Negative Poisson's ratio polyethylene foams

Various polyethylene foams were subjected to thermo-mechanical processing w ith the aim of transforming them into re-entrant materials exhibiting negat ive Poisson's ratio. Following transformation, large cell foams (cell sizes of 1 and 2 mm) exhibited re-entrant cell structure and negative Poisson's ratio over a range of processing times and temperatures. Poisson's ratio vs . strain for these foams was similar to prior results for reticulated polyu rethane foams. Following processing, microcellular polyethylene foam was de nsified but cells remained convex; it did not exhibit a substantial negativ e Poisson's ratio. This foam had a different transition temperature as dete rmined via DSC than the large cell foams. (C) 2001 Kluwer Academic Publishe rs.