Nanofiber web mass produced via electrospinning has many potential applications due to its large specific area, very small pore size, high porosity and so forth. Despite these potentials, the application of nanofiber web has been limited by its poor mechanical properties. To remedy these poor mechanical properties, laminating processes have been applied to its manufacture. For use in clothing, fabric should have not only adequate mechanical properties, but also the durability to withstand laundering. Hence, the purpose of this study was to measure the mechanical properties of mass-produced nanofiber web, and then to investigate the change of these mechanical properties after laundering in order to evaluate the possibility of using such fiber in a breathable fabric for outdoor wear. We concluded that the maintenance of nanofiber web morphology, despite repeated laundering, allowed for the retention of the mechanical properties.

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