Research on characterization methods for the anti-sagging performance of polyethylene

Research on characterization methods for the anti-sagging performance of polyethylene | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Research on characterization methods for the anti-sagging performance of polyethylene Jingfan Wang, Yucheng Jin, Liqi Zhuang, Ruiheng He, Shicheng Zhao This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4811074/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 24 Sep, 2024 Read the published version in Journal of Polymer Research → Version 1 posted 5 You are reading this latest preprint version Abstract The quality of anti-sagging performance directly influences the application scope of bimodal polyethylene. Although research exists on the characterization methods of anti-sagging performance in bimodal polyethylene, few studies have indicated which testing methods can most accurately characterize this property. This study compares different testing indicators, including melt flow index, melt strength, rheological behavior, molecular weight, and entanglement of molecular chains, to identify the most precise ones for characterizing the anti-sagging performance of polyethylene. A comprehensive analysis combining the properties of the test materials and the test results indicates that zero shear viscosity and relaxation time can effectively characterize the anti-sagging resistance properties of polyethylene. In contract, melt flow index, melt strength, and entanglement of molecular chains are inadequate for accurately characterizing anti-sagging performance. This study will provide an effective and accurate method for characterizing the modification of anti-sagging performance of polyethylene. bimodal polyethylene rheology anti-sagging performance Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Introduction Bimodal polyethylene is a type of polyethylene composed of low molecular weight homopolymers and high molecular weight copolymers, characterized by a bimodal molecular weight distribution [ 1 – 3 ] . Bimodal polyethylene exhibits excellent processing properties, high resistance to slow crack growth, and rapid crack propagation resistance [ 4 – 5 ] , making it an ideal material for use in pipes. However, during the production of large-diameter thick-walled pipe materials, the bimodal polyethylene melt tends to flow downward under the influence of gravity, leading to uneven wall thickness. This phenomenon, known as melt sagging [ 6 ] , significantly impacts its performance. Therefore, assessing the anti-sagging performance of bimodal polyethylene is of paramount importance. Recent studies have proposed various experimental methods to characterize the anti-sagging performance of polyethylene. Research indicates that testing dynamic rheological properties is one approach to characterize the anti-sagging performance of polyethylene. Some studies have found that higher complex viscosity at low angular frequencies is associated with better anti-sagging performance [ 7 ] . Other studies suggest that fitting the zero-shear viscosity from dynamic rheological property tests can characterize anti-sagging performance of polyethylene, with increased zero-shear viscosity improving this performance [ 8 – 12 ] . Combining solid-state nuclear magnetic resonance analysis with shear rheology tests has also been used to characterize anti-sagging performance of polyethylene, finding that the spin-lattice relaxation time (T 1 ) is closely related to anti-sagging performance. Longer T 1 correlates with higher zero-shear viscosity and stronger anti-sagging performance [ 13 ] . Additionally, related studies have found that melt strength and melt flow rate can also characterize anti-sagging performance of polyethylene, with lower melt flow rates and higher melt strength corresponding to better anti-sagging performance [ 8 , 14 ] . Currently, practical experience indicates that some methods used to characterize the anti-sagging performance of polyethylene do not fully align with its actual anti-sagging performance. To accurately evaluate the anti-sagging performance of bimodal polyethylene, it is necessary to identify the most effective characterization method. In this study, a series of experimental methods were explored, including measuring the melt strength of polyethylene samples using a melt extensional rheometer, evaluating the dynamic rheological behavior of samples using a rotational rheometer, and assessing the degree of chain entanglement using a dynamic mechanical analysis. Ultimately, testing indicators such as melt flow index, melt strength, zero-shear viscosity, relaxation time, and molecular chain entanglement were investigated to identify which ones can accurately characterize the anti-sagging performance of polyethylene. One type of non-anti-sagging bimodal polyethylene (HDPE100S) and one type of polyethylene with anti-sagging performance (4902T) are selected to explore methods capable of accurately characterizing the anti-sagging performance of polyethylene through relevant tests. This study is significant for characterizing the anti-sagging performance of bimodal polyethylene and its applications. Experiments 2.1 Materials The conventional bimodal polyethylene HDPE100S is provided by PetroChina Jilin Petrochemical Company. The anti-sagging polyethylene 4902T is purchased from Sinopec Yangzi Petrochemical Company. 2.2 Characterization The melt flow indexer (MI-4 by Gottfert GmbH) was used to test the melt flow rate of the samples. In the test, 190 ℃ and 21.6 kg was used as the testing temperature, and weight. The melt extensional rheometer (GottfertRHEOTENS71.97 by Gottfert GmbH) was used to measure the melt strength of the samples under the following test conditions: a test temperature of 190 ℃ and a test acceleration of 24 mm/s 2 . The rotational rheometer (MCR302 by Anton Paar) was used to measure the rheological behavior of the sample. The diameter of the parallel plates is 25 mm and the gap is 1mm. Frequency sweep was conducted at 200 ℃ with a frequency range of 0.01–100 rad/s. The shear strain was fixed at 1%. The high-temperature gel permeation chromatography instrument (GPC-IR Polymer Char) was used to determine the weight-average molecular weight (M w ), number-average molecular weight (M n ), and distribution (M w /M n ) of the samples. The testing standard that was adhered to was GB/T36214.1-2018. 