HIGH-PERFORMANCE PET FIBERS VIA LIQUID ISOTHERMAL BATH HIGH-SPEED SPINNING - FIBER PROPERTIES AND STRUCTURE RESULTING FROM THREADLINE MODIFICATION AND POSTTREATMENT

Poly(ethylene terephthalate) fibers with improved mechanical propertie s and dimensional stability were spun via controlled threadline dynami cs by a liquid isothermal bath (LIB) spinning process: followed by pos tdrawing and annealing. Control fibers were made by unperturbed spinni ng and posttreatment similar to a traditional spin-draw process. The t wo sets of as-spun fibers were spun at take-up speed in the range of 2 000-5000 m/min. Fiber properties of the as-spun fibers and posttreated fibers of each process were compared. Two commercial tire cords, i.e. , conventional tire cord and low shrinkage tire cord, were also includ ed. Unlike unperturbed spinning, the LIB as-spun fibers show unique st ructural properties of high amorphous orientation, low crystallinity, high strength, and high initial modulus. Moreover, noncrystalline chai ns are further extended during posttreatment. The posttreated LIB fibe rs exhibit mechanical properties with tenacity higher than approximate ly 9 g/d, initial modulus higher than 120 g/d, and ultimate elongation less than approximately 10%. They also demonstrate superior dimension al stability with thermal shrinkage less than 6% and LASE-5 higher tha n 5 g/d. The overall properties are not obtainable by either the tradi tional spin-draw process or any modified process that produces low shr inkage tire cord. Unlike the case fbr unperturbed fibers, the mechanic al properties of the posttreated LIB fibers demonstrate a strong/depen dency on the birefringence of their respective as-spun fibers. There a re at least three significant pieces of evidence that strongly indicat e the existence of a third phase, referred to as the taut-tie noncryst alline phase (TTNC), in addition to the traditional two-phase model, i .e., crystalline and random amorphous phases. A unique feature involvi ng a high fraction of taut-tie noncrystalline phase (TTNC %) in the LI B as-spun and the posttreated fibers is also found and which is, in fa ct, achieved neither by the traditional spin-draw nor the commercial t ire cord processes. Further, different from the posttreated unperturbe d fibers, the posttreated LIB fibers have an enhanced fraction of taut -tie noncrystalline chains with shorter length, which is believed to b e one of the important factors leading to the superior mechanical prop erties and excellent dimensional stability achieved. (C) 1997 John Wil ey & Sons, Inc.