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박동협,오제곤,김상범,김우년,김환기 한국고분자학회 2013 Macromolecular Research Vol.21 No.11
Polyurethane (PU) dispersion was prepared with sulfonate groups to make the PU dispersible. Then, polyurethane-polyacrylate (PU-PA) hybrid emulsions were synthesized by seeded emulsifier-free emulsion polymerization with the previously synthesized PU dispersion as a source of seed particles. In the results of the particle-size distribution of the PU-PA hybrid emulsions, the average particle size of the hybrid emulsions increased from 1.2 to 9.1 μm when the polyacrylate content was increased from 0.2 to 1.0 by weight. In addition, the scanning electron microscopy results showed that the size of the polyacrylate latex particles was increased with increases in polyacrylate content. This result suggests that the hydrophobic polyacrylate can easily diffuse into PU particles, where the free radical chain-growth polymerization takes place. In the thermal analysis results, shifts in Tg,1 and Tg,2 were observed, which are related to the partial compatibility and inter-diffusion of the PU dispersion and PA components. The TGA curves shifted to a higher temperature with increases in polyacrylate content, which indicates a higher thermal stability of the PU-PA hybrid emulsion films. The PU-PA hybrid emulsion films showed improvement in the thermal stability and mechanical properties when compared with the pure polyurethane film, due to the increase in the formation of strong interaction between the PU and PA molecules.
박동협,이윤균,박상성,이춘수,김성현,김우년 한국고분자학회 2013 Macromolecular Research Vol.21 No.8
In this study, the effects of hybrid fillers on the electrical conductivity and electromagnetic interference shielding efficiency (EMI SE) of the polypropylene (PP)/ Ni-coated carbon fiber (NCCF) composites with the second fillers, such as multi-walled carbon nanotube (MWCNT), carbon black and TiO2, were investigated. The morphological behavior showed that the NCCF and the second fillers, such as MWCNT, carbon black and TiO2,seemed to disperse evenly in the PP phase. Among the PP/NCCF composites with MWCNT, carbon black and TiO2,the PP/NCCF/TiO2 composites showed the higher electrical conductivity and EMI SE compared with those of the PP/NCCF/MWCNT and PP/NCCF/carbon black composites. This was the case because TiO2 has high dielectric constant with dominant dipolar polarization. The estimated EMI SE values of the PP/NCCF composites with MWCNT, carbon black and TiO2 are in good agreement with the experimentally obtained values of the composites. Based on the electrical properties of the composites, it was suggested that TiO2 was the most effective second filler when it was hybridized with the NCCF of the PP/NCCF/TiO2 composite. Based on the analysis of the flexural modulus, the PP/NCCF/MWCNT composite had a higher flexural modulus than the PP/NCCF/TiO2 and PP/NCCF/carbon black composites because of the higher aspect ratio of the MWCNT.
박동협,박건표,김성현,김우년 한국고분자학회 2013 Macromolecular Research Vol.21 No.8
The effects of the isocyanate (NCO) index and blowing agent on the morphology, mechanical strength,thermal conductivity and thermal stability of the polyisocyanurate-polyurethane (PIR-PUR) foams were investigated. When the NCO index was increased, the isocyanurate ring content in the PIR-PUR foams was found to be increased regardless the type of blowing agents. As a results, the thermal stability of the PIR-PUR foams was improved. When the isocyanurate ring content in the PIR-PUR foams was increased, the cell size was slightly decreased. The decreased cell size of the foams affected the decrease in the thermal conductivity of the PIR-PUR foams regardless the type of the blowing agents. From the results of thermogravimetric analysis (TGA), the thermal stability of the PIR-PUR foams was found to increase with an increase in the NCO index. When the NCO index was 200, the compressive strength was maximal for the PIR-PUR foams regardless the type of the blowing agents. The compressive strength of the foams blown by cyclopentane was higher than that of the water blown foams. From the above results, it is suggested that the thermal insulation property and thermal stability of the PIR-PUR foams increased with an increase in the NCO index. However, the compressive strength of the PIR-PUR foams showed maximum value at a specific NCO index.
박동협,김민수,양준호,이동준,김경남,홍병권,김우년 한국고분자학회 2011 Macromolecular Research Vol.19 No.2
The effects of compatibilizers and hydrolysis on the mechanical, morphological and rheological properties of polypropylene (PP)/ethylene-propylene-diene monomer rubber (EPDM)/poly(lactic acid) (PLA) blends were studied. The compatibilizers used were polypropylene-g-maleic anhydride (PP-g-MAH) and styrene-ethylene-butylene-styrene-g-maleic anhydride (SEBS-g-MAH) copolymers. Before hydrolysis, mixing the compatibilizers PP-g-MAH (5 phr) and SEBS-g-MAH (5 phr) effectively increased the impact strength of PP/EPDM/PLA (64/16/20)blends without any loss of tensile strength. This result is consistent with the morphological and rheological properties of the PP/EPDM/PLA blends. After hydrolysis, the tensile strength of the PP/EPDM/PLA blends for the PLArich compositions decreased sharply until the hydrolysis time was 3 days. This suggests that the mechanical strength of the PLA already lost its mechanical properties, mostly when the hydrolysis time was 3 days under such hydrolysis conditions. The increase in viscosity and decrease in interfacial tension of the compatibilized PP/EPDM/PLA (64/16/20) blends was interpreted with the qualitative picture of the Palierne emulsion model. The interfacial tension calculated from the emulsion model is consistent with the mechanical and morphological properties of the PP/EPDM/PLA (64/16/20) blends.