Dowan Kim

Step-reduced synthesis of starch-silver nanoparticles

In the present process, silver nanoparticles were directly synthesized in a single step by microwave irradiation of a mixture of starch, silver nitrate, and deionized water. This is different from the commonly adopted procedure for starch-silver nanoparticle synthesis in which silver nanoparticles are synthesized by preparing a starch solution as a reaction medium first. Thus, the additional step associated with the preparation of the starch solution was eliminated. In addition, no additional reducing agent was utilized. The adopted method was facile and straight forward, affording spherical silver nanoparticles with diameter below 10nm that exhibited good antibacterial activity. Further, influence of starch on the size of the silver nanoparticles was noticed.

Microwave assisted antibacterial chitosan-silver nanocomposite films.

In the current approach, antibacterial chitosan-silver nanocomposite films were fabricated through microwave irradiation. During the process, by utilizing chitosan as reducing agent, silver nanoparticles were synthesized within 11 min by microwave irradiation. Further, films were fabricated within 90 min. It involved an energy consumption of just 0.146 kWh to synthesize silver nanoparticles. This is many times less than the energy consumed during conventional methods. The silver nanoparticles were examined through UV-vis spectrum and transmission electron microscopy (TEM). The fabricated films were characterized by using scanning electron microscopy coupled with an energy dispersive spectrometer (SEM-EDS), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and contact angle (CA) measurements. The films exhibited antibacterial properties against both Gram-negative micro-organisms (Escherichia coli; E. coli) and Gram-positive micro-organisms (Staphylococcus aureus; S. aureus). In overall, the procedure adopted for fabricating these antibacterial films is environmental friendly, time-saving and energy-saving.

Enhanced moisture barrier films based on EVOH/exfoliated graphite (EGn) nanocomposite films by solution blending

AbstractA series of ethyl-vinyl alcohol (EVOH) nanocomposite films with exfoliated graphite nanosheets (EGn) were prepared via a solution blending method and their physical and moisture barrier properties were investigated as a function of the EGn content. The physical properties were strongly dependent upon the chemical and morphological structures originating from the differences in EGn composition. The nanocomposite films showed no strong interactions between the polymer and EGn filler, and this resulted in poor dispersion in relatively high content EVOH/EGn nanocomposites. With increasing content of EGn particles, the water vapor transmission rate varied in the range of 1.29 to 3.14 cc/m2/day and the water uptake greatly decreased from 9.1 to 3.4 wt%. The water resistance capacity of EVOH was greatly enhanced and moisture diffusion in the pure EVOH film was retarded by introducing the EGn. However, thermal stabilities were not improved by incorporating EGn due to the poor interaction between EVOH polymer chains and the EGn surface.n

Preparation and properties of poly(vinyl alcohol)/vinyltrimethoxysilane (PVA/VTMS) hybrid films with enhanced thermal stability and oxygen barrier properties

To enhance the thermal stability and barrier properties of pure poly(vinyl alcohol) (PVA), a series of poly(vinyl alcohol)/vinyltrimethoxysilane (PVA/VTMS) hybrid films were prepared via a sol-gel process, and their physical properties were investigated as a function of VTMS content. During the sol-gel process, simultaneous reactions between hydroxyl groups of PVA and silanol groups of hydrolyzed VTMS and self-condensation of VTMS occurred, inducing a cross-linked network structure and greatly enhanced thermal stability and oxygen barrier properties. The glass transition temperature and thermal decomposition temperature (T5%) of the PVA/VTMS hybrid films increased from 72.6 to 84.3 °C and 273.6 to 342.2 °C, respectively, with increasing VTMS content from 0 to 20%. Oxygen transmission rates of the hybrid films decreased from 6.12 to 0.17 cm3/m2×day, and those of the hybrid films incorporating 5%, 10%, and 20% VTMS were suppressed by 65.7%, 95.6%, and 97.2%, respectively, versus a pure PVA film. These are dependent on the chemical structure and morphology of the films with differing initial amounts of VTMS. The chemical affinity for water, intermolecular packing, and rigidity in polymer chains increased with increasing cross-linking by VTMS, leading to enhanced oxygen barrier properties and thermal stability in the PVA/VTMS hybrid films.

Effects of the paraffin wax (PW) content on the thermal and permeation properties of the LDPE/PW composite films

A series of low density polyethylene/paraffin wax (LDPE/PW) composite films were fabricated via a twin-screw extruder, and their morphologies, thermal properties, gas and vapor permeations, and surface properties were interpreted as functions of the PW contents. The PW was well dispersed into the LDPE matrix at low PW contents, whereas phase separation and an increase in surface roughness occurred with increasing PW content. The parameter results of surface properties such as contact angle, surface free energy, and solubility showed that the hydrophobicity of the LDPE/PW composite films also increased, and their phase changes and permeation properties were significantly dependent on the PW contents in the LDPE matrix. With increasing PW contents, both the oxygen transmittance rate (OTR) and water vapor transmittance rate (WVTR) of the LDPE/PW composite films decreased at a relatively low measuring temperature (23xa0°C), and increased at a relatively high temperature (48xa0°C). These results relate to the morphological structure (including tortuous paths and crystallinity) of the composite films via the incorporation of PW.

