Method for detecting magnetic foreign matter content of ultrapure polyethylene raw material

Abstract

The application relates to a method for detecting the content of magnetic foreign matters in ultra-pure polyethylene raw materials, which comprises the following steps: mixing polyethylene powder samples and a dispersion solvent to form a slurry; placing a magnetic component in the slurry to adsorb the magnetic foreign matters in the slurry; collecting the magnetic foreign matters on the magnetic component and testing the content of the magnetic foreign matters; wherein the dispersion solvent is configured by components including the following weight parts: pure water 100 parts, an anionic surfactant 0.3-0.6 parts, a non-ionic surfactant 0.15-0.35 parts, a low HLB surfactant 0.05-0.15 parts and a metal chelating agent 0.02-0.08 parts. The application realizes effective acquisition of magnetic foreign matters in polyethylene with a wide distribution of particle sizes through the compound dispersion solvent, and provides a reliable means for accurate detection of the magnetic foreign matters in the ultra-pure polyethylene.

Description

Technical Field

[0001] This invention relates to the field of ultrapure polyethylene, and in particular to a method for detecting the content of magnetic foreign matter in ultrapure polyethylene raw materials. Background Technology

[0002] With the widespread application of high-end polyolefin materials in new energy, semiconductors, and medical fields, the purity requirements are becoming increasingly stringent. Taking ultrapure polyethylene prepared by the slurry method as an example, micron-sized and even submicron-sized magnetic foreign matter (such as iron, chromium, nickel, and their oxides) is a key factor affecting the quality of downstream products. For example, in lithium-ion battery separator applications, such impurities can lead to separator breakdown, micro-short circuits, and even thermal runaway. Therefore, accurate detection of magnetic foreign matter in products has become crucial for quality control.

[0003] Currently, the industry generally adopts the JOMESA cleanliness test method using anhydrous ethanol as the medium, which involves adsorbing magnetic particles with a magnetic rod and then filtering and counting them. However, this method has significant limitations: firstly, there are safety and environmental issues, as ethanol is flammable and volatile, resulting in high costs for use and wastewater treatment; secondly, the accuracy of the test is subject to deviation. Because ethanol has poor wettability on polyethylene powder, the powder tends to agglomerate and accumulate at the bottom of the container, making it difficult for the magnetic foreign matter encapsulated inside to be captured by the magnetic rod. The cleaning process also easily causes the loss of foreign matter, ultimately leading to a systematically low test result and a risk of missed detection.

[0004] Existing technologies, such as patent CN116296720A, disclose the use of deionized water and the surfactant sodium dodecylbenzenesulfonate (SDBS) as a dispersion system, but still have the following shortcomings: the single surfactant used is difficult to achieve the dispersion effect of polyethylene powder with a wide particle size range (10–500 μm), especially with insufficient wetting of large-diameter particles and limited stability of small-diameter particles; in addition, there is a lack of effective pretreatment methods to break down the original agglomerates, resulting in the inability to fully release internal magnetic foreign matter, and the method has limited ability to capture and identify submicron (<5 μm) magnetic foreign matter, resulting in insufficient detection sensitivity.

[0005] Therefore, there is an urgent need to develop a novel detection method that can achieve uniform dispersion of wide-particle-size polyethylene, effectively release encapsulated magnetic foreign matter, and possess high sensitivity detection capabilities (such as for particles <5μm). Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a highly sensitive detection method for the content of magnetic foreign matter in ultrapure polyethylene raw materials. By constructing a compound dispersion solvent combined with low-frequency ultrasonic pretreatment, efficient dispersion of polyethylene with a wide particle size distribution and full release of magnetic foreign matter are achieved. Through a multi-level magnetic adsorption strategy and enrichment with submicron particles, effective capture and accurate quantification of magnetic foreign matter <5μm are achieved.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A method for detecting the magnetic foreign matter content in ultrapure polyethylene raw materials includes:

[0009] The polyethylene powder sample was thoroughly mixed with the dispersion solvent to form a slurry.

