Experimental study of melting of LDPE/PS polyblend in an intermeshing counter-rotating twin screw extruder

An experimental study is presented of the melting mechanism in a starve-fed closely intermeshing counter-rotating twin screw extruder of a modular Leistritz design. Various polymeric materials, semicrystalline low density polyethylene (LDPE), amorphous polystyrene (PS), and (LDPE/PS) polyblend were investigated at various operating conditions. A screw pulling-out technique was used to investigate polymer behavior along the screw axis. In particular, the solid conveying, melting positions, the extent of starved character along the screw, and the fully filled regions were observed. Polymer samples were stripped off from each screw which was removed from the machine to investigate melting mechanism. Generally, it has been concluded that the melting mechanism revealed by White and Wilczynski for polyolefines has been proved for other polymeric materials under study. This mechanism consists of pellets being dragged into the calendering gap where they are melted due to calendering action. The molten polymer is expelled from the gap and pushes against the pellet bed which is continuously dragged into the gap. The composite modeling of an intermeshing counter-rotating twin screw extrusion of polyblends has also been discussed. POLYM. ENG. SCI., 52:449458, 2012. (C) 2011 Society of Plastics Engineers