Takeshi Kitano

Viscosity of particle filled polymer melts

SummaryViscosities of particle filled polymer melts were measured at fairly low shear rate. Particles were glass beads, glass balloons, and silas balloons. Polymers were polyethylene and polystyrene. Flow curves were superimposed with respect to concentration of filler. The relative viscosity defined as the ratio of viscosity of filled polymer to that of unfilled polymer at the same shear stress is obtained as an asymptotic value even for highly filled material. The relation between relative viscosity and volume fraction of filler was represented by the equations derived byMaron andPierce orMooney. Only the distribution of particle size had influence on relative viscosity at a defined filler concentration. Yield stresses were estimated, and found to increase exponentially in the range of volume fraction from 0.1 to 0.5.ZusammenfassungViskositäten von Polymerschmelzen, die mit Teilchen gefüllt worden waren, wurden bei mittleren Schergeschwindigkeiten bestimmt. Als Teilchen wurden Voll- und Hohlkugeln aus Glas, sowie sog. „silas balloons“, als Polymere Polyäthylen und Polystyrol verwendet. Die Fließkurven für verschiedene Füllstoffkonzentrationen wurden überlagert. Die relative Viskosität, definiert als das Verhältnis der Viskositäten von gefülltem und ungefülltem Polymer bei gleicher Schubspannung, besitzt einen asymptotischen Wert selbst für hoch gefülltes Material. Die Beziehung zwischen relativer Viskosität und Füllstoff-Volumenkonzentration läßt sich durch eine vonMaron undPierce oder eine vonMooney abgeleitete Gleichung beschreiben. Nur die Teilchengrößenverteilung hat bei einer definierten Füllstoffkonzentration einen Einfluß auf die relative Viskosität. Fließspannungen werden abgeschätzt und dafür in einem Konzentrationsbereich zwischen 0,1 und 0,5 ein exponentieller Anstieg gefunden.

The effect of dielectric properties on the electrorheology of suspensions of silica particles coated with polyaniline

The flow behaviour of silicone-oil suspensions of five types of silica particles coated with a polyaniline base in a DC electric field has been linked to their dielectric properties. The relaxation frequencies corresponding to the position of the dielectric-loss maxima in the frequency spectra identify the interfacial polarization of suspension particles as a controlling factor for a strong electrorheological effect. The yield stresses of suspensions under the influence of electric field and critical shear rates, at which the chains of polarized particles were broken by shear forces, is correlated with the difference between the limit values of dielectric constants above and below the relaxation frequency. The analysis of particle dipole coefficient β showed that particle polarizability is the main factor affecting rigidity of the electrorheological structure. In contrast with this, particle shape and size, controlling the field-off suspension viscosity, become unimportant after the electric field has been applied. The plots of the relative viscosity of studied suspensions vs. Mason number characterizing the relation between shear and polarization forces have been discussed. While the results obtained at different shear rates and field strengths were reduced to a single dependence, for various particle suspensions these dependences differed.

Shear flow rheological properties of vinylon- and glass-fiber reinforced polyethylene melts

Shear viscosity, shear stress and first normal-stress difference have been investigated for glass- and vinylon-fiber filled polyethylene melts over a wide range of shear rate by means of three kinds of instruments. The influence of fiber content and fiber properties on the rheological properties is discussed. The viscosity increases with increasing aspect ratio and fiber content, and the influence of these parameters on the flow properties is evident at low shear rates. The first normalstress difference increases more rapidly with increasing glass fiber content, especially at low shear stresses. The influence of vinylon fibers on the first normal stress-difference vs. shear-stress relationship is different from that of glass fibers.

Influence of particle concentration on the electrorheological efficiency of polyaniline suspensions

The dependence of the efficiency of positive electrorheological (ER) phenomenon, expressed as a ratio of the low-shear electroviscosity to the field-off viscosity, on the particle concentration of polyaniline base suspensions in silicone oil has been studied. A simple analysis reveals that the dependence of the efficiency on the volume fraction of suspended particles may have a maximum at which the optimum ER performance of material is expected. Experimental results confirmed this expectation. It is demonstrated that with higher temperature the maximum is shifted to higher particle concentration.

Viscous properties of calcium carbonate filled polymer melts

SummaryThe viscous properties of calcium carbonate filled polyethylene and polystyrene melts were examined. The relative vircosityηr defined in the previous paper gave an asymtptotic value(ηr)l in the range of the shear stress below 105 dyne/cm2.(ηr)l of the calcium carbonate filled system was higher than that of the glass beads or glass balloons filled system at the same volume fraction of the fillerφ. Maron-Pierce equation withφ0 = 0.44 was able to approximate the(ηr)l — φ relationship. However, it was deduced here that the high value of(ηr)l of calcium carbonyl filled system was due to the apparent increase ofφ and this increase was attributed to the fixed polymer layer formed on the powder particle. By assuming the particle as a sphere with a diameter of 2 µm, the thickness of the fixed polymer layer was estimated as about 0.17 µm. The yield stress estimated from the Cassons plots increased exponentially withφ.ZusammenfassungEs wurden die viskosen Eigenschaften von Polyäthylen-und Polystyrol-Schmelzen untersucht, die mit Kalziumkarbonat-Teilchen gefüllt waren. Für die relative Viskositätηr, wie sie in einer vorangegangenen Veröffentlichung definiert worden war, ergab sich bei Schubspannungen unterhalb 105 dyn/cm2 ein asymptotischer Wert(ηr)l. Dieser war bei den mit Kalziumkarbonat gefüllten Schmelzen höher als bei Schmelzen, die bis zur gleichen Volumenkonzentrationφ mit Glaskugeln oder Glasballons gefüllt waren. Die (ηr)l —φ-Abhängigkeit ließ sich durch eine Gleichung nachMaron und Pierce mitφ0 = 0,44 beschreiben. Es wurde jedoch geschlossen, daß der hohe(ηr)l-Wert der mit Kalziumkarbonat gefüllten Schmelzen auf eine scheinbare Zunahme vonφ zurückzuführen ist, verursacht durch eine feste Polymerschicht auf der Teilchenoberfläche. Unter Annahme kugelförmiger Teilchen mit einem Durchmesser von 2 µm ließ sich die zugeordnete Schichtdicke zu 0,17 µm abschätzen. Die mittels der Casson-Beziehung geschätzte Fließspannung ergab eine exponentielleφ-Abhängigkeit.

