Evaluation method of polyethylene powder for physical processing

Abstract

The invention provides an evaluation method of polyethylene powder for physical processing. The evaluation method comprises the following steps: S1, obtaining a performance test result of a to-be-tested sample according to polyethylene evaluation indexes; wherein the polyethylene evaluation indexes comprise a basic index, a fluidity index, a uniformity index, a structure index and a processing performance index; s2, on the basis of the performance test result of the to-be-tested sample, determining the score of the to-be-tested sample in each evaluation index according to the evaluation standard corresponding to each evaluation index; s3, performing summation calculation on the scores of the to-be-tested sample in each evaluation index to obtain a total score; and S4, evaluating the comprehensive performance of polyethylene according to the total score. By comprehensively evaluating and judging the use performance of the polyethylene powder in the polyethylene application field, compared with the prior art, the problem that common product indexes are insufficient to completely reveal the use performance of the polyethylene powder can be avoided.

Description

Technical Field

[0001] This invention relates to a method for evaluating polymer materials, specifically a method for evaluating polyethylene powder used in physical processing. Background Technology

[0002] Chlorinated polyethylene (CPE) is a chlorinated polymer obtained by a substitution reaction between polyethylene resin and chlorine. Because polar chlorine atoms are introduced into the polyethylene molecule, their random distribution along the polyethylene chain disrupts the original structural regularity, giving chlorinated polyethylene a certain degree of elasticity, making it an elastic material between rubber and plastic. CPE is mainly divided into resin-type and rubber-type. Based on its application, CPE is mainly classified into three types: A, B, and C. Types A and C are resin-type CPE, while type B is rubber-type CPE. Type A is mainly used as a toughening and impact modifier for PVC, while type C is mainly used as a flame-retardant modifier for engineering plastics (such as ABS plastic). Type C is a new type of environmentally friendly rubber with excellent cold resistance, aging resistance, oil resistance, and flame retardancy, mainly used in the manufacture of wires and cables, hoses, and escalator handrails. The performance of chlorinated polyethylene is closely related to the performance of the polyethylene resin used; high-quality polyethylene resin is a key step in CPE production.

[0003] Ultra-high molecular weight polyethylene (UHMWPE) is a linear thermoplastic engineering plastic with excellent impact resistance, abrasion resistance, corrosion resistance, and self-lubricating properties. It is widely used in transportation, agriculture, chemical industry, petroleum, machinery, construction, papermaking, packaging, textiles, food, electrical engineering, medical, and sports industries. Currently, the largest consumer of UHMWPE in China is the production of sheets, profiles, and pipes, while its applications in high-performance fibers and lithium-ion battery separators are also booming. In the future, the UHMWPE industry will trend towards higher performance and specialized resins.

[0004] The production of polyethylene powder does not require the addition of additives or high-temperature extrusion granulation, significantly improving the level of green and clean production. This can promote high-quality, low-carbon, and green economic development, and has broad prospects. Commonly used polyethylene powder indicators such as density, melting point, melt flow rate (molecular weight), bulk density, and average particle size are often used as product technical indicators for quality control in petrochemical production enterprises and as a reference for raw material selection by downstream users. However, these indicators only reveal the basic properties of polyethylene powder and are insufficient to reveal its performance characteristics in use.

[0005] CN106770949A discloses a method for evaluating the storage stability of powders containing amorphous components. This method employs a dynamic moisture adsorption experiment, measuring the critical relative humidity (RHg,c) and critical moisture content (MCg,c) for the glass transition of amorphous powders at a specific temperature (5-60℃) by varying the relative humidity increase rate (2-10%RH / hour) at a range of 0-90% RH. This method is used to evaluate the storage stability of products.

[0006] CN105259019A discloses an evaluation method for preparing ultra-high molecular weight polyethylene resin for lithium battery separators. The method first analyzes the apparent physical properties of the ultra-high molecular weight polyethylene resin to obtain the apparent parameters of the resin. Then, the ultra-high molecular weight polyethylene resin is pressed into tablets to analyze the mechanical properties of the resin. Finally, the film-forming performance is judged by film-forming techniques such as thermally induced phase separation and biaxial stretching.

[0007] CN101710052A discloses a method for evaluating the wear resistance of ultra-high molecular weight polyethylene.

