Evaluation method of polyethylene powder for chemical modification

Abstract

The invention provides an evaluation method of polyethylene powder for chemical modification. 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 evaluation methods for polymer materials, specifically to an evaluation method for chemically modified polyethylene powder. 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 chemically modified polyethylene powder. 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 chemically modified polyethylene powder, 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, 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 melt flow ratio and particle size distribution;

[0016] The structural parameters include pore volume;

[0017] The processing performance indicators include reaction time;

[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 deviates from the center by more than or equal to 40%;

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

[0024] (3) The reaction time deviates from the center value by more than or equal to 30%.

[0025] In the above evaluation method, preferably, the evaluation criteria for the melt flow rate 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 and less than 20%, 5 points for a deviation of 20% or more and less than 40%, and 40% or more is considered as a failure in the comprehensive performance evaluation of the sample.

[0026] The 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℃ and a weight of 2.16 kg or 5.0 kg selected according to the characteristics of the sample.

[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 and less than 20%, 5 points for a deviation of 20% or more and 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 melt flow ratio 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%.

[0037] Melt flow ratio (HLMFR) is the ratio of the melt flow rate of a sample under different weights. It is calculated by comparing the high-load melt flow rate (HLMFR) and the low-load melt flow rate (MFR) measured at 190°C and under a load of 21.6 kg. The HLMFR / MFR value of polyethylene reflects its molecular weight distribution and indicates the sensitivity of the resin melt viscosity to shear forces.

[0038] 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.

[0039] 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.

[0040] In the above evaluation method, preferably, the evaluation criteria for the reaction time are as follows: 10 points are awarded for deviation from the center value of less than 10%, 8 points are awarded for deviation of 10% or more and less than 20%, 5 points are awarded for deviation of 20% or more and less than 30%, and if the deviation is greater than or equal to 30%, the overall performance evaluation result of the sample to be tested is deemed unqualified.

[0041] According to a specific embodiment of the present invention, preferably, the reaction time is simulated by peroxide mixing to mimic the sample reaction process, including the following steps:

[0042] The sample to be tested and the peroxide are mixed evenly and then added to a mixer. The mixer is run and the data is recorded to obtain a torque-time graph. The time T1 corresponding to the feeding peak and the time T2 corresponding to the maximum torque value are read from the torque-time graph. The reaction time is obtained by subtracting T1 from T2. The peroxide is dicumyl peroxide. The amount of peroxide added is 1-3% of the mass of the sample to be tested. The mixing temperature is 160-190℃.

[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 center value or index value is determined according to the characteristics of the product's use.

[0046] In the above evaluation method, preferably, the evaluation indicators include three veto indicators: melt flow rate, density, and reaction time. If the indicators exceed the range, the comprehensive performance evaluation result of the sample to be tested is deemed unqualified.

[0047] 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 of the sample; the density, average particle size, melting point, melt flow ratio and pore volume of the sample; the reaction time 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.

[0048] In the above evaluation method, preferably, the index values ​​of the evaluation indicators are minimum or maximum required values, including apparent density, angle of repose or outflow time, and particle size distribution. For chemically modified polyethylene powder, high apparent density, small angle of repose or outflow time, and narrow particle size distribution indicate good performance.

[0049] 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.

[0050] 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:

[0051] Table 1

[0052]

[0053] 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 and application. The evaluation criteria and scoring 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.

[0054] The properties of polyethylene powder are evaluated by measuring density, melting point, melt flow rate, 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 reaction processing performance of chemically modified polyethylene.

[0055] The present invention provides an evaluation method for polyethylene powder, which measures the basic indicators, flowability, particle size distribution, melt flow ratio, and pore structure of polyethylene powder. It also adds flowability, structural, and reactivity indicators for specific application fields, allowing for a comprehensive evaluation of the sample's performance. This method can be used for product quality monitoring in petrochemical enterprises, and raw material testing in polymer material modification and processing enterprises. Compared with existing technologies, it avoids the problem that commonly used product indicators are insufficient to fully reveal the performance of polyethylene powder.

[0056] Compared with existing technologies, the evaluation method provided by this invention has the following advantages:

[0057] (1) Determine the evaluation index system for polyethylene, quantify and score each evaluation index of chemically modified polyethylene 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.

[0058] (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.

[0059] (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 reaction performance during use, so as to avoid adverse effects on user processing caused by a small amount of components.

[0060] (4) The processing performance indicators reflect the degree of reactivity of powdered polyethylene products, providing a reference for users to formulate reaction process parameters. The process parameters are 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

[0061] 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.

[0062] 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.

[0063] Example 1

[0064] The sample to be tested is polyethylene L5200, a product of Lanzhou Petrochemical's slurry-process polyethylene unit, which is used to react with chlorine gas to prepare chlorinated polyethylene.

