Chain Dynamics of Partially Disentangled UHMWPE around Melting Point Characterized by 1H Low-Field Solid-State NMR

Zhao, Yan; Liang, Yuling; Yao, Yingjie; Wang, Hao; Lin, Tong; Gao, Yun; Wang, Xiaoliang; Xue, Gi

doi:10.3390/polym15081910

Cited by 3 publications

(4 citation statements)

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“…Thus, the NMR experiments do not confirm the existence of a disentangled melt state that was suggested based on rheological experiments. ,, Contrary to the rheological experiments, the NMR results are not affected by sample preparation, whereas the rheological data can suffer from systematic errors, as will be discussed below. A low-field double-quantum (DQ) 1 H NMR method was also used for studying low-entangled freeze-dried UHMWPE samples and their melts . A significant difference in the DQ NMR signal was observed for the amorphous phase of freeze-dried UHMWPE samples that were prepared from dilute polymer solutions with different concentrations and, consequently, different entanglement densities.…”

Section: Results and Discussionmentioning

confidence: 99%

Disentangled Melt of Ultrahigh-Molecular-Weight Polyethylene: Fictitious or Real?

Litvinov,

Christakopoulos,

Lemstra

2024

Macromolecules

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There are two opposing views on the role of the melting of low-entangled polyethylenes on the obtained entanglement density in the molten state and the time required for its equilibration, namely, instantaneous recovery to the equilibrium melt state upon melting (chain explosion) versus slow recovery (melt memory effect). A series of rheological studies have shown that slow heating of low-entangled nascent ultrahigh-molecularweight polyethylene (UHMWPE) powders to temperatures above the equilibrium melting temperature causes the formation of "the disentangled nonequilibrium melt" due to consecutive detachment of chain stems from the edges of crystals keeping the largely intact low-entangled middle part of chains in the melt. Contrary to the rheology findings, studies of several mechanical properties of recrystallized UHMWPE have found that the equilibrium entanglement density is reached instantly upon the melting of lowentangled UHMWPE, suggesting a chain explosion mechanism. To obtain additional information that can help in understanding the melt memory phenomenon better, several UHMWPE samples are studied by 1 H NMR T 2 relaxometry. The NMR experiments are performed for melts prepared from UHMWPE powders with different entanglement densities that were molten using fast (∼10 K/ min) and slow (∼0.2 K/min) heating rates. In all cases, the existence of "the disentangled nonequilibrium melt" was not observed. The results are explained by the chain explosion mechanism that leads to the equilibrium volume-average entanglement density, already at the final stage of melting. Cautious rheological experiments also do not detect "the disentangled nonequilibrium melt". Possible artifacts of previous rheological studies of disentangled UHMWPE melts are discussed. The conclusion of the present study is supported by a large number of previous investigations that are briefly reviewed. Is the disentangled melt state fictitious or real? The answer is yes and no. Chain explosion causes instantaneous equilibration of the volume-average entanglement density upon melting by the formation of local entanglements that play a major role in several volume-average properties, i.e., modulus, drawability, adhesion, segmental mobility, and some other properties. However, the uniform distribution of topological knots between chains is a slow process that is largely governed by chain reptation. The heterogeneity of the entanglement network as well as the impurities in UHMWPE can influence (1) the local nucleation phenomenon at crystallization that does not characterize the entanglement network and (2) deformation properties at ultimate strains. Therefore, the definition of melt memory and chain explosion should be specified to properties that are used for the characterization of low-entangled and equilibrium melt states.

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Section: Results and Discussionmentioning

confidence: 99%

Disentangled Melt of Ultrahigh-Molecular-Weight Polyethylene: Fictitious or Real?

