Viscosity of polydimethylsiloxane gum: Shear and temperature dependence from dynamic and capillary rheometry

The rheology of Dow Corning polydimethylsiloxane gum (PDMS/silicone gum) was studied over a time range of 10^?2 to 10⁵ s^?1 and a temperature range of 23–150°C using both capillary and dynamic rheometry. A low shear Newtonian region is observed at room temperature below 0.01 rad/s (increasing to 0.1 rad/s at 150°C) for which an Arrhenius activation energy for a viscous flow of 13.3 kJ/mol was determined. The Cox–Merz rule for merging of shear and complex viscosities is found to be valid up to 10 s^?1. Viscosity is found to be independent of temperature above 100 s^?1, where terminal power‐law flow is encountered. This is exhibited in the dynamic data as equal plateau moduli for the various temperature curves. Gross wall slippage is seen in capillary flows above approximately 100 s^?1, corresponding to a stress value of 70–100 kPa. Slip‐stick (spurt) flow is not observed. The viscosity data are best fitted by the Carreau–Yasuda model with a fitting parameter a of 0.7, a power‐law index n of 0.05 (low because of slip effect), and a zero shear viscosity of 32 kPa s at 23°C. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2533–2540, 2002     

Thermotropic liquid‐crystalline copolyester/thermoplastic elastomer in situ composites. I. Rheology,morphology, and mechanical properties of extruded strands

A thermotropic liquid‐crystalline polymer (TLCP), a copolyester with a 60/40 molar ratio of p‐hydroxy benzoic acid and poly(ethylene terephthalate), was blended with a styrene/ethylene butylene/styrene thermoplastic elastomer with a twin‐screw extruder. The rheological behavior, morphology, and mechanical properties of the extruded strands of the blends were investigated. The rheological measurements were performed on a capillary rheometer in the shear rate range of 5–2000 s^?1 and on a plate‐and‐plate rheometer in the frequency range of 0.6–200 rad s^?1. All the neat components and blends exhibited shear thinning behavior. Both the shear and complex viscosities of all the blends decreased with increasing TLCP contents, but the decrease in the shear viscosity was more pronounced. The best fibrillar morphology was observed in the extruded strands of a blend containing 30 wt % TLCP, and a lamellar structure started to form at 40 wt % TLCP. With an increasing concentration of TLCP, the tensile modulus of the blends was greatly enhanced, whereas the tensile strength was almost unchanged. The elongation at break of the blends first slightly decreased with the addition of TLCP and then sharply dropped at 40 wt % TLCP. The tension set measured at 200% deformation slightly increased with increasing TLCP contents up to 30 wt %, over which the set value was unacceptable for a thermoplastic elastomer. A remarkable improvement in the dynamic mechanical properties of the extruded strands was observed in the blends with increasing amounts of TLCP. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2676–2685, 2003     

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.     

Dynamic and capillary shear rheology of natural fiber‐reinforced composites

An extended dynamic and capillary rheological study of molten flax and sisal polypropylene (PP) composites was performed. Fiber concentration varied from 20 to 50 wt% and shear rate from 0.1 rad s^?1 to 10,000 s^#142;?1. Maleic anhydride‐grafted‐PP was used as compatibilizer; it strongly reduces PP and composite viscosity. Composites are yield‐stress shear‐thinning fluids with solid‐like behavior being more pronounced at high fiber content. Composites do not obey Cox–Merz rule, which was explained by different macrostructures of the molten composites in parallel plates and capillary die geometries: random fiber orientation versus strong alignment in the flow direction, respectively. Theories describing the viscosity of suspensions of solid particles were applied to the composites studied and rheological parameters and maximal packing fiber volume fraction were calculated. POLYM. ENG. SCI., 53:2582–2593, 2013. ©2013 Society of Plastics Engineers.     

