Analytical method for identifying native PET and regenerated PET through chloride ion determination
By employing hot water immersion and anion exchange column assay, the challenge of distinguishing between virgin and recycled PET has been solved, enabling rapid and accurate identification and quantitative analysis, which is applicable to the detection of actual samples.
Patent Information
- Application Number
- CN202511763630.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-27
- Publication Date
- 2026-01-27
AI Technical Summary
Existing technologies struggle to quickly and accurately distinguish between virgin PET and recycled PET, especially due to differences in chemical safety and physical properties caused by the introduction of chlorine-containing contaminants during the recycling process of rPET.
The chloride ions in the rPET plastic bottle were migrated by immersion in hot water, and then trace chloride ions were accurately measured using an anion exchange column. Quantitative analysis was performed using a chloride ion standard curve.
It enables rapid and accurate identification and quantitative analysis of PET and rPET, providing technical support for assessing the safety of recycled plastics. The methodology is optimized and applicable to the testing of actual samples.
Smart Images
Figure FT_1 
Figure FT_2 
Figure FT_3
Abstract
Description
Technical Field
[0001] This invention belongs to the field of instrumental analysis technology, specifically relating to an analytical method for identifying virgin PET and recycled PET by measuring chloride ions. Background Technology
[0002] In today's world, polyethylene terephthalate (PET), a major material widely used in food packaging and beverage bottles, has an annual production exceeding 70 million tons. While this massive production meets the needs of daily life and industrial production, it also places a heavy burden on the environment. Large quantities of discarded PET plastic products are difficult to degrade naturally and accumulate in the environment over time, causing significant damage to the balance and stability of ecosystems such as soil and water.
[0003] To alleviate environmental pressures, recycled PET (rPET), with its significant advantages of low carbon emissions and resource recycling, is gradually becoming a key pathway for the plastics industry towards sustainable development. rPET primarily transforms waste PET into usable materials through a series of scientifically sound processing methods. However, the raw material sources for rPET are extremely complex. During the recycling process, these raw materials may contain additives and dyes not completely removed during the initial production, or various byproducts generated from natural degradation after disposal. The presence of these impurities leads to significant differences in chemical safety and physical properties compared to virgin PET. Therefore, developing a rapid and accurate identification technology for virgin PET and rPET is particularly important.
[0004] Ion chromatography, as a highly sensitive anion detection method, has been widely used for the analysis of trace ions in the environment and food. Detection techniques based on ion migration behavior have attracted much attention due to their lack of complex pretreatment. Related studies have shown that reprocessed PET may introduce chlorine-containing contaminants, such as residual polyvinyl chloride or flame retardants, during recycling, while virgin PET, due to its relatively pure polymerization process, has extremely low chloride ion content. This significant difference provides a theoretical basis for differentiating PET and reprocessed PET through chloride ion detection. However, in the practical detection of ion migration behavior in plastics, many challenges remain.
[0005] Therefore, this invention innovatively proposes a green and efficient detection method—inducing the migration of chloride ions in rPET plastic bottles by immersion in hot water, and then using an anion exchange column to achieve accurate determination of trace chloride ions. Summary of the Invention
[0006] The purpose of this invention is to provide an analytical detection method for identifying virgin PET and recycled PET by measuring chloride ions. This method is applicable to the identification and quantitative analysis of rPET in actual samples (e.g., plastic bottles).
[0007] The technical solution of the present invention is as follows: An analytical method for identifying PET (virgin PET) / rPET (recycled PET) by chloride ion determination, comprising: (1) Sample pretreatment Take the sample, add deionized water, keep it at 90℃ for 30 min, then cool it to room temperature, filter it with a 0.45 μm microporous membrane, and collect the filtrate as the sample to be tested. The preferred mass-to-volume ratio of sample to deionized water is 1:15, g / mL; Sample example: plastic bottle. After washing the plastic bottle with deionized water and drying it at room temperature, it is then cut into 3mm×3mm fragments for later use. (2) Plot the chloride ion standard curve Sodium chloride standard was used to prepare a series of chloride ion standard solutions with deionized water as solvent for ion chromatography analysis. A standard curve was plotted with chloride ion concentration as the abscissa and chloride ion peak area as the ordinate. The preferred concentration range for chloride ion standard solutions is 0.01–100 mg / L; Ion chromatography analysis conditions: Column: Anion exchange column (4.6 mm × 150 mm i.d.); Conductivity detector; Suppression current, 25 mA; Isocratic elution, eluent: a mixed aqueous solution of 2 mmol / L sodium carbonate and 2 mmol / L sodium bicarbonate; Flow rate: 1.0 mL / min; Column temperature: 30℃; Sample quantification loop volume: 25 μL; Data were acquired at a rate of 5.0 Hz and processed by the Chameleon Chromatography Workstation; (3) Sample determination Take the sample to be tested in step (1) and perform ion chromatography analysis. The analysis conditions are the same as in step (2). Substitute the chloride ion peak area in the sample spectrum into the standard curve to obtain the chloride ion content in the sample. Based on the chloride ion content data, distinguish PET / rPET and calculate the proportion of rPET in the sample.
