Effect of carbon black on the mechanical performances of magnetorheological elastomers

Several magnetorheological elastomer (MRE) samples, with different weight percentages of carbon black, were fabricated under a constant magnetic field. Their microstructures were observed by using an environmental scanning electron microscope (SEM), and their mechanical performance including magnetorheological (MR) effect, damping ratio and tensile strength were measured with a dynamic mechanical analyzer (DMA) system and an electronic tensile machine. The experimental results demonstrate that carbon black plays a significant role in improving the mechanical performance of MR elastomers. Besides the merits of high MR effect and good tensile strength, the damping ratio of such materials is much reduced. This is expected to solve a big problem in the application of MR elastomers in practical devices, such as in adaptive tuned vibration absorbers.     

Determination of reliable fatigue life predictors for magnetorheological elastomers under dynamic equi-biaxial loading

Fatigue life prediction is of great significance in ensuring magnetorheological elastomer (MRE) based rubber components exhibit reliability and do not compromise safety under complex loading, and this necessitates the development of plausible fatigue life predictors for MREs. In this research, silicone rubber based MREs were fabricated by incorporating soft carbonyl iron magnetic particles. Equi-biaxial fatigue behaviour of the fabricated MREs was investigated by using the bubble inflation method. The relationship between fatigue life and maximum engineering stress, maximum strain and strain energy density were studied. The results showed that maximum engineering stress and stored energy density can be used as reliable fatigue life predictors for SR based MREs when they are subjected to dynamic equi-biaxial loading. General equations based on maximum engineering stress and strain energy density were developed for fatigue life prediction of MREs.     

Effects of structural imperfections on the dynamic mechanical response of main-chain smectic elastomers

We examine the influence of structural imperfections on mechanical damping in polydomain smectic main-chain liquid crystalline elastomers (MCLCE) subjected to small strain oscillatory shear. The mechanical loss factor tan δ = G″(ω)/G′(ω) exhibits a strong maximum (tan δ ≈ 1.0) near the smectic-isotropic (clearing) transition. “Optimal” elastomers that exhibit minimal equilibrium swelling in a good solvent are compared with highly swelling “imperfect elastomers” that contain higher concentrations of structural imperfections such as pendant chains. For the imperfect elastomers, tan δ is markedly enhanced in the isotropic state because of relaxation of pendant chains and other imperfections. However, within the smectic state, the magnitude of tan δ and its temperature dependence are similar for optimal and imperfect elastomers at ω = 1 Hz. The prominent loss peak near the clearing transition arises from segment-level relaxations that are insensitive to the details of chain connectivity. Smectic MCLCE can be tailored for applications as vibration-damping materials by manipulating the clearing transition temperature through the backbone structure or by deliberate introduction of structural imperfections such as pendant chains. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3267–3276, 2007     

Influence of formulation parameters on the mechanical failure energy of filled elastomers

Ways to increase, by optimizing the formulation, the energy of mechanical failure of filled 3D-crosslinked elastomers intended for application of a frost-resistant and waterproof layer onto road asphalt were examined.     

Influence of particle size and particle loading on mechanical and dielectric properties of biochar particulate-reinforced polymer nanocomposites

This research work emphasizes using pulverized biochar obtained by the pyrolysis of rice husk as a particulate reinforcement in unsaturated polyester matrix. The influence of particle size and particle loading on the mechanical and dielectric properties of particulate composites were investigated. The mean size of particles obtained through pulverizing using ball mill varied from 510 to 45 nm when milled for a duration ranging from 6 to 30 h. The particle loading in the composite varied from 0.5 to 2.5 wt%. The impact strength of the specimen having particle loading of 2.5 wt% with 45 nm particle size increased by 77.50%, and its dielectric constant increased by 7% when compared to that of cured pure resin; however, the tensile strength decreased. The biochar particles were subjected to X-ray diffraction, Fourier transform infrared spectroscopy (FT-IR), and atomic force microscopy (AFM) analysis for characterization. Morphological studies were performed on tested samples by scanning electron microscope.     

