Polymer rheology viscous dissipation

Although considerable progress has been made in understanding heat transfer in polymeric systems, much still remains to be done. There are a number of reasons why this is so, including lack of good physical data such as (thermal conductivities, specific heats, and rheological behavior), and failure to cope with such complexities of polymer behavior as elastic effects, compressibility, and viscous dissipation. 

Filled polymer rheology is basically concerned with the description of the deformation of filled polymer systems under the influence of applied stresses. Softened or molten filled polymers are viscoelastic materials in the sense that their response to deformation lies in varying extent between that of viscous liquids and elastic solids. In purely viscous liquids, the mechanical energy is dissipated into the systems in the form of heat and cannot be recovered by releasing the stresses. Ideal solids, on the other hand, deform elastically such fliat the deformation is reversible and the energy of deformation is fully recoverable when the stresses are released. 

Further development of flow curves for polymer melts are discussed in more advanced rheology texts. Compared with many regular fluids, where simplifying assumptions can be used in the analysis of flow behavior, the significant of viscous dissipation for polymers must be considered as must entrance effects, where the polymer melt first enters a tube. However, successful models have been developed that even allow scale-up for commercially relevant processes. 

Viscous heating effects play an important role in the measurement of viscosity using the slit rheometer. The increase of temperature due to viscous dissipation decreases the viscosity, making this value unacceptably from the estimation of the real effect of pressure on the rheology of the polymer. 

The dilational rheology behavior of polymer monolayers is a very interesting aspect. If a polymer film is viewed as a macroscopy continuum medium, several types of motion are possible [96], As it has been explained by Monroy et al. [59], it is possible to distinguish two main types capillary (or out of plane) and dilational (or in plane) [59,60,97], The first one is a shear deformation, while for the second one there are both a compression - dilatation motion and a shear motion. Since dissipative effects do exist within the film, each of the motions consists of elastic and viscous components. The elastic constant for the capillary motion is the surface tension y, while for the second it is the dilatation elasticity e. The latter modulus depends upon the stress applied to the monolayer. For a uniaxial stress (as it is the case for capillary waves or for compression in a single barrier Langmuir trough) the dilatational modulus is the sum of the compression and shear moduli [98]... 

Melt rheology is concerned with the description of the deformatitm of the material under the influence of stresses. Deformation and flow naturally exist when the thermoplastics are melted and then reformed into solid products of various shapes. All polymer melts are viscoelastic materials that is, their response to external load lies in varying extent between that of a viscous liquid and an elastic solid. In an ideal viscous liquid, the energy of deformation is dissipated in the form of heat and cannot be recovered just by releasing the external forces whereas, in an ideal elastic solid, the deformation is fiilly recovered when the stresses are released. 

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