- CO2 in the solid state (dry ice) as physical blowing agent
- No modifications to the extruder needed
- Foam densities comparable with those of chemical foaming
In a recent research project on the topic of foam extrusion, the Institute of Plastics Processing (IKV) in Industry and the Skilled Craftsat RWTH Aachen University has been examining the use of dry ice as a physical blowing agent. In cooperation with Motan-colortronic GmbH a new process technology has been developed that uses CO2 in the solid state, so-called dry ice, for the production of medium-heavy foams. The newly developed process combines the advantages of physical foaming with those of chemical foaming.
Advantage: blowing agent does not leave any reaction residues behind
Like the masterbatch in chemical foaming, the dry ice is fed into the extruder via the hopper in the form of pellets. Modifications to the extruder itself are therefore not needed. Another advantage is that the blowing agent does not leave any reaction residues (e.g. water) behind in the extrudate. Therefore it is also suitable for hydrolysis-sensitive materials. The new metering technique is able to feed dry ice pellets via a metering screw and gravity mixer directly into the feed zone of the extruder. In this way, premature sublimation of the dry ice and cooling of the plastics granules is avoided. Through rapid melting of the plastic and fast pressure build-up, the dry ice becomes dissolved in the melt.
Foam densities of min. 350 kg/m³ (e.g. LDPE) can be achieved
With the new process technology, foam densities of min. 350 kg/m³ (e.g. LDPE) can be achieved, which are comparable with those of chemical foaming. By adjusting the process temperatures, the method can also be applied to other plastics such as polypropylene. Despite the comparatively high sublimation losses in the metering of the blowing agent, the process can compete with chemical blowing agents due to the lower cost of CO2. The process allows an inexpensive entry into foam extrusion because of the fact that any retrofitting is confined to the metering technology.
Picture: Foam extrusion testing with dry ice in IKV’s Extrusion pilot plant (source: Jacobs/IKV)