Single Screw Extrusion with Low Pressurized Blowing Agents.

For the continuous production of foam products, the extrusion process is commonly used. Typical extrusion systems include an extruder for melting and mixing the thermoplastic material(s) as well as an extruder for cooling the melt. Both tasks can also be performed in one extruder. Between these extruders or extruder zones the blowing agent (e.g. CO2, N2) is injected into the melt with relatively high pressure. This study presents a foam extrusion process utilizing a twostage- screw in which the blowing agent is injected at a low-pressure range and extruded as a strand. The study uses PP as well as nitrogen and carbon dioxide as blowing agents which are widely used for foaming. The screw concept makes it possible to produce a blowing agent loaded polymer melt with the present pressure of a standard gas bottle (or other gas storage devices) thus eliminating the need for expensive gas cooling, dosing and pumping technology. The influence of melt temperature and gas injection pressure on foam quality (expansion ratio, cell structure) is investigated. The produced foam has a regular cell structure. [ABSTRACT FROM AUTHOR]