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     

Viscoelastic properties of polyamic acid solutions—precursors of polyimides

The rheology of polyamic acid (PAA) solutions, precursors of polyimides used in microelectronic device applications, has been investigated by dynamic (oscillatory) shear flow measurements. Frequency dependent storage and loss moduli and dynamic viscosity were measured in the frequency range 10^?1 to 10³ rad/s at 23°C. The storage modulus G′ (ω) and loss modulus G″ (ω) exhibited quadratic and linear dependence in frequency at low frequencies respectively, the viscoelastic fluid behavior commonly predicted for polymer solutions from many molecular theories. At high frequencies both dynamic moduli become proportional to ω^2/3. The results show that PAA solutions are very high loss viscoelastic fluids, judging from the loss tangent values which far exceed unity. It is suggested that dynamic viscoelastic properties could be used to monitor the degree of imidization since there is a gradual change from viscoelastic fluids to soft viscoelastic solids to hard viscoelastic solids as PAA is converted to polyimides. Onset of non-Newtonian flow as shown on the frequency dependent dynamic viscosity was in the range 30 to 200 rad/s. The viscoelastic constants, zero-shear rate viscosity η_o and steady-state compliance J_e⁰, where also determined from the dynamic data and compared to previous steady shear flow results.     

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 copolymers containing carbon black

The storage and loss moduli of random copolymers of styrene and butyl methacrylate containing carbon black of varied surface area were determined by dynamic mechanical analysis at several temperatures about 100°C above the glass-transition temperature, T_g. At low frequencies, the pure polymers exhibit linear double log plots of moduli against frequency, with slopes of unity and approaching two for G″ and G′, respectively. With the addition of carbon black filler, both G′ and G″ become independent of frequency and temperature at low frequencies, consistent with yield behavior arid the formation of a carbon black network. The limiting dynamic complex modulus exceeds the yield stress from steady shear rheology, perhaps indicating the extent of the carbon black network, which was highest for low-molecular-weight copolymer and polystyrene. The filled random copolymers behaved Theologically like similarly filled polystyrenes of comparable molecular weights. Plasticization effects observed in the steady shear rheology of filled copolymers containing small concentrations of carbon black were not observed in dynamic mechanical analysis, although dynamic moduli converge at high frequency.     

Rheological properties of polystyrene blends with rigid ladderlike polyphenylsilsesquioxane

Polystyrene (PS) blends with rigid ladderlike polyphenylsilsesquioxane (PPSQ) were prepared by solution casting followed by hot pressing. The rheological properties of these blends were studied under dynamic shear and uniaxial elongation conditions. The loss modulus (G″) and dynamic shear viscosity (η*) of the 95/5 PP/PPSQ blend were slightly lower than those of pure PS at low frequencies (≤10^?2 rad/s). However, the storage modulus (G′), G″, and η* of the other blends (90/10, 85/15, and 80/20) were higher than those of pure PS and increased with PPSQ content. The η_E data demonstrated that PS/PPSQ blends exhibited slightly weaker (5% PPSQ) or much weaker (10% PPSQ) strain hardening than PS. In contrast, the 85/15 and 80/20 PP/PPSQ blends showed strain softening, and the extent of strain softening increased with PPSQ content. PS entanglements might have been reduced by the specific interactions between PS and PPSQ, which locally ordered some PS molecules in the 95/5 blend sample, because most of the PPSQ might have been well dispersed in the PS continuous phase, and only a few small PPSQ particles (～1.3 μm) were formed because of good miscibility. However, at high PPSQ contents (≥10%), many larger hard PPSQ particles were formed, which acted as fillers during the rheological measurements. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 706–713, 2005     

Rheology and Mechanical Properties of PVC/Acrylonitrile–Chlorinated Polyethylene-Styrene/MAP-POSS Nanocomposites

The nanocomposite of the Poly(vinyl chloride)/acrylonitrile-chlorinated- polyethylene-styrene (ACS)/methylacryloylpropyl-contaning polyhedral oligomeric silsesquioxane (MAP-POSS) (PVC/ACS/MAP-POSS) was prepared. Plasticizing behavior, dynamic rheology behavior and mechanical properties of the nanocomposites were investigated. The results showed that the plastic time decreased with increasing MAP-POSS content. The dynamic storage modulus G ′, loss modulus G″ and complex viscosity η* of the nanocomposites all exhibit a monotonic change with increasing frequency, and all have maximum when MAP-POSS content is 4 wt%, at the same frequency. The MAP-POSS can be used as an efficient process aid and impact aid of PVC/ACS blend at appropriate content.     

