Properties Of Polyethylene Films Research Articles

The structure and properties of polyethylene films obtained during orientational crystallization

Highly oriented films possessing increased tensile strengths (based on initial cross section) and elastic moduli are produced directly in the extrusion process. The dependence of the structure and properties of these films on hardening temperature is studied. Assumptions are made concerning the formation and crystallization mechanisms of films produced with higher molecular orientation.

Effect of formation conditions on the supermolecular organization and mechanical properties of polyethylene film

Films formed by extruding medium-pressure polvethylene through a flat-slot have a spherulitic supermolecular organization whose principal parameters (size and shape of the spherulites) are determined by the extrusion conditions. Thus, as the draw-down ratio increases, the radius of the spherulites decreases, and their degree of flattening relative to the direction of extension increases. Stretching these films leads to a transition from a spherulitic to an orientational supermolecular order, whose period is genetically related to the diameter of the starting spherulites. Films containing flattened spherulites have a yield point anisotropy opposite in sign to the degree of flattening. The mechanical anisotropy, like the degree of flattening, increases with increase in the draw-down ratio. The probable cause of flattened spherulite formation is the draw-down process, whose mechanical field may retard the radial growth of the spherulites in the take-off direction.

Combined determination of the mechanical characteristics of polymer films

A description is given of an apparatus for determining the Poisson ratios of orthotropic films in the longitudinal and transverse directions of orientation and also with respect to thickness. This apparatus makes it possible to determine various mechanical characteristics in time under different temperature conditions. The properties of polyethylene film are taken as an example.