Crystallization under stress and non-gaussian behavior of macromolecular networks

Abstract (a) Shape of the isotherm.—The appearance of a “first” upturn in the conventional isotherm is associated with non-gaussian behavior. Crystallization takes place, under usual conditions, in a range of elongation where non-gaussian behavior prevails and tends, initially, to reduce the stress below the value expected for the amorphous non-gaussian network. On further stretching a “second”, steeper up turn may be observed which is associated with a substantial reduction of amorphous content and, therefore, with crystallization. This interpretation, which is coherent with most of the experimental observations (particularly the lack of correspondence between the first upturn and the downturn of the energy component, the swelling behavior and the independence of the first upturn upon the mode of obtaining the isotherm and upon temperature) is satisfactorly fitted in the present picture of behavior of the network under stress. (b) Energy component.—Extensive measurements and theoretical analysis indicate...