A Simplified Model for the Melting of Polymer Pellets under Compression in a Twin-Screw Extruder
Plastic energy dissipation (PED) is an important mechanism involving the melting of polymer in a twin-screw extruder. In the present study, the melting behavior of polymer pellets under compression is studied by a simplified model with the finite element method, based on the fact that mechanical energy from the deformation of a single pellet is converted into heat energy. The model shows that the heating of the pellet is not uniform. Under compression, the contact area of the pellet yields first, and the deformation in the pellet depends on the compression ratio and properties of the pellet. The simulated results show that the temperature in the volume around the line passing through the contacting point and the center of the pellet is higher than the temperature further from the contact area.
Experimental investigation of polymer pellets melting mechanisms in corotating twin‐screw extrusion
With the visualization corotating twin-screw extruder, the melting of HDPE pellets under different screw configurations and operational conditions was investigated on-line. It is shown that the melting progression of polymer pellets in corotating twin-screw extruders is different from that in single-screw extruders. Screw configuration, screw speed, and feed rate are three decisive factors in polymer melting. Based on the melting phenomena, a new melting mechanism, island-sea melting model, was defined. It was found that island-sea melting model is an important mechanism to realize high efficiency melting progression. The state of polymer, the degree of fill, and the structure of kneading blocks are factors in determining the energy consumption of kneading blocks in melting zone. The conveying of polymer pellets in kneading blocks, in which pellets were compressed and deformed, consumed much more energy than the conveying of polymer melt. This indicates that the control of the deformation of polymer pellets in corotating twin-screw extrusion is a useful concept in developing new screw elements for high efficiency polymer melting. © 2002 Wiley Periodicals, Inc. Adv Polym Techn 21: 188–200, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/adv.10021
Processing-morphology relationships of compatibilized polyolefin/polyamide blends
The emulsifying effect of a polyethylene-based ionomer on the phase size/composition relationship was studied for polypropylene/polyamide and polyethylene/polyamide blends. The particle size measured for the uncompatibilized blends increased with minor phase concentration, particularly as the region of dual phase continuity was approached. This relationship was less pronounced when ionomer was added, and the dimensions of the dispersed phase were significantly reduced. A narrowing of the region of dual phase continuity was observed due to the addition of ionomer. An increase in the torque measured during melt blending in a Brabender mixing chamber resulted when ionomer was added, due to the increase in the interactions at the interface. The particle size determined for the uncompatibilized blends increased with viscosity ratio. The effect was also less pronounced for the compatibilized blends. From these observations, it was possible to conclude that the effect of interfacial modification on morphology predominates over that of composition and viscosity ratio. The effects were interpreted in terms of the reduction of interfacial mobility due to the compatibilization.