Extrusion processes single-screw extruder mechanisms

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. 

Nishimura et al. (2005) produced PLLA fibers using a melt spinning process. PLLA was first dried in vacuum at 70 °C, melted and extraded at a melt temperature of 220 °C in order to avoid thermal degradation. Pellets were extruded with a single-screw extruder, at the end of which a spinning nozzle with 12 holes was placed. Extrusion took place in a water bath kept at 45 °C, and spun fibers were drawn at 98 °C in order to have enough energy to achieve solvent evaporation. The mechanical and other properties of the PLLA fibers were preserved. 

The study on this in situ reactive compatibilization of polyolefin and polystyrene, using Friedel-Crafts benzene ring alkylation, was extended to a single screw extrusion process for PE/PS and PP/PS blends [27]. The mechanical characterization of various blends showed that the in situ compatibilization of PE/PS and PP/PS blends was again achieved within the processing time in a single screw extruder. 

Sheet extrusion was carried out on a Welex single screw extruder. A temperature profile of 90, 150, 160, 170, 175, 175, 180, and 180 °C was maintained from feed throat to film die. The cooling rolls were kept at 24-25 °C while the screw speed was set at 17 RPM. Only the 2 and 5 wt% nanocomposites were processed in this fashion, the 10 wt% formulation producing inhomogeneous films due to its greater viscosity and propensity for thermal degradation. These sheets were then analyzed with respect to their barrier and mechanical properties, with pure FPVC also sheet-extruded as a control. 

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