• Journal of the Korean Wood Science and Technology
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• v.42 no.5
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• pp.605-614
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• 2014

This study investigated microstructural changes of cured urea-formaldehyde (UF) resins mixed with aqueous rubber latex emulsion after intentional acid etching. Transmission electron microscopy (TEM) was used in order to better understand a hydrolytic degradation process of cured UF resins responsible for the formaldehyde emission from wood-based composite panels. A liquid UF resin with a formaldehyde to urea (F/U) molar ratio 1.0 was mixed with a rubber latex emulsion at three different mixing mass ratios (UF resin to latex = 30:70, 50:50, and 70:30). The rate of curing of the liquid modified UF resins decreased with an increase of the rubber latex proportion as determined by differential scanning calorimetry (DSC) measurement. Ultrathin sections of modified and cured UF resin films were exposed to hydrochloric acid etching in order to mimic a certain hydrolytic degradation. TEM observation showed spherical particles and various cavities in the cured UF resins after the acid etching, indicating that the acid etching had hydrolytically degraded some part of the cured UF resin by acid hydrolysis, also showing spherical particles of cured UF resin dispersed in the latex matrix. These results suggested that spherical structures of cured UF resin might play an important role in hindering the hydrolysis degradation of cured UF resin.

• Journal of Environmental Science International
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• v.11 no.3
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• pp.263-269
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• 2002

This study was conducted to know the removal characteristics of ammonia nitrogen by commercially available cation exchange resins. Eight acidic cation exchange resins were investigated in batch reactors. Among them, the most effective resin for ammonia removal in solution was PK228, which was a strong acidic resin of $Na^{+}$ type. PK228 was compared with activated carbon and natural zeolite. The effects of cation exchange capacity, ammonia concentration, resin amount, temperature and pH on ammonia removal by PK228 were investigated in batch reactor, and the effect of effluent velocity in continuous column reactor. Strong acidic resins of porous type were more effective than week acidic resins or gel type resins for ammonia removal in solution. PK228 was more effective than activated carbon and natural zeolite for ammonia removal in batch reactor. With increasing initial ammonia concentration, the amount of ammonia removed by PK228 increased, but the proportion of removed ammonia to initial ammonia concentration decreased. The effect or temperature on ammonia removal by PK228 was very slight. The ammonia removal to acidic solution was more effective than that at basic solution. With decreasing effluent velocity of solution through column, breakthrough point extended, and ammonia removal capacity increased.d.

• Journal of Technologic Dentistry
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• v.35 no.4
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• pp.333-341
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• 2013

Purpose: The purpose of this study was to evaluate the flexural strength of indirect composite resins with different polymerization conditions. Methods: Ten specimens ($2mm{\times}2mm{\times}25mm$) of each composite resins (Tescera (T), Gradia (S) and Sinfony (S)) were fabricated by two polymerization methods : manufacturers's and light heat pressure. Composite resins polymerized by manufacturers's method and light heat pressure served as control (TS, GS and SS) and experimental groups (TE, GE and SE), respectively. The composite resins were tested for flexural strength and the surface of composite resins were observed with scanning electron microscope (SEM) under X1,000 magnification. Results: The flexural strength values of cured composite resin decreased in the following order: TE (195.4MPa), TS (179.8MPa), GE (169.9MPa), SE (137.7MPa), SS (111.1MPa) and GS (100.9MPa) groups. Conclusion: The flexural strength values between the control and the experimental groups were not significantly different although experimental groups showed higher flexural strength values than control groups.

• Journal of Technologic Dentistry
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• v.35 no.4
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• pp.313-320
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• 2013

Purpose: The purpose of this study was to know the physical properties of UDMA dental composite resins containing two photosensitizers, PD, DA, as a photosensitizer instead of CQ. We want to know Remaining Double Bond(RDB) of UDMA unfilled resin and diametral tensile strength and flexural strength of composite resin containing PD and DA were compared with those of CQ, most widely used photosensitizer for dental composite resins. Methods: The RDB of UDMA studied by FT-IR spectroscopy increased with irradiation time. The composite resins were tested for their physical properties. The dental composite resins were made with UDMA as a monomer, silanized silica as filler, N,N-dimethylaminoethyl methacrylate (DAEM) as amine initiator, and one of the two kinds of new photosensitizers. Results: The relative RDB of UDMA was in the order: DA > CQ > PD but the physical properties of the composite resins show PD and DA with higher results compared with that containing CQ. The reason for the results is that PD and DA serve not only as a photosensitizer but also as a photo-crosslinking agent. Conclusion: PD and DA show as effective photosensizers, suitable for UDMA dental composite resin compare with a higher efficiency than CQ.

