Creep of Polyethylene Above Room Temperature

Abstract

Previous work has shown that the creep data of a slow-cooled polyethylene can be superposed by means of a series of horizontal and vertical shifts to give a creep master curve at room temperature. The curve is smooth and regular with the exception of a discontinuity in the region of 2000 sec. In the time and temperature range of the measurements, polyethylene has two overlapping relaxation mechanisms, the α and α′. If it is assumed that the logarithmic decrements of the two relaxations are additive, the theory of linear viscoelasticity can be simply extended to cover this case, and it is shown that the discontinuity in the master creep curve arises quite naturally as a result of the differing activation energies of the two relaxations. This is a general conclusion and is independent of the nature of the relaxation mechanisms involved.