Non-isothermal crystallization behavior of poly(ethylene terephthalate) was studied by means of infrared spectroscopy

differential-scanning calorimetry

X-ray diffraction and density method.The PET began to crystallize as the temperature higher than 110.There isn't obvious change in the crystallinity from 160 to 230℃.But the crystallinity of PET continually increases during the later cooling process.The crystallinity of slowly cooled sample from 230℃ is much higher than that of rapidly quenched sample.These results provide strong evidence for chain folding existing before crystallization.