In situ study of fiber structure development of poly(butylene terephthalate) in a continuous laser-heated drawing process

Abstract

The structural development of poly(butylene terephthalate) (PBT) fibers was analyzed using in situ wide angle X-ray diffraction and fiber temperature measurements during CO 2 laser-heated drawing, in which the necking position on the running fiber could be fixed by CO 2 laser irradiation. The measured parameters were determined as functions of the elapsed time after necking with a time resolution of 0.3 ms. The as-spun PBT fibers, which exhibited a low-oriented a-crystalline structure, were drawn to a draw ratio of 5 using laser heating. The (001 0 ) reflection, which indicates a quasi-smectic fibrillar structure, was not observed before crystallization in contrast to measurements of poly(ethylene terephthalate) (PET) and poly(ethylene 2,6-naphthalene dicarboxylate) (PEN). The a-crystal was transformed into an oriented b-form crystal at the necking position, and the developed b-crystallites exhibited increased size and altered orientation o2 ms after necking. The fiber temperature increased rapidly at around T g , and the rearrangement of the b-crystal primarily occurred as the fiber's temperature rose from 100 to 160 1C. Keywords: crystal-crystal transition; laser-heated drawing; poly(butylene terephthalate) INTRODUCTION Poly(butylene terephthalate) (PBT) is a type of polyester produced by the polymerization of 1,4-butanediol and terephthalic acid. PBT has two more methylene (CH 2 ) groups than poly(ethylene terephthalate) (PET), which results in reduced coherence among molecules and provides the PBT fiber with increased flexibility. The higher chain flexibility causes a reversible crystal-crystal transition, and the PBT fiber thus exhibits good stretching properties with high stretch recovery.PBT has two different crystalline forms: the a-form and the bform. 1-7 The a-form crystalline structure, in which the chain consists of four methylene groups with a gauche-trans-gauche conformation, is found in a relaxed state and is the most stable structure. The a-crystal is transformed into the b-crystal when the polymer is held under strain, and the polymer reversibly transforms to the a-crystal upon removal of the strain. The b-crystal consists of an all-trans conformation chain. This difference in conformation between the b-crystal and the a-crystal, which is not fully extended, primarily affects the unit cell parameter c, which is very sensitive to the transition and is often used to detect the transition. Mencik 1 was the first to index the unit cell of the a-crystal, which is triclinic and has

Systematic Study of Thermal and (Bio)Degradable Properties of Semiaromatic Copolyesters Based on Naturally Occurring Isosorbide

“…The α structure is often formed when the material is crystallized or heat-treated in a relaxed state, while the β structure is formed instead when the material is under stress. 34,35 Both crystal structures can be transformed to each other, depending upon the stretched or relaxed treatment of the materials. 33 From the method of polymer treatment and diffraction patterns, we can conclude that the PBIT copolyesters with ≤40 mol % IS content purified by HFIP/ methanol recrystallization possess α crystal structures.…”

Structure and mechanical properties of multi-hollowed fibers produced by CO2 laser irradiated neck drawing

“…A schematic of the CO 2 laser irradiated drawing system used in this study is shown in Fig. , a detailed explanation of which can be found in our previous papers . The CO 2 laser beam, which was generated by a PIN‐20S laser source manufactured by Onizuca Glass, was irradiated onto the running fiber.…”

“…When this deformation occurs in the neck region, the fiber diameter decreases rapidly, molecular chains align to the fiber axis, and the fiber structure is developed through orientation‐induced crystallization, all in just a few milliseconds. There have been several reports on the structure development by CO 2 laser irradiated neck drawing of various synthetic fibers, and our research group has studied the fiber structure development though in situ characterization of X‐ray diffraction .…”

Supermolecular Structure of Poly(Butylene Terephthalate) Fibers Formed with the Addition of Reduced Graphene Oxide

“…The α-form can change into the β-form with an all-trans (ttt) conformation when the polymer is subjected to stress [ 43 ]. Nevertheless, the β-form is unstable because, after the removal of the stress, the β-form returns to the α-form [ 44 , 45 ]. The smectic phase occurs when amorphous PBT is stretched at room temperature and transforms into the α-form upon heating [ 45 ].…”