• Polymer(Korea)
• /
• v.30 no.5
• /
• pp.385-390
• /
• 2006

In this work, the effect of carbon nanofiber (CNF) on thermal properties, and friction and wear behavior of CNF/PMMA composites were examined. While thermal properties of the composites were investigated with differential scanning calorimetry, thermograyimetric analyzer, and dynamic mechanical analyzer friction and wear behaviors were examined using a friction and wear tester. The glass transition temperature (Tg), integral procedural decomposition temperature (IPDT), storage modulus (E'), and tan ${\delta}$ appeared at higher temperatures with increasing CNF content, which were probably attributed to the presence of strong interactions between the carbonaceous fillers and the PMMA resins matrix. The wear loss in the composites decreased at 0.1 wt% CNF and then increased with 5-10 wt% CNF content. This was due to the existence of large aspect ratio CNF in PMMA which led to an alignment of PMMA chains and an increase of mechanical interlocking, resulting in the formation of crosslinked structures between CNF and PMMA in the composite.

• Polymer(Korea)
• /
• v.35 no.2
• /
• pp.106-112
• /
• 2011

Aromatic copolyamides were prepared and their applicability to proton exchange membrane was studied. The copolymers contain two segments; thermally stable and mechanically strong poly (p-phenylene terephthalamide) (PPTA), and easily processable and good film-forming polysulfone. For the copolymers, different ratios of amine-terminated sulfonated ether sulfone monomer, terephthaloyl chloride, and p-phenylene diamine were sequentially reacted. The obtained copolymers were mixed with trimethylolpropane triglycidyl ether (TMPTGE), thermally cured, and converted into proton exchange membranes for fuel cell application. The reactions at each step and the molecular characteristics of precursor copolymers were confirmed by $^1H$ NMR, FTIR, and titration. The performance of the membranes was measured in terms of water uptake and proton conductivity. The water uptake, ion exchange capacity (IEC), and proton conductivity of the membranes increased with the increase of sulfonated ether sulfone segment content. Membrane containing 60 mol% sulfonic acid sulfone segment showed 1.88 meq/g IEC value. Water uptake was limited less than 110 wt% and the highest proton conductivity was up to $7.4{\times}10^{-2}$ S/cm ($25^{\circ}C$, RH=100%).

• Journal of Adhesion and Interface
• /
• v.11 no.2
• /
• pp.57-62
• /
• 2010

Photo-curable material can be crosslinked among molecules by light source such as UV and visible light materials. Material properties are controlled by crosslink reaction. Shrinkage is occured during the curing reaction of material structure. Phenomenon of shrinkage stress occurs inside the product and reduce the stability of the product causes problems. Heat shrink the evaluation of the phenomenon has been formalized. But the evaluation of photo shrink is not enough. In this experiment, real-time contract with shrinkage tester phenomena and analysis degree of shrinkage of the material differences. According to the research, experimental results and theoretical analysis of the results were big differences. Shrinkage, especially for a number of different functional groups that were very different theory. These differences are occurred by the molecular structure different and not enough reaction.

• Clean Technology
• /
• v.27 no.1
• /
• pp.55-60
• /
• 2021

Antibiotics are compounds broadly used to treat patients with infectious diseases and to enhance productivity in agriculture, fisheries, and livestock industries. However, due to the overuse of antibiotics and their low biodegradability, a substantial amount of antibiotics is leaking into the sewer, subsequently resulting in pollution and the emergence of antibiotic-resistant bacteria. This study explores biodegradable serum albumin's potential as an adsorbent to remove antibiotics from water. Serum albumin is a natural blood protein that transports various metabolites and hormones to all tissues' extravascular spaces. While serum albumin is highly water-soluble, it has intrinsic binding sites which readily accommodate ionic, hydrophilic, or hydrophobic molecules, rendering it a good building block for a nano-adsorbent. To induce coacervation, a desolvating agent, ethanol, was added dropwise into the aqueous albumin solution, resulting in dehydration and liquid-liquid phase separation of albumins into albumin nanoparticles within a size range of 150 ~ 170 nm. The addition of glutaraldehyde as a cross-linker improved the size stability and homogeneity of albumin nanoparticles. Adsorption of amoxicillin antibiotics on albumin nanoparticles was dependent upon glutaraldehyde concentration used in desolvation and pH during adsorption. The maximum adsorption capacity measured by spectrophotometry was found to be 12.4 micrograms of amoxicillin per milligram of albumin nanoparticle. These results demonstrate serum albumin's potential as a building block for fabricating a natural nano-adsorbent to remove antibiotics from water.

