Structure and properties of biaxially stretched poly(ethylene terephthalate) sheets

Abstract

Huge numbers of PET (polylethylene terephthalate]) bottles are produced in the world. Especially in Japan, the number of hot-fillable PET bottles used is extremely large and is still increasing. This type of bottle is generally manufactured by the heat-set method using hot molds after stretch-blow molding. Herein, we examined how the PET sheet stretching condition affects the PET heat-shrinkage behavior at 85"C, which is the hot-filling temperature. Sheets stretched at a higher temperature and higher speed had higher thermal stability for a wider range of draw ratios. This is because those sheets have a higher crystallinity and relaxed amorphous regions. The higher stretch speed gives the sheet a higher crystallinity with self heat generation during rapid deformation. A higher stretch temperature makes the molecular segments relaxed.We were interested in how the thermal stability changes by varying the stretch condition (speed and temperature) and by what structure the thermal stability is achieved. There are a few reports on the thermal stability of fiber (3-5) and film ( 6 4 , none of which deal with the thermal shrinkage at 8 5 9 5°C of biaxialy stretched film. We have examined the thermal stability by stretching PET sheets at various conditions. EXPERIMENTAL MeasurementsCrystallinity X , (%) The crystallinity is estimated by a density gradient method (Ikeda Scientific Co.). Carbon tetrachloride and n-heptane were used in the density gradient column. The expression used was X=100 d, (d-d,)/d(d,-d,) (1) where X is the crystallinity (%); d is the measured sample density (lo3 kg/m3); d, is the crystal density (lo3 kg/m3) = 1.455 (8); and d, is the amorphous density (lo3 kg/m3) = 1.335 (9). Refractive Index nRefractometer (Atago Co.) following Samuels (10).The refractive index was measured using the Abbe

Thermally stimulated current studies on molecular relaxation and blow moulding of poly(ethylene terephthalate)

“…The relaxation time changes not only when the sample is stretched, but also after stretching. Maruhashi and Asada 49 reported that the best thermal stability (in terms of shrinkage) in biaxially stretched PET was found at higher stretching temperature and higher stretching speed. They proposed that the better thermal stability is controlled by the larger number of crystalline regions and the larger relaxed amorphous regions.…”

Extremely enhanced hydrolytic stability of poly(ethylene terephthalate) films

“…Early investigations for PET were concerned with its thermal degradation [9][10][11][12][13][14][15] and the kinetics and mechanisms of hydrolytic depolymerization [16][17][18][19]. Previous studies revealed that biaxial stretching of PET films greatly influences the ordered structure and properties of PET [20]. The concerns of PET researchers regarding the effect of biaxial stretching on hydrolytic stability have also been addressed [21][22][23][24][25].…”

Glass transition and cold crystallization in carbon dioxide treated poly(ethylene terephthalate)

“…The crystallization of PET is influenced by various factors, such as molecular weight, orientation, annealing, and crystallization conditions 5. For example, the orientation can cause stress‐induced crystallization and influence the crystallinity 5–9. PET is a semirigid crystalline polymer with slow crystallization behavior; this usually leads to the presence of a large amount of metastable crystals or imperfect crystals that are not at thermodynamic equilibrium.…”