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Polymers
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Rheology as a Tool for the Investigation of Structures of...
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Rheology as a Tool for the Investigation of Structures of Polymeric Materials

A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Polymer Physics and Theory".

Deadline for manuscript submissions: closed (28 February 2022) | Viewed by 13755

Special Issue Editor

Prof. Dr. Helmut Münstedt

E-Mail Website1 Website2
Guest Editor
Department of Materials Science and Engineering, Institute of Polymer Materials, Friedrich-Alexander-University Erlangen-Nürnberg, Martensstr. 7, D-91058 Erlangen, Germany
Interests: general aspects of rheology; flow analysis of polymer melts; rheology and processing; polymer rheology and molecular structure; modification of polymers by physical means; particle-filled polymeric materials; polymer blends
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Rheological properties of polymer melts have been widely applied to optimize processing operations. Less frequently used is the potential of rheology as a tool to support the structure analysis of polymeric materials. This Special Issue of Polymers intends to contribute to this field by bringing together existing knowledge and new insights. Measurements of the viscous and elastic behavior and thermorheological properties will be discussed with respect to molar mass, molar mass distribution, and branching, in particular. Moreover, their potential for following up degradation and crosslinking processes is a topic of interest for reaction kinetics and polymer applications. Furthermore, the structural aspects underlying the reversible property changes due to strong mechanical pretreatments–the so-called refinement effect–are still a matter of research. Contributions of rheological investigations to the development of crystalline structures in a melt as found for polyvinylchloride or polycarbonate, for example, and to the formation of agglomerates in heterogeneous polymers like particle-filled systems and polymer blends, are other challenging topics that are welcomed in this issue.

Prof. Dr. Helmut Münstedt
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Polymers is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • molecular structures
  • viscoelastic properties
  • degradation
  • crosslinking
  • refining effect
  • particle-filled polymers
  • polymer blends

Published Papers (5 papers)

