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Polypropylene (PP) foams have become\ud essential items due to their excellent properties. Nevertheless,\ud obtaining net-shaped PP foams with medium relative\ud densities is a complicated issue. In this article, two\ud processes able to produce moulded PP foams in this density\ud range are presented. One of them is based on a modification\ud of the pressure quench foaming method and therefore\ud uses a physical blowing agent (CO2). The second one is the\ud improved compression moulding technique which uses a\ud chemical blowing agent (azodicarbonamide). PP foams\ud with relative densities in the range between 0.25 and 0.6\ud and cylindrical shape were prepared using these foaming\ud techniques. A common PP grade (instead a highly branched\ud one) was used to obtain the samples, showing, that by\ud combining the appropriate foaming technique, the adequate\ud moulds, suitable blowing agent and proper foaming\ud parameters, net-shaped PP foams with excellent properties\ud can be produced starting from a conventional PP grade.\ud Samples were characterized by analyzing their cellular\ud structure and their mechanical properties. Results have\ud showed that depending on the chosen foaming route isotropic\ud or anisotropic structures with cell sizes ranging from 40 to 350 lm and open cell content in the range between 0\ud and 65% can be obtained. Moreover, mechanical properties\ud are highly influenced by the production route and chemical\ud composition of the foams. For instance, the stiffer materials\ud at relative densities higher than 0.4 are the ones produced\ud using the chemical blowing agent while at relative densities\ud lower than 0.4 are the ones produced using the physical\ud blowing agent.Peer ReviewedPostprint (published version

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This paper is focused on the production and characterization of a collection of polypropylene (PP) foams with relative densities ranging from 0.3 to 0.6. Samples were foamed using the improved compression moulding method. The process allows controlling density and cellular structure independently as well as obtaining PP foams without fillers, crosslinking or using special PP grades. The influence of blowing agent content, density, cellular structure and foaming conditions on the mechanical response measured in compression, tensile, bending and Charpy impact tests was determined. Results show that density, open cell content and blowing agent concentration have a significant influence on the mechanical performance of medium‐density PP foams. © 2013 Society of Chemical Industry