• Korean Chemical Engineering Research
• /
• v.49 no.1
• /
• pp.75-82
• /
• 2011

Five different composition UV-cured poly(urethane acrylate-co-acrylic acid) (PU-co-AA) films have been prepared by reacting isophorone diisocyanate(IPDI), polycaprolactone triol(PCLT), 2-hydroxyethyl acrylate(HEA), and different weight ratio trimethylolpropane triacrylate(TMPTA) and acrylic acid(AA) as diluents, and characterized using a Fourier transform infrared spectroscopy(FT-IR). The adhesion properties onto the stainless steel, morphology, mechanical hardness, and electrical property of UV-cured PU-co-AA films were investigated as a function of acrylic acid(AA) content. All the PU-co-AA films are structure-less and the molecular ordering and packing density decreased with increasing content of AA due to the flexible structure and -COOH side chains in AA. The crosscut test showed that PU-co-AA films without AA and with low content of AA showed 0% adhesion(0B) and the adhesion of PU-co-AA films in the range of 40-50% AA increased dramatically as the content of AA increases. The pull-off measurements showed that the adhesion force of PU-co-AA films to stainless steel substrate varied from 6 to 31 kgf /$cm^2$ and increased linearly with increasing AA content. The mechanical hardness also decreased as the content of AA increases. This may come from relatively linear and flexible structure in AA and low crystallinity in PU-co-AA films with higher content of AA. The higher AA-containing PU-co-AA films showed higher dielectric constant due to the increase of polarization by introducing AA monomer. In conclusion, the physical properties of UV-cured PU-co-AA films are strongly dependent upon the content of AA and the incorporation of AA in polyurethane acrylate is very useful way to increase the adhesion strength of UV-curable polymers on the stainless steel substrate.

• Applied Chemistry for Engineering
• /
• v.4 no.4
• /
• pp.823-829
• /
• 1993

The basic medium oil modified alkyd resin was synthesized from linseed oil fatty acid(LOFA), phthalic anhydride(PAA), trimellitic anhydride(TMA ), and trimthylol propane(TMP) by condensation polymerization at $230^{\circ}C$. TMPTA modified water-reducible alkyd resins were synthesized with TMPTA graft copolymerization onto the basic resin at $180^{\circ}C$. Acid value of the resin was controlled by the addition of TMA and N,N-Dimethylethanol amino(DMEA) was used as an neutralizing agent to prepare water-reducible alkyd. To evaluate the optimum formulation for anionic alkyd resin, water proofness and water reducibility were estimated from the acid value or TMA contents. The effect of TMPTA on the graft copoymerization of the resin was studied by measuring molecular weight, glass transition temperature(Tg), viscosity, and gel contents. The suitable balance of water proofness and water reducibility of the resin was obtained at range of 5.3~7.0wt.% of TMA contents or 40~50 of acid value of basic resin. The molecular weight, viscosity, and gel contents of water-reducible alkyd resin were increased according to the TMPTA graft copolymerization, but Tg was decreased.

