• Korean Chemical Engineering Research
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• v.50 no.1
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• pp.88-92
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• 2012

Decrosslinking of crosslinked polypropylene(XLPP) in supercritical methanol was investigated compared with that of crosslinked polyethylene(XLPE). Effect of reaction temperature and initial gel contents was studied using a batch reactor. Gel contents of samples before and after reaction were measured for quantitative analysis. As reaction temperature and initial gel contents increased, the decrosslinking rate increased. The rate of decrosslinking reaction is dependent linearly on the gel contents. Experimental results indicated that the decrosslinking of XLPP was faster than that of XLPE, and it was confirmed quantitatively by the calculation of kinetic constants. In conclusion, it is considered that XLPP has better recyclability than XLPE.

• Clean Technology
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• v.20 no.3
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• pp.241-250
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• 2014

In this study, performance and environmental characteristics of cyclone vacuum cleaners are analyzed and product improvement methods are investigated to minimize environmental effect of the cleaners using the result. A simplified LCA method is used to analyze environmental characteristics of the cyclone vacuum cleaners. Two cyclone vacuum cleaners with similar specifications are chosen for the experiment. Typical characteristics of cyclone vacuum cleaners such as energy consumption, suction force, noise and temperature are measured and compared. Most environmental effect was caused by the energy consumption in use phase of life cycle. Some ideas are created to reduce energy consumption of the vacuum cleaners in use phase like installing baffle, and methods to extend exchange period of filter. It is analyzed how recyclability rate of vacuum cleaners could be improved to reduce the environmental effect in whole life of the vacuum cleaners.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.635-635
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• 2013

We report three-dimensional polycrystalline anatase TiO2 structures (3D a-TiO2) for environmental and bio-medical applications. The 3D a-TiO2 was synthesized without thermal treatment by the growth of rod-like polycrystals on Degussa P25 (P25) via low temperature (< $85^{\circ}C$) modified alkali hydrothermal processing. X-ray diffraction and high-resolution transmission electron microscopic results showed that the rod-like polycrystals of 3D a-TiO2 possessed the highly anatase nanostructures. The photocatalytic activity of 3D a-TiO2 was found to be 2.2 times higher than that of P25. The recyclability of the 3D a-TiO2 was found to be high: the decolorization rate was 94.8% of the initial value after fifteen cycles. In addition, 3D a-TiO2 exhibited excellent antibacterial activities for the sterilization of gram-negative Escherichia coli (E. coli) and gram-positive Staphylococcus aureus (S. aureus). Even at the 10th recycled use, more than 98.4% of E. coli and S. aureus can be killed. These results indicated that 3D a-TiO2 might have utility in several promising applications such as photocatalytic water/air purification and bactericidal agents.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2013.05a
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• pp.62-62
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• 2013

Magnesium alloys exhibit many attractive properties such as low density, high strength/weight ratio, high thermal conductivity, very good electromagnetic features and good recyclability. However, most commercial magnesium alloys require protective coatings because of their poor corrosion resistance. Attempts have been made to improve the corrosion resistance of the Mg alloys by surface treatments, such as chemical conversion coatings, anodizing, plating and metal coatings. Among them, chemical conversion coatings are regarded as one of the most effective and cheapest ways to prevent corrosion of Mg alloys. In this study, the effects of various $Zn^{2+}$ concentrations and pH levels on the formation of zinc phosphate conversion coatings (ZPCCs) on AZ31 magnesium alloy were investigated, and corrosion resistances of the coated samples were evaluated by immersion test and potentiodynamic polarization experiment. The corrosion resistance of the coated AZ31 samples was found to increase with increasing $Zn^{2+}$ concentration and the lowest corrosion rate was obtained for the samples coated at pH of 3.07, independent of $Zn^{2+}$ concentration. The best coatings on AZ31 were obtained at [$Zn^{2+}$] = 0.068 M and pH 3.07. At the conditions of [$Zn^{2+}$] = 0.068 M and pH 3.07, the formation and growth processes of ZPCCs on AZ31 Mg alloy are divided into four stages: formation of a dense layer, precipitation of fine crystals on the dense layer, growths of the inner and outer layers, and reorganization of outer crystalline layer.

• Composites Research
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• v.33 no.2
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• pp.39-43
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• 2020

Recently, fabrication process of thermoplastic polyamide-based composites with recyclability as well as impact, chemical, and abrasion resistance have been widely studied. In particular, thermoplastic reactive resin transfer molding (TRTM) in which monomer with low viscosity is injected and in-situ polymerized inside mold has received a great attention, because thermoplastic melts are hard to impregnate fiber preform due to their very high viscosity. However, it is difficult to optimize the processing conditions because of high reactivity and sensitivity to external environments of the used monomer, ε-caprolactam. In this study, viscosity as an important process parameter in TRTM was measured during in-situ anionic polymerization of ε-caprolactam and the solutions for problems caused by high polymerization rate and sensitivity to moisture and oxygen were suggested. Reliability of the improved measurement technique was verified by comparing the viscosity behavior at various environmental conditions including humidity and atmosphere, and it is expected to be helpful for optimization of TRTM process.

• Clean Technology
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• v.25 no.4
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• pp.311-315
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• 2019

The cation extraction and impurity separation were studied in order to investigate the recyclability of a slag produced from the steel refinery industry. Two types of slag (Slag-A, B) were collected and characterized in this study. The initial characterization by X-ray diffraction (XRD) and X-ray fluorescence (XRF) confirmed the existence of various kinds of ions in the slag such as Ca²⁺ (30 ~ 40%), Fe³⁺ (20 ~ 30%), Si⁴⁺ (15%), Al³⁺ (10%), Mn²⁺ (7%), and Mg²⁺ (3 ~ 5%). Inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis on the extracted slag using 2 M HCl as a solvent indicated that a higher concentration of Ca²⁺ was extracted as the S/L ratio was increased. The Ca²⁺ extraction concentration were found to be 8,940 mg L^-1 (Slag-A) and 10,690 (Slag-B) mg L^-1 when the S/L ratio for Ca²⁺ extraction was 0.1. However, the extract was strongly acidic ( < pH 1) at 0.1 S/L. Also the other ions (impurities) were extracted simultaneously in addition to Ca²⁺. To increase the purity of Ca²⁺ in order to transform the slag to a high value resource, a pH-swing was conducted. The impurities tended to precipitate at higher rate as the pH was increased. Notably, the Ca²⁺ rapidly precipitated above a certain pH and at a pH of 10.5, while the selectivity of Ca²⁺ was over 99%. It is expected that the aqueous solution in which high contents of Ca²⁺ was selectively dissolved in this study would be suitable for the carbonation process for reducing CO₂ and for the production of calcium carbonate.