An extrusion die with rollers for foaming polymers

Abstract

Operation of a flat slot die with rollers for the extrusion foaming of polymers, which has been originally designed by Benkreira et al. (Int. Polym. Proc., 19, 111 (2004)), is considered. The rotation of rollers makes it possible to independently control shear rate inside the die, in the bubble nucleation zone, thus influencing the cell density. In experimental studies of low‐density polyethylene foaming, the influence of the roller rotation speed on the cell density at variable isobutane and talc concentrations and die outlet area has been determined. Based on the fluctuational nucleation theory, a simple model is proposed for estimating the number density of supercritical nuclei formed at the nucleation stage and evaluating the cell density in the foam with allowance for bubble coalescence effects. POLYM. ENG. SCI., 54:96–109, 2014. © 2013 Society of Plastics Engineers

Development of an extrusion die with rollers for foaming polymers

“…In the first case, the nucleation of bubbles was assumed to be most intense in the die outlet cross section (although a certain fraction of bubbles was also formed in the die). In this case, the number density of supercritical nuclei N n obeys the following relationship [23]:…”

“…As the die outlet area increases, the zone of predominant bubble nucleation shifts inward the die. This regime is realized provided that the following criterion is valid [23]:…”

“…This regime of polymer foaming is typical of the cases with high concentration of a blowing agent and large areas of the die outlet. If criterion (2) is satisfied, the number density of supercritical nuclei is described by the following relationship [23]:…”

“…This work is a continuation of our previous study [23]. Based on the results of experimental investigation of the low-density polyethylene foaming with isobutane, we analyze the influence of polymer viscosity, die temperature, talc concentration, and gap width between rollers on the cell density in the extruded foam.…”

Die opening-induced microstructure growth in extrusion foaming of thermoplastic sheets

“…Continuous manufacturing of low-density foamed thermoplastic sheets has unremittingly remained to be a big challenge for many manufacturers despite the initial breakthroughs that have been accomplished in the last two decades [1][2][3][4][5][6][7]. Numerous researchers and diverse inter-disciplinary industries have been very active in the field of extrusion foaming in the last few years, primarily because it allows them to manufacture thermoplastic foams continuously [8][9][10][11][12][13][14].…”