High- Performance and Sustainable Expanded Plastics by Graded Foaming Technologies

Abstract

Designing the foam structures in terms of density and morphology gives the chance to tune their mechanical and functional properties to the specific application. Nowadays this design has been levelled up by the introduction of graded foams, characterized by spatially non-uniform densities and/or morphologies. Graded foams have shown superior with respect to their uniform counterpart in numerous examples. When using sintered beads foams, macroscopic pure compression may induce local bending on the single bead, which can be exploited to induce stiffening. We herein prove this idea on both polystyrene and thermoplastic polyurethane beads, sintered in a cylindrical mold for compressive tests. We compared foams made by sintering beads with uniform as well as graded morphologies, evidencing, on foams with the same average density, a 10% ca. increase of the Young's modulus when the beads are characterized by a denser outer layer.