Method for measuring ash content of recycled polystyrene plastic through X-ray fluorescence spectrum

Abstract

The invention discloses a method for determining ash content of recycled polystyrene plastic by X-ray fluorescence spectroscopy, which comprises the following steps: selecting recycled polystyrene plastic with different ash content as a standard sample, determining the content of all elements of the plastic by using an X-ray luminoscope, taking organic components of the recycled polystyrene plastic as equilibrium phases to participate in calculation, and determining the ash content of the recycled polystyrene plastic by using the X-ray luminoscope to determine the ash content of the recycled polystyrene plastic. And dividing the standard sample into two sections according to the ash content, and fitting the two sections with the actual ash content function respectively. And measuring the fluorescence spectrum of the sample to be measured, calculating the theoretical ash content, and correcting the theoretical ash content by using a function. Compared with a standard ash content measuring method, the method does not need to burn plastic, and is simple, rapid, environment-friendly and safe. Compared with an empirical coefficient method of X rays, a direct tabletting method can be selected, a calibration curve of elements does not need to be established, and the analysis efficiency is improved; meanwhile, matrix effect and element spectral line overlapping caused by matrix difference between an actual sample and a standard sample are avoided, and the analysis precision is improved.

Description

Technical Field

[0001] This invention belongs to the field of plastic testing, and in particular relates to a method for determining the ash content of recycled polystyrene plastic by X-ray fluorescence spectrometry. Background Technology

[0002] In 2022, global polystyrene production capacity reached 15.32 million tons. Due to its good plasticity and processability, it accounts for a large proportion of recycled plastics. Rational polystyrene recycling can not only control environmental pollution and transform waste into resources, but also has good environmental benefits and economic value. Ash content is a crucial indicator determining the value of recycled plastics and also reflects the amount of impurities. Improper ash content control can easily cause blockages in production equipment, affect product performance, and hinder the secondary processing and utilization of recycled plastics.

[0003] X-ray fluorescence spectrometry (XRF) is a rapid and non-destructive method for elemental analysis, widely used in quantitative and qualitative elemental analysis. However, this method suffers from matrix effects. The homogeneity, particle size, density, surface condition, and chemical differences of the sample affect theoretical calculations. When there are many types of elements, the characteristic X-rays of elements can be affected by spectral background and spectral line overlap, all of which affect the accuracy of theoretical calculation results. Therefore, the results calculated using the basic parameter method deviate significantly from the actual values. XRF spectroscopy often uses standard calibration methods or empirical coefficient methods for quantitative analysis of elemental content. This method is not suitable for samples such as recycled plastics, which have large matrix variations and numerous elements, and it is difficult to prepare suitable standard samples. CN110596170A discloses a method for determining the ash content of thermoplastic plastics using wavelength dispersive XRF spectroscopy. This method uses polypropylene plastic and additives, not recycled materials, resulting in a relatively simple composition and controllable matrix effects. Moreover, this method only considers metallic elements, using standard calibration methods for quantitative calculation of metallic elements, without considering the influence of non-metallic elements such as sulfur and phosphorus on ash content. CN 109596654 B discloses a method for determining bromine and antimony in plastics using a combination of X-ray fluorescence spectroscopy and infrared spectroscopy. This method measures fewer elements, and the elemental spectral lines do not overlap or exhibit absorption effects. The method does not use recycled polystyrene plastic, resulting in a relatively simple matrix. Gao Xinhua et al., "Practical X-ray Spectroscopic Analysis," *Journal of Chemistry of Higher Education*, 05(2017):132, introduced the principle of the basic parameter method of X-ray fluorescence. Summary of the Invention

[0004] The purpose of this invention is to provide a method for determining the ash content of recycled polystyrene plastics using X-ray fluorescence spectroscopy. This method effectively avoids the shortcomings of matrix effects, spectral overlap, and inhomogeneity that occur when measuring the X-ray fluorescence spectrum of recycled polystyrene plastics, thereby improving the accuracy of ash content measurement.

