Method for identifying recycled polyester fibers by recycling bottle flakes

Abstract

The invention belongs to the technical field of fiber identification, and discloses a method for identifying regenerated polyester fibers by recycling bottle flakes, which comprises the following steps: firstly, determining whether a polyester fiber alcoholysis reaction product to be identified contains dimethyl isophthalate or not, and if not, directly judging that the polyester fibers are native polyester fibers; otherwise, further, measuring free-state isophthalic acid ultrasonically extracted from the polyester fiber by using liquid chromatography, and if the difference between the molar weight of the detected free-state isophthalic acid and the molar weight of dimethyl isophthalate detected in the alcoholysis reaction product is not more than 20%, determining that the polyester fiber is in the free state; and if the difference between the molar weight of the detected free-state isophthalic acid and the molar weight of dimethyl isophthalate detected in the alcoholysis reaction product is not more than 20%, determining that the polyester fiber is in the free state. Determining that the polyester fibers are native polyester fibers added with isophthalic acid (IPA); otherwise, determining that the polyester fiber is the regenerated polyester fiber. According to the method, the native polyester fibers and the regenerated polyester fibers can be efficiently, accurately and qualitatively identified, and meanwhile, artificial adding interference can be accurately analyzed.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of fiber identification, and particularly relates to a method for identifying bottle flake recycled polyester fibers. BACKGROUND

[0002] In recent years, the market scale of imported commodities has continued to expand, and imported consumption has become an important force driving consumption upgrading. Among them, the proportion of imported light and textile consumer goods is increasing. Polyester fibers, with high strength, durability and other excellent properties, account for a large share in the light and textile consumer goods industry.

[0003] The European Parliament voted to pass the Sustainable Product Eco-Design Regulation, which expands the scope of sustainable products to any product that consumes energy during use, and issued the Sustainable and Circular Textile Strategy. These two regulations complement each other and aim to curb the excessive waste of resources in the production and consumption of light and textile consumer goods, and require durability, recyclability and repairability of light and textile consumer goods. The minimum content of recycled materials in light and textile consumer goods is specified, and each product is required to provide information on the content of recycled materials in itself.

[0004] However, as the scale of recycled polyester fiber production expands, there have been cases of artificially adding isophthalic acid to produce recycled polyester fibers. In order to identify whether the fiber is recycled polyester, a method for identifying the fiber is needed. In the field of research on the recycling of waste textiles, researchers have studied the forming mechanism, aggregate structure and properties of recycled polyester fibers, and have developed a method for identifying recycled polyester and virgin polyester using liquid chromatography. However, this method is only suitable for chemically recycled polyester, and is complex and not very accurate.

[0005] In document 1 (Research on identification method of recycled polyester fiber [J]. Synthetic fiber, 2019. DOI: 10.16090 / j.cnki.hcxw.20190614.006.), based on the theory that the production process of recycled polyester causes changes in the content and distribution of macromolecular heterogeneous chain segments and oligomers when refining terephthalic acid, the macromolecular heterogeneous chain segments and oligomers of virgin polyester and recycled polyester were studied and compared to find specific indicators to accurately identify the two types of polyester. The study extracted the heterogeneous chain segments and oligomers of the two types of polyester, analyzed them using high-performance liquid chromatography, established a data model using function analysis, and concluded that the two types of polyester could be identified by the two indicators of macromolecular heterogeneous chain segments and oligomers. This method can theoretically quickly identify the two types of polyester, filling the technical gap in this field at home and abroad, but it requires a large number of representative samples to establish a database and data model, and the calculation is complex and time-consuming. In addition, it cannot directly conclude whether the polyester is recycled, making it difficult for ordinary testing laboratories to implement.

[0006] Therefore, it is of great significance to study a method for identifying bottle flake recycling regenerated polyester fibers to solve the above problems. SUMMARY

[0007] The present application aims to solve the problems in the prior art and provide a method for identifying bottle flake recycling regenerated polyester fibers, which can efficiently and accurately qualitatively identify virgin polyester fibers and regenerated polyester fibers and accurately analyze artificial additions.

