• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.11
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• pp.24-30
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• 2018

Various investigations of vegetable oil extracted from natural resources are underway because of their low cost and environmental value. On the other hand, the double bonds in vegetable oil should be substituted to other high reactive functional groups due to their low reactivity for synthesizing bio-polymeric materials. ${\alpha}$-eleostearic acid, which consists of a conjugated triene, is the main component of tung oil, and the conjugated triene allows tung oil to have higher reactivity than other vegetable oils. In this study, tung oil was copolymerized with styrene and divinylbenzene to make a thermoset resin without any substitution of functional groups. The thermal and mechanical properties were measured to examine the effects of the composition of each monomer on the synthesized thermoset resin. The results showed that the products have only one Tg, which means the synthesized thermoset resins are homogeneous at the molecular level. The mechanical properties show that tung oil acts as a soft segment in the copolymer and makes a more elastic product. On the other hand, divinylbenzene acts as a hard segment and makes a more brittle product.

• Journal of Life Science
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• v.29 no.9
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• pp.955-963
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• 2019

This study evaluated the characteristics and antioxidant properties of cookies prepared with different amounts (0%, 1%, 3%, 5%, and 7%) of Lentinus edodes water extract (LEWE). The baking loss rate of cookies increased as the amount of LEWE increased (p<0.05). The pH of cookies significantly decreased when amounts of LEWE increased (p<0.05), but spread factor, leavening rate, and moisture content showed no significant difference among the samples. L value and b value of cookies significantly decreased when amounts of LEWE increased (p<0.05), but a value of cookies significantly increased when amounts of LEWE increased (p<0.05). Hardness was higher in the 7% LEWE cookies. Chewiness and brittleness increased with increasing LEWE concentration, but cohesiveness and springiness showed no significant differences among the samples. Total polyphenol content and DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging activity significantly increased upon the addition of LEWE (p<0.05). In a sensory evaluation, the appearance, color, and taste of the cookies were rated higher in groups containing 0% LEWE, but the flavor, texture, and overall acceptability scores were highest for cookies with 1% LEWE added. These results suggest that cookies prepared by adding 1-3% LEWE achieve the best sensory evaluation and antioxidant activity.

• The Journal of Korean Academy of Prosthodontics
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• v.57 no.1
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• pp.1-7
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• 2019

Purpose: The laser processability of dental prosthesis is investigated using two ceramic composites, including 3M, Lava Ultimate and Ivoclar vivadent, IPS e.max. Materials and methods: The $CO_2$ laser, picosecond laser and femtosecond laser are used to assess the processing power of dental prosthetic materials Lava Ultimate and IPS e.max and the line processing shape was measured using a confocal microscope. Results: The brittleness, carbonization and micro crack of the ceramic composite were influenced by heat accumulation of the material and could be controlled by the laser power and pulse time. Conclusion: In the case of $CO_2$ lasers, micro crack and carbonation occurred immediately, and in the picosecond laser processing, the micro cracks are partially improved, but the carbonization occurs continuously. Finally, we confirmed the high efficiency of laser processing with femtosecond laser. In particular, Lava Ultimate, a ceramic resin composite material, showed the best processability when processed using a femtosecond laser.

• Journal of Life Science
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• v.29 no.5
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• pp.588-595
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• 2019

