Foam extrusion of semi-crystalline Polymers

The foam extrusion of semi-crystalline polymers is highly challenging due to their narrow processing window compared to amorphous polymers. This narrow processing window arises due to disadvantageous melt properties such as low viscosity and low elasticity of the melt. Hence typical challenges encountered are cell coalescence and collapse, which lead to high density, large cells and a broad cell size distribution. In order to obtain foams with good morphology and low density, a very accurate temperature control of the melt is essential, since a deviation of 1°C only can lead to profound changes in foam morphology or the break-down of the process. Also the stabilisation of the foam is critical.

The improvement of the foamability of semi-crystalline polymers can be achieved process- or material-vice. So the material can be modified via reactive extrusion in a way that its’ molecular weight and weight distribution increase and branching of the polymer chains is introduced. Those modifications lead to a higher viscosity and elasticity of the melt, which results in a widened processing window as well as much better foam morphology and distinctly reduced density. Process-vice, the stabilisation of the foam can be improved by using the technique of under-water pelletisation. Due to the high surface area of the beads and the advantageous heat removal in the water stream, the resulting foamed beads can have a much better cell morphology compared to foams from standard foam extrusion.

 

Contact: M.Sc. Nick Weingart
Phone: +49 921 5574-90
Fax: +49 921 5574-73
Email: nick.weingart@uni-bayreuth.de