Dynamic Rheological Behavior Research Articles

Rheology of physically evolving suspensions

The objective of this work was to investigate the modeling of the whole dynamic rheological behavior of physically evolving suspensions (e.g., polyvinyl chloride plastisols). The evolutions of the complex viscosity with time (isothermal) and with temperature (non-isothermal) were analyzed. To understand the physically involved phenomena, the determination of relationships between the solid volume fraction evolution and the rheological behavior was investigated. Firstly, the evolution of the volume fraction in relation with the variation of radii particle suspensions using a modified Avrami equation was determined. Actually, the rheological study of this physically evolving system is far too complicated due to the many factors involved in the evolving process. Consequently, a phenomenological law using Carreau–Yasuda equation and percolation laws combined with the evolution of the solid volume fraction is investigated to obtain the modeling of the whole dynamic rheological behavior at any frequency and temperature.

Wormlike micelles in poly(oxyethylene) surfactant solution: Growth control through hydrophilic-group size variation

Viscoelastic micellar solutions are formed in poly(oxyethylene) cholesteryl ether (ChEO m , m = 15 , 30) aqueous solutions on addition of tri(ethyleneglycol) mono n-dodecyl ether (C 12EO 3). The steady-shear and dynamic rheological behavior of the systems is characteristic of wormlike micellar solution. In either system, the plateau modulus ( G 0 ) and relaxation time ( τ) are found to increase with increasing cosurfactant mixing fractions. The plateau modulus of the ChEO 30–C 12EO 3 system at the maximum viscosity region is found to be higher than that in the ChEO 15–C 12EO 3 system at the maximum viscosity region, whereas for the relaxation time the opposite relation is found. The maximum viscosities obtained in the two systems are of the same order of magnitude. In the ChEO 30–C 12EO 3 system, the maximum viscosity is obtained at a higher cosurfactant mixing fraction than that in the ChEO 15–C 12EO 3 system. It is concluded that decreasing the head-group size of the hydrophilic surfactant favors micellar growth. Monolaurin, another hydrophobic surfactant known to induce growth in some systems, is found to cause phase separation before significant micellar growth occurs in ChEO m solutions, although the effect of head-group size of ChEO m is found to be similar to the ChEO m –C 12EO 3 systems.

Rheological Behavior of Immiscible PS/PMMA Blends during Dynamic Plasticating Extrusion

Abstract PS/PMMA blends were prepared using a twin screw extruder and then extruded using an electromagnetic dynamic plasticating extruder equipped with a specially designed split die. During dynamic plasticating extrusion, the dynamic rheological behavior of PS/PMMA blends was investigated. The extrudates were cooled immediately and collected for morphology measurements using a scanning electron microscope (SEM). Results show that the average shear stress decreases with the introduction of vibration force field into the whole extrusion process, and reaches a minimum at the vibration amplitude of 0.15 mm and the vibration frequency of 5 Hz. At the same shear stress, the melt viscosity of the blend under dynamic plasticating extrusion is lower than that under static extrusion and decreases with vibration intensity. With increasing vibration intensity, the power-law index of the blend melt has a tendency to increase. The drop size of the dispersed phase in 25/75 PS/PMMA blend decreases at a faster rate with an increase of shear stress, compared with that in 75/25 PS/PMMA blends, correspondingly, the melt viscosity of 25/75 PS/PMMA blend has a stronger shear rate dependence. During dynamic plasticating extrusion, a negative deviation from the additivity rule is observed for the studied blend compositions.

Effects of magnesium hydroxide and its surface modification on crystallization and rheological behaviors of polypropylene

AbstractIn this article, polypropylene composites filled with magnesium hydroxide (PP filled with MH) were prepared in corotating twin‐screw extruder. The effects of MH particles content and types of treatment agents on the crystallization and melting behaviors, crystal structure, and rheological properties of PP/MH composites were studied by differential scanning calorimetry (DSC), a wide‐angle X‐ray diffraction, and dynamic rheological measurements. The DSC results show that MH particles act as a good heterogeneous nucleation effect on PP. Surface treatment of MH weakens its heterogeneous nucleation effect. The nucleating efficiency of MH on PP is found to depend strongly on its content and type of treatment agents. The dynamic rheological behaviors of MH filled PP is found that the complex viscosity (η*) increases with increasing MH content, whereas with increasing filler concentration the network structure becomes the prevailing process, which raises the η* values, especially at the low frequency zone. The η* values of the composites, however, decrease with the addition of various treatment agents. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers

Dynamic rheology behavior of electron beam-irradiated cellulose pulp/NMMO solution

