• Membrane Journal
• /
• v.16 no.2
• /
• pp.85-105
• /
• 2006

Poly(lactic acid) is a linear aliphatic thermoplastic polyester, produced by the ring-opening polymerization of lactides and the lactic acid monomers, which are obtained from the fermentation of sugar feed stocks, corn, etc. PLA has high mechanical, thermal plasticity, fabric-ability, and biocompatibility, So PLA is a promising polymer far various end-use applications. In recent time, the intercalation of polymers from either solution or the melt in the silicate galleries of clay is the best technique to prepare nanocompoiste material which often exhibit remarkable improvement of mechanical, thermal, optical and physicochemical properties when compared with the pure polymer or conventional composites. Layered silicate is naturally abundant, economic, and more importantly benign to the environment.

• Membrane Journal
• /
• v.29 no.6
• /
• pp.323-328
• /
• 2019

It is a highly important problem for mankind to supply sufficient energy, which has been connected to production and supply of electricity. In terms of the problems, this study fabricated a new sort of solid polymer electrolyte membrane for supercapacitors. The fabricated electrolyte employed grafting poly(oxyethylene methacrylate) (POEM) side chain on poly(vinyl alcohol) (PVA) main chain by free-radical polymerization. It is the first time to utilize PVA-g-POEM graft copolymer as an electrolyte membrane for supercapacitor. The chain behavior of PVA was transformed by grafting POEM side chains, which was analyzed by FT-IR spectra. Also, the capacitance performances of fabricated supercapacitors were explored by cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and ragone plot. We suggest a new point, the grafting of the electrolyte of supercapacitor in this study.

• KOREAN JOURNAL OF CROP SCIENCE
• /
• v.61 no.4
• /
• pp.235-241
• /
• 2016

Three different transplanting dates for two rice cultivars grown in Daegu, Republic of Korea, were examined to identify the changes in growth, rice quality, and characteristics of amylopectin. An early transplanting date caused a reduction in the number of panicles in both rice cultivars compared to that in the optimal and late transplanting dates. The 1000-grain weight in the two rice cultivars was significantly increased in the late transplanting date. The rice cultivar tolerant to high temperatures, Donganbyeo, exhibited the lowest milky grain rate in the late transplanting date. The highest rate of head grain was observed in the late transplanting date in both rice cultivars. Regarding the pattern of pasting properties, peak viscosity increased with delayed transplanting dates. With respect to changes in the amylopectin branch-chain length distribution, the amylopectin structure of the translucent Dongan rice cultivar transplanted on April 25 was characterized by a significant increase in A chains with DP > 12, and a decrease in long chains $DP{\geq}37$ compared to that transplanted on June 25. In contrast, the amylopectin structure of the chalky Dongan rice cultivar transplanted on April 25 exhibited further decrease in 13 < DP < 19 than that transplanted on June 25. In the Ungwang rice cultivar, the amylopectin structure of the translucent Ungwang rice cultivar transplanted on April 25 and June 25 was characterized by a significant decrease in the lengths of total amylopectin chains. Furthermore, the amylopectin structure of the chalky Ungwangbyeo rice cultivar transplanted on April 25 was characterized by a significant increase in 7 < DP < 30, while a significant decrease was observed in that transplanted on June 25. These results indicate that the amylopectin structure is altered by different transplanting dates depending on the characteristics of the rice cultivar.

