STRUCTURE-ANALYSIS OF THE NONCRYSTALLINE MATERIAL IN POLY(ETHYLENE-TEREPHTHALATE) FIBERS

The structures of the noncrystalline material of four poly(ethylene terephthalate) fiber samples have been studied by analyzing the X-ray scattering patterns. The noncrystalline scattering Patterns of the three semicrystalline fibers are revealed by removal of the crystalline contribution from the diffraction patterns. The crystalline phase diffraction is calculated from a structure model determined by a full-pattern X-ray fiber diffraction analysis. The noncrystalline material is further divided into an amorphous and an oriented, intermediate phase. The azimuthal scattering pattern of the former is isotropic, the latter anisotropic. The intermediate phase does not only show parallel chains along the fiber direction, but a crystal-like correlation is also possible, primarily in the material between the oriented, fibrillar crystallites. The growth of the crystalline phase in fibers is intimately coupled to this intermediate phase. Both amount and detailed structure of the intermediate phase depend on the thermal and mechanical history of the fiber. A first discussion is given of the correlation between the three phases derived by X-ray diffraction and three phases identified earlier by thermal analysis (crystalline, mobile amorphous and rigid amorphous). The mechanical properties of the fibers are seemingly more dependent on the intermediate phase than on the crystalline or amorphous phases.