Rheological Characterization of Yield-Stress Fluids with Brookfield Viscometer

This paper analyzes various techniques to use viscometers equipped with vane spindles to characterize rheological properties of yield stress fluids. Specifically, application of Brookfield viscometers to this end is discussed. A wide selection of toothpastes and lotions were tested. It is shown that a simple method based on apparent shear rate and stress, commonly referred to as a representative viscosity method, works well for moderately non-Newtonian samples but may significantly underestimate viscosity for samples with a more pronounced yield stress behavior. To get more accurate data an integral equation relating torque to angular velocity needs to be solved which can be easily done numerically to get a good agreement between the data collected on an inexpensive viscometer and the data from high-end rheometers.

End pressure effects of polypropylene composites reinforced with multi-walled carbon nanotubes in capillary flow

The influence of the size and content of multi-walled carbon nanotubes (MWCNTs) on the end pressure effects of polypropylene (PP) composite melts during capillary extrusion flow was investigated, with the test temperature varying from 190°C to 230°C and apparent shear rate ranging from 50 s−1 to 3000 s−1. The results showed that the end pressure drop increased with increasing apparent shear rates, while decreased with increasing test temperature, and the sensitivity of the end pressure drop to apparent shear rate for the composites was higher than that for the unfilled PP. The end pressure drop increased with increasing weight fraction and the specific surface area of the MWCNTs. The end pressure drop increased almost linearly with increasing the aspect ratio of the MWCNTs. Moreover, the end pressure effect mechanisms of the composite melts during a capillary extrusion flow were discussed.

The effects of manganese ions on rheology and thermal properties of polyether ether ketone

Polyether ether ketone (PEEK) mixed with manganese (Mn) of different valences was prepared to simulate conditions of impurity. The melt flow rate (MFR) and rheological behaviour were systematically studied to characterize the mobility from different angles. MFR test was used for the preliminary exploration of mixtures of Mn ions. The results showed that Mn, Mn(II), and Mn(IV) had little impact on the mobility of PEEK contrary to Mn(VII) and that long chain branching or cross-linking was suspected. Mn(VII) was determined to be the main object of this research. Capillary rheometer test demonstrated that the apparent shear viscosity constantly reduced with the increase of apparent shear rate, and that the addition of Mn(VII) could worsen the mobility of PEEK. Similarly, parallel plate rheometer studies proved that the complex viscosity increased along with the content of Mn(VII) and LCB was confirmed. Thermal analysis revealed that LCB occurred internally and that thermal stability was worse.

Comparative Analysis of the Effect of Organoclay, Boron Nitride, and Fluoropolymer on the Rheology and Instabilities in the Extrusion of High Density Polyethylene

The effect of different processing additives on the extrusion instabilities of high density polyethylene (HDPE) was investigated. The concentration of each processing additive was fixed at 0.05 wt%. Organoclay, boron nitride, and fluoropolymer reduced transient shear and extensional viscosities of HDPE melt. Drop in extrusion pressure occurred during the extrusion experiment. The initial loss of glossiness in HDPE was restored with the addition of these additives. However, the fluoropolymer did not succeed in eliminating the stick-slip fracture. Despite the inclusion of the processing additives, gross-melt fracture in HDPE reappeared at apparent shear rate of 141 s−1. Both moment and distortion factor methods of analyses were employed and their findings support the observed visual trends of the extrudate surface. The quantifying tools indicated that combined organoclay and fluoropolymer reduced the pressure fluctuations and its performance surpassed that of the individual additives.

Study of Rheology of Flame-Retardant Copolyester Nanocomposites

A new type of nanocomposite was composited by the way of copolymerization of flame-retardant monomer DDP, PET monomer, terephthalic acid and ethylene dlycol. This article mainly researched the rheology behavior of different slices such as its apparent shear rate and shear stress and the relationship of the both in the use of capillary rheometer, and at the same time, the data of viscous flow activation energy of different sample were obtained. The result shows that under the same temperature, it is the PET/10%DDP/3% BaSO4 that is the best on the mobile performance that needs less shear stress and the temperature control in need is less strict than PFRP.

Influence of Varying the Powder Loading Content on the Homogeneity and Properties of Extruded PZT-Fibers

In this study PZT-green fibres containing 50, 54 and 58 vol.% PZT powder were extruded. The influences on the mixing torque, the apparent shear rate and the extrudability were investigated and a theoretical maximum powder loading content was calculated using a model introduced by Frankel and Acrivos. The influence of powder loading content on the microstructure (porosity and grain size), the phase composition and on the final ferroelectric properties of sintered PZT fibres was investigated. The measurements revealed that the production of PZT fibres with homogeneous properties requires a minimum powder loading content of 58 vol.% PZT powder.

Experimental and Theoretical Analysis of Magnetic Head-Disk Interface Equilibrium in the “Rupture” Regime of the Starved-Liquid Bearing

Previous friction measurements in the magnetic head-disk interface (HDI) indicated some anomalous friction force behavior with low sliding speeds (.25 mm/s to 0.25 m/s) and lubricant film thicknesses in the range of 20–80 nm, showing decreasing friction force with increasing apparent shear rate. The physical explanation for such behavior has not yet been established. Possible explanations for such behavior have included dramatic shear thinning, interfacial slip and partial loss of contact with the lubricant film due to slider tipping. In the present study, we investigate the possibility of slider tipping as an explanation for the decreasing friction force with increasing sliding speed. Measurements with an optical probe indicate that slider tipping does not occur for the conditions tested. Numerical analysis of slider equilibrium also supports this conclusion.