Study on mechanical properties of elastomers reinforced by zinc dimethacrylate

In this work, mechanical properties of various elastomers with the representative structural features reinforced by zinc dimethacrylate (ZDMA) were studied. The results showed that there is great difference in reinforcing effects of ZDMA for different elastomers. Strain-stress curves revealed that the tensile-induced crystallization of chains might be the main reason for high strength of ZDMA/rubber composites at room temperature. The saturation and regularity of rubber chains are two essential features to determine the mechanical properties of the composites at room temperature. The kind of ZDMA makes considerable impact on performances of ZDMA/rubber composites, except for ZDMA/hydrogenated nitrile-butadiene rubber (HNBR) composite. The high temperature strengths of ZDMA/rubber composites are not high and are dominated by the polarity and saturation of matrix. Basing on the previous researching, a possible model for microstructure of ZDMA/rubber composites was put forward, which could well interpret the observed phenomenon.     

Impact of lipopolysaccharide coating on clay particle wettability

Impact of lipopolysaccharide coating on kaolinite and Na-montmorillonite wettability was investigated. Kaolinite had greater diiodomethane contact angles, smaller water and formamide contact angles than Na-montmorillonite. After lipopolysaccharide coating, diiodomethane and formamide contact angles decreased, while water contact angles increased for both kaolinite and Na-montmorillonite. The decrease and increase in liquid contact angles after lipopolysaccharide coating were most pronounced for lipopolysaccharide extracted from Pseudomonas aeruginosa, followed by Pseudomonas fluorescens and Echerichia coli. Clay particle wettability was determined by particle surface thermodynamic properties. Both kaolinite and Na-montmorillonite exhibited a monopolar surface and the monopolarity decreased after lipopolysaccharide coating, indicating an increase in hydration or surface wetness. The origins of interactions of clay particles with water molecules were discussed and related to clay particle water wettability.     

Influence of surface characteristics of carbon blacks on cure and mechanical behaviors of rubber matrix compoundings

In this work, the effect of chemical modification on the surface energetics and cure kinetics of carbon blacks (CBs) modified with KOH and C6H6 was investigated by contact angle and rheometer measurements, respectively. Also, the resulting mechanical properties of the CBs/styrene-butadiene composites were studied in terms of tensile and dynamic mechanical analysis. As experimental results, the polar basic and nonpolar chemical treatments showed an increase of the London dispersive component (gamma(S)(L)) of gamma(S) of the CBs without significantly changing the surface properties and microstructures that resulted from the deaggregation of microstructures and decrease of the swollen weight of the sample in the equilibrium state. Also, it was clearly revealed that the increase of gamma(S) of the CBs could largely affect the vulcanization and mechanical properties of the composites, resulting from the increase in gamma(S)(L) of the CBs. These results were evident that the mechanical properties of the composites were controlled more by the gamma(S)(L) of gamma(S) than by the specific (or polar) component (gamma(S)(SP)), including electron acceptor and donor parameters on CB surfaces in an organic matrix composite system.     

Structural and mechanical study of elastomers under plane deformation

The plane shrinkage of various elastomers [natural rubber, synthetic isoprene rubber, and plasticized poly(vinyl chloride)] at room temperature has been studied via direct microscopic observations. Prior to deformation, the surface of polymer samples is decorated with a thin (several nanometers) metallic layer. Further deformation leads to formation of the surface relief in the coating. An analysis of the formed microreliefs allows one to visualize and characterize the induced stress field in the sample. The shrinkage of poly(vinyl chloride) samples is accompanied by development of the uniform surface relief over the whole surface of the deformed polymer. This fact suggests a homogeneous character of the stress field and, hence, a homogeneous structure of the polymer sample. In the case of crosslinked rubbers (natural rubber and synthetic isoprene rubber), their plane shrinkage leads to the development of an irregular pattern on the polymer surface. In addition to the folded surface relief that is typical of the poly(vinyl chloride) structure, one can observe 20-to 50-μm “islands,” which are characterized by their own morphological features. Information on structural inhomogeneity of rubbers that is obtained by scanning electron microscopy correlates with the data of DSC measurements. The advantages of electron microscopic procedure for studying structural rearrangements in polymers during strain recovery of elastomers are demonstrated.     

