• Journal of the korean academy of Pediatric Dentistry
• /
• v.26 no.2
• /
• pp.296-309
• /
• 1999

Autopolymerized resin facilitates a more rapid and easier means for the construction of removable orthodontic appliances than heat cured resin. But many reports reveal that more unreacted monomer is found in autopolymerized resin. It is very important to achieve maximum degree of polymerization because if polymerization is inadequate, high level of unreacted monomer has been shown to adversely affect mechanical and physical properties, and also the question of allergy or toxicity to methylmethacrylate must be considered. The purpose of this study was to compare the degree of polymerization according to curing method and curing time. Five groups were desinged ; Group 1 was polymerizied at room temperature($28^{\circ}C$) ; Group 2 in $28^{\circ}C$ water ; Group 3 in $28^{\circ}C$ water under 30psi pressure ; Group 4 in $43^{\circ}C$ water ; Group 5 in $43^{\circ}C$ water under 30psi pressure for 10 minutes, 1 hour 12 hours, 1 day and 3 days. The degree of polymerization was measured by means of Fourier Transform Infrared spectroscopy. The results were as follows: 1. The degree of polymerization increased constantly in accordance with curing time in all groups and after curing for 10 minutes, Group 1 showed significantly higher degree of polymerization after 12 hours and Group 2, Group 3, Group 4, Group 5 after 1 hour(p<0.05). 2. The degree of polymerization decreased in the order of Group 5, Group 4, Group 3, Group 2, Group 1 except when the curing time was 1 hour and 12 hours(p<0.05). 3. The degree of polymerization of Group 4, Group 5 cured at $43^{\circ}C$ showed significantly higher degree of polymerization than Group 2, Group 3 at $28^{\circ}C$ except when the curing time was 1 day(p<0.05). 4. Among Group 2, Group 3 and Group 4, Group 5, the pressure had no effect on polymerization except when the curing time was 12 hours(p<0.05). 5. Between Group 1 and Group 2, the method of storage had no effect on polymerization except when the curing time was 1 hour(p<0.05).

• Food Science of Animal Resources
• /
• v.32 no.6
• /
• pp.740-748
• /
• 2012

This research was conducted to develop a new approach to Chuncheon Dakgalbi processing by various chicken materials, seasoning (conventional sauce/CS and new approach of seasoning by adding the curing mixture/CSA), and cooking methods. Three chicken breeds (broiler, old broiler and spent laying hen) were divided into five experimental groups: broiler-CS, old broiler-CS, old broiler-CSA, spent laying hen-CS, and spent laying hen-CSA. All samples were stored at $5^{\circ}C$ for 12 d. For sensory evaluation, all samples were cooked with conventional cooking (pan grilling) or high temperature and pressure cooking (at $121^{\circ}C$ with pressure 1.5 $Kg_f/cm^2$ for 30 min). The chicken material analysis showed that the moisture and crude protein content, cooking loss and shear-force of the old broiler and spent laying hen were higher (p<0.05) than those of the current broiler, but the crude ash, crude lipid and WHC were lower (p<0.05). The addition of CSA increased the pH value and reduced the lipid oxidation at the end of storage regardless of chicken breeds (p<0.05). The high temperature and pressure cooking method seemed to increase the taste, smell and overall-acceptability scores of the old broiler and spent laying hen Chuncheon Dakgalbi regardless of the implementation of new approach of seasoning (CSA). In conclusion, an old broiler and spent laying hen can be used as material of Chuncheon Dakgalbi by the application of a new approach of seasoning and cooking method.

• Journal of the Korean Wood Science and Technology
• /
• v.51 no.6
• /
• pp.431-446
• /
• 2023

Samama wood (Anthocephalus macrophyllus (Roxb) Havil) is a fast-growing and lesser-utilized wood species that has inferior properties; therefore, its quality needs to be improved. This research aimed to determine the effect of citric acid impregnation at high curing temperatures on the dimensional stability and mechanical properties of wood. Citric acid solution with 10% concentration (w/w) was impregnated into wood samples by vacuum-pressure method (-0.5 cmHg, 30 min; 0.7 MPa, 3 h), followed by curing process at 140℃, 160℃, and 180℃ of temperature for 1 h. In comparison, the other wood samples were heat treated at the same temperatures and time. The results showed that the increase in curing and heat temperatures for both treatments were directly proportional to the dimensional stability, but inversely proportional to the mechanical properties. Citric acid impregnated had higher density, dimensional stability, and mechanical properties, except for modulus of rupture, than that of heat treatment. The optimum temperature is suggested at 160℃ in both treatments.

• Korean Journal of Materials Research
• /
• v.30 no.9
• /
• pp.489-494
• /
• 2020

SiC is a material with excellent strength, heat resistance, and corrosion resistance. It is generally used as a material for SiC invertors, semiconductor susceptors, edge rings, MOCVD susceptors, and mechanical bearings. Recently, SiC single crystals for LED are expected to be a new market application. In addition, SiC is also used as a heating element applied directly to electrical energy. Research in this study has focused on the manufacture of heating elements that can raise the temperature in a short time by irradiating SiC-I₂ with microwaves with polarization difference, instead of applying electric energy directly to increase the convenience and efficiency. In this experiment, Polydimethylsilane (PDMS) with 1,2 wt% of iodine is synthesized under high temperature and pressure using an autoclave. The synthesized Polycarbosilane (PCS) is heat treated in an argon gas atmosphere after curing process. The experimental results obtain resonance peaks using FT-IR and UV-Visible, and the crystal structure is measured by XRD. Also, the heat-generating characteristics are determined in the frequency band of 2.45 GHz after heat treatment in an air atmosphere furnace.

