Eunkyoung Shim

Scalable Liquid Shear‐Driven Fabrication of Polymer Nanofibers

A simple process for batch or continuous formation of polymer nanofibers and other nanomaterials in the bulk of a sheared fluid medium is introduced. The process may be of high value to commercial nanotechnology, as it can be easily scaled up to the fabrication of staple nanofibers at rates that may exceed tens of kilograms per hour.

Luminescence and Mechanical Properties of Photoluminescent Core Bicomponent Fibers

Photoluminescent fibers with a sheath-core morphology are produced to impart good mechanical properties. Both photoluminescent and mechanical properties are examined for these fibers with respect to photoluminescent pigment concentrations in the core, draw ratios, and polymer types. The photoluminescent pigment concentration in the core of the fibers directly influences their luminance intensity and afterglow properties as well as their mechanical properties.

Three‐dimensional analysis of segmented pie bicomponent nonwovens

Three‐dimensional structural analysis utilizing digital volumetric imaging is used to fully understand the splitting of bicomponent fibers by hydroentangling. It was found that lower fabric density measured by solid volume fraction, higher degree of splitting and a higher thickness fiber orientation direction was evident at the jet streak valley position. Splitting was found to be more dominant on the surface of the fabrics. Washing the fabric increased fiber splitting and also resulted in more uniform splitting, but did not result in any significant change in local fiber orientation, that is, the structure.

A Note on Jet Streaks in Hydroentangled Nonwovens

Hydroentanglement is the fastest growing bonding method in the nonwoven arena. Its strengths are good fabric aesthetics, and the lack of any complex binder chemistry with its inherent environmental concerns. Hydroentanglement is used for mechanically bonding both staple and filament nonwovens as well as being used for post-treatment of fabrics. As hydroentangling uses fine, closely spaced, high-speed waterjets, they create ridges or streaks that are quite visible to the naked eye. This may be undesirable if it interferes with other textures on the surface or if a smooth flat surface is desired. This study reports on methodology used for the analysis of jet streaks using texture-based methods.

Three-Dimensional Structural Characterization of Nonwoven Fabrics

Nonwoven materials are found in a gamut of critical applications. This is partly due to the fact that these structures can be produced at high speed and engineered to deliver unique functionality at low cost. The behavior of these materials is highly dependent on alignment of fibers within the structure. The ability to characterize and also to control the structure is important, but very challenging due to the complex nature of the structures. Thus, to date, focus has been placed mainly on two-dimensional analysis techniques for describing the behavior of nonwovens. This article demonstrates the utility of three-dimensional (3D) digital volumetric imaging technique for visualizing and characterizing a complex 3D class of nonwoven structures produced by hydroentanglement.

Electrostatic Capture Efficiency Enhancement of Polypropylene Electret Filters with Barium Titanate

This study reports on the effects of BaTiO3—a high dielectric constant additive—addition on charging and filtration properties of meltblown polypropylene (PP) electret filters. Since electrostatic capture efficiency of electret filters is mainly dependent on electrical forces, surface potential and aerosol filtration properties were analyzed and compared. Due to quasi-permanent nature of electret property, stability of charging and filtration performance was also investigated via following an isothermal charge decay procedure. Addition of BaTiO3 did not alter fiber morphology significantly. Particularly, the stability of electrostatic filtration performance was found to be promising with the addition of BaTiO3. Possible microstructural changes after addition of BaTiO3 were investigated via wide angle X-ray diffraction. Changes in crystal structure of PP upon addition of BaTiO3 did not deteriorate electrostatic properties. Copyright 2015 American Association for Aerosol Research

Impacts of high-speed waterjets on web structures

Hydroentangling, where a fabric is formed by striking of fine, closely spaced, high speed waterjets, is one of the fastest growing bonding methods in the nonwoven industry. Softness, drape, conformability, and relatively high strength are the major characteristics that make this bonding technology unique. Despite the method appeal, few understand the impact of waterjet on fabric structures. The primary function of waterjet is to produce fiber entangling, which induces web integrity. In this paper, we have analyzed the interaction of waterjets on web structures to provide a better understanding of the hydroentangling mechanism. We have successfully visualized and analyzed structures of entangled regions through 2D and 3D imaging techniques. The influence of water-jet pressure, jet diameter, and number of jets on hydroentangled web structures is reported.

Reverse Phase HPLC Analysis of Commercial Surfactants used as Melt Additives

Abstract Reverse phase HPLC (High Performance Liquid Chromatography) was used to analyze the length distribution of polyoxyethylene (POE) chains in commercial surfactants that can be used as melt additives for hydrophilic polypropylene surface modification. Ten nonionic surfactants including ethoxylated alcohols, nonyl phenols and amines, PEG esters, and mono glycerides were investigated. HPLC methods described herein are capable of analyzing ethoxylated nonionic surfactants and offer the advantage of separating the components in surfactants according to both the hydrophobe and hydrophile chain length. Moreover, the method is rapid and gradient elution allows for good baseline separation of the several components in the additives.

Hydroentangling knitted fabrics for improving abrasion resistance

Abstract Hydroentangling is used as the mechanical finish to improve abrasion resistance of knitted fabrics. The hydroentangling process successfully reduced the amount of loose surface fibers and led to improved abrasion resistance. However, other properties such as fabric thickness and softness were also affected by the treatment.

Nylon-Graphene Composite Nonwovens As Monolithic Conductive or Capacitive Fabrics

Here we describe a nylon-graphene nonwoven (NGN) composite, prepared via melt-blowing of nylon-6 into nonwoven fabrics and infiltrate those with graphene oxide (GO) in aqueous dispersions, which were further chemically reduced into graphene to offer electrical conductivity. The correlation between the conductivity and the graphene loading is described by the percolation scaling law σ = (p - pc)t, with an exponent t of 1.2 and a critical concentration pc of 0.005 wt %, the lowest among all the nylon composites reported. Monolithic supercapacitors have been further developed on the nylon-GO nonwoven composites (NGO), via a programed CO2-laser patterning process. The nylon nonwoven works as an efficient matrix, providing high capacity to GO and ensuring enough electrode materials generated via the subsequent laser patterning processes. Our best monolithic supercapacitors exhibited an areal capacitance of 10.37 mF cm-2 in PVA-H2SO4 electrolyte, much higher than the 1-3 mF cm-2 reported for typical microsupercapacitors. Moreover, our supercapacitors were able to retain a capacitance density of 5.07 mF cm-2 at an ultrahigh scan rate (1 V s-1), probably due to the facilitated ion migration within the highly porous nonwoven framework. This is the first report of highly functional nylon-6 nonwovens, fabricated via industrially scalable pathways into low-cost conductive polymer matrices and disposable energy storage systems.