Search results for "Shear flow"

1988

An apparatus for turbidimetric measurements of demixing temperatures under shear flow is presented, and the results of experiments with trans-decahydronaphthalene/polystyrene (TD/PS) solutions, investigating molecular weights ranging from 100 kg/mol to 1770 kg/mol, are compared with viscometric data. It is found that the sign and magnitude of shear effects depend on molecular weight (Mw), polymer concentration (c2), and shear rate (). For the first time, it was possible to study a solution which exhibits shear dissolution at low shear rates but shear demixing at high shear rates.

Rheological behavior of a semirigid liquid crystal polymer

1993

The rheological behavior of liquid crystal polymers is still far from completely clarified from both experimental and theoretical points of view. In this paper, the shear flow and the non-isothermal elongation flow behavior of a semi-rigid liquid crystal copolyester is discussed. The viscosity strongly decreases when the test temperature is increased above the crystal-nematic transition temperature; below this temperature the viscosity is very high. The thermal history strongly affects the shear viscosity. The elongational flow behavior depends also on temperature. Above the crystal-nematic transition temperature and the mesophase is easily spinnable, whereas below this temperature, the spi…

Compressed Polymer Brushes under the Shear Flow

1998

The structure and dynamics of two compressed polymer brushes under the shear deformation were investigated by the methods of stochastic dynamics. The shear was created by the move-ment of grafting planes with the constant velo-cities in opposite directions along the planes.

Rheological behaviour, filmability and mechanical properties of biodegradable polymer films

2014

The rheological properties in shear flow and non isothermal elongational flow of two biodegradable polymers, belonging to two different classes of materials, have been measured and compared with those of a film blowing grade high density polyethylene in order to assess the filmability of these polymers. The mechanical properties of isotropic and anisotropic samples have been also reported.

Scattering function and the dynamics of phase separation in polymer mixtures under shear flow

1988

The phenomenological mean-field theory describing concentration fluctuations and spinodal decomposition of binary mixtures of long flexible macromolecules is generalized to mixtures under steady shear flow. This shear flow leads to a partial orientation and stretching of the coils, as well as to an anisotropic deformation of concentration fluctuations. Generalizing the approach of Onuki and Kawasaki, we obtain the collective scattering function describing these concentration fluctuations in the mixture under shear flow. Both the steady-state situation in the one-phase region and the initial stages of spinodal decomposition for concentrations inside of the spinodal curve are considered.

Transient birefringence of polymer melts in intermittent shear flow: Model analysis of the non-linear viscoelastic behaviour

1977

A non-linear viscoelastic model has been used to interpret transient flow birefringence in changing shear flow for a polymer melt. It is shown how the new model is consistent with the basic hypothesis of the linear stress-optical law. Stress growth in shear flow and relaxation after different amounts of shearing are compared with the predictions of the non-linear model. A good agreement between experimental data and theoretical predictions is found.

Shear flow characterization of blends containing liquid crystal polymers

1992

A simple phenomenological approach is proposed in order to predict the presence of minima in the viscosity-composition curves of blends of thermoplastic with liquid crystal polymer (LCP). When the viscosity of the liquid crystal polymer is larger than that of the thermoplastic matrix, a minimum is observed. A possible explanation of the presence of yield stress in the flow curves of these blends is also given.

The Role of Elongational Flow in Morphology Modification of Polyethylene/OMMt Nanocomposite System

2011

The formulation of high-performance polymer based nanocomposites depend on many factors, such as polymeric matrix type, nanoparticle type, loading and morphology, affinity between the polymeric matrix and nanoparticles, presence of compatibilizer and processing conditions [1-4]. During the industrial processing the polymer based systems are subjected to two different processing flows, i.e. the shear and elongational flow. The shear flow plays a significant role in polyethylene/OMMt manufacture processing but it is not able to change the system morphology, while, the elongational flow, involved in spinning and film-blowing processing operations, can induce considerably clay morphology variat…

Rheological Properties of Different Film Blowing Polyethylene Samples Under Shear and Elongational Flow

2005

Summary: The rheological behavior of polyethylenes ismainly dominated by the molecular weight, the molecularweight distribution and by the type, the amount and thedistribution of the chain branches. In this work a linearmetallocenecatalyzedpolyethylene(m-PE),abranchedme-tallocene catalyzed polyethylene (m-bPE), a conventionallinear low density polyethylene (LLDPE) and a low densitypolyethylene (LDPE) have been investigated in order tocompare their rheological behavior in shear and in elonga-tional flow. The four samples have similar melt flow indexand in particular a value typical of film blowing grade.The melt viscosity has been studied both in shear and inisothermal and non-isothermal elonga…