[0008] CN112724290A discloses an ultra-high molecular weight polyethylene powder, characterized in that the powder contains 10-100 ppm aluminum, 0.1-5 ppm titanium, 1-10 ppm magnesium, 5-40 ppm halogen, and 0.05-1 ppm phosphorus; the powder has a viscosity-average molecular weight of 5-10 million; the average sphericity of the powder particles is between 0.65 and 0.95; and the proportion of powder particles with a sphericity of 0.8 or higher is greater than 75%. Summary of the Invention

[0009] To address the aforementioned technical problems, the present invention aims to provide an evaluation method for polyethylene powder used in physical processing. Compared with existing technologies, the evaluation method of the present invention avoids the problem that commonly used product indicators are insufficient to fully reveal the performance of polyethylene powder.

[0010] To achieve the above objectives, the present invention provides a method for evaluating polyethylene powder for physical processing, comprising the following steps:

[0011] S1: Obtain the performance test results of the sample to be tested based on the polyethylene evaluation index;

[0012] The evaluation indicators for polyethylene include basic indicators, flowability indicators, uniformity indicators, structural indicators, and processing performance indicators.

[0013] The basic indicators include melt flow rate or viscosity-average molecular weight, density, apparent density, average particle size, and melting point.

[0014] The liquidity indicators include the angle of repose or outflow time;

[0015] The uniformity indicators include molecular weight distribution and particle size distribution;

[0016] The structural parameters include pore volume;

[0017] The processing performance indicators include melting enthalpy, viscous flow activation energy, or zero-shear viscosity;

[0018] S2: Based on the performance test results of the sample to be tested, determine the score of the sample to be tested in each evaluation index according to the evaluation criteria corresponding to each evaluation index;

[0019] S3: Sum the scores of the sample under test in each evaluation index to obtain the total score;

[0020] S4: Evaluate the overall performance of polyethylene based on the total score;

[0021] The overall performance evaluation result of the sample is deemed unqualified if the performance test results meet one of the following conditions:

[0022] (1) The melt flow rate or viscosity-average molecular weight deviates from the center by more than or equal to 40%;

[0023] (2) The density deviation from the center is greater than or equal to 0.003;

[0024] (3) The enthalpy of fusion, activation energy of viscous flow, or zero-shear viscosity deviates from the center by more than or equal to 30%.

[0025] In the above evaluation method, preferably, the evaluation criteria for melt flow rate or viscosity-average molecular weight are as follows: 10 points for deviation from the center value of less than 10%, 8 points for deviation of greater than or equal to 10% and less than 20%, 5 points for deviation of greater than or equal to 20% and less than 40%, and 5 points for deviation of greater than or equal to 40%, in which case the overall performance evaluation result of the sample to be tested is deemed unqualified.

[0026] Melt flow rate was determined according to the national standard "Determination of melt mass flow rate (MFR) and melt volumetric flow rate (MVR) of thermoplastics - Part 1: Standard method GB / T 3682.1", with a test temperature of 190℃. The weight of the weights was selected as 2.16 kg or 5.0 kg depending on the characteristics of the sample. Viscosity-average molecular weight was determined according to the national standard "GB / T 1632.3 Plastics - Determination of viscosity of dilute polymer solutions using a capillary viscometer - Part 3: Polyethylene and polypropylene", based on the intrinsic viscosity, and then the viscosity-average molecular weight was calculated. The choice between melt flow rate and viscosity-average molecular weight was based on the sample type; melt flow rate was selected for conventional polyethylene, and viscosity-average molecular weight was selected for ultra-high molecular weight polyethylene.

[0027] In the above evaluation method, preferably, the evaluation criteria for density are as follows: 10 points for a deviation from the center value less than 0.001, 8 points for a deviation greater than or equal to 0.001 and less than 0.002, 5 points for a deviation greater than or equal to 0.002 and less than 0.003, and 5 points for a deviation greater than or equal to 0.003, in which case the overall performance evaluation result of the sample to be tested is deemed unqualified.

[0028] Density was determined according to the national standards "Determination of density of non-foamed plastics - Part 2: Density gradient column method GB / T1033.2" or "Determination of density of non-foamed plastics - Part 1: Impregnation method, liquid specific gravity bottle method and titration method GB / T1033.1-2008".

[0029] In the above evaluation method, preferably, the evaluation standard for apparent density is: 10 points for a value greater than or equal to the index value, and 5 points for a value less than the index value. Apparent density is determined according to the national standard "Determination of Apparent Density of Plastic Materials That Can Flow Out of a Specified Funnel GB / T 1636".

