• Elastomers and Composites
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• v.46 no.2
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• pp.132-137
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• 2011

In the present investigation, thermal aging behavior of H-NBR/NBR blend with various H-NBR content was investigated. Mixture of dicumyl peroxide and sulfur were used as a curing agent. The influence of the thermal aging of the H-NBR/NBR blends on the solid state properties such as tensile strength, elongation at break, hardness and abrasion resistance was investigated. Tensile strength was increased with increasing H-NBR content, while abrasion resistance was decreased. Both elongation at break and hardness were not affected by the addition of H-NBR. The properties such as hardness, tensile strength and elongation at break of the aged samples were lower than unaged samples. However, the rate of deterioration of those properties was decreased by increasing the H-NBR content, which indicated that improved thermal aging behavior was obtained by the addition of H-NBR. Abrasion loss was increased with increasing aging time, but it became less by the addition of H-NBR addition.

• The Korean Journal of Rheology
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• v.7 no.3
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• pp.181-191
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• 1995

점탄성유체의 물성치들 중 정압열팽창계수 및 밀도는 자연대류 열전달 연구에 전단 속도 0에서의 점도는 점탄성유체에 대한 모델들 사용 시 필요하다. 본 연구에서는 점탄성유 체이며 마찰 감소 첨가제, 유전자 분리용액동으로 사용하는 Separan AP-273 용액의 정압열 팽창계수, 밀도 및 전단속도 0에서의 점도에대한 농도 및 온도의 영향을 조사하였다. 작동유 체의 물성치들은 10~6$0^{\circ}C$의 온도범위와 100~20,000wppm의 농도범위에서 측정되었다. 작 동유체의 물성치들에 미치는 열주기와 노화의 영향을 조사하기 위해서 정압열팽창계수와 전 단속도 0에서의 점도를 교대로 두 번씩 측정했다. 정압열팽창계수 및 밀도를 측정하는 장치 의 측정 정밀도는 증류수에 대한 측정치와 문헌에 나타난 자료를 비교하여 얻었고 이는 $\pm$ 2%이내였다. Separan AP-273용액의 정압열팽창계수 및 밀도는 증류수의 값들로 대치될수 있다. 작동유체의 정압열팽창계수와 밀도는 열주기와 노화의 영향을 받지 않았다. 낙하식 점 도계를 사용해 측정한 겉보기점도 값들을 나타내느 flow curve에서 전단속도가 0이 되는방 향으로 겉보기점도를 외삽시켜 Separan AP-273용액에 대한 전단속도0에서의 점도를 얻었 다. 정압열팽창계수 측정 전후에 측정한 작동유체에 대한 전단속도 0에서의 점도는 열주기 와 노화로 인해 퇴화되었다.

• Elastomers and Composites
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• v.47 no.1
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• pp.9-17
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• 2012

Herein, life time prediction based on the deterioration of physical properties of chloroprene rubber (CR)aged by heat and seawater was performed. CR samples were experienced an accelerated test at $80^{\circ}C$, $100^{\circ}C$, $120^{\circ}C$ for heat aging, and $40^{\circ}C$, $60^{\circ}C$, $80^{\circ}C$ for seawater aging for 20,000 hrs. The change in tensile strength, maximum elongation,hardness was measured. As a result, the decrease in elongation was a major factor causing failure. The life time estimated using an Arrhenius model was 125 years at $23^{\circ}C$ for thermal aging and 9 years at $23^{\circ}C$ for seawater aging. SEM and elemental analysis reveal that cracks were generated and the content of oxygen was increased for CR agined by seawater. FT-IR spectrum shows the new C-O and C = O bonds were generated by the chemical reaction with seawater. Also, the glass transtion temperature was increased and the thermal decomposition was decreased by seawater aging.

• Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
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• 2000.11a
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• pp.139-139
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• 2000