Improving the electrical conductivity of ethylene 1‐octene copolymer/cyclic olefin copolymer immiscible blends by interfacial localization of MWCNTs

The localization of multiwall carbon nanotubes (MWCNTs) in the immiscible blends of ethylene–1‐octene copolymer (EOC) and cyclic olefin copolymer (COC) with the sea–island morphology and electrical conductivity of resulting nanocomposites were investigated. Depending on the feeding orders, as the MWCNTs were located in the COC droplet, the electrical conductivity was obtained as high as 5.71 × 10^?7 S/cm, while the MWCNTs were located in EOC/COC interface, the electrical conductivity increased significantly up to 1.72 × 10^?2 S/cm. The improved electrical conductivity in EOE/COC/MWCNTs nanocomposite is attributed to the interfacial localization of MWCNTs which is resulted from thermodynamic affinity of MWCNTs to COC, as well as an interconnected structure via deformed and swelled COC droplets. Thermodynamic affinity of MWCNTs to COC and established interconnected structure are confirmed by rheological characterization, microscopic observations, dynamic mechanical analysis, and electrical conductivity measurements. Therefore, as a result of selective localization of MWCNTs and well‐designed phase morphology, lower rheological and especially electrical percolation thresholds could be obtained in the ternary nanocomposites compared to the binary systems. POLYM. ENG. SCI., 59:447–456, 2019. © 2018 Society of Plastics Engineers     

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     

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     

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     

Melt‐processed biodegradable polyester blends of poly(L‐lactic acid) and poly(ε‐caprolactone): Effects of processing conditions on biodegradation

Biodegradable polyester blends were prepared from poly(L ‐lactic acid) (PLLA) and poly(ε‐caprolactone) (PCL) (50/50) by melt‐blending, and the effects of processing conditions (shear rate, time, and strain) of melt‐blending on proteinase‐K‐ and lipase‐catalyzed enzymatic degradability were investigated using gravimetry, differential scanning calorimetry, and scanning electron microscopy. The proteinase‐K‐catalyzed degradation rate of the blend films increased and leveled off with increasing the shear rate, time, or strain for melt‐blending, except for the shortest shear time of 60 s. The optimal processing conditions of melt‐blending giving the maximum rate of lipase‐catalyzed degradation were 9.6 × 10² s^?1 and 180 s, whereas a deviation from these conditions caused a reduction in lipase‐catalyzed enzymatic degradation rate. At the highest shear rate of 2.2 × 10³ s^?1, PCL‐rich phase was continuous in the blend films, irrespective of the shear time (or shear strain), whereas PLLA‐rich phase changed from dispersed to continuous by increasing the shear time (or shear strain). This study revealed that the biodegradability of PLLA/PCL blend materials can be manipulated by altering the processing conditions of melt‐blending (shear rate, time, or strain) or the sizes and morphology of PLLA‐rich and PCL‐rich domains. The method reported in the present study can be utilized for controlling the biodegradability of other biodegradable polyester blends. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 831–841, 2007     

Nylon 6/poly(ethylene terephthalate) polymer blends: Rheological properties of melts

Melt rheological studies of nylon 6/polyethylene terephthalate (PETP) blends (PETP content varying from 10 to 50%) were carried out using capillary rheometer in the shear rate range of 58 s^?1 to 1.15 · 10³ s^?1. With increasing PETP content in the blend a decrease of the melt viscosity as well as non-Newtonian behaviour was observed. The model equation developed by Uemura and Takayanagi for viscoelastic melt blends has been used to understand the state of dispersion and morphology of a nylon 6/PETP blend system. Further, an inverse relationship between polymer melt viscosity (η) and elastic modulus (E') of fibres was observed.     

Liquid crystalline copolyester/polyethylene in situ composite film: Rheology,morphology, molecular orientation,and tensile properties

A thermotropic liquid crystalline copolyester (TLCP) was blended with low density polyethylene using a corotating twin screw extruder and then fabricated by extrusion through a miniextruder as cast film. Rheological behavior, morphology, and tensile properties of the blends were investigated. Melt viscosities of neat components and blends measured by using plate‐and‐plate and capillary rheometers at 240°C, in the shear rate range 1–10⁴ s^?1, showed similar shear thinning effect. The viscosity values measured by the two techniques in the overlapping range of shear rate are found to be identical, which is in accord with the Cox–Merz rule. Addition of TLCP slightly reduces the matrix melt viscosity. TLCP dispersed phase in the extruded strand appeared in the form of spherical droplets. These droplets were elongated into fibrils with high aspect ratio (length to width) at the film extrusion step. As a result, the Young's modulus in machine direction (MD) of the composite film was greatly enhanced. At 20 wt % of TLCP, the MD Young's modulus was found to be about 16‐fold increase compared to that of the neat polyethylene film. However, the elongation at break sharply dropped with the increase of TLCP content. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 561–567, 2002; DOI 10.1002/app.10307     