[0008] To achieve the above-mentioned purposes, the technical solutions adopted by the present application are as follows:

[0009] The present application aims to detect samples of bottle flake recycling regenerated polyester fibers to determine whether they are true bottle flake recycling regenerated polyester fibers. For the polyester fibers to be identified, it is first determined whether the alcoholysis reaction product contains isophthalic acid dimethyl ester. If not, the polyester fibers are directly determined to be virgin polyester fibers. Otherwise, further, liquid chromatography is used to determine the free state of isophthalic acid extracted from the polyester fibers by ultrasonic extraction. If the molar mass of the free state of isophthalic acid detected is not more than 20% different from the molar mass of isophthalic acid dimethyl ester detected in the alcoholysis reaction product, the polyester fibers are determined to be virgin polyester fibers with added isophthalic acid (IPA). Otherwise, the polyester fibers are determined to be regenerated polyester fibers.

[0010] As a preferred technical solution:

[0011] The method for identifying bottle flake recycling regenerated polyester fibers as described above uses GCMS (gas chromatography mass spectrometry) to determine whether the alcoholysis reaction product contains isophthalic acid dimethyl ester.

[0012] The method for identifying bottle flake recycling regenerated polyester fibers as described above, the alcoholysis reaction process is: the polyester fibers and methanol are depolymerized under the action of a catalyst to obtain an alcoholysis reaction product; the reaction temperature is 215-225 DEG C, and the reaction time is 2h.

[0013] The method for identifying bottle flake recycling regenerated polyester fibers as described above, the alcoholysis reaction product is filtered before being determined by GCMS.

[0014] The method for identifying bottle flake recycling regenerated polyester fibers as described above, the dosage ratio of polyester fibers and methanol ranges from 1g:500-2000mL; the catalyst is zinc acetate, and the dosage ratio of the catalyst and methanol ranges from 30-40mg:1L.

[0015] The identification method of the bottle piece recycling regenerated polyester fiber as described above extracts isophthalic acid in a free state from polyester fiber by ultrasonic extraction, and the specific process is as follows: the polyester fiber is frozen and ground into powder in a grinding tube in a liquid nitrogen freezing grinder, methanol is added, and ultrasonic extraction is carried out at 60±5℃ for 2-3h, and then cooled to room temperature.

[0016] The identification method of the bottle piece recycling regenerated polyester fiber as described above, the freezing temperature is-196℃, that is, the temperature of liquid nitrogen, the freezing time is 5-10min, and the grinding is carried out under vibration after freezing, the vibration frequency is 10-20cps, and the grinding time is 2-4min; the ultrasonic extraction frequency is 40kHz.

[0017] Invention principle:

[0018] Isophthalic acid (IPA) is an additive of bottle-grade PET, which can delay the crystallization speed of PET bottles during processing and ensure the transparency of PET container products. The content of isophthalic acid in the recycled PET bottle piece will not change after being processed into fibers by physical recycling. Therefore, the virgin polyester fiber and the bottle piece recycling polyester fiber can be qualitatively distinguished by whether IPA is contained. When no isophthalic acid dimethyl ester is detected in the alcoholysis reaction product, it can be directly determined as virgin polyester; when isophthalic acid dimethyl ester is detected, it cannot be determined whether it comes from the high polymer cracking or the subsequent addition of isophthalic acid in a free state. The applicant found through years of accumulation that if it is a regenerated polyester fiber, most of the IPA is embedded in the macromolecular chain segment; and if it is artificially added isophthalic acid, most of it exists in the macromolecular chain segment in a free state. Therefore, by using liquid chromatography to further test the isophthalic acid in a free state extracted from the polyester fiber by ultrasonic extraction, if no isophthalic acid is detected by liquid chromatography, or although isophthalic acid is detected, there is no obvious difference in the detection amount of isophthalic acid dimethyl ester measured by GCMS, it indicates that the isophthalic acid dimethyl ester measured by GCMS comes from the high polymer cracking product, and combined with the GCMS result, it can be determined as a regenerated polyester fiber; on the contrary, if the liquid chromatography result detects isophthalic acid, and there is no obvious difference in the detection amount of isophthalic acid dimethyl ester measured by GCMS, it indicates that the isophthalic acid dimethyl ester measured by GCMS comes from the subsequent addition of isophthalic acid in a free state, and it can be determined as a virgin polyester fiber with added IPA.

