• The korean journal of orthodontics
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• v.19 no.2
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• pp.85-93
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• 1989

The purpose of this study was to evalute the corrosion resistance of chemically and thermally recycled metal brackets. In vivo, two types of recycled metal brackets and new brackets were directly bonded for 1 year, and then the microstructure of bracket surface was examined by S.E.M. (J.S.M.-840 Scanning Electron Microscope, Japan). The following results were obtained. 1) The microstructure of new and chemically recycled metal bracket surfaces showed regular structure without island formation and recrystallization; and after 1 year, the same appearance except some scratches. 2) The microstructure of thermally recycled metal bracket surfaces showed a beginning of island formation and recrystallization by annealing, and after 1 year, a typical corrosive appearance, completely island formation with some metal grains by recrystallization. 3) Chemically recycled metal brackets showed better corrosion resistance than thermally recycled metal brackets.

• The korean journal of orthodontics
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• v.23 no.2 s.41
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• pp.147-163
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• 1993

The purpose of this stuy was to evaluated the cytotoxicity of brackets which were recycled thermally or chemically. New brackets and used brackets which had been in mouth for at least 2years were used as samples and human gingival cell culture and agar overlay technique was used to evaluate the cytotoxicity. From the experiment the following results were obtained : 1. New brackets in the as received state showed mild cytotoxicity. 2. Thermally recycled brackets except the used bracket not electropolished showed moderate cytotoxicity and among them new brackets showed greater cytotoxicity than used ones. 3. Used brackets which were thermally recycled without electropolishing showed mild cytotoxicity. 4. Among thermally recycled brackets, electropolished brackets showed greater cytotoxicity than not electro-polished ones. 5. Chemically recycled brackets showed moderate cytotoxicity, and among them, new brackets appeared to be more cytotoxic than used ones.

• Journal of the Korean Applied Science and Technology
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• v.24 no.2
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• pp.182-189
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• 2007

Used polyurethane was chemically degraded by treatments with flame retardants such as tris(3-chloropropyl) phosphate (TCPP), triethyl phosphate (TEP), and trimethyl phosphate (TMP). The structure of degraded products (DEP) was analyzed by FT-IR and P-NMR and it turned out to be phosphorus containing oligourethanes. Rigid polyurethane foam was produced by using the degraded products (DEP) as flame retardants. The flammability of recycled rigid polyurethane was investigated. The recycled polyurethane shows a reduced flammability over virgin polyurethane. In order to evaluate flame retardant properties of the recycled polyurethane foams with various amounts of DEP, the combustion parameters of the foam was measured by a cone calorimeter. Scanning electron micrograph of recycled PU shows the same uniform cell morphology as virgin PU.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2011.11a
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• pp.39-40
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• 2011

This study is to analyse possibility cementitious powder from waste concrete as row material of recycled cement. From the results, we ascertained possibility as recycled cement through XRF & XRD of cementitious powder & recycled cement. As a result of the experiment, cementitious powder from waste concrete, which appeared to recovery hydration chemically at the calcining temperature of 700, suggested highly possibility as recycled cement.

• Textile Coloration and Finishing
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• v.27 no.2
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• pp.119-125
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• 2015

The effects of e-beam irradiation on water-repellency and washing durability of water-repellent finished chemically-recycled PET(CR-PET) fabrics were investigated. As results, more doses of e-beam irradiation damaged the fabric surface more severely. It was thought because the high densed energy was formed, where the more e-beam was converged. The contact angle measurement showed that as the dose of e-beam irradiation increased, water wettability of the CR-PET fabric increased slightly. It was thought to be due that the surface etching by e-beam irradiation let water droplet permeate into the fabric surface better. The concentration of the water-repellent finishing agent was more important factor than curing temperature as finishing parameter. It was considered because the water-repellent finishing agent used in this study got to cure sufficiently at low temperature. Consequently, e-beam irradiation improved the washing durability of water-repellent finishing on the CR-PET fabrics.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2016.05a
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• pp.207-208
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• 2016

The most important things for the production of recycled aggregates are saving energy, suppressing the generation of by-product fine particles and sustaining the performance of concrete. As solutions, this study proposes this technology of improving the performance of recycled aggregates through forced carbonation.1) It is to stimulate and carbonate the bond paste part that causes the deterioration of recycled aggregates. Particularly, the purpose of this technology is to fill and chemically stabilize pores inside the bond paste, further improving the quality of recycled aggregates with a decreased absorption rate and an enhanced aggregate strength. Ultimately, it is possible to obtain a carbonation model, depending on the paste ratio and particle-size distribution of recycled aggregates. Moreover, by calculating the optimum carbonation period through the verification of this carbonation model, it is possible to examine how much the strength is improved by the reformation of recycled aggregated.

• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.1
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• pp.34-42
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• 2015

The paper investigates environmental hazards and characteristics of the artificial lightweight aggregate manufactured by using dyestuff sludge from dyeing industrial complex. The dyestuff sludge used in this study is chemically treated with Ti and Fe salt for the purpose of recycling. The artificial lightweight aggregate is manufactured through 3 step; 1) Selecting the optimum moisture content by evaluating plasticity from the mixing ratio of the clay and sludge, 2) shaping round type based on the optimum mixing ratio, 3) drying and Sintering process. Based on KS F 2534 "Lightweight Aggregate for Structural concrete", the particle size, fineness modulus, the density, absorption, unit volume weight, stability and environmental hazards of the manufactured lightweight aggregate are evaluated. Experimental results show that the particle size and fineness modulus is out of the range. However, it is observed that other physical properties are within criteria. In addition, it is confirmed that the problem of the particle size and fineness modulus could be solved in the manufacturing process.

• The korean journal of orthodontics
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• v.20 no.2
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• pp.283-291
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• 1990

The purpose of this study was to measure and compare tensile and shear strength for 4 types of new direct-bonding brackets and same brackets after recycling and to evaluate the change of bracket slot width after recycling. Four types of new direct-bond brackets were bonded to recently extracted human premolar teeth and the tensile and shear strength was measured by Universal Testing Machine. The brackets were recycled by chemical process and the tensile and shear test was repeated. To evaluate the change of the bracket slot width, slot width was measured by the Topcon Universal Measuring Microscope before and after recycling. Following results were obtained: 1. There was no satistically significant difference between the tensile and shear strength of recycled brackets and those of new brackets. 2. In both new and recycled brackets, the tensile and shear strength of perforated base bracket was lower than those of photoetched, foilmesh and contou-lok mesh base brackets. (P<0.01) 3. There was no statistically significant difference in bonding strengths of control group bonded only once and two times. 4. There was no statistically significant difference in the change of the bracket slow width after recycling process. 5. Of the failure, the combination type (58%) in the tensile strength and the tooth adhesive interface (65%) in the shear strength was the most common type.

• Resources Recycling
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• v.14 no.3
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• pp.55-62
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• 2005

Mechanical properties of shell powder containing mixed recycled plastics were investigated depending on the shell content and surface modification. First, shell powder and LDPE were compounded using the twin screw extruder to manufacture 40 wt% master batch(M/B), and the M/B was blended with LDPE to produce bulk specimens with 10, 20, 30 and 40 wt% shell content. To improve the compatibility of shell powder with mixed recycled plastics matrix, surface of shell powder was chemically modified with cations or cationic surfactant. Surface modified shell was also used to prepare bulk specimens with the same shell content. Mechanical property analysis showed obvious improvement for the surface modified shell containing bulk specimens compared to unmodified ones. These results can lead to the development of new applications for the mixed recycled plastics.

• Applied Chemistry for Engineering
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• v.18 no.4
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• pp.376-380
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• 2007

Used polyurethane (PU) was chemically degraded by the treatment with flame retardants such as tris(1,3-chloro-2-propyl) phosphate (TCPP), triethyl phosphate (TEP), and trimethyl phosphate (TMP). Analysis of FT-IR and P-NMR showed that the degraded products (DEP) contained oligourethanes. Rigid polyurethane foam was produced using the DEP as flame retardants. The flammability and thermal stability of recycled rigid polyurethane were investigated. The mechanical properties such as compressive strength of recycled polyurethane were also studied. The recycled polyurethane reduced flammability and enhanced thermal stability over intrinsic polyurethane. Mechanical strength of recycled polyurethane also shows as high as that of intrinsic polyurethane. In order to evaluate flame retardant properties of the recycled polyurethane foams with various amounts of DEP, heat release rate (HRR) of the foam was measured by cone calorimeter. Scanning electron micrograph of recycled PU showed a uniform cell morphology as a intrinsic PU.