Investigation on crosslinking behaviors of NBR/PVC filled with anhydrous copper sulfate particles by dynamic mechanical analysis

Crosslinking behaviors of acrylonitrile butadiene rubber (NBR)/poly (vinyl chloride) (PVC) alloy, filled with anhydrous copper sulfate (CuSO₄) particles, were investigated for the first time by dynamic mechanical analysis (DMA) under hetero and isothermal modes, respectively. In the heterothermal testing, (NBR/PVC)/CuSO₄ compound showed two marked increases in the storage modulus (E′), corresponding to coordination crosslinking of NBR-CuSO₄ and self-crosslinking of NBR and PVC respectively. During the isothermal testing, a dramatic increase in E′ was found at the initial stage while that of original NBR/PVC alloy was not detected. The marked increase in E′ of (NBR/PVC)/CuSO₄ compound was mainly due to the crosslinking induced by coordination between  CN and Cu²⁺. The increasing extent of E′ increased with the rise of CuSO₄ content, suggesting the formation of a greater number of crosslinks. Moreover, the activation energy (E_a) of crosslinking process was about 139 kJ/mol. In this work, fourier transform infrared spectrum (FT-IR) and equilibrium swelling method were also performed for the characterization of the compound. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 41–51, 2007     

Some observations on dynamic coating of capillary columns

Summary The influence of the drying speed on dynamic coating of capillary columns was investigated. Fast drying speeds improve efficiency and increase film thickness.     

Some dynamic features of the preparation of liquid crystalline elastomers

Liquid crystalline elastomers derived from siloxane polymers, PMHS and PEHS, were prepared following a two-stage reaction scheme to investigate the effects of processing conditions and thermal treatment on mesomorphic characteristics. The LC elastomer samples were analysed by FTIR, DSC, stress-strain relationship, polarized optical microscopy, and X-ray diffraction techniques. Key findings include: (1) Chain length of the precursor siloxane polymer is critical to achieving a bulk alignment via stretching during the second-stage reaction; (2) the imposed strain is also critical to achieving a monodomain nematic character, which is completely recoverable upon heating beyond the clearing temperature followed by cooling back to room temperature (i.e. thermal treatment); (3) enthalpy is stored in an elastomer freshly prepared without an imposed strain, but the imposed strain helps to release the stored enthalpy, which can be almost completely released upon thermal treatment; and (4) while the stored enthalpy does not increase order parameter (HOF_A), its release through molecular relaxation contributes to an increased HOF_A value.     

Aggregation structure and mechanical properties of functionally graded polyurethane elastomers

Functionally graded polyurethane elastomers (FGPUEs) were prepared with two molds fixed at different temperatures (30 and 150 °C). The effects of the molar ratio of the curing agent (60/40, 75/25, or 97/3 1,4‐butane diol/1,1,1‐trimethylol propane) and the molecular weight of the polymer glycol (number‐average molecular weight = 2000 or 3000) on the molecular aggregation state and mechanical properties of the FGPUEs were investigated with differential scanning calorimetry, polarized optical microscopy, dynamic viscoelastic measurements, and tensile tests. The aggregation state of the FGPUEs was changed continuously from the one side (lower temperature side) to the other side (higher temperature side); for example, the glass‐transition temperature gradually increased in this direction. Also, the number of spherulites formed in the FGPUEs increased in the same manner. In the mechanical tests, the tensile strength and elongation at break of the lower temperature side were higher than those of the higher temperature side. This was correlated with the strong phase separation of the lower temperature side. The poly(oxytetramethylene glycol)‐based FGPUE with a chain extender of 75 wt % showed the largest degree of the temperature gradient. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2355–2363, 2003     

Influence of molecular weight on the dynamic mechanical properties of poly(methyl methacrylate)

Using a new parallel beam apparatus, the dynamic mechanical properties of poly-(methyl methacrylate) were determined over a wide range of molecular weights (1500< < <600 000). Results showed that the modulus (25 °C) was only slightly dependent on chain length, and equalled 2.3×10⁹ Pa for the highest molecular weight scanned. Simultaneous acquisition of- and-relaxations indicated a decrease inT in accordance with Gibbs' relation, whileT was invariant. BothT =111° andT =40° corroborated previous results from several sources, including dynamic mechanical measurements. Such modulus and glass transition data are essential to the calculation of fracture toughness and to the assessment of radiation damage of acrylic, respectively.