[0019] Beneficial effects:

[0020] The application can efficiently and accurately identify virgin polyester fiber and regenerated polyester fiber by using GCMS method and liquid chromatography method, and can accurately analyze artificial addition interference, and the operation is simple. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 Flow chart of the identification method of bottle flake recycling regenerated polyester fiber of the present application;

[0022] Figure 2 Gas chromatography mass spectrum of the alcoholysis product of polyester fiber in Example 1 of the present application;

[0023] Figure 3 Gas chromatography mass spectrum of the alcoholysis product of polyester fiber in Example 2 of the present application;

[0024] Figure 4 Liquid chromatogram of the free state isophthalic acid ultrasonically extracted from polyester fiber in Example 2 of the present application;

[0025] Figure 5 Gas chromatography mass spectrum of the alcoholysis product of polyester fiber in Example 3 of the present application;

[0026] Figure 6 Liquid chromatogram of the free state isophthalic acid ultrasonically extracted from polyester fiber in Example 3 of the present application; in the figure, a represents the characteristic peak of isophthalic acid. DETAILED DESCRIPTION

[0027] The present application will be further described in conjunction with the specific embodiments. It should be understood that these embodiments are only used to illustrate but not to limit the scope of the present application. Furthermore, it should be understood that after reading the content taught by the present application, those skilled in the art can make various alterations or modifications to the present application, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

[0028] In order to ensure the performance of the substances used in each embodiment to be fully disclosed, the manufacturers and brands of the substances are written, and the products of other manufacturers and brands conforming to the definition of the present application are also feasible.

[0029] An identification method of bottle flake recycling regenerated polyester fiber, the flow chart is shown in Figure 1 The steps are as follows:

[0030] (1) The polyester fiber and methanol are depolymerized at 215-225℃ under the action of zinc acetate for 2h, then taken out, cooled to room temperature, the supernatant in the reaction tube is filtered through a needle filter into a 2mL sample bottle, and placed in the cold storage room of a refrigerator at 4-6℃ for cold storage for more than 8h, then filtered again through a needle filter and placed at room temperature to obtain the filtered alcoholysis reaction product; wherein the ratio of the amount of polyester fiber and methanol is 1g:500-2000mL, and the ratio of the amount of zinc acetate and methanol is 30-40mg:1L;

[0031] (2) The alcoholysis reaction product filtered in step (1) is detected by GCMS to determine whether it contains dimethyl isophthalate. If it does not, the polyester fiber is determined to be virgin polyester fiber. If it does, the next step is performed;

[0032] (3) The same mass of polyester fiber as in step (1) is placed in a grinding tube in a liquid nitrogen cryogenic grinder, and then the grinding tube is placed in liquid nitrogen at -196°C and frozen for 5-10 min. After being frozen and ground at a vibration frequency of 10-20 cps for 2-4 min, it is taken out and placed in a reaction tube. Then, methanol is added thereto, and ultrasonic extraction is performed at 60±5°C for 2-3 h at a frequency of 40 kHz. After cooling to room temperature, it is filtered through a needle filter to obtain an isophthalic acid solution;

[0033] (4) The isophthalic acid solution is detected by liquid chromatography. If the molar mass of free isophthalic acid detected differs from the molar mass of dimethyl isophthalate detected in the alcoholysis reaction product by no more than 20%, the polyester fiber is determined to be virgin polyester fiber to which isophthalic acid has been added. Otherwise, the polyester fiber is determined to be recycled polyester fiber.

[0034] To verify the accuracy of the above-mentioned identification method of bottle flake recycled polyester fiber, the following identification is performed on different polyester fibers:

[0035] Example 1

[0036] An identification method of bottle flake recycled polyester fiber, the steps of which are as follows:

[0037] (1) The polyester fiber (virgin polyester fiber, manufacturer: Sinopec Yizheng Chemical Fibre Co., Ltd., brand: ZW101) and methanol are depolymerized at 215°C for 2 h under the action of zinc acetate. After cooling to 25°C, the upper clear liquid in the reaction tube is filtered through a needle filter into a 2 mL sample bottle and placed in the cold storage room of a 4°C refrigerator for 8 h. Finally, it is filtered again through a needle filter and placed at 25°C to obtain a filtered alcoholysis reaction product. The ratio of the amount of polyester fiber to methanol is 1 g:500 mL, and the ratio of the amount of zinc acetate to methanol is 40 mg:1 L;