[0010] The magnetic component is placed in the slurry to adsorb magnetic foreign matter in the slurry;

[0011] Collect the magnetic foreign matter on the magnetic component and test the content of the magnetic foreign matter;

[0012] The dispersing solvent is prepared from the following components in parts by weight: 100 parts pure water, 0.3-0.6 parts anionic surfactant, 0.15-0.35 parts nonionic surfactant, 0.05-0.15 parts low HLB surfactant, and 0.02-0.08 parts metal chelating agent.

[0013] As a preferred technical solution, the dispersing solvent is prepared from the following components in parts by weight: 100 parts pure water, 0.45 parts anionic surfactant, 0.25 parts nonionic surfactant, 0.1 parts low HLB surfactant, and 0.05 parts metal chelating agent.

[0014] As a preferred technical solution, the resistivity of the pure water is ≥5 MΩ·cm, preferably ≥10 MΩ·cm, and even more preferably ≥18 MΩ·cm;

[0015] The anionic surfactant is selected from one or more of sodium dodecylbenzenesulfonate (SDBS), sodium fatty alcohol polyoxyethylene ether sulfate (AES), and sodium α-alkenyl sulfonate (AOS);

[0016] The nonionic surfactant is selected from one or more of alkyl glycosides (APG, such as dodecyl glucoside), fatty alcohol polyoxyethylene ether (AEO), and fatty alcohol polyether (XL).

[0017] The low HLB surfactant is selected from dehydrated sorbitan fatty acid esters with an HLB value of 3-6;

[0018] The metal chelating agent is selected from one or more of EDTA-2Na, citric acid, and gluconic acid.

[0019] As a preferred technical solution, the anionic surfactant is selected from sodium fatty alcohol polyoxyethylene ether sulfate (AES).

[0020] The nonionic surfactant is selected from alkyl glycosides (such as APG-1214).

[0021] The low HLB surfactant is selected from dehydrated sorbitan oleate (Span-80).

[0022] The metal chelating agent is selected from disodium ethylenediaminetetraacetate (EDTA-2Na).

[0023] As a preferred technical solution, the dispersion solvent is prepared by the following method:

[0024] Step 1: Add the metal chelating agent to pure water and stir at 45-55℃ for 10-15 minutes until completely dissolved;

[0025] Step 2: Premix the anionic surfactant and the low HLB surfactant evenly, stir at 35-45℃ until a homogeneous mixture is formed, and then slowly add it to the aqueous phase obtained in Step 1, and stir and mix at 35-45℃ for 15-20 minutes.

[0026] Step 3: Add nonionic surfactant and stir at room temperature for 30-40 minutes until the solution is uniformly milky white;

[0027] Step 4: Let stand for 1.5-2.5 hours to allow the components to reach interfacial adsorption equilibrium, thus obtaining the compound dispersion solvent.

[0028] As a preferred technical solution, the mass ratio of the polyethylene powder sample to the dispersing solvent is 1:2-6, preferably 1:3-4.

[0029] As a preferred technical solution, the polyethylene powder sample is mixed with a dispersing solvent and then pretreated with low-frequency ultrasonication for 5-15 minutes at a frequency of 20-40kHz and a power density of 0.5-2W / mL to obtain a uniform slurry.

[0030] As a preferred technical solution, the magnetic component includes a magnetic rod and a removable coating layer covering the magnetic rod;

[0031] Before the polyethylene powder sample is mixed with the dispersion solvent, the dispersion solvent and exogenous magnetic foreign matter in the container are first adsorbed and removed using a magnetic component. Then, the magnetic rod is removed and a new clean coating layer is replaced.

[0032] As a preferred technical solution, the magnetic component employs multi-stage magnetic adsorption to capture magnetic foreign objects:

[0033] First-stage adsorption: A primary magnetic rod with a magnetic induction intensity of 8000-10000GS is placed into the slurry and stirred at a low speed of 30-50r / min for 20-30min to capture large magnetic foreign objects with a diameter >50μm.

[0034] Second-stage adsorption: After removing the primary magnetic rod and replacing it with a new coating layer, a secondary magnetic rod with a magnetic induction intensity of 12000-16000GS is placed into the slurry and stirred at a speed of 60-80r / min for 15-25min to capture medium-sized magnetic foreign matter of 5-50μm.

