Viscosity and die swell of acrylonitrile-butadiene-styrene filled with glass beads and glass fibers

Shear viscosity and die swell ratio of acrylonitrile-butadiene-styrene filled with glass beads and glass fibers were measured. The relative viscosity of the composites increased with filler content, but decreased with shear rate. At low shear rates, fiber filled systems had higher relative viscosities than bead filled systems. At high shear rates, the opposite was observed. The die swell ratio of the unfilled material increased linearly with the logarithm of the shear rate. Systems highly filled with glass beads or fibers showed a maximum in the die swell ratio at medium shear rates. The magnitude of the maximum in the die swell ratio increased with the filler content and the die length, up to a certain length, in a series of dies that had the same radius. The presence of a maximum in the die swell ratio of the filled melts is explained by an order-disorder phenomenon observed earlier by Wu.     

Shear viscosity of nylon 6 melts reinforced with microfibrous calcium silicate hydrate

Steady shear viscosity of nylon 6 melts reinforced with xonotlite, microfibrous calcium silicate hydrate (6CaO · 6SiO₂ · H₂O), is investigated. The highly filled nylon 6 melt tends to exhibit a yield value, resulting in remarkable viscosity increase particularly at low shear rates. Addition of the xonotlite significantly increases activation energy of viscous flow of the nylon 6 melt, leading the viscosity to be strongly temperature dependent. Comparisons with the melts filled with glass fibers and wollastonite are made. Flow-induced orientation becomes more important at low volume fractions. Shortening of the xonotlite during shear flow measurement can also be observed.     

Study on the viscosity of polypropylene composites filled with different size and size distribution CaCO3

Two kinds of different size calcium carbonates are blended and filled into polypropylene in 30 wt%. The melting viscosity of PP composites samples is measured by capillary extrusion rheometer at 230°C. The results show that the melt viscosity of PP composites evidently decreased when that was filled with the blending 325 and 1,500 mesh CaCO₃ and the 1,500 mesh proportion in fillers was from 20 to 60 wt%. The viscosity in the low shear velocity decreased more than that in the high shear velocity. The shear viscosity of single filler and filler samples with the size distribution at the different temperature was studied by capillary extrusion rheometer. The results show that the flow activation energy and the flow activation entropy of composites filled with the size distribution filler increased. The change of the flow activation entropy and the model of the efficient arrangement of the structure are used to explain the phenomenon in melting viscosity decrease of PP filled with the size distribution fillers. A structural model of composites that filled with the size distribution fillers was set up. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

The Melt Flow Properties of Poly(propylene)/Glass Bead Composites

The effects of filler content and its surface treatment on the melt flow properties of A‐glass bead‐filled poly(propylene) (PP) composites have been investigated using a capillary rheometer at a wide apparent shear rate scope of 150 to 7 200 s^–1 and a temperature range of 160 to 200°C. It was found that the melt shear flow obeyed roughly the power law. The melt shear viscosity (η_w) of the treated glass bead‐filled system with a silane coupling agent was somewhat higher than that of the raw glass bead‐filled system when both the systems were subjected to the same test conditions. The increase of the resistance to flow and flow satiability for the former system can be attributed to the improvement of the compatibility and interfacial adhesion between the filler and matrix as well as the dispersion of the filler in the matrix due to the surface treatment of the glass beads. The dependence of η_w on temperatures can be expressed with an Arrhenius relationship. The temperature sensitivity of η_w for the composite melts is greater than that of the unfilled PP. Furthermore, η_w increases obviously with the volume fraction (ϕ_f) of the fillers at lower shear rates, while the dependence of η_w on ϕ_f decreases with the increase of shear rates. This is attributable to the increase of the ability of relative movement between the filler and matrix melt at high extrusion rates.     

The rheology of filled polymers

The flow properties of polymer melts containing fillers of various shapes and sizes have been examined. If there is no failure of either the filler or polymer in the solid state, then the modulus enhancement for randomly distributed filler is equal to the melt viscosity enhancement under medium shear stress conditions (10⁴ Nm^?2) in simple shear flow or in oscillatory shear flow. Submicron-size fillers, in particular, can form weak structures in the melt that greatly increase the low shear rate viscosity without changing the modulus of the solid proportionately. The highly pseudo-plastic nature of polymer melts at shear stresses of 10⁶ Nm^?2 means that, even without orientation of filler particles toward the flow direction, the viscosity enhancement is less than at lower shear stresses.     

