Dynamic mechanical properties of conductive carbon black‐reinforced closed cell microcellular oil‐extended EPDM rubber vulcanizates: Effect of blowing agent,temperature, frequency,and strain

Dynamic viscoelastic properties of Vulcan XC 72 (excess conductive carbon black)‐reinforced solid‐ and closed‐cell microcellular controlled long chain branching grade oil‐extended EPDM (Keltan 7341A) rubber vulcanizates were studied at four frequencies of 3.5, 11, 35, and 110 Hz, and at a temperature range of ?100 to 160°C.The effect of blowing agent (ADC 21) loading on storage modulus (E′) and loss tangent (tan δ) was studied. The log of storage modulus bears a linear relationship with the log of density for both solid and microcellular rubber. Relative storage modulus (E/E) decreases with decrease in relative density (ρ_f/ρ_s). Both E′ and tan δ were found to be dependent on frequency and temperature. The master curves of the storage modulus versus log temperature‐reduced frequency were formed by superimposing E′ results and by using shift factors calculated by Arrhenius equation. Strain‐dependent isothermal dynamic viscoelastic properties were carried out for dynamic strain amplitude of 0.08–7%. Cole–Cole plots of microcellular vulcanizates show a circular arc with blowing agent (density). Empirical relationship between tan δ versus E′ is found to be linear, whose slope is independent of blowing agent loading or density. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1600–1608, 2006     

Dynamic viscoelastic properties of carbon black loaded closed-cell microcellular ethylene-propylene-diene rubber vulcanizates: Effect of blowing agent,temperature frequency,and strain

Dynamic mechanical analysis of carbon black loaded solid and closed-cell microcellular ethylene-propylene-diene (EPDM) vulcanizates was studied at four frequencies of 3.5, 11, 35, and 110 Hz and temperatures from −100 to 150°C. A plot of the log of the storage modulus bears a linear relationship with the log of density for solid as well as closed-cell microcellular rubber. The slope of the line is found to be temperature-dependent. The relative storage modulus decreases with decrease in the relative density. It was also observed that the storage modulus and tan δ are both frequency- and temperature-dependent. The storage modulus results are superposed to form master curves of the modulus vs. Iog temperature-reduced frequency, using shift factors calculated by the Arrhenius equation. Strain-dependent isothermal dynamic mechanical analysis was carried out for DSA varying from 0.07 to 5%. The effect of blowing agent loading on the storage modulus (E′) and loss tangent (tan δ) were also studied. Cole-Cole plots of microcellular rubber shows a circular arc relationship with the density. Plots of tan δ against E′ were found to exhibit a linear relationship. © 1996 John Wiley & Sons, Inc.     

Investigation on the dynamic melt rheological properties of polypropylene/wood flour composites

The rheological behavior of polypropylene/wood flour (WF) composite was investigated at constant temperature over a wide range of frequencies using a mechanical compact rheometer operated in the dynamic mode. The effect of WF content, particle size, and coupling agent on melt rheological properties were investigated. The melt rheological data in terms of complex viscosity (η*), storage modulus (G′), loss modulus (G″), and loss tangent (tan δ) were studied and compared for different samples. It was found that complex viscosity increases with increasing wood content and coupling agent. Compatibilization using coupling agent increased both storage modulus and loss modulus, but the variation of storage modulus is more. By increasing wood content storage modulus increases. Complex viscosity, storage modulus, and loss modulus showed a minimum value by increasing of wood particle size. Tan δ decreases with increasing of wood content. Cole–Cole plot indicated that relaxation process changes with addition WF, coupling agent, and using different mesh size of wood. The Han plots revealed the sensitivity of rheological properties with composition at constant temperature. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Dynamic mechanical behavior of flexible graphite made from exfoliated graphite

The low-frequency dynamic mechanical properties of low density flexible graphite (0.027–0.089 g/cm³, obtained by compressing exfoliated graphite at 0.3–1.7 MPa without a binder) are different in flexure and compression. The storage and loss moduli and the loss tangent are higher under flexure than compression. Under flexure, the storage modulus is essentially unaffected by increasing the static strain while the loss tangent and loss modulus decrease. Under compression, both storage and loss moduli increase with increasing static strain, while the loss tangent slightly decreases. The storage and loss moduli are higher and the loss tangent is lower for out-of-plane compression than for in-plane compression. The storage and loss moduli increase with increasing fabrication pressure, while the loss tangent decreases. Energy dissipation is much more effective under flexure than compression. Flexure appears to provide more sliding of the graphite layers than compression. For the highest energy dissipation under flexure, a low static strain is recommended; for high energy dissipation under compression, a high static strain is recommended.     

