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Elastomers: From Theory to Applications

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

Deadline for manuscript submissions: closed (25 October 2020) | Viewed by 51320

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Special Issue Editors

Prof. Dr. Gert Heinrich

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1. Leibniz-Institut für Polymerforschung Dresden e.V., 01069 Dresden, Germany
2. Faculty of Mechanical Science and Engineering, Technische Universität Dresden, 01069 Dresden, Germany
Interests: polymer nanocomposites; friction and adhesion of polymer systems, wear; fracture mechanical characterization and modelling of crack formation and propagation in elastomers; statistical-mechanics of polymer networks, material laws, engineering applications; rubber elasticity and viscoelasticity of filled polymer networks; filler-polymer and filler-filler interactions in elastomers: modelling, testing, engineering applications; tire physics, mechanics and engineering (e.g. traction and braking, road-tire interactions), advanced tire materials compounding and testing
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Dr. Michael Lang

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Guest Editor

Leibniz-Institut für Polymerforschung Dresden e.V., 01069 Dresden, Germany
Interests: theory and modeling of polymer networks; rubber elasticity, cyclic polymers; grafted polymers; polymer melts and solutions; nanostructured networks and gels

Special Issue Information

Dear Colleagues,

This Special Issue focuses on the current state-of-the-art of elastomers, both in modern applications and from a theoretical perspective. The main characteristic of elastomer materials is the high elongation and (entropy) elasticity of these materials, and the ability to swell multiple times in a suitable solvent. The use of filled elastomers, especially of new kinds of elastomer nanocomposites, is of high interest for rubber technologies. Nanostructured adaptable gels allow tailoring of responsive materials or filtering systems. These materials enable widespread applications in engineering fields, ranging from modern tire technologies to medical applications and consumer goods. Elastomers also find utility in a range of biomaterial applications. Bioelastomers are widely available in nature, and have been shown to have specific properties often far superior to their synthetic counterparts. All elastomers share typical features, such as entropy-driven elasticity, the presence of entanglements, and topological constraints of network chain conformations. These features still offer fascinating scientific challenges in synthesis, characterization, and application, as well as for the theory of polymer networks and the modeling of elastomeric solids.

Papers are sought that discuss the latest research in the area or summarize selected areas in the field. The scope of the Special Issue encompasses frontier-of-science contributions in synthesis, characterization, modeling, and the theory of elastomers. Of particular interest are new structures and functionalities incorporated into elastomers, leading to enhanced properties of crosslinked elastomeric materials. Examples include conductive elastomers, mechanically adaptive elastomers, bioelastomers, photosensitive and light-controlled elastomers, elastomers with autonomous self-healing properties, and other novel elastomer-based materials.

Prof. Dr. Gert Heinrich
Dr. Michael Lang
Guest Editors

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Keywords

elastomer nanocomposites
conductive elastomers
bioelastomers
light-controllable elastomers
elastomers with self-healing properties
smart and adaptive elastomers
elastomers for future tire technologies
advanced modeling and simulation of elastomers
cutting-edge characterization of elastomers
theory of rubber elasticity
elastomers with novel network structure
nanostructured amphiphilic gels

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Published Papers (13 papers)

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17 pages, 6765 KiB

Open AccessArticle

Effect of Fillers on the Recovery of Rubber Foam: From Theory to Applications

by Thridsawan Prasopdee and Wirasak Smitthipong

Polymers 2020, 12(11), 2745; https://doi.org/10.3390/polym12112745 - 19 Nov 2020

Cited by 27 | Viewed by 4441

Abstract

Natural rubber foam (NRF) can be prepared from concentrated natural latex, providing specific characteristics such as density, compression strength, compression set, and so on, suitable for making shape-memory products. However, many customers require NRF products with a low compression set. This study aims to develop and prepare NRF to investigate its recoverability and other related characteristics by the addition of charcoal and silica fillers. The results showed that increasing filler loading increases physical and mechanical properties. The recoverability of NRF improves as silica increases, contrary to charcoal loading, due to the higher specific surface area of silica. Thermodynamic aspects showed that increasing filler loading increases the compression force (F) as well as the proportion of internal energy to the compression force (F_u/F). The entropy (S) also increases with increasing filler loading, which is favorable for thermodynamic systems. The activation enthalpy (∆H_a) of the NRF with silica is higher than the control NRF, which is due to rubber–filler interactions created within the NRF. A thermodynamic concept of crosslinked rubber foam with filler is proposed. From theory to application, in this study, the NRF has better recoverability with silica loading. Full article

