Stress Growth Experiments Research Articles

A new class of Finitely Extensible Nonlinear Elastic FENE-P model obtained with a thermodynamical approach and the use of compressible natural configurations. Part I: Isothermal deformations

In a recent contribution to the fundamental understanding of polymer fluid dynamics, Khambhampati and Rajagopal (2021) established a connection between the natural configuration theory of Rajagopal and Srinivasa (2000) and the FENE-P model of Bird et al. (1987 [6]). In this paper we capitalize on the result in Khambhampati and Rajagopal (2021) and present a new class of FENE-P models using a more general Helmholtz potential within the conceptual framework of evolving natural configurations. To show its qualitative behavior, we exemplify with a classical Couette flow between infinite parallel plates. The model is capable of reproducing key features experimentally observed such as stress relaxation and the overshoot of the shear stress at the beginning of typical shear stress growth experiments. Comparison against the FENE-P type model obtained in Khambhampati and Rajagopal (2021) is used for comparison.

Effects of superabsorbent polymers (SAP) on the rheological behavior of cement mortars: A rheological study on performance requirements for 3D printable cementitious materials

While the potential of incorporating superabsorbent polymers (SAP) as an additive in 3D printing cementitious materials has been a subject of interest recently, little research has been conducted on the effects of SAP incorporation on the rheological properties of cement mortars and the required performance of 3D printable cementitious materials when no other additives, such as superplasticizer (SP), are present or when SAP is added up to 1.0% by weight of the binder. Accordingly, the effects of SAP on the rheological behavior of cement mortar were analyzed in this study from the perspective of the performance requirements for 3D printable material with the SAP dosage (0%, 0.5%, and 1.0% by weight of cement), SAP particle size (100–180 and 355–425 μm), and superplasticizer (SP) presence (polycarboxylate-ether) as variables. The rheological properties of cement mortars with the same initial slump flow (180 mm ± 5 mm) were measured using a vane rotational rheometer, and their conformance to the performance requirements for 3D printable cementitious materials was studied. Static yield stress, dynamic yield stress, and plastic viscosity were calculated for each specimen using measured torque data obtained from the stress growth and flow curve experiments. The ratios of static to dynamic yield stress, plastic viscosity, and thixotropic areas were analyzed from the perspective of pumpability and extrudability, whereas the yield stress evolution and structural build-up rate were analyzed from the perspective of buildability. The results demonstrated that although the rheological properties of the SAP-incorporated cement mortar with a low water–cement ratio were similar to those of the SAP-incorporated cement mortar with a high water–cement ratio when SP was incorporated, the change in rheological properties with time and shear differed. SAP incorporation promoted the structuration of the mixtures without SP that have a high water–cement ratio due to the physical effects of SAP particles, but the effect was reversed in the mixtures with SP and a low water–cement ratio due to the water migration kinetics associated with SAP. Because a low water–cement ratio with SP is commonly applied for 3D printable materials, the findings of this study indicate that the water migration kinetics of SAP critically determines the printability of cementitious materials mixed with SAP. Given that observed effects are substantial, SAP arguably has potential as a rheology modifier for 3D printable cementitious materials.

Super enhancement of rheological properties of amorphous PLA through generation of a fiberlike oriented crystal network

Blends containing 85 wt. % of an amorphous polylactide with 15 wt. % of three different semicrystalline PLA (cPLA) grades with different crystallizabilty were separately blended via a twin-screw extruder below the melting temperature of the cPLAs. The extrudates were either directly pelletized or pelletized after being drawn at a draw ratio of 10. The small amplitude oscillatory shear behavior of the samples revealed that while the rheological properties of the undrawn samples were enhanced, those of the drawn samples were much more dramatically increased. In undrawn samples, the enhancements were due to the presence of unmelted crystal clusters, which could form a solid network structure in the blend. The much more pronounced increases in drawn samples, however, were due to the transformation of the crystal clusters into the fiberlike oriented crystal network, which formed a stronger solid network. This reinforcing behavior in both undrawn and drawn samples was even more pronounced when cPLA with a higher degree of crystallinity and a higher melting temperature was used. In drawn samples, the stress growth experiments confirmed the formation of such oriented crystal structure during which the primary overshoot caused by the crystal network structure could be formed again after molecular relaxation. This was while, in undrawn samples, stress overshoots were barely visible.

