• 반도체디스플레이기술학회지
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• 제18권3호
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• pp.52-59
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• 2019

Styrene-butadiene rubber (SBR) composites, incorporated with graphene, molybdenum disulfide and their hybrid in different filling ratio, were fabricated by a two roll-mill. The dispersion states of all the samples' matrix were employed by carbon black dispersion tester. The curing properties of the pre-vulcanized rubber composites were investigated, after molding by heating press machine, the tensile strength, storage modulus, friction coefficient, the swelling property had also been tested according to ASTM. The composite G1M10 (filling with 1 phr graphene and 10 phr molybdenum) showed the best mechanical properties and viscoelastic properties in this research with a better filler dispersion state and more compact matrix structure.

• Elastomers and Composites
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• 제54권3호
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• pp.225-231
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• 2019

Bio-based polyester polyol was synthesized via esterification between azelaic acid and isosorbide. After esterification, bio-based polyurethanes were synthesized using polyester polyol, 1,3-propanediol as the chain extender, and 4,4'-diphenylmethane diisocyanate, in mixing ratios of 1:1:1.5, 1:1:1.8, 1:1:2, and 1:1:2.3. The bio TPU (Thermoplastic Polyurethane) samples were characterized by using FT-IR (Fourier Transform Infrared Spectroscopy), TGA (Thermal Gravimetric Analysis), DSC (Differential Scanning Calorimetry), and GPC (Gel Permeation Chromatography). The mechanical properties (tensile stress and hardness) were obtained by using UTM, a Shore A tester, and a Taber abrasion tester. The viscoelastic properties were tested by an Rubber Processing Analyzer in dynamic strain sweep and dynamic frequency test modes. The chemical resistance was tested with methanol by using the swelling test method. Based on these results, the bio TPU synthesized with the ratio of 1:1:2.3, referred to as TPU 4, showed the highest thermal decomposition temperature, the largest molecular weight, and most compact matrix structure due to the highest ratio of the hard segment in the molecular structure. It also presented the highest tensile strength, the largest elongation, and the best viscoelastic properties among the different bio TPUs synthesized herein.

• Journal of Microbiology and Biotechnology
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• 제31권3호
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• pp.429-438
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• 2021

Bacterial cellulose (BC) is widely used in the food industry for products such as nata de coco. The mechanical properties of BC hydrogels, including stiffness and viscoelasticity, are determined by the hydrated fibril network. Generally, Komagataeibacter bacteria produce gluconic acids in a glucose medium, which may affect the pH, structure and mechanical properties of BC. In this work, the effect of pH buffer on the yields of Komagataeibacter hansenii strain ATCC 53582 was studied. The bacterium in a phosphate and phthalate buffer with low ionic strength produced a good BC yield (5.16 and 4.63 g/l respectively), but there was a substantial reduction in pH due to the accumulation of gluconic acid. However, the addition of gluconic acid enhanced the polymer density and mechanical properties of BC hydrogels. The effect was similar to that of the bacteria using glycerol in another carbon metabolism circuit, which provided good pH stability and a higher conversion rate of carbon. This study may broaden the understanding of how carbon sources affect BC biosynthesis.

• 농업과학연구
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• 제49권4호
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• pp.667-676
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• 2022

The soil physical and chemical properties are the main factors that influence plant productivity and soil fertility. Since 1999, South Korea has been conducting a survey on changes in the agricultural environment survey every four years. The purpose of the present study is to monitor the physical and chemical properties of soil in Chungcheongbuk-do. Soil samples were collected from the exact sites of the aforementioned environment survey, and land use and cultivated crops were also investigated. From a Pearson correlation analysis, it was found that the total carbon contents were most negatively affected by the soil depth. The bulk density of soil increased up to a depth of 40 cm but decreased to a depth of 60 cm. The porosity and moisture of soil generally decreased, but the porosity increased at a depth of 50 - 60 cm. Chemical properties of soil gradually decreased with an increase of the soil depth from 0 to 70 cm, but little change was observed in soil pH with soil depth. In addition, the organic matter contents of the soil at a depth of 30 cm or more were below the optimal range. The soil of Chungcheongbuk-do thus requires organic matter application as a whole, and correction of items that are partially out of the optimal range is necessary.

• Elastomers and Composites
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• 제58권3호
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• pp.136-141
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• 2023

Polyacrylic rubber (ACM) is well known for its excellent heat resistance and chemical stability. Additionally, its performance can be readily manipulated by modifying its functional groups, rendering it highly attractive to various industries. However, extreme climate changes have necessitated an expansion of the operating temperature range and lifespan of ACM products. This requires the optimization of both the compounding process and functional-group design. Hence, we investigated the relationship between the cross-linking system and mechanical properties of an ACM with a carboxylic cure site. The crosslink density is determined by chemical kinetics according to the structure of additives, such as diamine crosslinkers and guanidine accelerators. This interaction enables the manipulation of the scotch time and mechanical properties of the compound. This fundamental study on the correlation analysis between cross-linking systems, physical properties, and storage stability can provide a foundation for material research aimed at satisfying the increasingly demanding service conditions of rubber products.