The rheological behavior of irradiated cellulose pulp solution by electron beam was investigated. Storage modulus G′, loss modulus G″, the dependence of complex viscosity η* and frequency ω of cellulose solutions were measured by DSR-200 Rheometer (Rheometrics co., USA). The molecular weight of irradiated cellulose was measured via the intrinsic viscosity measurement using an Ubbelohde capillary viscometer. The crystalline structure was studied by FTIR Spectroscopy. The results congruously showed that the molecular weight of pulp cellulose decrease and the molecular weight distribution of cellulose become narrow with increase in the irradiation dose. Moreover, the crystalline structure of the cellulose was destroyed, the force of the snarl between the cellulose molecules weakens and the accessibility of pulp spinning is improved. The study supplies some useful data for spinnability of irradiated cellulose and technical data to the filature industry.

Influence of Compatibilizer on Morphology and Dynamic Rheological Behavior of Polyethylene-Octene Elastomer/Starch Blends

The morphology and rheology of polyethylene-octene elastomer (POE)/crosslinked starch (CS) immiscible blends with various amounts of compatibilizer were experimentally examined. A graft copolymer, POE-g-MAH, acting as the compatibilizer, was used to modify the interface of the blend. The particle radius in the POE/CS 80/20 system decreased with increasing compatibilizer up to 5 wt%, beyond which the particle size slightly increased. This indicates that the interface reaches saturation when the compatibilizer content is 5 wt%, leading to reduced effectiveness of the compatibilizer. From the SEM micrographs, the compatibilized blends were found to have better interfacial adhesion between the POE and starch phase than the uncompatibilized blends. Rheological examination shows a sharp reduction of the viscoelastic modulus and complex viscosity in blends containing 10 wt% compatibilizer. When the content of compatibilizer is less than 5 wt%, the viscoelastic modulus and complex viscosity of the blends increase with increasing the content of compatibilizer.

Effect of coupling agents on the crystallinity and viscoelastic properties of composites of rice hull ash-filled polypropylene

This paper focuses on the application of silica rich, rice hull ash (RHA) from the rice industry as filler in polypropylene (PP). The dynamic rheological behaviour and the crystallinity of its composites with semi-amorphous polypropylene were used as performance indicators. The effect of coupling agents on RHA/PP compatibility was also investigated. Addition of RHA increased storage modulus (G′), and the onset (Tco) and peak (Tc) crystallinity temperatures, and decreased the degree of crystallinity of the system. Two coupling agents, maleated polypropylene (MAPP) and an amino functional silane, were used to improve the interfacial adhesion of RHA and PP. Addition of MAPP increased G′, Tc and Tco and the crystalline phase of the system. Addition of silane had mixed effects. It increased the rheological properties at higher concentrations, it increased Tc and Tco at all the concentrations and increased crystallinity at lower concentrations and decreased it at higher concentrations. Results from a thermogravimetric analyser were useful in revealing the mechanism by which silane bond to RHA and its effect on the rheology and crystallisation behaviour of the composites.

Influência da temperatura no comportamento reológico da polpa de jabuticaba

O comportamento reológico em estado estacionário e dinâmico da polpa de jabuticaba foi estudado em diferentes temperaturas (5, 25, 45, 65 e 85 °C). As amostras foram submetidas a ensaios em estado estacionário (0 a 300 s-1) para o ajuste dos diferentes modelos de escoamento. O modelo de Herschel-Bulkley foi o que melhor se ajustou aos dados experimentais, no qual se observou a redução do índice de consistência (k) e um leve aumento do índice de comportamento de escoamento (n) com o aumento da temperatura. Ensaios oscilatórios, com valores de tensão dentro do intervalo linear, foram realizados para obtenção dos espectros mecânicos. As amostras analisadas a 5 °C apresentaram maior módulo de armazenamento (G'), indicando uma maior interação entre as partículas a esta temperatura, o que contribui para o fortalecimento da rede elástica. A polpa analisada a 45 °C não apresentou a mesma tendência que as outras temperaturas, o que pode ser um indício do início da estruturação da pectina natural presente na polpa.

Effect of the extent of pasting on the dynamic rheological properties of acidified skim milk gels containing normal rice starch

The dynamic rheological behaviour of skim milk gels containing 2% normal rice starch granules pasted to different temperatures was investigated. The extent of swelling of the starch granules was also measured. It was found that the complex modulus G* was maximal when the starch granules were pasted to the temperature of maximum swelling and not to the temperature of maximum viscosity. It is suggested that, in these systems, the starch granules behave as inactive fillers and that their main effect is to increase the milk protein concentration during swelling by absorbing water from the continuous phase. A simple empirical model that agrees qualitatively well with the experimental results is proposed.