Effect of branching on flow-induced crystallization of poly (lactic acid)

Using rheometry in this study, we comprehensively investigated the effect of shear and extensional flow fields on the crystallization behavior of linear and branched poly(lactic-acid) (PLA). The shear-induced isothermal crystallization was explored in a stress-growth experiment during which continuous low shear rates of 0.01 and 0.1 s−1 were applied at a given temperature. To examine the effect of strong shear flow on the crystallization of PLAs, the samples were pre-sheared at high shear rates of 1 and 10 s−1 and subsequently isothermally crystallized at 140 °C. Results revealed that, at a given deformation rate, branched PLA exhibited a much faster crystallization rate than that of linear PLA. Also, altering the deformation rate at low shear rates could hardly affect the crystallization kinetics of both PLAs whereas the crystallization was strongly dependent on the shear rate value when pre-sheared at strong shear flows. The elongational flow-induced crystallization behavior of branched PLA by means of rheometry was also explored for the first time. It was shown that the elongational flow introduced a much more pronounced influence on branched PLA crystallization kinetics than that induced by the shear flows. The crystallization kinetics and structure of the sheared and stretched branched PLA samples were also investigated and confirmed using a differential scanning calorimeter (DCS), and wide- and short-angle X-ray scattering (WAXS and SAXS).

Rheological characterization of a polyethylene melt, filled with different concentrations of fumed silica at 453 K

Fumed silica is widely used as filler / thickening agent to increase the viscosity or to change the flow behavior type of a suspension. Strong hydrogen bonds between silica-silica and silica-matrix can lead to a suspension with a yield stress. We wanted to know if fumed silica can also form a three-dimensional network in a polyethylene melt at 453 K. The systems with the polyethylene LDPE 1810H (LDPE) filled with different concentration of the fumed silica Cab-o-sil TS720 (silica) were investigated with the MCR300 rheometer from Anton Paar at 453 K. The shear stress τ and the 1st normal stress difference were measured simultaneously in stress growth experiments. The points of the flow curves represent the steady state values from the start-up experiments with a constant shear rate. Just after the steady state values are reached, the stress deformation is stopped, and the stress relaxation begins. The relative residual shear stress is an important value. The absence of residual shear stress means that the structure of the system is destroyed in the stress growth experiment and the system has shear-thinning flow behavior. The systems with high residual shear stress form a strong network that leads to a system with plastic flow behaviour with a yield stress. The shear stress changes insignificantly in the yield stress region with the shear rate. The yield stress can be determined also from the relative residual shear stress curve.

Structural recovery mechanism after shear induced orientation of multiwalled carbon nanotube in polypropylene matrix

In this work the flow induced orientation and the governing mechanism of structural recovery of multi-walled carbon nanotube (MWCNT) filled polypropylene nanocomposites were investigated. A series of linear and nonlinear melt rheological measurements including stress growth and time sweep experiments were performed at different temperatures to study the structural breakdown, nanoparticles orientation, subsequent structural recovery and MWCNT loadings. The results showed that the structural recovery occurred in two stages. The first stage, initial agglomeration, showed a quick recovery which was independent of temperature, can be interpreted in terms of inter-particle van der Waals interactions. This structural recovery stage had major contribution in the storage modulus increment. The second stage of the recovery, secondary agglomeration, was slower and dependent on temperature, can be attributed to rotary diffusion of nanoparticles. This stage had minor contribution to the storage modulus increase. Storage modulus increment in both of these agglomeration was attributed to the increase of nanotube-nanotube contacts. Both of these stages were confirmed by transmission electron micrographs. These result were in a good agreement with those calculated using van der Waals and diffusion concepts.

Rheological properties of phosphorylated exopolysaccharide produced by Sporidiobolus pararoseus JD-2

The exopolysaccharide (EPS) produced by Sporidiobolus pararoseus JD-2 contained about 2.0% phosphorus and its zeta potential was −30mV at pH 6.0. This indicated that it was an anionic polymer. In steady shear measurements, there was a Newtonian plateau in low shear rates, but power-law behavior exhibited at high shear rates. So Williamson model was used to study the flow character of the EPS solutions. This phenomenon was according to its high molecular weight and entanglement networks. Considering the EPS was an anionic polymer, the influence of added salts on apparent viscosity of EPS were studied. Different NaCl concentrations had little effect on the viscosity of the EPS, but high concentrations of CaCl2 increased the viscosity of EPS significantly. EPS solutions showed inapparent thixotropic properties in stress growth and thixotropic loop experiment. According to the flow curve results and oscillatory shear results obtained, the rheological properties of EPS solutions were closer to that of entanglement network system, like carboxy methyl cellulose rather than weak gel structure such as xanthan gum. The EPS had the function to enhance immunological functions. Understanding the rheological characteristics of EPS was essential to exploit the functionality of this EPS in different food or medicine systems.

