Melting behavior of poly(ethylene terephthalate) industrial fibres from various domestic and overseas factories is studied by differential scanning calorimetric (DSC) measurements.The thermograms of polyester fibres often show double melting endotherms.This behavior has been attributed to melting of less stable crystallites followed by recrystallization during scanning in differential scanning calorimetry experiment.Combined with data obtained from wide-angle X-ray diffraction

small-angle X-ray scattering

birefringence and density

it is pronounced that the continuous network structure plays an important part on melting behavior of industrial poly(ethylene terephthalate)fibers in addition to the effect of crystal size

crystal perfection and crystal size distribution.In addition

the degree of crystallinity fwc(DSC) calculated from the heat of fusion is not very satisfying for describing crystalline weight fraction of industrial PET fibres.