• Restorative Dentistry and Endodontics
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• v.17 no.1
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• pp.126-133
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• 1992

Tooth colored resin restorative materials are widely used in anterior teeth restorations. The color instability of resin was the main cause of failure in resin restorations. The purpose of this study was to investigate color stability and microhardness of serval visible light curing resins. Colorimetric measurements(Tokyo Denshoku Co., Japan) and microhardness tests(Matusuzawa, MXT 70, Japan) were made on six composite resins before and after controlled immersion treatments. The six composite resins were BIS - FILM(BISCO, USA), Durafill(Kulzer, Germany), Helioprogess(VIVADENT, Germany), Palfique(TOKUYAMA SODA, Japan), Silux(3M, USA), Photoclearfil(KURARAY, Japen). Six light curing resins showed significant color change after 2 weeks. Palfique exhibited the hightest $dE^*$ values and Helio progress presented the lowest $dE^*$ values. Photoclearfil showed the highest microhardness value. Durafill and Helio progress showed lower microhardness values. Microhardness values were decreased after 8 weeks in Bisfil, Palfique light, and Photoclearfil.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.462-463
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• 2007

SF6 widely used as insulating gas is rising as the environment problem. For decreasing this greenhouse gas, electrical breakdown characteristics of composite insulation composed of epoxy resins with N2, air are studied in non-uniform field. The gap of needle to plane was 3mm, 5mm. The pressure of air, nitrogen was varied within the range of 0.1~0.6MPa. The thickness of a needle is 1mm and the curvature radius of the end of needle is 100um. The diameter of a plane made of the stainless steel is 50mm. As a result of the experiment, the breakdown voltage is increased about 3 times when epoxy resins is composited. The thickness of epoxy resins filled opposite to electrode concentrated electric field weakly influences on breakdown voltage.

• Journal of the Korean Wood Science and Technology
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• v.47 no.2
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• pp.200-209
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• 2019

To improve the water resistance of melamine-urea-formaldehyde (MUF) resins, different levels of blocked polymeric 4,4 diphenyl methane diisocyanate (B-pMDI) were blended with MUF resins to prepare B-pMDI/MUF hybrid adhesives, and their adhesion performances were evaluated for the surface lamination of fancy veneer on plywood. FT-IR spectra showed that the de-blocked -NCO groups reacted with the -OH of hydroxymethyl groups of the MUF resins to form urethane bonds at 2% B-pMDI/MUF, which was detected before and after their hydrolysis. The mass loss after the hydrolysis consistently decreased as the B-pMDI level increased, indicating an improvement in the water resistance. As the B-pMDI level increased, the activation energy of hybrid adhesives decreased, which improved the reactivity of the hybrid adhesives. Additionally, the water resistance improvement of the hybrid adhesives increased the tensile shear strength of the surface laminated plywood in semi-water proof and water-proof by 23 % and 8 %, respectively, at 2% B-pMDI level. This was likely due to the urethane linkages in the hybrid adhesives. However, the formaldehyde emission from plywood panels bonded with the hybrid adhesives increased in the dry state, indicating incomplete curing of the hybrid adhesives.

• Journal of Technologic Dentistry
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• v.42 no.4
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• pp.341-347
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• 2020

Purpose: This study aimed to evaluate the effect of post-curing method on the flexural strength of provisional restorative resins produced by a digital light processing printer. Methods: A total of 20 specimens were produced, with a length of 64 mm, width of 10 mm, and thickness of 3.3 mm using a digital light processing printer. Two types of provisional restorative resins made with different post-curing methods were investigated and divided into conventional and vacuum groups. For the flexural strength test, each group was prepared by each method according to ISO 10477, and the flexural strength was measured with a universal testing machine. For statistical analysis, data were analyzed by independent t-test and Mann-Whitney U test. Results: The flexural strengths of the conventional and vacuum groups were 151.89 MPa and 131.94 MPa, respectively, showing a statistically significant difference (p<0.05). Conclusion: Within the limitation of this study, provisional restorative resins produced with vacuum demonstrated lower flexural strength than those produced with conventional postcuring method.

• Proceedings of the KIEE Conference
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• 1990.07a
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• pp.275-278
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• 1990

This study investigated electrical characteristics of solid and liquid epoxy rosins by measuring dielectric breakdown and dielectric loss when epoxy resins were exposed to a mixing cure, i.e., Fusion Blend Method. It was found that mixing epoxy resins were superior to dielectric breakdown and has shorter curing time compare with those of pure liquid epoxy resins.

• Proceedings of the KACD Conference
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• 2001.11a
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• pp.585.1-585
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• 2001

The use of flowable composite resins as liners in class II packable composite resins has been suggested by some manufacturers. However, the contributions of this technique are unproven. Objectives: The aim of this study was to compare the gingival microleakage in class II packable composite restorations with or without the use of flowable composite resins as liners.. Method: Slot cavities were prepared on both proximals of 80 extracted human molars and randomly assigned to 8 groups of 20 each.(중략)