[0035] Third-stage adsorption: Remove the secondary magnetic rod and transfer the slurry to a constant magnetic field with a magnetic induction intensity of 3000-5000GS. Let it stand for 30-60 minutes to enrich submicron magnetic foreign matter <5μm at the bottom of the container.

[0036] As a preferred technical solution, the following methods are employed: graded collection and graded detection and analysis of magnetic foreign objects.

[0037] (1) Take out the primary magnetic rod and the secondary magnetic rod respectively, rinse the outer wall of the coating layer repeatedly with pure water, collect the rinsing liquid to obtain a suspension of large-particle magnetic foreign matter, filter and dry it, and use a cleanliness tester to analyze particles with a particle size ≥5μm.

[0038] (2) After the slurry has undergone the third adsorption, the upper clear liquid is discharged under the condition of maintaining the magnetic field, and 50-100 mL of the bottom enrichment liquid is retained. Pure water is added to the enrichment liquid to the original volume. The operation is repeated 2-3 times to obtain the submicron magnetic foreign matter enrichment liquid. The liquid is collected by vacuum filtration on a filter membrane with a pore size ≤0.22 μm. After drying, the morphology of <5 μm particles is observed and the elements are identified by scanning electron microscopy combined with energy dispersive spectroscopy, or the trace metal elements are quantitatively analyzed by inductively coupled plasma mass spectrometry.

[0039] As a preferred technical solution, the covering layer is a heat shrink tubing, and the port is sealed with a heat sealing machine during use.

[0040] In a specific implementation, a method for detecting the magnetic foreign matter content in ultrapure polyethylene raw materials includes the following steps:

[0041] S1. Preparation of dispersing solvent and low-frequency ultrasonic pretreatment: The polyethylene powder sample and the dispersing solvent are mixed according to the mass ratio and pretreated with low-frequency ultrasonic to obtain a uniform slurry;

[0042] S2. System background purification: Encapsulate the magnetic rod with a clean coating layer, place it in a container containing the dispersion solvent, and stir at a speed of 40-80 r / min for 10-20 min to adsorb and remove the dispersion solvent and exogenous magnetic foreign matter on the inner wall of the container. Remove the magnetic rod and replace it with a new clean coating layer.

[0043] S3. Multi-stage magnetic adsorption capture: The slurry pretreated in step S1 is transferred to a container that has undergone background purification, and a multi-stage magnetic adsorption strategy is used to capture magnetic foreign matter.

[0044] First-stage adsorption: A primary magnetic rod with a magnetic induction intensity of 8000-10000GS is placed into the slurry and stirred at a low speed of 30-50r / min for 20-30min to preferentially capture large magnetic foreign objects with a diameter >50μm.

[0045] Second-stage adsorption: After removing the primary magnetic rod and replacing it with a new coating layer, a secondary magnetic rod with a magnetic induction intensity of 12000-16000GS is placed into the slurry and stirred at a speed of 60-80r / min for 15-25min to capture medium-sized magnetic foreign matter of 5-50μm.

[0046] Third-stage adsorption: Remove the secondary magnetic rod and transfer the slurry to a constant magnetic field with a magnetic induction intensity of 3000-5000GS. Let it stand for 30-60 minutes to allow submicron magnetic foreign objects <5μm to slowly migrate and accumulate at the bottom of the container in the weak magnetic field.

[0047] S4. Grading and Collection of Magnetic Foreign Matter: (S4-1) Collection of Large-Particle Foreign Matter: Take out the primary and secondary magnetic rods respectively, rinse the outer wall of the coating layer repeatedly with pure water, and collect the rinsing liquid to obtain a suspension of large-particle magnetic foreign matter; (S4-2) Enrichment of Submicron-Scale Foreign Matter: Slowly discharge the upper clear liquid from the slurry after the third-stage adsorption under the condition of maintaining the magnetic field, and retain 50-100 mL of the bottom enrichment liquid; add pure water to the enrichment liquid to the original volume, and repeat the standing-draining operation 2-3 times to obtain a submicron-scale magnetic foreign matter enrichment liquid.

