Melt rheological behavior of intimately mixed short sisal–glass hybrid fiber‐reinforced low‐density polyethylene composites. I. Untreated fibers

The melt rheological behavior of intimately mixed short sisal–glass hybrid fiber‐reinforced low‐density polyethylene composites was studied with an Instron capillary rheometer. The variation of melt viscosity with shear rate and shear stress at different temperatures was studied. The effect of relative composition of component fibers on the overall rheological behavior also was examined. A temperature range of 130 to 150°C and shear rate of 16.4 to 5470 s^?1 were chosen for the analysis. The melt viscosity of the hybrid composite increased with increase in the volume fraction of glass fibers and reached a maximum for the composite containing glass fiber alone. Also, experimental viscosity values of hybrid composites were in good agreement with the theoretical values calculated using the additive rule of hybrid mixtures, except at low volume fractions of glass fibers. Master curves were plotted by superpositioning shear stress and temperature results. The breakage of fibers during the extrusion process, estimated by optical microscopy, was higher for glass fiber than sisal fiber. The surface morphology of the extrudates was analyzed by optical and scanning electron microscopy. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 432–442, 2003     

Melt rheological behavior of intimately mixed short sisal–glass hybrid fiber‐reinforced low‐density polyethylene composites. II. Chemical modification

The effect of chemical modification of both fiber and matrix on melt rheological behavior of intimately mixed short sisal–glass hybrid fiber‐reinforced low‐density polyethylene composites was studied with an Instron capillary rheometer. The variations of melt viscosity with different shear rate and shear stress values for different temperatures were studied. A temperature range of 130 to 150°C and shear rates of 16.4 to 5468 s^?1 were chosen for the analysis. Chemical modifications with stearic acid, maleic anhydride, silane, and peroxides were tested for their ability to improve the interaction between the matrix and fiber. The viscosity of the hybrid composites increases with every chemical modification. In the case of peroxide‐treated composites, the increase can be attributed to the peroxide‐induced grafting of the polyethylene matrix to the fiber surface and to the crosslinking of the polyethylene matrix. These phenomena are both activated by temperature, whereas temperature causes a reverse effect for all other chemical modifications. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 443–450, 2003     

Rheological characterization of PP/jute composite melts

The present article summarizes an experimental study on the molten viscoelastic behavior of PP/jute composites under steady and dynamic mode. Variations in melt viscosity and die swell of the composites with an increase in shear rate, fiber loading, and coupling agent concentration have been investigated using capillary rheometer. It was observed that with the addition of fibers and MAPP, the melt viscosity of the composites increased due to improved fiber‐matrix interfacial adhesion. Further, the dynamic viscoelastic behavior, measured using parallel plate rheometer, revealed an increase in the storage modulus (G′), indicating higher stiffness in case of fiber‐filled composites as compared with the virgin matrix. Time–temperature superposition was applied to generate various viscoelastic master curves. The fiber‐matrix morphology of the extrudates was also examined using scanning electron microscopy, which corroborated the findings of rheological properties. The treated composites displayed uniform distribution of fibers within the PP matrix with lesser surface irregularities. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1476–1484, 2006     

Comparison of superimposed effects in high‐shear‐rate capillary rheology of polystyrene,polypropylene, and linear low‐density polyethylene melts

Polymer melts exhibit unique rheological behaviors at high shear rate up to 10⁶ s^?1, which is a common phenomenon in micro‐injection molding. Both online and commercial capillary rheometers, which were modified to allow regulation of back pressure, were used for measuring the melt shear viscosities of polystyrene (PS), polypropylene (PP), and linear low‐density polyethylene (LLDPE) under high shear rates. The rheological characteristics of the three melts were compared through the systematical analyses for three significant effects, namely the end pressure loss, pressure dependence, and dissipative heating in capillary flow. Pronounced end effect begins to appear at the shear rates of 1.6 × 10⁵, 8.0 × 10⁵, and 2.8 × 10⁶ s^?1 for the PS, PP, and LLDPE melts, respectively. The significance of the end effect can be ordered as PS > PP > LLDPE. It seems that the polymers with more complex molecular structures exhibit a higher degree of divergence between the comprehensively corrected and uncorrected melt viscosity curves. Moreover, the dissipation effect begins to predominate over the pressure effect under the lowest shear rate of 10⁵ s^?1 for the PS melt among the three melts. POLYM. ENG. SCI., 55:506–512, 2015. © 2014 Society of Plastics Engineers     

