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김우년,Yu-taek Sung,Won Jin Seo,Jong Sung Kim,Dong-Hwan Kwak,Tae-Won Hwang 한국유변학회 2005 Korea-Australia rheology journal Vol.17 No.1
Rheological properties and crystallization kinetics of the polypropylene (PP) block copolymer and recycled PP block copolymer were studied by advanced rheometric expansion system (ARES), differential scanning calorimetry (DSC), and optical microscopy. In the study of the dynamic rheology, it is observed that the storage modulus and loss modulus for the PP block copolymer and recycled PP block copolymer did not change with frequency. In the study of the effect of the repeated extrusion on the crystallization rate, half crystallization time of the PP samples was increased with the number of repeated extrusion in isothermal crystallization temperature (Tc). From the isothermal crystallization kinetics study, the crystallization rate was decreased with the increase of the number of repeated extrusion. Also, from the result of Avrami plot, the overall crystallization rate constant (K) was decreased with the increase of the number of the repeated extrusion. From the study of the optical microscopy, the size of the spherulite of the PP samples did not change significantly with the number of repeated extrusion. However, it was clearly observed that the number of the spherulite growth sites was decreased with the number of repeated extrusion. From the results of the crystallization rate, isothermal crystallization kinetics, Avrami plots, and optical microscopy, it is suggested that the crystallization rate of the PP block copolymer is decreased with the increase of the number of repeated extrusion.
Properties of Rigid Polyurethane Foams Blown by HFC-365mfc and Distilled Water
김우년,Youn Hee Kim,Jae Won Lee,Seok Jin Choi,한미선,Ji Mun Kim,김상범 한국공업화학회 2007 Journal of Industrial and Engineering Chemistry Vol.13 No.7
Rigid polyurethane foams (PUFs) were prepared from polymeric 4,4-diphenylmethane diisocyanate (PMDI), polyether polyol, silicone surfactant, amine catalysts, and hydrofluorocarbon (HFC-365mfc) and distilled water as blowing agents. The density and compressive strength of the PUF samples were decreased with the increase of the blowing agent. This is mainly due to that the cell size of the PUF samples is increased with the increase of blowing agent. From the result of the effect of blowing agents on the thermal conductivity of the PUF samples, it was observed that, when the amount of the distilled water was fixed, the thermal conductivity of the PUF samples decreased with the increase of the amount of HFC-365mfc. Also, when the amount of HFC-365mfc was fixed, the thermal conductivity of the PUF samples decreased with the increase of the amount of distilled water. From the results of thermal conductivity of PUF samples, it is suggest that the thermal conductivity of the PUF samples depends on the thermal conductivity of blowing agent as well as the total amount of the entrapped blowing gas inside the closed cell of the PU foams. Also, PU foams blown by mixed blowing agent such as HFC-365mfc and distilled water may increase in the structural stability of the PU foams by matching of the rates of gelling and foaming reactions for the formation of desired foams compared the PU foams blown by HFC-365mfc or distilled water alone.