Dissipative mix-melting

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). 

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).]...

When molten polymer regions are formed because of FED and FED and if the deforming stresses persist, then both FED and VED will act simultaneously as heat sources, resulting in the powerful mechanism of dissipative mix-melting, which we will deal with again below. 

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