[0048] S5. Grading and Analysis: (S5-1) After vacuum filtration and drying, the suspension of large-particle magnetic foreign matter is analyzed for particles with a diameter ≥5μm using a cleanliness tester; (S5-2) The enriched liquid of submicron-sized magnetic foreign matter is collected on a filter membrane with a pore size ≤0.22μm after vacuum filtration and drying. The morphology of particles <5μm is observed and elemental identification is performed using scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (EDS), or quantitative analysis of trace metal elements is performed using inductively coupled plasma mass spectrometry (ICP-MS).

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] 1. This invention addresses the characteristics of polyethylene powder with a wide particle size distribution (10-500 μm) and significant differences in surface properties among particles of different sizes. By employing a compounded dispersion solvent, it achieves efficient dispersion of polyethylene across the entire particle size range, shortening the wetting time of large particles, increasing the suspension rate of small particles, and improving the agglomerate breakage rate. Utilizing an HLB gradient crossing strategy, anionic surfactants provide electrostatic repulsion, suitable for medium-sized particles; nonionic surfactants form a steric hindrance layer of hydration, resulting in a high agglomerate breakage rate and effectively releasing encapsulated magnetic foreign matter, providing strong steric hindrance and high suspension rate for particles <150 μm; low-HLB surfactants enable rapid wetting of large particles >200 μm, preventing agglomeration. Furthermore, by introducing a metal chelating agent, exogenous metal ions are pre-chelated during the dispersion solvent preparation stage to form soluble complexes, reducing the amount of exogenous metal introduced, avoiding background interference, ensuring the authenticity and reliability of the test data, and simultaneously reducing the dispersing activity of the surfactant, minimizing interference from free metal ions in water for subsequent tests.

[0051] 2. In this invention, low-frequency ultrasonic pretreatment is introduced into the mixture of polyethylene and dispersion solvent before magnetic adsorption. The cavitation bubbles generated by low-frequency ultrasound have a large diameter. When they collapse, the mechanical shock waves released effectively destroy the dense aggregates in the polyethylene powder, release the physically encapsulated magnetic foreign matter, and couple with the compounded dispersion solvent, so that the magnetic foreign matter is released more effectively and captured and collected.

[0052] 3. To address the differences in magnetic response characteristics of magnetic foreign objects with different particle sizes, this invention employs a three-stage progressive magnetic adsorption: the first stage uses a low magnetic induction intensity and low-speed stirring to prevent large-particle magnetic foreign objects from rapidly covering the surface of the magnetic rod and forming a "magnetic shielding layer" due to excessive magnetic force; the second stage uses a high magnetic induction intensity to enhance the driving force for capturing medium-sized weakly magnetic particles; the third stage uses a weak constant magnetic field for static placement, achieving slow but sufficient enrichment by extending the action time.

[0053] 4. This invention enables the detection of submicron (<5μm) magnetic foreign matter. Addressing the challenge of accurately counting <5μm particles using conventional cleanliness testers, this invention employs magnetic field-assisted sedimentation enrichment combined with high-resolution detection: submicron particles are allowed to migrate directionally to the bottom of the container by overcoming Brownian motion through a constant magnetic field. After multiple washes to increase local concentration, SEM-EDS is used for single-particle morphology-composition analysis, or ICP-MS is used for quantification of metal content, thus achieving precise characterization of submicron magnetic foreign matter.

[0054] 5. This invention reduces testing costs and improves economic efficiency. By using industrial-grade reagents and pure water instead of organic solvents, raw material costs are reduced, flammability and explosion risks are eliminated, and testing is safer and more environmentally friendly. Detailed Implementation

[0055] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0056] Experimental Materials and Testing Equipment

[0057] Polyethylene samples: Three different batches of ultrapure polyethylene powder products (density approximately 0.94 g / cm³) from the polyethylene production unit of Puxi Crystal New Materials (Shanghai) Co., Ltd.

[0058] Pure water: homemade in the laboratory;

[0059] Anionic surfactant: Sodium fatty alcohol polyoxyethylene ether sulfate (AES), industrial grade, HLB value approximately 11-12, Zhejiang Zanyu Technology Co., Ltd.

[0060] Nonionic surfactant: Alkyl glycoside (APG-1214), industrial grade, HLB=13, carbon chain C12-C14, Shanghai Fakai Chemical.

[0061] Low HLB surfactant: Span-80, Guangzhou Huana Chemical Co., Ltd.