[0030] In the above evaluation method, preferably, the evaluation criteria for the average particle size are as follows: 10 points for a deviation from the center value of less than 10%, 8 points for a deviation of 10% or more but less than 20%, 5 points for a deviation of 20% or more but less than 40%, and no points for a deviation of 40% or more. The average particle size is the equivalent diameter of the largest particle when the cumulative distribution in the particle size distribution curve is 50%, and is preferably measured using a laser particle size analyzer, denoted as D50.

[0031] In the above evaluation method, preferably, the evaluation criteria for the melting point are as follows: 10 points for a deviation from the center value of less than 1℃, 8 points for a deviation of 1℃ or more but less than 3℃, 5 points for a deviation of 3℃ or more but less than 5℃, and no points for a deviation of 5℃ or more. The melting point can be determined using a melting point apparatus or DSC, preferably according to the national standard "Differential Scanning Calorimetry (DSC) for Plastics - Part 3: Determination of Melting and Crystallization Temperatures and Enthalpies GB / T 19466.3-2004".

[0032] In the above evaluation method, preferably, the evaluation criteria for the angle of repose or outflow time are: 10 points for being less than the index value, 5 points for being equal to the index value, 5 points for being within 20% of the index value, and no points for being more than 20% of the index value.

[0033] The angle of repose is measured when a particle slides on a free inclined plane of a powder mass layer, reaching equilibrium between gravity and interparticle friction, and is in a static state. It is the maximum angle formed between the free inclined plane of the powder mass layer and the horizontal plane. Commonly used measurement methods include the injection method, the discharge method, and the tilt angle method. Different test methods for the same index have consistent evaluation standards. The smaller the angle of repose, the lower the friction and the better the flowability. The outflow time is the time required for all material to flow out after being added to a funnel. It is measured according to the national standard "GB / T 40934-2021 Test Method for Flowability of Rotationally Molded Powders".

[0034] The angle of repose or outflow time is selected as the evaluation metric based on the usual practices in the field and the available testing conditions.

[0035] The evaluation method of this invention uses the flowability index as an evaluation index to judge the long-term storage stability of powder products. Powder products with good flowability are less likely to agglomerate and clump during storage, and have better storage stability in high-temperature weather. Powder products with poor flowability may clump in high-temperature weather, which will have an adverse effect on subsequent use.

[0036] In the above evaluation method, preferably, the evaluation criteria for the molecular weight distribution are as follows: 10 points for a deviation from the center of less than 10%, 5 points for a deviation greater than or equal to 10% and less than 20%, 3 points for a deviation greater than or equal to 20% and less than 30%, and no points for a deviation greater than or equal to 30%. The molecular weight distribution is tested using gel permeation chromatography to measure the degree of dispersion of polyethylene molecular weight.

[0037] In the above evaluation method, preferably, the evaluation criteria for particle size distribution are as follows: less than the index value, 10 points; equal to the index value, 5 points; greater than the index value by less than 20%, 5 points; greater than the index value by 20% but less than 40%, 3 points; greater than or equal to 40% of the index value, 0 points. Particle size distribution is determined using a laser particle size analyzer.

[0038] In the above evaluation method, preferably, the evaluation criteria for pore volume are as follows: 10 points for deviation from the center value less than 10%, 5 points for deviation greater than or equal to 10% and less than 20%, 3 points for deviation greater than or equal to 20% and less than 30%, and no points for deviation greater than or equal to 30%. The pore volume is calculated using a nitrogen isothermal adsorption-desorption curve at a single point.

[0039] In the above evaluation method, preferably, the evaluation criteria for the melting enthalpy, viscous flow activation energy or zero shear viscosity are as follows: 10 points for deviation from the center value less than 10%, 8 points for deviation greater than or equal to 10% and less than 20%, 5 points for deviation greater than or equal to 20% and less than 30%, and if the deviation is greater than or equal to 30%, the comprehensive performance evaluation result of the sample to be tested is deemed unqualified.

[0040] The enthalpy of melting was determined using differential scanning calorimetry (DSC) to measure the area enclosed by the melt peak curve and the baseline during sample melting, i.e., the enthalpy of melting of the crystalline portion of polyethylene ΔHf. The heating rate during the test was 20 K / min, and the data from the first heating curve of the powder were used.