This study was carried out to investigate the total polyphenol content and DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging activity of hot water (EIW) and 80% ethanol (EIE) extracts of Enteromorpha intestinalis and the quality characteristics of Topokkidduk prepared with different amounts (0, 1, 3, and 5%) of Enteromorpha intestinalis powder (EIP). The total polyphenol contents of the EIW and EIE extracts were 2.04 and 6.73 mg tannic acid equivalents (TAE)/g, respectively. The DPPH radical scavenging activities of EIW and EIE were markedly increased in a dose-dependent manner, and were about 19.74% and 81.69%, respectively, at 10 mg/ml. The moisture content was higher at 0% EIP (p<0.05). The L value and the a value of Topokkidduk significantly decreased when the amounts of EIP increased (p<0.05), but the b value of Topokkidduk significantly increased when the amounts of EIP increased (p<0.05). Hardness, chewiness, adhesiveness, springiness, and brittleness increased with increasing EIP concentration. The cohesiveness was higher at 3% EIP, but no significant difference was noted between 0% and 1% EIP. The total polyphenol content and DPPH radical scavenging activity significantly increased upon addition of EIP (p<0.05). A sensory evaluation revealed a higher color, texture, and taste of Topokkidduk in groups containing 0% EIP, but the flavor was highest for Topokkidduk with 0% EIP added. Overall acceptability was higher at 0% EIP, but no significant difference was noted between 0 and 1%. These results suggest that Enteromorpha intestinalis has great potential as a source for natural health products.

• Food Engineering Progress
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• v.21 no.4
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• pp.367-374
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• 2017

The aim of this study was to evaluate the quality characteristics, antioxidant activities, and sensory properties of macaron with cabbage powder (CP). Physicochemical and sensory properties of macaron with different amounts (0%, 1%, 3%, 5%, and 7%) of CP were examined. The quality of macarons was evaluated based on spread factor, baking loss rate, color, texture, antioxidant activities, and sensory evaluation. As amount of CP addition increased, spread factor, baking loss rate, and L and a values decreased, whereas b value increased (p<0.05). For texture properties, hardness, cohesiveness, and springiness were increased by addition of CP (p<0.05). The gumminess and brittleness did not show significant changes up to 3% CP addition although significant changes in 5-7% CP addition (p<0.05) were evident. The total polyphenolic contents, DPPH radical scavenging activities, and reducing power were significantly increased by addition of CP at high concentrations (p<0.05). In the consumer acceptance of macarons, 3% CP showed the highest in color, flavor, texture, and overall acceptance and 5% CP showed the highest in taste. Meanwhile, macaron containing 7% CP showed the lowest scores in texture and overall acceptance (p<0.05). These data suggested that adding 3% of CP was the optimal concentration for making macaron.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.3
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• pp.330-337
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• 2021

3D printing is not only at the fundamental study and small-scale level, but has recently been producing buildings that can be inhabited by people. Buildings require a lot of cost and labor to work on the form work, but if 3D printing is applied to the building, the construction industry is received attention from technologies using 3D printing as it can reduce the construction period and cost. 3D printing technology for buildings can be divided into structural and non-structural materials, of which 3D printing is applied to non-structural materials. Because 3D printing needs to be additive manufacturing, control such as curing speed and workability is needed. Since cement mortar has a large shrinkage due to evaporation of water, cement polymer dispersion is used to improve the hardening speed, workability, and adhesion strength. The addition of polymer dispersion to cement mortar improves the tensile strength and brittleness between the cement hydrate and the polymer film. Cement mortar using polymer materials can be additive manufacturing but it has limited height that can be additive manufacturing due to its high density. When light-weight materials are mixed with polymer cement mortar, the density of polymer cement mortar is lowered and the height of additive manufacturing, so it is essential to use light-weight materials. However, the use of EVA redispersible polymer powder and light-weight materials, additional damage such as cracks in cement mortar can occur at high temperatures such as fires. This study produced a test specimen incorporating light-weight materials and EVA redispersible polymer powder to produce exterior building materials using 3D printing, and examined flame resistance performance through water absorption rate, length change rate, and cone calorimeter test and non-flammable test. From the test result, the test specimen using silica sand and light-weight aggregate showed good flame resistance performance, and if the EVA redispersible polymer powder is applied below 5%, it shows good flame resistance performance.