1,2,4-trichlorobenzene (1,2,4-TCB) was chosen as the solvent; the investigation was conducted under nitrogen; the dissolution temperature was set at 150 ℃; the testing temperature ranged from 40 to 120 ℃ and the analysis flow rate was maintained at 1 ml/min. The dynamic mechanical analysis (DMA by Mettler-Toledo) was used to characterize the degree of entanglement by measuring the entanglement density and entanglement molecular weight of the samples. During the experiment, the samples were heated from 30 to 120 ℃ with a heating rate of 3 ℃/min and an experimental frequency of 1Hz. The micro-mixing rheometer (minilab by ThermoFisher Scientific) was selected to measure the torque variation of polyethylene samples over time. 4 g samples were weighed and then tested with a screw rotation speed of 150 rpm for 5 min. Results and discussion 3.1 Melt flowability and melt strength The melt flow rate (MFR) is a numerical value that describes the flowability of a plastic during processing. Generally, a higher melt flow rate indicates better flowability of the plastic during processing, while a lower melt flow rate suggests poorer flowability. MFR has been used as a standard to characterize the sag resistance of the melt, and studies have shown that lower MFR corresponds to greater melt strength of the material [ 7 , 15 ] . Additionally, it has been proposed that higher melt strength in polyethylene results in better melt sag resistance [ 8 ] . MFR and melt strength tests on three experimental samples are tested by melt flow indexer and melt extensional rheometer, and the results are presented in Fig. 3.1 and Tables 3.1 . Table 3.1 Melt strength and melt flow rate test results of polyethylene Samples Melt strength (N) MFR (g/10min) HDPE100S 0.35 8.9 4902T 0.26 10.1 The test results in Tables 3.1 show that HDPE100S has the lowest melt flow rate (MFR) and the highest melt strength, consistent with the observed pattern that a lower MFR corresponds to higher melt strength. HDPE100S is a bimodal polyethylene with an MFR lower than that of the melt sag resistant polyethylene 4902T, and its melt strength is higher than that of these polyethylene samples. This indicates that MFR and melt strength may not accurately reflect the sag resistance of polyethylene. Analysis suggests that melt sag resistance refers to the ability of the melt to resist gravity without flowing, unaffected by other external forces. However, during the MFR and melt strength tests, the samples were subjected to forces other than gravity, causing displacement. Therefore, these tests cannot be used to characterize anti-sagging performance accurately. 3.2 Melt rheological properties Rotational rheometers are widely used to characterize polymer properties and investigate polymer structures. The zero-shear viscosity of polymers, tested by a rotational rheometer, has been used to characterize the anti-sagging performance of polymers [ 6 ] . Generally, a higher zero-shear viscosity indicates better anti-sagging performance [ 11 , 13 ] . The zero-shear viscosity of three polyethylene samples was measured using a rotational rheometer, and the test results are presented in Fig. 3.2 . By fitting the results from Fig. 3.2 with the Cross Equation [ 16 ] (Eq. 1), the values of η 0 and λ for the samples can be calculated: In the equation, η 0 represents the zero-shear viscosity, and λ represents the relaxation time. The fitting results of the parameters are listed in Table 3.2 . Table 3.2 Fitting results for polyethylene samples Samples η 0 (×10 5 Pa·s) λ (s) HDPE100S 2.5 27 4902T 3.7 79 From the fitting results shown in Table 3.2 it can be seen that the zero shear viscosity η 0 and relaxation time λ of HDPE100S are both smaller than those of the anti-sag polyethylene. The zero-shear viscosity η 0 is the viscosity of the polymer adjusted at a zero shear rate, which may reflect the viscosity of polyethylene melt under no external force. The relaxation time λ refers to the time taken for the sample to return to the maximum deformation value of \(\:\frac{1}{e}\) after the external force is removed. The relaxation time is also measured in the absence of any external force and is only related to the properties of the polymer. Based on this, the flow behavior of the polyethylene melt under no external force can be inferred, thereby assessing the anti-sagging performance of polyethylene. From the test results, it can be seen that the anti-sagging performance of 4902T is superior to that of HDPE100S. Therefore, we believe that η 0 and λ can be used as experimental parameters to characterize the anti-sagging performance of polyethylene, and the larger the values of η 0 and λ, the better the anti-sagging performance of the polyethylene material. 3.3 Molecular weight From the results in section 3.2 , it can be concluded that the zero-shear viscosity of polyethylene effectively characterizes its anti-sagging performance. According to the Fox-Flory equation, the zero-shear viscosity of melt materials is closely related to the weight-average molecular weight; as the weight-average molecular weight increases, the zero-shear viscosity also increases. The molecular weights of HDPE100S and 4902T were tested using GPC-IR, and the test results are presented in Fig. 3.3 and Table 3.3 . Table 3.3 Test results of molecular weight and molecular weight distribution based on GPC-IR Samples M n (g/mol) M w (g/mol)_ PDI HDPE100S 7287 273951 37.59 4902T 10500 299978 28.57 From Table 3.3 , it can be seen that the weight-average molecular weight and number-average molecular weight of 4902T are both higher than those of HDPE100S, which corresponds to the higher zero-shear viscosity of 4902T compared to HDPE100S, thus verifying the accuracy of the zero-shear viscosity fitting results. The test results in Fig. 3.3 show that both HDPE100S and 4902T exhibit bimodal molecular weight distributions. HDPE100S has a significantly higher proportion of the low molecular weight fraction compared to 4902T, while the high molecular weight fraction is lower in HDPE100S than in 4902T. Analysis suggests that high molecular weight polyethylene chains are more prone to entanglement and flow less readily in the molten state than low molecular weight polyethylene chains, thereby enhancing the anti-sagging performance of polyethylene. Consequently, polyethylene 4902T, with its higher proportion of high molecular weight fractions, demonstrates better anti-sagging performance compared to HDPE100S. This finding is consistent with the results obtained from the rotational rheometer tests. For the same weight average molecular weight, polymers with broader molecular weight distributions have significantly lower shear rates for non-Newtonian flow than those with narrower distributions. At lower shear rates, polymers with broader distributions have higher viscosity than those with narrower distributions. The test results from Table 3.3 show that HDPE100S has a broader molecular weight distribution compared to 4902T, suggesting that HDPE100S has a higher viscosity than 4902T at lower shear rates. The results of the GPC-IR test are consistent with the results of the melt flow index and melt strength tests in section 3.1 . Both melt flow index and melt strength tests were carried out at low shear rates. The higher viscosity of HDPE100S results in its lower melt flow index and higher melt strength. 