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Zusammenfassung Unter Anwendung eines neuen Parallelstrahlgerätes wurden die dynamischen mechanischen Eigenschaften von Poly(methylmethacrylat) in einem weiten Molmassenbereich (1500< <600 000) bestimmt. Die Ergebnisse zeigten, daß der Modul (25°) nur wenig von der Kettenlänge abhängig und für die höchste erfaßte Molmasse gleich 2.3× ×10⁹ Pa war. Die gleichwertige Erfassung der- und-Relaxationen zeigte in Übereinstimmung mit der Gibbs-schen Abhängigkeit eine Abnahme vonT währendT unverändert blieb. SowohlT =111° als auchT =40° bestätigten frühere Ergebnisse verschiedenen Ursprungs, dynamische mechanische Messungen mit inbegriffen. Solch ein Modul und Glas-Übergangsdaten sind zur Berechnung der Bruchfestigkeit bzw. zur Bestimmung der Bestrahlungsschäden in Acrylaten unerläßlich.

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Résumé En se servant d'un nouvel appareil à rayons parallèles, on a déterminé les propriétés mécaniques dynamiques du poly(méthyl-méthacrylate) dans un large intervalle de poids moléculaires (1500< <600 000). Les résultats on montré que le module (25°) ne dépend que peu de la longueur de la chaîne et est égal à 2.3×10⁹ Pa pour le plus haut poids moléculaire étudié. L'acquisition simultanée des relaxations et a indiqué, en accord avec la relation de Gibbs, une diminution deT tandis queT s'avere invariable. Les valeursT =111°et}T =40° ont corroboré toutes deux des résultats antérieurs de diverses sources, y compris des mesures mécanique dynamiques. Un tel module ainsi que les données de la transition vitreuse sont essentiels pour calculer la résistance à la rupture, et pour déterminer les dommages par irradiation des matières acryliques.

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, (1500 < < 600 000). , (25°) 2.3&#x0445;10⁹ . - - T , T . T =111° T =40° , . .

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This investigation was supported by NIH Research Grant No. DE 02668, RCDA number DE 00052 (R.P.K.), and RFA number DE 05132 (A.R.G.).     

Influence of static strain on dynamic mechanical behavior of amorphous networks prepared from aromatic polyesters

Dynamic mechanical experiments were performed between ?140 and 50°C on both poly(diethylene glycol isophthalate) and poly(triethylene glycol terephthalate) networks. Plots of loss tangent versus temperature show a well-defined α peak, associated with the transition from glasslike to rubberlike consistency, and two overlapping peaks (β₁ and β₂) in the glassy region. Dynamic deformations of small amplitude were superimposed on large static deformations. It was found that the position of the β₁ and β₂ peaks as well as their intensities are independent of the static elongation ratio. However, the intensity of the loss tangent associated with the glass–rubber transition tends to decrease with increasing static deformation. Moreover, the position of the maximum of the α peaks shifts to lower temperatures as the elongation ratio increases. This behavior suggests that for both networks the volume effects (shifting the α peaks to lower temperatures with increasing elongation ratio) overcome the entropic effects (shifting the α peaks to higher temperatures with decreasing entropy).     

