NMR studies of the structural development of high‐speed melt‐spun poly (ethylene terephthalate) fibers

Lineshape simulation of ¹³C nuclear magnetic resonances was employed to characterize the structural development of poly (ethylene terephthalate) (PET) during fiber formation and subsequent processing. In all spectra the carbonyl (CA) and glycoethylene (GE) resonances can be simulated with two components. The intensity variation of these components has been interpreted quantitatively on the basis of four morphological components in the solid‐state structure, with clearly defined differences in order between them. The four components are, in decreasing structural order, (i) crystalline (C), (ii) noncrystalline with order in both CA and GE environments (NC1), (iii) noncrystalline with order only in the GE environment (NC2), and (iv) amorphous (NCA). The crystalline component has been taken here to correspond to the high‐density component which has been estimated from flotation and optical density measurements. Such an analysis reveals a smooth pattern of evolution of order within a range of conditions in melt spinning and subsequent thermomechanical processing of PET fibers. Cold drawing at room temperature was seen to induce substantial ordering only in the GE environment. In contrast, annealing at a temperature significantly above glass transition temperature (T_g) for 2 h appears to cause the conversion of amorphous component to crystalline from with little accumulation of the intermediate components.