Poly(propylene carbonate)/exfoliated graphite nanocomposites: Selective adsorbent for the extraction and detection of gold(III)

In this study, poly(propylene carbonate) (PPC) and exfoliated graphite (PPC–EG) composites were prepared by the solution blending method and their selective extraction and detection of gold(III) were investigated. Specifically, a new effective adsorbent was developed for a selective extraction and determination of gold(III) by use of inductively coupled plasma optical emission spectrometry. The selectivity of PPC (PPC–EG 0.5, PPC–EG 1, PPC–EG 2, PPC–EG 3 and PPC–EG 5) was investigated toward several metal ions, including Au(III), Cd(II), Co(II), Cu(II), Hg(II), Pb(II), Pd(II) and Zn(II). Based on selectivity and pH studies, Au(III) was the most quantitatively adsorbed on PPC–EG 0.5 phase at pH 2, indicating that PPC–EG 0.5 was the most selective toward Au(III) among other metal ions. The adsorption isotherm followed the Langmuir model with adsorption capacity of 157.61 mg g−1 of PPC–EG 0.5 for Au(III), which was in agreement with experimental data of adsorption isotherm study. The kinetic of adsorption for Au(III) was investigated by a pseudo-first- and second-order models. Results of kinetic models displayed that the adsorption of Au(III) on the PPC–EG 0.5 phase obeyed a pseudo-second-order kinetic model. In addition, results of thermodynamic investigation demonstrated that the adsorption mechanism of PPC–EG 0.5 toward Au(III) was a general spontaneous process and favourable.

Effect of tetrapod ZnO whiskers on the physical and moisture barrier properties of transparent polyimide/TZnO-W composite films

Tetrapod zinc oxide whiskers (TZnO-Ws) were successfully prepared by a thermal oxidation method and confirmed using scanning electron microscopy (SEM) and wide angle X-ray diffraction (WAXD). A series of polyimide (PI)/TZnO-W composite films containing the as-prepared various TZnO-W contents were prepared and their physical properties were investigated to understand their potential use in flexible displays. The morphology, physical, and moisture barrier properties of the PI/TZnO-W composite films were interpreted as a function of the TZnO-W content. The PI/TZnO-W composite films exhibited an optical transparency greater than 80% at 550 nm (≤0.5 wt% TZnO-W content), a low coefficient of thermal expansion (CTE), and enhanced glass transition temperature. However, the thermal decomposition temperature decreased as the TZnO-W content increased. Although the mechanical strength increased up to 0.3 wt% TZnO-W content, it decreased due to poor interfacial interaction with high TZnO-W loading. The water vapor transmission rate (WVTR) and water uptake of the composite films, which were strongly dependent upon their morphological and chemical structure, varied from 508.3 to 325.2 g/m2/day and 3.7 to 1.3 wt%, respectively, greatly decreased as the TZnO-W content increased. The water resistance capacity of PI was greatly enhanced and moisture diffusion in the pure PI was retarded by incorporating the TZnO-W.

One-step synthesis of starch-silver nanoparticle solution and its application to antibacterial paper coating

Antibacterial starch-silver nanoparticles (ST-AgNPs) for use as coating solutions were prepared in a single step by ultrasonicating a mixture of starch, silver nitrate, and distilled water. The starch was used as an eco-friendly and inexpensive reducing agent. UV-vis spectra and transmission electron microscopy indicated that our single-step process was effective for synthesizing starch-based coating solution with AgNPs. Further, the as-prepared coating solution with AgNPs was applied to expand the application of paper for antibacterial packaging. The starch-coated paper with AgNPs showed not only highly enhanced oil resistance, but also excellent antibacterial activity, making our biodegradable starch-coated paper with AgNPs highly feasible for packaging applications.

Chitosan-mediated synthesis of flowery-CuO, and its antibacterial and catalytic properties

In the current investigation, CuO with a flower-like morphology has been successfully synthesized in situ in a chitosan medium (0.0015gmL-1) from copper nitrate (Cu(NO3)2·3H2O) and ammonia solution via a facile microwave-induced method. The as-prepared CuO was characterized by SEM, TEM, EDX, XRD, FTIR and TGA. The antibacterial activity of the flower-CuO against Escherichia coli was examined by analyzing colony forming units, and it was proved that the flower-CuO was able to kill >99% bacteria. Further, the flower-CuO exhibited excellent catalytic activity towards the reduction of 4-nitrophenol to 4-aminophenol in the presence of NaBH4. The reaction kinetics followed a pseudo-first-order rate law with a rate constant of 0.183min-1. To the best of our knowledge, this is the first time that copper oxide with the flower-like morphology has been synthesized by using a chitosan solution.

Improving properties of Hanji by coating chitosan–silver nanoparticle solution

A chitosan-silver nanoparticle solution (CSNS) was applied as a coating material to Hanji (Korean traditional paper), and the properties of the coated paper were investigated as a function of the dilution ratio. The required CSNS was first prepared from AgNO3 (30mmol) by utilizing chitosan as a reducing and stabilizing agent via ultrasonication. The as-prepared CSNS was diluted to various ratios (undiluted, 1/10, 1/100, and 1/1000) and applied to Hanji by a dip-coating method. The tensile, burst, oil resistance, and antibacterial properties of the coated Hanji against Escherichia coli were evaluated. Among the various dilution ratios, the maximum level of dilution that can positively influence the tensile, burst, oil resistance, and antibacterial properties of Hanji was identified as 1/10, 1/100, 1/10 and 1/1000 of the pure CSNS, respectively. These findings are significant because a specific property of Hanji can be economically improved by changing the dilution ratio.