Flow properties of polymers

The flow characteristics of a polymer largely determine the type of machinery used for extrusion and influence the choice of the process and processing conditions. The rheological and thermal properties of a polymer determine the flow characteristics and are discussed here. The rheological properties define the manner in which a material will deform when certain stresses are applied, a characteristic that is important in the plasticizing zone and the die-forming regions of the process. In a bulk process, the flow properties of the material are directly linked to the transport behaviors, which are 

In melt blowing, for example, surface tension-driven instabilities have been observed both in laboratories and in industrial processes when finer fibers are generated. These create droplets that are dispersed in the fiber mat. Systematic research has proved that altering the rheological properties of the polymer suppresses, and in some cases eliminates, their stability.  

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J. A. Brydson, Flow Properties of Polymer Melts, 2nd ed., Godwin/Plastics and Rubber Institute, 1981. 

BRYDSON, J. A., Flow Properties of Polymer Melts, (2nd Edn), Geo. Godwin, London (1981) BRYDSON, J. A., Handbook for Plastics Processors, Butterworth-Heinemann, Oxford (1990) CRAWFORD, R. J., Plastics Engineering, 2nd Edn, Pergamon, Oxford (1990)... 

The flow properties of polymers provide a basis for predicting processing characteristics and are usually determined by measurements which relate a shear stress to some shear rate. Any polymer is characterized by its flow curves. Even interactions between compounding ingredients and the polymer can be detected in this way. 

Brydson, J.A. (1981) Flow properties of polymer melts. George Godwin, London... 

E. B. Christiansen and W. R. Leppard, Steady-State and Oscillatory Flow Properties of Polymer Solutions, Trans. Soc. Rheol., 18, 65-86 (1974). 

Brydson JA, "Flow Properties of Polymer Melts", Uiffe Books Ltd, London, 2nd Ed, 1981. 

Viscosity measurements alone cannot be directly used in the Mark-Houwink-Sakurada equation to relate absolute viscosity and polymer molecular weight, since additional unknowns, K and a must be determined. Therefore, viscometry does not yield absolute molecular weight values it rather gives only a relative measure of polymer s molecular weight. Viscosity measurements based on the principle of mechanical shearing are also employed, most commonly with concentrated polymer solutions or undiluted polymer these methods, however, are more applicable to flow properties of polymers, not molecular weight determinations. 

In the subsequent 20 years (1960-80), the main principles of modern polymer physics were developed. These include the Edwards model of the polymer chain and its confining tube (Chapters 7 and 9), the modern view of semidilute solutions established by des Cloizeaux and de Gennes (Chapter 5), and the reptation theory of chain diffusion developed by de Gennes (Chapter 9) that led to the Doi-Edwards theory for the flow properties of polymer melts. 

A dilute polymer solution is a system where polymer molecules are dispersed among solvent molecules. An assumption common to any existing theory for flow properties of polymer solutions is that the structure of solvent molecules is neglected and the solvent is assumed to be replaced by a continuous medium of a Newtonian nature. Thus, macroscopic hydrodynamics may be used to describe the motion of the solvent. Recently, some ordering or local structure of solvent molecules around a polymer chain has been postulated as an explanation of the stress-optical coefficient of swollen polymer networks (31,32) so that the assumption of a solvent continuum may not apply. The high frequency behavior shown in Chapter 4 could possibly due to such a microscopic structure of the solvent molecules. Anyway, the assumption of the continuum is employed in every current theory capable of explicit predictions of viscoelastic properties. In the theories of Kirkwood or... 

The binding interactions of polymers to hair The chemical nature of polymers used in hair products In situ polymerization reaction mechanisms Rheological or flow properties of polymer solutions Film formation and adhesional properties of polymers... 

High flow properties of polymers and excipients are usually necessary. 

Rheology is a relatively young branch of natural science that deals with the relationships between forces (stresses) and deformations of material bodies. Hence, it is also connected to the flow properties of polymers both in solution and in the melt, as well as the reaction of materials in the solid state to mechanical stresses. Most polymeric materials exhibit the combined reactions of both liquid and solid states, called viscoelasticity, a combination of the viscosity of a liquid and the elasticity of a solid. 

Lyngaae-Jorgensen, J., Thomsen, L.D., Rasmussen, K., Soondergaard, K and Andersen, F.E. (1988) On the influence of interfadal slip on melt flow properties of polymer blends. Intern. Pdym. Process,... 

The book by Schenkel [2] is a translation of the German text Kunststoff Extruder-Technik [3], which is an extension of the original book Schneckenpressen fuer Kunststoffe [4]. This book is very complete dealing with flow properties of polymers, extrusion theory, and design of extrusion equipment. The emphasis of Schen-keTs book is on the mechanical or machinery aspects of extruders. As in Bernhardt s... 

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