• Resources Recycling
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• v.31 no.1
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• pp.46-55
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• 2022

The recycling of coated cemented carbide scraps is becoming increasingly significant for the recovery of rare metals. However, coatings consisting of Group IV and V transition metal nitrides are one of the challenging factors in obtaining high-purity materials. We investigated the structural, elastic, and mechanical properties of Group IV and V transition-metal nitrides (TiN, VN, ZrN, NbN, HfN, and TaN) using first-principle calculations. Convergence tests were performed to obtain reliable calculated results. The equilibrium structures of the nitrides were in good agreement with those of a previous study, indicating the reliability of the data. Group IV transition metal nitrides show a higher covalent bonding nature. Thus, they exhibit a higher degree of brittleness than that of Group V transition metal nitrides. In contrast, Group V transition metal nitrides show weaker resistance to shear loading and more ductile behavior than Group IV transition metal nitrides because of the metallic bonds characterized by valence electron concentration. The results of the crystal orbital Hamilton population analysis showed good agreement with the shear resistance tendencies of all transition metal nitrides.

• Journal of the Korean Institute of Gas
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• v.26 no.6
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• pp.16-23
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• 2022

In this study, characteristics of effect on hydrogen gas was investigated to hydrogen embrittlement by disk and tensile tests. The developed and commercial alloy was fabricated to a plate material made from an alloy ingot. The prepared materials were processed in the form of a disk to measure rupture pressure by hydrogen and helium gas at a rate of 0.1 to 1,000 bar/min. In the hydrogen pre-charged tensile test, a specimen was hydrogenated using an anode charging method, and the yield strength, ultimate tensile strength, elongation, and reduction in area rate were carried by a strain rate test. Also, the microstructure was observed to the fracture surface of the tensile test specimen. As a result, the developed materials satisfied endurable hydrogen embrittlement, and the fractured surface showed a brittleness fracture surface with a depth of several ㎛, but dimple due to ductile fracture could be observed.

• Clean Technology
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• v.28 no.4
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• pp.301-308
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• 2022

Since nanoporous silica aerogel was first synthesized in 1931, its potential as an ultra-lightweight superinsulation material has been steadily attracting attention. Silica aerogel is the best thermal insulation material to date. However, the potential applications of this lightweight material have so far been hindered by its inherent fragibility and brittleness arising from its ultra-porous nature. Although the monolithic form of silica aerogel has the best ultra-lightweight superinsulation properties, it cannot be used in this form. Instead it is used in the form of powders, particles, and blankets. However, these forms still have shortcomings. Silica aerogel is most widely applied in the form of a fiber-reinforced aerogel blanket, but this form is likely to generate dust when handled. Although silica aerogel particles have been proven to be non-toxic to humans, dust formation remains a major barrier to the widespread application of silica aerogel blankets. This paper will investigate the unique properties of silica aerogel and determine what fields it can be used in or potentially be used in due to its unique properties. In addition, we will review the important advances in silica aerogel synthesis technology and its commercialization so far, and then consider the problems that exist for its widespread commercialization in the future and how to overcome them.

• Composites Research
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• v.36 no.4
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• pp.246-252
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• 2023

A secondary barrier made of glass fiber reinforced composites has been installed infinitely using automatic bonding machine(ABM) in membrane type LNG cargo containment system (CCS). At the same time, significant thermal stress due to cryogenic heat shrinkage has occurred in the composite on the non-bonding area between the adhesive fixation at both ends. There have been studies from the perspective of structural safety evaluation taking this into account, but none that have analyzed mechanical property taking an prolonged length into account. In this study, 2-parameter Weibull distribution statistical analysis was used to standardize reliable mechanical property for actual length, taking into account the composite's brittle fracture of ceramic material with wide fracture strength dispersion. Related experimental data were obtained by performing uniaxial tensile tests at specific temperatures below cryogenic condition considering LNG environment. As a result, the mechanical strength increased about 1.5 times compared to -20℃ at -70℃ and initial non-linear behavior of fiber stretched was suppressed. As the temperature decreased until the cryogenic, the mechanical strength continued to increase due to cold brittleness. The suggested mechanical property in this study would be employed to secure reliable analysis support material property when assessing the safety of secondary barrier's structures.