X-ray CT microtomography and mechanical response of foamed polysiloxane elastomers

3D X-ray computer microtomography (CT) experiments have been performed to assess the microstructure of scaled cellular polysiloxane elastomers and to predict how key morphological features alter as a function of compressive loading. In the work reported here, full scale (nominally 600 μm pore size) and half scale (nominally 300 μm pore size) polydimethylsiloxane foams (M97) were prepared using extractable urea particles, and tested. CT test methodology was developed to image foam microstructure at different levels of compression. 1D magnetic resonance imaging (MRI) experiments have also been performed on full scale foams for baseline characterisation. Material porosity, bulk density and dynamic mechanical analysis (DMA) stress/strain responses as a function of compression were recorded. Our results show that undesirable engineering stress responses are evident when the material microstructure (cell size and shape) is non-uniform and complex. This is particularly evident when non-spherical urea particles are used, leading to undesirable scaled foam microstructures with mechanical responses that do not match that shown by ‘full scale’ versions. Through the use of X-ray CT and MRI, our studies have provided insights into the link between manufacturing, polymer architecture (cell size/shape) and mechanical response of scaled M97 cellular materials. The data collected will support materials FEA (finite element model) code development activities, as well as help identify how the material architecture can be modified to achieve more controlled and uniform mechanical responses.     

Influence of orthogonal prestrain on the viscoelastic behaviour of highly-filled elastomers

Highly-filled elastomers exhibit a complex nonlinear mechanical behaviour that is difficult to characterize experimentally. This paper presents a Dynamic Mechanical Analysis (DMA) method coupled with orthogonal prestrains, applied in two distinct steps. A localization operator between measurements at the arms of a cross-shaped specimen and the stress and strain fields at its center was determined using elastic small strain finite element computations. The operator makes estimating the storage and loss moduli at the center of the specimen possible. A mathematical model is then fitted to the moduli values. These results are compared to DMA measurements of highly-filled elastomers under uniaxial prestrain. Although the storage and loss moduli increase with the prestrain under both loadings, the nonlinear behaviour is quantitatively modified by adding an orthogonal prestrain. In addition, the modification of the behaviour under a horizontal prestrain is cancelled out by an increase of the vertical prestrain, which may be explained by fillers aligning in the direction of the prestrain.     

Dielectric relaxation in segmented polyurethane elastomers: Influence of 1:3 and 1:4 butanediol cure on the dynamic properties

Dielectric relaxation measurements are reported on a series of segmented polyurethane elastomers produced with mixtures of varying 1:3 and 1:4 butanediol as chain extender. The changes observed in the glass transition temperature, activation energies for dipolar relaxation and the nature of the dispersion for varying composition of the chain extender are discussed in terms of the extent of phase separation and the influence of the “hard” phase structure on the relaxation of the “soft” phase.     

Mechanical and thermo‐mechanical studies of double networks based on thermoplastic elastomers

A new approach to prepare and characterize double network elastomeric systems was investigated. A styrene‐ethylene‐co‐butylene‐styrene (SEBS) triblock copolymer system containing physical crosslinks was used to achieve a double network by additional crosslinking using ultra‐violet (UV) light. An ethylene–propylene–diene monomer (EPDM) terpolymer system containing chemical crosslinks was used to achieve a conventional double network using UV crosslinking. Properties from conventional monotonic tensile tests, dynamic mechanical analysis, and thermomechanical properties were investigated. These double network elastomers show a transition between competitive and collaborative behavior in their mechanical properties and lower coefficients of thermal expansion arising from a competition of the networks. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 778–789, 2010     

Influence of fillers on the thermal stability of elastomers. Thermogravimetric study

The thermal degradation of hydrocarbon elastomers and polychloroprene in the presence of silica, clay, precipitated calcium carbonate and carbon black has been studied using dynamic thermogravimetry. The influence of fillers on degradation parameters of elastomers and activation energy was discussed.

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Zusammenfassung Mittels DTG wurde der thermische Abbau von Kohlenwasserstoffelastomeren und Polychloropren in Gegenwart von Siliziumdioxid, Tonerde, gefälltem Calciumcarbonat und Ruß untersucht. Weiterhin wurde der Einfluß der Streckmittel auf den Abbau der Elastomere und auf die Aktivierungsenergie besprochen.