Challenge to the Production of Low-Density, Fine-Cell HDPE Foams Using CO 2 t

This paper presents an experimental study on the manufacture of low-density fine-cell high density polyethylene (HDPE) foams in extrusion using CO2 as a blowing agent. The strategies adopted to produce low-density, fine-cell HDPE foams were to generate a large number of cells by a rapid pressure drop, to suppress cell coalescence by strengthening the melt via melt temperature control, and to promote expansion by cooling the extrudate surface and blocking the gas escape. A continuous extrusion process has been designed and implemented based on these strategies. The concept of promoting large expansion while preventing cell coalescence to maintain a high cell density has been successfully demonstrated through experiments. Low-density, fine-cell HDPE foams were produced with a expansion ratio in the range of 1.5 - 20 times, a cell density on the order of 10 8 cells cm -3 , and a cell size of the order of 50 µm.