• Polymer(Korea)
• /
• v.34 no.6
• /
• pp.540-546
• /
• 2010

In this manuscript, in order to reduce methanol permeability and, at the same time, to increase proton conductivity THS-PSA containing silica compound, responsible for methanol permeability reduction, and sulfonic acid, responsible for proton conductivity enhancement, was applied onto PVA/PSSA-MA membranes. And in order to improve durability, the resulting membranes, PVA/PSSAMA/THS-PSA, were exposed to 500ppm F2 gas at varying reaction times. The surface-fluorinated membranes were characterized through the measurement of contact angles, thermo-gravimetric analysis, and X-ray photoelectron spectroscopy to observe the physico-chemical changes. For the evaluation of the electro-chemical changes in the resulting membranes, its water contents, ion exchange capacity, proton conductivity, and methanol permeability were measured and then compared with the commercial membrane, Nafion 115. Finally, the membran electrode assembly(MEA) was prepared and the cell voltage against the current density was measured. As fluorination time increased, the contents of F2 increased up to maximum 4.3% and to depth of 50 nm. At 60 min of fluorination, the proton conductivity was 0.036 S/cm, larger than Nafion 115 at 0.024 S/cm, and the methanol permeability was $9.26E-08cm^2/s$, less than Nafion 115 at $1.17E-06cm^2/s$.

• Journal of Food Hygiene and Safety
• /
• v.18 no.3
• /
• pp.101-106
• /
• 2003

The aim of this study is to develop a label-free immunosensor for microbial detection and to evaluate its applicability to Pseudomonas aeruginosa detection in various food samples. The antibodies used were a polyclonal antiserum from rabbit (polyvalent type) and a monoclonal antibody raised against the flagella of P. aeruginosa. Antibody immobilization was done by a thiolated antibody chemisorption onto one gold electrode of a piezoelectric quartz crystal with a thiol-cleavable, heterobifunctional cross-linker, sulfosuccinimidyl 6-[3-(2-pyridyldithio)propionamido]hexanoate. To the Stomacher-treated samples from various raw and processed foods under cold storage, comprising sirloin, cod and pettitoes, spiking and enrichment culture were done to prepare the model samples, followed by the measurements of the frequency shifts after sample injections. The frequency shifts obtained by the sample matrices themselves were in the range of 52~89 Hz. The injections of the spiked samples caused the frequency shifts of 108~200 Hz, whereas the enriched samples decreased the steady-state resonant frequencies by 162~222 Hz. All sample measurements including baseline stabilization, sample injection and acquisition of the steady-state response were accomplished within 30 min.

