CREEP-BEHAVIOR OF HIGH-DENSITY POLYETHYLENE FILMS HAVING WELL-DEFINEDMORPHOLOGIES OF STACKED LAMELLAE WITH AND WITHOUT AN OBSERVABLE ROW-NUCLEATED FIBRIL STRUCTURE

Creep behaviour of melt-extruded high density polyethylene films, havi ng a stacked lamellar morphology (either with or without the visible ( by transmission electron microscopy, TEM) presence of row-nucleated fi bril structures) and compression moulded slow-cooled isotropic films o f the same resins, was investigated. The creep experiments were carrie d out at different temperatures and stresses, and the orientation depe ndence of the creep behaviour for the melt-extruded films was studied by performing the creep experiments at three angles (0 degrees, 45 deg rees 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 vol ume, activation energy and the availability of creep sites, were obtai ned by fitting the plateau creep rate according to the Eyring-rate equ ation. It was concluded that the creep behaviour of all the films was basically controlled by the deformation of the amorphous phase and, mo re specifically, by the density and tautness of tie-chains. The orient ation dependence on the melt-extruded films was explained by the diffe rent constraint effects of crystalline lamellae to the tie-chains at e ach orientation. (C) 1998 Published by Elsevier Science Ltd. All right s reserved.