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RISS 인기검색어
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- 저자 : Kewei Xiang (검색결과 3 건)
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Kewei Xiang,Guangsu Huang,Siduo Wu,Jing Zheng,Jingyun Huang,Guangxian Li 한국고분자학회 2014 Macromolecular Research Vol.22 No.8
In this work, styrene-butadiene rubber (SBR) was thermally aged at 130 ℃with ageing period up to 4days. The relaxation behavior was studied by dynamic mechanical analysis (DMA) in temperature scanning modeat multifrequencies and the crosslinking network was characterized by swelling method. Glass transition temperature(Tg) and activation energies (Ea) during transition evaluated by Starkweather method were found to increaseafter ageing. Time-temperature superposition (TTS) procedure was performed to obtain master curve and shift factors(αT). The derived αTs were fitted by William-Landel-Ferry (WLF) and Vogel-Fulcher-Tamman (VFT) equations. WLF fitting parameters confirmed decreased free volume fraction ( f ) and thermal expansion coefficient (αf)near Tg versus ageing time. Temperature dependent relaxation properties were examined by VFT fitting parameterD. It was found that the aged SBR displayed more brittle behavior, becoming more and more deviated from Arrheniusfashion. This phenomenon was illustrated by the enhanced intermolecular coupling and severe crosslinkingduring ageing.
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Investigation on the Thermal Oxidative Aging Mechanism and Lifetime Prediction of Butyl Rubber
Kewei Xiang,Guangsu Huang,Jing Zheng,Xiaoan Wang,Jingyun Huang 한국고분자학회 2013 Macromolecular Research Vol.21 No.1
Accelerated thermal aging experiments were conducted on butyl rubber materials in order to investigate aging behavior using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), positron annihilation lifetime spectroscopy (PALS), and differential scanning calometry (DSC). The XPS results suggested that the thermal oxidation process took place heterogeneously along the samples thicknesses. The aging mechanism was identified to be crosslinking by means of the combined use of PALS and DSC results. Lifetime and intensity of ortho-positronium (o-ps) diminished, and the glass transition temperature (Tg) increased during aging. The dispersion condition of silica particles, observed by SEM images, showed that the filler agglomerated after aging. Time temperature superposition was carried out using compression set measurements in the temperature range of 100 to 60 oC. The Arrhenius plot clearly exhibited a curvature around 75 oC, and the activation energy dropped from 126.7to 58.8 kJ/mol across this region. Relative importance of different processes, over the entire temperature range, was discussed; lifetime at room temperature was predicted.
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Xiaoan Wang,Kewei Xiang,Yijing Nie,Guangsu Huang,Jinrong Wu,Zhiqing Su 한국고분자학회 2013 Macromolecular Research Vol.21 No.5
The investigation of the gradual cooling crystallization process of α-trans-1,4-polyisoprene (α-TPI) was carried out for different wavenumber regions by conventional spectral analysis and two-dimensional correlation infrared spectroscopy (2DIR) methods. Interestingly, an intermediate state has been confirmed by the fascinating intensity variation of the 1666 cm-1 band, and the motion of side-chain (CH3 group) seems to be the initial driving force and precondition for forming the ordered 21 helix conformation. It is also found that the occurrence for the splitting of the CH3 group-related bands is consistent with the appearance of the intermediate state, indicating that the interchain interactions between CH3 groups play an important role in controlling the intermediate state and should be the primary driving force for stabilizing the specific 21 helix conformation.
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