Experimental analysis of the influence of pellet shape on single screw extrusion

Abstract

Extrusion technology is one of the most prominent methods for processing polymers. The shape of polymer pellets plays an important role in conveying solid material through the extruder and thus directly influences the mass flow rate. In the course of this article, the influence of the pellet shape of a polypropylene homopolymer on the processing conditions using a smooth barrel single‐screw extruder is evaluated. Especially the mass flow rate, the melt temperature, and the pressure build up in the barrel are investigated. It can be shown that processing long cylindrical pellets leads to a higher mass flow rate than comparable experiments with virgin pellets or short cylinders. Additionally, screw cool and pull‐out tests, measurements of the external coefficient of friction as well as the bulk density of the different pellet geometries are performed. The interaction of the screw geometry and the pellet shape is found to have the biggest influence. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41716.

Experimental study of the influences of the pellet shape on the bulk density and the frictional behavior of polypropylene

“…3 They show that long cylindrical pellets exhibit a higher mass flow rate in all of the experiments while the counterpressure is comparable. For low screw speeds and high counterpressure, the achievable rise in the mass flow rate is 33%.…”

“…3,19 In the aforementioned previous study, a major effect of the pellet shape on the external frictional coefficient could be demonstrated when working at standard conditions on a screw tribometer. It was found that long cylindrical polypropylene pellets exhibit a higher ECOF than spheroidal pellets.…”

“…It was found that long cylindrical polypropylene pellets exhibit a higher ECOF than spheroidal pellets. 3 This study deals with the properties of two polypropylene pellet shapes of the same grade. One is a spheroidal virgin shape, generated in hot-face pelletizing, while the other is a long cylindrical shape that was made from the virgin material.…”

“…The chosen velocity relates well to the extrusion experiments in the previous study. 3 The polymer pellets are arranged in a monolayer, so the applied pressure is not reduced due to frictional forces at the sample chamber walls. The ECOF for 10 turns of the shaft is observed.…”

Evaluation of the melting behavior and the melt penetration into the solid bed using a model experiment

“…A previous work [14] has shown, that the throughput of SSE is strongly dependent on the geometry of the polymer bulk solids, at least when small screw diameters are used. It has been figured out that cylindrical pellets caused a much higher throughput than spheroidal ones.…”