Dynamic mechanical properties of highly loaded ferrite-filled thermoplastic elastomer

The dynamic mechanical properties in terms of the storage modulus E′, loss modulus E″, and the loss tangent δ has been studied for highly filled magnetic polymer composites. The effect of surface treatment on the relaxation spectra has been clearly elucidated and quantitative values indicating the extent of polymer–filler interactions have been given. Various models have been tested for describing the viscoelastic behavior of such highly filled systems. The Wiechert model using a single-arm with a Cole–Cole parameter has been shown to effectively fit the Argand diagram in the case of the present highly filled systems.     

Morphology and physical properties of closed-cell microcellular ethylene–propylene–diene terpolymer (EPDM) rubber vulcanizates: Effect of blowing agent and carbon black loading

The morphology of the microcellular ethylene–propylene–diene terpolymer (EPDM) vulcanizes of both an unfilled and filled compound was studied from SEM photomicrographs. Carbon blacks adversely affect the average cell size, maximum cell size, and cell density. Enclosed gas pressure in a closed cell increases the relative modulus at higher strain. Tensile strength decreases more steeply than the expected value obeying the additive rule. At higher temperature, tensile strength, elongation at break, and modulus values decrease. The stress-relaxation behavior is independent of blowing agent loading, i.e., the density of closed-cell microcellular rubber. The elastic nature of the closed cell, i.e., the gas bubble in the microcellular rubber, reduces the hysteresis loss compared to solid rubber vulcanizates. Theoretically calculated flaw sizes are found to be about 3.4 times larger than the maximum cell sizes observed from SEM photomicrographs. It reveals that tear path deviates from the linear front and gives an effective larger depth of the flaws. © 1996 John Wiley & Sons, Inc.     

Mechanical and viscoelastic behavior of natural rubber and carboxylated styrene‐butadiene rubber latex blends

The morphology, mechanical and viscoelastic behavior of latex blends of unvulcanized natural rubber (NR) with carboxylated styrene‐butadiene rubber (XSBR) were investigated, with special reference to the effect of the blend ratio, temperature, and frequency. Mechanical properties like tensile strength, modulus, and elongation at break were also studied. As the XSBR content increased, the tensile strength increased up to a 50:50 NR/XSBR ratio and then decreased as a result of the self‐curing nature of XSBR. The dynamic mechanical properties of these latex blends were analyzed for loss tangent, storage modulus, and loss modulus. The entire blend yielded two glass‐transition temperatures, which corresponded to the transitions of individual components, indicating that the system was immiscible. To determine the change in modulus with time, a master curve of 50:50 NR/XSBR blends was plotted. Time–temperature superposition and Cole–Cole analysis were done to understand the phase behavior of the latex blends. The experimental and theoretical values of storage modulus of blends were compared using the Kerner and Halpin–Tsai models. With the help of optical micrographs, attempts were made to correlate the morphology and viscoelastic behavior of these blends. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2639–2648, 2003     

Preparation and characterization of microcellular thin polycarbonate sheets

A new method was developed for the microcellular processing of polycarbonate (PC) thin sheets by compression molding above PC's glass‐transition temperature and below its melting temperature within a few minutes. The effects of the foaming time, foaming pressure, foaming temperature, and foaming agent active ratio on the cell size, cell density, and relative density were studied. The structures of the microcellular PC foam were controlled in the foaming process by carefully choosing the foaming parameters. In addition, the thermal, dynamic mechanical thermal, and electrical properties of the microcellular PC foam were investigated. A differential scanning calorimetry analysis showed that the microcellularly processed PC may have a plastication effect. The variation of the storage modulus, loss modulus, and tan δ under dynamic mechanical thermal analysis was in accord with the calorimetry analysis. The measurement of the electrical property demonstrated that the insulation ability of the microcellular PC thin sheet was obviously enhanced and the dielectric strength of the microcellular PC foam was decreased compared to the unfoamed PC. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1760–1766, 2006     