Litvinov,

Christakopoulos,

Lemstra

2024

Macromolecules

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“…It is known that semicrystalline polymers contain alternating amorphous and crystalline layers. [ 26 ] Previous studies have shown that entanglement has a greater impact on the melting kinetics of crystals than lamellar thickness in the UHMWPE system, [ 27–31 ] and the lateral size of the whole crystal is not a significant factor in determining the melting kinetics of polymer lamellar crystals, since there are new lateral surfaces generated by the local melting within lamellae. [ 10,32–35 ] Larger deviation from the equilibrium entanglement state will enhance the free energy of the amorphous layer, thereby accelerating the melting process.…”

Section: Resultsmentioning

confidence: 99%

“…However, by a comparative analysis of less‐entangled and well‐entangled UHMWPE samples in both molten and solid states, Xue et al. [ 27 ] pointed out that the low mobility of the amorphous region in less‐entangled samples is primarily due to the restriction imposed by the crystalline region, rather than the entanglement. Then, we can cautiously point out that the entanglement density of the amorphous region in nascent samples in the solid state is lower than that of melt‐crystallized samples.…”

Section: Resultsmentioning

confidence: 99%

The Isothermal Melting Kinetics of Ultra‐High Molecular Weight Polyethylene Crystals

Xue,

Lu,

Wang

et al. 2024

Macromol. Rapid Commun.

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The isothermal melting behaviors of ultrahigh molecular weight polyethylene (UHMWPE) with different entangled states (i.e., nascent and melt‐crystallized samples) have been studied. For two kinds of UHMWPE samples, our result shows that the relative content of survived crystals (Xs) exponentially decreases with time and reaches a constant value. We suggest that such a melting behavior is related to the observed nonlinear growth of crystals induced by the kinetically rejected entanglements accumulated at the growth front. Additionally, the exponential decay of Xs with time provides a characteristic melting time (τ) for the melting process. Compared to the melt‐crystallized UHMWPE, the τ value of nascent UHMWPE is generally longer even in a higher temperature range, which is mainly because the former has a larger entanglement density difference. Furthermore, our observations demonstrated that UHMWPEs with different entangled states have an analogous melting mechanism since they exhibit a similar melting activation energy (∼1300 kJ/mol).This article is protected by copyright. All rights reserved

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“…Moreover, the UHMWPE membrane provides excellent safety protection for overcharging, short circuit, and explosions when the temperature rises, thus rendering it remarkably suitable for high-efficiency and high-power batteries. At elevated temperatures, the UHMWPE melts smoothly, transitioning into a rubber-like gel without mobility due to the highly entangled molecular chain, thereby impeding undesired membrane collapse [ 35 , 36 , 37 ]. Preparation methods for polyolefin microporous membranes for LIB separators mainly include the dry method (i.e., melt extrusion stretching method) and the wet method (i.e., thermally induced phase separation method, TIPS) [ 30 , 38 , 39 , 40 , 41 ].…”

Section: Introductionmentioning

confidence: 99%

Engineering Polymer-Based Porous Membrane for Sustainable Lithium-Ion Battery Separators

Li,

Duan

2023

Polymers

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Due to the growing demand for eco-friendly products, lithium-ion batteries (LIBs) have gained widespread attention as an energy storage solution. With the global demand for clean and sustainable energy, the social, economic, and environmental significance of LIBs is becoming more widely recognized. LIBs are composed of cathode and anode electrodes, electrolytes, and separators. Notably, the separator, a pivotal and indispensable component in LIBs that primarily consists of a porous membrane material, warrants significant research attention. Researchers have thus endeavored to develop innovative systems that enhance separator performance, fortify security measures, and address prevailing limitations. Herein, this review aims to furnish researchers with comprehensive content on battery separator membranes, encompassing performance requirements, functional parameters, manufacturing protocols, scientific progress, and overall performance evaluations. Specifically, it investigates the latest breakthroughs in porous membrane design, fabrication, modification, and optimization that employ various commonly used or emerging polymeric materials. Furthermore, the article offers insights into the future trajectory of polymer-based composite membranes for LIB applications and prospective challenges awaiting scientific exploration. The robust and durable membranes developed have shown superior efficacy across diverse applications. Consequently, these proposed concepts pave the way for a circular economy that curtails waste materials, lowers process costs, and mitigates the environmental footprint.

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Chain Dynamics of Partially Disentangled UHMWPE around Melting Point Characterized by 1H Low-Field Solid-State NMR

Cited by 3 publications

References 62 publications

Disentangled Melt of Ultrahigh-Molecular-Weight Polyethylene: Fictitious or Real?

Disentangled Melt of Ultrahigh-Molecular-Weight Polyethylene: Fictitious or Real?

The Isothermal Melting Kinetics of Ultra‐High Molecular Weight Polyethylene Crystals

Engineering Polymer-Based Porous Membrane for Sustainable Lithium-Ion Battery Separators

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