Effect of nano‐silica filler on the rheological and morphological properties of polypropylene/liquid‐crystalline polymer blends

A fumed hydrophilic nano‐silica‐filled polypropylene (PP) composite was blended with a liquid‐crystalline polymer (LCP; Rodrun LC5000). The preblended polymer blend was extruded through a capillary die; this was followed by a series of rheological and morphological characterizations. The viscosity of the PP matrix increased with the addition of the hydrophilic nano‐silica. At shear rates between 50 and 200 s^?1, the composite displays marked shear‐thinning characteristics. However, the incorporation of LC5000 in the PP composite eliminated the shear‐thinning characteristic, which suggests that LC5000 destroyed the agglomerated nano‐silica network in the PP matrix. Although the viscosity ratio of LCP/PP was reduced after the addition of nano‐silica fillers, the LCP phases existed as droplets and ellipsoids. The nano‐silicas were concentrated in the LC5000 phase, which hindered the formation of LCP fibers when processed at high shear deformation. We carried out surface modification of the hydrophilic nano‐silica to investigate the effect of modified nano‐silica (M‐silica) on the morphology of the PP/LC5000 blend system. Ethanol was successfully grafted onto the nano‐silica surface with a controlled grafting ratio. The viscosity was reduced for PP filled with ethanol‐M‐silica when compared to the system filled with untreated hydrophilic nano‐silica. The LC5000 in the (PP/M‐silica)/LC5000 blend existed mainly in the form of fibrils. At high shear rates (e.g., 3000 s^?1), the LC5000 fibril network was formed at the skin region of the extrudates. The exclusion of nano‐silica in the LC5000 phase and the increased viscosity of the matrix were responsible for the morphological changes of the LCP phase. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1484–1492, 2003     

Glass-fiber-reinforced polypropylene/EPDM blend. I. Melt rheological properties

Melt rheological properties of the blend of isotactic polypropylene (PP) and ethylene propylene diene rubber (EPDM) at varying ratios and of the glass fiber (GF) filled PP and PP/EPDM blend by varying both GF loading and blending ratio of the polyblend matrix are studied. Rheological measurements at 220°C in shear rate range 10¹?10⁴s^?1 were made on a capillary rheometer. Scanning electron micrographs of the extrudates are presented to show the morphology and the alignment of the glass fibers with respect to the flow direction. Variations of pseudoplasticity index, melt viscosity, and melt elasticity with EPDM content in PP/EPDM blend, and with varying GF content at any given composition of the matrix in PP/EPDM/GF ternary system, in the studied range are presented and discussed. Resultes on melt viscosity and melt elasticity show (i) reduced effect of GF at high shear rates on these properties and (ii) upward deviation of melt viscosity versus shear rate curve at low shear rates. A change in flow behavior in presence of GF is observed around a critical shear rate 2 × 10³ s^?1 and is attributed to the difference of interaction of GF and the dispersed rubber droplets at high and low shear rates. Elastic recovery showed nonequilibrium behavior at low shear rates.     

Superimposed effects in high‐shear‐rate capillary rheology of polystyrene melt

During micro‐injection molding, the polymer melt may undergo a shear rate up to 10⁶ s^?1, at which the rheological behaviors are obviously different from those in conventional molding process. Using both online and commercial rheometers, high‐shear‐rate capillary rheology of polystyrene (PS) melt is analyzed systematically in this work. The accurate end pressure drop and pressure coefficient of viscosity are determined via the enhanced exit pressure technique. Experimental and theoretical investigations are conducted on four significant effects, that is, the dissipative heating, end pressure loss, pressure dependence, and melt compressibility in capillary flow. For the PS melt, which exhibits distinct temperature and pressure dependence of viscosity, both dissipation and end effects become pronounced as the shear rate exceeds 2 × 10⁵ s^?1. From lower to higher shear rates (10³–10⁶ s^?1), the competition between dissipation and pressure effects results in the overestimation to underestimation of Bagley‐corrected pressure drop, and finally the comprehensively corrected viscosity becomes about half of the uncorrected one owing to the enhanced superimposed effects. Moreover, the compressibility shows a minor influence on the shear viscosity. Under the shear rate range investigated, the power‐law relationship is sufficient for describing the corrected viscosity curve of PS melt used. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Rheological Properties of Short Polyester Fiber-Polyurethane Elastomer Composite with Different Interfacial Bonding Agents

