Advanced Thermoforming, 2nd Edition

Chapter 36Foam Packaging with PP and PS

36.1 POLYPROPYLENE¹

Polymeric foams consume around 3.5 million tons of plastics materials annually and account for about 10% of all polymer usage in Europe. Foamed polymers are used in a wide number of application areas, which range from construction, automotive, and household products to food and protective packaging. Among the many benefits of foamed materials are their good mechanical rigidity at low specific gravity, thermal and acoustic insulation, cushioning against mechanical shock, and a significant contribution to source reduction in raw material usage.

The foam market is dominated by the amorphous polymers (PS, PU, PVC, etc.), which have been industrially foamed for more than 50 years. Polypropylene (PP) foams are a relative latecomer to this market. The reasons for this lie in the molecular structure: standard polypropylene grades are semicrystalline materials with a linear molecular structure. They lack the required extensional rheological properties in the melt phase for the production of extruded low‐density foams with a fine and controlled cell structure. This limitation is resolved by high melt strength polypropylene (HMS‐PP) such as the Borealis Daploy. These are long‐chain branched materials that combine both high melt strength and extensibility in the melt phase. They open up the possibility of bringing the many well‐known property benefits of PP into the world of low‐density polymeric foams. These benefits include ...