종이는 제조 후 시간의 경과에 따라 노화가 야기되기 시작하며 이에 수반되는 현상으로서 종이의 기계적 강도 손실 및 종이의 색 변화를 들 수 있다. 종이의 노화 현상은 주로 빛, 열, 대기 오염물질, 미생물, 곤충 및 화학약품 등의 외부 인자들에 의해 종이 내에서의 가수 분해 또는 산화작용을 발생시키며 이는 종이의 폭넓은 이용올 제한하는 중요한 원인이 되고 있다. 종이의 노화기작은 주로 산 가수분해 및 산화작용 그리고 가교결합 둥으로 해석되고 있다. 이는 종이의 주 구성요소인 셀룰로오스의 수산기가 반웅하여 카르보닐기를 형성하면 서 저분자화 되거나 산소에 의해 산화되면서 저분자화 되어 종이의 강도적 손실이 일어난다 고 보고되고 있으며 종이의 황색화(Yellowing) 현상은 주원인이 종이에 잔존하고 있는 리그 년이 빛과 열에 의해 반응하여 산화됨으로써 야기된다고 설명되고 있다. 즉, 열이나 자외선 및 가시광션의 조사로 인한 셀룰로오스 및 기타 종이 구성물의 산화에 의해 종이가 퇴색되 거나 강도가 저하되는 현상이 일어나게 된다. 특히 이러한 노화 거동은 상온의 경우에서는 펄프와 종이의 황색화가 천천히 일어나지만 옹도가 점차 올라갈수록 그 속도는 빨라진다. 종이가 노화되면서 일어나는 산화반용은 주로 대기 중의 산소와 접촉하기 쉬운 표변에서부 터 발생하기 쉽다. 열처리를 통해 표면에서의 산화 작용은 촉진되고 종이의 구성원소의 결 합에 화학적 변화가 야기된다. 이를 분석하기 위해서 모든 원소가 독특한 결합에너지를 가 지고 있다는 것에 착안 시료 표면에 특정 x-선 및 전자빔을 입사하여 방출하는 광전자의 에너지를 측정함으로써 시료 표면의 조성 및 화학적인 결합상태를 알 수 있는 ESCA ( (Electron Spectroscopy for Chemical Analysis)를 이용하였다 .. ESCA는 주로 표면 원소의 규 명 및 정량분석과 화학결합 상태의 정성, 정량 분석, 깊이에 따른 원소의 농도 분포 분석, 고분자화합물의 특성 조사, 표면 원소의 화학결합에 따른 전자상태 연구 둥에 활용되 고 있 다. 즉, 종이가 노화되면서 원소들 사이에 변화되는 결합을 이러한 에너지 분석에 의해 원소 정성분석 또는 정량분석을 하고자 하였으며, 이를 분석하여 열처리 시 종이 표면에서 일어 나는 변화를 구명하고자 하였다. 이에 따라 본 연구에서는 종이의 노화를 가속화시키는 빛, 대기오염물질, 및 기타 다른 인 자들은 배제하고 열 만을 가해 노화의 진행속도를 높인 후, 노화 진행 시 종이 표변에 일어 나는 산화작용 및 가수분해를 표면 분석 장치인 ESCA를 이용하여 종이의 주 구성원소인 탄소와 산소가 열처리 시 변하는 에너지를 측정하였다. 또한 카르복실기 정량과 종이의 pH 측정 및 X -ray Diffractometer를 이용하여 결정화도를 측정하였다. 본 연구의 결과, 시간의 경과에 따라서 탄소의 결합에너지는 분포가 C-H에서 COO-, 또는 C=O로 달라짐으로써 종 이가 산화되고 있다는 것을 알 수 있었다. 또한 이 결합에너지 분포의 변화가 펄프의 종류 에 따라서 다르게 이동함으로써 제조된 시트의 표면 산화반응이 서로 다르게 일어나고 있음 을 알 수 있었으며, 이는 사용한 펄프의 화학 조성분의 차이에 기인한 것이라 사료된다.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.42 no.1
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• pp.57-64
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• 2016

Just like UV radiation, heat increases collagen degradation and accumulation of abnormal elastin fiber and this is termed thermal skin aging. Dunaliella salina (DS), a green alga, is known for its beta-carotene accumulation, having various applications in the health and nutritional products. However, the effects of DS on heat-induced skin aging remain unexplored. In this study, we performed anti-thermal aging tests of the ethanol extract of DS (DSE). We measured the cellular levels of type I procollagen and MMP-1 using ELISA in human dermal fibroblast cells after heat shock. DSE reduced the expression of MMP-1 protein and increased the expression of type I procollagen. In addition, DSE upregulated the mRNA expression of HSP47 reduced by heat shock, which is involved in collagen synthesis. Also, DSE reduced the expression of inflammation mediator (TGF-${\beta}$, IL-12, etc). We demonstrate that DSE regulates the heat-induced solar elastosis through the regulation of tropoelastin and fibrillin-1, two major proteins of elastic fibers, and MMP-12 expression. These results suggest that DSE may be effective for preventing thermally induced skin aging.

