Gravimetric determination of diffusion coefficients and volumetric properties of polyethylene closed cell foams

This work has developed experimental techniques that measure diffusion coefficients by volumetric expansion and change in cell air mass for Low Density Polyethylene (LDPE) cross linked, closed cell foams. This study investigated a range of foam densities (15 to 70 kgm[sup]-3), compressive durations (30 minutes to 2 weeks), compressive strains (0.1 to 0.7) and foam sample sizes (30 to 110 mm square slabs with nominal thickness of 26 mm). The results show that near steady state mass flow is achieved during foam recovery, post long term compression. It was also found that slab thickness with respect to time needs to be included when applying Fick's 2nd Law in determining air diffusion coefficients. A theoretical model has been developed that accounts for slab edge effects and has been applied to the results. Within experimental uncertainty, this study found that the air diffusion coefficient was not dependent on foam density which is contrary to that generally reported in literature. The air diffusion coefficient for Zotefoams's, closed cell, cross linked, Low Density Polyethylene foam was found to be 0.90 ± 0.12 x 10 [sub]-11 m2s-1; irrespective of foam density or slab size.