Strain-induced crystallization in uniaxially drawn PETG plates

The copolyester poly(ethylene glycol-co-cyclohexane-1,4-dimethanol terephth alate) (PETG) is used industrially as an uncrystallizable polymer, whereas PET is an inherently crystallizable polymer. Nevertheless, a crystalline ph ase could appear in the material. To create a strain-induced crystalline ph ase in an initially amorphous PETG material, plates were placed in the heat ing chamber of a tensile machine at 100 degreesC and uniaxially drawn to ob tain different samples with various draw ratios. During DSC analysis of hig hly drawn samples, perturbations of the baseline appear above the glass-tra nsition temperature, consisting of weak exothermic and endothermic phenomen a. Comparison of DSC and X-ray diffraction analysis of drawn PETG and PET s hows that a strain-induced crystalline phase appears in this copolyester. A spherulitic superstructure could also appear after lengthy annealing. Anal ysis of this semicrystalline material allowed estimation of the degree of c rystallinity, about 3% after a drawing at high draw ratio and about 11% for undrawn annealed material. (C) 2001 John Wiley & Sons, Inc.