The rheological behavior of a short-polyester-fiber-filled polyurethane elastomer composite containing different bonding agents has been studied in the temperature range 120–160°C and in the shear rate range 63–608s^?1. The composite with and without bonding agents showed a pseudoplastic behavior which decreased with the increase of temperature. Composites containing bonding agents based on polypropyleneglycol and 4,4′-diphenylmethane-diisocyanate showed the lowest viscosity values at a particular shear rate, whereas composites containing a glycerol-(GL) based bonding agent showed the highest viscosity. The viscosity of the composite decreased sharply after a particular temperature (140°C) and the fall was less drastic in the composite containing a GL-based bonding agent.     

Melt fracture behavior of polypropylene‐type resins with narrow molecular weight distribution. I. Temperature dependence

Polypropylene (PP)‐type resins with narrow molecular weight distribution, such as PP‐type thermoplastic elastomer PER and controlled‐rheology PP (CRPP) made by peroxide degradation of high molecular weight PP, have a problem of easy generation of skin roughness at extrusion. To examine the present state, the occurrence of skin roughness in PER and CRPP at extrusion was investigated with a capillary rheometer in a shear rate range of 12–6100 s^?1 and a temperature range of 180–280°C. A homo‐PP (HPP) and a block‐PP (BPP) with usual molecular weight distributions were used for comparison. HPP and BPP with usual molecular weight distributions show smooth extrudates at low shear rates and abruptly generate severe skin roughness “elastic failure” originating at the die entrance at a higher shear rate. PER and CRPP with narrow molecular weight distributions easily generate “sharkskin” melt fracture originating at the die exit, from a shear rate nearly one decade lower than rates of elastic failure of HPP and BPP. The sharkskin becomes more severe, with increasing shear rate, and attains to the elastic failure. The critical shear rate at which sharkskin occurs increases with increasing extrusion temperature. The critical shear rate is about 20 s^?1 at 180°C and about 120 s^?1 at 280°C, which is in the range encountered by the molten resin at extrusion processing. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2111–2119, 2002     

Effects of carbon fillers on the rheology of highly filled liquid‐crystal polymer based resins

Adding conductive carbon fillers to insulating resins increases the composite electrical and thermal conductivity. Often, enough of a single type of carbon filler is added to achieve the desired conductivity while still allowing the material to be molded into a bipolar plate for a fuel cell. In this study, various amounts of three different carbons (carbon black, synthetic graphite particles, and carbon fiber) were added to Vectra A950RX liquid‐crystal polymer. The rheological properties of the resulting single‐filler composites were measured. In addition, the rheological properties of composites containing combinations of different carbon fillers were studied via a factorial design. In all cases, the viscosity increased with increasing filler volume fraction and followed a shear‐thinning power‐law model. The factorial design results indicated that each of the single fillers and all the filler combinations caused a statistically significant increase in the composite viscosity when compared at a shear rate of 500 s^?1 or at a stress of 10⁵ Pa. For composites containing synthetic graphite particles and/or carbon fiber, the viscosity variation with the volume fraction of carbon followed a modified Maron–Pierce equation. When compared at a constant volume fraction of carbon, composites containing carbon black showed viscosity enhancement above and beyond that shown by the other composites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Rheological behaviors of glass bead‐ and wollastonite‐filled polypropylene composites modified with thermoplastic elastomers

