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Rubber-toughened polypropylene (PP) is an important resin for many engineering applications. Through the structural foaming of materials, material cost-saving and lightweight structures can be achieved. In this study, physical blends of PP and poly(ethylene/octene) at various compositions were characterized for their melt strength and shear viscosity. The high pressure MuCell ® foaming process was used to obtain structural foams with average cell diameters of <50 μm and cell densities of approximately 8 million cells/cm3. This study presents key understandings between material rheology and its suitability for structural foaming that are in turn linked to blend composition and melt temperature.

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This paper is dealing with structural foam moulding of polypropylene (PP) thermoplastics utilising the MuCell approach to introduce the blowing agent as well as advanced moulding technologies. Till today, structural foam moulding is facing several different challenges, which are limiting a full acceptance in industrial applications. Encountering issues of those parts are the critical surface appearance, the limited density reduction and finally the mechanical properties (stiffness, strength and toughness). Here, two surface improving techniques have been evaluated according to their effectiveness and feasibility. Furthermore, in this experimental study, six different typical automotive PP compounds have been processed to structural foams with a density reduction of 50% and evaluated in regard to their morphologies and mechanical performance. The modulus and strength of structural foams can be correlated to their build-up (skin-layers, foam density), as the toughness performance is heavily dependent on molecular weight, filler-type and filler orientation.

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