(This article belongs to the Special Issue Elastomers: From Theory to Applications)

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12 pages, 6078 KiB

Open AccessArticle

Adherence Kinetics of a PDMS Gripper with Inherent Surface Tackiness

by Umut D. Çakmak, Michael Fischlschweiger, Ingrid Graz and Zoltán Major

Polymers 2020, 12(11), 2440; https://doi.org/10.3390/polym12112440 - 22 Oct 2020

Cited by 10 | Viewed by 2658

Abstract

Damage and fiber misalignment of woven fabrics during discontinuous polymer processing remain challenging. To overcome these obstacles, a promising switchable elastomeric adherence gripper is introduced here. The inherent surface tackiness is utilized for picking and placing large sheets. Due to the elastomer’s viscoelastic material behavior, the surface properties depend on loading speed and temperature. Different peeling speeds result in different adherence strength of an interface between the gripper and the substrate. This feature was studied in a carefully designed experimental test set-up including dynamic thermomechanical, as well as dynamic mechanical compression analyses, and adherence tests. Special emphases were given to the analyses of the applicability as well as the limitation of the viscoelastic gripper and the empirically modeling of the gripper’s pulling speed-dependent adherence characteristic. Two formulations of poly(dimethylsiloxane) (PDMS) with different hardnesses were prepared and analyzed in terms of their applicability as gripper. The main insights of the analyses are that the frequency dependency of the loss factor tanδ is of particular importance for the application along with the inherent surface tackiness and the low sensitivity of the storage modulus to pulling speed variations. The PDMS-soft material formulation exhibits the ideal material behavior for an adhesive gripper. Its tanδ varies within the application relevant loading speeds between 0.1 and 0.55; while the PDMS-hard formulation reveals a narrower tanδ range between 0.09 and 0.19. Furthermore, an empirical model of the pulling speed-dependent strain energy release rate G(v) was derived based on the experimental data of the viscoelastic characterizations and the probe tack tests. The proposed model can be utilized to predict the maximum mass (weight-force) of an object that can be lifted by the gripper Full article

(This article belongs to the Special Issue Elastomers: From Theory to Applications)

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14 pages, 3626 KiB

Open AccessArticle

Elastic Properties of Polychloroprene Rubbers in Tension and Compression during Ageing

by Rami Bouaziz, Laurianne Truffault, Rouslan Borisov, Cristian Ovalle, Lucien Laiarinandrasana, Guillaume Miquelard-Garnier and Bruno Fayolle

Polymers 2020, 12(10), 2354; https://doi.org/10.3390/polym12102354 - 14 Oct 2020

Cited by 27 | Viewed by 4739

Abstract

Being able to predict the lifetime of elastomers is fundamental for many industrial applications. The evolution of both tensile and compression behavior of unfilled and filled neoprene rubbers was studied over time for different ageing conditions (70 °C, 80 °C and 90 °C). While Young’s modulus increased with ageing, the bulk modulus remained almost constant, leading to a slight decrease in the Poisson’s ratio with ageing, especially for the filled rubbers. This evolution of Poisson’s ratio with ageing is often neglected in the literature where a constant value of 0.5 is almost always assumed. Moreover, the elongation at break decreased, all these phenomena having a similar activation energy (~80 kJ/mol) assuming an Arrhenius or pseudo-Arrhenius behavior. Using simple scaling arguments from rubber elasticity theory, it is possible to relate quantitatively Young’s modulus and elongation at break for all ageing conditions, while an empirical relation can correlate Young’s modulus and hardness shore A. This suggests the crosslink density evolution during ageing is the main factor that drives the mechanical properties. It is then possible to predict the lifetime of elastomers usually based on an elongation at break criterion with a simple hardness shore measurement. Full article

(This article belongs to the Special Issue Elastomers: From Theory to Applications)

