ABSTRACT:The behavior of a polybutadiene-carbon black composite entering into contact with organic solvents and gasoline was investigated. The composite used has a conductivity of 3.0 { 0.1 V 01 cm 01 . However, if it comes into contact with organic solvents (gasoline, for instance) the matrix absorbs them and consequently swells. This swelling causes the separation of the carbon particles and the concomitant diminution of the composite conductivity. During the tests performed, the resistivity of the composite grows exponentially with the exposure time to solvents. Typically, the material samples show a reduction of approximately 30% of its initial conductivity after only 1.5 min of exposure to solvents. Also, it was observed that the rate at which the conductivity decreases is related to the chemical nature of the solvent used in the test. To model the drop on composite conductivity induced by solvent swelling we use an effective media percolation approach. This approach was adapted to the needs of our experiments by modifying the definition of one of its main parameters (the critical volume of the low-conductivity fraction). The experimental data were successfully described by this model. Finally, the test performed shows that this composite is a very promising material that can be employed, for example, in various security and control devices to warning of accidental organic solvent or hydrocarbon leaks in pipelines or containers of chemical industries and refineries.

ABSTRACT:The rheological and electric properties of blends of poly(ethylene terephthalate) (PET) and high-density polyethylene (HDPE) filled with various types of carbon black (CB) were analyzed in detail in this project. Four types of CB samples with available values of surface area, particle size, porosity, density, and maximum packing fraction were considered. Blends were prepared using an internal mixing chamber at two different rotational speeds, prior to mold compression of the samples. The rheological properties of the blends with varying polymer composition and a constant amount of CB were recorded in terms of torque variation with time for two shear rates (in terms of rotational speed). Rheological data were related to the resistivity of blends. Results show that the CB structure (porosity, surface area, apparent bulk density, and particle size) largely determine the resulting equilibrium torque and electrical properties. Furthermore, since CB is preferentially located in the HDPE phase, higher conductivity is observed as the PET content decreases, since the relative CB content in this phase increases.

In this work, metabolic syndrome was very common among patients with gout. Sixteen percent of the patients, although previously asymptomatic, had IHD, they all had metabolic syndrome. Gouty patients frequently first seek medical care from a rheumatologist. The rheumatologist can have an important role in detecting metabolic syndrome and risk factors for cardiovascular disease.

In this work we develop an empirical method to calibrate the measuring head of a torque‐rheometer to obtain the power‐law parameters of polymer melts. This method is based on a similar analysis developed by Lee and Purdon. However, in this work, only one geometrical parameter, with well‐defined physical limits, is needed for calibration, instead of the two arbitrary parameters proposed by the previous authors. Moreover, this parameter is closely related to the ordinate of the logarithmic relationship between the torque (MT) and the angular velocity (S1), obtained from the torque‐rheometer data. This allows us to define a calibration function for this parameter, which is used to evaluate the consistency index (m) of the melt. On the other hand, experimental results confirm the equivalence between the slope of the logarithmic values of torque and angular velocity obtained from the torque‐rheometer data and those of shear stress vs. shear rate obtained from capillary rheometry. This further highlights the feasibility of evaluating the melt flow index (n) and the consistency index (m) from the torque‐rheometer data.