Melt rheology and interfacial properties of binary and ternary blends of PS,EOC, and SEBS

This works systematically investigates the interfacial properties of the binary and the ternary blends based on polystyrene (PS), ethylene octene copolymer (EOC), and styrene–ethylene–butylene–styrene (SEBS) by analyzing the melt linear rheological behavior of the blends and neat components. Moreover, the relationship between rheology, phase morphology, and mechanical properties of PS/EOC ternary blends with various quantities of SEBS were studied. The surface shear modulus (β) and interfacial tension values obtained by Palierne model indicated that the EOC/SEBS blend has the best interfacial properties, while the lowest interaction was found for PS/EOC blend. Based on the Palierne model and Harkin's spreading coefficients a core–shell type morphology with EOC phase encapsulated by the SEBS shell dispersed in the PS matrix was determined for the ternary blends. Scanning electron microscopy results revealed that both fibrillar and droplet forms of dispersed phase could be developed during the blending of PS and EOC in presence of SEBS. The extent of fibrillar morphology and interfacial interactions in PS/EOC/SEBS ternary blends was dependent on the SEBS content. The improvement of the mechanical properties of PS/EOC blends in the presence of SEBS was evidenced by the tensile and impact resistance experiments. The tensile strength reinforcement was more pronounced for the ternary blends with more fibrillar dispersed phase. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48791.     

Mechanical,rheological, thermal,and morphological properties of blends based on poly(propylene)/poly(propylene‐co‐1‐octene)/poly(ethylene‐co‐1‐octene)

The effect of addition of propylene copolymer, produced by metallocene catalysts, on the mechanical, rheological, and morphological properties of blends based on poly(propylene) (PP) and ethylene–1‐octene copolymer (EOC) was evaluated. It was observed that the addition of 2 wt % propylene–1‐octene copolymer (POC) improved the impact strength of the EOC/PP blends. The rheological analysis indicated that the addition of propylene copolymer produced materials with improved processability. Thermal and morphological analysis showed that the POC acts as a compatibilizer on the EOC/PP blends. © 2003 Wiley Periodicals, J Appl Polym Sci 89: 1690–1695, 2003     

Fiber Formation in Medium and Ultra‐High‐Molecular‐Weight Polyhydroxybutyrate Blends under Shear Flow

Summary: Polyhydroxybutyrate (PHB) is an ideal bioplastic, however, this polymer undergoes a severe embrittlement process because of its spherulitic structure, rendering the material brittle. Using a series of in‐situ rheo techniques, we have previously observed only the rapid initial stage of shish formation, we term a partial shish, which existed at high shears in medium‐molecular‐weight PHB, = 360 000. The shish kebab morphology is anticipated to remove or severely lessen this embrittlement process whilst providing new properties and applications. For medium and ultra high‐molecular‐weight (MMWT, = 360 000/UHMWT, = 5 × 10⁶) PHB 99/1 and 99.5/0.5 blends only a partial shish is identified. However, the initial shish formation stage and subsequent stages were observed at 98/2 and 97/3 blend ratios resulting in a complete shish, we term the full shish, and fiber formation was evident. We believe this fiber morphology achieved by high molecular weights is crucial to sustaining the shish kebab structure for an excessive period.

Left: In‐situ rheo‐light scattering micrograph; 97/3 MMWT/UHMWT PHB at 100 s^?1 for 1 s shear shish held at 75 s. Right: In situ rheo‐optical micrograph; PHB fiber morphology observed at 50 s^?1 for 2 s shear 98/2 MMWT/UHMWT PHB after 1 min.     

Melt rheology of blends of semicrystalline polymers. I. Degradation and viscosity of poly(ethylene terephthalate)–polyamide-6,6 mixtures

Melt rheology of poly(ethylene terephthalate)–polyamide-6,6, and their blends was studied between 240°C and 300°C, in capillary and rotational rheometers. The flow curves were determined in the range of rate shear from about 10^?2to 10⁵ (s^?1). The results indicate a considerable degree of compatibility, presence of associations between the two types of macromolecules, and cocrystallization. A new mechanism of flow for the blends has been proposed. The study also considers the kinetics of thermal degradation.     

