Fine Structure of Polyethylene Terephthalate Fibers

Abstract

In order to obtain informations concerning submicrostructure of polyethylene terephthalate (PETP) fibers, the sorption isotherms of undrawn and drawn fibers heat-treated at various temperatures were obtaind, by measuring the amounts of phenol adsorbed by the fibers from the aqueous solutions of phenol. Mechanical properties are also measured in the phenol solutions in the corresponding concentration range. The results obtained may be summerized as follows: 1) the sorption isotherms support the view that such variations in the degree of internal geometrical order as in cellulosic fibers occur in the amorphous and low order regions of PETP fibers (The high order regions could not be studied by this sorption experiment). 2) In undrawn fibers, crystallization occurs above 100°C and the crystallites grow into more perfect ones with increasing temperature. 3) Even in drawn fibers, crystallization does not occur until the temperature exceeds 100°C, although the stretch faciliates the transformation from the low order to the higher order regions. 4) The stress-strain curves of undrawn monofilaments show a great deal of yield in the phenol solutions, and the “yield” stress decreases rapidly with the increasing concentration of phenol. 5) The drawn monofilaments begin to exhibit remarkable shrinkage when they are immersed in the phenol solutions having the concentrations above 4.5%(or 5.1% for the samples heat-treated at 95°C). This critical concentration just corresponds to a transition point in the sorption isotherm, above which the amount of phenol adsorbed rapidly increases.