• 한국가구학회지
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• 제11권2호
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• pp.37-43
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• 2000

Ginkgo trees have long been planted in Korea as roadside trees and ornamental trees, but the wood was seldom used except some utilization f3r small artifacts. Soaring prices of imported wood and future uncertainty about long-term supply of foreign woods have stimulated research on value-added utilization of less-utilized domestic wood resources such as Ginkgo wood. The processing properties of Ginkgo wood were investigated to determine its utilization potential in this study, and the results of treatability, drying characteristics, gluability, paintability, bending properties, chemical discoloration characteristics were presented.

• Journal of Electrochemical Science and Technology
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• 제3권2호
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• pp.80-84
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• 2012

The polyaniline (PANI) electrodes are prepared by chemical synthesis and electrodeposition methods and their supercapacitive properties are characterized and compared by morphology observation, cyclic voltammetry as a function of scan rate, and impedance spectra analysis. In particular, the supercapacitive properties obtained in the range of higher potential scan rates (e.g., over $200mV\;s^{-1}$) are emphasized to be capable of utilizing adequately the high power capability of supercapacitor. As a result, the PANI electrode by the electrodeposition shows superior specific capacitance (max. $474F\;g^{-1}$ at $10mV\;s^{-1}$ and about $390F\;g^{-1}$ at $500mV\;s^{-1}$) than those by the chemical synthesis method. This is mainly due to highly porous structure obtained by the electrodeposition to yield higher specific surface area.

• 한국디지털건축인테리어학회논문집
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• 제12권4호
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• pp.87-95
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• 2012

Autoclaved lightweight concrete (ALC), also known as autoclaved aerated concrete (AAC), is a lightweight, precast building material that simultaneously provides structure, insulation. ALC is a unique building material. Because of its cellular nature, it is lightweight, self-insulating, as well as sound and fireproof. ALC products include blocks, wall panels, floor and roof panels, and lintels. Recently, the use of ALC has became increasingly popular. However, ALC have high water absorption, low compressive strength and popout the origin of the low surface strength in its properties. Thus, this study is to improve the fundamental strength by controls of increasing of admixtures and chemical reactants. Admixtures make use of meta kaolin and silica fume, chemical reactants make use of sodium silicate and sodium hydroxide. From the test result, the ALC using admixtures and chemical reactants have a good fundamental properties compared with plain ALC. These good fundamental properties is caused by the admixtures and chemical reactants of ALC by the reason of the micro filling effect and chemical binding of C-S-H gel, tobermolite and quartz.

• Bulletin of the Korean Chemical Society
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• 제32권3호
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• pp.1017-1021
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• 2011

Two new benzimidazolyl-containing complexes have been synthesized by reactions of $Cu^{II}$ salts and 1,2-bis(benzimidazolyl) benzene ($H_2bbbz$) with two different dicarboxylate ligands. When phthalate acid ($H_2pt$) was employed as secondary ligand, a 0D molecular complex Cu$(H_2bbbz)(pt){\cdot}(H_2pt)$ (1)was furnished and when the secondary ligand was instead by a linear bridging ligand of terephthalic acid ($H_2tp$) a 1D zipper-like coordination polymer $[Cu(H_2bbbz)(tp){\cdot}2(C_2H_5OH){\cdot}H_2O]_n$ (2) was obtained, suggesting the structure-direction effect of the secondary dicarbxylate ligand. The preliminary investigation on the spectral properties of the complexes was also presented.

• Bulletin of the Korean Chemical Society
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• 제35권4호
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• pp.1043-1049
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• 2014

Density functional theory (DFT) calculations at the B3LYP/6-31G(d,p) theoretical level were performed for two novel explosives (compounds B and C) based on the guanidine-fused bicyclic skeleton $C_4N_6H_8$ (A). The heats of formation (HOFs) were calculated via isodesmic reaction. The detonation properties were evaluated by using the Kamlet-Jacobs equations. The bond dissociation energies (BDEs) for the thermolysis initiation bond were also analyzed to investigate the thermal stability. The results show that the compounds have high positive HOF values (B, 1064.68 $kJ{\cdot}mol^{-1}$; C, 724.02 $kJ{\cdot}mol^{-1}$), high detonation properties (${\rho}$, D and P values of 2.04 $g{\cdot}cm^{-3}$ and 2.21 $g{\cdot}cm^{-3}$, 9.98 $km{\cdot}s^{-1}$ and 10.99 $km{\cdot}s^{-1}$, 46.44 GPa and 59.91 Gpa, respectively) and meet the basic stability requirement. Additionally, feasible synthetic routes of the these high energy density compounds (HEDCs) were also proposed via retrosynthetic analysis.