Properties of polypropylene and polypropylene/poly(ethylene-co-vinyl alcohol) blend/CNC nanocomposites

Abstract Rheological, mechanical and thermal properties of polypropylene (PP)/cellulose nanocrystal (CNC) nanocomposites were compared with those of nanocomposites containing poly(ethylene-co-vinyl alcohol) used as a compatibilizer (CO). The nanocomposites were prepared by an internal mixer at a CNC content of 5 wt%. The complex viscosity and storage modulus of the nanocomposite sample containing the compatibilizer prepared by a solution method were increased at low frequencies, compared to those of the non-compatibilized nanocomposite samples. Moreover, a pronounced overshoot of the transient viscosity in a shear stress growth experiment was observed for the compatibilized nanocomposite. Scanning electron microscopy (SEM) showed the disappearance of large agglomerates when using the compatibilizer. The Young modulus of the nanocomposite samples containing the compatibilizer was increased up to ca. 47% compared to the neat PP. The elongation at break was decreased in all PP/CNC nanocomposite samples, but less for those containing the compatibilizer. The crystallinity of the PP in the nanocomposites and the crystallization temperature were increased after compatibilization. These results show that the poly(ethylene-co-vinyl alcohol) is an efficient compatibilizer that favors a better dispersion and wetting of the hydrophilic CNCs within the hydrophobic PP phase.

Analysis of Shear Stress Growth Experiments for Linear Constitutive Equations

Shear stress growth curves for viscoelastic fluids at low shear rates are analyzed using two linear rheological constitutive equations, an integral constitutive equation and a mixed type constitutive equation. It is shown that some published solutions do not satisfy all of the pertinent boundary conditions. For the low shear rate region, available experimental shear stress curves show a monotonic increase with decreasing slope in the shear stress. Shear stress curves calculated using a mixed type constitutive equation are found to exhibit this type of behavior while curves calculated using an integral constitutive equation do not. For the mixed type constitutive equation, the calculated developing velocity distribution is used to examine its effect on the developing shear stress distribution. For low values of E (the elasticity number), there is a moderate effect, but, for sufficiently large values of E, the developing velocity distribution has a negligible effect. It is also shown that results consistent with experimental data obtained at low shear rates can be attained using a single relaxation time. Additionally, incompressible Newtonian fluids are considered, and it is found that there can be single maxima in some shear stress curves with no maxima occurring in the velocity curves. Multiple maxima were not obtained in the Newtonian shear stress results unlike some published results.

Large amplitude oscillatory shear rheology of three different shear-thickening particle dispersions

We present a large amplitude oscillatory shear rheology (LAOS) investigation of three different shear-thickening particle dispersions - fumed silica in polyethylene oxide (FLOC), fumed silica in polypropylene glycol (HydroC), and cornstarch in water (JAM). These systems shear-thicken by three different mechanisms - shear-induced formation of particle clusters flocculated by polymer bridging, hydrocluster formation, and jamming. The viscoelastic non-linearities of the three fluids were studied as a function of strain and strain-rate space through the use of Lissajous-Bowditch curves and local nonlinear viscoelastic moduli of an oscillatory shear cycle. The nonlinear behaviors of the three fluids were compared and contrasted to understand the nonlinear shear-thickening mechanism of each. Both HydroC and JAM dispersions were found to exhibit strong strain stiffening of the elastic moduli and strain thickening of the loss moduli behavior associated with possible hydrocluster formation and particle jamming. However, the FLOC dispersion, in contrast, showed strong strain softening and strain thinning behavior at large strain amplitudes associated with yielding of the microstructure. The expected thickening of the loss modulus of FLOC in LAOS with increasing strain was not observed even though viscosity of FLOC was found to shear-thicken in steady-shear measurements. This disagreement is likely due to very large strain amplitudes required for shear-thickening to occur by shear-induced polymer bridging mechanism. The hypothesis was confirmed through stress growth experiments. Conversely, the HydroC and JAM dispersions required relatively small applied strains for shear-thickening to occur by hydrocluster and jamming mechanism. The comparison of local intra-cycle nonlinearity through Lissajous-Bowditch plots and nonlinear viscoelastic parameters indicated that the elastic nonlinearities of all three systems are primarily driven by a strong dependence on the magnitude of the applied strain-rates within an oscillatory cycle rather than the amplitude of the applied strain. A close inspection of the LAOS data reveals strong differences in the viscoelastic nonlinearities of these three different shear-thickening dispersions which can be used to create a nonlinear rheological fingerprint for each and offers valuable new insights into the nonlinear dynamics associated with each of the shear-thickening mechanisms.