Effect of montmorillonite on properties of styrene–butadiene–styrene copolymer modified bitumen

AbstractClay/styrene–butadiene–styrene (SBS) modified bitumen composites were prepared by melt blending with different contents of sodium montmorillonite (Na‐MMT) and organophilic montmorillonite (OMMT). The structures of clay/SBS modified bitumen composites were characterized by XRD. The XRD results showed that Na‐MMT/SBS modified bitumen composites may form an intercalated structure, whereas the OMMT/SBS modified bitumen composites may form an exfoliated structure. Effects of MMT on physical properties, dynamic rheological behaviors, and aging properties of SBS modified bitumen were investigated. The addition of Na‐MMT and OMMT increases both the softening point and viscosity of SBS modified bitumens and the clay/SBS modified bitumens exhibited higher complex modulus, lower phase angle. The high‐temperature storage stability can also be improved by clay with a proper amount added. Furthermore, clay/SBS modified bitumen composites showed better resistance to aging than SBS modified bitumen, which was ascribed to barrier of the intercalated or exfoliated structure to oxygen, reducing efficiently the oxidation of bitumen, and the degradation of SBS. POLYM. ENG. SCI., 47:1289–1295, 2007. © 2007 Society of Plastics Engineers

Structure and properties of in situ compatibilized polystyrene/polyolefin elastomer blends

AbstractTo increase the compatibility of polystyrene (PS) and polyolefin elastomer (POE) blends, a Lewis acid catalyst, aluminum chloride (AlCl3), was adopted to initiate the Friedel–Crafts alkylation reaction for the formation of PS‐graft‐POE copolymer. Dynamic mechanical analysis indicated that PS/POE and PS/POE/AlCl3 blends are partially miscible, and the formation of PS‐graft‐POE copolymer increased the compatibility between PS and POE. Scanning electron microscope and transmission electron microscope results showed that the domain size of the blends decreased dramatically and the size distribution became more uniform with the addition of AlCl3. Such in situ compatibilization also induced hindrance to the macromolecular chain movement, as reflected by the results of the dynamic rheological analysis. The dynamic rheological behaviors of PS/POE and PS/POE/AlCl3 blends under different temperature showed that in situ compatibilization weakened the effects of thermooxidation on PS/POE blends. Moreover, in situ compatibilization decreased the activation energy of viscous flow and reduced the influence of temperature on PS/POE blends. POLYM. ENG. SCI., 47:951–959, 2007. © 2007 Society of Plastics Engineers

Viscoelastic Behavior of Cellulose Acetate in a Mixed Solvent System

The effect of increasing water composition on the rheological and microstructural behavior of a ternary cellulose acetate (CA)/N,N-dimethylacetamide (DMA)/water system is examined. Addition of water to the CA/DMA system results in enhanced steady shear viscosity and dynamic viscoelastic properties and ultimately to phase-separated gel formation. The changes in dynamic rheological behavior of the system during gelation correlate well with the combined solubility parameter (delta) and, in particular, the Hansen hydrogen-bonding solubility parameter index (delta(h)) of the solvent system, suggesting hydrogen-bonding interactions may be the major route initiating the sol-gel process. For all gels studied, the elastic modulus and the critical stress to yield shifts to higher values with increasing CA concentration and/or water content. In addition, the elastic modulus exhibits a power-law behavior with water content, with the same power-law exponent observed for gels containing different CA concentrations. Addition of water leads to formation of a denser gel network, as evidenced from direct visualization of the gel microstructure through confocal microscopy.

Dynamic mechanical and rheological behavior of fluoroelastomer‐organoclay nanocomposites obtained from different preparation methods

AbstractA comparison among different preparation methods of fluoropolymer/clay nanocomposites based on a fluoroelastomeric matrix (Tecnoflon® P959) and organomodified montmorillonite clay (Cloisite®20A) is reported. While melt blending leads to intercalated structures, the X‐ray diffraction patterns of solution blended nanocomposite suggest a better delamination of the clay platelets within the fluoropolymeric matrix (no diffraction peaks) if the solvent evaporation step is carried out very slowly (72 h) at ambient pressure and moderate temperature. For the solution blended‐slow evaporation nanocomposite, dynamic mechanical analysis and dynamic rheological measurements show a strong increase in G′, a lower damping peak at Tg, and a pseudosolid like behavior in the terminal flow region, suggesting a likely exfoliation of the organomodified clay in the fluoroelastomeric matrix. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4484–4487, 2006