• Journal of the korean academy of Pediatric Dentistry
• /
• v.35 no.3
• /
• pp.477-486
• /
• 2008

Acrylic resin is widely used in dental practice. However, the residual monomer in acrylic resin could act as a negative biocompatability on human body. The aim of this study was to evaluate the amount of the monomer elution from polymerized orthodontic acrylic resin. Orthodontic acrylic resin was used in the study. The curing condition of the resin was controlled by temperature, pressure, aquatic and atmospheric environment. The duration and amount of monomer elution and timedependent plot was recorded by high performance liquid chromatography. The result showed that the only monomer eluted from the resin was methyl methacrylic acid. And the amount of the monomer elution has diminished considerably by time progress especially within 24 hours. Furthermore, elution of the residual monomer was significantly lower in group of pressure, moisture and elevated temperature than control (p<.05). According to this study, it was thought that the elution of residual monomer might be influenced by curing environment.

• Composites Research
• /
• v.34 no.5
• /
• pp.269-276
• /
• 2021

PCM (Prepreg Compression Molding) process is a high-speed molding technology that can manufacture high-quality CFRP (Carbon Fiber Reinforced Plastic) parts. Compared to the autoclave process, it generates less waste and can significantly reduce cycle time, so various studies are being conducted in the aerospace and automobile industries. In this study, in order to improve the quality of the PCM process, a molding method was developed to increase the compression pressure of the press step by step according to the curing behavior of the prepreg. It was confirmed that this multi-stage compression molding technology is a good means to produce high-quality CFRP products and shorten cycle times. And, the laminated prepreg at room temperature was immediately put into the mold and preheated and molded at the same time, so that it could be molded without a separate preheating process. In addition, as a result of applying the same process conditions optimized for flat plate molding to three-dimensional shapes, a product similar to a flat plate in appearance could be made without the process of establishing process conditions.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.9 no.6
• /
• pp.1775-1781
• /
• 2008

The effects of the type of curing agent on the swelling of the natural rubber(NR) sponge applicable to the self-sealing layer of a helicopter fuel tank were investigated. The curing systems employed were peroxide and mixed ones of sulfur and peroxide. The NR compounds were prepared in a kneader and a roll-mill. The compounds were partially cured in a press at high pressure and subsequently cured fully with expansion in another press at atmospheric pressure. The apparent density of the NR sponge was measured and the cell structure was observed with scanning electron microscopy. The swelling experiments were performed at room temperature using toluene, iso-octane, and an aircraft fuel as a solvent. More rapid volume swelling of the NR sponge cured by peroxide was achieved than cured by sulfur and peroxide with similar amount of curing agent added in rubber compounds. The apparent density and cell structure of the sponge were extremely sensitive to the amount of peroxide, which influences again the swelling behavior of the NR sponge. It is important to control properly two reactions of decomposition of foaming agent and crosslinking of NR in the mold to obtain rapid swelling of the NR sponge on contact of the fuel.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.04a
• /
• pp.441-444
• /
• 2008

Ultra high performance concrete (UHPC) in this study is composed of sand, cement, silica fume, siliceous powder, superplasticizer and steel fiber. UHPC is composed of fine mineral particles below 0.5mm in diameter. In general, siliceous powder improves the mechanical properties of concrete by physical and chemical effect. Physical effect is related with filling interior voids which weaken the mechanical properties and chemical effect with reaction of $SiO_2$ with cement hydrates in a condition of high temperature and pressure. We evaluated the effect of siliceous powder's particle size on the mechanical properties of ultra high performance concrete in air pressure and $90^{\circ}C$ steam curing condition. siliceous powder's particle size in this study is in the range of $2{\mu}m$ to $26{\mu}m$. Fluidity in a fresh concrete, compressive strength, ultimate strain, elastic modulus and flexural strength in a hardened concrete was evaluated. We could find out that the smaller siliceous powder's particle size is, the better the fluidity and strength properties.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2012.05a
• /
• pp.41-42
• /
• 2012

High temperature / high pressure spray equipment using a conventional method, unlike spray polyurea adjustable pot life and yellowing caused by UV light and chemicals do not occur, or discoloration of Self-Leveling Type of rugged hand-polyurea resin for technology development is underway. This new concept of polyurea resin roller, brush, airless spray, and they installed easily using the unfamiliar labor, and curing time of approximately four hours to gain control of the glass because it is Pot. Construction, but does not like the spray polyurea resin, compared to the existing degradation of the adhesion strength is concerned. In this study, Self-Leveling Type Manual of polyurea resin adhesion strength of target deterioration Let's minimize problems by reviewing existing domestic and infrastructure long-term durability for long life of the facility is to obtain.

• Applied Chemistry for Engineering
• /
• v.32 no.4
• /
• pp.449-455
• /
• 2021

Composite materials are substances that are configured to have excellent physical properties by combining the properties of a single substance, and are in the limelight as materials that exceed the performance of metals and polymers. However, it has the disadvantages of long cycle time and high unit price, and much research is being performed to overcome these disadvantages. In this study, we developed an epoxy resin curing agent that can shorten the time required for mass production of composite materials, and tried to expand the applicability of objections by imparting flame retardancy. The epoxy resin used as a basic substance utilized two types of bisphenol F and resorcinol structure, which was further modified using 9,10-dihydro-9-oxa-10-phosphaphenantrene-10-oxide (DOPO) to impart flame retardancy. Triethylphosphate (TEP) and bis [(5-ethyl-2-methyl-1,3,2-dioxaphosphorinan-5-yl)methyl] methyl phosphonate P,P'-dioxide (FR-001) were used as additives, seven kinds of compositions were blended, thermal characteristics (gelation time, glass transition temperature) and flame retardant performance were evaluated. We successfully developed an epoxy matrix that can be applied to high pressure resin transfer molding (HP-RTM) process.