Experimental study for starve‐fed single screw extrusion of thermoplastics

Abstract

An experimental study of the polymer behavior in a starve‐fed single screw extrusion is presented. Various polymeric materials, semicrystalline low density polyethylene (LDPE), polypropylene (PP), and (LDPE/PS) polyblends were investigated at various operating conditions. A “screw pulling‐out” technique was used to study polymer behavior along the screw. The solid conveying, melting position, the extent of starvation, and the fully filled regions were observed. Polymer samples were stripped off from the screw which was removed from the machine to investigate melting mechanism. It was seen that filling of the screw channel increases with the flow rate at a fixed screw speed, and decreases with the screw speed at a fixed flow rate. Contiguous solids melting mechanism was observed for flood fed extrusion, but it was not observed for starve‐fed extrusion. A new two‐stage physical model of polymer melting has been proposed with conductive mechanism for melting in the starve‐fed region and dispersed melting mechanism in the fully filled region. Melting action seems to be faster for starve feeding than for flood feeding, since the pellets are not compacted into a dense solid bed. It was observed that the pressure and power consumption considerably decrease with starvation. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

Analysis of process parameters related to the single-screw extrusion of recycled polypropylene blends by using design of experiments

“…The coefficients suggest that screw speed (B) is the most significant effect on mass output, consistent with Borgaonkar et al 32 and with predictions from the melt pumping analysis in single screw extrusion, consisting of laminar shear flow due to drag forces induced by screw rotation [2][3][4] . Figure 3 is a typical Output versus Pressure (Q/P) diagram derived from basic theoretical considerations, which illustrates the effects of rotational screw speed (N B > N A ) consistent with the dominating effect of this variable predicted in Equation (8). This figure also implies that at a given screw speed there will be only a relatively small change in the operation viscosity, as reported elsewhere 1 .…”

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

“…As starve feeding usually improves mixing and melting capacities of the extruder, this way of feeding has been applied for single-screw extruders. [1,2,[11][12][13][14] These studies have been discussed by Wilczyński et al [15] General review on modeling of polymer extrusion has been presented elsewhere. Tadmor et al [4][5][6] first developed a mathematical model of fusion of polymers in single-screw extruders, and later a composite model of the process that includes polymer solid conveying, polymer fusion and polymer melt conveying.…”

“…[1][2][3] Flood fed single-screw extrusion is generally well understood, and the literature is very rich here. [16][17][18][19] Wilczyński et al [15,20,21] first developed a mathematical model of fusion of polymers in starve fed single-screw extruders, and subsequently a composite model of the process, first for conventional screws, and later for non-conventional screws. [7][8][9][10] Starve fed extrusion process is much less known.…”

A composite model for starve fed single screw extrusion of thermoplastics

“…The composite model we propose is based on our previous experimental observations which are summarized in Fig. .…”

“…Melting mechanisms in single screw extruders: (a) flood fed extrusion (of PP at the screw speed N = 50 rpm and flood feed rate GFF = 12.85 kg/h), (b) starve fed extrusion (of PP at the screw speed N = 50 rpm and metered feed rate GSF = 90% GFF = 11.56 kg/h) .…”