[0038] (2) The filtered alcoholysis reaction product in step (1) is detected by GCMS to obtain a chromatogram as shown in FIG. 1. Figure 2The gas chromatography mass spectrum chart is shown, from the figure, the characteristic peak of dimethyl terephthalate appears at the retention time of 10.97 min (esterification reaction of terephthalic acid occurs in the alcoholysis process), but there is no response near the characteristic peak of dimethyl isophthalic acid at the retention time of 11.11 min, indicating that the polyester fiber measured in the embodiment does not contain isophthalic acid, and finally the polyester fiber can be determined to be virgin polyester fiber according to the identification method of the application; wherein the chromatographic column is HP-5MS, 30m x 0.25mm x 0.25μm; the injection port temperature is 300℃, the mass spectrometry interface temperature is 270℃, the mass scan range is 35amu-350amu; the injection mode is split injection, the split ratio is 100:1; the carrier gas is helium (purity≥99.999%); the injection amount is 1uL; the ionization mode is EI source; the temperature program is (duration of 2min).

[0039] Example 2

[0040] A method for identifying a bottle flake recycled polyester fiber, comprising the following steps:

[0041] (1) The polyester fiber (recycled polyester fiber, manufacturer is Hangzhou Benma Chemical Fiber Spinning Co., Ltd., brand is Baima BM7) and methanol are depolymerized at 225℃ under the action of zinc acetate for 2h, then the upper clear liquid in the reaction tube is filtered to a 2mL sample bottle through a needle filter after cooling to 20℃, and is placed in the cold storage room of a refrigerator at 6℃ for 14h, and finally filtered through a needle filter and placed at 20℃ to obtain a filtered alcoholysis reaction product; wherein the ratio of the amount of polyester fiber and methanol is 1g:2000mL, and the ratio of the amount of zinc acetate and methanol is 30mg:1L;

[0042] (2) The filtered alcoholysis reaction product in step (1) is detected by GCMS method to obtain a chromatogram as shown in Figure 2. Figure 3The gas chromatography mass spectrum shown in the figure shows that the characteristic peak of dimethyl terephthalate appears at a retention time of 10.97 min (esterification of terephthalic acid occurs in the alcoholysis process), and the characteristic peak of dimethyl isophthalate appears at a retention time of 11.11 min (esterification of isophthalic acid occurs in the alcoholysis process), so according to the identification method of the present application, it can be determined that the polyester fiber measured in this embodiment contains IPA, but whether it is a regenerated polyester fiber needs to continue to perform the subsequent steps to determine; wherein the chromatographic column is HP-5MS, 30m x 0.25mm x 0.25μm; the injection port temperature is 300℃, the mass spectrometry interface temperature is 270℃, the mass scan range is 35amu-350amu; the injection mode is split injection, the split ratio is 100:1; the carrier gas is helium (purity ≥ 99.999%); the injection amount is 1uL; the ionization mode is EI source; the temperature program is (duration 2min);

[0043] (3) Put the same mass of polyester fiber as in step (1) in the grinding tube in the liquid nitrogen cryogenic grinder, then put the grinding tube into liquid nitrogen at-196℃ and freeze for 5min, then take out and put into the reaction tube after freezing and grinding at a vibration frequency of 20cps for 2min, then add methanol to it and ultrasonically extract at 65℃ for 2h at a frequency of 40kHz, then cool to 20℃, and filter it through a needle filter to obtain an isophthalic acid solution;

[0044] (4) Detect the isophthalic acid solution using liquid chromatography; wherein the chromatographic column is XDB C18 (5μm), 250mm x 4.6mm, the flow rate is 1.0mL / min, the column temperature is 40℃; the injection amount is 10μL; the detector is a diode array detector (DAD); the detection wavelength is 210nm and 242nm; run for 5min after; the gradient table of the mobile phase is as follows (in the table, the volume concentration of methyl acetate is 0.2%, and the volume concentration of acetic acid aqueous solution is 0.2%):