Steady‐ and oscillatory‐shear rheological behaviors of polypropylene/glass bead (PP/GB) and PP/wollastonite (PP/W) melts modified with thermoplastic elastomers, poly(styrene‐b‐ethylene‐co‐butylene‐b‐styrene) copolymer (SEBS) and the corresponding block copolymer grafted with maleic anhydride (SEBS‐g‐MA), were examined by means of a parallel‐plate rheometer. With adding the elastomers (SEBS and SEBS‐g‐MA) and fillers (spherical GB and acicular W) to PP, viscosity especially at low shear rates and shear‐thinning flow behavior at high shear rates were pronounced as evidenced quantitatively by Carreau–Yasuda (CY) parameters, but Cox–Merz analogy became weakened. Besides, melt‐elasticity in terminal region and relaxation time (t_c) in crossing point increased, indicating an enhancement in quasi‐solid behavior of molten PP. Comparing with the elastomers, rheological behaviors of molten PP were more influenced with adding the rigid fillers, especially with W due to distinct acicular shape of W particles. SEBS‐g‐MA elastomer more affected rheological behaviors of the ternary composites than SEBS elastomer, implying that SEBS elastomer and the filler particles behaved individually (i.e., development of separate microstructure) in (PP/GB)/SEBS and (PP/W)/SEBS ternary composites, but core‐shell microstructure developed with strong interfacial adhesion by adding SEBS‐g‐MA elastomer, and the filler particles encapsulated with the thick SEBS‐g‐MA elastomer interlayer (i.e., core‐shell particles) acted like neither big elastomer particles nor like individual rigid particles in melt‐state. Moreover, effects of SEBS‐g‐MA elastomer reached a maximum on rheological behaviors of (PP/W)/SEBS‐g‐MA ternary composite, indicating a synergy between core‐shell microstructure and acicular W particles. Correlations between oscillatory‐shear flow properties and microstructures of the blends and composites were evaluated using Cole–Cole (CC), Han–Chuang (HC), and van Gurp–Palmen (vGP) plots. COMPOS., 2012. © 2012 Society of Plastics     

Shear Thinning Behavior of Calcium Silicate‐Based Mold Fluxes at 1623 K

There have been consistent efforts on understanding rheological behavior of molten mold flux, used in continuous casting of steels. It is prevalent view that molten mold flux shows non‐Newtonian behavior, meaning that the viscosity varies with shear rate history. Hence, the present study attempts to evaluate shear thinning, which is one of the characteristic non‐Newtonian behaviors, by measuring its viscosity with a rotating type viscometer at 1623 K. Furthermore, Raman spectroscopy analysis is used to appreciate the structure of molten mold flux and shear thinning. Mold fluxes tested reveal definite shear thinning characteristic of decreasing viscosity with increasing shear rate. The degree of shear thinning has been well quantified by Oswald‐De Waele power law model. Lastly, the degree of polymerization, obtained from Raman spectroscopic data has proportional relationship with degree of shear thinning in the range of 1–5 s^?1 shear rate. Also, it has a downward parabolic relationship with degree of shear thinning at entire shear rate ranges up to 100 s^?1. This study also verifies possibility to use shear thinning behavior on actual continuous casting process.     

Rheological and morphological properties of high‐density polyethylene and poly(ethylene–octene) blends

The rheological and morphological properties of blends based on high‐density polyethylene (HDPE) and a commercial ethylene–octene copolymer (EOC) produced by metallocene technology were investigated. The rheological properties were evaluated in steady and dynamic shear experiments at 190°C in shear rates ranging from 90 s^?1 to 1500 s^?1 and frequency range between 10^?1 rad/s and 10² rad/s, respectively. These blends presented a high level of homogeneity in the molten state and rheological behavior was generally intermediate to those of the pure components. Scanning electron microscopy (SEM) showed that the blends exhibit dispersed morphologies with EOC domains distributed homogeneously and with particle size inferior to 2 μm. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2240–2246, 2002     

Effect of filler treatments on rheological behavior of calcium carbonate and talc‐filled polypropylene hybrid composites

Commercial stearic acid treated calcium carbonate (CaCO₃) was used to make a comparative study on rheological behavior of the CaCO₃ and talc‐filled polypropylene (PP) hybrid composites with nontreated filler. Apparent shear viscosity and extrudate swell were investigated with variation of filler ratio and temperature with 30% by weight total of filler was used in PP composite. The Shimadzu capillary rheometer was used to evaluate shear viscosity and shear rate of the composite. It was found that the shear viscosities decrease with increasing shear rate. The apparent shear viscosity of the composite containing the stearic acid treated is slightly lower than untreated filler. Shear thickening behavior at higher shear rate has also shown by 15/15 treated composites at higher temperature about 220°C and investigation by SEM has proved that filler being densely packed at that condition. Treated composites also exhibit lower swelling ratio value than untreated composite, and swelling ratio also decreases linearly with increasing temperature and the die length–diameter ratio. It is believed that dispersion of filler play an important role not only on shear viscosity but also on swelling ratio of PP composite. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5421–5426, 2006     