[0062] Metal chelating agent: Disodium ethylenediaminetetraacetate (EDTA-2Na), analytical grade, Xilong Scientific Co., Ltd.

[0063] Commercially available dishwashing liquid: White Cat Natural Plant APG Dishwashing Liquid contains anionic surfactants (sodium C10-16 alcohol polyoxyethylene ether sulfate, sodium C10-16 alkylbenzene sulfonate), nonionic surfactants (alkyl glycosides, APG), amphoteric surfactants (cocamidopropyl betaine, CAB), chelating agents (tetrasodium diacetate of glutamate), and other additives and components.

[0064] Anhydrous ethanol: commercially available, industrial grade, density 0.789 g / cm³;

[0065] Disk: Magnetic flux density 6000GS, diameter 120mm;

[0066] Heat shrink tubing: wall thickness 0.3mm, diameter 25mm;

[0067] Filter membrane: 50 mm in diameter, 0.45 μm in pore size;

[0068] Analytical instrument: JOMESA cleanliness tester (equipped with automatic scanning and particle identification functions).

[0069] Dispersion solvent preparation

[0070] Take a clean container, add approximately 3000 g (3 L) of pure water, add 1.5 g of EDTA-2Na, and magnetically stir for 10 min (320 r / min) in a 50°C water bath until completely dissolved and the solution is clear and transparent. Take 13.5 g of AES and 3.0 g of Span-80, premix them thoroughly, and magnetically stir for 5 min in a 40°C water bath until a homogeneous and transparent mixture is formed. Then slowly add the mixture to the aqueous phase and magnetically stir for 15 min (280 r / min) in a 40°C water bath. Allow the solution to cool naturally to room temperature, add 7.5 g of APG-1214, and magnetically stir for 30 min (180 r / min) until the solution is uniformly milky white. Let the prepared dispersion solvent stand for 2 h to allow the components to reach interfacial adsorption equilibrium, thus obtaining the compound dispersion solvent, for later use (no more than 24 h).

[0071] Example 1-A

[0072] For batch number A-V565A ultrapure polyethylene samples, perform magnetic foreign matter detection according to the following steps:

[0073] (1) Take a clean 5L ball mill jar, add 3L of pre-prepared dispersion solvent, take a heat shrink tube with a wall thickness of 0.3mm and a diameter of 25mm, cut it to an appropriate length, heat seal one end, put a magnetic rod with a length of 240mm, a diameter of 24mm and a magnetic induction intensity of 12000GS into the tube, heat seal the other end, put the sealed magnetic rod into the ball mill jar, and roll it on a bottle rolling machine at 60r / min for 15min to adsorb background foreign matter, take out the magnetic rod and replace it with a new heat shrink tube.

[0074] (2) Add 1000g of polyethylene powder to the tank, roll it for 15 min under the same conditions, and then pre-treat it with ultrasound for 10 min under the conditions of 35kHz frequency and 1.2W / mL power density to obtain a uniform slurry.

[0075] (3) Multi-stage magnetic adsorption: Place a primary magnetic rod with a magnetic induction intensity of 9000GS into the pretreated slurry, roll it at 40r / min for 25min, remove the magnetic rod, and collect the heat shrink tubing rinsing liquid A; replace with a new heat shrink tubing, place a secondary magnetic rod with a magnetic induction intensity of 14000GS, roll it at 60r / min for 20min, remove the magnetic rod, and collect the rinsing liquid B; transfer the remaining slurry to a flat-bottomed container and place it in a constant magnetic field (generated by a Helmholtz coil) with a magnetic induction intensity of 4000GS and let it stand for 45min.

[0076] (4) Graded collection: Rinse solutions A and B were combined, filtered through a 0.45 μm filter membrane, dried at 80℃ for 5 min, and analyzed for particles ≥5 μm using a JOMESA cleanliness tester. The magnification was set to 2.5 times, the focus value was adjusted to the maximum value, and the automatic scanning program was started. The instrument automatically identified and counted the magnetic foreign particles on the filter membrane, and output the counting results according to the particle size range (5-15 μm, 15-25 μm, 25-50 μm, 50-100 μm, >100 μm). The enriched liquid (about 80 mL) at the bottom of the flat-bottomed container after standing was filtered through a 0.22 μm filter membrane, dried, and analyzed for <5 μm particles using SEM-EDS according to the standard method. The specific test results are detailed in Table 1.