Experimental study of the melt fracture behavior of filled high‐density polyethylene melts

In this work, the melt fracture behavior of microfilled polymer melts based on a high‐density polyethylene (HDPE) was investigated by means of a capillary rheometer, which operated at constant piston velocity. The microfilled melts examined had the same filler content (10 vol%), but differed for the type of filler (glass beads, discontinuous glass fibers, and talc). The results demonstrated that the presence of rigid fillers influences the melt fracture behavior of the filled melts in a way that is dependent on the type of filler dispersed in the HDPE melt. Opposite effects were induced by lamellar particles of talc and by glass fillers (either beads or fibers): the former promoted flow stability, whereas the latter fostered the occurrence of instabilities of “stick‐slip” type. The effects induced by the presence of the glass fillers on the oscillating flow that takes place when “stick‐slip” instabilities occur were also analyzed and discussed. POLYM. ENG. SCI., 54:364–377, 2014. © 2013 Society of Plastics Engineers     

Increased flow property of polycarbonate by adding hollow glass beads

The steady shear viscosity and dynamic viscoelastic properties of glass beads (GB) filled polycarbonate (PC) melts were studied at varying filler diameters and concentrations. The PC/GB composites containing small amounts of GB bore lower melt viscosity and dynamic modulus than those of pure PC at studied frequencies and shear rates, showing a “ball‐bearings” effect. For highly filled systems, the viscosity and dynamic modulus were decreased further at higher frequencies and shear rates. This ball‐bearings effect was enhanced by changing the GB from larger to smaller one. The oscillatory experiments with modified shear stress showed a stress‐dependent decrease of the viscoelastic properties, and revealed an interfacial slip mechanism, combined with the polymer chains disentanglement at melt/solid interfaces. The scaling relationship between the relative viscosity and the mean interparticle gap confirmed that the interfacial slip and polymer chains disentanglement were induced by the extremely high local shear developed in the narrow gaps between the nearby rotating spheres. POLYM. ENG. SCI., 45:1119–1131, 2005. © 2005 Society of Plastics Engineers     

Comparative rheological studies on jute-fiber- and glass-fiber-filled polypropylene composite melts

An experimental study of the melt rheological properties of composites of isotactic poly-propylene (IPP) filled with chopped jute-fibers (JF) and glass-fiber (GF) is reported. Fiber concentration is 5–20 wt %. Variation of shear stress with shear rate at constant temperature indicates increase in shear stress with shear rate and fiber loading. Shear stress values for IPP/GF melts are higher at the same shear rate and temperature. Variation of melt viscosity and melt elasticity with fiber concentration and shear stress or shear rate are also illustrated. Melt viscosity increases with fiber loading, while melt elasticity parameters such as dieswell and first normal stress difference decrease for both systems. For IPP/GF composite melts the viscosity values are higher, the die-swell and first normal stress difference values are lower compared to IPP/JF composites melts. Processing temperature of the filled IPP composites increase with respect to the nonfilled polymer, being a little higher in case of IPP/GF composites. © 1992 John Wiley & Sons, Inc.     

The effect of glass fibers on the rheological behavior of polypropylene melts between rotating parallel plates

The Rheometrics mechanical spectrometer has been employed in the parallel plate mode to study the rheological behavior of pure polypropylene resin and melts filled with 10, 20, 30, and 40 percent by weight glass fibers. Steady-state shear data show that, for loadings above 20 percent fiber, increasing fiber loading leads to an increase in viscosity of the melt. The effect of increasing fiber content becomes smaller at higher shear rates. For the same loading range, fiber addition increases the first normal stress difference, and the effect of fiber loading becomes smaller with increasing shear rate. At 10 percent loading, the viscosity of the filled polymer melt is lower than that of the pure resin melt. These results require further confirmation. Strain sweeps employing dynamic measurements in conjunction with the parallel plate mode of the Mechanical Spectrometer were carried out. In general, it was found the dynamic properties are strain dependent. Steady shear data employing the cone-and-plate mode were not repeatable.     

Noticeable viscosity reduction of polycarbonate melts caused jointly by nano‐silica filling and TLCP fibrillation

Nano‐SiO₂ was introduced into in‐situ composites of polycarbonate (PC) and a thermotropic liquid crystalline polymer (TLCP) using a twin‐screw extruder. The rheology of these composites was characterized with capillary rheometry, and the morphology of the dispersed TLCP observed with scanning electron microscopy. The rheological data revealed that the viscosity decrease of PC melts by only the addition up to 20 wt% TLCP remained smaller than 30%, while it became ～48% upon further addition of only about 1 wt% nano‐SiO₂ and larger than 60% upon ～9 wt% nano‐SiO₂ filling, in contrast to a 50% viscosity increase of PC melts with increase in nanosilica loading up to ～9 wt%. These silica‐filled composites exhibited markedly low viscosity, especially at relatively high shear rates. The morphology of TLCP extracted from unfilled and silica‐filled composites indicated that the largest viscosity reduction was correlated well with the fibrillation of TLCP droplets enhanced by nano‐SiO₂. The TLCP/SiO₂/PC composites exhibited rheological hybrid effect with fillers at nanometer scale. POLYM. ENG. SCI., 47:757–764, 2007. © 2007 Society of Plastics Engineers     

