Experimental study of melting of polymer blends in a starve fed single screw extruder

Abstract

Experimental study is presented of the melting mechanism of polymer blends in a starve fed single screw extruder. Various polyblends were investigated such as PP/PS, HDPE/PS, and PP/PMMA. “Screw pulling‐out” technique was used to study the solid conveying, melting mechanism, and extent of starvation. It has been concluded that melting mechanism consists of two stages: conductive melting in the starve fed region and dispersed melting in the fully filled region. Substantial differences between melting of neat polymers and polymer blends were observed. In the case of polyblends, in the starved region a mixture of two solid polymers is melted by conduction, and in the fully filled region a dispersion of one or two solid polymers in a molten matrix is observed. Although contiguous solids melting mechanism was not seen for starve fed extrusion of polyblends, it was clearly observed for flood fed extrusion. Melting action seems to be faster for starve fed extruders than for flood fed machines, since the polyblend granules are not compacted into a dense solid bed. It was observed the pressure considerably decreases with level of starvation. Filling of the screw increases with an increase of the feed rate of polyblend, and decreases with an increase of the screw speed. Global modeling of the starve fed single screw extrusion of polyblends has been discussed. POLYM. ENG. SCI., 56:1349–1356, 2016. © 2016 Society of Plastics Engineers

Optimization for Starve Fed/Flood Fed Single Screw Extrusion of Polymeric Materials

“…According to this model, two stages of melting are distinguished: melting by conduction in the partially filled region of the screw where the polymer granules are collected at the active screw flight and melting by energy dissipation in the fully filled region where the unmolten solid particles are suspended in the previously molten material ( Figure 1b). This basic model was later extended to non-conventional screw configurations [31,32] and extrusion of polymer blends and composites [56][57][58][59].…”

A computer model for starve‐fed single‐screw extrusion of polymer blends

“…The modeling basis is an assumption that the parameters that define the process at the onset of each element are equal to the parameters at the end of the previous element, that is, where π is the parameter that defines the process, π i_in is the parameter at the onset of i-element, π i−1_out is the [36] parameter at the end of (i − 1)-element, and z is the element position in the direction of the channel length.…”

“…[36] It results from these studies that mechanisms of fusion of polymer blends in the flood fed extruder and starve fed extruder are fundamentally different. [36] It results from these studies that mechanisms of fusion of polymer blends in the flood fed extruder and starve fed extruder are fundamentally different.…”

“…[36] Four different areas of extrusion process have been distinguished: solid conveying (SOLIDS) in the partially filled area and fusion by conduction (MELTING_I) in this area, as well as dispersive fusion of one or two components of polymer blend (MELTING_II) in the fully filled area and melt flow (MELT) in this area. [36] Four different areas of extrusion process have been distinguished: solid conveying (SOLIDS) in the partially filled area and fusion by conduction (MELTING_I) in this area, as well as dispersive fusion of one or two components of polymer blend (MELTING_II) in the fully filled area and melt flow (MELT) in this area.…”

“…The composite model, which is proposed here, results from our recent experimental studies on fusion of polymer blends in starve fed single-screw extruders. [36] It results from these studies that mechanisms of fusion of polymer blends in the flood fed extruder and starve fed extruder are fundamentally different. CSM (contiguous solid melting) mechanism of Tadmor was clearly visible in the flood fed extruder.…”