| Abstract: | Samples of ultradrawn high density polyethylene were studied by thermomechanical analysis. The purpose was to study the dimensional changes in polyethylene morphologies of extreme orientation. Dimensional changes were measured from ?140 to +70°C with a precision of better than 1%. A negative thermal expansion coefficient was observed along the length (c axis) of the fibers containing the polyethylene morphologies of extreme orientation. A change in negative coefficient is observed between ?35 and ?45°C. The sign and magnitude of the expansion coefficient confirm, along with other evidence, the existence of extended chain structures in these morphologies. A series-parallel model has been developed for the ultradrawn polyethylenes to describe the dimensional changes with temperature. |
