Melting dissipative melt mixing

The microstructure of the melt-mixed blend, however, was dependent on the thermal history of the specimen. By an appropriate heat treatment at 130 C, it underwent phase separation 5 with an attendant seven fold increase in room temperature impact strength.The mechanism of energy dissipation involves both crazing and shear flow processes. These observations suggest the existence of UCST. The phase domains in the annealed samples are likely to be extremely small. 

Extrusion, melting, mixing, polymer blends, reactive extrusion, viscosity, energy dissipation, phase inversion. 

Internal surfactant antistats ate physically mixed with the plastic resin prior to processing. When the resin is melted, the antistat distributes evenly in the polymer matrix. The antistat usually has some degree of solubiUty in the molten polymer. However, when the polymer is processed (extmded, molded, etc) into its final form and allowed to cool, the antistat migrates to the surface of the finished article due to its limited solubiUty in the solidified resin. The molecule of a surface-active agent is composed of a polar hydrophilic portion and a nonpolar hydrophobic portion. The hydrophilic portion of the surfactant at the surface attracts moisture from the atmosphere it is the moisture that has the static dissipative effect. 

The extruder is used since it mixes, melts, and degases the polymer. However, as said in the previous paragraph, from an exergetic point of view, it is not an efficient apparatus, since it dissipates mechanical work into heat by frictional forces. A possible alternative to the extruder could therefore be a separate degasser, a static mixer, or a gear pump to push the polymer melt through the mixer and perforated plate (Figure 11.6). 

On the other hand, we discussed and presented in physical terms the very powerful melting mechanisms resulting from repeated, large deformations, forced on compacted particulate assemblies by twin co- or counterrotating devices. These mechanisms, which we refer to in Section 5.1, are frictional energy dissipation (FED), plastic energy dissipation (PED), and dissipative mix-melting (DMM). 

FED (3)] and viscous dissipation in the molten regions. As melting progresses the latter mechanism becomes dominant. Mixing disperses the newly formed melt into the mass [creating a solids-rich suspension] the melt that comes in intimate contact with solid particles cools down and at the same time heats up the surface layer of the particles the particulate solid charge is eventually converted into a richer, thermally inhomogeneous suspension and ultimately into a... 

However, experimental studies (50), using either powder feed or pelletized feed with some recycled melt over the channel block into the feed port, have not exhibited drag removal melting but a dissipative mix-melting mechanism, discussed in Chapter 5. As... 

Fig. 10.12 Schematic representation of two melting mechanisms observed by Janssen (24) with PP processed in a double-flighted 47-mm counterrotating TSE operating at low rotational speeds, (a) Melting when the die pressure was set at the low value of 50 psi, where chamber-to-chamber leak pressure backflows are negligible, (b) Melting under the high die pressure of 2700 psi, which enables leak backflows, which result in chamber solid bed compaction and introduce the possibility of dissipative mix melting. [Reprinted by permission from L. P. B. M. Janssen, Twin Screw Extrusion, Elsevier Scientific, Amsterdam, 1978.]...

Fig. 10.34 Schematic representation of the two regions in the melting zone of CRNI TSEs with matched screw arrays. In the two regions (A), away from the tangent interscrew plane, the melting mechanism is that of SSEs. In the interscrew plane, a melt-particulates suspension undergoes dissipative mix-melting. [Reprinted by permission from R J. Nichols and F. Kher-adi, Melting in CRT Twin Screw Extruders, Mod. Plast., 61, 70 (1984).]...

The flow on the suspension visualized and simplified in the model just discussed generates VED and heats the pellets, but does not deform them. Thus, they do not include the dissipative mix-melting (DMM) melting mechanism, only VED. However, with the proper parameter adjustments, they are able to make fair predictions of the overall melting... 

Fig. 11.31 Schematic representation of the Twin Screw Mixing Element Evaluator (TSMEE) in (a) the melt-melt (M-M) mode, and (b) the dissipative mix-melting (DMM) mode. The last section of both the M-M and DME modes consists of two separate HBRs. The mixing element sequences are a design variable. [Reprinted with permission from Proceedings of the Sixth Semi-annual Meeting of the Polymer Mixing Study, Polymer Processing Institute, Hoboken, NJ (1993).]...

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