[0041] Viscous flow activation energy reflects the ease or difficulty of material flow, and more importantly, it reflects the temperature sensitivity of material viscosity changes, which has important guiding significance for the processing of plastic products. Viscous flow activation energy is defined as the minimum energy required for a flow element to overcome the potential barrier and jump from its original position to a nearby "cavity" during the flow process. The literature "Study on Viscous Flow Activation Energy of Several Different PE and PP Resins" (Applied Chemical Industry, 2008, 37(1)) introduces commonly used methods for determining viscous flow activation energy.

[0042] Zero-shear viscosity test method: Mix the sample with white oil at a mass ratio of 1:2.5 for 1 hour, then test the mixture using a rheometer at 190°C. The test can be performed using a capillary rheometer or a rotational rheometer.

[0043] In the above evaluation method, preferably, in S4, the comprehensive performance of polyethylene is evaluated according to the following criteria based on the total score:

[0044] Samples with a total score below 50 or deemed unqualified are classified as contracted products or waste; samples with a total score between 50 and 75 are qualified products; and samples with a total score above 75 are superior products.

[0045] In the above evaluation method, preferably, the method for determining the center value of the evaluation index is as follows: different batches of samples are tested to obtain the following test results: the melt flow rate or viscosity-average molecular weight of the sample; the density, average particle size, melting point, molecular weight distribution and pore volume of the sample; the enthalpy of melting, viscous flow activation energy or zero shear viscosity of the sample; application tests are conducted on the sample; at least 5 batches of samples that meet the usage requirements in all aspects are selected, and the average value of the test results of these samples is taken as the center value.

[0046] In the above evaluation method, preferably, the evaluation index values ​​are minimum or maximum required values, including apparent density, angle of repose or outflow time, and particle size distribution. For polyethylene powder used in physical processing, high apparent density, small angle of repose or outflow time, and narrow particle size distribution indicate good performance.

[0047] In the above evaluation method, preferably, the method for determining the index value of the evaluation index is as follows: different batches of samples are tested to obtain the following test results: the apparent density and particle size distribution of the sample; the angle of repose or effluent time of the sample; application test of the sample; at least 3 batches of samples that meet the usage requirements in all aspects are selected, and the lowest value of the apparent density in the test results of these samples is taken as the index value of apparent density, and the highest values ​​of the angle of repose, effluent time and particle size distribution in the test results of these samples are taken as the index values ​​of the angle of repose, effluent time and particle size distribution, respectively.

[0048] In the above evaluation method, preferably, the physical processing method is thermal processing or solvent processing.

[0049] In the evaluation method of this invention, different processing performance indicators are used to evaluate the processing performance of the sample depending on whether the processing method is thermal processing or solvent processing.

[0050] In the above evaluation method, preferably, when the physical processing method is thermal processing, the processing performance index is the enthalpy of melting or the activation energy of viscous flow; the selection is made according to the sample type, with the activation energy of viscous flow selected for conventional polyethylene and the enthalpy of melting selected for ultra-high molecular weight polyethylene.

[0051] In the above evaluation method, preferably, when the physical processing method is solvent processing, the processing performance index is zero shear viscosity.

[0052] In the above evaluation method, preferably, the evaluation index includes three veto indicators: melt flow rate or viscosity-average molecular weight, density, and processing performance. If the index exceeds the range, the comprehensive performance evaluation result of the sample to be tested is deemed unqualified.

[0053] According to a specific embodiment of the present invention, preferably, the evaluation indicators and evaluation criteria of the present invention can be summarized as shown in Table 1:

[0054] Table 1

[0055]

[0056]

[0057] The evaluation criteria and scoring of this invention are based on two points: (1) the ease of production control; and (2) the magnitude of the impact on downstream processing applications. The evaluation criteria and scoring criteria of this invention can find a relative balance between the two, so that a large number of defective products will not appear in normal production, nor will downstream processing be unable to use them.

[0058] The properties of polyethylene powder are evaluated by measuring density, melting point, melt flow rate, or viscosity-average molecular weight, bulk density, and average particle size. However, these indicators only reveal the basic properties of polyethylene powder and are insufficient to reveal its performance in use, especially the reactive processing performance of polyethylene for physical processing.

