Volume 20, Issue 1

The present work deals with the study of the rheological behaviour of PVC (polyvinylchloride) pastes containing particles of ≈ 150 mm in diameter obtained by polymerization in suspension. The rheological properties of the PVC pastes were characterized by creep experiments using 6-bladed vane geometry. The pastes show a very small compliance and a very narrow linear domain. The effects of temperature, of interstitial liquid and of saturation level of the wet paste were studied in detail and it was found that they significantly modify the creep behaviour. Other techniques allowed us to characterise rearrangements of the particles under load, in compression, by their oedometric modulus and by the failure stresses measured using a shear box. A very high oedometric modulus was measured (20 MPa) and by application of the Mohr-Coulomb criterion the internal friction coefficient (m ≈ 0.6) and the cohesion of the materials were deduced. We conclude from this investigation that the interfacial properties of the grains play a major role in the behaviour of the wet pastes under shear or in compression. The paper illustrates the difficulties in measuring the rheological and the structural properties of jammed systems made from non-ideal (real) particles and reveals the key parameters in studying such media.

The effect of classical compatibilizers and silica fillers, which are a new potential type of compatibilizers, on the rheological properties of PP/LCP blends was investigated. The frequency sweep, shear stress growth and stress relaxation upon cessation of steady shear were performed to probe the effect of the interfacial modification and the role of silica, on the rheological behaviour of the blend. It was found that SEBS-g-MA improves the interfacial interaction more than SEBS due to the possible chemical bonding between maleic anhydride groups and LCP chains. The results showed while the hydrophilic silica fills both matrix and the LCP dispersed phases, the hydrophobic silica has some compatibilizing effect on PP/LCP blend samples.

A review of rheological in situ measurement techniques applied to liquids and soft solids at high pressures of more than 100 MPa is presented. The instruments reported in the literature fall into four groups: concentric cylinder rheometers, falling body and rolling ball viscometers, capillary viscometers and oscillatory systems. The measurement techniques are classified with respect to the possibility of carrying out an absolute measurement. Some typical experimental problems and error sources connected with high-pressure conditions are outlined and briefly discussed. The majority of the measurement techniques described in the literature are designed for the determination of the dynamic shear viscosity or viscosity function and only a few contributions report on the development of devices for the determination of other rheological parameters, e.g. normal stress differences or viscoelastic moduli.

In this work, we consider model fluids which are dispersions of clay particles in aqueous solutions of carboxymethyl cellulose. Their rheological properties are measured in both steady and oscillatory shear flows. We present the experimental results obtained for different polymer concentrations and for three different molecular weights of the polymer. The clay is a bentonite sample and the particle concentration is fixed to a value of 5 %. The mechanical properties of these materials is the result of a competition between different mechanisms: association-dissociation of aggregates of particles, adsorption of polymer on the particles and desorption of solvent molecules from the particles, bridging of the particles by long polymer chains.