Highly crystalline and oriented high-strength poly(ethylene terephthalate) fibers by using low molecular weight polymer Huseyin Avci, 1,2 Mesbah Najafi, 1 Ali Kilic, 3 Richard Kotek 1 1 College of Textiles, Textile Engineering Chemistry and Science, North Carolina State University, Raleigh, North Carolina 2 Metallurgical and Materials Engineering, Eskisehir Osmangazi University, Eskisehir, Turkey 3 Department of Textile Engineering, Istanbul Technical University, Istanbul, Turkey Correspondence to: R. Kotek; (E - mail: rkotek@ncsu.edu) ABSTRACT: High-strength poly(ethylene terephthalate) (PET) fibers were obtained using low molecular weight (LMW) polymervia horizontal isothermal bath (hIB), followed by postdrawing process. We investigated the unique formations of different precursors, which differentiated in its molecular orientation and crystalline structures from traditional high-speed spinning PET fibers. Sharp increase in crystallinity was observed after drawing process even though the fibers showed almost no any crystallinity before the draw- ing. Properties of as-spun and drawn hIB and control filaments at different process conditions were compared. As would be expected, performances of resulted treated undrawn and drawn fibers have dramatically improved with developing unique morphologies. Tenac- ities more than 8 g/d for as-spun and 10 g/d for drawn treated fibers after just drawn at 1.279 draw ratio were observed. These per- formances are considerably higher than that of control fibers. An explanation of structural development of high-strength fibers using LMW polymer spun with hIB is proposed. V C 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42747. KEYWORDS: extrusion; fibers; mechanical properties; polyesters; X-ray Received 25 March 2015; accepted 18 July 2015 DOI: 10.1002/app.42747 INTRODUCTION High-strength polyester fibers are widely used in industry and our daily lives. Hence, studies on structural improvement of fil- ament and its relation to production conditions have been examined carefully by researchers for many years. This resulted in 60% of the world’s total polyester production having been consumed as fiber in 2010. 1 In general, zone drawing/zone annealing, microwave heating, one or two step drawing high- speed spinning, vibrational hot drawing, two-step spin draw processes, solution spinning, and solid-state extrusion are the most important production methods to manufacture high- performance polyester fibers. 2,3 Structural development of fibers in one-step high-speed spinning process is limited even if it appears promising in the case of economical and high through- puts. Therefore, two-step spin-draw and multistep drawing processes are widely accepted and utilized to obtain high modu- lus and tenacity polyester filaments. 2,4 On the other hand, the solution spinning technique is one of the crucial methods by using ultra-high molecular weight polymers to produce high- performance poly(ethylene terephthalate) (PET) fibers, but use some organic solvents raise questions about their toxicity. 5,6 This method is expensive and the production speed is slow. Sometimes more than one bath is required in the production lines and a very high draw ratio (DR) is needed to manufacture high-performance fibers. Full understanding of precursors for crystallization and crystalli- zation in polyester fibers is limited because of fast crystallization kinetic and the different formation of precursors. According to process conditions and polymer properties, a number of precur- sor models have been proposed. These precursors can be nematic, smectic, other less unidentified structures, and some- times microvoids and/or banded structure can be associated with these forms. 7 In addition, all these forms have some com- mon structural properties, as they are highly oriented but have noncrystallized molecular chains or chain segments. Nicholson et al. 8 have observed mesophase formation by drawing at the drawing temperature of 1108C with the DR of 4 using a very low oriented as-spun yarn. After the drawing process, the fibers were rapidly cooled to inhibit the crystallization, which showed a different usual form of triclinic and were described as “mesophase” form. However, this mesophase form, yet still exhibiting spatial order, was not very stable, and the annealing process could easily destroy it. In addition, Carr et al. 9 have produced nematic phase by drawing PEN: Polyethylene naph- thalate films uniaxially at 1208C at the DRs range from 3.5 to 5.5 with observing long-range noncrystalline order when the V C 2015 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM J. APPL. POLYM. SCI. 2015, DOI: 10.1002/APP.42747 42747 (1 of 15)