Morphology and property of polyethylene pipe extruded at the low mandrel rotation

Abstract

During the rotation extrusion of polyethylene (PE) pipes, with the rotating mandrel, compressed air as a cooling medium was introduced through their interior to achieve the quick cooling of the inner wall. The experimental results showed that the hoop stress exerted by mandrel rotation could promote the molecular orientation in the hoop direction; moreover, the introduction of compressed air could quicken its inner wall's cooling rate so as to slow down the relaxation of the oriented molecule and to reserve the orientation structure. Therefore, the hoop orientation degree increased with the increasing inner wall's cooling rate. As a result, the performance of the PE pipe was greatly enhanced. The hoop tensile strength of the PE pipe produced by the novel extrusion method increased from original 24.1 MPa up to 35 MPa; the pipe's crack initiation time increased from 27 to 60 h and the crack growth rate slowed down.

Rheological Modeling of Polymeric Melts in Extruders upon Two-Dimensional Shear Flow

“…In some geometry, working surfaces of the main elements of the die are assembled in circular cylindrical channels to produce extruded tubular blanks, which are then used for the manufacture of final products. Extrusion of polymer pipes, extrusion-blow formation of plastic tare and packing, manufacture of tubular films are among such technological processes (Michaeli, 1992;Nie et al, 2010).…”

“…Usage of arotating mandrel ( Fig. 1) in construction of a shaping die results in ar elative increase of productivity upon extrusion of polymers through ac ircular cylindrical channel (Nie et al, 2010;Worth, 1980). Rotation extrusion has attracted much attention due to its easy implementation in comparison to conventional extrusion.…”

Control of rotation extrusion over shish‐kebab crystal alignment in polyethylene pipe and its effect on the pipe's crack resistance

“…Among the above approaches, rotation extrusion has attracted much attention. [17][18][19] This article further focused on the effects of the mandrel-die-same direction-rotation extrusion on the obtained PE pipe's microstructure and resistance to SCG and studied the relationship among the stress, cooling rate, and final structure, so as to prepare the PE pipe with better resistance to SCG. 10,12 However, the previous studies focused on mandrel rotation extrusion where the inner layer of the pipe rotated together with the mandrel while the outer layer remained stationary, so the hoop stress imposed by the mandrel rotation was gradually decreased from the inner to the outer layer.…”

“…In this way, the crystallization and orientation of PE could be adjusted to produce the PE pipes with higher performances. [17][18][19] This article further focused on the effects of the mandrel-die-same direction-rotation extrusion on the obtained PE pipe's microstructure and resistance to SCG and studied the relationship among the stress, cooling rate, and final structure, so as to prepare the PE pipe with better resistance to SCG.…”

Effect of the inner wall cooling rate on the structure and properties of a polyethylene pipe extruded at a high rotation speed

“…In this way, the relaxation of the oriented molecules was slowed, and the orientation structure was reserved in the PE pipes. Therefore, the performance of the obtained PE pipes was enhanced 19–22. Previous studies on rotation extrusion have mainly focused on the low rotation speed, in which the hoop orientation degree in the PE pipes was lower.…”