[0077] Example 1-B

[0078] For ultrapure polyethylene samples with batch number A-V565A, perform magnetic foreign matter detection according to the following steps:

[0079] (1) Preparation of dispersing solvent: Take a clean 5L ball mill jar, add 3L of high-purity water and 15mL of commercially available ordinary detergent, shake well and set aside.

[0080] (2) Magnetic rod encapsulation: Take a heat shrink tube with a wall thickness of 0.3 mm and a diameter of 25 mm, cut it to an appropriate length, and heat seal one end. Place a magnetic rod with a length of 240 mm, a diameter of 24 mm, and a magnetic induction intensity of 12000 GS into the tube, and heat seal the other end.

[0081] (3) Background purification: Place the packaged magnetic rod into the ball mill jar and roll it on the bottle roller at 60r / min for 15min to adsorb background foreign matter. Remove the magnetic rod and replace it with a new heat shrink tubing.

[0082] (4) Sample extraction: Weigh 1000 g of the well-mixed sample and add it to the container. Roll it for 15 min under the same conditions. Remove the magnetic rod and place it upright in a 500 mL beaker. Peel off the heat shrink tubing and rinse the outer wall of the heat shrink tubing with pure water 3 times.

[0083] (5) Cleaning and separation: Add pure water to the beaker until it is almost full, and sonicate for 2 min; place it on a disk with a diameter of 120 mm and a magnetic induction intensity of 6000 GS and let it stand for 5 min; tilt the beaker and gently blow the white polyethylene powder on the surface of the liquid with a wash bottle until there is no powder on the surface of the liquid; use a pipette to remove the supernatant until 200 mL remains.

[0084] (6) Repeated purification: Repeat the "add water-let stand-powder-absorb liquid" operation 3 times until the washing liquid is completely clear and transparent.

[0085] (7) Filtration and drying: Use a filter membrane with a diameter of 50 mm and a pore size of 0.45 μm for vacuum filtration, and rinse the beaker and funnel three times with pure water. Remove the filter membrane and place it in a weighing bottle, bake it at 80℃ for about 5 minutes, and remove it when the filter membrane is slightly curled.

[0086] (8) JOMESA Cleanliness Analysis: Place the dried filter membrane on the stage of the JOMESA cleanliness tester, set the magnification to 2.5x, adjust the focus value to the maximum value, and start the automatic scanning program. The instrument automatically identifies and counts the magnetic foreign particles on the filter membrane, and outputs the counting results according to the particle size range (5-15 μm, 15-25 μm, 25-50 μm, 50-100 μm, >100 μm). The test results are detailed in Table 1.

[0087] Comparative Example 1

[0088] Take ultrapure polyethylene samples with the same batch number A-V565A as in Example 1, and perform magnetic foreign matter detection using the traditional ethanol method according to the following steps:

[0089] (1) Take 1000 g of sample and place it in a ball mill jar, and add about 3 L of anhydrous ethanol as a dispersion medium.

[0090] (2) Place the magnetic rod (using a common sleeve) and stir at the same speed for 15 minutes on a bottle roller.

[0091] (3) Remove the magnetic rod, rinse the magnetic rod and sleeve with anhydrous ethanol, and collect the washing solution.

[0092] (4) The washing solution was vacuum filtered, and after the filter membrane was dried, it was scanned and analyzed using a JOMESA cleanliness tester under the same parameters as in Example 1 (magnification 2.5x, maximum focus value). The counting results were output according to the particle size range (5-15 μm, 15-25 μm, 25-50 μm, 50-100 μm, >100 μm). The test results are detailed in Table 1.

[0093] Example 2-A

[0094] Following the same test method as in Example 1-A, the ultrapure polyethylene samples with batch numbers A-V562A were subjected to magnetic foreign matter detection. The test results are detailed in Table 1.

[0095] Example 2-B

[0096] Following the same test method as in Example 1-B, the ultrapure polyethylene samples with batch numbers A-V562A were subjected to magnetic foreign matter detection. The test results are detailed in Table 1.