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14 pages, 2407 KiB

Open AccessArticle

Electrorheological Properties of Polydimethylsiloxane/TiO₂-Based Composite Elastomers

by Alexander V. Agafonov, Anton S. Kraev, Alexander E. Baranchikov and Vladimir K. Ivanov

Polymers 2020, 12(9), 2137; https://doi.org/10.3390/polym12092137 - 18 Sep 2020

Cited by 4 | Viewed by 3128

Abstract

Electrorheological elastomers based on polydimethylsiloxane filled with hydrated titanium dioxide with a particle size of 100–200 nm were obtained by polymerization of the elastomeric matrix, either in the presence, or in the absence, of an external electric field. The viscoelastic and dielectric properties of the obtained elastomers were compared. Analysis of the storage modulus and loss modulus of the filled elastomers made it possible to reveal the influence of the electric field on the Payne effect in electrorheological elastomers. The elastomer vulcanized in the electric field showed high values of electrorheological sensitivity, 250% for storage modulus and 1100% for loss modulus. It was shown, for the first time, that vulcanization of filled elastomers in the electric field leads to a significant decrease in the degree of crosslinking in the elastomer. This effect should be taken into account in the design of electroactive elastomeric materials. Full article

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18 pages, 3496 KiB

Open AccessArticle

Micromechanics of Stress-Softening and Hysteresis of Filler Reinforced Elastomers with Applications to Thermo-Oxidative Aging

by Jan Plagge and Manfred Klüppel

Polymers 2020, 12(6), 1350; https://doi.org/10.3390/polym12061350 - 15 Jun 2020

Cited by 7 | Viewed by 3207

Abstract

A micromechanical concept of filler-induced stress-softening and hysteresis is established that describes the complex quasi-static deformation behavior of filler reinforced rubbers upon repeated stretching with increasing amplitude. It is based on a non-affine tube model of rubber elasticity and a distinct deformation and fracture mechanics of filler clusters in the stress field of the rubber matrix. For the description of the clusters we refer to a three-dimensional generalization of the Kantor–Webman model of flexible chain aggregates with distinct bending–twisting and tension deformation of bonds. The bending–twisting deformation dominates the elasticity of filler clusters in elastomers while the tension deformation is assumed to be mainly responsible for fracture. The cluster mechanics is described in detail in the theoretical section, whereby two different fracture criteria of filler–filler bonds are considered, denoted “monodisperse” and “hierarchical” bond fracture mechanism. Both concepts are compared in the experimental section, where stress–strain cycles of a series of ethylene–propylene–diene rubber (EPDM) composites with various thermo-oxidative aging histories are evaluated. It is found that the “hierarchical” bond fracture mechanism delivers better fits and more stable fitting parameters, though the evolution of fitting parameters with aging time is similar for both models. From the adaptations it is concluded that the crosslinking density remains almost constant, indicating that the sulfur bridges in EPDM networks are mono-sulfidic, and hence, quite stable—even at 130 °C aging temperature. The hardening of the composites with increasing aging time is mainly attributed to the relaxation of filler–filler bonds, which results in an increased stiffness and strength of the bonds. Finally, a frame-independent simplified version of the stress-softening model is proposed that allows for an easy implementation into numerical codes for fast FEM simulations Full article

(This article belongs to the Special Issue Elastomers: From Theory to Applications)

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23 pages, 4753 KiB

Open AccessArticle

Graphene Layers Functionalized with A Janus Pyrrole-Based Compound in Natural Rubber Nanocomposites with Improved Ultimate and Fracture Properties

by Gea Prioglio, Silvia Agnelli, Lucia Conzatti, Winoj Balasooriya, Bernd Schrittesser and Maurizio Galimberti

