STRUCTURE DEVELOPMENT OF POLYETHYLENE TEREPHTHALATE FIBERS DURING POSTSPINNING ANNEALING

The fast structure development process in the early stage of crystalli zation in commercial polyethylene terephthalate (PET) fibers during ca refully controlled postspinning annealing treatments has been followed . In addition to conventional structure characterization techniques, t ransmission electron microscopy (TEM) has been employed to probe the s equence of structural events. In the earliest stage of structural deve lopment, direct observation showed an embryonic microfibrillar structu re, the microfibril diameter being ca. 5 nm. Upon modest heat treatmen t, the microfibrils become axially punctuated with crystallites. As fu rther crystallization occurs, the crystallites become more perfect and lateral alignment of crystallites takes place, particularly in extens ively crystallized materials, that is, higher temperature and/or longe r time of heat treatment. The lateral alignment results finally in a l amellar microstructure.