[0065] The following steps were used for evaluation:

[0066] S1: Obtain the performance test results of the sample to be tested based on the polyethylene evaluation index;

[0067] 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;

[0068] S3: Sum the scores of the sample under test in each evaluation index to obtain the total score;

[0069] S4: Evaluate the overall 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; and samples with a total score above 75 are superior products. The performance and scores of the tested samples are shown in Table 2.

[0070] Table 2 L5200 Evaluation Indicators and Evaluation Standards

[0071]

[0072]

[0073]

[0074] The sample reaction time test result was 381 seconds, which is more than 30% off the center value, and the evaluation result is unqualified.

[0075] Example 2

[0076] The sample to be tested was polyethylene L5200, produced by Lanzhou Petrochemical using a slurry-process polyethylene unit. Its intended use is in the reaction with chlorine gas to prepare chlorinated polyethylene. The difference between this sample and the sample in Example 1 lies in the different production batch.

[0077] The evaluation method and process are the same as in Example 1. The performance and scores of the tested samples are shown in Table 3.

[0078] Table 3 L5200 Evaluation Indicators and Evaluation Standards

[0079]

[0080]

[0081] The sample scored a total of 91 points, classifying it as a superior product.

[0082] Example 3

[0083] The sample to be tested was polyethylene L5200, produced by Lanzhou Petrochemical using a slurry-process polyethylene unit. Its intended use is in the reaction with chlorine gas to prepare chlorinated polyethylene. The difference between this sample and the sample in Example 1 lies in the production batch. The evaluation methods and procedures were the same as in Example 1. The performance and scores of the sample are shown in Table 4.

[0084] Table 4. Evaluation Indicators and Standards for L5200

[0085]

[0086]

[0087] The sample scored a total of 68 points, which is considered a qualified product.

[0088] Example 4

[0089] The sample to be tested is product L5520 produced by Lanzhou Petrochemical using the slurry method high-density polyethylene unit. Its purpose is to react with maleic anhydride to prepare maleic anhydride-grafted polyethylene.

[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 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 considered qualified products; samples with a total score above 75 are considered superior products. The performance and scores of the samples to be tested are shown in Table 5.

[0091] Table 5 L5520 Evaluation Indicators and Evaluation Standards

[0092]

[0093]

[0094] The sample scored a total of 46 points, qualifying it as a standard product.

[0095] Example 5

[0096] The sample to be tested was polyethylene L5520, produced by Lanzhou Petrochemical using the slurry process polyethylene unit. Its intended use is for reacting with maleic anhydride to prepare maleic anhydride-grafted polyethylene. The difference between this sample and the sample in Example 4 lies in the different production batches. The performance and scores of the sample are shown in Table 6.

[0097] Table 6. Evaluation Indicators and Standards for L5520

[0098]

[0099]

[0100]

[0101] The sample reaction time test result was 131 seconds, which deviated from the center value by more than 30%, and the evaluation result was unqualified.

[0102] Example 6

[0103] The sample to be tested was polyethylene L5520, produced by Lanzhou Petrochemical using the slurry process polyethylene unit. Its intended use is for reacting with maleic anhydride to prepare maleic anhydride-grafted polyethylene. The difference between this sample and the sample in Example 4 lies in the different production batches. The performance and scores of the sample are shown in Table 7.

[0104] Table 7 L5520 Evaluation Indicators and Evaluation Standards

[0105]

[0106]

[0107]

[0108] The total score of the sample is 81 points, and it is a superior grade product.

[0109] Comparative Example 1

[0110] The sample to be tested is product L5200 produced by Lanzhou Petrochemical using a slurry process high-density polyethylene plant. Its use is to react with chlorine to prepare chlorinated polyethylene, and the product batch is the same as that in Example 1. The product technical indicators are shown in Table 8. The product test results are qualified.

[0111] Table 8

[0112] project index Test value Melt flow rate (5.0 kg), g / 10 min 0.42-0.60 0.51 <![CDATA[Density, g / cm 3 > 0.950-0.955 0.9516 <![CDATA[Bulk density, g / cm 3 > ≥0.36 0.39 Average particle size, μm 125-315 146 Melting point, °C 133-139 137.0 Melting ratio 10-13 12.0

[0113] Comparative Example 2

[0114] The sample to be tested is product L5520 produced by Lanzhou Petrochemical using a slurry process high-density polyethylene plant. Its use is to react with maleic anhydride to prepare maleic anhydride grafted polyethylene, and the product batch is the same as that in Example 4. The product technical indicators are shown in Table 9. The product test results are qualified.

[0115] Table 9

[0116]

[0117]

[0118] Comparative Example 3

[0119] The sample to be tested is product L5520 produced by Lanzhou Petrochemical using a slurry process high-density polyethylene plant. Its use is to react with maleic anhydride to prepare maleic anhydride grafted polyethylene, and the product batch is the same as that in Example 5. The product technical indicators are shown in Table 10. The product test results are qualified.