The rheological behavior and dynamic mechanical properties of syndiotactic 1,2‐polybutadiene

The rheological behavior and the dynamic mechanical properties of syndiotactic 1,2‐polybutadiene (sPB) were investigated by a rotational rheometer (MCR‐300) and a dynamic mechanical analyzer (DMA‐242C). Rheological behavior of sPB‐830, a sPB with crystalline degree of 20.1% and syndiotactic content of 65.1%, showed that storage modulus (G′) and loss modulus (G″) decreased, and the zero shear viscosity (η₀) decreased slightly with increasing temperature when measuring temperatures were lower than 160°C. However, G′ and G″ increased at the end region of relaxation curves with increasing temperature and η₀ increased with increasing temperature as the measuring temperatures were higher than 160°C. Furthermore, critical crosslinked reaction temperature was detected at about 160°C for sPB‐830. The crosslinked reaction was not detected when test temperature was lower than 150°C for measuring the dynamic mechanical properties of sample. The relationship between processing temperature and crosslinked reaction was proposed for the sPB‐830 sample. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Viscoelastic behavior of polybutadienes with high 1,4‐microstructure and narrow molecular weight distribution

Polybutadienes (PBs) of narrow molecular weight distributions with high 1,4‐microstructure were synthesized by sec‐butyllithium‐initiated, living polymerization. The shoulder‐like anomalous behavior of the storage modulus G′(ω) in the terminal zone for PBs was studied using size exclusion chromatography (SEC) and rheometric mechanical spectrometry (RMS). It was found that a high‐molecular‐weight fraction in the PBs was the main reason for the occurrence of the shoulders. The linear viscoelastic spectra were successfully obtained by the Pade–Laplace method from experimental dynamic data, using either the dynamic storage, G′(ω), or loss, G"(ω), modulus. Both the dynamic moduli and stress relaxation in the linear regime were then calculated with reasonable precision. The feasibility of time–temperature–molecular weight superposition for PBs using this method was demonstrated. The dependencies of relaxation spectra on temperature and molecular weight were obtained by a fitting procedure. Thus, with a known reference state, the relaxation spectrum for a given molecular weight PB at a given temperature can be predicted. The predicted dynamic moduli are in good agreement with experimental data. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1315–1324, 1999     

Dynamic rheological behavior and mechanical properties of PVC/CPE/MAP–POSS nanocomposites

Poly(vinyl chloride)/chlorinated polyethylene (PVC/CPE)/methylacryloylpropyl‐containing polyhedral oligomeric silsesquioxane (MAP–POSS) nanocomposites are prepared. The plastic behavior and dynamic rheological behavior of PVC/CPE/MAP–POSS are investigated. The influences of composition on dynamic storage modulus G′, loss modulus G″, and complex viscosity η* of PVC/CPE/MAP–POSS melts are discussed. The dynamic mechanical properties, mechanical properties, and morphology are determined. The results show that both plastic time and balance torque of the nanocomposites decrease, but the G′, G″, and η* all increase with increasing MAP–POSS content. The maximum value of the dynamic mechanical loss tan δ decreases and elasticity increases when MAP–POSS is added. The impact strength of the nanocomposites increases with increasing MAP–POSS content and has the best value at 10% content of MAP–POSS, which is 5.38 kJ/m² higher than that of the blend without MAP–POSS. The MAP–POSS can be used as an efficient process aid and impact aid for the PVC/CPE blend. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Dispersion of multiwalled carbon nanotubes in thermoplastic elastomer gels: Morphological,rheological, and electrical properties

