VATIS UPDATE Article

Researchers at Institut für Kunststoffverarbeitung (IKV), Germany, studied a new injection technique for introducing physical blowing agents into molten polymer for its application in foam extrusion. Therefore, a special injection device was mounted on a standard laboratory scale single screw extruder. By means of this device, CO2 was injected into PS melt. A polystyrene (PS) of BASF, PS158K, was used in this study.

The density of this resin is 1.05 g/cm3 and its melt volume rate is 3 cm3/10 min. CO2 from Linde AG, Germany with a purity of 99.7% was used as the physical blowing agent. A 20 wt% masterbatch of a sodium bicarbonate/citric acid system in PS (Hydrocerol CF 20 S, Clariant Masterbatches GmbH, Germany) was used as nucleating agent. The foam extrusion tests were conducted on a 25 mm single-screw extruder (Collin, Germany) with a length of 25 D.

The blowing agent was introduced into the melt by means of an Optifoam® 22 system (Sulzer Chemtech AG, Switzerland) which is based on the fluid injection nozzle invented at the IKV. A static mixer (SMK 22, Sulzer Chemtech) with 22 mm in diameter is integrated in this system. The blowing agent was provided by a dosing unit (LEWA, Germany) featuring two high pressure membrane pumps. The foams produced with this new technique exhibit a cell size in the range of 100 microns.