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

Huge numbers of PET (poly[ethylene 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.