Viscoelastic properties of solutions of polystyrene melts and carbon dioxide: Analysis of a transient shear rheology approach

In this work, the viscoelastic, thermal, and diffusion properties of solutions of polystyrene melts and carbon dioxide (CO2) were analyzed using plate–plate rheometry in the transient mode. The objective of this study was to evaluate a transient shear rheology approach for high viscosity polymer melts, to verify superposition principles for polystyrene/CO2 solutions, and to measure the glass transition temperature as a function of pressure and CO2 concentration. Two different procedures of saturating polystyrene with carbon dioxide were applied, i.e., loading with the blowing agent below the glass transition temperature of polystyrene and at the measurement temperature. Stress-growth experiments in shear were performed in order to measure the transient viscosity of polystyrene/CO2 solutions in the linear regime. A shift of the transient viscosity data to a mastercurve was applied in order to determine the shift factor of the viscosity and the average relaxation time. Our data indicate that the steady-state viscosity and the average relaxation time are proportional to the temperature–pressure–concentration shift factor aT,p,c within experimental scatter, and consequently a time–temperature–pressure–concentration superposition principle holds for polystyrene/CO2 solutions. Whereas the viscosity of polystyrene strongly depends on the applied temperature and pressure, the elastic equilibrium compliance depicts only a weak dependence on temperature and pressure.

Nested dipolar Halbach arrays for the determination of magnetorheological properties at variable magnetic field

A new apparatus for the measurement of magnetorheological properties of magnetic fluids in a commercial strain-controlled rheometer is proposed. The new setup makes use of the concept of the Halbach cylinder to generate a homogeneous dipolar magnetic field, using only permanent magnets. Two of these Halbach cylinders are combined, allowing the magnetic field to be varied by simply rotating the cylinders relatively to one another. The magnetic field achieved in the middle of the cylinders varies from nearly zero to about 0.6 T without a significant variation on the high homogeneity (ΔB/B < 2 × 10 − 2) of the resulting field. To perform the rheological experiments inside a strong magnetic field, measurement geometries (concentric cylinders and a four-bladed vane) were constructed from a non-magnetic material (polyoxymethylene). For the first experiments with the new setup, a commercial magnetic suspension of carbonyl iron particles in hydrocarbon oil was investigated. Stress growth experiments at varying shear rates in the steady shear regime, as well as strain sweep experiments at constant frequency in the dynamic oscillatory regime, were performed. The results show a shift of the linear (elastic) regime in oscillatory shear to higher strain values for increasing magnetic field. The steady shear viscosity increases with increasing magnetic field. The behaviour of the magnetic suspension was understood in the context of the ratio from the viscous to the polarisation forces, the so-called Mason number.

Rheology of LDPE‐based semiflexible fiber suspensions

AbstractMolten LDPE suspensions containing fibers of different flexibilities have been investigated in simple shear and small and large amplitude oscillatory shear (LAOS) flow. The suspensions exhibited viscosity and normal stress overshoots in stress growth experiments, and the magnitude and width of the overshoots became larger as the fiber flexibility increased. LAOS was used to help understanding the relationship between stress growth and fiber orientation. For all composites, the stress signal decreased with time in LAOS, and this behavior was more pronounced in the case of the more rigid fibers. The energy dissipated per LAOS cycle was evaluated for each composite, and it showed that less energy was dissipated as fiber flexibility decreased. In addition, the dissipated energy decreased with time and this has been interpreted in terms of a reduction of fiber contacts. The first normal stress difference showed a nonsinusoidal periodic response, and fast Fourier transform analysis indicated the presence of a first harmonic corresponding to the applied frequency for the fiber‐filled systems, in addition to the second harmonic observed for the neat LDPE. It resulted in asymmetrical strain‐normal force Lissajou curves for the suspensions, with this asymmetry being more pronounced in the case of the more rigid fibers. This has been attributed to a more extensive fiber orientation for the latter. POLYM. COMPOS., 31:1474–1486, 2010. © 2009 Society of Plastics Engineers