• Textile Coloration and Finishing
• /
• v.22 no.3
• /
• pp.187-193
• /
• 2010

The effects of molecular weight (MW) and concentration on the rheological properties of poly(vinyl alcohol) (PVA) solutions in dimethyl sulfoxide (DMSO) were investigated at $30^{\circ}C$. Ubbelohde viscometer and rotational rheometer were employed for dilute and concentrated regime, respectively. In the dilute regime, the Mark-Houwink exponent ($\alpha$) of the solutions determined from three different MWs proved 0.73. The critical concentration (C*), in which the entanglement and overlap of polymer molecules began to take place, decreased with increasing the MW of PVA. Huggins constant ($K_H$) values ranged from 0.33 to 0.45 over the MW examined. In the log-log plot of $\eta_{sp}$ versus [$\eta$]C, the PVA with higher degree of polymerization (DP) gave a greater slope exhibiting the inflection point in the vicinity of C*. In the dynamic viscosity ($\eta'$) curve, the PVA solutions of DP 1700 presented Newtonian fluid behavior over most of the frequency range examined. However, the lower Newtonian flow region reduced with increasing the DP. As the PVA concentration increased, $\eta'$ was increased and the onset shear rate for pseudoplasticity was decreased. In the Cole-Cole plot, PVA solutions showed almost a single master curve in a slope of ca. 1.65 regardless of the DP. However, the increase of the concentration from 8 to 12 wt% for PVA solutions of DP 5000 decreased the slope from 1.73 to 1.57. In the tan $\delta$ curve, the onset frequency for sol-gel transition was shifted from 154 to 92 rad/s with increasing the DP from 3300 to 5000 and from 192 to 46 rad/s with increasing the concentration from 8 to 12 wt%. In addition, longer relaxation time ($\lambda$) was observed with increasing the DP and concentration.

• Journal of the Korean Vacuum Society
• /
• v.21 no.6
• /
• pp.354-361
• /
• 2012

The organic memory device was made by the plasma polymerization method which was not the dry process but the wet process. The memory device consist of the styrene and MMA monomer as the insulating layer, MMA monomer as the tunneling layer and Au thin film as the memory layer which was fabricated by thermal evaporation method. The I-V characteristics of fabricated memory device got the hysteresis voltage of 27 V at 40/-40 V double sweep measuring conditions. At this time, the optimized structure was 7 nm of Au thin film as floating gate, 400 nm of styrene thin film as insulating layer and 30 nm of MMA thin film as tunneling layer. Therefore we got the charge trapping characteristics by the hysteresis voltage. From the paper, styrene indicated a good charge trapping characteristics better than MMA. In the future, we expect to make devices by using styrene thin film rather than Au thin film.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.08a
• /
• pp.281-281
• /
• 2010

Very low refractive index (<1.4) materials have been proved to be the key factor improving the performance of various optical components, such as reflectors, filters, photonic crystals, LEDs, and solar cell. Highly porous SiO2 are logically designed for ultralow refractive index materials because of the direct relation between porosity and index of refraction. Among them, ordered macroporous SiO2 is of potential material since their theoretically low refractive index ~1.10. However, in the conventional synthesis of ordered macroporous SiO2, the time required for the crystallization of organic nanoparticles, such as polystyrene (PS), from colloidal solution into well ordered template is typical long (several days for 1 cm substrate) due to the low interaction between particles and particle - substrate. In this study, polystyrene - polyacrylic acid (PS-AA) nanoparticles synthesized by miniemulsion polymerization method have hydrophilic polyacrylic acid tails on the surface of particles which increase the interaction between particle and with substrate giving rise to the formation of PS-AA film by simply spin - coating method. Less ordered with controlled thickness films of PS-AA on silicon wafer were successfully fabricated by changing the spinning speed or concentration of colloidal solution, as confirmed by FE-SEM. Based on these template films, a series of macroporous SiO2 films whose thicknesses varied from 300nm to ~1000nm were fabricated either by conventional sol - gel infiltration or gas phase deposition followed by thermal removal of organic template. Formations of SiO2 films consist of interconnected air balls with size ~100 nm were confirmed by FE-SEM and TEM. These highly porous SiO2 show very low refractive indices (<1.18) over a wide range of wavelength (from 200 to 1000nm) as shown by SE measurement. Refraction indices of SiO2 films at 633nm reported here are of ~1.10 which, to our best knowledge, are among the lowest values having been announced.