Polymers 2020, 12(4), 944; https://doi.org/10.3390/polym12040944 - 18 Apr 2020

Cited by 11 | Viewed by 3304

Abstract

The ultimate properties and resistance to fracture of nanocomposites based on poly(1,4-cis-isoprene) from Hevea Brasiliensis (natural rubber, NR) and a high surface area nanosized graphite (HSAG) were improved by using HSAG functionalized with 2-(2,5-dimethyl-1H-pyrrol-1-yl)propane-1,3-diol (serinol pyrrole) (HSAG-SP). The functionalization reaction occurred through a domino process, by simply mixing HSAG and serinol pyrrole and heating at 180 °C. The polarity of HSAG-SP allowed its dispersion in NR latex and the isolation of NR/HSAG-SP masterbatches via coagulation. Nanocomposites, based either on pristine HSAG or on HSAG-SP, were prepared through traditional melt blending and cured with a sulphur-based system. The samples containing HSAG-SP revealed ultimate dispersion of the graphitic filler with smaller aggregates and higher amounts of few layers stacks and isolated layers, as revealed by transmission electron microscopy. With HSAG-SP, better stress and elongation at break and higher fracture resistance were obtained. Indeed, in the case of HSAG-SP-based composites, fracture occurred at larger deformation and with higher values of load and, at the highest filler content (24 phr), deviation of fracture propagation was observed. These results have been obtained with a moderate functionalization of the graphene layers (about 5%) and normal lab facilities. This work reveals a simple and scalable way to prepare tougher NR-based nanocomposites and indicates that the dispersion of a graphitic material in a rubber matrix can be improved without using an extra-amount of mechanical energy, just by modifying the chemical nature of the graphitic material through a sustainable process, avoiding the traditional complex approach, which implies oxidation to graphite oxide and subsequent partial reduction. Full article

(This article belongs to the Special Issue Elastomers: From Theory to Applications)

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10 pages, 3809 KiB

Open AccessArticle

Fatigue Life Assessment of Filled Rubber by Hysteresis Induced Self-Heating Temperature

by Wenbo Luo, Youjian Huang, Boyuan Yin, Xia Jiang and Xiaoling Hu

Polymers 2020, 12(4), 846; https://doi.org/10.3390/polym12040846 - 7 Apr 2020

Cited by 27 | Viewed by 3486

Abstract

As a viscohyperelastic material, filled rubber is widely used as a damping element in mechanical engineering and vehicle engineering. Academic and industrial researchers commonly need to evaluate the fatigue life of these rubber components under cyclic load, quickly and efficiently. The currently used method for fatigue life evaluation is based on the S–N curve, which requires very long and costly fatigue tests. In this paper, fatigue-to-failure experiments were conducted using an hourglass rubber specimen; during testing, the surface temperature of the specimen was measured with a thermal imaging camera. Due to the hysteresis loss during cyclic deformation, the temperature of the material was found to first rise and then level off to a steady state temperature, and then it rose sharply again as failure approached. The S–N curve in the traditional sense was experimentally determined using the maximum principal strain as the fatigue parameter, and a relationship between the steady state temperature increase and the maximum principal strain was then established. Consequently, the steady state temperature increase was connected with the fatigue life. A couple of thousand cycles was sufficient for the temperature to reach its steady state value during fatigue testing, which was less than one tenth of the fatigue life, so the fatigue life of the rubber component could be efficiently assessed by the steady state temperature increase. Full article

(This article belongs to the Special Issue Elastomers: From Theory to Applications)

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9 pages, 1499 KiB

Open AccessArticle

Effect of Stabilizer States (Solid Vs Liquid) on Properties of Stabilized Natural Rubbers

by Khwanchat Promhuad and Wirasak Smitthipong

Polymers 2020, 12(4), 741; https://doi.org/10.3390/polym12040741 - 27 Mar 2020

Cited by 13 | Viewed by 3635

Abstract

The main objective of this work is to study the effect of hydroxylamine sulfate or stabilizer states (solid vs liquid) on the storage hardening of natural rubber (NR). Several types of natural rubber samples were prepared: unstabilized NR samples and stabilized NR samples: (i) dry NR with 0.2 and 2.0 parts per hundred rubber (phr) of dry hydroxylamine sulfate, and (ii) natural latex with 0.2 and 2.0 phr of liquid hydroxylamine sulfate. The samples were characterized immediately (time 0) and after 12 weeks of storage at room temperature, respectively. We found that the Mooney viscosity, gel content, and Wallace plasticity of NR without a stabilizer increases with storage hardening for 12 weeks. However, two types of stabilized NR samples represent constant values of those three parameters, because hydroxylamine sulfate inhibits network and gel formation in NR. Interestingly, the mixing states (solid vs liquid) between natural rubber and the stabilizer affect the properties of stabilized NR. This could be explained by the better dispersion and homogeneous nature of liquid stabilizers in natural latex (liquid state), and thus the higher loading of the stabilizer in the liquid state. This is important, as the stabilization of NR properties as a function of time is required by rubber industry. This study is a utilization model from theory to application. Full article

