Mechanical and acoustical behaviour of novel PE Open Cell Foam

In this work the mechanical and acoustic behaviour of novel polyethylene open cell foam (PEOC) is investigated. Thanks to the production route, this material displays a peculiar structure characterized by almost closed cell interconnected by small pores. Crushing the foam up to 90% of its original thickness allows obtaining a foam with different structure. The mechanical behaviour of non-deformed and deformed samples of PEOC foam was compared to that of a PE closed cell foam of similar density and to other open cell foams (flexible polyurethane and melamine resin foams) via quasi-static compression test and dynamic mechanical analysis (DMA). Moreover, the cell size distribution and the diameter of the holes interconnecting the cells was assessed by quantitative analysis of SEM images. In compression tests, PEOC displays the constant stress plateau, typical of open cell foams, in the stress strain curves at strain rates up to 1.6x10-1s-1, while at higher strain rate the behaviour resembles that of closed cell foams, probably due to the resistance to airflow through the very small pores interconnecting the cells. DMA characterization performed at fixed frequency (1Hz) and several static strains evidences the differences among the studied materials which can be related to their structure. The comparison between PEOC and crushed PEOC seems to confirm that the change in the structure have an effect not only on the modulus, as expected, but also on the loss factor; its reduction could be correlated to increased size of the pores interconnecting the cells. In the case of closed cell foams, the observed reduction of loss factor with increasing static strain might be attributed to the contribution of air pressure to E’. Finally, the transmission loss and the absorption coefficient were measured for the considered materials in the frequency range 500-6400 Hz and a simple correlation between the structure geometry and the acoustic response is proposed.