[0008] The beneficial effects of this invention are as follows: This invention innovatively proposes a green and efficient detection method to distinguish between PET and rPET. First, hot water immersion is used to induce the migration of chloride ions in regenerated polyethylene terephthalate (rPET). Then, an anion exchange column is used to achieve accurate determination of trace chloride ions.
[0009] This invention not only provides new ideas and methods for identifying virgin PET and rPET and estimating the rPET content in plastic bottles, but also establishes reliable technical support for assessing the safety of recycled plastics. During the experiment, the soaking time was optimized, and the methodology was established and evaluated. The performance of the detection method was thoroughly assessed from multiple aspects, including linearity, limit of detection, limit of quantitation, precision, and spiked recovery rate. Finally, this method was successfully applied to the quantitative detection of chloride ions in actual samples. Attached Figure Description
[0010] Figure 1 Chromatograms of chloride ion standard and PET plastic bottle soaking solution; (a) Chromatogram of 1 mg / L chloride ion standard solution, (b) Chromatogram of 50% PET plastic bottle soaking solution, (c) Chromatogram of virgin PET plastic bottle soaking solution, (d) Chromatogram of blank experimental soaking solution.
[0011] Figure 2 Schematic diagram showing the effect of different soaking times (15 min, 30 min, 45 min, 60 min) of 50%rPET plastic bottles on the migration of chloride ions.
[0012] Figure 3 Schematic diagram of chloride ion concentration in immersion solution for plastic bottles with different rPET contents (rPET contents of 10%, 20%, 30%, 50%, and 100%). Detailed Implementation
[0013] The present invention is further described below through specific embodiments, but the scope of protection of the present invention is not limited thereto.
[0014] Example 1: Establishment of a detection method
[0015] (1) Pretreatment of plastic bottles
[0016] The plastic bottle sample was washed with deionized water and dried at room temperature. The dried sample was then cut into 3mm × 3mm fragments. 1 g of sample was weighed into a 15 mL centrifuge tube, rinsed three times with deionized water, and then 5 mL of deionized water was added. The tube was then placed in a 90℃ water bath for 30 min. After the sample solution cooled to room temperature, it was filtered through a 0.45 μm microporous membrane, and the filtrate was collected for ion chromatography analysis.
[0017] Blank experiment: Add 5 mL of deionized water to a 15 mL centrifuge tube and place it in a 90℃ water bath for 30 min to obtain a blank sample.
[0018] To ensure the accuracy of the experimental results, all plastic products that must be used in the experiment were washed three times with deionized water before use, and each sample was tested three times.
[0019] (2) Preparation of chloride ion standard solution
[0020] Preparation of chloride ion standard solutions: Sodium chloride standard was prepared into a 1000 mg / L standard solution using deionized water as the solvent. This solution was then diluted with deionized water to obtain a series of chloride ion standard solutions of different concentrations (0.01, 0.05, 0.5, 1, 5, 20, 50, 100 mg / L). These standard solutions were measured on ion chromatography to generate a standard curve for quantitative analysis of chloride ions.
[0021] (3) Instrument conditions
[0022] Ion chromatography conditions: Column: Anion exchange column (4.6 mm × 150 mm i.d.); Conductivity detector; Analytical conditions: Suppression current, 25 mA; Isocratic elution, eluent concentration: 2 mmol / L sodium carbonate and 2 mmol / L sodium bicarbonate; Flow rate: 1.0 mL / min; Column temperature: 30 °C; Sample loop volume: 25 μL. Data were acquired at a rate of 5.0 Hz and processed using a Chameleon chromatography workstation.
[0023] Example 2: Results of soaking plastic bottles
[0024] Immersion solutions from virgin PET, 50% rPET, and a blank experiment were analyzed by ion chromatography, and the chromatograms are shown below. Figure 1 As shown in the figure, by comparing the chromatograms of a 1 mg / L chloride ion standard solution, it can be seen that the 50% rPET sample can migrate chloride ions in hot water, while the virgin PET sample does not. Therefore, immersing a PET plastic sample in hot water can be used to distinguish whether the plastic sample contains rPET.
[0025] Example 3: Optimization of soaking time
[0026] At a constant immersion temperature, increasing the immersion time increases the migration of chloride ions in the plastic sample. To investigate the effect of different immersion times on chloride ion migration, this experiment dispersed 1 g of 50%rPET sample in 5 mL of deionized water and immersed it in a 90℃ water bath for different times (15 min, 30 min, 45 min, and 60 min), then measured the chloride ion content in the immersion solution. The experimental results are as follows: Figure 2 As shown, the peak area remains essentially unchanged after soaking for more than 30 minutes. Considering that the amount of chloride ions migrating in the sample may have reached its maximum within 30 minutes, 30 minutes was chosen as the optimal soaking time.