Rheological properties and microstructural evolution of semi-flexible fiber suspensions under shear flow

The mechanical properties of fiber-reinforced polymers are highly dependent on fiber orientation. A key factor is fiber flexibility, which varies with the intrinsic properties of the fiber, its aspect ratio, and the force of the flow field. In this work, the rheological behavior of model suspensions consisting of a Newtonian silicone oil and fibers with different flexibilities has been studied in transient shear flow. The viscous and elastic properties of the fiber suspensions were shown to increase markedly with fiber flexibility. The suspensions exhibited a viscosity overshoot in stress growth experiments and the magnitude and width of the overshoot became larger as the fiber flexibility increased. The evolution of the suspensions microstructure has also been monitored at different shear rates. The components of the second-order orientation tensor at different times (or strain) were calculated using the images obtained from the visualization experiments. Those experiments showed that fiber orientation was dependent on shear rate and magnitude of applied strain. At low shear rates, rigid fibers oriented to a larger extent in the flow direction as compared to more flexible fibers and their orientation was also faster. Finally, a mesoscopic model in the framework of the general equation for non-equilibrium reversible-irreversible coupling (GENERIC) has been used to predict the rheological behavior of semi-flexible fiber suspensions as well as their microstructure. The model takes into account fiber-fiber interactions and also the semi-flexible nature of the fibers. The predictions of the model are in good qualitative agreement with the rheological and visualization data.

Experimental and theoretical studies of agglomeration effects in multi-walled carbon nanotube-polycarbonate melts

In this study we report on morphological and rheological characterization of multi-walled carbon nanotube (MWNT)-polycarbonate composites produced by injection molding. The main focus is to carry out nonlinear viscoelastic experiments that allow following the structural rearrangements of carbon nanotubes in the polycarbonate melt. Small angle X-ray scattering reveals only a slight orientation of MWNTs in the as-received samples, i.e. after application of extremely high shear rates. Thus, the main structural effect observed during the stress growth experiment is the breakage of MWNT agglomerates. To study this effect in detail a flocculation experiment, in which the sample undergoes oscillatory deforma- tion first at a small strain amplitude in the linear regime succeeded by higher amplitudes in the nonlinear regime, has been carried out. The agglomeration process manifests itself in an increase of the storage and loss moduli in the linear regime, whereas the deagglomeration process does vice versa. The corresponding effects can be described in the frame of a super- position approach that takes into account the stress contribution of the polycarbonate matrix, the hydrodynamic reinforce- ment due to embedded nanotubes and the viscoelastic stress due to the presence of a MWNT-network.

Transient shear flow of model lithium lubricating greases

This paper deals with the analysis of the transient shear flow behavior of lithium lubricating greases differing in soap concentration and base oil viscosity. The shear-induced evolution of grease microstructure has been studied by means of stress-growth experiments. With this aim, different lubricating grease formulations were manufactured by modifying the concentration of lithium 12-hydroxystearate and the viscosity of the base oil, according to a RSM statistical design. Moreover, atomic force microscopy (AFM) observations were carried out. The transient stress response can be successfully described by the generalized Leider-Bird model based on two exponential terms. Different rheological parameters, related to both the elastic response and the structural breakdown of greases, have been analysed. In this sense, it has been found that the elastic properties of lithium lubricating greases were highly influenced by soap concentration and oil viscosity. The stress overshoot, τ max , depends linearly on both variables in the whole shear rate range studied, although the effect of base oil viscosity on this parameter is opposite at low and high shear rates. Special attention has been given to the first part of the stress-growth curve. In this sense, it can be deduced that the “yielding” energy density not only depends on grease composition, but also on shear rate. Moreover, an interesting asymptotic tendency has been found for both the “yielding” energy density and the stress overshoot by increasing shear rate. The asymptotic values of these parameters have been correlated to the friction coefficient obtained in a ball-disc tribometer.

