THE DOUBLE YIELD IN THE TENSILE DEFORMATION OF THE POLYETHYLENES

Double yields, as well as other complex yielding behavior, that are ob served during the tensile deformation of the polyethylenes have been s tudied in a systematic manner. The conditions under which such yieldin g is observed were established by studying a set of linear polyethylen es and well-characterized ethylene copolymers of narrow molecular weig ht and composition distributions. A wide range in crystallinity levels were developed and the rate of deformation and the deformation temper ature were varied. These experimental results make clear why such comp lex yielding processes are not always observed. A qualitative explanat ion, based on the postulate of a partial melting-recrystallization pro cess during deformation, is given that encompasses all of the experime ntal data.