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Research

23 pages, 9877 KiB  
Article
New Insights on Expandability of Pre-Cured Epoxy Using a Solid-State CO2-Foaming Technique
by Uy Lan Ngoc Du, Christian Bethke, Volker Altstädt and Holger Ruckdäschel
Polymers 2021, 13(15), 2441; https://0-doi-org.brum.beds.ac.uk/10.3390/polym13152441 - 24 Jul 2021
Cited by 5 | Viewed by 1982
Abstract
Foaming an epoxy is challenging because the process involves the curing reaction of epoxy and hardener (from monomer to oligomer, to a gel and a final three-dimensional crosslinked network) and the loading of gas phase into the epoxy phase to develop the cellular [...] Read more.
Foaming an epoxy is challenging because the process involves the curing reaction of epoxy and hardener (from monomer to oligomer, to a gel and a final three-dimensional crosslinked network) and the loading of gas phase into the epoxy phase to develop the cellular structure. The latter process needs to be carried out at the optimum curing stage of epoxy to avoid cell coalescence and to allow expansion. The environmental concern regarding the usage of chemical blowing agent also limits the development of epoxy foams. To surmount these challenges, this study proposes a solid-state CO2 foaming of epoxy. Firstly, the resin mixture of diglycidylether of bisphenol-A (DGEBA) epoxy and polyamide hardener is pre-cured to achieve various solid-state sheets (preEs) of specific storage moduli. Secondly, these preEs undergo CO2 absorption using an autoclave. Thirdly, CO2 absorbed preEs are allowed to free-foam/expand in a conventional oven at various temperatures; lastly, the epoxy foams are post-cured. PreE has a distinctive behavior once being heated; the storage modulus is reduced and then increases due to further curing. Epoxy foams in a broad range of densities could be fabricated. PreE with a storage modulus of 4 × 104–1.5 × 105 Pa at 30 °C could be foamed to densities of 0.32–0.45 g/cm3. The cell morphologies were revealed to be star polygon shaped, spherical and irregularly shaped. The research proved that the solid-state CO2-foaming technique can be used to fabricate epoxy foams with controlled density. Full article
(This article belongs to the Special Issue Rheology as a Tool for the Investigation of Structures of Polymeric Materials)
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11 pages, 2507 KiB  
Article
Gelation and Crystallization Phenomena in Polyethylene Plastomers Modified with Waxes
by Markus Gahleitner, Jingbo Wang, Floran Prades and Klaus Bernreitner
Polymers 2021, 13(13), 2147; https://0-doi-org.brum.beds.ac.uk/10.3390/polym13132147 - 29 Jun 2021
Cited by 2 | Viewed by 1893
Abstract
Polyethylene (PE) plastomers, single-site catalyst-based homogeneous linear low-density PEs (LLDPEs), combine low crystallinity, softness, and elasticity, making them ideal candidates for numerous applications such as hot-melt adhesives (HMA). As plastomers crystallize rather slowly, a number of possible low molecular weight polyolefin components were [...] Read more.
Polyethylene (PE) plastomers, single-site catalyst-based homogeneous linear low-density PEs (LLDPEs), combine low crystallinity, softness, and elasticity, making them ideal candidates for numerous applications such as hot-melt adhesives (HMA). As plastomers crystallize rather slowly, a number of possible low molecular weight polyolefin components were tested to accelerate solidification. An ideal modifier should accelerate solidification while maintaining transparency and softness of the base polymer. A Queo plastomer type was modified with different PE and PP waxes at concentrations of 5 to 25 wt.-%. Next to conventional calorimetry, a rheological technique was applied to study solidification. The resulting morphology was studied by atomic force microscopy, and the final compositions were investigated regarding their mechanical and optical performance. Accelerated solidification was observed in all cases, but a quite different course of structure formation could be concluded. PE waxes dissolve in the melt state, forming a lamellar network during cooling, whereas PP waxes form a heterogeneous blend in the melt for which the wax droplets solidify before the matrix. The particulate-type modification by the PP wax also affects stiffness less while retaining transparency better. Full article
(This article belongs to the Special Issue Rheology as a Tool for the Investigation of Structures of Polymeric Materials)
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21 pages, 5831 KiB  
Article
In-Line Rheo-Optical Investigation of the Dispersion of Organoclay in a Polymer Matrix during Twin-Screw Compounding
by Paulo F. Teixeira, José A. Covas and Loïc Hilliou
Polymers 2021, 13(13), 2128; https://0-doi-org.brum.beds.ac.uk/10.3390/polym13132128 - 29 Jun 2021
Cited by 5 | Viewed by 1810
Abstract
The dispersion mechanisms in a clay-based polymer nanocomposite (CPNC) during twin-screw extrusion are studied by in-situ rheo-optical techniques, which relate the CPNC morphology with its viscosity. This methodology avoids the problems associated with post extrusion structural rearrangement. The polydimethylsiloxane (PDMS) matrix, which can [...] Read more.
