Microstructure anisotropy in polyolefin flexible foams

Abstract. The use of polyolefin flexible foams with typical thicknesses between 1 and 3 mm produced by a physical foaming extrusion process is nowadays quite widespread in the packaging sector. Their high flexibility and closed-cell structure allows them to show good energy absorption properties under low loading conditions. Although the compressive response of these materials is well known, the inner microstructure developed during processing induce a high anisotropy that is responsible for their direction-dependent tensile and fracture behaviours. In this work, two different polyolefin-based foams, with densities ranging from 20 to 45 kg/m, were studied. The induced microstructure anisotropy was characterized by microRaman. With this technique, the relative orientations of both crystalline and amorphous phases in the foam’s base polymer could be determined and thus related to their mechanical properties measured in the different directions.