Polymer, Vol.39, No.16, 3597-3609, 1998
Creep behaviour of high density polyethylene films having well-defined morphologies of stacked lamellae with and without an observable row-nucleated fibril structure
Creep behaviour of melt-extruded high density polyethylene films, having a stacked lamellar morphology (either with or without the visible (by transmission electron microscopy, TEM) presence of row-nucleated fibril structures) and compression moulded slow-cooled isotropic films of the same resins, was investigated. The creep experiments were carried out at different temperatures and stresses, and the orientation dependence of the creep behaviour for the melt-extruded films was studied by performing the creep experiments at three angles (0 degrees, 45 degrees and 90 degrees), with respect to the original machine direction. An Eyring-rate model was used to analyse the creep data, and the three parameters associated with the Eyring-rate model, i.e. activation volume, activation energy and the availability of creep sites, were obtained by fitting the plateau creep rate according to the Eyring-rate equation. It was concluded that the creep behaviour of all the films was basically controlled by the deformation of the amorphous phase and, more specifically, by the density and tautness of tie-chains. The orientation dependence on the melt-extruded films was explained by the different constraint effects of crystalline lamellae to the tie-chains at each orientation.