(This article belongs to the Special Issue Elastomers: From Theory to Applications)

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16 pages, 3805 KiB

Open AccessArticle

Decoupling the Contributions of ZnO and Silica in the Characterization of Industrially-Mixed Filled Rubbers by Combining Small Angle Neutron and X-Ray Scattering

by Mariapaola Staropoli, Dominik Gerstner, Aurel Radulescu, Michael Sztucki, Benoit Duez, Stephan Westermann, Damien Lenoble and Wim Pyckhout-Hintzen

Polymers 2020, 12(3), 502; https://doi.org/10.3390/polym12030502 - 25 Feb 2020

Cited by 6 | Viewed by 2652

Abstract

Scattering techniques with neutrons and X-rays are powerful methods for the investigation of the hierarchical structure of reinforcing fillers in rubber matrices. However, when using only X-ray scattering, the independent determination of the filler response itself sometimes remains an issue because of a strong parasitic contribution of the ZnO catalyst and activator in the vulcanization process. Microscopic characterization of filler-rubber mixtures even with only catalytic amounts of ZnO is, therefore, inevitably complex. Here, we present a study of silica aggregates dispersed in an SBR rubber in the presence of the catalyst and show that accurate partial structure factors of both components can be determined separately from the combination of the two scattering probes, neutrons, and X-rays. A unique separation of the silica filler scattering function devoid of parasitic catalyst scattering becomes possible. From the combined analysis, the catalyst contribution is determined as well and results to be prominent in the correction scheme. The experimental nano-structure of the ZnO after the mixing process as the by-product of the scattering decomposition was found also to be affected by the presence or absence of silica in the rubber mixture, correlated with the shear forces in the mixing and milling processes during sample preparation. The presented method is well suited for studies of novel dual filler systems. Full article

(This article belongs to the Special Issue Elastomers: From Theory to Applications)

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9 pages, 3172 KiB

Open AccessArticle

Efficient Chain Formation of Magnetic Particles in Elastomers with Limited Space

by Shota Akama, Yusuke Kobayashi, Mika Kawai and Tetsu Mitsumata

Polymers 2020, 12(2), 290; https://doi.org/10.3390/polym12020290 - 1 Feb 2020

Cited by 3 | Viewed by 2430

Abstract

The magnetic response of the storage modulus for bimodal magnetic elastomers containing magnetic particles with a diameter of 7.0 μm and plastic beads with a diameter of 200 μm were investigated by varying the volume fraction of plastic beads up to 0.60 while keeping the volume fraction of the magnetic particles at 0.10. The storage modulus at 0 mT for monomodal magnetic elastomers was 1.4 × 10⁴ Pa, and it slightly increased with the volume fraction of plastic beads up to 0.6. The storage modulus at 500 mT for bimodal magnetic elastomers at volume fractions below 0.25 was constant, which was equal to that for the monomodal one (=7.9 × 10⁴ Pa). At volume fractions of 0.25–0.40, the storage modulus significantly increased with the volume fraction, showing a percolation behavior. At volume fractions of 0.40-0.60, the storage modulus was constant at 2.0 × 10⁵ Pa, independently of the volume fraction. These results indicate that the enhanced increase in the storage modulus was caused by the chain formation of the magnetic particles in vacancies made of plastic beads. Full article

(This article belongs to the Special Issue Elastomers: From Theory to Applications)

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15 pages, 3700 KiB

Open AccessArticle

Cationic Copolymerization of Isobutylene with 4-Vinylbenzenecyclobutylene: Characteristics and Mechanisms

by Zhifei Chen, Shuxin Li, Yuwei Shang, Shan Huang, Kangda Wu, Wenli Guo and Yibo Wu