[0045] Time / min Acetic acid in methanol solution / % Acetic acid in water solution / % 1 50 50 5 50 50 20 90 10 25 90 10

[0046] Through the detection of step (4), the liquid chromatogram as shown in Figure 4 is obtained, from which it can be known that the characteristic peak of isophthalic acid does not appear in the extraction product of the polyester fiber, and in combination with the gas chromatogram as shown in Figure 3The results show that the polyester fiber in step (1) alcoholysis cleavage of isophthalic acid, which is polymerized in the chain segment of polyester fiber macromolecule, so that the free state of isophthalic acid cannot be obtained by extraction in step (3), which proves that isophthalic acid is added in the macromolecular polymerization stage before granulation, aiming to delay the crystallization speed of the initial virgin bottle-grade polyester particles in the processing process, so as to ensure the initial virgin bottle-grade PET product transparency; and in the process of recycling bottle flakes into fibers again, isophthalic acid is polymerized in the chain segment of polyester fiber macromolecule, and the melting spinning process cannot change the content of isophthalic acid, so according to the method of the application, the polyester fiber detected in this embodiment contains polymerized IPA, which can be determined as recycled polyester fiber.

[0047] Example 3

[0048] A method for identifying recycled polyester fiber from bottle flakes, the steps are as follows:

[0049] (1) preparing suspected recycled polyester fiber;

[0050] (1.1) first dry the virgin polyester particles (manufacturer: Sinopec Yizheng Chemical Fibre Co., Ltd., brand: FD501) at 90℃ for 1h, then continue to heat to 110℃ and dry for 1h, then heat to 130℃ and dry for 1h, and finally heat to 160℃ and dry for 5h;

[0051] (1.2) uniformly stir the dried virgin polyester particles and isophthalic acid powder in step (1.1) by a high-speed mixer, then melt at 250℃, and extrude the filaments into the water area to cool and slice by a granulator, then send the slices to a double-screw spinning machine for spinning to prepare suspected recycled polyester fiber; wherein the mass ratio of the dried virgin polyester particles and isophthalic acid powder is 99.7g:0.3g;

[0052] (2) depolymerize the suspected recycled polyester fiber prepared in step (1) and methanol under the action of zinc acetate at 225℃ for 2h, then cool to 20℃, filter the upper clear liquid in the reaction tube to a 2mL sample bottle by a needle filter, and put it in the cold storage room of a 4℃ refrigerator for 14h, then filter again by a needle filter and put it at 20℃ to obtain the filtered alcoholysis reaction product; wherein the dosage ratio of the suspected recycled polyester fiber and methanol is 1g:2000mL, and the dosage ratio of zinc acetate and methanol is 40mg:1L;

[0053] (3) detect the filtered alcoholysis reaction product in step (2) by GCMS method to obtain the isophthalic acid content in the polyester fiber as shown in Table 1. Figure 5The gas chromatography mass spectrum shown in the figure shows that the characteristic peak of dimethyl terephthalate appears at a retention time of 10.97 min (esterification of terephthalic acid occurs in the alcoholysis process), and the characteristic peak of dimethyl isophthalate appears at a retention time of 11.11 min (esterification of isophthalic acid occurs in the alcoholysis process), so according to the identification method of the present application, it can be determined that the polyester fiber measured in this embodiment contains IPA, but whether it is a regenerated polyester fiber needs to continue to perform the subsequent steps to determine; wherein the chromatographic column is HP-5MS, 30m x 0.25mm x 0.25μm; the injection port temperature is 300℃, the mass spectrometry interface temperature is 270℃, the mass scan range is 35amu-350amu; the injection mode is split injection, the split ratio is 100:1; the carrier gas is helium (purity ≥ 99.999%); the injection amount is 1uL; the ionization mode is EI source; the temperature program is (duration 2min);

[0054] (4) Put the same mass of suspected regenerated polyester fiber as in step (2) in the grinding tube in the liquid nitrogen cryogenic grinder, then put the grinding tube into liquid nitrogen at-196℃ and freeze for 10min, then take it out and put it into the reaction tube, then add methanol to it and ultrasonically extract at 60℃ for 3h at a frequency of 40kHz, then cool to 20℃, and filter it through a needle filter to obtain an isophthalic acid solution;