[0059] This invention provides a method for evaluating polyethylene in powder form. By measuring the basic indicators, flowability, particle size distribution, molecular weight distribution, and pore structure of polyethylene powder, and comprehensively evaluating its performance based on its processing method, this method can be used for product quality monitoring in petrochemical enterprises, raw material testing in polymer material modification and processing enterprises, etc. Compared with existing technologies, it avoids the problem that commonly used product indicators are insufficient to fully reveal the performance of polyethylene powder.

[0060] Compared with existing technologies, the evaluation method provided by this invention has the following advantages:

[0061] (1) Determine the evaluation index system for polyethylene, quantify and score each evaluation index of polyethylene for physical processing according to the evaluation standard, and sum the scores of each evaluation index. Evaluate the comprehensive performance of polyethylene based on the quantitative summing score results. Production units and users can make reasonable arrangements for product sales and use based on the evaluation results.

[0062] (2) Use flowability indicators to evaluate the flowability and storage stability of powdered polyethylene products, provide a basis for the transportation, storage and use of powdered products, and make up for the deficiency that existing polyethylene product indicators do not reflect this performance.

[0063] (3) The uniformity index is used to represent the uniformity of powdered polyethylene products. Products with a large deviation from the uniformity index need to be paid attention to their impact on processing performance during use, so as to avoid the adverse effects of a small amount of components on the user's processing.

[0064] (4) The processing performance indicators reflect the sensitivity of the reaction powder polyethylene product to temperature and solvent in terms of easy reaction, melting and flow properties. This provides a reference for users to formulate reaction processing parameters. The process parameters can be adjusted in a timely manner according to the changes in the processing performance indicators of different batches of products, thereby enhancing the guidance of product indicators for downstream users. Detailed Implementation

[0065] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0066] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and such ranges or values ​​should be understood to include values ​​close to such ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0067] Example 1

[0068] The sample to be tested is ultra-high molecular weight polyethylene LU2600 produced by Lanzhou Petrochemical using the slurry method polyethylene unit. Its purpose is to prepare sheets or pipes.

[0069] The evaluation is conducted using the following steps: S1: Obtain the performance test results of the sample to be tested according to the polyethylene evaluation indicators; S2: Based on the performance test results of the sample to be tested, determine the score of the sample to be tested in each evaluation indicator according to the evaluation standards corresponding to each evaluation indicator; S3: Sum the scores of the sample to be tested in each evaluation indicator to obtain the total score; S4: Evaluate the comprehensive performance of polyethylene based on the total score. Samples with a total score below 50 or deemed unqualified are considered standard products or waste; samples with a total score between 50 and 75 are qualified products; samples with a total score above 75 are superior products. The performance and scores of the tested samples are shown in Table 2. A score of 78 indicates the sample is a superior product.

[0070] Table 2. Evaluation Indicators and Standards for LU2600

[0071]

[0072]

[0073]

[0074] Example 2

[0075] The sample to be tested is ultra-high molecular weight polyethylene LU0350 produced by Lanzhou Petrochemical using the slurry process polyethylene unit. Its purpose is to prepare wet-process lithium battery separators.

[0076] The evaluation is conducted using the following steps: S1: Obtain the performance test results of the sample to be tested according to the polyethylene evaluation indicators; S2: Based on the performance test results of the sample to be tested, determine the score of the sample in each evaluation indicator according to the evaluation criteria corresponding to each evaluation indicator; S3: Sum the scores of the sample to be tested in each evaluation indicator to obtain the total score; S4: Evaluate the comprehensive performance of polyethylene based on the total score. Samples with a total score below 50 or deemed unqualified are considered standard products or waste; samples with a total score between 50 and 75 are qualified products; samples with a total score above 75 are superior products. The performance and scores of the samples to be tested are shown in Table 3. A zero-shear viscosity deviation from the center value greater than or equal to 30% is considered unqualified.

[0077] Table 3 Evaluation Indicators and Standards for LU0350

[0078]

[0079]

[0080]

[0081] Example 3

[0082] The sample to be tested is polyethylene L5550, produced by Lanzhou Petrochemical using the slurry method polyethylene unit, and is intended for use as a color masterbatch.

[0083] The evaluation is conducted using the following steps: S1: Obtain the performance test results of the sample to be tested according to the polyethylene evaluation indicators; S2: Based on the performance test results of the sample to be tested, determine the score of the sample in each evaluation indicator according to the evaluation criteria corresponding to each evaluation indicator; S3: Sum the scores of the sample to be tested in each evaluation indicator to obtain the total score; S4: Evaluate the comprehensive performance of polyethylene based on the total score. Samples with a total score below 50 or deemed unqualified are considered standard products or waste; samples with a total score between 50 and 75 are qualified products; samples with a total score above 75 are superior products. The performance and scores of the samples to be tested are shown in Table 4. A viscosity flow activation energy exceeding the center value by more than 30% is considered unqualified.

