WonSool Ahn

A Study on Physical Properties and Life Time Prediction of ACM Rubber for Automotive Engine Gasket

Material characteristics and the prediction of life time of polyacrylic rubber (ACM) for automotive engine gasket were studied. Two kinds of ACM rubber compounds, having chlorine cure-site and carboxyl cure-site, were made with optimum formulations and the properties of each materials were examined. As a test results for the thermal properties and compression set, which are very important in the application for the automotive engine gasket, the compound using ACM with carboxyl cure-site was evaluated as having a better characteristics than that of ACM with chlorine cure-site. Arrhenius relationship based on time-temperature superposition principle (TTSP) was obtained through the accelerated heat aging test to predict the useful life-time for the compound using ACM with carboxyl cure-site.

Temperature-Induced Phase Separation of Side-Chain LCP/LMWLC Blends

A blend of side-chain liquid crystal polymer (SCLCP) and low molecular weight liquid crystal (LMWLC) was used to investigate a phase separation behavior induced by temperature. Phase separation at room temperature was observed only for the compositions higher than 60 wt% LMWLC because of good miscibility between two components. An interesting phenomenon was observed when the film transmittance for a phase-separated sample as a function of temperature was measured under cross-polarizer. That is, transmittance below TNI of LMWLC was observed lower than that below TSI of SCLCP, which was not expected initially. The fact was considered as a micro-phase separation induced by an interfacial effect between SCLCP and LMWLC phase.

Characterization of orientation of perfluorostearic acid Langmuir–Blodgett multilayers by infrared spectroscopic methods

Abstract The molecular orientation of perfluorostearic acid [CF3(CF2)16COOH] deposited by Langmuir–Blodgett technique has been investigated by grazing incidence reflection absorption and transmission infrared spectroscopy. In the former, the electric field vector is normal to the film surface whereas in the latter, it is parallel to the surface. The intensities of the infrared bands that tend to exhibit perpendicular polarization, e.g. symmetric stretching of COO−, are much higher in reflection absorption than in transmission for deposited perfluorostearic acid. Therefore, these Fourier transform infrared results strongly support that the perfluorostearic acid molecules are preferentially oriented with their chain axes perpendicular to the substrate surface.

Non-isothermal TGA Study on Thermal Degradation Kinetics of ACM Rubber Composites

R&D Center, HanKook Sealtech, Inc., Daegu 704-833, Korea(Received April 23, 2013, Revised May 13, 2013, Accepted May 15, 2013)요 약：비등온 TGA 실험방법을 이용하여 가교 사이트가 서로 다른 chlorine cure-site ACM 고무와 carboxylic cure-site ACM 고무 두 종류에 대하여 열분해 거동을 연구하였다. 분해 반응이 최대인 점의 온도는 모든 승온 속도에서 carboxylic cure-site ACM 고무의 열분해 특성이 상대적으로 더 안정함을 보여 주었다. Kissinger의 해석 방법에 의한 활성화에너지는 chlorine cure-site ACM 및 carboxylic cure-site ACM 고무에 대하여 각각 118.6 및 105.5 kJ/mol로 나타났으며, Flynn-Wall-Ozawa의 해석방법에서의 전환율 0.1∼0.2 범위의 평균과 유사한 값을 나타내었다. 반응차수 해석으로부터 두 시험편 모두 일반적인 고무와 유사한 다중 복합반응에 의하여 열분해 반응이 진행됨을 알 수 있었다.ABSTRACTThermal degradation behavior of chlorine cure-site ACM and carboxylic cure-site ACM rubbers was studied by non-isothermal TGA thermal analysis. Carboxylic cure-site ACM rubber exhibited comparatively more thermally stable than chlorine cure-site ACM, showing higher peak temperature, at which maximum reaction rate occurred. Activation energies from Kissinger method were calculated as 118.6 kJ/mol for the chlorine cure-site ACM and 105.5 kJ/mol for the carboxylic cure-site ACM, showing similar values from Flynn-Wall-Ozawa analysis over the conversion range of 0.10.2. From the analysis of the reaction order change, both samples seemed thermally decomposed through the multiple reaction mechanism as is the common rubber materials.KeywordsACM Rubber, TGA, Kissinger, Flynn-Wall-Ozawa

Fabrication and Thermal Properties of Fumed Silica/Ceramic Wool Inorganic Composites

This study examined the fabrication and thermal properties of fumed silica/ceramic wool inorganic composites. A predetermined quantity of fumed silica and ceramic wool was mixed uniformly into a slurry state and stabilized in the mold at room temperature, and converted to a massive foamed body through a complete drying process at 150 °C. Although the samples without polyvinyl alcohol (PVA) as an interfacial adhesive showed a bulk

A Study on Life Time Prediction of ACM Rubber Composite Using Accelerated Test and Thermogravimetric Analysis