• Korean Journal of Food Science and Technology
• /
• v.23 no.5
• /
• pp.578-581
• /
• 1991

The antioxidative effects of three kinds of commercial lecithin in fish oil(EPA 25%, DHA 10%) were investigated through active oxygen method (AOM, hrs. at $97.8^{\circ}C$), Oven test, polymer test by gel chromatography and coloring test. Although there were difference of antioxidative effect among commercial lecithins, antioxidative effects of the lecithins added to the fish oil increased with increasing the concentration of lecithin. Lecithin III(acetone insoluble content 65%) had the greatest antioxidative effect and the addition of 1%, 5 and 10% enhanced the oxidative stability to 310%, 620% and 840%, respectively. The results also showed that the polymerization in presence of 10% lecithin III did not occur up to 10 hours at the AOM condition, and the degree of color(Gardner number) increased as storage time went by and was accerated at high temperature.

• Korean journal of food and cookery science
• /
• v.30 no.5
• /
• pp.526-530
• /
• 2014

The effect of roasting on particle size distribution, water-holding capacity, and viscosity of sunsik was investigated in this study using non-roasted one as control. Roasting increased the size of particles in sunsik, in particular, particles larger than $1{\mu}m$ in diameter, indicating that roasted sunsik is likely to sediment faster, thereby decreasing the time to maintain dispersibility when mixing with water. Roasting also increased the water-holding capacity of sunsik, indicating that polymerization occurred greater than a pyrolysis during roasting, leading to increased viscosity in roasted sunsik. These results indicate that the roasting affected the dispersibility and viscosity of sunsik by increasing particle size and water-holding capacity, respectively.

• Proceedings of the Membrane Society of Korea Conference
• /
• 2003.11a
• /
• pp.61-63
• /
• 2003

A major research objective related to proton exchange membrane(PEM) for DMFC is to achieve high proton conductivity over 10$^{-2}$ S/cm, high hydrolytic stability and low methanol permeability with low cost base materials. for the purpose, a lot of thermoplastic polymers such as polysulfones, polyethersulfone, polyetherketones, polyimides, polyoxadiazole, polyphosphazene and polybenzimidazol have been investigated. Amongst those polymers, polyimides have been suggested as a potential PEM due to their excellent thermal, chemical stability and good mechanical properties. Generally, polyimides are synthesized by polycondensation with numerious diamines and dianhydriedes. In our study, polyimide was prepared using non-sulfonated diamine, sulfonated diamine directly synthesized by fuming sulfuric acid, and naphthalenic dianhydride to improve the hydrolysis stability under acidic condition. Through monomer sulfonation-subsequent polymerization method, the high proton conducting capability and the desired sulfonation level were effectively controlled at the same time. To reduce severe methanol transport through the membrane, the chemical crosslinking among polymer chains was introduced using various crosslinking agents with different chain lengths. The crosslinked sulfonated polyimide membranes showed high proton conductivity up to 8.09$\times$10$^{-2}$ S/cm and from crosslinking effect methanol transport through the membranes was considerably reduced as compared with unmodified membranes. For increase of chain length of crosslinker, methanol permeability was adversely reduced to 10$^{-8}$ $\textrm{cm}^2$/s due to decrease of IEC and increase of crosslinking desity.

• Polymer(Korea)
• /
• v.24 no.5
• /
• pp.638-645
• /
• 2000

Linear and star-shaped, poly(lactic acid) (PLA) stereo-block copolymers were synthesized by sequential polymerization of DL-lactic acid and L-lactide in the presence of diol or polyol compounds. The molecular weight of block copolymers could be controlled to some extent by the variation of alcohol content. These block copolymers had relatively narrow molecular weight distributions. The glass transition temperature and melting temperature of block copolymers appeared at around 5$0^{\circ}C$ and 100~14$0^{\circ}C$, respectively. The block copolymers were found to crystallize even at the high D-stereoisomer concentration of 35 mol%, in contrast to the amorphous nature of the random copolymer with similar composition. Also we could observe the crystallinity of PLA stereo-block copolymers varying with annealing temperature and time.