[0097] Comparative Example 2

[0098] The ultrapure polyethylene samples with batch numbers A-V562A were subjected to magnetic foreign matter detection using the same test method as Comparative Example 1. The test results are detailed in Table 1.

[0099] Example 3-A

[0100] Following the same test method as in Example 1-A, the ultrapure polyethylene sample with batch number A563A (ton bag mixed sample) was subjected to magnetic foreign matter detection. The test results are detailed in Table 1.

[0101] Example 3-B

[0102] Following the same test method as in Example 1-B, the ultrapure polyethylene sample with batch number A563A (ton bag mixed sample) was subjected to magnetic foreign matter detection. The test results are detailed in Table 1.

[0103] Comparative Example 3

[0104] Following the same test method as Comparative Example 1, the ultrapure polyethylene sample with batch number A563A (ton bag mixed sample) was subjected to magnetic foreign matter detection. The test results are detailed in Table 1.

[0105] Table 1 Sample test results

[0106]

[0107] Note: Particles <5μm were analyzed using SEM-EDS (scanning electron microscope-energy dispersive spectroscopy), and this particle size range was not included in the total comparison; "—" indicates that this particle size range was not detected in this example.

[0108] As shown in Table 1, the test results demonstrate that this invention achieves a breakthrough in the detection of magnetic foreign matter in ultrapure polyethylene through a combination of compound dispersant, low-frequency ultrasonic pretreatment, and a multi-stage magnetic adsorption strategy. Compared to the traditional ethanol method, taking samples A-V565A from the same batch as an example, the detection rate of magnetic foreign matter using this invention is significantly improved, with increases of 157% and 140% in the small particle size ranges (5-15μm and 15-25μm), respectively. This is because, in the traditional ethanol method, polyethylene powder has poor wettability in ethanol and is prone to agglomeration, making it difficult for the magnetic rod to reach the interior of the agglomerates, resulting in a large number of magnetic foreign matter not being captured. In contrast, this invention uses a compound dispersant to form a stable suspension dispersion system in water, ensuring sufficient contact with the magnetic rod and allowing the encapsulated foreign matter to be completely released. Taking batch A-V565A as an example, the detergent method failed to detect particles <5μm. The total amount of magnetic foreign matter detected by this invention increased by 37.7%, indicating that by accurately matching the HLB gradient (combination of anionic, nonionic and low HLB surfactants), this invention can achieve better full-range dispersion effect and improve the release efficiency of small-diameter foreign matter.

[0109] Furthermore, this invention achieves precise detection of submicron magnetic foreign matter <5μm. By combining static enrichment under constant magnetic field with SEM-EDS analysis, it overcomes the challenges of significant Brownian motion, weak magnetic response, and difficulty in enrichment of submicron particles, providing more comprehensive data support for the quality control of high-cleanliness polyethylene materials. This invention uses a JOMESA cleanliness tester for automatic scanning; the coefficient of variation for repeated scans of the same sample is less than 5%, demonstrating good method stability. The foreign matter levels show a consistent trend across different batches, indicating that this invention does not introduce random errors and obtains detection results that more closely approximate the true values.

[0110] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for detecting the content of magnetic foreign matter in ultrapure polyethylene raw materials, characterized in that, include: The polyethylene powder sample was thoroughly mixed with the dispersion solvent to form a slurry. The magnetic component is placed in the slurry to adsorb magnetic foreign matter in the slurry; Collect the magnetic foreign matter on the magnetic component and test the content of the magnetic foreign matter; The dispersing solvent is prepared from the following components in parts by weight: 100 parts pure water, 0.3-0.6 parts anionic surfactant, 0.15-0.35 parts nonionic surfactant, 0.05-0.15 parts low HLB surfactant, and 0.02-0.08 parts metal chelating agent.

2. The detection method according to claim 1, characterized in that, The anionic surfactant is selected from one or more of sodium dodecylbenzene sulfonate, sodium fatty alcohol polyoxyethylene ether sulfate, and sodium α-alkenyl sulfonate. The nonionic surfactant is selected from one or more of alkyl glycosides, fatty alcohol polyoxyethylene ethers, and fatty alcohol polyethers; The low HLB surfactant is selected from dehydrated sorbitan fatty acid esters with an HLB value of 3-6; The metal chelating agent is selected from one or more of disodium ethylenediaminetetraacetate, citric acid, and gluconic acid.