R&D Center, Datwyler Korea, Inc., Daegu 704-833, Korea(Received April 28, 2014, Revised May 9, 2014, Accepted May 14, 2014)요 약：자동차 엔진 부품용으로 많이 사용되는 ACM 고무 샘플에 대하여 150℃, 160℃, 170℃, 및 180℃의 등온 상태에서 시간에 따른 압축영구줄음율(CS)과 열중량감소율을 측정하여 상관관계를 구하고, 이를 비등온 TGA를 이용하는 Toop의 해석방법에 이용하여 사용온도에서의 수명을 예측하고자 하였다. 노화촉진시험으로부터 측정된 중량감소율는 CS에 대하여 선형적으로 변화하는 것이 관찰되었으며, 이로부터 CS 40%에 이르는 시간을 재료의 수명시간으로 했을 때 중량감소에 의한 전환율은 4.2%로 나타났다. TGA 곡선으로부터 Flynn-Wall-Ozawa법에 의하여 전환율 4.2%에서의 활성화에너지는 120.2 kJ/mol로 계산되었으며, 이를 Toop의 해석법에 적용하였을 때의 예측수명은 사용온도 120℃에서 약 9,700 시간으로 계산되었다.ABSTRACTCompression set (CS) and weight loss by thermal degradation of the ACM rubber composite sample prepared for an automotive part were measured simultaneously at several given temperatures of 150, 160, 170, and 180. Using the relationship between them, thermal life of the sample could be predicted at a given operating temperature by applying Toops method which is based on the analysis of non-isothermal TGA thermograms. Conversion by weight loss showed a linear relationship with CS changes, exhibiting 4.2% at CS 40%. Activation energy of thermal degradation was calculated as 120.2 kJ/mol at 4.2% of weight loss from Flynn-Wall-Ozawa analysis. When the expected life was set as time to reach CS 40% at 120, the life time of the sample was calculated as 9,700 hrs when Toops method was applied.KeywordsACM rubber, toop method, TGA, life time prediction

Open-Cell Rigid Polyurethane Foam Using Reactive Cell Opening Agents

Cell opening characteristics dependent on the cell openers for the conventional formulation of a closed-cell polyurethane foam (PUF) was studied using 1-butanol and lithium salt of 12-hydroxystearic acid (Li-12HSA) as the reactive cell opening agents. While cell openining content of only 10.5 % was obtained for the sample with 4 phr of 1-butanol as the single reactive cell opener, that of 98.0% could be obtained for the sample with 2 phr of Li-12HSA as the reactive co-cell opener. As the results, it showed that a fully open-cell rigid PUF could be obtained by introducing a novel reactive cell opener, having a functional group able to form a bulky side-chain on the urethane networks, without severe loss of mechanical properties of the closed-cell PUF like cell size, bulk density, and thermal conductivity.

A Study on Compressive Creep Behavior of ACM Rubber using TMA Thermal Analysis

A study on compressive creep behavior of ACM rubber for automotive engine gasket was performed using TMA thermal analysis. From the results of isothermal measurements with constant load of 1 N at several different temperatures of 160, 180, 200, and , compressive creep data at the given temperatures were obtained, and therefrom, shift factor () and master curve at reference temperature of were obtained using time-temperature superposition principle (TTSP). and of WLF (Williams-Landel-Ferry) equation were calculated through the WLF plot as -1.107 and 11.571, respectively. From this, life time of ACM rubber at was predicted as about 24,000 hrs.

Field-Induced Liquid Crystal Texture Development of a Side-Chain LCP/7CB Blend

A blend of side-chain liquid crystal polymer (SCLCP) and 7CB, a low molecular weight liquid crystal (LMWLC), was prepared and used to investigate phase separation behavior induced by applied electric field, and thereby electro-optic property changes. An interesting field-induced LC texture development phenomenon was observed when the film transmittance of a phase-separated sample was measured under crossed-polarizer as function of applied field at a given temperature. That was, when measured at 50°C with applied field for a 20 μm-thick 3/7 SCPMMA/7CB blend film, the light transmittance drastically decreased initially, following unexpected increases from about 10 to 18 V and going down again. This phenomenon could be verified by POM observations and considered as the results of the destruction of LC texture within the blend at initial lower field and re-development at following higher applied field.

The Energetic and Electronic Properties of Atomic Hydrogen on MgO(001) Surface: Tight-Binding and Ab Initio Calculations

We report the computational results of hydrogen adsorption atop Mg and O atoms on the MgO(001) surface, followed by its absorption under the target atoms, using two approaches: tight-binding and ab initio methods. We present the energetic and electronic aspects of these interactions and discuss the qualities of the non-self-consistent field tight-binding results compared with the ab initio results. There is the qualitative reproduction of ab initio results in the hydrogen adsorption phase on both types of ions. The tight-binding results are found to be more accurate in the hydrogen absorption phase than in the adsorption phase. In the adsorption calculations the introduction of the surface dipole term in the tight-binding total energy would be required to compensate for the absence of electronic relaxation in the MgO(001) surface.