Deformation and energy absorption characteristics of microcellular ethylene‐octene copolymer vulcanizates

Compressive stress‐strain properties of unfilled, CaCO₃, silica and aluminum silicate filled closed‐cell microcellular ethylene‐octene co‐polymer vulcanizates were studied with variation of blowing agent loading (density). With decrease in density, the compressive stress‐strain curves for microcellular vulcanizates behave differently from those of the solid vulcanizates. The stress‐strain properties are found to be strain rate dependent. The log‐log plots of relative compressive moduli versus relative density of the microcellular vulcanizates show a fairly linear correlation. The energy absorption behavior was also studied from the stress‐strain properties. The efficiency, E, and Ideality parameter, I, were evaluated. These parameters were plotted against stress to find the maximum efficiency and maximum ideality region, which will make these materials suitable for cushioning and packaging applications. The cushioning factor, C, for microcellular vulcanizates has also been evaluated for various systems.     

Evaluation of fatigue lifetime and elucidation of fatigue mechanism in plasticized poly(vinyl chloride) in terms of dynamic viscoelasticity

The fatigue behavior of plasticized poly(vinyl chloride) was investigated by means of a tension–compression-type fatigue apparatus. Complex elastic modulus and mechanical loss tangent were obtained continuously with time under the conditions of constant ambient temperature as a function of imposed strain amplitude. Brittle failure was observed under the conditions of low ambient temperatures and small strain amplitudes, or forced convection of air, whereas thermal failure was observed under the conditions of high ambient temperatures, or large strain amplitudes and natural convection of air. In the case of brittle failure, the dynamic storage modulus E′ exhibited a maximum and the loss tangent tanδ exhibited a minimum on approaching the point of failure. In the case of thermal failure, E′ decreased and tanδ increased monotonously until the onset of thermal failure. It was found that failure occurs when the effective energy loss reaches a certain magnitude depending on an ambient temperature. The fatigue criterion was represented schematically from a standpoint of self-heating. When the heat generation rate of the specimen under cyclic staining is larger than that of the heat transfer to the surroundings, thermal failure takes place. In this case, the specimen temperature increases up to a limiting constant temperature corresponding to the α-absorption temperature. When the heat generation rate is nearly equal to that of the heat transfer to the surroundings, the specimen temperature does not change appreciably and brittle failure takes place.     

Dynamic rheological properties of high‐density polyethylene/polystyrene blends extruded in the presence of ultrasonic oscillations

The linear rheological properties of high‐density polyethylene (HDPE), polystyrene (PS), and HDPE/PS (80/20) blends were used to characterize their structural development during extrusion in the presence of ultrasonic oscillations. The master curves of the storage shear modulus (G′) and loss shear modulus (G″) at 200°C for HDPE, PS, and HDPE/PS (80/20) blends were constructed with time–temperature superposition, and their zero shear viscosity was determined from Cole–Cole plots of the out‐of‐phase viscous component of the dynamic complex viscosity (η″) versus the dynamic shear viscosity. The experimental results showed that ultrasonic oscillations during extrusion reduced G′ and G″ as well as the zero shear viscosity of HDPE and PS because of their mechanochemical degradation in the presence of ultrasonic oscillations; this was confirmed by molecular weight measurements. Ultrasonic oscillations increased the slopes of log G′ versus log G″ for HDPE and PS in the low‐frequency terminal zone because of the increase in their molecular weight distributions. The slopes of log G′ versus log G″ for HDPE/PS (80/20) blends and an emulsion model were used to characterize the ultrasonic enhancement of the compatibility of the blends. The results showed that ultrasonic oscillations could reduce the interfacial tension and enhance the compatibility of the blends, and this was consistent with our previous work. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3153–3158, 2004     