Rheological properties of new polymer compositions for sand consolidation and water shutoff in oil wells

The rheological properties of some newly developed polymer compositions have been investigated with and without crosslinking. These polymer compositions were developed as a water shutoff and sand consolidation treatment agents for producing oil and gas wells. The effects of several variables on the rheology of the compositions were evaluated over a wide range of temperatures (25–110°C), shear rates (0–500 s^?1), brine percentages (0–15%), crosslinker types and concentrations (0–3%), and polymer concentrations (6–50%). It was found that increasing the shear rate from 0 s^?1 to 100 s^?1 caused shear thinning and reduction of the viscosity of the dilute solutions (6–13%) from 25 cP to ～ 3 cP at 80°C. In contrast, for the concentrated solutions (20–50%), the viscosity dropped slightly in the shear rate range 0–10 s^?1, and subsequently decreased more slowly up to shear rates of 500 s^?1. The viscosities of all polymer solutions dropped by a factor of 2 as the brine concentration increased from 0% to 15%. Finally, aging time coupled with shear rates and higher percentages of crosslinkers accelerate the buildup of viscosity and gelation time of the polymer compositions. For concentrated solutions, shear rates ranging within 0–200 s^?1 accelerated gelation time from 9.75 h to 2–3 h, when they were sheared at 80°C. The polymeric solutions exhibited Newtonian, shear‐thinning (pseudo‐plastic), and shear‐thickening (dilatant) behavior, depending on the concentration, shear rate, and other constituents. In most cases, the rheological behavior could be described by the power law. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Melt rheology and morphology of PP/SEBS/PC ternary blend

Melt rheological properties of the ternary blend of isotactic polypropylene (PP), styreneethylene–butylene–styrene terpolymer (SEBS), and polycarbonate (PC), PP/SEBS/PC, are studied in a wide range of composition, such that PP is the matrix and SEBS and PC are the minor components, with the proportion of one varying from 0 to 30% at various fixed compositions of the other. The respective binary blends, PP/SEBS and PP/PC, studied as the reference systems for interpretation of results on the ternary blends yielded interesting new information about the morphology development and its correlation with melt rheological properties of these binary blends. The studies include the measurement of melt rheological properties on a capillary rheometer in the shear rate range 10¹–10⁴ s^?1 at a fixed temperature of 240°C. The data presented as conventional flow curves are analyzed for the effect of blend composition and shear rate on pseudoplasticity, melt viscosity, and melt elasticity, and role of each individual component is identified. Morphology of dispersed phases of these blends is studied through scanning electron microscopy of the cryogenically fractured and suitably etched surfaces. Variations of morphology with blend composition and shear rate showed interesting correlation with melt rheological properties, which are discussed in detail. An important finding of the morphological studies is that in the PP/SEBS/PC ternary blend the SEBS phase forms two types of morphologies depending on the blend composition and shear rate: (i) simple droplets and (ii) boundary layer at the surface of the PC droplets. © 1993 John Wiley & Sons, Inc.     

Effects of extrusion conditions on rheological behavior of acrylonitrile–butadiene–styrene terpolymer melt

The influence of temperatures and flow rates on the rheological behavior during extrusion of acrylonitrile–butadiene–styrene (ABS) terpolymer melt was investigated by using a Rosand capillary rheometer. It was found that the wall shear stress (τ_w) increased nonlinearly with increasing apparent shear rates and the slope of the curves changed suddenly at a shear rate of about 10³ s^?1, whereas the melt‐shear viscosity decreased quickly at a τ_w of about 200 kPa. When the temperature was fixed, the entry‐pressure drop and extensional stress increased nonlinearly with increasing τ_w, whereas it decreased with a rise of temperature at a constant level of τ_w. The relationship between the melt‐shear viscosity and temperature was consistent with an Arrhenius expression. The results showed that the effects of extrusion operation conditions on the rheological behavior of the ABS resin melt were significant and were attributable to the change of morphology of the rubber phase over a wide range of shear rates. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 606–611, 2002     