3.4 Entanglement Polymer chain entanglement refers to the phenomenon where long polymer chains interweave, reflecting the structure between polymer molecular chains. The studies have shown that polyethylene with a higher degree of chain entanglement possesses longer molecular chains, a higher weight-average molecular weight, and better anti-sagging performance [ 17 ] . Consequently, the degree of entanglement of the samples has been investigated by using DMA and the torque of the samples has been investigated by using minilab, with the results presented in Figs. 3.4 and 3.5. Based on the storage modulus (E') and corresponding temperature in Fig. 3.4 , the entanglement molecular weight and entanglement density of 4902T and HDPE100S can be calculated using Equations 2 and 3 [ 18 ] , as shown in Table 3.4 . $$\:{M}_{e}=\frac{3\rho\:RT}{E{\prime\:}}$$ (Eq. 2) $$\:{V}_{e}=\frac{\rho\:}{{M}_{e}}$$ (Eq. 3) Where M e is the entanglement molecular weight, V e is the entanglement density, ρ is the density of the test sample, and T is the thermodynamic temperature. Table 3.4 The calculated results of M e and V e for 4902T and HDPE100S at 170°C Samples M e (g/mol) V e (mol/m 3 ) HDPE100S 21546 35.64 4902T 23983 31.89 The test results presented in Fig. 3.4 and Table 3.4 demonstrate that HDPE100S exhibits a lower entanglement molecular weight a higher entanglement density than 4902T. Entanglement density is defined as the average number of molecular chain crossings per unit volume. Consequently, a higher entanglement density indicates a greater degree of polymer entanglement. The test results in Fig. 3.5 indicate that the test torque of HDPE100S is higher than that of 4902T, consistent with the test results shown in Fig. 3.4 . HDPE100S has a higher degree of entanglement than 4902T, but exhibits poorer anti-sagging performance. It is believed that anti-sagging performance is influenced by two aspects of polymer properties: the degree of entanglement and the ease of disentanglement. The greater the degree of entanglement and the more challenging the disentanglement, the better the anti-sagging performance. However, DMA tests can only assess the degree of entanglement and not the ease of disentanglement, rendering the characterization incomplete and insufficient for accurately reflecting the anti-sagging performance of polyethylene. To further investigate the reason why HDPE100S has a high entanglement degree but poor anti-sagging performance, this study measured the number of methyl groups per thousand carbons in the polyethylene samples. The results are shown in Fig. 3.6 . The test results in Fig. 3.6 reveal that HDPE100S has a higher number of methyl groups per thousand carbons than 4902T in the low molecular weight part. And the high molecular weight fraction exhibits the opposite trend. This indicates that HDPE100S has more branches in the low molecular weight part, while 4902T has more branches in the high molecular weight part. It is believed that the degree of entanglement of polyethylene is influenced by the length of molecular chains and the number of short branches; the longer the molecular chain and the fewer the short branches, the higher the degree of entanglement [ 17 ] . As shown in Table 3.3 , HDPE100S has a relatively low weight-average molecular weight, indicating shorter molecular chains. And the high molecular weight fraction of HDPE100S contains fewer short branches, leading to a higher degree of entanglement within this fraction. Consequently, the increased chain entanglement in the high molecular weight fraction contributes to a greater overall degree of entanglement in HDPE100S. It is believed that the anti-sagging performance is determined by both the degree of entanglement and the ease of disentanglement of the polymer. Although HDPE100S exhibits a higher degree of entanglement compared to 4902T, it contains more polyethylene chains with molecular weights below the critical entanglement molecular weight, which facilitates easier disentanglement. The possible mechanism of polyethylene disentanglement is shown in Fig. 3.7 . Figure 3.7 demonstrates that during the disentanglement process, low molecular weight polyethylene molecules below the critical entanglement molecular weight act as lubricants, facilitating the movement of longer molecular chains. The higher the content of low molecular weight polyethylene in the polymer, the easier the disentanglement process becomes. According to the test results shown in Fig. 3.3 , HDPE100S contains a higher proportion of low molecular weight polyethylene, which makes it easier to disentangle. This is consistent with the rheological test results, which show that the relaxation time (λ) of 4902T is greater than that of HDPE100S. In summary, a high degree of entanglement but easy disentanglement leads to the poor anti-sagging performance of HDPE100S. Conclusion This study utilized one conventional bimodal polyethylene (HDPE100S) and one anti-sagging polyethylene (4902T). A series of measurements and analyses were conducted on several properties of the selected bimodal polyethylene samples, including melt flow index, melt strength, rheological behavior, molecular weight, and molecular chain entanglement. The aim was to develop a methodology suitable for laboratory use that can accurately characterize the anti-sagging performance of polyethylene. The results indicate that zero shear viscosity (η 0 ) and relaxation time (λ), obtained by fitting from rotational rheometer, effectively characterize the anti-sagging performance. Higher zero shear viscosity and relaxation time correlate with better anti-sagging performance in polyethylene samples. In contrast, melt flow index, melt strength and the degree of entanglement are inadequate for accurately reflecting the anti-sagging performance of polyethylene. This study provides some guidance for characterizing the anti-sag performance of bimodal polyethylene. Declarations Acknowledge The authors gratefully acknowledge the financial support of this work by National Natural Science Foundation of China (Grants 21878089). Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. References SONG SJ, WU PY, YE MX, FENG JC, YANG YL. Effect of small amount of ultrahigh molecular weight component on the crystallization behaviors of bimodal high density polyethylene[J]. Polymer, 2008, 49(12): 2964-2973. ROLAND S. 