Extrusion processes melting mechanism

The fundamental processes and mechanisms that control single-screw extrusion are presented in Chapters 5 through 8. These processes include solids conveying, melting, polymer fluid flow, and mixing. The analyses presented in these chapters focus on easily utilized functions needed to assess the operation of the single-screw extruder. The derivation of these relationships will be presented in detail in the appendices for those who desire to explore the theory of extrusion in more detail. 

The paper gives an overview of effects occurring or acoustic treatment of dissolved and molten polymers. Emphasis is made on acoustic cavitation discovered recently not only in low-viscous fluids but also in molten polymers. Major guidelines have been specified for practical utilization of acoustic treatment of flowable polymers in molding intensification of extrusion processes, reduction in thickness of produced films, directed mechanical destruction, chemical activation of melts, etc. Efficiency of overlapping high-frequency vibrations in molding of molten thermoplastics is discussed in terms of power consumption. 

Chokshi, R. J., H. K. Sandhu, R. M. Iyer, N. H. Shah, A. W. Malick, and H. Zia. 2005. Characterization of physico-mechanical properties of indomethacin and polymers to assess their suitability for hot-melt extrusion process as a means to manufacture solid dispersion/soJUflbarm ScB4 2463-2474. 

However, the melting or plasticating process that follows the solids conveying zone is a relatively complex one, and unlike the melt extrusion and solids conveying processes, the detailed physical melting mechanisms cannot be easily visualized, predicated, and modeled from basic principles without experimental investigation. 

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.]...

PEG 400, and potentially other plasticizers, to evaporate or degrade under hot-melt extrusion processing and storage. It is also evident that these findings for PEG 400 explain changes upon mechanical testing of PEG 400-incorporated HPC films. ... 

Spinlaying. This process includes various steps, i.e. filament extrusion, drawing, lay down, and bonding. The first two steps can be easily conceived from a typical melt extrusion process. The latter steps involve the deposition of filaments in a random manner on to the conveyor belt. It should be noted that the spunlaid nonwovens are generally self-bonded but additionally they can be bonded by means of thermal, chemical, or mechanical means in order to enhance their mechanical properties. 

---