Polymers 2020, 12(1), 201; https://doi.org/10.3390/polym12010201 - 13 Jan 2020

Cited by 9 | Viewed by 4347

Abstract

A random copolymer of isobutylene (IB) and 4-vinylbenzenecyclobutylene (4-VBCB) was synthesized by cationic polymerization at −80 °C using 2-chloro-2,4,4-trimethylpentane (TMPCl) as initiator. The laws of copolymerization were investigated by changing the feed quantities of 4-VBCB. The molecular weight of the copolymer decreased, and its molecular weight distribution (MWD) increased with increasing 4-VBCB content. We proposed a possible copolymerization mechanism behind the increase in the chain transfer reaction to 4-VBCB with increasing of feed quantities of 4-VBCB. The thermal properties of the copolymers were studied by solid-phase heating and crosslinking. After crosslinking, the decomposition and glass transition temperatures (T_g) of the copolymer increased, the network structure that formed did not break when reheated, and the mechanical properties remarkably improved. Full article

(This article belongs to the Special Issue Elastomers: From Theory to Applications)

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13 pages, 5810 KiB

Open AccessArticle

A Nonequilibrium Model for Particle Networking/Jamming and Time-Dependent Dynamic Rheology of Filled Polymers

by Christopher G. Robertson, Sankar Raman Vaikuntam and Gert Heinrich

Polymers 2020, 12(1), 190; https://doi.org/10.3390/polym12010190 - 10 Jan 2020

Cited by 13 | Viewed by 3663

Abstract

We describe an approach for modeling the filler network formation kinetics of particle-reinforced rubbery polymers—commonly called filler flocculation—that was developed by employing parallels between deformation effects in jammed particle systems and the influence of temperature on glass-forming materials. Experimental dynamic viscosity results were obtained concerning the strain-induced particle network breakdown and subsequent time-dependent reformation behavior for uncross-linked elastomers reinforced with carbon black and silica nanoparticles. Using a relaxation time function that depends on both actual dynamic strain amplitude and fictive (structural) strain, the model effectively represented the experimental data for three different levels of dynamic strain down-jump with a single set of parameters. This fictive strain model for filler networking is analogous to the established Tool–Narayanaswamy–Moynihan model for structural relaxation (physical aging) of nonequilibrium glasses. Compared to carbon black, precipitated silica particles without silane surface modification exhibited a greater overall extent of filler networking and showed more self-limiting behavior in terms of network formation kinetics in filled ethylene-propylene-diene rubber (EPDM). The EPDM compounds with silica or carbon black filler were stable during the dynamic shearing and recovery experiments at 160 °C, whereas irreversible dynamic modulus increases were noted when the polymer matrix was styrene-butadiene rubber (SBR), presumably due to branching/cross-linking of SBR in the rheometer. Care must be taken when measuring and interpreting the time-dependent filler networking in unsaturated elastomers at high temperatures. Full article

(This article belongs to the Special Issue Elastomers: From Theory to Applications)

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27 pages, 550 KiB

Open AccessReview

Theory of Flexible Polymer Networks: Elasticity and Heterogeneities

by Sergey Panyukov

Polymers 2020, 12(4), 767; https://doi.org/10.3390/polym12040767 - 1 Apr 2020

Cited by 30 | Viewed by 7891

Abstract

A review of the main elasticity models of flexible polymer networks is presented. Classical models of phantom networks suggest that the networks have a tree-like structure. The conformations of their strands are described by the model of a combined chain, which consists of the network strand and two virtual chains attached to its ends. The distribution of lengths of virtual chains in real polydisperse networks is calculated using the results of the presented replica model of polymer networks. This model describes actual networks having strongly overlapping and interconnected loops of finite sizes. The conformations of their strands are characterized by the generalized combined chain model. The model of a sliding tube is represented, which describes the general anisotropic deformations of an entangled network in the melt. I propose a generalization of this model to describe the crossover between the entangled and phantom regimes of a swollen network. The obtained dependence of the Mooney-Rivlin parameters

C_{1}

and

C_{2}

on the polymer volume fraction is in agreement with experiments. The main results of the theory of heterogeneities in polymer networks are also discussed. Full article

(This article belongs to the Special Issue Elastomers: From Theory to Applications)

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