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Polymer Engineering & Science, 2004, 44(10): 1848–1857. Cite Share Download PDF Status: Published Journal Publication published 24 Sep, 2024 Read the published version in Journal of Polymer Research → Version 1 posted Reviewers agreed at journal 12 Aug, 2024 Reviewers invited by journal 12 Aug, 2024 Editor invited by journal 31 Jul, 2024 Editor assigned by journal 30 Jul, 2024 First submitted to journal 29 Jul, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4811074","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":338917114,"identity":"3bd8102d-9e4b-4244-9d89-01badc91832b","order_by":0,"name":"Jingfan Wang","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Jingfan","middleName":"","lastName":"Wang","suffix":""},{"id":338917115,"identity":"9bf6a0b9-4406-4931-a38b-370dfc5001ea","order_by":1,"name":"Yucheng 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GPC-IR\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4811074/v1/74b44f60897c4ef28346d88b.png"},{"id":64097697,"identity":"58f1969e-f1aa-49da-b9db-fa9ec711b07f","added_by":"auto","created_at":"2024-09-06 18:04:49","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":13388,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFig 3.4 DMA test results of polyethylene samples\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4811074/v1/87fe8cb4a362bc1cf69e4850.png"},{"id":64097843,"identity":"21d273ed-a742-4acc-b508-a32a47616d84","added_by":"auto","created_at":"2024-09-06 18:12:49","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":11815,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFig 3.5 Micro-mixing rheometer test results of polyethylene samples\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-4811074/v1/3c632ed3c16f59af4ac6540d.png"},{"id":64097699,"identity":"c4e61edc-b018-424f-b7e8-d5cf09382813","added_by":"auto","created_at":"2024-09-06 18:04:49","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":12488,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFig.3.6 The test results of the number of methyl groups per thousand carbons\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-4811074/v1/700183f82869fe64fcda49ce.png"},{"id":64097702,"identity":"db393d7d-d505-42f2-8bd6-28853e060f38","added_by":"auto","created_at":"2024-09-06 18:04:49","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":329888,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFig.3.7 The possible mechanism of polyethylene disentanglement\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-4811074/v1/310fa7761e1776ac785672c1.png"},{"id":65628074,"identity":"1c52b81b-1693-4956-9d93-8d76da0e95de","added_by":"auto","created_at":"2024-09-30 16:17:36","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":861995,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4811074/v1/e1cd0f8d-9b90-4df5-8dea-885a48b497e5.pdf"}],"financialInterests":"","formattedTitle":"Research on characterization methods for the anti-sagging performance of polyethylene","fulltext":[{"header":"Introduction","content":"\u003cp\u003eBimodal polyethylene is a type of polyethylene composed of low molecular weight homopolymers and high molecular weight copolymers, characterized by a bimodal molecular weight distribution \u003csup\u003e[\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e–\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]\u003c/sup\u003e. Bimodal polyethylene exhibits excellent processing properties, high resistance to slow crack growth, and rapid crack propagation resistance \u003csup\u003e[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e–\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]\u003c/sup\u003e, making it an ideal material for use in pipes. However, during the production of large-diameter thick-walled pipe materials, the bimodal polyethylene melt tends to flow downward under the influence of gravity, leading to uneven wall thickness. This phenomenon, known as melt sagging \u003csup\u003e[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]\u003c/sup\u003e, significantly impacts its performance. Therefore, assessing the anti-sagging performance of bimodal polyethylene is of paramount importance.\u003c/p\u003e \u003cp\u003eRecent studies have proposed various experimental methods to characterize the anti-sagging performance of polyethylene. Research indicates that testing dynamic rheological properties is one approach to characterize the anti-sagging performance of polyethylene. Some studies have found that higher complex viscosity at low angular frequencies is associated with better anti-sagging performance \u003csup\u003e[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]\u003c/sup\u003e. Other studies suggest that fitting the zero-shear viscosity from dynamic rheological property tests can characterize anti-sagging performance of polyethylene, with increased zero-shear viscosity improving this performance \u003csup\u003e[\u003cspan additionalcitationids=\"CR9 CR10 CR11\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e–\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]\u003c/sup\u003e. Combining solid-state nuclear magnetic resonance analysis with shear rheology tests has also been used to characterize anti-sagging performance of polyethylene, finding that the spin-lattice relaxation time (T\u003csub\u003e1\u003c/sub\u003e) is closely related to anti-sagging performance. Longer T\u003csub\u003e1\u003c/sub\u003e correlates with higher zero-shear viscosity and stronger anti-sagging performance \u003csup\u003e[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]\u003c/sup\u003e. Additionally, related studies have found that melt strength and melt flow rate can also characterize anti-sagging performance of polyethylene, with lower melt flow rates and higher melt strength corresponding to better anti-sagging performance \u003csup\u003e[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]\u003c/sup\u003e. Currently, practical experience indicates that some methods used to characterize the anti-sagging performance of polyethylene do not fully align with its actual anti-sagging performance. To accurately evaluate the anti-sagging performance of bimodal polyethylene, it is necessary to identify the most effective characterization method.\u003c/p\u003e \u003cp\u003eIn this study, a series of experimental methods were explored, including measuring the melt strength of polyethylene samples using a melt extensional rheometer, evaluating the dynamic rheological behavior of samples using a rotational rheometer, and assessing the degree of chain entanglement using a dynamic mechanical analysis. Ultimately, testing indicators such as melt flow index, melt strength, zero-shear viscosity, relaxation time, and molecular chain entanglement were investigated to identify which ones can accurately characterize the anti-sagging performance of polyethylene. One type of non-anti-sagging bimodal polyethylene (HDPE100S) and one type of polyethylene with anti-sagging performance (4902T) are selected to explore methods capable of accurately characterizing the anti-sagging performance of polyethylene through relevant tests. This study is significant for characterizing the anti-sagging performance of bimodal polyethylene and its applications.\u003c/p\u003e \u003cdiv id=\"Sec2\" class=\"Section2\"\u003e \u003cdiv id=\"Sec3\" class=\"Section3\"\u003e \u003c/div\u003e \u003c/div\u003e "},{"header":"Experiments","content":"\u003ch2\u003e2.1 Materials\u003c/h2\u003e\u003cp\u003eThe conventional bimodal polyethylene HDPE100S is provided by PetroChina Jilin Petrochemical Company. The anti-sagging polyethylene 4902T is purchased from Sinopec Yangzi Petrochemical Company.\u003c/p\u003e\u003ch2\u003e2.2 Characterization\u003c/h2\u003e\u003cp\u003eThe melt flow indexer (MI-4 by Gottfert GmbH) was used to test the melt flow rate of the samples. In the test, 190 ℃ and 21.6 kg was used as the testing temperature, and weight.