Determination of the onset of shear thinning of polydimethylsiloxane

AbstractThe shear stress and the first normal stress difference were simultaneously measured in shear flow start‐up experiments and a subsequent stress relaxation. The measured polydimethylsiloxane show shear thinning flow behavior with a first Newtonian region up to the shear rate at the onset of shear thinning. We found that the shear stress and the first normal stress difference have an equal shear rate at the onset of shear thinning. The shear stress at the onset of shear thinning does not depend on the molecular weight of the polymer and on temperature. Similar to the viscosity master curve, it is possible to create a normal stress master curve, outgoing from the first normal stress coefficient. The shear rate at the onset of shear thinning is estimated from the viscosity master curve and the shear rate at the onset of normal stress thinning from the normal stress master curve. The shear stress and the first normal stress difference have similar transient behavior with start‐up stress curves without maximum in stress growth experiments with shear rates from the first Newtonian region. The shear flow start‐up experiment with the shear rate at the onset of shear thinning leads to the first indication of an overshoot of the start‐up curve. The shear flow start‐up experiments with shear rates from the shear thinning region show start‐up curves with a maximum for the shear stress and for the first normal stress difference. It was found that the shear rate at the onset of shear thinning and the shear rate at the onset of normal stress thinning, determined by the shear flow start‐up measurements, are equal to the values obtained from the master curves. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008

A Rheotens-based setup for the constant strain rate uniaxial extension of uncured elastomers

A novel experimental setup for the uniaxial extension of uncured elastomers is presented, and room temperature experiments at constant Hencky strain rate are performed by means of a commercial Rheotens tensile tester originally designed for the determination of the melt strength of polymer melts. Successful results are obtained for materials related to many aspects of the elastomers production, namely, gum elastomers and carbon black compounds. Stress growth experiments are reported for filled and unfilled high-cis-polybutadiene, and the extensional behavior is related to the carbon black dispersion. Although originally thought as an experimental tool for polymer melts, the proposed Rheotens setup can also perform constant strain rate tensile testing on thermoplastic rubbers. Stress-strain experiments are performed on a microphase separated polystyrene-b-poly(ethylene butylene)-b-polystyrene (SEBS) copolymer and related blends with polypropylene, showing the effect of a constant deformation rate on the network response. Relaxation experiments after cessation of extensional flow are also reported for the investigated materials. With respect to commonly used tensile testing procedures for elastomers at constant elongation rate and time decreasing strain rate, a complete and accurate investigation of the extensional behavior of many uncured elastomers can be carried out with the additional advantage of using a reduced amount of material.

Stress overshoots of organoclay nanocomposites in transient shear flow

Forward and reverse stress growth experiments have been conducted on polypropylene/organoclay nanocomposites containing the same clay loading but characterized by different microstructures. Stress overshoots have been observed for the initial start-up experiments and for the following reverse start-up experiments after a certain rest time. The amplitude of these overshoots increased with the applied shear rate and rest time, but the overshoots occurred at the same strain of about 1.7. The overshoots are related to the structure of the nanocomposites, in particular the magnitude of the overshoots increased with the degree of the clay exfoliation in the matrix. Two models, initially developed for colloidal suspensions and fiber suspensions, have been used to describe the observed phenomena. The overshoots are fairly well predicted by the first (structure network) model and explained by the competing effects of the structure breakdown under flow and reorganization during rest time. However, the model predicts that the shear stress following the overshoot decreases and reaches steady-state too rapidly. The second model developed for ellipsoid suspensions describes quite well the stress overshoots for the initial forward flow, but no effect of rest time is predicted. A modified version has been proposed by adding a molecular diffusivity contribution in the Folgar–Tucker equation. The effect of the particle disorientation is qualitatively predicted, but the kinetics is too slow compared to that deduced from experiments.

Effects of compatibilization on rheological properties of PS/PB blends and investigation of Doi–Ohta scaling relationship in double start-up of shear experiments

The rheological properties for the blends of polystyrene and polybutadiene were investigated and the effect of compatibilizer styrene butadiene rubber (SBR), on the blends were studied and the results compared with the non-compatibilized blends. The frequency sweep, step shear strain and shear stress growth experiments were carried out for the blends. The results showed that with addition of compatibilizer the changes in behavior of the rheological properties of blends are observed. These rheological variations could be related to the reduction of interfacial tension and size of dispersed phase. Furthermore, the validity of Doi–Ohta scaling relationship in double start-up experiments was studied. It is shown that this scaling relationship becomes more reliable with increasing the amount of PB and compatibilizer.