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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

Natural rubber foams are biobased and lightweight products which have found their main field of application in comfort products such as mattresses and pillows. They are generally produced from chemical foaming processes in which the expansion of the polymer is isotropic and hence, their properties are not directionally dependent. However, this dependency could be interesting for certain structural and thermal insulating applications. In this work, elastomeric foams based on natural rubber with a medium relative density (around 0.3) and with varied cellular structures in terms of the shape anisotropy ratio of the cells were produced by a chemical foaming process in which expansion was restricted to only one direction inside a mold. The use of solid precursors of different dimensions, the elastomeric properties of natural rubber and the crosslinking by sulfur of the polymer matrix during foaming allowed foams to be obtained with anisotropy ratios between 0.90 and 2.48 at the same density and with the same properties as the polymeric matrix. In this particular case the study was focused on analysing their compressive modulus and its relationship with the anisotropy of the cellular structure by employing analytical models generally used to describe the mechanical behavior of anisotropic foams.

The main goal of this work is to analyze the relationships between the extensional rheological behavior of solid nanocomposites based on high melt strength polypropylene (HMS PP) and montmorillonites (MMT) and the cellular structure and mechanical properties of foams produced from these materials. For this purpose two systems have been analyzed. The first one incorporates organomodified MMT and a compatibilizer and the second system contains natural clays and is produced without the compatibilizer. Results indicate that the extensional rheological behavior of both materials is completely different. The strain hardening of the polymer containing organomodified clays decreases as the clay content increases. As a consequence, the open cell content of this material increases with the clay content and hence, the mechanical properties get worse. However, in the materials produced with natural clays this relationship is not so clear. While no changes are detected in the extensional rheological behavior by adding these particles, the nano-filled materials show an open cell structure, opposite to the closed cell structure of the pure polymer, which is caused by the fact of having particle agglomerates with a size larger than the thickness of the cell walls and a poor compatibility between the clays and the polymer.