[0084] Table 4. Evaluation Indicators and Standards for L5550

[0085]

[0086]

[0087]

[0088] Example 4

[0089] The sample to be tested is polyethylene LU1500, a product of Lanzhou Petrochemical's slurry-method polyethylene unit, which is used to prepare lithium battery separators.

[0090] The evaluation is conducted using the following steps: S1: Obtain the performance test results of the sample to be tested according to the polyethylene evaluation indicators; S2: Based on the performance test results of the sample to be tested, determine the score of the sample to be tested in each evaluation indicator according to the evaluation standards corresponding to each evaluation indicator; S3: Sum the scores of the sample to be tested in each evaluation indicator to obtain the total score; S4: Evaluate the comprehensive performance of polyethylene based on the total score. Samples with a total score below 50 or deemed unqualified are considered standard products or waste; samples with a total score between 50 and 75 are qualified products; samples with a total score above 75 are superior products. The performance and scores of the tested samples are shown in Table 5. A score of 91 indicates a superior product.

[0091] Table 5. Evaluation Indicators and Standards for LU1500

[0092]

[0093]

[0094]

[0095] Example 5

[0096] The sample to be tested is polyethylene L5550, produced by Lanzhou Petrochemical using the slurry method polyethylene unit, and is intended for use as a color masterbatch.

[0097] The evaluation is conducted using the following steps: S1: Obtain the performance test results of the sample to be tested according to the polyethylene evaluation indicators; S2: Based on the performance test results of the sample to be tested, determine the score of the sample in each evaluation indicator according to the evaluation criteria corresponding to each evaluation indicator; S3: Sum the scores of the sample to be tested in each evaluation indicator to obtain the total score; S4: Evaluate the comprehensive performance of polyethylene based on the total score. Samples with a total score below 50 or deemed unqualified are considered standard products or waste; samples with a total score between 50 and 75 are qualified products; samples with a total score above 75 are superior products. The performance and scores of the tested samples are shown in Table 6. A score of 54 indicates that the sample is qualified.

[0098] Table 6. Evaluation Indicators and Standards for L5550

[0099]

[0100]

[0101]

[0102] Comparative Example 1

[0103] The test sample is the ultra-high molecular weight polyethylene LU2600 produced by Lanzhou Petrochemical using a slurry-phase polyethylene plant, and its use is for preparing plates or pipes. The product batch is the same as that in Example 1. The product technical indicators are shown in Table 7. The product test results are qualified.

[0104] Table 7

[0105] project index Test value <![CDATA[Viscosity-average molecular weight, ×10 4 > 200-300 235 <![CDATA[Apparent density, g / cm 3 > ≥0.35 0.45 Ash content, % (mass fraction) ≤0.030 0.01 Melting point, °C Actual measurement 137.1 Sieving rate (20 mesh), % ≥99.0 99.8

[0106] Comparative Example 2

[0107] The test sample is the ultra-high molecular weight polyethylene LU0350 produced by Lanzhou Petrochemical using a slurry-phase polyethylene plant, and its use is for preparing wet lithium battery diaphragms. The product batch is the same as that in Example 2. The product technical indicators are shown in Table 8. The product test results are qualified.

[0108] Table 8 [[ID=二十]]

[0109]

[0110]

[0111] Comparative Example 3

[0112] The test sample is the polyethylene L5550 produced by Lanzhou Petrochemical using a slurry-phase polyethylene plant, and its use is for masterbatch. The product batch is the same as that in Example 3. The product technical indicators are shown in Table 9. The product test results are qualified.

[0113] Table 9

[0114] project index Test value Melt flow rate (2.16 kg), g / 10 min 42-58 56 <![CDATA[Density, g / cm 3 > 0.952-0.958 0.9544 <![CDATA[Bulk density, g / cm 3 > ≥0.38 0.42 Average particle size, μm 125-315 160 Melting point, °C 136-140 138.9

[0115] Comparative Example 4

[0116] The test sample is the polyethylene L5550 produced by Lanzhou Petrochemical using a slurry-phase polyethylene plant, and its use is for masterbatch. The product batch is the same as that in Example 5.

