• Macromolecular Research
• /
• v.12 no.1
• /
• pp.112-118
• /
• 2004

With the goal of enhancing the creep resistance of ultra-high molecular weight polyethylene (UHMWPE), we performed gamma irradiation and post-irradiation annealing at a low temperature, and investigated the crystalline structures and mechanical properties of the samples. Electron spin resonance spectra reveal that most of the residual radicals are stabilized by annealing at 100$^{\circ}C$ for 72 h under vacuum. Both the melting temperature and crystallinity increase after increasing the dose and by post-irradiation annealing. When irradiated with the same dose, the quenched sample having a higher amorphous fraction exhibits a lower swell ratio than does the slow-cooled sample. The measured tensile properties correlate well to the crystalline structure of the irradiated and annealed samples. For enhancing creep resistance, high crystallinity appears to be more critical than a high degree of crosslinking.

• Elastomers and Composites
• /
• v.41 no.1
• /
• pp.10-18
• /
• 2006

Influence of low molecular weight polybutadiene (liquid PB) treated with maleic anhydride on properties of a silica-filled SBR compounds was studied. Silica dispersion was improved by adding liquid PB. The liquid PB treated with maleic anhydride (liquid MAPB) was found to be more effective for the improvement of silica dispersion than the liquid PB without maleic anhydride (liquid NPB). Viscosity of the SBR compound decreased by adding the liquid PB. The crosslink density decreased with increase of the liquid PB content and the cure rate became slower with increasing the liquid PB content. Considering the experimental results, it was believed that addition of small amount of the liquid PB (less than 5 phr) was desirable to improve properties of silica-filled SBR compounds.

• Preventive Nutrition and Food Science
• /
• v.7 no.3
• /
• pp.293-298
• /
• 2002

Carnitine is considered a conditionally essential nutrient because dietary sources may become important under conditions which either reduce biosynthesis or increase urinary excretion of carnitine. Therefore, it is important to have a database for dietary analysis for carnitine content. Because there is limited data available for the carnitine content of Korean foods, this study was undertaken to analyze the total carnitine (TCNE) content of 146 commonly consumed Korean foods. TCNE concentrations were assayed using a modified radioisotopic method. Beef and pork contained 91.09 and 17.21 mg TCNE / 100 g weight, respectively. Fish and shellfish ranged from 0.28 to 24.87 mg TCNE / 100g weight. TCNE concentration in milk was 1.77 mg / 100 mL and cheese was 0.49 mg / 100 g weight. Cereals and pulses contained between 0 and 1.43 mg TCNE / 100 g weight. The TCNE concentration of most fruits and vegetables was between 0 and 0.7 mg 1100 g weight. However, mushrooms contained between 2.77 and 7.02 mg of TCNE / 100 g weight. Soy sauce, soybean paste and fermented red pepper soybean paste contained 1.05, 0.28 and 0.5 mg TCNE / 100 g weight, respectively. These results demonstrate that TCNE concentrations are high in meat, fish, shellfish and milk, but low or non-existent fruits and vegetables. However, mushrooms are a substantial source of vegetable derived TCNE. These data will be useful in establishing a database for determining the TCNE content of Korean diets.

• Journal of Life Science
• /
• v.5 no.3
• /
• pp.117-120
• /
• 1995

Human milk was examined for antiangiogenic activities by using the chick embryo chorioallantoic membrane (CAM) assay and endothelial cell growth. The low molecular weight (20 KD>$\sim$ ) fraction of human milk stimulated the angiogenesis and increased the endothelial cell growth. These results suggest that the increase of angiogenesis and endothelial cell growth might be attributed to several growth factors and/or angiogenic factors in low molecular fraction (20 KD>$\sim$) of human milk.

• Journal of the Korean Wood Science and Technology
• /
• v.44 no.1
• /
• pp.124-134
• /
• 2016

The main goal of this study was to investigate biomodification mechanism of lignin by white rot fungus, Abortiporus biennis, and to depolymerize ethanol organosolv lignin for industrial application. In nitrogen-limited culture, A. biennis polymerized mainly lignin showing a rapid increase of molecular weight and structural changes depending on incubation days. At the initial incubation days, cleavage of ether bonds increased phenolic OH content, while the results were contrary in of the later part of the culture. Based on these results, ascorbic acid as a reducing agent was used to induce depolymerization of lignin during cultivation with white rot fungus. As a result, the degree of increase of average molecular weight of lignin was significantly declined when compared with those of the ascorbic acid free-experiment, although the molecular weight of fungus treated sample slightly increased than that of control. Furthermore, lignin derived oligomers in culture medium were depolymerized with the addition of ascorbic acid, showing that the average molecular weight was 381 Da, and phenolic OH content was 38.63%. These depolymerized lignin oligomers were considered to be applicable for industrial utilization of lignin. In conclusion, A. biennis led to the polymerization of lignin during biomodification period. The addition of ascorbic acid had a positive effect on the depolymerization and increase of phenolic OH content of lignin oligomers in medium.

