. (6) In the above embodiment, the discrimination is made based on the infrared absorption spectrum obtained by infrared spectroscopy. However, this is not limited to this, and the discrimination may be made based on the near-infrared absorption spectrum obtained by near-infrared spectroscopy. (7) In the above embodiment, PET fibers are identified as PET resin products. However, the present invention is not limited to this, and PET films and other PET resin molded products may be identified. [Industrial Applicability]

[0063] There are many resin products and textile products in circulation on the market for a wide range of applications. In addition, in today's world where the production and consumption of resin products and textile products are expanding globally, a rapid and accurate method of identification is required to ensure the safety and reliability of transactions when importing and exporting these products. In particular, there is a need for accurate identification of the same type of polyester resin (including fibers) that have almost the same chemical composition.

[0064] The present invention provides an accurate means of discrimination in response to such market demands, and is an unprecedented, revolutionary means of discrimination because it can objectively discriminate between the types of polyester-based resins (including fibers) of the same type and system, and can obtain accurate discrimination results even if erroneous or false information is present.

Claims

1. A method for distinguishing between recycled PET resin and virgin PET resin in polyethylene terephthalate resin (PET resin), comprising: A plurality of comparative resins known to be recycled PET resins were classified into group A, and a plurality of comparative resins known to be virgin PET resins were classified into group B. The comparative resins in each group were irradiated with infrared or near-infrared light to obtain their respective absorption spectra. a database creation step of extracting spectral data in a predetermined wavenumber range from these absorption spectra, and accumulating a group of analysis data obtained by multivariate analysis of the spectral data as a database; A resin, which is unknown as to whether it is a recycled PET resin or a virgin PET resin, is used as a test resin, and test data is obtained by extracting spectral data in a predetermined wavenumber range similar to that of the comparative resin to which the test resin is to be compared, from an absorption spectrum obtained from the test resin in the same manner as in the database creation step; The PET discrimination method includes a discrimination process in which the test data is compared with the analysis data group of the database by the multivariate analysis, and the consistency between the test data and the analysis data group of the database is used as an indicator to discriminate whether the test resin is recycled PET resin or virgin PET resin.

2. For the comparative resins and test resins of each group, a wave number of 4000 cm －１ ~600cm －１ and determining the absorption spectrum by irradiating infrared light within a range of extracting spectral data in the predetermined wavenumber range to obtain the database and the test data; 2. The PET discrimination method according to claim 1, further comprising discriminating whether the test resin is a recycled PET resin or a virgin PET resin.

3. The predetermined wavenumber range is a wavenumber range of 1400 cm －１ ~600cm －１ Within the range or the vicinity thereof The PET discrimination method according to claim 2, characterized in that the spectral data in these wavenumber ranges are used for analysis.

4. The PET discrimination method according to any one of claims 1 to 3, characterized in that the multivariate analysis is partial least squares discriminant analysis (PLS-DA).

5. 5. The PET discrimination method according to claim 4, wherein the PET resin is a fibrous PET fiber.

6. 5. The PET discrimination method according to claim 4, wherein the method for determining the absorption spectra of the comparative resin and the test resin is an ATR method (attenuated total reflection method).

7. The PET discrimination method according to claim 6, wherein the PET resin is a fibrous PET fiber.

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