[0027] Example 4 Methodological Investigation
[0028] This experiment requires quantifying the content of migrated chloride ions in actual samples; therefore, a chloride ion standard curve was established. A series of prepared chloride ion standard solutions were measured using an ion chromatograph, and a standard curve was plotted based on the response values and the prepared concentrations for quantitative analysis of chloride ions.
[0029] Table 1. Linear equation, correlation coefficient, linear range, limit of detection, limit of quantitation, and reproducibility of chloride ions.
[0030] Experimental results show that the slope of the linear equation is 0.1783, the intercept is -0.2057, and the linear correlation coefficient is 0.9993. The linear relationship is good within the chloride ion concentration range of 0.01–100.00 mg / L. The limit of detection (S / N≥3) for chloride ions is 2.10 μg / L, and the limit of quantitation (S / N≥10) is 7.00 μg / L. Intra-day precision studies of chloride ions at low, medium, and high concentrations showed a relative standard deviation (RSD) of less than 4.8% for the calculated peak area. Similarly, inter-day precision studies of chloride ions over three consecutive days showed an RSD of less than 3.8%. Detailed results are shown in Tables 1 and 2.
[0031] Table 2 Intra-day and Inter-day Precision of Chloride Ions
[0032] Example 5: Actual Sample Measurement
[0033] To evaluate the applicability of this method in real samples, five types of plastic bottles (rPET content of 10%, 20%, 30%, 50%, and 100%) were tested under optimized conditions. The chloride ion content in the soaking solution of each sample was quantified using an established chloride ion standard curve. The chloride ion content in the soaking solution of different samples is shown below. Figure 3 As shown in the figure, the chloride ion concentration in the soaking solution increases with the increase of rPET content. A linear fit was performed on the data of rPET content and chloride ion concentration in the plastic bottle, yielding the linear equation y = 0.5487x + 0.1554, with a linear correlation coefficient of 0.9425. Therefore, by measuring the chloride ion concentration in the hot water soaking solution of PET plastic bottles, it is possible not only to distinguish between PET / rPET but also to estimate the rPET content in the plastic bottle.
[0034] To verify the practicality of the above linear equation, a 60% rPET plastic bottle was used as the unknown sample. After soaking in hot water at 90℃, the chloride ion concentration in the soaking solution was determined using an anion exchange chromatography column. The average chloride ion concentration obtained from three parallel experiments was 0.45 mg / L, with an RSD of 3.3%. Based on the linear equation y = 0.5487x + 0.1554, the rPET content in the unknown sample can be calculated to be 54%, with a relative error of 10.0%.
[0035] In addition, the recoveries of chloride ions in the soaking solutions of three plastic samples with different rPET contents were determined at low, medium, and high concentrations. The results are shown in Table 3. The recoveries of the three samples ranged from 91.2% to 108.0%, and the reproducibility of the recoveries ranged from 0.9% to 9.1%. This indicates that the method can be applied to the rapid identification and quantitative analysis of rPET in real samples.
[0036] Table 3. Spiked recoveries and reproducibility of chloride ions in immersion solutions of different samples.
Claims
1. An analytical method for identifying PET / rPET by chloride ion determination, characterized in that, The method includes: (1) Sample pretreatment Take the sample, add deionized water, keep it at 90 ℃ for 30 min, then cool it to room temperature, filter it with a 0.45 μm microporous membrane, and collect the filtrate as the sample to be tested. (2) Plot the chloride ion standard curve Sodium chloride standard was used to prepare a series of chloride ion standard solutions with deionized water as solvent for ion chromatography analysis. A standard curve was plotted with chloride ion concentration as the abscissa and chloride ion peak area as the ordinate. Ion chromatography analysis conditions: Column: Anion exchange column (4.6 mm × 150 mm id); Conductivity detector; Suppression current, 25 mA; Isocratic elution, eluent: a mixed aqueous solution of 2 mmol / L sodium carbonate and 2 mmol / L sodium bicarbonate; Flow rate: 1.0 mL / min; Column temperature: 30 ℃; Sample quantification loop volume: 25 μL; (3) Sample determination Take the sample to be tested in step (1) and perform ion chromatography analysis. The analysis conditions are the same as in step (2). Substitute the chloride ion peak area in the sample spectrum into the standard curve to obtain the chloride ion content in the sample. Based on the chloride ion content data, distinguish PET / rPET and calculate the proportion of rPET in the sample.
2. The analytical method for identifying PET / rPET by chloride ion determination as described in claim 1, characterized in that, In step (1), the sample is a plastic bottle. The plastic bottle is washed with deionized water and dried at room temperature, and then cut into 3 mm × 3 mm fragments for later use.
3. The analytical method for identifying PET / rPET by chloride ion determination as described in claim 1, characterized in that, In step (1), the mass-to-volume ratio of the sample to deionized water is 1:15, g / mL.
4. The analytical method for identifying PET / rPET by chloride ion determination as described in claim 1, characterized in that, In step (2), the concentration range of the chloride ion standard solution is 0.01~100 mg / L.