Dae-won Chung

Improvement of frictional properties and abrasive wear resistance of nylon/graphite composite by oil impregnation

A nylon composite with graphite and oil was investigated for anti-static sliding applications. Electric conductivity, mechanical properties and frictional properties were measured where graphite, up to 8% and oil up to 4%, were incorporated into the nylon. Generally, what improved the conductivity, lowered the coefficient of friction and decreased the abrasive wear rate, tended to decrease the mechanical properties of the nylon composites.

Isolation and anti‐inflammatory effect of astragalin synthesized by enzymatic hydrolysis of tea seed extract

BACKGROUND The application of tea seed extract (TSE) has been widely investigated because of its biological activities. In this paper, two flavonol triglycosides in TSE-camelliaside A (CamA) and camelliaside B (CamB)-were subjected to hydrolysis in the presence of two commercial enzyme complexes (Pectinex™ series): Smash and Mash. RESULTS Smash hydrolyzed only the xylosyl moiety of CamB, and the main product was kaempferol diglycoside (nicotiflorin, NF). On the other hand, Mash induced the hydrolysis of both CamA and CamB, and kaempferol monoglycoside (astragalin, AS) was found to be a main product. Pure AS with > 96% purity was prepared by enzymatic hydrolysis of TSE using Mash, and the chemical structure of AS was confirmed by (1)H- and (13)C-nuclear magnetic resonance analyses. The prepared pure AS showed anti-inflammatory activities by significantly inhibiting cellular nitrite oxide (IC(50) = 363 µg mL(-1)), prostaglandin E(2) (IC(50) = 134 µg mL(-1)) and interleukin-6 production (IC(50) = 289 µg mL(-1)) by lipopolysaccharide -stimulated RAW 264.7 cells. CONCLUSION It was concluded that pure AS can be prepared by enzymatic partial hydrolysis of TSE and employed as an anti-inflammatory material. This is the first study to address the preparation of pure AS from natural sources.

Isolation and characterization of nicotiflorin obtained by enzymatic hydrolysis of two precursors in tea seed extract.

Two flavonol triglycosides, camelliaside A (CamA) and camelliaside B (CamB), of tea seed extract (TSE) were subjected to enzymatic hydrolysis. Among five kinds of glycosidases investigated, beta-galactosidase (Gal) induced selective hydrolysis of CamA. On the other hand, pectinase (Pec) and cellulase (Cel) induced hydrolysis of CamB. For Gal and Pec, only kaempferol diglycoside (nicotiflorin, NF) was produced; on the other hand, significant amounts of kaempferol monoglycoside (astragalin, AS) and kaempferol (KR) were also detected for Cel. The combination of the use of Gal and Pec in the enzymatic hydrolysis of TSE afforded NF with high specificity. Crude NF with 22% purity was recovered from the enzymatic reaction mixture by extraction with organic solvent, and pure NF with >95% purity was obtained by crystallized in water. The chemical structure of NF was confirmed by (1)H and (13)C NMR analyses.

The synthesis and frictional properties of lubricant-impregnated cast nylons

In order to make a new dry-friction engineering material, lubricant-impregnated cast nylons were synthesized by anionic polymerization of e-caprolactam (CL) in the presence of mineral oil and wax. The reaction rate of the products was not affected by the addition of lubricant less than 8%. Nylons from 0% to 8% lubricant content were synthesized and the frictional properties were tested. Under various sliding speeds and pressures, the lubricant-impregnated cast nylon with oil content of 6% showed the lowest coefficient of friction, while the cast nylon with wax content of 4% showed the smallest. At the wide range of sliding speeds, the PV limit of nylon with optimum lubricant content was 400% larger than that of the lubricant-free nylon. However, when the PV limit of oil-impregnated nylon was compared with that of wax-impregnated nylon, it was found that the higher PV limit of oil-impregnated nylon could be obtained only at lower sliding speed and lower content of lubricant than that of the wax-impregnated nylon.

Effect of Modification of SeO 2 /Acrylamide Ratios on Diffraction Efficiencies in PVA/AA Photopolymer Films

The highest diffraction efficiency(DE) value after illumination and post-curing of photopolymer films were obtained at the

Novel synthesis of leucoside by enzymatic hydrolysis of tea seed extract

SeO_2

Fabrication Process of Bilayer RGO/PEDOT:PSS Film for Flexible Transparent Conductive Electrode

/Acrylamide(AA) Ratios of AA 3.0 g,

Synthesis and Purification of Kaempferol by Enzymatic Hydrolysis of Tea Seed Extract

SeO_2

Study on the effect of structure of polydimethylsiloxane grafted with polyethyleneoxide on surface activities

1.0g and the DEs were stable values of over 90%. By the addition of

Study on the Effect of Platinum Catalyst for the Synthesis of Polydimethylsiloxane Grafted with Polyoxyethylene

SeO_2