The dispersion mechanisms in a clay-based polymer nanocomposite (CPNC) during twin-screw extrusion are studied by in-situ rheo-optical techniques, which relate the CPNC morphology with its viscosity. This methodology avoids the problems associated with post extrusion structural rearrangement. The polydimethylsiloxane (PDMS) matrix, which can be processed at ambient and low temperatures, is used to bypass any issues associated with thermal degradation. Local heating in the first part of the extruder allows testing of the usefulness of low matrix viscosity to enhance polymer intercalation before applying larger stresses for clay dispersion. The comparison of clay particle sizes measured in line with models for the kinetics of particle dispersion indicates that larger screw speeds promote the break-up of clay particles, whereas smaller screw speeds favor the erosion of the clay tactoids. Thus, different levels of clay dispersion are generated, which do not simply relate to a progressively better PDMS intercalation and higher clay exfoliation as screw speed is increased. Reducing the PDMS viscosity in the first mixing zone of the screw facilitates dispersion at lower screw speeds, but a complex interplay between stresses and residence times at larger screw speeds is observed. More importantly, the results underline that the use of larger stresses is inefficient per se in dispersing clay if sufficient time is not given for PDMS to intercalate the clay galleries and thus facilitate tactoid disruption or erosion. Full article
(This article belongs to the Special Issue Rheology as a Tool for the Investigation of Structures of Polymeric Materials)
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25 pages, 6973 KiB  
Article
Rheological Measurements and Structural Analysis of Polymeric Materials
by Helmut Münstedt
Polymers 2021, 13(7), 1123; https://0-doi-org.brum.beds.ac.uk/10.3390/polym13071123 - 01 Apr 2021
Cited by 21 | Viewed by 4481
Abstract
Rheological measurements of polymer melts are widely used for quality control and the optimization of processing. Another interesting field of rheology is to provide information about molecular parameters of polymers and the structure build-up in heterogeneous polymeric systems. This paper gives an overview [...] Read more.
Rheological measurements of polymer melts are widely used for quality control and the optimization of processing. Another interesting field of rheology is to provide information about molecular parameters of polymers and the structure build-up in heterogeneous polymeric systems. This paper gives an overview of the influence of molar mass, molar mass distribution and long-chain branching on various rheological characteristics and describes the analytical power following from established relations. With respect to applications, we discuss how rheological measurements can be used to gain insight into the thermal stability of a material. A special impact lies in the demonstration, how long-chain branching can be analyzed using rheological means like the zero-shear viscosity as a function of molar mass and strain hardening occurring in elongation. For contributions to branching analysis, the thermorheological behavior and activation energies are particularly discussed. The use of elastic quantities in the case of mechanical pretreatment effects is briefly addressed. The influence of fillers on recoverable properties in the linear range of deformation is analyzed and the role of their specific surface area for interactions described. It is shown how the fundamental results can be applied to study the state of nanoparticle dispersions obtained under special conditions. Furthermore, it is demonstrated that the findings on polymer/filler systems are the base of structure analyses in heterogeneous polymeric materials like polyvinylchloride (PVC) and acrylonitrile–butadiene–styrene copolymers (ABS). Full article
(This article belongs to the Special Issue Rheology as a Tool for the Investigation of Structures of Polymeric Materials)
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20 pages, 2111 KiB  
Article
Rheological Behavior of Blends of Metallocene Catalyzed Long-Chain Branched Polyethylenes. Part I: Shear Rheological and Thermorheological Behavior
by Chuangbi Chen, Mehdihasan I. Shekh, Shuming Cui and Florian J. Stadler
Polymers 2021, 13(3), 328; https://0-doi-org.brum.beds.ac.uk/10.3390/polym13030328 - 20 Jan 2021
Cited by 7 | Viewed by 2610
Abstract
Long-chain branched metallocene-catalyzed high-density polyethylenes (LCB-mHDPE) were solution blended to obtain blends with varying degrees of branching. A high molecular LCB-mHDPE was mixed with low molecular LCB-mHDPE at varying concentrations. The rheological behavior of those low molecular LCB-mHDPE is similar but their molar [...] Read more.
Long-chain branched metallocene-catalyzed high-density polyethylenes (LCB-mHDPE) were solution blended to obtain blends with varying degrees of branching. A high molecular LCB-mHDPE was mixed with low molecular LCB-mHDPE at varying concentrations. The rheological behavior of those low molecular LCB-mHDPE is similar but their molar mass and molar mass distribution are significantly different. Those blends were characterized rheologically to study the effects of concentration, molar mass distribution, and long-chain branching level of the low molecular LCB-mHDPE. Owing to the ultra-long relaxation times of the high molecular LCB-mHDPE, the blends exhibited a clearly more long-chain branched behavior than the base materials. The thermorheological complexity analysis showed an apparent increase in the activation energies Ea determined from G′, G″, and especially δ. Ea(δ), which for LCB-mHDPE is a peak function, turned out to produce even more pronounced peaks than observed for LCB-mPE with narrow molar mass distribution and also LCB-mPE with broader molar mass distribution. Thus, it is possible to estimate the molar mass distribution from the details of the thermorheological complexity. Full article
(This article belongs to the Special Issue Rheology as a Tool for the Investigation of Structures of Polymeric Materials)
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