[0005] To achieve the above objectives, the present invention provides a method for determining the ash content of recycled polystyrene plastics using X-ray fluorescence spectroscopy, comprising the following steps:

[0006] (1) Select recycled polystyrene plastics with different ash contents as standard samples, and determine the actual ash content of the recycled polystyrene plastics using standard methods;

[0007] (2) The recycled polystyrene plastic is crushed into powder and prepared into plastic discs;

[0008] (3) The total element content of the plastic disc was determined by X-ray fluorescence spectrometry. The organic components of the recycled polystyrene plastic were used as the equilibrium phase in the calculation. The sum of the masses of all elements except the equilibrium phase was the theoretical ash content.

[0009] (4) Correction of theoretical ash content: All recycled polystyrene plastics are divided into segments according to their ash content; the actual ash content of the segmented recycled polystyrene plastics is mathematically fitted with the theoretical ash content;

[0010] (5) For recycled polystyrene plastics with unknown ash content, the sample is crushed and made into plastic discs. The full elemental analysis results of the sample are determined by fluorescence spectrometer, and the equilibrium phase is input and used to calculate the theoretical ash content. According to the magnitude of the theoretical ash content, the theoretical ash content is corrected by applying the segmented formula.

[0011] The present invention relates to a method for determining the ash content of recycled polystyrene plastics using X-ray fluorescence spectroscopy, wherein the X-ray fluorescence spectroscopy employs wavelength-dispersive X-ray fluorescence.

[0012] The present invention relates to a method for determining the ash content of recycled polystyrene plastic by X-ray fluorescence spectroscopy, wherein the recycled polystyrene plastic is mainly composed of polystyrene.

[0013] The present invention relates to a method for determining the ash content of recycled polystyrene plastic using X-ray fluorescence spectroscopy, wherein the pulverization method is cryogenic ball milling.

[0014] In the X-ray fluorescence spectrometry method for determining the ash content of recycled polystyrene plastic of the present invention, in step (2), the method for preparing plastic discs includes at least one of direct pressing, injection molding, and hot pressing; during the preparation of plastic discs, the pressure is greater than or equal to 10 tons, the pressing time is greater than or equal to 30 seconds, the disc diameter is greater than 20 mm, and the thickness is greater than 2 mm.

[0015] The present invention relates to a method for determining the ash content of recycled polystyrene plastic by X-ray fluorescence spectroscopy, wherein the total elements are presented in oxide form, and the total elements include at least one of Na2O, K2O, MgO, Al2O3, SiO2, P2O5, SO3, CaO, TiO2, Fe2O3, ZnO, BaO, Cr2O3, and CdO.

[0016] In the method for determining the ash content of recycled polystyrene plastic by X-ray fluorescence spectroscopy of the present invention, in step (1), the method used to determine the actual ash content of recycled polystyrene plastic by standard method is GB / T9345.1-2008 "Determination of ash content in plastics - Part 1: General method", and the calcination temperature is greater than or equal to 850℃±50℃.

[0017] In the method for determining the ash content of recycled polystyrene plastic by X-ray fluorescence spectroscopy of the present invention, in step (4), the ash mass fraction content is in segment A between 0.0% and a%, and the content is in segment B between a% and b%, where a is 1.0-3.0% and b is greater than 10.0%.

[0018] In the method for determining the ash content of recycled polystyrene plastic by X-ray fluorescence spectroscopy of the present invention, in step (3), the calculation method is the basic parameter method, which assumes that the elements are uniformly distributed in the sample, and the fluorescence X-ray intensity is expressed as a function of the chemical composition of the sample and the basic parameters; the basic parameters include at least one of physical constants and spectrometer sensitivity.

[0019] The present invention relates to a method for determining the ash content of recycled polystyrene plastic using X-ray fluorescence spectroscopy. The equilibrium phase refers to the carbon-hydrogen atom ratio of the recycled polystyrene plastic. When determining the ash content of recycled polystyrene plastic with unknown ash content, the theoretical ash content needs to be corrected using a fitting function.

