Polystyrene melt

How does yield stress depend on the size of particles We have mentioned above that increasing the specific surface, i.e. decreasing an average size of particles of one type, causes an increase in yield stress. This fact was observed in many works (for example [14-16]). Clear model experiments the purpose of which was to reveal the role of a particle s size were carried out in work [8], By an example of suspensions of spherical particles in polystyrene melt it was shown that yield stress of equiconcentrated dispersions may change by a hundred of times according to the diameter d of non-... 

Modification of filler s surface by active media leads to the same strong variation in viscosity. We can point out as an example the results of work [8], in which the values of the viscosity of dispersions of CaC03 in polystyrene melt were compared. For q> = 0.3 and the diameter of particles equal to 0.07 nm a treatment of the filler s surface by stearic acid caused a decrease in viscosity in the region of low shear rates as compared to the viscosity of nontreated particles more than by ten times. This very strong result, however, should not possibly be understood only from the point of view of viscometric measurements. The point is that, as stated above, a treatment of the filler particles affects its ability to netformation. Therefore for one and the same conditions of measuring viscosity, the dispersions being compared are not in equivalent positions with respect to yield stress. Thus, their viscosities become different. 

Figure 7.56 Extrudate swelling in polystyrene melts for ( ) broad molecular weight distribution and (O, a) narrow molecular weight distribution samples. From Z. Tadmor and C. G. Gogos, Principles of Polymer Processing, Copyright 1979 by John Wiley Sons, Inc. This material is used by permission of John Wiley Sons, Inc.

For the unfilled polystyrene melt at low elongational rates a constant value of Tjg is achieved given by three times the zero shear viscosity according to Trou-... 

Ballman and co-workers have used carbon particles to determine flow patterns for polystyrene melts in plate-cone and capillary viscometers (70). Complex patterns, rather than the simple flow expected, were observed for high molecular weight samples. These may have been caused, however, by differences in viscosity between adjacent layers of pure melt and melt with suspended particles. 

Fig. 5.8. Storage modulus vs frequency for narrow distribution polystyrene melts, reduced to 160° C by temperature-frequency superposition. Molecular weight range from Mw = 8900 (L9) to Mw= 581000 (L18) (124). [Reproduced from Macromolecules 3, 111 (1970).]...

Fig. 5.10. Loss modulus vs frequency for a narrow distribution polystyrene melt reduced to...

Ballman,R.L Rademacher,L.E., Farnham,W.H. Visualization of polystyrene melt flow. Presented at 1972 August U.S.-Japan joint seminar on polymer processing and rheology, Knoxville, Tenn. See J. Appl. Polymer Symp. 20 (1973). 

Mills,N.J., Nevin,A. Oscillatory shear measurements on polystyrene melts in the terminal region. J. Polymer Sci. Pt. A-2 9,267-281 (1971). 

Mieras,H.J.M.A. Elastic or normal-stress behavior of monodisperse polystyrene melts or solutions. Paper presented at the conference Advances in Rheology, Glasgow, September 1969. 

Vinogradov,G.V., Belkin,I.M. Elastic strength, and viscous properties of polymer (polyethylene and polystyrene) melts. J. Polymer Sci. PL A 3,917-932 (1965). 

In this respect, additional results, as obtained on polymer melts 40), seem of interest. Fig. 1.9 shows results obtained on a polystyrene melt (Styron 666 at 190° with the aid of the discussed slit-apparatus. In this figure the total path difference is plotted in the form (P/d) against apparent shear rate Ds. Extrusion defect occurs only at the highest... 

Fig. 1.9. Total path difference P, divided by slit width d, as a function of apparent shear rate D, for a polystyrene melt (Styron 666) at 190° C [Wales (40)]...

The method of incomplete mold filling is effective for investigating injection molding of fiber glass-loaded polypropylene and polystyrene melts.283 After solidification, samples were prepared for microscopic investigation. The authors determined the distribution and orientation of the fibers in different sections of the article and thus were able to clarify the pattern of flow in different parts of the mold as a function of the process parameters. They concluded that the width of the (cavity)... 

A. Tukachinsky, Y. Talmon, and Z. Tadmor Foam-enhanced Devolatilization of Polystyrene Melt in a Vented Extruder, AIChE J., 40, 670-675 (1994). 

Fig. 12.12 Comparison of the viscosity and swelling ratio dependence on shear rate for a polystyrene melt of Mw = 2.2 x 105 and Mw/Mn = 3.1. [Reprinted hy permission from W. W. Graessley, S. D. Glasscock, and R. L. Crawley, Die Swell in Molten Polymers, Trans. Soc. Rheol., 14, 519 (1970).]...

Fodor JS, Hill DA (1994) Determination of molecular weight distribution of entangled cis-polystyrene melts by inversion of normal-mode dielectric loss spectra. J Phys Chem 98(31) 7674-7684... 

Figure 3.12 Time-temperature superposition along 45° trajectories (x=const.) to a reference temperature T0= 170°C for the viscosity function of the polystyrene melt whose viscosity functions were measured between 150 and 200°C...

H. Miinstedt Dependence of the elongational behavior of polystyrene melts on molecular weight and molecular weight distribution, J. Rheol. 24 6 (1980) 847-867... 

The SPM image in Fig. la shows a typical example of the lateral distribution of the surface potential for a polystyrene melt film. 

Free volume approach to polystyrene melt viscosity. J. Appl. Phys- 29, 1395-1398 (1958). 

Figure 9 shows a typical temporal series XRD patterns, for a polystyrene Mw= 30,000 (PS30)/octadecyl-ammonium modified fluorohectorite (C18FH) mixture annealed in-situ at 160 °C in vacuum. Details regarding the data collection and analysis are presented in reference [ 12]. The width of the original unintercalated peak and the final intercalated peak appear to be similar, suggesting that the polystyrene melt intercalation does not drastically alter the coherence length or disrupt the layer structure of the silicate crystallites. 

Procedure. Specimen Fabrication. The reinforcements were mixed into the polystyrene melt on a Farrell two-roll mill at 320°F. It was necessary to dry the asbestos fibers for 24 hr at 250°F prior to mixing to ensure the breakup of bundle aggregates. The milling/fluxing time was held to 8 min for all samples. The sheets obtained in milling were cut, crossplied, and compression molded in an open frame on a Wabash press. After they reached the platen temperature the material was held at 330 °F and 2000 psi for 6 min. The frame was then transferred to a cold press, and the sample was cooled under the same pressure. The test specimens were cut from ys-inch thick plates prepared in the foregoing manner. 

How would you expect the viscosity of a polystyrene melt to vary with molecular weight How does it vary with strain rate ... 

Lomellini P (1992) Williams-Landel-Ferry versus Arrhenius behaviour polystyrene melt viscoelasticity revised. Polymer 33 4983-89. 

Venerus DC, Zhu S-H and Ottinger HC (1999) Stress and birefringence measurements during the uniaxial elongation of polystyrene melts. J Rheol 43 795-813. 

It is not clear why this transition should occur at such a higher level of arm entanglement for polystyrene stars than for other star polymers. This observation is in direct conflict with the standard assumption that through a proper scaling of plateau modulus (Go) and monomeric friction coefficient (0 that rheological behavior should be dependent only on molecular topology and be independent of molecular chemical structure. This standard assumption was demonstrated to hold fairly well for the linear viscoelastic response of well-entangled monodisperse linear polyisoprene, polybutadiene, and polystyrene melts by McLeish and Milner [24]. 

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