[0055] (5) Detect the isophthalic acid solution using liquid chromatography; wherein the chromatographic column is XDB C18 (5μm), 250mm x 4.6mm, the flow rate is 1.0mL / min, the column temperature is 40℃; the injection amount is 10μL; the detector is a diode array detector (DAD); the detection wavelength is 210nm and 242nm; run for 5min after; the gradient table of the mobile phase is as follows (in the table, the volume concentration of methyl acetate is 0.2%, and the volume concentration of acetic acid aqueous solution is 0.2%):

[0056] Time / min Acetic acid in methanol solution / % Acetic acid in water solution / % 1 50 50 5 50 50 20 90 10 25 90 10

[0057] Through the detection of step (5), it is obtained as Figure 6The liquid chromatogram is shown in the figure. It can be seen from the figure that the characteristic peak of isophthalic acid appears in the extraction product of the suspected regenerated polyester fiber. After quantification by external standard method, the content of isophthalic acid is 2213 mg / kg. Combined with GCMS detection, isophthalic acid dimethyl ester produced by alcoholysis and cleavage of the suspected regenerated polyester fiber in step (2) is quantified by GC-MS external standard method as 2889.2 mg / kg, and converted to the content of isophthalic acid as 2470.3 mg / kg. This shows that the content of isophthalic acid dimethyl ester produced by alcoholysis and cleavage of step (2) and the free state isophthalic acid obtained by extraction of step (4) is very close. This proves that isophthalic acid is in free state and does not participate in the polymerization stage of the polyester macromolecule. Therefore, according to the identification method of the present application, it is known that most of the isophthalic acid in the suspected regenerated polyester fiber measured in this embodiment is in free state, and it can be determined that the original polyester fiber artificially added with IPA.

Claims

1. A method for identifying recycled polyester fibers from bottle flakes, characterized in that: For the polyester fiber to be identified, first determine whether dimethyl isophthalate is present in its alcoholysis reaction product. If not, the polyester fiber is directly identified as virgin polyester fiber. Otherwise, further, liquid chromatography is used to determine the free isophthalic acid extracted from the polyester fiber by ultrasonication. If the molar amount of free isophthalic acid detected is no more than 20% different from the molar amount of dimethyl isophthalate detected in the alcoholysis reaction product, the polyester fiber is identified as virgin polyester fiber with added isophthalic acid. Otherwise, the polyester fiber is identified as recycled polyester fiber.

2. The method for identifying recycled polyester fibers from bottle flakes according to claim 1, characterized in that, The presence of dimethyl isophthalate in the alcoholysis product was determined by GCMS.

3. The method for identifying recycled polyester fibers from bottle flakes according to claim 2, characterized in that, The alcoholysis process is as follows: polyester fiber and methanol are depolymerized under the action of a catalyst to obtain the alcoholysis product; the reaction temperature is 215-225℃ and the reaction time is 2h.

4. The method for identifying recycled polyester fibers from bottle flakes according to claim 3, characterized in that, The products of the alcoholysis reaction were filtered before being analyzed by GCMS.

5. The method for identifying recycled polyester fibers from bottle flakes according to claim 3, characterized in that, The ratio of polyester fiber to methanol is 1g:500-2000mL; the catalyst is zinc acetate, and the ratio of catalyst to methanol is 30-40mg:1L.

6. The method for identifying recycled polyester fibers from bottle flakes according to claim 1, characterized in that, The process of ultrasonically extracting free isophthalic acid from polyester fibers is as follows: the polyester fibers are placed in the grinding tube of a liquid nitrogen cryogenic grinder and ground into powder. Methanol is added and ultrasonically extracted at 60±5℃ for 2-3 hours, and then cooled to room temperature.

7. The method for identifying recycled polyester fibers from bottle flakes according to claim 6, characterized in that, The freezing time is 5 to 10 minutes. After freezing, the material is ground under vibration conditions with a vibration frequency of 10 to 20 cps and a grinding time of 2 to 4 minutes. The ultrasonic extraction frequency was 40 kHz.

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