• Peuvrel-Disdier, Edith
• Laure, Patrice
• Hibert, Geoffrey
• Sandino, Carlos
• Trolez, Yves
• Agassant, Jean-François
• Boyer, Séverine A. E.

Abstract

This study aims at a better understanding of the polypropylene (PP) foamability by physical extrusion foaming.Trials were conducted in a single screw extruder equipped with a gear pump for the gas dissolution step (same extrusion parameters, 1wt% CO2) and a static mixer cooler allowing to decrease the melt temperature before the final die (referred as foaming temperature). The effect of decreasing this temperature on the PP foamability and on the pressure drop in the die is analyzed. The behavior of branched and linear PP grades is compared. The foam density of branched PPs varies from high to low values while decreasing the foaming temperature. In the same processing conditions, the foam density of linear PPs does not decrease so much as already evidenced in the literature. The foamability transition coincides with an increase of the pressure drop in the die.The thermomechanical analysis of the polymer flow in the die is used to identify the relevant physical phenomena for a good foamability. The comparison of experimental pressure drops in the die and computed ones (analytical expressions for converging and capillary dies with identified purely viscous behaviors) points out the influence of the foaming temperature and of the polypropylene structure. At high foaming temperature the discrepancy between experimental and computed pressure drops remains limited. It increases when decreasing the foaming temperature, but the mismatch is much more important for branched PPs than for linear ones. This difference is analyzed as a combination of the activation energy of the viscosity, extensional flow in the converging part of the die, and onset of crystallization in the die.These hypotheses will be examined and discussed for the different polymer grades in order to clarify the physical scenario for the foaming process [1].Reference : 1. Sandino C., Peuvrel-Disdier E., Agassant J.F., Laure P., Boyer S.A.E., Hibert G., Y. Trolez Y., Extrusion foaming of linear and branched polypropylenes-Input of the thermomechanical analysis of pressure drop in the die, Intern. Polym. Proc., 2022 accepted

Topics

• density
• impedance spectroscopy
• polymer
• melt
• extrusion
• viscosity
• activation
• crystallization