T. Asano et al., Crystallization of oriented amorphous poly(ethylene terephthalate) as revealed by X-ray diffraction and microhardness, POLYMER, 40(23), 1999, pp. 6475-6484
The structural changes occurring when amorphous cold-drawn poly(ethylene te
rephthalate) films are annealed at different temperatures (50 degrees C-240
degrees C) for different annealing times (10-10(4) s) were investigated by
means of X-ray diffraction and microhardness techniques. The X-ray results
reveal the appearance of smectic order at 60 degrees C with a period of 10
.7 Angstrom. At 70 degrees C, a layer structure in the scale of 110 Angstro
m emerges. Finally, triclinic order is observed above 80 degrees C. The app
earance of a layer structure prior to the development of triclinic crystals
is associated with a density difference along the molecular direction prod
uced by a molecular tilting mechanism. The microhardness behaviour of annea
led cold-drawn PET films is correlated to the developing morphologies. At h
igh annealing temperatures (>100 degrees C), the plastic component of hardn
ess is shown to vary with the occurring microstructural changes. Results in
dicate that the hardness of the amorphous intrafibrilar regions is higher t
han that of a fully amorphous material. The indentation anisotropy, Delta H
, which is related to the elastic recovery of the material shows a conspicu
ous decrease at T-a similar to 70 degrees C, which is explained in terms of
a relaxation of the fibrils in the chain direction. (C) 1999 Elsevier Scie
nce Ltd. All rights reserved.