Seonghyuk Ko

Facile biosynthesis and antioxidant property of nanogold-cellulose fiber composite

Direct synthesis of gold nanoparticles (AuNPs) on cellulose fiber has been successfully performed via facile green approach using lignin-containing unbleached kraft softwood pulp. The resulting AuNPs composited fibers showed apparent color change from pale yellow to purplish-dark brown by varying the amount of gold ions (Au3+) due to the surface plasmon resonance of nanogold. Further confirmation of AuNP formation on the fiber surface was conducted by UV-Vis diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD), and field emission scanning electron microscopy (FE-SEM). X-ray photoelectron spectroscopy (XPS) analysis revealed that gold nanoparticles formed on the fiber are well-defined pure metallic gold, indicating that Au3+ ions are efficiently bioreduced into Au0 and bind to the fiber surface. Antioxidant activity was evaluated by decomposition of 2,2-diphenyl- 1-picryl-hydrazyl (DPPH) in dark and light condition. As-prepared unbleached kraft fiber-AuNP composite showed significantly enhanced antioxidant activity and its DPPH scavenging rate reached about 86.05%.

The green fabrication, characterization and evaluation of catalytic antioxidation of gold nanoparticle-lignocellulose composite papers for active packaging

Gold nanoparticles (AuNPs) were directly synthesized and anchored on lignocellulose fiber without an external immobilizing agent via a facile green approach using unbleached kraft (UBK) softwood pulp. The obtained AuNPs were confirmed by UV-vis diffuse reflectance spectroscopy, field-emission scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The antioxidant behavior of the as-prepared AuNP-UBK fiber nanocomposite was evaluated by free radical scavenging of 2,2-diphenyl-1-picrylhydrazyl hydrate (DPPH). The nanocomposite fiber exhibited greatly enhanced radical scavenging activity compared to that of the pure fiber. As a consequence, AuNP-UBK nanocomposite paper showed exceptional antioxidant performance with a radical scavenging rate of over 98%, which is attributed to the synergistic effects of adsorption by the fiber-fiber network and subsequent catalytic activity of the AuNPs. This research indicated that AuNP-UBK fiber nanocomposites could be a new candidate for antioxidant active packaging for use in food preservation.

A Study on the Functionality and Stability of LDPE-Nano ZnO Composite Film

In this work, nano ZnO was introduced into low density poly ethylene (LDPE) composites films with various contents (0, 0.5, 1.0, 3.0 and 5.0 wt%) by melt-extrusion. Their basic properties such as crystallinity, chemical bonds and surface morphology were examined by XRD, FTIR and SEM. XRD patterns and FTIR peaks intensity were increased in proportion to the ZnO contents. SEM images showed well dispersed nano ZnO in LDPE composite films. Antimicrobial functionality of LDPE-nano ZnO composite films was also studied and the presence of nano ZnO resulted in significant improvement of antimicrobial functionality compared to the pure LDPE film. To evaluate influence of nano ZnO on LDPE properties required as packaging material, thermal, mechanical, gas barrier and optical properties of LDPE-nano ZnO composite films were characterized with various analytical techniques including TGA, UTM, OTR, WVTR and UV-Vis spectroscopy. As a result, except optical and mechanical properties of LDPE, no significant effects were found in other properties. Opacity of pure LDPE was greatly increased with increasing concentration of nano ZnO and tensile strength was also improved at 0.5wt% ZnO content.

INFLUENCE OF MONTMORILLONITE NANOCLAY CONTENT ON THE OPTICAL, THERMAL, MECHANICAL, AND BARRIER PROPERTIES OF LOW-DENSITY POLYETHYLENE

Although low density polyethylene (LDPE) has long been widely used in packaging applications, some limitations in its use still exist and are due to its relatively poor gas barrier properties and low mechanical strength which can restrict its extensive use for more advanced applications, such as electronic and pharmaceutical packaging. The purpose of this study was to investigate the possibility of using montmorillonite (MMT) nanoclay as a means to enhance the thermal, mechanical, and barrier properties of LDPE prepared via melt extrusion. The level of exfoliated dispersion of the MMT nanoclay in the prepared LDPE-MMT composite was confirmed using transmission electron microscopy (TEM). The relationship between the resulting morphology and the thermal, mechanical, and barrier properties as a function of the MMT content was evaluated. The results showed that incorporating >3 wt.% of MMT nanoclay produced significant changes in the morphology of the LDPE-MMT nanoclay composite in that the segregated matrix adopted an oriented arrangement of exfoliated clay platelets. Thermogravimetric analysis (TGA) showed that the thermal stability of LDPE improved significantly as a result of MMT nanoclay incorporation. Furthermore, differential scanning calorimetry (DSC) analysis indicated that increasing clay content above 3 wt.% effectively reduces the crystallinity of LDPE-MMT composites through the suppression effect. The tensile strength of LDPE increased gradually with an increased content of MMT nanoclay and the maximum value of 16.89 N/mm2 was obtained at 10 wt.% MMT content. This value represents a 40.87% increase relative to the tensile strength of the pristine LDPE. Barrier properties of LDPE and LDPE-MMT nanoclay composites were assessed by examining the permeability with respect to oxygen and water vapor. As the content of MMT nanoclay was increased to 10 wt.%, the permeability of the nanocomposite films to oxygen and water vapor notably decreased to 42.8% and 26.2%, respectively.