초록
In order to investigate the fine structure of PET films, PET films were stretchd at various draw ratios (2, 3, 4, 5) below $T_g$ ($72^{\circ}C$) and then annealed at various temperatures (125, 150, 175, $200^{\circ}C$) under free-annealed (FA) and taut-annealed (TA) conditions. Such changes as thermal shrinkage, crystallinity, crystallite size, dynamic viscoelasticity and thermal behaviour were measured in relation to the draw ratio and annealing condition.The following results were obtained. 1. Thermal shirinkage increased with increasing annealing temperature and draw ratio, but decreased in case of draw ratio 4 (draw ratio 3 at $200^{\circ}C$) and above it. 2. The degree of crystallinity of FA samples were higher than those of TA samples. 3. Tan 5 of TA samples were less than those of FA samples, and storage moduli (E') and loss moduli (E") of FA samples were less than those of TA samples; moreover, maximum tan '||'&'||' temperature of FA samples were shifted toward higher temperature than those of TA samples. 4. The melting endotherm ($T_m$) and heat of fusion $(\DeltaH)$ of the PET film increased with the draw ratio and annealing temperature; in addition, premelting endotherm ($T_m$) and heat of fusion $(\DeltaH)$ of the local crystallization in the FA samples were larger than those of TA samples. 5. The X-ray diffraction pattern displayed sharp peaks gradually with the draw ratio and annealing temperature. 6. Crystallite sizes of FA samples were larger than those of TA samples.