\u003c/p\u003e\u003cp\u003eThe melt extensional rheometer (GottfertRHEOTENS71.97 by Gottfert GmbH) was used to measure the melt strength of the samples under the following test conditions: a test temperature of 190 ℃ and a test acceleration of 24 mm/s\u003csup\u003e2\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eThe rotational rheometer (MCR302 by Anton Paar) was used to measure the rheological behavior of the sample. The diameter of the parallel plates is 25 mm and the gap is 1mm. Frequency sweep was conducted at 200 ℃ with a frequency range of 0.01–100 rad/s. The shear strain was fixed at 1%.\u003c/p\u003e\u003cp\u003eThe high-temperature gel permeation chromatography instrument (GPC-IR Polymer Char) was used to determine the weight-average molecular weight (M\u003csub\u003ew\u003c/sub\u003e), number-average molecular weight (M\u003csub\u003en\u003c/sub\u003e), and distribution (M\u003csub\u003ew\u003c/sub\u003e/M\u003csub\u003en\u003c/sub\u003e) of the samples. The testing standard that was adhered to was GB/T36214.1-2018. 1,2,4-trichlorobenzene (1,2,4-TCB) was chosen as the solvent; the investigation was conducted under nitrogen; the dissolution temperature was set at 150 ℃; the testing temperature ranged from 40 to 120 ℃ and the analysis flow rate was maintained at 1 ml/min.\u003c/p\u003e\u003cp\u003eThe dynamic mechanical analysis (DMA by Mettler-Toledo) was used to characterize the degree of entanglement by measuring the entanglement density and entanglement molecular weight of the samples. During the experiment, the samples were heated from 30 to 120 ℃ with a heating rate of 3 ℃/min and an experimental frequency of 1Hz.\u003c/p\u003e\u003cp\u003eThe micro-mixing rheometer (minilab by ThermoFisher Scientific) was selected to measure the torque variation of polyethylene samples over time. 4 g samples were weighed and then tested with a screw rotation speed of 150 rpm for 5 min.\u003c/p\u003e"},{"header":"Results and discussion","content":"\u003cdiv id=\"Sec6\"\u003e\n \u003ch2\u003e3.1 Melt flowability and melt strength\u003c/h2\u003e\n \u003cp\u003eThe melt flow rate (MFR) is a numerical value that describes the flowability of a plastic during processing. Generally, a higher melt flow rate indicates better flowability of the plastic during processing, while a lower melt flow rate suggests poorer flowability. MFR has been used as a standard to characterize the sag resistance of the melt, and studies have shown that lower MFR corresponds to greater melt strength of the material \u003csup\u003e[\u003cspan\u003e7\u003c/span\u003e, \u003cspan\u003e15\u003c/span\u003e]\u003c/sup\u003e. Additionally, it has been proposed that higher melt strength in polyethylene results in better melt sag resistance \u003csup\u003e[\u003cspan\u003e8\u003c/span\u003e]\u003c/sup\u003e. MFR and melt strength tests on three experimental samples are tested by melt flow indexer and melt extensional rheometer, and the results are presented in Fig. \u003cspan\u003e3.1\u003c/span\u003e and Tables \u003cspan\u003e3.1\u003c/span\u003e.\u003c/p\u003e\n \u003cdiv\u003e\n \u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 3.1\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eMelt strength and melt flow rate test results of polyethylene\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"3\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSamples\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMelt strength (N)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMFR (g/10min)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHDPE100S\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e8.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4902T\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eThe test results in Tables \u003cspan\u003e3.1\u003c/span\u003e show that HDPE100S has the lowest melt flow rate (MFR) and the highest melt strength, consistent with the observed pattern that a lower MFR corresponds to higher melt strength. HDPE100S is a bimodal polyethylene with an MFR lower than that of the melt sag resistant polyethylene 4902T, and its melt strength is higher than that of these polyethylene samples. This indicates that MFR and melt strength may not accurately reflect the sag resistance of polyethylene. Analysis suggests that melt sag resistance refers to the ability of the melt to resist gravity without flowing, unaffected by other external forces. However, during the MFR and melt strength tests, the samples were subjected to forces other than gravity, causing displacement. Therefore, these tests cannot be used to characterize anti-sagging performance accurately.\u003c/p\u003e\n\u003c/div\u003e\n\u003ch3\u003e3.2 Melt rheological properties\u003c/h3\u003e\n\u003cp\u003eRotational rheometers are widely used to characterize polymer properties and investigate polymer structures. The zero-shear viscosity of polymers, tested by a rotational rheometer, has been used to characterize the anti-sagging performance of polymers \u003csup\u003e[\u003cspan\u003e6\u003c/span\u003e]\u003c/sup\u003e. Generally, a higher zero-shear viscosity indicates better anti-sagging performance \u003csup\u003e[\u003cspan\u003e11\u003c/span\u003e, \u003cspan\u003e13\u003c/span\u003e]\u003c/sup\u003e. The zero-shear viscosity of three polyethylene samples was measured using a rotational rheometer, and the test results are presented in Fig. \u003cspan\u003e3.2\u003c/span\u003e.\u003c/p\u003e\n\u003cp\u003eBy fitting the results from Fig. \u003cspan\u003e3.2\u003c/span\u003e with the Cross Equation \u003csup\u003e[\u003cspan\u003e16\u003c/span\u003e]\u003c/sup\u003e (Eq. 1), the values of \u0026eta;\u003csub\u003e0\u003c/sub\u003e and \u0026lambda; for the samples can be calculated:\u003c/p\u003e\n\u003cp\u003e\u003cspan\u003e\u0026nbsp;\u003cimg src=\"https://myfiles.space/user_files/122228_c8a1650c59388082/122228_custom_files/img1725645433.png\"\u003e\u003c/span\u003e\u003c/p\u003e\n\u003cp\u003eIn the equation, \u0026eta;\u003csub\u003e0\u003c/sub\u003e represents the zero-shear viscosity, and \u0026lambda; represents the relaxation time. The fitting results of the parameters are listed in Table \u003cspan\u003e3.2\u003c/span\u003e.