MEMORY EFFECTS IN POLYMERS .5. PROCESSING HISTORY VERSUS THERMALLY-INDUCED SELF-ORIENTATION OF UNORIENTED POLY(CHLOROTRIFLUOROETHYLENE) FILMS

A peculiar phenomenon is reported whereby a melt-extruded, low-crystal linity, unoriented film of poly(chlorotrifluoroethylene) upon unconstr ained thermal treatment, self-extends in the machine direction (MD) wh ile shrinking along the transverse (TD) and normal/thickness (ND) dire ctions. In addition to the expected increase in crystallinity, the ann ealing process leads to an unexpected development of crystalline orien tation along the MD. This phenomenon is an example of ''processing-ind uced memory effects'' since it depends on the processing history of th e starting film, e.g., melt-extrusion leads to the subject behavior wh ereas compression molding does not. We must mention that the melt-extr uded films of poly( chlorotrifluoroethylene) are isotropic to start wi th, that is, MD and TD are indistinguishable prior to the annealing pr ocess. Furthermore, this phenomenon has not been observed for any othe r semicrystalline polymer and is believed to be the first citation for poly(chlorotrifluoroethylene) since its commercialization in 1957. Th ermomechanical analysis (TMA) is the analytical technique that led to this novel phenomenon which was later substantiated by x-ray diffracti on (XRD). (C) 1995 John Wiley & Sons, Inc.