[0020] This invention uses actually recycled polystyrene plastic as a sample and determines the total elemental content using X-ray fluorescence spectrometry. The carbon-hydrogen atomic ratio of the recycled polystyrene plastic is used as the equilibrium phase to calculate the theoretical ash content. The theoretical ash content is then fitted and corrected to the actual ash content, improving the accuracy of ash content determination. This method is simple and convenient, as it does not require establishing numerous standard curves for specific elements or preparing standard samples. Compared to the standard ash content measurement method GB / T 9345.1 for determining plastic ash, it eliminates the need for calcination and burning of the plastic, making it simpler, faster, reducing environmental pollution, and saving significant time. Compared to the empirical coefficient method using X-rays, it allows for the use of a direct pellet method, eliminating the need to establish elemental calibration curves, thus improving analytical efficiency. Simultaneously, it avoids matrix effects and elemental spectral overlap caused by matrix differences between the actual sample and the standard sample, improving analytical precision. Attached Figure Description

[0021] Figure 1a The ash content of segment A of the recycled polystyrene plastic in Example 1 was calculated using XRF and fitted to the actual ash content.

[0022] Figure 1b The ash content of the recycled polystyrene plastic segment B was calculated using XRF and fitted to the actual ash content in Example 1.

[0023] Figure 2a The ash content of the low-ash recycled polystyrene plastic A segment in Example 2 was fitted to the XRF calculation of ash content and actual ash content.

[0024] Figure 3a The XRF calculation of ash content and the actual ash content of segment B of high ash recoverable polystyrene plastic in Example 3 were fitted. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to specific embodiments, but the present invention is not limited to the following embodiments. Any modifications that do not depart from the concept and scope of the present invention are within the scope of the present invention.

[0026] Example 1:

[0027] Seventeen recycled polystyrene plastics (PS-3) were collected and their actual ash content was determined according to GB / T 9345.1-2008 "Determination of Ash Content in Plastics - Part 1: General Method". The calcination temperature was 870℃±20℃. These samples were used as calibration samples.

[0028] Recycled polystyrene plastic was pulverized into powder using a cryogenic ball mill in a liquid nitrogen environment. It is important to thoroughly clean the sample after each pulverization to prevent contamination. The tablet press was set to a pressure of 10 tons, a pressing time of 30 seconds, and a 30 mm die size to press the sample into discs.

[0029] The elemental composition of 17 plastic discs was determined using X-ray fluorescence spectrometry (XRF). The instrument was a Rigaku ZSX Primus II wavelength XRF spectrometer with the following parameters: X-ray tube target element Rh, tube voltage 50kV–60kV, tube current 40mA–80mA, and PHA pulse height measurement range 100–300. The basic parameter method (FP method) of this instrument was used to determine the carbon-hydrogen ratio (C / H) of the recycled polystyrene plastic. 8.15 H 8.06 As an equilibrium phase, the theoretical ash content of 17 samples was calculated using the fundamental parameter method. The elemental analysis results of the recovered polystyrene plastic PS-3 samples are shown in Table 1.

[0030] Table 1. Elemental analysis results of recycled polystyrene plastic PS-3

[0031]

[0032]

[0033] The theoretical and actual ash content calculation results are shown in Table 2. Correction of theoretical ash content: All 17 recycled polystyrene plastics were divided into two segments, A and B, according to their ash content. Segment A had a mass fraction content of 0.0%-3.0%, and segment B had a mass fraction content of 3.0%-15.0%. Five samples were selected from segment A and six from segment B as correction samples. The theoretical ash content of the two segments was linearly fitted to the actual ash content. The fitting formula for segment A was: y = 1.0415x - 0.153, with a correlation coefficient R0. 2 =0.9965. The fitting formula for segment B is: y = 1.052x - 0.812, and the correlation coefficient R is 0.9965. 2 =0.969. Figure 1a To calculate the ash content of segment A of recycled polystyrene plastic using XRF and fit it to the actual ash content. Figure 1b To calculate the ash content of segment B of recycled polystyrene plastic using XRF and fit it to the actual ash content.

[0034] Table 2. Calculated and Actual Ash Content of Recycled Polystyrene Plastics

[0035]

[0036]

[0037] The remaining six samples were divided into two segments, A and B, based on their ash content for calibration. The results are shown in Table 3. Table 3 shows that, regardless of segment A or B, the ash content after calibration is closer to the measured ash content than the theoretical ash content calculated by XRF, indicating that this method is accurate and reliable.