Uniaxial elongational viscosity of various molten polymer composites

Uniaxial elongational viscosity of low density polyethylene (LDPE) that was filled with glass bead, glass flake, talc, or glass fiber was measured. The effect of various inorganic fillers on the strain-hardening property in elongational viscosity was investigated. The strain-hardening property of LDPE became weaker by the addition of fillers in the order of glass bead, glass flake, and talc. Glass fiber filled LDPE showed a strain-softening property. The smaller the particle and the larger the aspect ratio, the weaker the strain-hardening property. Their causes were analyzed from the two terms, i.e., the relaxation spectrum and the damping function, by Bernstein-Kearsley-Zapas (BKZ) model. By the incorporation of fillers, the relaxation modules became larger, and the damping function became stronger in the order of glass bead, glass flake, talc, and glass fiber. Recoverable strain was also measured to understand weaker strain-hardening properties. The degree of recovery became smaller by the addition of fillers. It was found that the smaller the particles and the larger the aspect ratio, the smaller the degree of recovery. It was concluded that weaker strain-hardening properties of LDPE composite than that of LDPE are caused by stronger damping function and smaller degree of recovery.     

Effect of fillers on the rheological behavior of thermoplastic 1,2 polybutadiene rubber

The influence of fillers like clay, silica, and carbon black on the rheological properties of 1,2 polybutadiene has been studied using a capillary rheometer. Silica filled compound exhibited the highest viscosity and clay filled compound the lowest viscosity at all shear rates. The effect of filler loading and temperature on the Theological behavior has also been studied. Smooth extrudates were obtained in most of the cases and die swell was lower for silica and carbon black filled compounds than for clay filled compounds. Rheograms of different 1,2 polybutadiene systems have been found to merge into a master curve using modified viscosity and shear rate functions that contain melt flow index as a parameter.     

Rheological properties of calcium carbonate-filled polypropylene melts

An experimental study was carried out to investigate the viscoelastic behavior of calcium carbonate-filled polypropylene melts, using the Han slit rheometer. In the analysis of the experimental data, the pressure gradient was used to determine the wall shear stress, and the exit pressure to determine the elasticity of the filled polymers. The study shows that the materials studied follow a power law in viscous behavior over the range of shear rates investigated and that the viscosity increases and elasticity decreases as filler concentration is increased. Also investigated was the effect of temperature on the viscoelastic properties of filled polypropylene melts.     

Rheological and optical properties of polypropylene filled with synthetic silicates and calcium carbonate

The rheology of PP filled with three different types of fillers, namely synthetic sodium aluminium silicate (SSAS), aluminium silicate (AS) and calcium carbonate (CaCO₃), at concentrations up to 40% was studied. Variation of shear and extensional viscosity was evaluated for all the compositions. When filler loading was less than 20%, the shear viscosity at low shear rates was less than that of virgin PP. Flow curves are described by the Ellis model. The onset of non-Newtonian shear thinning behaviour is related to parameter η₁₀/τ_1/2. Although fillers are white, they imparted a yellowish tone at lower loadings. At higher loadings, this yellowing effect was masked, yielding a lower yellowness index.     

Rheological behavior of polymer melts with natural fibers

Flow behavior of polymer liquids filled with short fibers (particulate fillers) was theoretically analyzed from the point of view of the free volume theory. Assuming that the filler addition changes the occupied volume, while the temperature variations cause mainly the free volume changes, a general expression describing the viscosity of the system as a function of the filter content, temperature variations, and rheological properties of the pure polymer liquid was derived. If the viscosity curve of the unfilled polymer is described by the Carreau equation, the corresponding viscosity curve of the filled polymer is also represented by an equation of Carreau type. However, this equation has other values of Newtonian viscosity and the power exponent in comparison with the initial equation. Both parameters depend on the filler content and temperature. The derived equation predicts a viscosity rise and a stronger non‐Newtonian behavior of the system with increasing filler content. The temperature rise exerts an opposite effect on the rheological behavior. The theoretical predictions are in good accordance with viscosity measurements for low‐density polyethylene and polystyrene melts filled with short cotton, flax, and hemp fibers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1401–1409, 2005     