Static and dynamic strain-dependent viscoelastic behavior of black-filled EPDM vulcanizates

The strain dependence of the dynamic mechanical properties of HAF-N330-filled EPDM vulcanizate was studied using a Rheovibron DDV III EP. It is shown that when a dynamic strain is superposed on a static strain, the viscoelastic response of filled rubbers becomes more complex. Under these conditions, dynamic mechanical properties do not correlate with the double strain amplitude. A strain called the “total strain” has been defined in order to interpret the experimental results. It is also shown that the dynamic mechanical properties are displacement velocity dependent, while the comparison is made under identical conditions of strain and frequency. Separability of time and strain effects is observed for the storage modulus, whereas the loss modulus is shown to be a nonseparable function. The elastic and the relaxation components, constituting the mixed function representing the storage modulus are shown to have similar deformation dependence. © 1994 John Wiley & Sons, Inc.     

Dynamic mechanical properties of SBR and EPDM vulcanisates filled with cryogenically pulverized flexible polyurethane foam particles

The dynamic mechanical properties of rubber vulcanisates filled with cryogenically pulverized polyurethane foam particles, used as a reinforcing filler, were investigated with respect to storage modulus (E′), loss modulus, and the variation of glass transition temperature. Two rubbers were using styrene–butadiene rubber (SBR) and ethylene–propylene copolymer (EPDM). The effects of filler concentration and filler characteristics (such as particle size and moisture content) were also monitored. It was found that the optimum dynamic mechanical properties of the compounds were obtained when introducing the PU particles of 40–50 parts per hundred (pph) rubber in the SBR and 30 pph in the EPDM, the properties being affected by the size of PU particles and moisture content. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1129–1139, 1999     

Viscoelastic behavior of carbon black and its relationship with the aggregate size

The viscoelastic behavior of binderless carbon black compacts under dynamic compression (0.2–10.0 Hz, static strain 1.0–2.5%, deformation amplitude 9.4–16 μm and packing density 0.18–0.45 g/cm³) is governed by the solid part of the compact, with the elastic character dominating the viscous character. The viscous character increases with increasing aggregate size, while the elastic character decreases. The interparticle movement in an aggregate contributes to the viscous deformation, while the connectivity among the aggregates contributes to the stiffness. The loss tangent of the solid part increases with increasing aggregate size up to 300 nm, which is optimum for viscoelasticity. A larger specific surface area weakly correlates with a lower storage/loss modulus of the solid part. The particle size does not correlate with the viscoelastic behavior. Both viscous and elastic characters increase with increasing static strain, due to the tightening of the solid part. The loss tangent of the solid part is up to 1.2, compared to 21 and 0.67 for exfoliated graphite and rubber respectively. The storage and loss moduli of the solid part (up to 21 and 180 kPa respectively) are below those of rubber, but are above or comparable to those of exfoliated graphite. Possible applications relate to mechanical isolation.     

Some considerations concerning the dynamic mechanical properties of cured styrene–butadiene rubber/polybutadiene blends

The dynamic mechanical response of several binary mixtures of a styrene–butadiene copolymer and high cis‐polybutadiene has been studied. The loss tangent and shear modulus were measured with a free damping torsion pendulum at temperatures between 143 and 343 K in argon atmosphere. From the loss tangent data the glass transition temperature of each sample was evaluated. The results can be represented by the Fox equation that relates the glass transition temperature of the blend with that of constituent polymers. The influence in the loss tangent data of the crystallization of the high cis BR used in the blend is discussed. A study of the separation of the crystalline and amorphous parts in the polybutadiene using the storage modulus data is presented. Finally, the loss of crystallinity at different contents of SBR in the blend is analysed using the dynamic mechanical data. © 2000 Society of Chemical Industry     

Unprecedented vibration damping with high values of loss modulus and loss tangent, exhibited by cement-matrix graphite network composite