• Polymer(Korea)
• /
• v.26 no.2
• /
• pp.218-226
• /
• 2002

For the preparation of high resilience polyurethane (PU) foams with polyether type cell openers which have different ethylene oxide (EO) content, molecular weight and chain structure, the influences of tell opener structure on the kinetics, rheology, structural stability, open cell content and mechanical properties of the obtained foam were investigated. It was observed that urea formation reaction was delayed with the increase of EO content and incorporation of ester linkage in cell opener molecule and was relatively independent on the molecular weight. With the rheological studies, the decreases of viscosity and storage modulus were confirmed for the increase of EO content and molecular weight, so that the resulted foam had low structural stability and high open cell content. The cell opener having ester linkage in molecule exhibited the lowest values of viscosity and storage modulus and the obtained foam has high open cell content. However, the structural stability increased due to the larger intermolecular interaction of ester linkage. The hardness, tensile strength, tear strength and elongation of foam were deteriorated with increase of EO content and molecular weight of tell opener. On the other hand, the cell opener having ester linkage in molecule improved the values of tensile strength, tear strength and elongation.

• Journal of the Korean Chemical Society
• /
• v.38 no.6
• /
• pp.427-434
• /
• 1994

The retention behaviors of poly(ethylene-co-vinyl acetate)s have been studied by thermal field-flow fractionation(ThFFF) with respect to effective separation and characterization of thermal diffusion coefficients($D_{\tau}$) as one of the physicochemical properties of polymers. The eight copolymers are different in vinyl acetate composition ranging from 25% to 70% and in molecular weight ranging from 110,000 to 285,000. The carrier solvents are THF, toluene and chlorobenzene which have different viscosities and thermal conductivities. It is shown that the retention of a copolymer is dependent on the type of the carrier, the molecular weight and chemical composition of the copolymer. The results show that the retention of a copolymer increases when either vinyl acetate composition or the molecular weight increase. $D_{\tau}$ values measured by experiments vary from 1.36∼5.97 $\cm^2/(s.K)$ depending on the copolymer composition and the type of the carrier solvent. These values increase $(r^2{\geq}0.928)$ with increase of weight % of vinyl acetate. THF is found to be the proper carrier solvent for separation of copolymers employed in this study due to the fact that a $D_{\tau}$ value greatly changes with variation of copolymer composition. From the above results, ThFFF can be used for separation of copolymers with similar molecular sizes but different compositions.

• Elastomers and Composites
• /
• v.48 no.1
• /
• pp.2-9
• /
• 2013

We synthesized polyethylene, poly(ethylene-co-1-decene), poly(ethylene-co-p-methylstyrene), and poly(ethylene-ter-1-decene-ter-p-methystyrene) using a rac-$Et(Ind)_2ZrCl_2$ metallocene catalyst and a methylaluminoxane cocatalyst system. The materials were characterized using nuclear magnetic spectroscopy and fourier transform infrared spectroscopy. To identify suitable reaction conditions for terpolymerization, we studied the effects of catalyst content, cocatalyst/catalyst molar ratio, polymerization time, and polymerization temperature. As the catalyst content increased, the catalytic activity and the molecular weight of the terpolymers increased. The catalytic activity sharply increased but little change was observed after a polymerization time of 30 min. The increase in the cocatalyst/catalyst molar ratio resulted in a decrease in the molecular weight of the terpolymers and an increase in the catalytic activity to some degree. The catalytic activity increased with increasing polymerization temperature, while the molecular weight of the terpolymers decreased.

• Polymer(Korea)
• /
• v.35 no.4
• /
• pp.284-288
• /
• 2011

For the purpose of the pre-industry production of poly(L-lactide) (PLLA) and full understanding of the supercritical polymerization system, large scale polymerization of L-iactide initiated by 1-dodecano/stannous 2-ethyl-hexanoate (DoOH/Sn(Oct)$_2$) was carried out in supercritical chlorodifluoromethane under various reaction conditions (time, temperature and pressure)and reactants (monomer and supercritical solvent) concentrations. A 3 L sized-reactor system was used throughout this study. The monomer conversion increased to 72% on increasing reaction time to 5 h. The molecular weight of PLLA product also increased to 68000 g/moi over the same period. An increase in monomer concentration resulted in a higher molecular weight, up to 144000 g/mol and 97% of monomer conversion. Raising the reaction pressure from 130 to 240 bar also resulted in an increased monomer conversion and molecular weight. To increase heat resistivity of PLLA, methanol treatment and heat-vacuum methods were evaluated. Both of them successfully improved the heat resistivity property of PLLA.

• Polymer(Korea)
• /
• v.38 no.1
• /
• pp.9-15
• /
• 2014

Polyamide4 (PA4)-polyurethane (PU)-PA4 triblock copolymers were synthesized by isocynated (NCO)-terminated PU prepared from 4,4'-diphenyl methane diisocyante (MDI) and polytetramethylene glycol (PTMG) as an initiator and potassium pyrrolidonate (P-py) as a catalyst for anionic ring opening polymerization of 2-pyrrolidone. Subsequently copolymer was controlled to contain different or same molecular weight of PA4 hard block with same or different molecular weight of PU soft block in order to investigate the effects of those differences on various properties of triblock copolymers as a thermoplastic elastomer. As the results shown in typical properties of block copolymeric elastomers, the mechanical strength and melting point ($T_m$) of the copolymers increased with an increase in molecular weight of PA4 block while the elongation at break increased with an increase in that of PU block.