Effect of degree of saponification on the rheological properties of syndiotactic poly(vinyl alcohol)/ water solution

To identify the effect of degree of saponification (DS) of syndiotactic poly(vinyl alcohol)s (s‐PVA)s having similar tacticity and molecular weight on the rheological properties of s‐PVA/water solution, four kinds of (s‐PVA)s with assigned (DS)s, from 93.1 to 97.5%, were prepared by copolymerization of vinyl pivalate (VPi) and vinyl acetate (VAc), followed by saponifying the corresponding copoly(VPi/VAc). The DS played a significant role in rheological behavior. Over the frequency range of 10^?1 to 10² rad/s s‐PVA with higher DS shows more shear thinning at similar molecular weight and tacticity of polymer, suggesting that PVA molecules are more readily oriented as DS increases. This may provide indirect evidence of the spontaneous in situ orientation of s‐PVA molecules at the late stage of saponification. Yield stress is higher for s‐PVA with higher DS at similar molecular weight and tacticity of s‐PVA. This indicates that more domains with internal order are produced at higher saponification. These facts result from increase in stiffness of s‐PVA molecules with proceeding the saponification reaction. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 463–467, 2002     

Effect of SBS Content on Low Temperature Impact Strength,Morphology and Rheology of PP-cp/SBS Blends

Izod impact strength of PP impact copolymer/Styrene-Butadiene-Styrene blends were evaluated at varied sub-zero temperatures and demonstrated 12 times enhancement in impact strength of 40% SBS containing blend over pure PP-cp at ?40°C. SBS content played a vital role in morphology development as it changes from droplet morphology to elongated ellipsoid to a seemingly networked structure leading towards different fracture mechanisms. Rheological properties of blends evaluated on capillary rheometer showed pseudoplastic behavior at varied shear rates (50 ? 10⁴ s^?1) at 220°C and good agreement between experimental shear viscosity and theoretical values as per log additivity principle at high shear rates.     

Slit die flow measurements of a liquid crystalline polyesteramide and its blends with polyarylate

A commercial thermotropic polyesteramide and its blends with polyarylate are the object of a slit die flow rheological study. The measurements are carried out at 280°C, a temperature slightly above the melting temperature of the thermotropic, covering a shear rate range 10^?1 s^?1 to 10²s^?1. Except in the case of the thermotropic polymer, the pressure profiles are upward parabolic which is attributed to the dependence of the viscosity on pressure. The most striking result is the observed downward curvature in pressure profiles obtained for the liquid crystalline polyesteramide: no explanation is given for this phenomenon, for the present. The elasticity of the polymer melts is expressed in terms of the exit pressure and the extrudate swell. The thermotropic polyesteramide presents negative values of both parameters (e.g. samples shrink instead of swell). Viscosity and elasticity present negative deviation from linearity when plotted against composition; this reduction in the rheological functions, caused by the addition of liquid crystal, is more pronounced at high shear rates.     

Effect of melt annealing on the phase structure and rheological behavior of propylene–ethylene copolymers

The morphological and rheological properties of a commercial propylene‐ethylene copolymer (PEC) and a series of blends with different concentrations of poly (ethylene‐co‐propylene) are investigated. The blends are prepared mixing PEC with fractions obtained from it by solvent extraction. The phase structure of samples exposed to different thermal and mechanical histories was analyzed using scanning electron microscopy. The linear viscoelastic properties of the molten polymers were measured using different test sequences that include dynamic frequency and time sweeps. The phase structure of most blends changes dramatically with time when the polymers are kept in the molten state due to the coalescence of the domains. For example, the initial morphology of PEC which presents domains of ～1 μm diameter changes to regions of more than 10 μm of average diameter after 90 min at 178°C at rest. Coincidentally, the dynamic moduli of the blends change during annealing reaching values that depend on the mechanical history. For example, the elastic modulus of PEC increases ～32% during a dynamic time sweep of 45 min using a frequency of 0.1 s^?1, while it decreases ～18% when a frequency of 1 s^?1 is applied. Moreover, the modulus measured at 0.1 s^?1 of samples annealed at rest during 45 min is ～58% larger than that of the fresh material. POLYM. ENG. SCI., 47:912–921, 2007. © 2007 Society of Plastics Engineers     

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.