[0038] Table 3. Ash content calculation results, actual values, and correction values ​​of recycled polystyrene plastics.

[0039]

[0040] Five plastic discs were repeatedly prepared from the recycled polystyrene plastics of samples A-3 and B-1, and the above measurement steps were repeated. The results are shown in Table 4. The standard deviation of A-3 after five repeated measurements was 0.090, and the standard deviation of B-1 after five repeated measurements was 0.071, which indicates that the method of the present invention has good repeatability.

[0041] Table 4 Ash correction values ​​for repeated determinations of recycled polystyrene plastics A-3 and B-2

[0042]

[0043] Example 2:

[0044] Eight recycled polystyrene plastics with low ash content were collected. The actual ash content of the recycled polystyrene plastics was determined according to GB / T 9345.1-2008 "Determination of Ash Content in Plastics - Part 1: General Method". The calcination temperature was 850℃±20℃. Six of these samples were used as calibration samples and two were used as verification samples.

[0045] Recycled polystyrene plastic was pulverized into powder using a cryogenic ball mill in a liquid nitrogen environment. Eight sample discs were then manufactured using a vacuum hot press from Suzhou Gongjiang Machinery Equipment Co., Ltd., under vacuum conditions, with a set temperature of 200℃, a pressure of 2 tons, and a holding time of 60 seconds.

[0046] The elemental composition of eight plastic discs was determined using X-ray fluorescence spectrometry (XRF). The instrument was a Rigaku ZSX Primus IV wavelength XRF spectrometer with the following parameters: X-ray tube target element Rh, tube voltage 50kV–60kV, tube current 40mA–80mA, and PHA pulse height measurement range 100–300 mm. The carbon-to-hydrogen ratio of this series of samples is known to be C. 8.21 H 8.12 Using the basic parameter method (FP method) of fluorescence spectrometry, the carbon-hydrogen ratio (C / H) of recycled polystyrene plastic was determined. 8.21 H 8.12 As an equilibrium phase, the theoretical ash content values ​​of the eight samples were obtained through XRF calculation.

[0047] Six samples were randomly selected as calibration samples. The calculated theoretical and actual ash contents are shown in Table 5. Since the actual ash contents of all samples were below 1.000%, these calibration samples are suitable for segment A. The fitting formula for segment A is: y = 6.942x 2 -0.516x + 0.0514, correlation coefficient R 2 =0.9858. Figure 2a XRF calculations were performed to fit the ash content of segment A of low-ash recycled polystyrene plastic to the actual ash content.

[0048] Table 5. Calculated and Actual Ash Content of Recycled Polystyrene Plastics

[0049]

[0050] The remaining two unknown samples were used for verification, and the results are shown in Table 6. As can be seen from Table 6, the corrected ash content shows a significantly reduced error compared to the ash content calculated by XRF theory, and is much closer to the actual value.

[0051] Table 6. Ash content calculation results, actual values, and correction values ​​of recycled polystyrene plastics.

[0052]

[0053] Example 3:

[0054] Seven recycled polystyrene plastics with high ash content were collected. The actual ash content of the recycled polystyrene plastics was determined according to GB / T 9345.1-2008 "Determination of Ash Content in Plastics - Part 1: General Methods" with a calcination temperature of 870℃±20℃. Five of these samples were used as calibration samples and two were used as verification samples.

[0055] Recycled polystyrene plastic was pulverized into powder using a cryogenic ball mill in a liquid nitrogen environment. The pressure of the tablet press was set to 20 tons, the pressing time to 50 seconds, and the disc mold to be 30 mm, and all samples were pressed into discs.