Experimental investigation of the rheological behaviors of polypropylene in a capillary flow

The rheological characterization of polymer melts is strongly related to their material properties. In this study, we focused on the rheological behaviors of a polypropylene (PP) melt through a capillary die. With an advanced twin‐bore capillary rheometer with dies measuring 1.0, 0.5, and 0.25 mm in diameter, experiments were performed over a shear‐rate range of 3 × 10² to 5 × 10³ s^?1 at three temperatures, 210, 220, and 230 °C. The results demonstrate that the geometry dependence of the PP viscosity relied on the die diameter and the temperature of the PP melt. The viscosity values of the PP melt in the 0.25‐mm diameter die were higher than were those in the 0.5‐ and 1.0‐mm dies at 220 and 230 °C. However, the viscosity values in all of the tested dies were similar at 210 °C. The tendency for the viscosity to decrease as the temperature of the polymer melt increased weakened in the 0.25‐mm diameter die. As a result, the pressure applied to the PP melt in the 0.25‐mm diameter die increased; this caused a decrease in the free volume between molecules. On the basis of the Barus equation, the contribution of pressure to the changed viscosity in each die at each of the tested temperatures was calculated and was found to be as high as 32.86% in the 0.25‐mm die at 230 °C. Additionally, the effect of the wall slip on the geometry dependence of the PP viscosity in the tested dies was investigated with a modified Mooney method. The values of the slip velocity revealed that wall slip occurred only in the 0.25‐mm die at 210 °C. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43459.     

Melt flow behavior in capillary extrusion of nanosized calcium carbonate‐filled poly(L‐lactic acid) biocomposites

Nanosized calcium carbonate (nano‐CaCO₃)‐filled poly‐L ‐lactide (PLLA) biocomposites were compounded by using a twin‐screw extruder. The melt flow behavior of the composites, including their entry pressure drop, melt shear flow curves, and melt shear viscosity were measured through a capillary rheometer operated at a temperature range of 170–200°C and shear rates of 50–10³ s^?1. The entry pressure drop showed a nonlinear increase with increasing shear stress and reached a minimum for the filler weight fraction of 2% owing to the “bearing effect” of the nanometer particles in the polymer matrix melt. The melt shear flow roughly followed the power law, while the effect of temperature on the melt shear viscosity was estimated by using the Arrhenius equation. Hence, adding a small amount of nano‐CaCO₃ into the PLLA could improve the melt flow behavior of the composite. POLYM. ENG. SCI., 52:1839–1844, 2012. © 2012 Society of Plastics Engineers     

Effect of nanosize CaSO4 and Ca3(PO4)2 particles on the rheological behavior of polypropylene and its simulation with a mathematical model

Nanosize CaSO₄ and Ca₃(PO₄)₂ fillers were synthesized with an in situ deposition technique, and their sizes were confirmed by X‐ray diffraction. CaSO₄ was prepared in 12‐ and 22‐nm sizes, and Ca₃(PO₄)₂ was prepared in 13‐ and 24‐nm sizes. Experimental variables, such as torque, shear viscosity, shear stress, and shear rate, of the nanofilled polypropylene (PP) composites were measured with torque rheometry and melt flow index (MFI) measurements. Torque versus time, shear viscosity versus weight percentage, and MFI versus weight percentage were plotted to investigate the rheological behavior of the nanofilled composites. The Cross–Williamson (CW) model was simulated with the MATLAB simulation package to study the thinning behavior of the PP composites. The experimental results show a decrease in the shear viscosity with increasing weight percentage of filler. Shear thinning in the molten PP composites was comparatively greater with decreasing nanosize of CaSO₄ and Ca₃(PO₄)₂. This kind of behavior was confirmed by the N parameter as determined from the CW model. The simulation of experimental data also showed similar trends as the theoretical data. At a certain stage, a violation of theoretical data was observed. This was because of practical limitations of the equation, as the equation does not include consideration of the physical situation of chain entanglements. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4190–4196, 2006