Showing papers by "Pierre J. Carreau published in 1991"

A correlation between critical end-to-end distance for entanglements and molecular chain diameter of polymers

Abstract: The critical molecular weight Mc of 36 flexible and semirigid polymers has been studied. A unique correlation between the critical end-to-end distance 〈Rc〉 for entanglements and the average polymer chain diameter D is found. This correlation is discussed in the light of the reptation concept.

Effect of filler treatment on the rheological and mechanical properties of polyethylene composites

Abstract: Mechanical and Theological properties of a high density polyethylene (HDPE) filled with mica flakes, rutile and carbon black are investigated. Experimental results show that the Young modulus and the tensile strength of mica and rutile-HDPE composites are significantly enhanced by surface treatment of fillers with silane and titanate coupling agents. Surface treatments are shown to reduce the peak of the loss tangent (tan δ) and slightly increase the glass transition temperature (T g). This is an indication of improved adhesion at the filler-matrix interface. The carbon black composites, however, hardly show any improvement by these treatments. The Theological properties are also effected by surface treatments, particularly at low shear rates. The low-shear rate viscosities (η O) and characteristic time (λ 0) of these systems are determined and compared. It is found that η 0 and λ 0 of carbon black composites are much higher than those of mica composites. This is probably due to the poor dispersi...

Property stabilization in filled, drawn polyethylene

Abstract: Mechanical properties of high density polyethylene (HDPE) extended to draw ratios in the 20–40 range have been determined and compared with corresponding properties of the polymers containing particulates including rutile, carbon black, iron oxide, and mica. Shrinkage of drawn structures was studied to temperatures near the fusion of the polymer host. The degree of interaction at polymer/additive interfaces was varied by surface coating certain of the solids with standard coupling agents. Solids were found to increase tensile moduli and to decrease shrinkage, particularly at higher exposure temperatures. The magnitude of changes due to the presence of solids was shown to depend on the apparent interaction at contacts between host and additive. In a dispersion–force matrix, like HDPE, benefits were optimized when the particulates were amphoteric or neutral, rather than having pronounced acid or base interaction potentials.

Axial phases distribution and homogenization in three-phase fluidized beds

Abstract: We have investigated the axial distribution of the liquid phase in a three-phase fluidized bed in which the particles were glass beads of two different diameters, 710–850 μm and 2 mm. Two methods were used to reduce the axial heterogeneity and homogenize the bed: the use of packing elements and the addition of a small quantity of a high molecular weight polymer. The use of packing elements was shown to be very efficient in controlling phases distribution in the bed. The packing consisted of 1 mm thick steel horizontal plates punched and stretched to obtain parallelogram-shaped openings. The addition of a high molecular weight polyisobutylene (BASF Oppanol B246, Mu, =6.15 Lo6) on the phase distribution was also studied. Low polymer concentrations up to 397 ppm (based on the liquid phase) were investigated. The addition of the polymer reduced bubble coalescence and allowed for a better distribution of the phases.

Transient heating and cooling of cocurrent three-phase fluidized beds

Abstract: The thermal transient behaviour of three-phase fluidized beds have been investigated for a liquid viscosity ranging from 35 to 75 mPa · s. For the operating conditions used in this study, a 6 mm glass particle bed was found to have a thermal response similar to that of a fixed bed. The transient responses, which were not significantly affected by gas sparging, were, however, faster for heating than for cooling. This result has been analyzed from a model assuming liquid plug flow through stationary particles using combined free and forced convection correlations for heat transfer around the particles. Different correlations are then proposed to predict the contribution of natural convection to the liquid-to-particle heat transfer in heating and cooling modes. The effect of gas sparging was found to strongly affect The 2.0 mm particle bed responses but only moderately the 3.9 mm bed responses. These responses were analyzed using axial dispersion models for the liquid and solid phases. For the 3.9 mm particle bed, the axial dispersion coefficient of the solids, EZS, was found to be of the same order of magnitude as that of the liquid coefficient, EZL. However, the value of Ezs for the 2 mm particle bed was found to be five times that of EZL. On a etudie le comportement thermique transitoire d'un lit fluidise triphasique mettant en oeuvre un liquide de viscosite variant entre 35 et 75 mPa · s. Dans ce travail, les lits de particules de verre de 6 mm, ont montre un comportement similaire a celui d'un lit fixe. De plus on a observe que les reponses du lit n'etaient pas affectees par le bullage du gaz et qu'elles etaient plus rapides en chauffage qu'en refroidissement. On a interprete ces differences en introduisant des effets mixtes de convection naturelle et de convection forcee autour des particules. Chacune de ces contributions au transfert de chaleur a ete quantifiee. Pour les experiences conduites respectivement avec des particules de 3.9 et 2.0 mm, le bullage du gaz avait des effets respectivement moderes et importants. Les reponses thermiques ont ete analysees en decrivant les melanges des phases liquide et solide par les modeles de dispersion axiale. Pour les lits de particules de 3.9 mm, les valeurs du coefficient de dispersion axiale du solide (Ezs) obtenues par regression, sont du mecme ordrede grandeur que celles du coefficient de dispersion du liquide, EZL. Pour les particules de 2.0 mm, les valeurs de Ezs sont approximativement 5 fois celles de EZL.