10 frequently asked questions about PO Foam

Question 1: Which physical foaming agent (gas) is the best in PP foam production?

Answer 1: The choice of the best physical foaming agent depends on the target foam. Hydrocarbons, like iso- or n-butane, are used in production of the lowest density foams, whereas inert gases, like supercritical CO2 or N2, are used in production of foams with densities typically higher than 200 kg/m3.

Question 2: Can I use a chemical foaming agent with Daploy HMS PP?

Answer 2: Yes. There are wide variety of different masterbatches for chemical foaming available, which are used in PP foaming. Chemical foaming agents are more common in production of high and medium density foams.

Question 3: What foaming technologies can I use with Daploy HMS PP?

Answer 3: The most commonly used foaming technology is extrusion foaming. However, Daploy HMS PP is very versatile and is also used in the production of expanded PP beads and foam blow moulding, and is occasionally used in foam injection moulding.

Question 4: Do I need to add any other recipe components when foaming Daploy HMS PP?

Answer 4: To foam Daploy HMS you need to add a foaming agent, either physical or chemical, and a nucleating agent to control the cell structure. It is also possible to add other polymeric and non-polymeric components to modify the foam properties to be suitable in the target application.

Question 5: What is the minimum and maximum thickness of the foams produced using Daploy HMS PP in extrusion foaming?

Answer 5: The thinnest foams are about 700-800 µm. The foams can be up 10 mm thick or even slightly thicker, depending on the foam density and cooling capacity of the line. The challenge in the production of thick foams is to stabilise (cool down) the foam core to avoid foam collapse.

Question 6: Can I use my old foaming line to foam polypropylene?

Answer 6: In many cases, this is possible without making hardware modifications, or by simply making minor ones. However, if the foaming line is not designed for PP foaming, it is possible that there would be a penalty in output or foam quality. It is also good to ensure that the heating and cooling of the line works well before testing PP foaming.

Question 7: Which die type is recommended: flat die or annular die?

Answer 7: Flat dies can be used in production of extruded foams with densities down to about 200 kg/m3. Annular dies are recommended if the foam target density is lower.

Question 8: Can I use my existing sheet extrusion line to produce foamed sheet instead of solid sheet?

Answer 8: If the sheet extrusion line is not equipped with a gas injection unit for physical foaming, it is possible to use chemical foaming agents instead. However, in most cases, only up 30% density reduction can be achieved.

Question 9: Why are the foam properties different in machine and transverse directions? What can I do to get better balance?

Answer 9: In most cases during foam production, there will be some cell orientation either in machine or transfer direction. This leads to different mechanical properties of the foam in different directions. The situation can be improved by optimising foam nucleating and production conditions.

Question 10: Is it possible to predict foam properties by computer simulation?

Answer 10: It is possible to simulate the basic foam properties using suitable simulation software. This will greatly shorten the development cycle time of new foam products. However, the simulation results are indicative and final performance needs to be demonstrated by real production trials.

Question 11: What is the definition of high, medium and low density foam?

Answer 11: The definition we use at Borealis: high density >700 kg/m3, medium density 300-700 kg/m3 and low density <300 kg/m3.