\u003c/p\u003e\n\u003cdiv\u003e\n \u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 3.2\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eFitting results for polyethylene samples\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"3\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSamples\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003e\u0026eta;\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e (\u0026times;10\u003csup\u003e5\u003c/sup\u003ePa\u0026middot;s)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003e\u0026lambda;\u003c/em\u003e (s)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHDPE100S\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e27\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4902T\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e79\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eFrom the fitting results shown in Table \u003cspan\u003e3.2\u003c/span\u003e it can be seen that the zero shear viscosity \u0026eta;\u003csub\u003e0\u003c/sub\u003e and relaxation time \u0026lambda; of HDPE100S are both smaller than those of the anti-sag polyethylene. The zero-shear viscosity \u0026eta;\u003csub\u003e0\u003c/sub\u003e is the viscosity of the polymer adjusted at a zero shear rate, which may reflect the viscosity of polyethylene melt under no external force. The relaxation time \u0026lambda; refers to the time taken for the sample to return to the maximum deformation value of \u003cspan\u003e\u003cspan\u003e\\(\\:\\frac{1}{e}\\)\u003c/span\u003e\u003c/span\u003e after the external force is removed. The relaxation time is also measured in the absence of any external force and is only related to the properties of the polymer. Based on this, the flow behavior of the polyethylene melt under no external force can be inferred, thereby assessing the anti-sagging performance of polyethylene. From the test results, it can be seen that the anti-sagging performance of 4902T is superior to that of HDPE100S. Therefore, we believe that \u0026eta;\u003csub\u003e0\u003c/sub\u003e and \u0026lambda; can be used as experimental parameters to characterize the anti-sagging performance of polyethylene, and the larger the values of \u0026eta;\u003csub\u003e0\u003c/sub\u003e and \u0026lambda;, the better the anti-sagging performance of the polyethylene material.\u003c/p\u003e\n\u003cdiv id=\"Sec8\"\u003e\n \u003ch2\u003e3.3 Molecular weight\u003c/h2\u003e\n \u003cp\u003eFrom the results in section \u003cspan\u003e3.2\u003c/span\u003e, it can be concluded that the zero-shear viscosity of polyethylene effectively characterizes its anti-sagging performance. According to the Fox-Flory equation, the zero-shear viscosity of melt materials is closely related to the weight-average molecular weight; as the weight-average molecular weight increases, the zero-shear viscosity also increases. The molecular weights of HDPE100S and 4902T were tested using GPC-IR, and the test results are presented in Fig. \u003cspan\u003e3.3\u003c/span\u003e and Table \u003cspan\u003e3.3\u003c/span\u003e.\u003c/p\u003e\n \u003cdiv\u003e\n \u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 3.3\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eTest results of molecular weight and molecular weight distribution based on GPC-IR\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"4\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSamples\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eM\u003csub\u003en\u003c/sub\u003e (g/mol)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eM\u003csub\u003ew\u003c/sub\u003e (g/mol)_\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ePDI\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHDPE100S\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7287\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e273951\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e37.59\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4902T\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10500\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e299978\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e28.57\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eFrom Table \u003cspan\u003e3.3\u003c/span\u003e, it can be seen that the weight-average molecular weight and number-average molecular weight of 4902T are both higher than those of HDPE100S, which corresponds to the higher zero-shear viscosity of 4902T compared to HDPE100S, thus verifying the accuracy of the zero-shear viscosity fitting results.\u003c/p\u003e\n \u003cp\u003eThe test results in Fig. \u003cspan\u003e3.3\u003c/span\u003e show that both HDPE100S and 4902T exhibit bimodal molecular weight distributions. HDPE100S has a significantly higher proportion of the low molecular weight fraction compared to 4902T, while the high molecular weight fraction is lower in HDPE100S than in 4902T. Analysis suggests that high molecular weight polyethylene chains are more prone to entanglement and flow less readily in the molten state than low molecular weight polyethylene chains, thereby enhancing the anti-sagging performance of polyethylene. Consequently, polyethylene 4902T, with its higher proportion of high molecular weight fractions, demonstrates better anti-sagging performance compared to HDPE100S. This finding is consistent with the results obtained from the rotational rheometer tests.\u003c/p\u003e\n \u003cp\u003eFor the same weight average molecular weight, polymers with broader molecular weight distributions have significantly lower shear rates for non-Newtonian flow than those with narrower distributions. At lower shear rates, polymers with broader distributions have higher viscosity than those with narrower distributions. The test results from Table \u003cspan\u003e3.3\u003c/span\u003e show that HDPE100S has a broader molecular weight distribution compared to 4902T, suggesting that HDPE100S has a higher viscosity than 4902T at lower shear rates. The results of the GPC-IR test are consistent with the results of the melt flow index and melt strength tests in section \u003cspan\u003e3.1\u003c/span\u003e. Both melt flow index and melt strength tests were carried out at low shear rates. The higher viscosity of HDPE100S results in its lower melt flow index and higher melt strength.\u003c/p\u003e\n\u003c/div\u003e\n\u003ch3\u003e3.4 Entanglement\u003c/h3\u003e\n\u003cp\u003ePolymer chain entanglement refers to the phenomenon where long polymer chains interweave, reflecting the structure between polymer molecular chains. The studies have shown that polyethylene with a higher degree of chain entanglement possesses longer molecular chains, a higher weight-average molecular weight, and better anti-sagging performance \u003csup\u003e[\u003cspan\u003e17\u003c/span\u003e]\u003c/sup\u003e. Consequently, the degree of entanglement of the samples has been investigated by using DMA and the torque of the samples has been investigated by using minilab, with the results presented in Figs. \u003cspan\u003e3.4\u003c/span\u003e and 3.5.\u003c/p\u003e\n\u003cp\u003eBased on the storage modulus (E\u0026apos;) and corresponding temperature in Fig. \u003cspan\u003e3.4\u003c/span\u003e, the entanglement molecular weight and entanglement density of 4902T and HDPE100S can be calculated using Equations 2 and 3\u003csup\u003e[\u003cspan\u003e18\u003c/span\u003e]\u003c/sup\u003e, as shown in Table \u003cspan\u003e3.4\u003c/span\u003e.\u003c/p\u003e\n\u003cdiv id=\"Equa\"\u003e\n \u003cdiv id=\"FileID_Equa\" name=\"EquationSource\"\u003e$$\\:{M}_{e}=\\frac{3\\rho\\:RT}{E{\\prime\\:}}$$\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003e(Eq.\u0026nbsp;2)\u003c/p\u003e\n\u003cdiv id=\"Equb\"\u003e\n \u003cdiv id=\"FileID_Equb\" name=\"EquationSource\"\u003e$$\\:{V}_{e}=\\frac{\\rho\\:}{{M}_{e}}$$\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003e(Eq.\u0026nbsp;3)\u003c/p\u003e\n\u003cp\u003eWhere M\u003csub\u003ee\u003c/sub\u003e is the entanglement molecular weight, V\u003csub\u003ee\u003c/sub\u003e is the entanglement density, \u0026rho; is the density of the test sample, and T is the thermodynamic temperature.