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A Comparison Study on Reinforcement Behaviors of Functional Fillers in Nitrile Rubber Composites
( Yoonjae Seong ),( Harim Lee ),( Seonhong Kim ),( Chang Hyun Yun ),( Changsin Park ),( Changwoon Nah ),( Gi-bbeum Lee ) 한국고무학회 2020 엘라스토머 및 콤포지트 Vol.55 No.4
To investigate the reinforcing effects of functional fillers in nitrile rubber (NBR) materials, high-structure carbon black (HS45), coated calcium carbonate (C-CaCO<sub>3</sub>), silica (200MP), and multi-walled carbon nanotubes (MWCNTs) were used as functional filler, and carbon black (SRF) as a common filler were used for oil-resistant rubber. The curing and mechanical properties of HS45-, 200MP-, and MWCNT-filled NBR compounds were improved compared to those of the SRF-filled NBR compound. The reinforcing effect also increased with a decrease in the particle size of the fillers. The CCaCO<sub>3</sub>- filled NBR compound exhibited no reinforcing effect with increasing filler concentration because of their large primary particle size (2 μm). The reinforcing behavior based on 100% modulus of the functional filler based NBR compounds was compared by using several predictive equation models. The reinforcing behavior of the C-CaCO3-filled NBR compound was in accordance with the Smallwood-Einstein equation whereas the 200MP- and MWCNT-filled NBR compounds fitted well with the modified Guth-Gold (m-Guth-Gold) equation. The SRF- and HS45-filled NBR compounds exhibited reinforcing behavior in accordance with the Guth-Gold and m-Guth-Gold equations, respectively, at a low filler content. However, the values of reinforcement parameter (100M<sub>f</sub>/100M<sub>u</sub>) of the SRF- and HS45-filled NBR compounds were higher than those determined by the predictive equation model at a high filler content. Because the chains of SRF composed of spherical filler particles are similarly changed to rod-like filler particles embedded in a rubber matrix and the reinforcement parameter rapidly increased with a high content of HS45, the higher-structured filler. The reinforcing effectiveness of the functional fillers was numerically evaluated on the basis of the effectiveness index (φ<sub>SRF</sub>/φf) determined by the ratio of the volume fraction of the functional filler (φf) to that of the SRF filler (φSRF) at three unit of reinforcing parameter (100M<sub>f</sub>/ 100M<sub>u</sub>). On the basis of their effectiveness index, MWCNT-, 200MP-, and HS45-filled compounds showed higher reinforcing effectiveness of 420%, 70%, and 20% than that of SRF-filled compound, respectively whereas C-CaCO<sub>3</sub>-filled compound exhibited lower reinforcing effectiveness of -50% than that of SRF-filled compound.
Development and Characterization of Asymmetric Swelling-Induced Wrinkles on Natural Rubber Surface
( Gi-bbeum Lee ),( Shibulal Gopi Sathi ),( Min Jung Kim ),( Changsin Park ),( Yang Il Huh ),( Changwoon Nah ) 한국고무학회 2016 엘라스토머 및 콤포지트 Vol.51 No.4
Characteristics of the swelling-induced wrinkles on the surfaces of natural rubber (NR) film were investigated. The wrinkle structure was generated by swelling of NR film pre-stretched and firmly bonded onto an aluminum substrate in hexane. A novel experimental method was adopted to replicate the swelling-induced wrinkles on the NR film using an epoxy-hardener system. To get insight into the wrinkle parameters; the wrinkle length (L), wrinkle distance (D), wrinkle height (H) and the angle between two consecutive wrinkles (θ), the cross-sections of the replicas obtained from saturated swollen NR film were examined using an optical microscopy (OM). From the OM images, the wrinkling parameters were measured as a function of the thickness of NR film from 0.42 to 1.76 mm. Also, it was evaluated that the effects of swelling time on the wrinkling parameters. The length (L), distance (D) and height (H) of wrinkles increased as the thickness of the NR film and the swelling time increased. However, the angle between the wrinkles (θ) showed a sharp decrease up to a swelling time of 200 minutes and slightly decreased afterwards.
Jeong, Kwang-Young,Ro, Young Jae,Kang, Tae Soon,Choi, Yang Ho,Kim, Changsin,Kim, Baek Jin The Korean Society of Marine Environment and safet 2020 海洋環境安全學會誌 Vol.26 No.3
This study examined the ef ects of freshwater discharge by artificial dikes from the Kanwol and Bunam lakes on the dynamics in the Chunsu Bay, Yellow Sea, Korea, during the summer season based on three-dimensional numerical modeling experiments. Model performances were evaluated in terms of skill scores for tidal elevation, velocity, temperature, and salinity and these scores mostly exceeded 90 %. The variability in residual currents before and after the freshwater discharge was examined. The large amount of lake water discharge through artificial dikes may result in a dramatically changed density field in the Chunsu Bay, leading to an estuarine circulation system. The density-driven current formed as a result of the freshwater inflow through the artificial dikes (Kanwol/Bunam) caused a partial change in the tidal circulation and a change in the scale and location of paired residual eddies. The stratification formed by strengthened static stability following the freshwater discharge led to a dramatic increase in the Richardson number and lasted for a few weeks. The strong stratification suppressed the vertical flux and inhibited surface aerated water mixing with bottom water. This phenomenon would have direct and indirect impacts on the marine environment such as hypoxia/anoxia formation at the bottom.