3. The detection method according to claim 2, characterized in that, The anionic surfactant is selected from sodium fatty alcohol polyoxyethylene ether sulfate; The nonionic surfactant is selected from alkyl glycosides; The low HLB surfactant is selected from dehydrated sorbitan oleate; The metal chelating agent is selected from disodium ethylenediaminetetraacetate.

4. The detection method according to any one of claims 1-3, characterized in that, The dispersion solvent is prepared by the following method: Step 1: Add the metal chelating agent to pure water and stir at 45-55℃ for 10-15 minutes until completely dissolved; Step 2: Premix the anionic surfactant and the low HLB surfactant evenly, stir at 35-45℃ until a homogeneous mixture is formed, and then slowly add it to the aqueous phase obtained in Step 1, and stir and mix at 35-45℃ for 15-20 minutes. Step 3: Add nonionic surfactant and stir at room temperature for 30-40 minutes until the solution is uniformly milky white; Step 4: Let stand for 1.5-2.5 hours to allow the components to reach interfacial adsorption equilibrium, thus obtaining the compound dispersion solvent.

5. The detection method according to claim 1, characterized in that, The mass ratio of the polyethylene powder sample to the dispersion solvent is 1:2-6.

6. The detection method according to claim 1, characterized in that, After mixing the polyethylene powder sample with the dispersion solvent, it was pretreated with low-frequency ultrasound for 5-15 minutes at a frequency of 20-40 kHz and a power density of 0.5-2 W / mL to obtain a homogeneous slurry.

7. The detection method according to claim 1, characterized in that, The magnetic component includes a magnetic rod and a removable coating layer covering the magnetic rod; Before the polyethylene powder sample is mixed with the dispersion solvent, the dispersion solvent and exogenous magnetic foreign matter in the container are first adsorbed and removed using a magnetic component. Then, the magnetic rod is removed and a new clean coating layer is replaced.

8. The detection method according to claim 1, characterized in that, The magnetic component employs multi-stage magnetic adsorption to capture magnetic foreign objects. First-stage adsorption: A primary magnetic rod with a magnetic induction intensity of 8000-10000GS is placed into the slurry and stirred at a low speed of 30-50r / min for 20-30min to capture large magnetic foreign objects with a diameter >50μm. Second-stage adsorption: After removing the primary magnetic rod and replacing it with a new coating layer, a secondary magnetic rod with a magnetic induction intensity of 12000-16000GS is placed into the slurry and stirred at a speed of 60-80r / min for 15-25min to capture medium-sized magnetic foreign matter of 5-50μm. Third-stage adsorption: Remove the secondary magnetic rod and transfer the slurry to a constant magnetic field with a magnetic induction intensity of 3000-5000GS. Let it stand for 30-60 minutes to enrich submicron magnetic foreign matter <5μm at the bottom of the container.

9. The detection method according to claim 8, characterized in that, Classified collection and classified detection and analysis of magnetic foreign objects: (1) Take out the primary magnetic rod and the secondary magnetic rod respectively, rinse the outer wall of the coating layer repeatedly with pure water, collect the rinsing liquid to obtain a suspension of large-particle magnetic foreign matter, filter and dry it, and use a cleanliness tester to analyze particles with a particle size ≥5μm. (2) After the slurry has undergone the third adsorption, the upper clear liquid is discharged under the condition of maintaining the magnetic field, and 50-100 mL of the bottom enrichment liquid is retained. Pure water is added to the enrichment liquid to the original volume. The operation is repeated 2-3 times to obtain the submicron magnetic foreign matter enrichment liquid. The liquid is collected by vacuum filtration on a filter membrane with a pore size ≤0.22 μm. After drying, the morphology of <5 μm particles is observed and the elements are identified by scanning electron microscopy combined with energy dispersive spectroscopy, or the trace metal elements are quantitatively analyzed by inductively coupled plasma mass spectrometry.

10. The detection method according to any one of claims 7-9, characterized in that, The covering layer is a heat shrink tubing, and the port is sealed with a heat sealing machine during use.

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