Polymer rheology bulk

Reduction in the apparent bulk viscosity due to a change in polymer rheology. It is well known that ultrasound can lead, via degradation, to a reduction in polymer solution viscosity. Although Fairbrother did not investigate whether degradation of the polymer, and subsequent reduction in R.M.M. and hence viscosity had occurred, it seems reasonable to assume that the polymer melt with an initial viscosity of 30000-100000 poise would certainly have resisted cavitation and thus degradation. 

S. Gratch and S. Loshaek Viscosity relationships for polymers in bulk and concentrated solutions, p. 431—493 dans "Rheology . Ed. F. R. Eirich, Vol. 1, New-York Academic Press 1956. 

Because NMR is so closely related to molecular motion, there has been much effort to tie spectroscopic parameters, such as relaxation times, to the known rheological and mechanical properties of materials. While there has been some success, as will be seen in Sec. III.D, a general correlation has yet to be established. One difficulty is that NMR is most sensitive to relatively rapid, local motions, while it is primarily slower, longer-range motions that are responsible for a polymer s bulk properties. Rheo-NMR experiments have attempted to provide the connection between micro- and macroscopic observations, and they will likely become a very useful tool in the NMR of polymers if the equipment becomes widely available [36]. 

Luengo G ef a/1997 Thin film rheology and tribology of oonfined polymer melts oontrasts with bulk properties Macromolecules 30 2482-94... 

Extensional Viscosity. In addition to the shear viscosity Tj, two other rheological constants can be defined for fluids the bulk viscosity, iC, and the extensional or elongational viscosity, Tj (34,49,100—107). The bulk viscosity relates the hydrostatic pressure to the rate of deformation of volume, whereas the extensional viscosity relates the tensile stress to the rate of extensional deformation of the fluid. Extensional viscosity is important in a number of industrial processes and problems (34,100,108—110). Shear properties alone are insufficient for the characterization of many fluids, particularly polymer melts (101,107,111,112). 

The behavior of colloidal suspensions is controlled by iaterparticle forces, the range of which rarely extends more than a particle diameter (see Colloids). Consequentiy suspensions tend to behave like viscous Hquids except at very high particle concentrations when the particles are forced iato close proximity. Because many coating solutions consist of complex mixtures of polymer and coUoidal material, a thorough characterization of the bulk rheology requires a number of different measurements. 

Viscoelastic polymers essentially dominate the multi-billion dollar adhesives market, therefore an understanding of their adhesion behavior is very important. Adhesion of these materials involves quite a few chemical and physical phenomena. As with elastic materials, the chemical interactions and affinities in the interface provide the fundamental link for transmission of stress between the contacting bodies. This intrinsic resistance to detachment is usually augmented several folds by dissipation processes available to the viscoelastic media. The dissipation processes can have either a thermodynamic origin such as recoiling of the stretched polymeric chains upon detachment, or a dynamic and rate-sensitive nature as in chain pull-out, chain disentanglement and deformation-related rheological losses in the bulk of materials and in the vicinity of interface. 

One of the most attractive features of TLCPs is their ability to alter the rheology of bulk thermoplastic polymers. Most reports in the academic literature are concerned with viscosity reduction. For example, Siegmann et al. [1] observed a steep viscosity drop when a TLCP... 

As a consequence of the irregular and rough structure of the xylan particles, entanglements between particles are promoted and this fact may explain the poor flow properties of this polymer (Kumar et al., 2002 Nunthanid et al., 2004). Additionally, rheological parameters of xylan powder have also been studied, such as bulk and tapped densities, Hausner ratio, Carr s index, and angle of repose values, and they are summarized in Table 1. 

Luengo, G., Schmitt, R, andHUl, R., Thin Film Rheology and Tribology of Confined Polymer Melts Contrasts with Bulk Properties," Macroniolecules,Vo. 30,1997, pp. 2482-2494. 

Rheological measurements are of central importance in the processing of siloxane polymers. Typical studies would include determination of the dependence of the bulk viscosity of the material on the average molecular weight, molecular weight distribution, and rate of shear. Characterization of the effects of any branched chains or reinforcing fillers present is also of great importance.16... 

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