Amorphous structure changes in poly(ethylene terephthalate) induced by annealing under dry and wet conditions and its dye uptake properties

Abstract

The amorphous structure changes in poly(ethylene terephthalate) (PET) induced by annealing under dry and wet conditions were discussed in terms of amorphous density ( ρ a) and dye uptake properties. The ρ a value of PET decreased with increasing annealing temperature, but it conversely increased at annealing temperatures above 210°C for the dry treatment and above 170°C for the wet treatment. With decreasing ρ a from 1.35 to 1.31 g cm −3, the conformation of amorphous molecules changed from the gauche to trans form. The ρ a value conversely increased on annealing at higher temperatures; however, the dye exhaustion continuously increased. The ratio of the absorbance of the α band to that of the β band of the basic dye crystal violet ( α β ratio), indicating the degree of dye aggregation, in PET decreased with a decrease in ρ a. The degree of dye aggregation further increased when ρ a conversely increased on high temperature annealing. These results suggested that the free volume content of PET increased as a result of conformational change from the gauche to trans form in amorphous molecules with increasing annealing temperature, and finally the increased free volume converted to microvoids around 1.31 g cm −3 of ρ a. The dye exhaustion increased with increasing annealing temperature according to microvoid formation.