Annealing effect in the cold-plastic deformation of amorphous PET material

When polyethylene terephthalate (PET) film specimen were stepwise elongated under tension with various speeds of about 0.5 similar to 500 mm/min, the necking area, consisted of transparent and opaque bands, was formed during plastic deformation. Stress oscillation was apparently obtained in the stress-strain curve of above specimen. However, stress oscillation was not obtained in the stress-strain curve of annealing specimen. Microstructure was examined dynamically using an optical microscopy and thermal analysis was carried out in a differential scanning calorimeter at a heating rate of 10 degreesC/min. Also, orientation and crystallization were examined using monochromatic-pinhole technique and elastic modulus was measured by a dynamic mechanical analyzer in the temperature range of -150 similar to 70 degreesC with the frequency of 1 Hz. Transparent PET products were fabricated by use of the PET pellets annealed at 83 degreesC for 30 min in an electric furnace.