Viscoelastic Micellar Solutions in Nonionic Fluorinated Surfactant Systems

The formation and rheological behavior of a viscoelastic wormlike micellar solution in an aqueous solution of a nonionic fluorinated surfactant, perfluoroalkyl sulfonamide ethoxylate, of structure C8F17SO2N(C3H7)(CH2CH2O)10H was studied. Temperature-induced viscosity growth is observed even at low-surfactant concentration (approximately 1 wt %), and viscosity reaches the maximum at a temperature T(eta)-max. Upon successive increases in the temperature, the viscosity decreases, and ultimately a phase separation occurs. Small-angle X-ray scattering (SAXS) measurements confirm the presence of cylindrical aggregates at low temperature, which undergo continuous one-dimensional growth with increasing temperature, and ultimately, an indication of a slight lamellarlike structural pattern is observed, which probably comes from the formation of micellar joints or branching. Such changes in the microstructure result in a decrease in the viscosity and stress-relaxation time, while the network structure is retained; the trends in the evolution of shear modulus (Go) and relaxation time (tauR) with temperature are in agreement with this. With increased surfactant concentration, the temperature corresponding to the viscosity maximum (T eta-max) in the temperature-viscosity curve shifts to lower values, and the viscosity at temperatures below or around T eta-max increases sharply. A viscoelastic solution with Maxwellian-type dynamic rheological behavior at low-shear frequency is formed, which is typical of entangled wormlike micelles. Rheological parameters, eta(o) and Go, show scaling relationships with the surfactant concentrations with exponents slightly greater than the values predicted by the living-polymer model, but the exponent of tauR is in agreement with the theory. Dynamic light-scattering measurements indicate the presence of fast relaxation modes, associated with micelles, and medium and slow modes, associated with transient networks. The disappearance of the slow mode and the predominance of the medium mode as the temperature increases support the conclusions derived from SAXS and rheometry.

Preparation and Properties of LLDPE/PMVS Blends

Reactive blending has been carried out by the melt mixing of linear low density polyethylene (LLDPE) and silicone rubber containing vinyl group (PMVS) to obtain grafted and crosslinked blends. Two methods involving the use of free radicals generated from (a) thermomechanical shear and (b) peroxide decomposition were used to prepare the LLDPE/PMVS blends. The occurrence of grafting and crosslinking of the PMVS molecular chains was deduced by considering the mixing torque, solvent extraction data and evidence from the Fourier transform infrared spectra (FTIR), as well as differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The experimental results indicated that reactive blending significantly improved the interfacial adhesion between the two phases and that peroxide decomposition had a higher initiation efficiency in respect of grafting and crosslinking than thermomechanical shear. Thermogravimetric analysis (TGA) showed that reactive blending with PMVS improved the thermal stability of LLDPE. Dynamic rheological behaviour and melt flow rate (MFR) results suggested that grafting and crosslinking between the two components increased the viscoelasticity of the blends and the addition of PMVS improved the processability of the LLDPE. Crosslinking by peroxides gave a higher tensile strength than thermomechanical shear but a lower elongation at break. The limiting oxygen index (LOI) test indicated that the flame retardancy of the LLDPE/PMVS blend increased with increasing amounts of PMVS.

Rheological properties in blends of poly(aryl ether ether ketone) and liquid crystalline poly(aryl ether ketone)

AbstractRheological properties of the blends of poly(aryl ether ether ketone) (PEEK) with liquid crystalline poly(aryl ether ketone) containing substituted 3‐trifluoromethylbenzene side group (F‐PAEK), prepared by solution precipitation, have been investigated by rheometer. Dynamic rheological behaviors of the blends under the oscillatory shear mode are strongly dependent on blend composition. For PEEK‐rich blends, the systems show flow curves similar to those of the pure PEEK, i.e., dynamic storage modulus G′ is larger than dynamic loss modulus G″, showing the feature of elastic fluid. For F‐PAEK‐rich systems, the rheological behavior of the blends has a resemblance to pure F‐PAEK, i.e., G″ is greater than G′, showing the characteristic of viscous fluid. When the PEEK content is in the range of 50–70%, the blends exhibit an unusual rheological behavior, which is the result of phase inversion between the two components. Moreover, as a whole, the complex viscosity values of the blends are between those of two pure polymers and decrease with increasing F‐PAEK content. However, at 50% weight fraction of PEEK, the viscosity‐composition curves exhibit a local maximum, which may be mainly attributed to the phase separation of two components at such a composition. The changes of G′ and G″ with composition show a trend similar to that of complex viscosity. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4040–4044, 2006