[0117] The following steps are used for evaluation: S1: Obtain the performance test results of the test sample according to the polyethylene evaluation indicators; S2: Based on the performance test results of the test sample, determine the scores of the test sample in each evaluation indicator according to the evaluation criteria corresponding to each evaluation indicator; S3: Add up the scores of the test sample in each evaluation indicator to obtain the total score; S4: Evaluate the comprehensive performance of the polyethylene according to the total score. Samples with a total score of less than 50 or determined to be unqualified are agreement products or waste; samples with a total score of 50 - 75 are qualified products, and samples with a total score of more than 75 are superior products. The performance and scores of the test sample are shown in Table 10. The score is 44 points, and the sample is treated as an agreement product.

[0118] Table 10 L5550 Evaluation Indicators and Evaluation Standards

[0119]

[0120]

[0121]

[0122] The storage and processing application of each sample in the statistical examples are described.

[0123] Storage conditions:

[0124] Polyethylene powder should be packaged in heavy-duty film bags or in woven plastic bags with an inner coating. The packaging materials should ensure that there is no contamination or leakage during transportation, stacking, and storage. Store in a well-ventilated, dry, clean warehouse with good fire-fighting facilities. Keep away from heat sources and prevent direct sunlight; open-air storage is strictly prohibited.

[0125] Processing:

[0126] Pipe processing: Ultra-high molecular weight polyethylene is processed using a 150-type single-screw extruder at a temperature of 170-220℃, a pressure of 14.5MPa, and a speed of 0.8m / h to obtain pipes with an outer diameter of 317mm.

[0127] Wet-process lithium-ion battery separator processing: Ultra-high molecular weight polyethylene powder and white oil are mixed in a weight ratio of 1:4. The resulting mixture is melt-extruded through a twin-screw extruder and extruded through a die to form a nascent membrane. The die temperature is 220℃, the screw speed is 35 r / min, and the cooling temperature is 50℃. Subsequently, the nascent membrane is biaxially heat-stretched, and the white oil is extracted with dichloromethane to obtain the lithium-ion battery separator.

[0128] Color masterbatch processing: Mix polyethylene powder and pigment in a 1:1 ratio, add 1% calcium stearate and 1% polyethylene glycol 10000 by weight of the total color masterbatch, and then extrude and granulate using an extruder to obtain the color masterbatch. The extrusion temperature is 150℃-180℃ and the screw speed is 100rpm / min.

[0129] Table 11 Storage and Processing Details of Examples

[0130]

[0131]

[0132] As can be seen from Table 11, the evaluation method of the present invention is used in each embodiment. The evaluation results have a guiding role in the processing. Samples evaluated as excellent or qualified are processed under normal process conditions. Samples evaluated as unqualified are processed under conditions that deviate from normal values ​​or are difficult to process.

[0133] For the same batch of samples, Example 1, evaluated using the method of this invention, was rated as superior, but its flowability index was poor, requiring use within a short period to avoid agglomeration. Comparative Example 1, tested only for basic indicators, was rated as qualified, but this aspect of the product was not reflected. For the same batch of samples, Comparative Examples 2 and 3, tested only for basic indicators, were rated as qualified. Examples 2 and 3, evaluated using the method of this invention, were rated as unqualified, indicating difficulties in sample processing or requiring more stringent processing conditions, affecting their usability.

[0134] For the same batch of samples, Comparative Example 4 used different scoring standards and score gradient values ​​for certain items compared to the examples. The evaluation results were unqualified and treated as protocol products, but the samples could be used normally during processing. This demonstrates that using the evaluation standards (gradients and score divisions) of this application can obtain more accurate evaluation results and avoid losses caused by inappropriate evaluation results.