An investigation was reported here with an aim to prepare nanocomposite thermoplastic elastomer gels by dissolving polystyrene‐b‐poly(ethylene/butylene)‐b‐polystyrene (SEBS) triblock copolymer in selective hydrocarbon oils with the presence of multiwalled carbon nanotubes (MWCNTs). The properties related to morphology, viscoelasticity, electrical and mechanical properties, and thermal stability were explored and discussed. Dynamic rheological measurements of the resultant nanocomposite thermoplastic elastomer gels (NCTPEGs) confirmed that addition of MWCNTs affects the linear viscoelastic properties in which dynamic storage and loss moduli increase to some extent. At a temperature between 30°C and 40°C below the gel point the NCTPEGs have dynamic storage modulus greater than loss modulus (G′ and G″), thereby indicating that at room temperature a physical network is still present despite the addition of MWCNTs. The morphological properties revealed that MWCNTs were dispersed and exfoliated within the swollen TPE. The incorporation of small quantity of MWCNTs improved the thermal stability and mechanical properties of NCTPEGs. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Rheological behavior of high‐density polyethylene (HDPE) filled with paper mill sludge

A comparative study was conducted of composites made with sludge from three different paper mills. Sludges were obtained from a thermomechanical pulp (TMP), a chemico‐TMP (CTMP), and a Kraft mill with a feedstock of primarily black spruce. The primary sludge (PS) and secondary sludge (SS) were mixed at two different ratios (PS:SS = 7:3 and 9:1) and blended with high‐density polyethylene (HDPE) at 20%, 30%, and 40% proportion. The blends were tested using plate–plate geometry before subjection to frequency sweep by oscillation rheometry. The storage modulus (G′), loss modulus (G″), and complex viscosity (η*) increased with increasing paper sludge content. Decreasing the PS:SS ratio from 9:1 to 7:3 decreased G′, G″, and η*. Differential scanning calorimetry showed that sludge addition increased both the melting and crystallization temperature, for a positive effect on crystallinity. Although the behavior of sludge–high‐density polyethylene blends differed from that of traditional wood plastic composite made with wood flour, they obtained G′, G″, and η* values of the same magnitude. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46484.     

Dynamic mechanical analysis of a uniaxial continuous carbon fiber-thermoplastic composite subjected to anodic and cathodic currents

The dynamic mechanical properties of a uniaxial continuous carbon fiber-thermoplastic composite were found to degrade significantly when subjected to anodic and cathodic currents in the presence of seawater. The composite tested was made of PAN-based graphite fibers (50 vol%) in Du Pont's J-2 thermoplastic resin (nylonbased). The shear storage modulus, G′, and the shear loss modulus, G″, of the composite were measured by subjecting a rod-shaped sample to small amplitude torsional oscillations. The moduli remained constant over time when the sample was in air and when it was submerged in seawater in the absence of applied currents. Both moduli decreased to ∼45% of their initial values when a constant anodic current of density 0.414 μA/cm² was applied for 2 h. A cathodic current of the same density and duration caused the moduli to decrease to ∼63% of their initial values. The moduli remained at these low levels after the current had been turned off. Inspection, under a scanning electron microscope, of the sample exposed to the anodic current revealed numerous cracks in the polymer matrix. In the sample exposed to the cathodic current, the fibers separated from the matrix of the composite.     

Pultruded fiber-reinforced poly(methyl methacrylate) composites. II. Static and dynamic mechanical properties,environmental effect,and postformability

This paper presents a novel process developed to manufacture poly(methyl methacrylate) (PMMA) pultruded composite. The mechanical, thermal, and dynamic mechanical properties, environmental effect, postformability of various fiber (glass, carbon, and Kevlar 49 aramid fiber) reinforced pultruded PMMA composites have been studied. Results show mechanical properties (i.e., tensile strength, specific tensile strength, tensile modulus, and specific flexural strength) and thermal properties (HDT) increase with fiber content. Kevlar fiber/PMMA composites possess the highest specific tensile strength and HDT, carbon fiber/PMMA composites show the highest tensile strength and tensile modulus, and glass fiber/PMMA composites show the highest specific flexural strength. Pultruded glass-fiber-reinforced PMMA composites exhibit good weather resistance. These composite materials can be postformed by thermoforming under pressure, and mechanical properties of postformed products can be improved. The dynamic shear storage and loss modulus (G′, G″) of pultruded glass-fiber-reinforced PMMA composites increased with decreasing pulling rate, and their shear storage moduli are higher than those of pultruded Nylon 6 and polyester composites.     

