The Microstructure and Macrostructure of Sulfonated Poly(ethylene Terethphalate) Fibers DEBRA A. TlMM* zyxwvutsr and zyxwvutsr YOU-LO HSIEHt Division of Textiles, University of California at Davis, Davis, California 9561 6-8722 SYNOPSIS zyxwvutsrqpon The effectsof fiber-forming processes on the microstructure and macrostructure and overall orientation in sulfonated poly (ethylene terephthalate) (SPET) fibers are reported. The processing parameters examined include drawing, crimping, relaxing, and annealing. Drawing and annealing cause changes in both the crystalline structure and molecular packing in the noncrystalline regions, while crimping and relaxing appear to affect only the non- crystalline regions. A bimodal melting endotherm was observed for the SPET fibers. Ex- perimental data suggest the low-temperature endotherm of the SPET fibers originates from melting of the crystalline structure formed on drawing, and that the high-temperature endotherm results from melting the heat-induced crystals formed during fiber processing and/or thermal analysis. Compared to the PET fibers, the SPET chains in the undrawn fibers appear to have higher mobility, are easier to crystallize, and form smaller crystals upon drawing as well as DTA heating. At the crimped stage, the SPET fibers have higher overall molecular packing but lower overall orientation than the PET fibers. The differences in physical and thermal properties between the analogous SPET and PET fibers are related to their different responses to processing variations because of molecular weight and side- group effects. zyxwvutsr 0 1993 John Wiley & Sons, Inc. zyxwvut Keywords: sulfonated poly (ethylene terethphalate) (SPET) poly (ethylene terethphal- ate) (PET) drawing and thermal processes physical and thermal characteristics INTRODUCTION The morphology (i.e., microstructure and macro- structure) of poly (ethylene terephthalate) (PET) fibers is strongly governed by manufacturing meth- ods, as in melting, spinning, drawing, and heat pro- cessing. The process-dependent morphology contrib- utes significantly to the fiber performance properties. The effects of processing on the fiber morphology of PET homopolymer have been extensively reported. Additionally, much of the fundamental understand- ing of crystallization and annealing effects has been obtained from unoriented PET. Other than the homopolymer, some of the most commonly used polyester fibers are spun from sul- fonated PET (SPET) , of which 2-3 mol zyxwvu 9% of the * Current Address: Optical Radiation Corporation, 1300 Op- ' To whom all correspondence should be addressed. tical Drive, Azusa, CA 91702. Journal of Polymer Science: Part B Polymer Physics, Vol. 31,1873-1883 (1993) 0 1993 John Wiley & Sons, Inc. CCC 0887-6266/93/121873-11 aromatic rings are sulfonated (-SO;Na+) .l The sulfonated PET fibers are of lower strength, but the anionic nature of these side groups provides desir- able binding sites for basic dyes. The structures and properties of the sulfonated PET fibers are not nearly as well documented as those of the homo- polymer. There has been increasing interest in new and better fiber properties, such as finer fiber sizes and specific surface and/or bulk properties. To de- velop such fibers through innovative fiber spinning and processing, the understanding of the structure- process relationship is essential. We specifically ex- amine the microstructure and macrostructure of the sulfonated PET fibers as affected by heat and draw- ing processes, and as compared with homopolymer fibers. The thermal behavior of a semicrystalline poly- mer directly reflects the processing history of the polymer. Thermal properties of polymers can be de- termined experimentally by differential thermal analysis (DTA) or differential scanning calorimetry 1873