MECHANICAL PRIMARY DISPERSION OF POLYETHYLENETEREPHTHALATEISOPHTHALATE COPOLYMER FIBERS

Abstract

Mechanical primary dispersions of polyethylene terephthalate fiber and polyethylene terephthalate-isophthalate copolymer fiber are measured and the cause for the difference of loss peak temperature between homopolymer and copolymers is discussed.
It is found that the glass transition temperatures of these copolymer at amorphous state conform to Gordon-Taylor's equation.
The difference in glass transition temperature between amorphous homopolymer and amorphous 9/1 copolymer (terephthalate 9: isophthalate 1) is 2 or 3 degrees. The results of dynamic mechanical measurements about undrawn fiber produced by melt spinning show that tho loss peak temperature of 9/1 copolymer is only 4 degrees lower than that of homopolymer.
But for drawn and drawn heat-treated fibers, the loss peak temperature of 9/1 copolymer is found to be about 20 degrees lower than that of homopolymer. The data of X-ray small angle scattering intensity, half width of (010) plane of X-ray diffraction and width of mechanical primary dispersion seem to suggest the following explanation: the density of amorphous region of copolymer is smaller than that of homopolymer and therefore the restriction of chain motion in amorphous region by the existence of fine crystallites is looser in copolymer fiber than in homopolymer.