Rheological and thermomechanical properties of long‐chain‐branched polyethylene prepared by slurry polymerization with metallocene catalysts

A series of polyethylene (PE) samples were prepared in a slurry polymerization with bis(cyclopentadienyl) zirconium dichloride (Cp₂ZrCl₂)/modified methylaluminoxane (MMAO) using a semibatch reactor. The samples had long‐chain branch densities (LCBDs) of a 0.03–1.0 branch per 10,000 carbons and long‐chain branch frequencies (LCBFs) up to a 0.22 branch per polymer molecule. The rheological and dynamic mechanical behaviors of these long‐chain branched PE samples were evaluated. Increasing the LCBF significantly increased the η₀'s and enhanced shear thinning. Long‐chain branching (LCB) also influenced the loss modulus and storage modulus. Increasing the LCBF led to enhanced G′ and G″ values at low shear rates and broader relaxation spectrums. The samples exhibited thermorheologically complex behavior. LCB also played a significant role in the dynamic mechanical behavior. Increasing the LCBF increased the stiffness of the polymer and enhanced the damping or energy dissipation. However, LCB had little influence on the crystalline structure of the PE. The α‐ and γ‐relaxations showed little dependence on the LCBF. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 307–316, 2004     

Short jute fiber‐reinforced polypropylene composites: Dynamic mechanical study

Short jute fiber‐reinforced polypropylene (PP) composites were prepared using a high‐speed thermokinetic mixer. A compatibilizer was used to improve the molecular interaction between jute and PP. Both the percent weight fraction of the jute fiber and compatibilizer were varied to study the dynamic mechanical thermal (DMT) properties. Dynamic parameters such as storage flexural modulus (E′), loss flexural modulus (E″), storage shear modulus (G′), loss shear modulus (G″), and loss factor or damping efficiency (tan δ) were determined in a resonant frequency mode. The transition peak nature, amplitude, and temperature of E′, E″, G′, G″, and tan δ of different compositions were shown to indicate possible improvements of molecular interaction in the presence of a compatibilizer. The modulus retention term, a plot of the reduced modulus with the weight fraction of the jute fiber, also indicate its improvement. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 531–539, 1999     

Rheological characterization of chitosan matrices: Influence of biopolymer concentration

Viscoelastic properties of chitosan (CH), chitosan‐poly(ethylene glycol) 400 (CH‐PEG), and chitosan‐poly(ethylene glycol) 400 with glyoxal as crosslinking agent (CH‐PEG‐Gly) systems were studied to analyze the effect of chitosan concentration (from 0.83 to 1.67%). Dynamic moduli increase as chitosan concentration increases for all systems. For CH and CH‐PEG systems the loss modulus (G″) is greater than the storage modulus (G′) with predominance of the viscous over the elastic behavior. This corresponds to the characteristic behavior of solutions (nonstructured systems). The presence of PEG 400 induces a complementary reinforcement of the mechanical properties of the system. Except for the lowest chitosan concentration, when glyoxal was added to the CH‐PEG systems, a gelled matrix was obtained. In this case, G′ is greater than G″, and practically independent of frequency. This behavior is typical of three‐dimensional networks and indicates true gel formation, showing clear elastic behavior (tan δ < 1). In creep and recovery analysis, CH‐PEG‐Gly systems exhibited distinct regions that were mathematically modeled using Burger's model. This analysis shows that the CH‐PEG‐Gly matrices (from 1.25 to 1.67%) recover almost totally (100%). Therefore, these matrices could be useful as systems for the development of films for topical hydrophilic drug delivery, and the levels of the residual viscosity (η₀) or the complex viscosity (η*) could be used to control drug release. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Pultruded fiber reinforced blocked polyurethane (PU) composites. II. Processing variables and dynamic mechanical properties