• Journal of Teachers' Pension
• /
• v.2
• /
• pp.47-102
• /
• 2017

오늘날 대다수의 선진 국가들은 고령화 사회에 대비하여 자국의 노후소득보장 제도를 대대적으로 개혁해 오고 있다. 우리나라의 경우에서도 지난 2015년 사학연금제도의 개혁이 이러한 취지에 해당될 수 있을 것이다. 본 연구에서는 고령화 사회의 문제가 단순히 노인부양비용의 증가 그 자체가 아니라, 평균수명의 증가에도 불구하고 늘어나게 된 노후의 삶에 대한 시간적 배분이 근로와 여가에 걸쳐 균형적으로 이루어지지 않고, 사회적 부양을 필요로 하는 노후의 여가만 일방적으로 늘어나고 있다는 점을 문제점으로 지적하였다. 따라서 이러한 차원에서 볼 때 고령화 사회의 문제는 생애근로기간의 연장을 통해서만 효과적으로 극복할 수 있을 것으로 생각된다, 하지만 이와는 반대로 개인별로 건강상태나 가족상황 등의 이유로 생애근로주기의 연장이 불가능한 사람들을 위하여 별도의 제도적 장치가 추가적으로 마련되어야 할 것이다. 종합해 보면, 고령화 사회의 노동시장 문제는 개인별로 다양한 욕구나 능력을 반영하여 각자에게 다양한 선택권을 보장해 줄 수 있는 방향으로 개선되어야 할 필요가 있다. 본 연구에서는 고령화 사회에 대비하여 연금수급연령 상향조정의 필요성을 사학연금제도를 중심으로 살펴보고, 대신 그로 인해 발생할 수 있는 소득공백문제와 연금가입경력 공백문제 등 제반의 충격을 흡수할 수 있는 제도적 장치로서 점진적 퇴직제도의 도입방안을 제안하였다. 개략적으로 사학연금제도에 있어서 점진적 퇴직모형은 법정연금수급연령의 인상 일정에 따라 다음과 같이 운영하는 방안을 제안하였다. 먼저 법정연금수급연령이 60세로 유지되는 2022년까지의 단기적 대책으로서 여기서 점진적 퇴직의 자격연령은 모든 가입자에게 60세로 적용하도록 한다. 이 경우 가입자들의 신분구분에 따라 각각 교수 5년, 교원 2년(문제해결에 대한 정책적 의지에 따라 이행구간을 확장할 수도 있음) 그리고 교직원 0년의 조기의 점진적 퇴직이 허용되므로, 현재 교원이나 교수의 임용대란문제에 효과적으로 대응을 할 수 있는 장점이 있다. 다음으로는 2023년 이후 2033년 사이 법정연금수급연령의 인상단계에 해당되는 기간 동안의 대책으로서 여기서는 교수, 교원, 교직원에게 적용되는 정년연령과 매년도 법정연금수급연령 사이의 기간을 조기의 점진적 퇴직 이행구간으로 정하도록 한다. 그리고 이러한 이행구간에 상당하는 기간만큼 후기의 점진적 퇴직 이행구간을 별도로 설정하여 그에 적절한 혜택이 주어질 수 있도록 한다. 마지막으로 2033년 이후부터는 교수, 교사, 교직원의 신분구분 없이 모두에게 적용되는 사항으로서 65세를 기준으로 그 이전의 5년은 사학연금의 적용을 받는 조기의 점진적 퇴직 그리고 그 이후의 5년은 국민연금의 적용을 받는 후기의 점진적 퇴직이 이루어질 수 있도록 한다. 그리고 전체 10년의 점진적 퇴직 이행구간 동안 개인별로 퇴직시점이나 퇴직형태의 선택이 자유롭게 이루어질 수 있도록 하기 위하여 보험수리의 원칙에 입각한 감액률 또는 가산율의 엄격한 적용을 제안하였다. 그리고 고령계층이 자신의 근로시간을 단계적으로 단축할 수 있도록 하고, 그 과정에서 발생하게 되는 소득의 감소부분은 별도의 제도적 방법(가교연금, 시간가치적립계정 등)으로 충당하도록 하는 방안을 제안하였다. 나아가 점진적 퇴직제도의 운영방식은 근로시간의 단축뿐만 아니라 작업부담의 경감 등에 대해서도 인정을 해주도록 해줌으로써 임금피크제도의 기능과 연계가 가능할 수 있도록 할 것을 제안하였다.

• Pediatric Gastroenterology, Hepatology & Nutrition
• /
• v.7 no.2
• /
• pp.208-214
• /
• 2004

Purpose: The prognosis of neonates with cholestasis is not clear. Some factors, such as high peak bilirubin levels and liver histologic findings have been claimed to affect the prognosis adversely. Our study aims to define which factors influence the prognosis of neonatal intrahepatic cholestasis. Methods: Retrospective reviews of the medical records were performed in 32 cases with neonatal intrahepatic cholestasis, who were admitted to Department of Pediatrics, Pusan National University Hospital from July 1995 to July 2002. Neonates were classified into 2 groups according to the duration of elevated serum alanine aminotransferase (ALT) levels more or less than 6 months. The data, such as biochemical, histopathologic and radiologic findings, were compared in both groups. Biochemical data included mean peak level of serum ALT, total bilirubin, direct bilirubin, and alkaline phosphatase. Histologic parameters related to lobular architecture, fibrosis, inflammatory infiltration and degenerative features of hepatocytes were arbitrary estimated on a scale of 1 to 3. Results: There were 19 males and 13 females, whose mean age was 48 days (14~77 days). The peak serum ALT levels were higher in the poor outcome group. Ductular proliferation and portoportal bridging were more severe in the poor outcome group. But the degree of multinucleated hepatocytes, hepatocellular swelling and canalicular plug did not appear to be significantly related to the long-term outcome. The DISIDA scintigraphy by visualization time of gall bladder and intestine was not useful in predicting outcome of neonatal intrahepatic cholestasis. Conclusion: Neonates who have intrahepatic cholestasis with high serum ALT levels, severe ductular proliferation and portoportal bridging in the liver biopsy specimen should be carefully followed up because they may have a poor prognosis.