[0120] Table 10

[0121] project index Test value Melt flow rate (2.16 kg), g / 10 min 20.0-30.0 24.1 <![CDATA[Density, g / cm 3 > 0.951-0.957 0.9521 <![CDATA[Bulk density, g / cm 3 > ≥0.36 0.42 Average particle size, μm 125-315 136 Melting point, °C 135-141 137.0 Melting ratio 32-39 38.1

[0122] Comparative Example 4

[0123] The sample to be tested is product L5520 produced by Lanzhou Petrochemical using a slurry process high-density polyethylene plant. Its use is to react with maleic anhydride to prepare maleic anhydride grafted polyethylene, and the product batch is the same as that in Example 4.

[0124] 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 considered qualified products; samples with a total score above 75 are considered superior products. The performance and scores of the samples to be tested are shown in Table 11.

[0125] Table 11 L5520 Evaluation Indicators and Evaluation Standards

[0126]

[0127]

[0128]

[0129] The sample scored a total of 59 points, which is considered a qualified product.

[0130] The storage and processing application of each sample in the statistical examples are described.

[0131] Storage conditions:

[0132] 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.

[0133] Processing:

[0134] Chlorinated polyethylene is prepared by reacting polyethylene with chlorine: the chlorination reaction is carried out by aqueous suspension chlorination.

[0135] Maleic anhydride-grafted polyethylene was prepared by reacting polyethylene with maleic anhydride: the grafting reaction was carried out by screw reactive extrusion, and the specific conditions were as shown in Table 12.

[0136] Table 12 Storage and Processing Details of Examples

[0137]

[0138]

[0139] As can be seen from Table 12, the evaluation method of the present invention was used in each embodiment. The evaluation results have a guiding role in the processing. Samples evaluated as excellent or qualified reacted normally during processing. Samples evaluated as unqualified deviated from the normal values ​​in terms of reaction conditions or product indicators.

[0140] For the same batch of samples, Comparative Example 1, which only tested basic indicators, was rated as qualified. Example 1, using the evaluation method of this invention, was rated as unqualified because the chlorination reaction pressure was high and the chlorination time was long during sample processing, resulting in poor chlorination. For the same batch of samples, Comparative Examples 2 and 3, which only tested basic indicators, were rated as qualified. Examples 4 and 5, using the evaluation method of this invention, were rated as unqualified because the grafting rate was higher or lower than normal during sample processing, affecting usability.

[0141] For the same batch of samples, the comparative example used different scoring standards and score gradient values ​​for some items compared to the examples. The evaluation results were qualified, but the samples had a low grafting rate during processing. This shows that using the evaluation standard (gradient and score division) of the present invention can obtain more accurate evaluation results.

[0142] In addition, commonly used factory indicators only test basic indicators and cannot reflect the storage performance of powder. For example, if the flowability index of Examples 1, 3, 4 and 6 exceeds the index value, it should be used within a short period of time to avoid agglomeration and clumping.

Claims

1. An evaluation method for chemically modified polyethylene powder, 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, density, apparent density, average particle size, and melting point. The liquidity indicators include the angle of repose or outflow time; The uniformity indicators include melt flow ratio and particle size distribution; The structural parameters include pore volume; The processing performance indicators include reaction time; 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 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 reaction time deviates from the center value by more than or equal to 30%.

2. The evaluation method according to claim 1, wherein, The evaluation criteria for the melt flow rate 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 melt flow ratio are as follows: 10 points for a deviation from the center value of less than 10%, 5 points for a deviation of 10% or more but less than 20%, 3 points for a deviation of 20% or more but less than 30%, and no points for a 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 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.

11. The evaluation method according to claim 1, wherein, The evaluation criteria for the reaction time are as follows: 10 points are given if the deviation from the central value is less than 10%, 8 points are given if it is greater than or equal to 10% and less than 20%, and 5 points are given if it is greater than or equal to 20% and less than 30%.

12. The evaluation method according to claim 11, wherein, The reaction time is simulated by peroxide internal mixing of the sample reaction process, including the following steps: Mix the sample to be tested and peroxide evenly and then add them to an internal mixer. Carry out internal mixing and record data to obtain a torque-time graph; Read the time T1 corresponding to the feeding peak and the time T2 corresponding to the maximum torque from the torque-time graph, and subtract T1 from T2 to obtain the reaction time; Among them, the peroxide is dicumyl peroxide; the addition amount of the peroxide is 1-3% of the mass of the sample to be tested; the temperature of the internal mixing is 160-190°C.

13. 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 samples to be tested with a total score below 50 or determined to be unqualified are protocol products or waste; The samples to be tested with a total score of 50-75 are qualified products; The samples to be tested with a total score above 75 are superior products.

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