This paper reports a material with unprecedented vibration damping ability, as shown by high values of both the loss tangent (vibration amplitude decay rate) and the loss modulus (energy dissipation ability, equal to the product of the storage modulus and the loss tangent) under flexure at 0.2 Hz at room temperature. The loss modulus (7.5 GPa) exceeds that of any previously reported material, including the best metal-based material, which suffers from a low loss tangent. The loss tangent (0.81) is comparable to or exceeds that of any previously reported material, including rubber, which suffers from a low loss modulus. This material is a cement-matrix graphite network composite containing 8 vol.% graphite and made by compressing a mixture of cement particles and exfoliated graphite, which binds by mechanical interlocking, followed by curing in water. The graphite network structure is supported by microscopy and the low electrical resistivity of the composite (0.04 Ω cm perpendicular to the compression direction and 0.5 Ω cm in the compression direction). The composite is much more conductive than the most conductive cement-matrix composite containing a conductive admixture. The high loss tangent is attributed to the graphite network, while the high storage modulus is attributed to the cement matrix.     

Preparation of microcellular poly(ethylene terephthalate) and its properties

Engineering plastics poly(ethylene terephthalate) (PET) is relatively difficult to process microcellularly compared to general thermal plastics because of its low melting viscosity. A new method was developed to microcellularly process PET in this study with a general hydraulic press above PET's crystallization temperature and below its melting temperature within times of a few minutes. A processing window existed in which to prepare microcellular PET under certain foaming time, pressure, temperature, and foaming reagent content scope. The effects of foaming time, temperature, pressure, and foaming reagent content on the thermal, mechanical, and dynamic mechanical thermal properties of microcellular PET foam were investigated. Differential scanning calorimetry (DSC) analysis showed that the transition temperature and crystallinity of microcellular PET had small changes with increasing foaming time. Under some processing conditions used in this study, the tensile strength and breaking extension of microcellular PET foam were both increased at the same time, indicating strengthening and toughening effects. The variation of storage modulus, loss modulus, and tan δ under dynamic mechanical thermal analysis was in accord with DSC analysis and mechanical measurements. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1956–1962, 2003     

Dynamic mechanical properties of sisal fiber reinforced polyester composites fabricated by resin transfer molding

The dynamic mechanical properties of sisal fiber reinforced polyester composites fabricated by resin transfer molding (RTM) were investigated as a function of fiber content, frequency, and temperature. Investigation proved that at all temperature range the storage modulus (E′) value is maximum for the composites having fiber loading of 40 vol%. The loss modulus (E″) and damping peaks (tan δ) were lowered with increasing fiber content. The height of the damping peaks depends upon the fiber content and the fiber/matrix adhesion. The extent of the reinforcement was estimated from the experimental storage modulus, and it has been found that the effect of reinforcement is maximum at 40 vol% fiber content. As the fiber content increases the T_g from tan δ curve showed a positive shift. The loss modulus, storage modulus, and damping peaks were evaluated as a function of frequency. The activation energy for the glass transition increases upon the fiber content. Cole–Cole analysis was made to understand the phase behavior of the fiber reinforced composites. Finally, attempts were made to correlate the experimental dynamic properties with theoretical predictions. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Dynamic viscoelastic properties of fluoroelastomer/clay nanocomposites

Nanocomposites based on fluoroelastomer and modified and unmodified sodium montmorillonite clays were prepared. Dynamic mechanical thermal analysis was performed on these nanocomposites over a range of temperatures (?60 to +60°C), frequencies (0.032–32 Hz), and strains (0.002%–2%). The results showed that there were significant changes in the glass transition temperature and storage modulus with the addition of small amount (4 phr) of the modified and the unmodified nanofillers. The tan δ peak heights decreased and the storage modulus increased in general, but it was more prominent in the case of the unmodified clay. With the addition of the nanoclays, the cross‐over point in the double logarithmic plot of storage modulus (E′) and complex viscosity (η*) with frequency, shifted toward higher frequency. Interestingly, with increasing strain, the nanocomposites demonstrated a sudden upturn in the storage modulus after ～0.2% strain amplitude, because of the formation of α‐crystallization in the elastomer structure. The uniaxial strain before strain sweep experiment increased the storage modulus remarkably. The results were explained with the help of X‐ray diffraction and transmission electron microscopy. POLYM. ENG. SCI., 47:1777–1787, 2007. © 2007 Society of Plastics Engineers