Rheological hybrid effect in dually filled polycarbonate melt containing liquid crystalline polymer

Polycarbonate (PC)/liquid crystalline polymer (LCP) blends dually filled with glass fiber and nano‐SiO₂ were prepared by melt blending, with the use of a commercial Vectra A130 as the source of LCP and glass fiber. In these dually filled PC/LCP melts, rheological hybrid effect occurred, confirmed by the melt viscosity of the quadruple polymer blends decreased with increasing nano‐silica loading, influenced by the minor LCP phase in the blend. The drastic viscosity reduction closely correlates with the deformation and fibrillation of LCP droplets in the system. The LCP fibrillation was controlled jointly by the thermodynamic and hydrodynamic driving forces. Finally, the dually filled PC/LCP melt had decreased viscosity lower than those of pure PC, silica‐filled PC, and PC/Vectra A130 blends, and furthermore had decreased glass fiber breakage, shown by larger average aspect ratio than that in PC/Vectra A130 blends. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Rheological properties of glass bead-filled low-density polyethylene composite melts in capillary extrusion

The melt flow of glass bead-filled low-density polyethylene composites in extrusion have been observed by using a capillary rheometer to investigate the effects of temperature, shear rate, and filler content on the rheological properties of the melts. The results show that the melt shear flow obeys a power law, and the dependence of the apparent shear viscosity, η_app, on temperature is in accord with an Arrhenius equation. At the same temperature and shear rate, η_app increases slightly with increasing the volume fraction of glass beads, but the flow behavior index decreases with increasing filler content. In addition, the first normal stress difference of the melts linearly increases with increasing wall shear stress. Good agreement is shown with the N₁ calculated with the equation presented in this article and the pressured data from the sample melts. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1451–1456, 1999     

Rheological Behaviour of Short Silk Fiber Filled Rubber Compounds

Abstract

Rheological behaviour of rubbers (natural (NR), nitrile (NBR) and polychloroprene (CR)) and short silk fiber filled rubber compounds have been studied. The shear viscosity-shear rate relationship of both non-fiber filled and short fiber filled rubber compounds obey power law model for fluids and is similar to that of short fiber filled polymer melts. The effect of fiber concentration on the shear viscosity is more pronounced at lower shear rates. Both extrudate deformation and die swell become less on the addition of fibers to the mixes and the improvement is more significant at higher fiber concentrations. Extent of fiber breakage by the shear force during mixing is severe and is similar for all the rubbers.     

Rheological properties of fumed silica filled Bis-GMA dispersions

The rheological properties of Bis-GMA dispersions filled with fumed silica were investigated to optimize the manufacturing process and mechanical properties by using a Rheometrics Mechanical Spectrometer (RMS). Steady and dynamic measurements on the RMS were carried out to obtain shear viscosity and dynamic mechanical properties. The effect of several factors on the rheological properties of fumed silica dispersions was also examined. The factors were a concentration of a silane coupling agent (γ-MPS), the methods of surface treatment of fillers, silica content, diluent concentration, shear rate, and operating temperatur. From these studies, it was observed that shear viscosity showed an asymptotic phenomenon at a higher concentration than a uniform multi-layer coverage concentration of γ-MPS. The silane coupling agent had a significant role in the reduction of tan δ, resulting from a decrease of loss modulus, while fillers decreased tan δ by increasing the storage modulus. In cases where the silica content and diluent concentration increased simultaneously, the Barcol hardness of Bis-GMA/silica composites was increased, but there was no change in the viscosity of dispersions and diametral tensile strength of those composites.     

The influence of titanium dioxide on the rheological and extrusion properties of polymer melts

An experimental study of the influence of titanium dioxide (TiO₂) on the rheological and extrusion properties of five polymer melts (two low-density polyethylenes, two high-density polyethylenes, and a polystyrene) has been carried out. Increasing TiO₂ loading increases the shear viscosity η, with the extent of increase being greater at lower shear rates. At moderate and high TiO₂ loadings, the filled melts may possess yield values. Empirical equations relating viscosity to filler loading have been developed. The first normal stress difference was measured for the melts and found to increase with increasing TiO₂ loading. However, the extent of increase was less than found for the viscosity function and interpretation in terms of the theory of viscoelasticity suggests that the characteristic relaxation time of the melts decreases with increasing TiO₂ level. Empirical equations relating the first normal stress difference coefficient to volume fraction of the filler have been developed. Addition of TiO₂ is found to decrease extrudate swell and retard the occurrence of extrudate distortion.