STRESS-INDUCED STRAIGHTENING OF TIE CHAINS IN ORIENTED PE FILMS AS REVEALED BY RAMAN (LAM) STUDY

The Raman longitude acoustical mode (LAM) study of axially stressed po lyethylene-made microfilms gave evidence of the formation of the strai ght tie molecules localized in two neighboring crystals and in an amor phous layer situated between them. The samples were bicomponent blends composed of polyethylenes with different MW (7 X 10(4) and 2 x 10(6)) . Each MW fraction exhibits an individual LAM band responding to cryst als with the size specific to a given fraction. Under tensile stress, the bands shift insignificantly towards an exciting laser line. In add ition, the LAM localized on all-trans sequencies with the length excee ding the mean crystallite size appear in the spectrum of a stressed sa mple. The reversibility of these spectral changes depends on the draw ratio of samples. We conclude the effect is due to stress-induced gauc h-to-trans transformations taking place in the amorphous layers. (C) 1 998 John Wiley & Sons, Inc.