Dynamic rheological behavior of polypropylene melts with pulsatile pressure flow in a dynamic capillary rheometer

AbstractA self‐made dynamic capillary rheometer (DCR) was designed to investigate the dynamic viscoelastic characteristic of polypropylene (PP) melt during the pulsatile pressure extrusion. A vibration force field was parallel superposed upon steady shear flow in this DCR by means of a vibration driven piston. During the pulsatile pressure extruding process in DCR, the PP melt displayed apparent viscoelasticity. The experiment results proved the pressure pulsatile extrusion could reduce the viscosity of polymer melts effectively. The phase difference between the shear stress and the shear rate decreased with the superposed vibration. But, at large amplitude conditions, the viscosity has an increasing tendency. This maybe illuminated that large amplitude could be harmful for the vibration‐assistant polymer processing. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1834–1838, 2006

Rheological properties of concentrated aqueous injectable calcium phosphate cement slurry

In this paper, the steady and dynamic rheological properties of concentrated aqueous injectable calcium phosphate cement (CPC) slurry were investigated. The results indicate that the concentrated aqueous injectable CPC showed both plastic and thixotropic behavior. As the setting process progressed, the yield stress of CPC slurry was raised, the area of the thixotropic hysteresis loop was enlarged, indicating that the strength of the net structure of the slurry had increased. The results of dynamic rheological behavior indicate that the slurry presented the structure similar to viscoelastic body and the property of shear thinning at the beginning. During the setting process, the slurry was transformed from a flocculent structure to a net structure, and the strength increased. Different factors had diverse effects on the rheological properties of the CPC slurry in the setting process, a reflection of the flowing properties (or injection), and the microstructure development of this concentrated suspension. Raising the powder-to-liquid ratio decreased the distance among the particles, increased the initial strength, and shortened the setting time. In addition, raising the temperature improved the initial strength, increased the order of reaction, and shortened the setting time, which was favorable to the setting process. The particle size of the raw material had much to do with the strength of original structure and setting time. The storage module G' of CPC slurry during the setting process followed the rule of power law function G'=A exp(Bt), which could be applied to forecast the setting time, and the calculated results thereafter are in agreement with the experimental data.

Relaxation behavior of polymer blends with complex morphologies: Palierne emulsion model for uncompatibilized and compatibilized PP/PA6 blends

This paper deals with the dynamic rheological behavior of polypropylene/polyamide6 (PP/PA6) uncompatibilized blends and those compatibilized with a maleic anhydride grafted PP (PP/PP-g-MAH/PA6). The terminal relaxation times of the blends predicted by the Palierne emulsion model were compared with those obtained from experimental relaxation time spectra. The Palierne model succeeded well in describing PP/PA6 uncompatibilized blends with relatively low dispersed phase contents (10wt%) and failed doing so for those of which the dispersed contents were high (30wt%). It also failed for the compatibilized ones, irrespective of the dispersed phase content (10 or 30wt%) and whether or not interface relaxation was taken into consideration. In the case of the uncompatibilized blend with high dispersed-phase content, interconnections among inclusions of the dispersed phase were responsible for the failure of the Palierne model. As for the compatiblized blends, in addition to particle interconnections, the existence of emulsion-in-emulsion (EE) structures was another factor responsible for the failure of Palierne model. A methodology was developed to use Palierne emulsion model upon taking into account the effects of the EE structure on the viscosity of the continuous phase and the effective volume fraction of the dispersed phase.

Polyurethane acrylate microgel synthesized by emulsion polymerization using unsaturated self-emulsified polymer

Polyurethane (PU) acrylate microgels were obtained by emulsion polymerization of self-emulsified PU acrylate terminated by 2-hydroxyethyl methacrylate without any extra emulsifier and crosslinker. Moreover, the PU acrylate was also used as stabilizer and crosslinker to synthesize poly(methyl methacrylate) (PMMA)–PU composite microgels via emulsion polymerization, which provided a new method to synthesize PU microgels and their composite microgels. The kinetics of microgel synthesis was studied by gel permeation chromatography. The dynamic rheological behaviors indicated that a crosslinked structure was formed. The frequency dependency of the loss tangent and complex viscosities showed strong relationships with the microgel structure. Those microgels with rigid PMMA core showed higher ability to slide than the soft PU acrylate microgel, which had influence on the changing of loss tangent with frequency. All the microgels swollen in tetrahydrofuran exhibited high viscosities and strong shear-thinning behaviors. As a sort of flexible microgel, the PU microgel was able to form a coherent film at room temperature, which was distinct from hard microgels.