Claims

1. An evaluation method for polyethylene powder used in physical processing, wherein, Includes the following steps: S1: Obtain the performance test results of the sample to be tested based on the polyethylene evaluation index; The evaluation indicators for polyethylene include basic indicators, flowability indicators, uniformity indicators, structural indicators, and processing performance indicators. The basic indicators include melt flow rate or viscosity-average molecular weight, density, apparent density, average particle size, and melting point. The liquidity indicators include the angle of repose or outflow time; The uniformity indicators include molecular weight distribution and particle size distribution; The structural parameters include pore volume; The processing performance indicators include melting enthalpy, viscous flow activation energy, or zero-shear viscosity; S2: Based on the performance test results of the sample to be tested, determine the score of the sample to be tested in each evaluation index according to the evaluation criteria corresponding to each evaluation index; S3: Sum the scores of the sample under test in each evaluation index to obtain the total score; S4: Evaluate the overall performance of polyethylene based on the total score; The overall performance evaluation result of the sample is deemed unqualified if the performance test results meet one of the following conditions: (1) The melt flow rate or viscosity-average molecular weight deviates from the center by more than or equal to 40%; (2) The density deviation from the center is greater than or equal to 0.003; (3) The enthalpy of fusion, activation energy of viscous flow, or zero-shear viscosity deviates from the center by more than or equal to 30%.

2. The evaluation method according to claim 1, wherein, The evaluation criteria for melt flow rate or viscosity-average molecular weight are as follows: 10 points for a deviation from the center value of less than 10%, 8 points for a deviation of 10% or more but less than 20%, and 5 points for a deviation of 20% or more but less than 40%.

3. The evaluation method according to claim 1, wherein, The evaluation criteria for density are as follows: 10 points for a deviation from the center value less than 0.001, 8 points for a deviation greater than or equal to 0.001 and less than 0.002, and 5 points for a deviation greater than or equal to 0.002 and less than 0.

003.

4. The evaluation method according to claim 1, wherein, The evaluation criteria for apparent density are: 10 points for being greater than or equal to the index value, and 5 points for being less than the index value.

5. The evaluation method according to claim 1, wherein, The evaluation criteria for the average particle size are as follows: 10 points for deviation from the center value of less than 10%, 8 points for deviation of 10% or more but less than 20%, 5 points for deviation of 20% or more but less than 40%, and no points for deviation of 40% or more.

6. The evaluation method according to claim 1, wherein, The evaluation criteria for the melting point are as follows: 10 points are awarded for a deviation from the center value of less than 1℃, 8 points are awarded for a deviation of 1℃ or more but less than 3℃, 5 points are awarded for a deviation of 3℃ or more but less than 5℃, and no points are awarded for a deviation of 5℃ or more.

7. The evaluation method according to claim 1, wherein, The evaluation criteria for the angle of repose or outflow time are as follows: 10 points for being less than the indicator value, 5 points for being equal to the indicator value, 5 points for being within 20% of the indicator value, and no points for being more than 20% of the indicator value.

8. The evaluation method according to claim 1, wherein, The evaluation criteria for the molecular weight distribution are as follows: 10 points for deviation from the center value of less than 10%, 5 points for deviation of 10% or more but less than 20%, 3 points for deviation of 20% or more but less than 30%, and no points for deviation of 30% or more.

9. The evaluation method according to claim 1, wherein, The evaluation criteria for particle size distribution are as follows: 10 points for particles smaller than the index value, 5 points for particles equal to the index value, 5 points for particles within 20% of the index value, 3 points for particles greater than 20% of the index value but less than 40% of the index value, and no points for particles greater than or equal to 40% of the index value.

10. The evaluation method according to claim 1, wherein, The evaluation criteria for the pore volume are as follows: 10 points are awarded if the deviation from the central value is less than 10%, 5 points are awarded if it is greater than or equal to 10% and less than 20%, 3 points are awarded if it is greater than or equal to 20% and less than 30%, and no points are awarded if it is greater than or equal to 30%.

11. The evaluation method according to claim 1, wherein, The evaluation criteria for the melt enthalpy, viscous flow activation energy or zero-shear viscosity are as follows: 10 points are awarded if the deviation from the central value is less than 10%, 8 points are awarded if it is greater than or equal to 10% and less than 20%, and 5 points are awarded if it is greater than or equal to 20% and less than 30%.

12. The evaluation method according to claim 1, wherein, In S4, when evaluating the comprehensive performance of polyethylene according to the total score, the following criteria are used: The test samples with a total score of less than 50 or determined to be unqualified are protocol products or scraps; The test samples with a total score of 50 - 75 are qualified products; The test samples with a total score of more than 75 are premium products.

13. The evaluation method according to claim 1, wherein, The physical processing method is thermal processing or solvent processing.

14. The evaluation method according to claim 13, wherein, When the physical processing method is thermal processing, the processing performance index is melt enthalpy or viscous flow activation energy; When the physical processing method is solvent processing, the processing performance index is zero-shear viscosity.

Images