Unidirectional fiber reinforced blocked polyurethane (PU) composites have been prepared by the pultrusion process. The effects of processing variables on the mechanical properties and dynamic mechanical properties of fiber reinforced PU composites by pultrusion have been studied. The processing variables investigated included pulling rate (in-line speed), die temperature, postcure time and temperature, and filler type and content. The dynamic mechanical properties of the composites produced by the process were studied utilizing dynamic mechanical spectrometer. Results show that the composites possessed various optimum pulling rates at different die temperatures. From the DSC data analysis, swelling ratio, and mechanical properties, the optimum die temperature was determined. It was found that the mechanical properties increase with filler content for various types of filler. The increasing of mechanical properties depends on the optimum postcure temperature and time. However, the properties decreased for longer postcure times since the composite materials were degraded. The glass-transition temperature (T_g) increased slightly and the damping peak (tan δ) was broadened due to fiber reinforcement. The dynamic mechanical moduli (G′, G″) of pultruded PU composites are apparently higher than those of the matrices. The moduli (G′, G″) increase with increasing fiber and filler content, and the damping peak becomes broad. Effect of postcuring on the degree of crosslinking, T_g, and dynamic modulus will be discussed.     

Dynamic rheological behavior of poly(ether ketone ketone) from solid state to melt state

High performance thermoplastic poly(ether ketone ketone) (PEKK) polymers with various meta phenyl links ratio were investigated by dynamical mechanical analysis. Analyses were carried out in a wide range of temperature from solid state (torsion rectangular mode) to the melt state (torsion parallel plates mode) as function of thermal history and environmental conditions. In the solid state, this study was focused on the secondary relaxations in the vitreous state. A complementary investigation conducted with different poly(aryl ether ketones) allowed us to propose a molecular interpretation of PEKK sub‐vitreous relaxations. In the molten state, storage modulus (G′), loss modulus (G″), storage viscosity (η′), and loss viscosity (η″) were studied to determine zero shear‐rate viscosity (η₀) and thermal activation energy E_a. Master curves were built and the shift factor a_T was determined. Thermal activation energies were extracted from an Arrhenius model on the shift factor temperature's dependency. Finally, E_a and η₀ were determined thanks to the dynamic viscosity fit with Cross model and Cole–Cole representation. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46456.     

Rheology of PVC. Part 5: Melt elasticity

The behavior of PVC changes drastically with the temperature and the method of sample preparation. In the steady-state shear mode, upon a decrease of the rate of deformation, the data may show either a steady increase of the shear viscosity or a leveling off to a Newtonian plateau. In the dynamic test mode, both the storage modulus, G′, and the loss modulus, G″, show an effect of the yield stress. Only at temperatures above 210°C are flow curves normal for polymer melts obtained. Rigid and nonrigid PVC formulations have been tested in Weissenberg Rheogoniometer, using steady-state or dynamic test modes at temperatures from 140 to 220°C. It was observed that yield affects elasticity more (measured by the first normal stress difference or the storage modulus) than viscosity (expressed by the shear stress or the loss modulus). The corrected for yield plots of elastic vs. viscous parameter can be easily interpreted in terms of a composite flow.     

Viscoelastic properties of suspensions with weakly interacting particles

Rheological characterization of a model suspension containing hydroxyl-terminated polybutadiene and glass beads with filler concentration up to 30% by volume was performed by using a Haake parallel disk rheometer. The rheological tests conducted were the measurement of the storage modulus, G′, loss modulus, G′, and complex viscosity, η*, as functions of the frequency and the steady shear viscosity as a function of the shear rate. The linear viscoelastic region was determined to extend up to 50% strain by measuring G′, G′, and η* as functions of strain amplitude. By using multiple gap separations between the disks, it was found that the suspension did not exhibit slip at the walls of the rheometer. G′ and G′ were used to determine the relaxation times distribution, G_i(λ_i, ⊘) as functions of the relaxation time, λ_i, and the filler content, ⊘. The relaxation moduli, G_i(λ_i, ⊘), decreased with the relaxation time, but increased with the filler content. The Cox–Merz rule was also observed to be valid for these suspensions. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 507–514, 1998