Friedrich Rudolf Schwarzl

Deformation and flow of polymeric materials

From the Contents: Introduction.- Physical Structure of Macromolecules.- Experimental Methods to Determine Molecular Quantities.- Structure and States of Polymers.- Linear Viscoelastic Deformation Behavior in Simple Shear.- Time-Temperature Shift of Mechanical Properties.- Linear Viscoelastic Deformation under Three-Dimensional Stresses.- Fundamentals of the Rheology of Large Deformations.- Large Deformations of Polymers.- Rheological Equations of State.-Shear Rheology.- Extensional Rheology.- Rheological Properties and Molecular Structure.- Thermorheological Behavior of Various Polymer Melts.- Rheometry.- Measurements of Flow Fields of Polymer Melts by Laser-Doppler Velocimetry.- Rheological Properties and Processing.

Time-Temperature Shift of Mechanical Properties

The time-temperature shift of the various relaxation processes of amorphous and semi-crystalline polymers is described. The shifting laws are treated theoretically.

Linear Viscoelastic Deformation Behavior in Simple Shear

The theory of linear viscoelastic behaviour in shear is described in detail and illustrated by many examples of the time and frequency-dependence of the characteristic functions of technical polymers in all states of aggregation.

Experimental Methods to Determine Molecular Quantities

In this chapter, experimental methods are described which are used to determine the molar mass and the interaction between macromolecules and solvent molecules.

Rheological Properties and Molecular Structure

In this chapter the dependence of viscous and elastic properties on molar mass, polydispersity and branching is presented. Furthermore, the influence of these molecular parameters on the uniaxial elongational behavior of polymer melts is discussed. The rheological behavior of polymer melts is significantly governed by the structure of the molecules which for a given chemical composition is described by the molar mass distribution and the architecture of the polymer chain.

Linear Viscoelastic Deformation Under Three-Dimensional Stresses

The theory of linear visco-elastic deformation in three dimensions is treated. The stress tensor and the equations for the balance of forces are introduced in Cartesian, cylindrical and polar coordinates. The strain tensor for small deformations is defined and the rheological equations of state for isotropic linear visco-elastic materials at small deformations are discussed. Simple shear, isotropic compression and uniaxial extension are treated as examples.

Large Deformations of Polymers

The stress-strain behavior of polymers is described. The rheological equations of state for isotropic elastic materials are discussed as well as the equation of state for the ideal rubber. The theory of rubber elasticity is shortly presented.

Fundamentals of the Rheology of Large Deformations

The kinematics of large deformations is discussed by introducing deformation tensors and the rate of strain tensor for finite strains. The dynamics of deformable bodies is treated, as well as the eigen-value problems of the stress tensor and the strain tensors.

Rheological Properties and Processing

Rheological properties of a polymer can be very useful to assess some aspects of processing. For a successful application of rheological data it has to be taken into account, however, that they strongly depend on temperature, time, and stress or strain rate, respectively. Therefore, the rheological behavior measured in laboratory tests can be of relevance for processing only, if the regimes of the parameters mentioned above are comparable to each other. The role of melt flow rate and viscosity functions for processing is discussed. Furthermore it is shown, how the measurement of flow profiles can be used to get a deeper insight into the reduction of “shark skin” and the extrusion of cast films. Finally, the importance of the elongational behavior of melts for film blowing and foaming is addressed.

Thermorheological Behavior of Various Polymer Melts

Polymer melts follow the time-temperature superposition principle. The shift factors of melts of amorphous polymers can be described by the so-called WLF-equation, those of semicrystalline polymer by an Arrhenius equation. In this chapter it is discussed how the coefficients of the corresponding equations depend on the molecular structure. Furthermore, it is shown how rheological complexity found for long-chain branched polyethylenes can be used for getting insight into their molecular structure.