\u003c/p\u003e\n\u003cdiv\u003e\n \u003ctable id=\"Tab4\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 3.4\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eThe calculated results of M\u003csub\u003ee\u003c/sub\u003e and V\u003csub\u003ee\u003c/sub\u003e for 4902T and HDPE100S at 170\u0026deg;C\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"3\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSamples\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eM\u003csub\u003ee\u003c/sub\u003e (g/mol)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eV\u003csub\u003ee\u003c/sub\u003e (mol/m\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHDPE100S\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e21546\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e35.64\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4902T\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e23983\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e31.89\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eThe test results presented in Fig. \u003cspan\u003e3.4\u003c/span\u003e and Table \u003cspan\u003e3.4\u003c/span\u003e demonstrate that HDPE100S exhibits a lower entanglement molecular weight a higher entanglement density than 4902T. Entanglement density is defined as the average number of molecular chain crossings per unit volume. Consequently, a higher entanglement density indicates a greater degree of polymer entanglement. The test results in Fig. 3.5 indicate that the test torque of HDPE100S is higher than that of 4902T, consistent with the test results shown in Fig. \u003cspan\u003e3.4\u003c/span\u003e. HDPE100S has a higher degree of entanglement than 4902T, but exhibits poorer anti-sagging performance. It is believed that anti-sagging performance is influenced by two aspects of polymer properties: the degree of entanglement and the ease of disentanglement. The greater the degree of entanglement and the more challenging the disentanglement, the better the anti-sagging performance. However, DMA tests can only assess the degree of entanglement and not the ease of disentanglement, rendering the characterization incomplete and insufficient for accurately reflecting the anti-sagging performance of polyethylene. To further investigate the reason why HDPE100S has a high entanglement degree but poor anti-sagging performance, this study measured the number of methyl groups per thousand carbons in the polyethylene samples. The results are shown in Fig. \u003cspan\u003e3.6\u003c/span\u003e.\u003c/p\u003e\n\u003cp\u003eThe test results in Fig. \u003cspan\u003e3.6\u003c/span\u003e reveal that HDPE100S has a higher number of methyl groups per thousand carbons than 4902T in the low molecular weight part. And the high molecular weight fraction exhibits the opposite trend. This indicates that HDPE100S has more branches in the low molecular weight part, while 4902T has more branches in the high molecular weight part. It is believed that the degree of entanglement of polyethylene is influenced by the length of molecular chains and the number of short branches; the longer the molecular chain and the fewer the short branches, the higher the degree of entanglement \u003csup\u003e[\u003cspan\u003e17\u003c/span\u003e]\u003c/sup\u003e. As shown in Table \u003cspan\u003e3.3\u003c/span\u003e, HDPE100S has a relatively low weight-average molecular weight, indicating shorter molecular chains. And the high molecular weight fraction of HDPE100S contains fewer short branches, leading to a higher degree of entanglement within this fraction. Consequently, the increased chain entanglement in the high molecular weight fraction contributes to a greater overall degree of entanglement in HDPE100S. It is believed that the anti-sagging performance is determined by both the degree of entanglement and the ease of disentanglement of the polymer. Although HDPE100S exhibits a higher degree of entanglement compared to 4902T, it contains more polyethylene chains with molecular weights below the critical entanglement molecular weight, which facilitates easier disentanglement. The possible mechanism of polyethylene disentanglement is shown in Fig. \u003cspan\u003e3.7\u003c/span\u003e.\u003c/p\u003e\n\u003cp\u003eFigure \u003cspan\u003e3.7\u003c/span\u003e demonstrates that during the disentanglement process, low molecular weight polyethylene molecules below the critical entanglement molecular weight act as lubricants, facilitating the movement of longer molecular chains. The higher the content of low molecular weight polyethylene in the polymer, the easier the disentanglement process becomes. According to the test results shown in Fig. \u003cspan\u003e3.3\u003c/span\u003e, HDPE100S contains a higher proportion of low molecular weight polyethylene, which makes it easier to disentangle. This is consistent with the rheological test results, which show that the relaxation time (\u0026lambda;) of 4902T is greater than that of HDPE100S. In summary, a high degree of entanglement but easy disentanglement leads to the poor anti-sagging performance of HDPE100S.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThis study utilized one conventional bimodal polyethylene (HDPE100S) and one anti-sagging polyethylene (4902T). A series of measurements and analyses were conducted on several properties of the selected bimodal polyethylene samples, including melt flow index, melt strength, rheological behavior, molecular weight, and molecular chain entanglement. The aim was to develop a methodology suitable for laboratory use that can accurately characterize the anti-sagging performance of polyethylene. The results indicate that zero shear viscosity (η\u003csub\u003e0\u003c/sub\u003e) and relaxation time (λ), obtained by fitting from rotational rheometer, effectively characterize the anti-sagging performance. Higher zero shear viscosity and relaxation time correlate with better anti-sagging performance in polyethylene samples. In contrast, melt flow index, melt strength and the degree of entanglement are inadequate for accurately reflecting the anti-sagging performance of polyethylene. This study provides some guidance for characterizing the anti-sag performance of bimodal polyethylene.\u003c/p\u003e "},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledge\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors gratefully acknowledge the financial support of this work by National Natural Science Foundation of China (Grants 21878089).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of competing interest\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eSONG SJ, WU PY, YE MX, FENG JC, YANG YL. Effect of small amount of ultrahigh molecular weight component on the crystallization behaviors of bimodal high density polyethylene[J]. Polymer, 2008, 49(12): 2964-2973.