Dynamic flow properties of vinylon fibre and glass fiber reinforced polyethylene melts

An experimental study of the dynamic shear flow properties of polyethylene melts filled with glass fibers and vinylon fibers was carried out and comparison with the steady shear flow properties was made. The effects of loading level and the characteristics of the fibers on the rheological properties of the fiber-filled systems is discussed. The rigidity and complex viscosity of the fiber-filled systems is sensitive not only to the quantity of fibers but also to their length, distribution and properties. The Cox-Merz empirical law for complex viscosity and steady shear viscosity, and Roscoes empirical relation for estimating the normal-stress coefficients are both able to be applied to pure polymer melts but not to fiber-filled systems.

High-density polyethylene (HDPE) hollow fiber membrane via thermally induced Phase separation. I. Phase separation behaviors of HDPE-liquid paraffin (LP) blends and its influence on the morphology of the membrane

Phase separation behaviors of the blends that consist of high-density polyethylene (HDPE) and LP was investigated by means of thermal analysis. The miscibility of the two components was evaluated in terms of the Flory–Huggins interaction parameter, determined from the Hoffman–Weeks plot, gave a value of 0.36. This leads us to a conclusion that this blend system is applicable to the preparation of microporous hollow fiber membrane by melt spinning of the blend. The homogeneous blends in the molten state become heterogeneous systems to yield microporous HDPE membranes in the course of cooling due to thermally induced phase separation. The influence of the phase separation on the membrane morphology was also discussed.

HDPE hollow‐fiber membrane via thermally induced phase separation. II. Factors affecting the water permeability of the membrane

Some major factors of the melt spinning of high-density polyethylene (HDPE) and a liquid paraffin (LP) blend, which affect the water permeability of HDPE hollow-fiber membrane obtained therefrom, were investigated. The water permeability of the membrane was found to increase as the membrane thickness decreases and as the melt-flow-rate value of HDPE and the LP content of the blend increases. The dependence of the water permeability on the major factors is also discussed in connection with the morphology of the membrane.

Dynamic viscoelastic properties of long organic fibre reinforced polypropylene in molten state

This paper deals with the dynamic viscoelastic properties of long organic fibre (aramid fibre (KF), polyvinyl alcohol fibre (VF) and polyamide fibre (PA6)) reinforced polypropylene in the molten state. Long organic fibres mixed with polypropylene fibres by an apparatus called a “fibre separating and flying machine″ were compression moulded into 3mm thick composites. Dynamic viscoelastic properties of these composites were measured in the molten state using a rotational parallel plate rheometer. It was found that the dependence of angular frequency on storage modulus, G′, for long organic fibre reinforced polypropylene is different from that of volume fraction of fibre, Vf and the relationships depend on the characteristics of the reinforcing organic fibres. The slope of the dynamic viscosity, η′ vs. angular frequency, ω curves increases gradually up to 45 degrees with increasing Vf. Influence of fibre content on dynamic viscoelastic properties depends on the organic fibre used. For low fibre content, G′ increases with increasing Vf in the same way as η′. However, the opposite trend is observed for high fibre content composites. It can be deduced that there is an apparent yield from the relations between complex viscosity, η* and complex modulus, G*. The yield value, G*y increases gradually with increasing fibre content and approaches a fixed value. All of the long organic fibre reinforced polypropylenes studied here are more sensitive to temperature than inorganic fibre reinforced composites.

Influence of steady shear flow on dynamic viscoelastic properties of un-reinforced and Kevlar, glass fibre reinforced LLDPE

An experimental study was conducted to observe the effects of parallel-superposed flow condition on viscoelastic properties of LLDPE, Kevlar fibre reinforced LLDPE and hybrid of short glass fibre and Kevlar fibre reinforced LLDPE. Parallel-plate rheometer was employed for these tests. Rheological parameters such as loss modulus (G″) and dynamic viscosity (η′) do not vary significantly on superposing steady state shear with oscillatory shear in the studied range of experiment at 185°C in un-reinforced LLDPE. Kevlar fibre reinforced LLDPE and Kevlar/glass fibre reinforced LLDPE showed significant changes in the flow behaviour under various sets of superposed conditions. Storage modulus (G′), andG″ become highly sensitive to low oscillatory angular frequencies (ω) under superposed conditions. These curves show two different regions with increased ω value. At low ω values, parametersG′ andG″ change sharply reaching a certain value, thereafter, changes are moderate with increased ω. In case of η′ a maxima is observed, position of which, depends upon the value of steady shear rate. Maxima shifts towards higher frequencies with the increased steady shear rate.