Effect of die surface on the onset of stick-slip flow in polymer processing

International audienceIn this paper, we investigate the relationships between stick-slip defect and molecular slip at the wall for linear polymers. By considering Brochard-de Gennes slip model and molecular chain dynamics at the wall, we propose an expression for the critical shear stress at the onset of stick-slip as a function of the wettability of the polymer on the die surface or, more precisely, as a function of the apparent contact angle between polymer and die surface

Oscillatory squeeze flow for the study of linear viscoelastic behavior

The squeezing of a sample between parallel plates has been used for many years to characterize the rheological behavior of soft, purely viscous materials, and in recent times, small-amplitude oscillatory squeezing has been proposed as a means to determine the linear viscoelastic properties of molten polymers and suspensions. The principal advantage of squeeze flow rheometer over rotational devices is the simplicity of the apparatus. It has no air bearing and is much less expensive and easier to use. Accuracy may be somewhat reduced, but for quality control purposes, it could be quite useful. It might also find application as the central component of a high-throughput rheometer for evaluating experimental materials. The deformation is not simple shear, but equations have been derived to show that the oscillatory compressive (normal) force that is measured can serve as a basis for calculating the storage and loss moduli. These theories as well as instruments that have been developed to generate the required deformation are described, and applications to a variety of materials are described

Momentum exchange in a confined circular jet with turbulent source

http://deepblue.lib.umich.edu/bitstream/2027.42/4514/5/bab4426.0001.001.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/4514/4/bab4426.0001.001.tx

Melt rheology and its applications in the plastics industry

This is the second edition of Melt Rheology and its Role in Plastics Processing, although the title has changed to reflect its broadened scope. Advances in the recent years in rheometer technology and polymer science have greatly enhanced the usefulness of rheology in the plastics industry. It is now possible to design polymers having specific molecular structures and to predict the flow properties of melts having those structures. In addition, rheological properties now provide more precise information about molecular structure. This book provides all the information that is needed for the intelligent application of rheology in the development of new polymers, the determination of molecular structure and the correlation of processability with laboratory test data. Theory and equations are limited to what is essential for the use of rheology in the characterization of polymers, the development of new plastics materials and the prediction of plastics processing behavior. The emphasis is on information that will be of direct use to practitioners. Extensive references are provided for those wishing to pursue certain issues in greater depth. While the primary audience is applied polymer scientists and plastics engineers, the book will also be of use to postgraduate students in polymer science and engineering and as a text for a graduate course

Activities in dilute molten alloys

http://deepblue.lib.umich.edu/bitstream/2027.42/4515/5/bab4429.0001.001.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/4515/4/bab4429.0001.001.tx