[0056] The elemental composition of five plastic discs used in the calibration sample was determined using X-ray fluorescence spectrometry (XRF). The instrument was a Rigaku ZSX Primus IV wavelength XRF spectrometer with the following parameters: X-ray tube target element Rh, tube voltage 50kV–60kV, tube current 40mA–80mA, and PHA pulse height measurement range 100–300. The carbon-hydrogen ratio (C / H) of the recycled polystyrene plastic was determined using the basic parameter method (FP method). 8.06 H 8.16 As an equilibrium phase, the theoretical ash content values ​​of the seven samples were obtained through XRF calculation. The calculated theoretical and actual ash contents of the corrected samples are shown in Table 7. Since the actual ash contents of all samples are higher than 3.000%, these corrected samples are suitable for segment B. The fitting formula for segment B is: y = -0.0149x 2 +1.1845x - 0.4395, correlation coefficient R 2 =0.9959. Figure 3a XRF calculations were performed to fit the ash content of high-ash recycled polystyrene plastic segment B to the actual ash content.

[0057] Table 7. Calculated and Actual Ash Content of Recycled Polystyrene Plastics

[0058]

[0059] The remaining two samples were corrected using a fitting formula, and the results are shown in Table 8. Table 8 shows that after correction using this method, the error in the theoretical calculation results is significantly reduced, and the results are closer to the actual values.

[0060] Table 8. Ash content calculation results, actual values, and correction values ​​of recycled polystyrene plastics.

[0061]

[0062] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the claims of the present invention.

Claims

1. A method for determining the ash content of recycled polystyrene plastic by X-ray fluorescence spectroscopy, characterized in that, Includes the following steps: (1) Select recycled polystyrene plastics with different ash contents as standard samples, and determine the actual ash content of the recycled polystyrene plastics using standard methods; (2) The recycled polystyrene plastic is crushed into powder and prepared into plastic discs; (3) The total element content of the plastic disc was determined by X-ray fluorescence spectrometry. The organic components of the recycled polystyrene plastic were used as the equilibrium phase in the calculation. The sum of the masses of all elements except the equilibrium phase was the theoretical ash content. (4) Correction of theoretical ash content: All recycled polystyrene plastics are divided into segments according to their ash content; the actual ash content of the segmented recycled polystyrene plastics is mathematically fitted with the theoretical ash content; (5) For recycled polystyrene plastics with unknown ash content, the sample is crushed and made into plastic discs. The full elemental analysis results of the sample are determined by fluorescence spectrometer, and the equilibrium phase is input and used to calculate the theoretical ash content. According to the magnitude of the theoretical ash content, the theoretical ash content is corrected by applying the segmented formula.

2. The method of claim 1, wherein, The X-ray fluorescence spectrum used is wavelength-dispersive X-ray fluorescence.

3. The method of claim 1, wherein, The recycled polystyrene plastic is mainly composed of polystyrene.

4. The method of claim 1, wherein, The pulverization method is cryogenic ball milling.

5. The method of claim 1, wherein, In step (2), the method for preparing the plastic disc includes at least one of direct pressing, injection molding, and hot pressing; during the preparation of the plastic disc, the pressure is greater than or equal to 10 tons, the pressing time is greater than or equal to 30 seconds, the disc diameter is greater than 20 mm, and the thickness is greater than 2 mm.

6. The method of claim 1, wherein, The elements are presented in oxide form, and the elements include at least one of Na2O, K2O, MgO, Al2O3, SiO2, P2O5, SO3, CaO, TiO2, Fe2O3, ZnO, BaO, Cr2O3, and CdO.

7. The method of claim 1, wherein, In step (1), the method used to determine the actual ash content of recycled polystyrene plastic using the standard method is GB / T9345.1-2008 "Determination of ash content in plastics - Part 1: General method", and the calcination temperature is greater than or equal to 850℃±50℃.

8. The method of claim 1, wherein, In step (4), the ash content is in segment A if it is between 0.0% and a%, and in segment B if it is between a% and b%. a is 1.0-3.0% and b is greater than 10.0%.

9. The method of claim 1, wherein, In step (3), the calculation method is the basic parameter method, which assumes that the elements are uniformly distributed in the sample, and the fluorescence X-ray intensity is expressed as a function of the sample chemical composition and basic parameters; the basic parameters include at least one of physical constants and spectrometer sensitivity.

10. The method of claim 1, wherein, The equilibrium phase refers to the carbon-hydrogen atom ratio of the recycled polystyrene plastic; when determining the ash content of recycled polystyrene plastic with unknown ash content, the theoretical ash content needs to be corrected using a fitting function.

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