\u003c/li\u003e\n\u003cli\u003eROLAND S. Critical review of the molecular topology of semi-crystalline polymers: The origin and assessment of inter-crystalline tie molecules and chain entanglements[J]. Journal of Polymer Science Part B: Polymer Physics, 2005, 43: 1729.\u003c/li\u003e\n\u003cli\u003eBOHM LL. The ethylene polymerization with ziegler catalysts: Fifty years after the discovery[J]. Angewantde Chemie-International Edition, 2003, 42, 5010-5030. \u003c/li\u003e\n\u003cli\u003eBROWN N, ZHOU ZJ. Tests for developing gas pipe resins[J]. Plastic, Rubber and Composites, 2005, 34: 289-293.\u003c/li\u003e\n\u003cli\u003eCHEN Y, ZOU HW, LIANG M, LIU PB. Study on the dynamic rheological behavior of four different bimodal polyethylenes[J]. Journal of Macromolecular Science Part B, 2013, 52(7): 924-936.\u003c/li\u003e\n\u003cli\u003eDESLAURIER PJ, MCDANIE MP, ROHLFING DC, KRISHNASWAMY RK, SECORA SJ, BENHAM EA, MAEGER PL, WOLF AR, BEAULIEU BB. A comparative study of multimodal vs. bimodal polyethylene pipe resins for PE-100 applications[J]. Polymer Engineering and Science, 2005, 45(9), 1203-1213.\u003c/li\u003e\n\u003cli\u003eSONG MJ, HE XL, LIU BP. Preparation of high-melt-strength polyethylene through ultrasonic irradiation wave treatment plus radial initiator[J]. China\u0026ensp;Synthetic\u0026ensp;Resin\u0026ensp;and\u0026ensp;Plastics, 2016, 33(1): 32-36. \u003c/li\u003e\n\u003cli\u003eWANG YP, GUO YC, GAO LY, GUO R. Structure and properties of bimodal PE100 pipe specialty[J]. China\u0026ensp;Synthetic\u0026ensp;Resin\u0026ensp;and\u0026ensp;Plastics, 2023, 40(5): 46-50. \u003c/li\u003e\n\u003cli\u003eZHENG XW, ZUN Q, ZHOU P, SONG KM, LI TY, MAI KC. Research on the structure and properties of materials for large diameter PE pipes[J]. Chemical Enterprise Management, 2020, 16: 90-91. \u003c/li\u003e\n\u003cli\u003eXU LF. Research of large-diameter polyethylene pipes with high-strength for nuclear power plants[D]. Hebei University of Science and Technology, 2021. \u003c/li\u003e\n\u003cli\u003eZHOU H, JIANG BB, ZHONG F, CHEN ZY, WONG XB, YANG YR. A polyethylene resin with anti melt sag performance and its preparation and application[P]. CN 114426718A, 2022-05-03.\u003c/li\u003e\n\u003cli\u003eJFT PITTMAN, GP WHITHAM, S BEECH, D GWYNN. Cooling and wall thickness uniformity in plastic pipe manufacture [J]. International Polymer Processing, 1994, 9: 130-140. \u003c/li\u003e\n\u003cli\u003eSHEN JH. Sag resistance of tubing PE100 resin by solid-state nuclear magnetic resonance technique[J]. China\u0026ensp;Synthetic\u0026ensp;Resin\u0026ensp;and\u0026ensp;Plastics, 2007, 24(4): 12-15.\u003c/li\u003e\n\u003cli\u003eLIU TC, JIN L, XU DM, NIE HK. Study on high melt strength polypropylene prepared by solid phase grafting method[J]. Engineering plastics application, 2015, 43(12): 35-38.\u003c/li\u003e\n\u003cli\u003eERIC JM, CARLOS UD, ARMEN HD. High melt strength polyethylene compositions[P]. US 6114457, 1998-02-06. \u003c/li\u003e\n\u003cli\u003eARDAKANI F, JAHANI Y, MORSHEDIAN J. Dynamic viscoelastic behavior of poly-propylene/polybutene-1 blends and its correlation with morphology[J]. Journal of Applied Polymer Science, 2012, 125(1): 640-648.\u003c/li\u003e\n\u003cli\u003eJOY JC, JOS\u0026Eacute; AAC, MARIA AP, ALEXANDER P. Chain entanglements and mechanical behavior of high density polyethylene[J]. Journal of Engineering Material and Technology, 2010, 132(1): 011016. \u003c/li\u003e\n\u003cli\u003eRIZWAN MG, FREDERICK JM. Processing of ultra‐high molecular weight polyethylene by hot isostatic pressing, and the effect of processing parameters on its microstructure[J]. Polymer Engineering \u0026amp; Science, 2004, 44(10): 1848\u0026ndash;1857.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-polymer-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jpol","sideBox":"Learn more about [Journal of Polymer Research](https://www.springer.com/journal/10965)","snPcode":"10965","submissionUrl":"https://www.editorialmanager.com/jpol/","title":"Journal of Polymer Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"bimodal polyethylene, rheology, anti-sagging performance","lastPublishedDoi":"10.21203/rs.3.rs-4811074/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4811074/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe quality of anti-sagging performance directly influences the application scope of bimodal polyethylene. Although research exists on the characterization methods of anti-sagging performance in bimodal polyethylene, few studies have indicated which testing methods can most accurately characterize this property. This study compares different testing indicators, including melt flow index, melt strength, rheological behavior, molecular weight, and entanglement of molecular chains, to identify the most precise ones for characterizing the anti-sagging performance of polyethylene. A comprehensive analysis combining the properties of the test materials and the test results indicates that zero shear viscosity and relaxation time can effectively characterize the anti-sagging resistance properties of polyethylene. In contract, melt flow index, melt strength, and entanglement of molecular chains are inadequate for accurately characterizing anti-sagging performance. This study will provide an effective and accurate method for characterizing the modification of anti-sagging performance of polyethylene.\u003c/p\u003e","manuscriptTitle":"Research on characterization methods for the anti-sagging performance of polyethylene","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-09-06 18:04:44","doi":"10.21203/rs.3.rs-4811074/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2024-08-12T05:01:43+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-08-12T04:50:29+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Journal of Polymer Research","date":"2024-07-31T19:42:03+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-07-30T12:46:56+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Polymer Research","date":"2024-07-30T01:43:33+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-polymer-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jpol","sideBox":"Learn more about [Journal of Polymer Research](https://www.springer.com/journal/10965)","snPcode":"10965","submissionUrl":"https://www.editorialmanager.com/jpol/","title":"Journal of Polymer Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"e27f6012-c323-4ba1-84c8-ebc0f3c35782","owner":[],"postedDate":"September 6th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-09-30T16:11:02+00:00","versionOfRecord":{"articleIdentity":"rs-4811074","link":"https://doi.org/10.1007/s10965-024-04145-7","journal":{"identity":"journal-of-polymer-research","isVorOnly":false,"title":"Journal of Polymer Research"},"publishedOn":"2024-09-24 15:57:58","publishedOnDateReadable":"September 24th, 2024"},"versionCreatedAt":"2024-09-06 18:04:44","video":"","vorDoi":"10.1007/s10965-024-04145-7","vorDoiUrl":"https://doi.org/10.1007/s10965-024-04145-7","workflowStages":[]},"version":"v1","identity":"rs-4811074","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4811074","identity":"rs-4811074","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}