• Composites Research
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• v.22 no.3
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• pp.35-43
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• 2009

In this study, for a radiator hose made of carbon black filled EPDM(ethylene-propylene diene monomer) rubber, a measuring method of crosslink density was established to analyze the aging behaviors under thermo-oxidative stresses. At $125^{\circ}C$, the crosslink density of the rubber specimens decreased slightly in the initial stage, but increased with increasing the aging time. Such variation in crosslink density was similar to that of tensile strength. This might be due to the formation of sulphoxide crosslinks as well as to additional crosslinks made by the reaction of unvalcunized sulfurs. A high temperature aging of rubber specimens at $180^{\circ}C$ caused a slight increase in crosslink density while it did a large decrease in tensile strength and elongation. With aging at high temperature, the formation of carbonyl groups in EPDM molecule chain and formation of sulphoxide crosslink, rather than the crosslink density variation itself, had a large influence on such changes in mechanical property.

• Composites Research
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• v.31 no.4
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• pp.122-127
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• 2018

Sandwich composites of carbon fiber reinforced plastic(CFRP) and polymer foam will be used to automobile and aerospace industry according to increasing importance of light weight. In this study, mechanical and heat resistance properties of sandwich composites were compared with type of polymer foam (polyethylene terephthalate(PET), polyvinylchloride(PVC), epoxy and polyurethane). All types of polymer foams were degraded to 30, 60, 120, 180 minutes in $180^{\circ}C$. After heat degradation, the polymer foams were observed using optical microscope and compressive test was performed using universal testing machine(UTM). Epoxy foam had the highest compressive property to 2.6 MPa and after thermal degradation, the mechanical property and structure of foam were less changed than others. Epoxy foam had better mechanical properties than other polymer foams under high temperature. Because the epoxy foam was post cured under high temperature. As the results, Epoxy foam was optimal materials to apply to structures that thermal energy was loaded constantly.

• Journal of the KSME
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• v.43 no.6
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• pp.62-65
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• 2003

이 글에서는 가속 열노화시험을 통하여 노화수명을 예측하고 방법을 고무 재료의 수평 선도와 유한요소해석 결과로 부터 고무부품의 피로숙명을 예측하여 신뢰성을 평가하는 방법을 소개하였다.

• Journal of Adhesion and Interface
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• v.3 no.2
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• pp.40-44
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• 2002

We invested effect of the keeping-time of uncured composite and thermal aging, of cured composite on adhesive strength for rubber-brass coated steel cord composite in this study. We also evaluated how the adhesive strength affects to tire endurance. Using PAD adhesion specimen, peel adhesive strength was measured. The uncured composite was kept for several days up to 35 days in factory. Cured composite was also kept for 5 and 10 days at $85^{\circ}C$ in dry oven. Peel adhesive strength was decreased with increasing keeping-time and showed lower value with increasing thermal aging time. The lower peel adhesive strength, the lower tire-endurance. This fact was caused by the humidity and thermal aging which affected in the decrease of adhesive strength of the rubber-steel cord composite and resulted in interface fracture between rubber and steel cord. This phenomenon was confirmed from SEM investigation and tire-endurance. It was just known that corrosion of steel cord's surface and aging of adhesive layer strongly affected to decrease of adhesive strength. This resulted in directly decreasing tire-endurance.

• Elastomers and Composites
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• v.46 no.3
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• pp.237-244
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• 2011

Five natural rubber (NR) composites with different reinforcing systems of unfilled, carbon black, carbon black with silane coupling agent, silica, and silica with silane coupling agent were thermally aged and change of the crosslink densities by the accelerated thermal aging was investigated. The crosslink densities on the whole increased as the aging time elapsed irrespective of the reinforcing systems. The crosslink density changes became noticeable by increasing the aging temperature. For carbon black-filled composites, the silane coupling agent made the crosslink density change to be increased. For silica-filled composites, however, the silane coupling agent made the crosslink density increment reduced at 60 and $70^{\circ}C$ and it hardly affect the degree of the crosslink density change at 80 and $90^{\circ}C$. The activation energies for the crosslink density changes of the carbon black-filled samples increased continuously in a logarithmic fashion, whereas that of the silica-filled one showed a quasi-steady state ranges at aging times of 30-150 days. The activation energy of the unfilled sample increased exponentially with the aging time. The experimental results were explained with sulfur donation from the silane coupling agent, surface modification of the filler by the silane coupling agent, adsorption of curative residues on the silica surface, and release of the adsorbed curative residues.