• 폴리머
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• 제27권6호
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• pp.576-582
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• 2003

열가소성 수지인 폴리프로필렌과 나일론 블렌드를 무기나노입자인 몬모릴로나이트와 상용화제 말레산 무수물 폴리프로필렌을 사용하여 복합화한 나노복합재료에 할로젠 계열의 난연제 데카브로모다이페닐옥사이드를 첨가하였을 때의 분산성과 난연특성 및 기계적 특성의 향상에 대해 실험하였다. 고분자 수지의 난연특성과 기계적 특성은 난연제의 첨가뿐만 아니라 나노복합화를 통해서도 향상될 수 있으며, 고분자 수지 내의 나노입자의 분산정도에 따라 매우 큰 차이가 생긴다. 고분자 수지와 무기나노입자 사이의 분산성과 그에 따른 난연특성 및 기계적 특성을 난연제와 무기나노입자의 함량에 .따라 정량적으로 측정하였다 폴리프로필렌/나일론 블렌드를 몬모릴로나이트로 복합화할 때 2회 이상 컴파운딩하면 완전히 분산되는 것을 XRD 결과로 확인하였다. 폴리프로필렌/나일론 블렌드를 복합화하면 나일론의 첨가로 인한 난연성의 저하를 극복할 수 있었으며, 무기나노입자가 완전히 분산되어 있을 때에는 추가적인 난연특성의 향상을 얻었다. 그리고 폴리프로필렌은 나일론의 첨가로 인하여 인장강도와 충격강도가 약간 증가하였으며, 무기나노입자와의 복합화를 통해서 추가적인 기계적 물성의 증가를 관찰하였다. 이로부터 폴리프로필렌의 기계적 물성의 향상을 위해 첨가한 나일론은 난연특성의 저하를 초래하지만 무기나노입자와의 복합화를 통해 난연특성의 향상과 추가적인 기계적 물성의 향상을 동시에 얻을 수 있었다.

• 방사성폐기물학회지
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• 제2권4호
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• pp.231-238
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• 2004

원자력 발전소에서 발생하는 고체 방사성 폐기물인 이온교환수지, 제올라이트, 활성탄 및 슬러지 에 포함된 성분 원소 분석을 위한 산분해 조건을 확립하였다. 방사성 폐기물의 분해 에는 흔합산을 이용한 밀폐형 극초단파 산분해법을 사용하였으며, 제안한 방법에 따른 산분해 후의 용액은 맑고 색이 없는 투명한 상태임을 확인할 수 있었다. 또한, 산분해 과정을 거친 각각의 용액 시료는 ICP-AES와 AAS를 사용하여 분석하였고, 모의 방사성 폐기물에 첨가한 5종의 금속 원소들은 $94{\%}$ 이상의 높은 회수율을 보여주었다. 화학적 특성을 고려하여 제안된 산분해 조건에 의해 용액화된 중${\cdot}$저준위 방사성 폐기물의 성분 원소 분석은 최적의 유리화 기술 개발을 위한 기초 자료로 유용하게 사용될 수 있을 것으로 판단된다.

• 한국표면공학회지
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• 제49권2호
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• pp.218-224
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• 2016

Thermal radiation pastes were prepared by dispersing carbon materials as fillers with a content of 1 weight percent in an acrylic resin. The kind of fillers was as follows; $25{\mu}m$ graphite, $45{\mu}m$ graphite, $15{\mu}m$ carbon nanotube(CNT), a 1:1 mixture of $25{\mu}m$ graphite and $15{\mu}m$ CNT, and a 1:1 mixture of $45{\mu}m$ graphite and $15{\mu}m$ CNT. Thermal emissivity was measured as 0.890 for the samples with graphite only, 0.893 for that with CNT only, and 0.892 for those containing both. After coating prepared pastes on a side of 0.4 mm thick aluminium plate and placing the plate over an opening of a box maintained at $92^{\circ}C$ with the coated side out, the temperatures on the uncoated side of the plates were measured. The samples containing graphite and CNT showed the lowest temperatures. The paste with mixed fillers was coated on the back side of the PCB of an LED module and thermal analysis was carried out using Thermal Transient Tester (T3ster) in a still air box. The thermal resistance of the module with coated PCB was measured as 14.34 K/W whereas that with uncoated PCB was 15.02 K/W. The structure function analysis of T3ster data revealed that the difference between junction and ambient temperatures was $13.8^{\circ}C$ for the coated case and $18.0^{\circ}C$ for the uncoated. From the infrared images of heated LED modules, the hottest-spot temperature of the module with coated PCB was lower than that of the uncoated one for a given period of LED operation.

• 한국재료학회지
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• 제19권7호
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• pp.403-406
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• 2009

The friction characteristics of automotive brake friction materials that contained different ceramic content were investigated. Several kinds of raw materials, such as resin-based binder, reinforcing fiber, friction restraint, abrasive, and filling materials were mixed, pressed, and heated in order to make the brake friction materials. The contents of SiC and $BaSO_4$ changed from 5 vol% to 20 vol%, respectively. In addition to this, the content of $Al_2O_3$ adjusted from 1 vol% to 16 vol%. The surface morphology of the SiC containing sample appeared rough while more debris was observed when the contents of SiC increased. This implies that the SiC containing brake composite was not adequate for the automobile. However, the relatively smooth surface was observed in samples that contained the $Al_2O_3$. But the roughness was low with a content of 11 vol% $Al_2O_3$ compared to the other samples. This is consistent with the abrasive properties of the samples. In the case of $BaSO_4$ containing samples, the smoothes surface was observed in the contents of 15 vol% $BaSO_4$. Thus, it was concluded that the 11 vol% $Al_2O_3$ and 15 vol% $BaSO_4$ containing composite would be the optimum content for the brake composite. Similar to the results of the surface morphology, the abrasion resistance consistently decreased when the content of SiC increased. On the contrary, the sample that contained 11 vol% $Al_2O_3$ and 15 vol% $BaSO_4$ showed the highest abrasion resistance compared to the other samples.

• 폴리머
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• 제33권2호
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• pp.175-182
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• 2009

Isophorone diisocyanate(IPDI)를 이소시아네이트 화합물로 사용하고, poly (tetramethylene glycol)(PTMG)과 polycarbonate diol(PCD)을 혼합한 폴리올을 사용하여 선형 수분산성 폴리우레탄(WPU)을 합성하고, 이들을 필름으로 캐스팅하여 폴리카보네이트(PC) 함량 변화에 따른 기계적 특성과 염색성, 내알칼리성 변화를 분석하였다. WPU 필름에 PC 성분의 함량이 증가함에 따라 인장강도는 증가하고 파단신도는 감소하였으며, 분산염료에 대한 겉보기 염착량이 감소하였지만, 내알칼리성은 영향이 없었다. 합성한 WPU 용액을 PET 섬유 인공피혁용 함침가공제로 사용한 결과, PTMG 만을 폴리올로 사용한 WPU 수지로 처리한 경우보다 인공괴혁의 마찰견뢰도, 일광견뢰도, 내세탁성 등 염색견뢰도를 크게 증가시킬 수 있었다.

• 대한치과재료학회지
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• 제43권1호
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• pp.81-89
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• 2016

The purpose of this study was to evaluate the effect of the experimental and commercial fluoride varnishes on the Vickers hardness of bovine teeth. The experimental fluoride varnishes with 5 wt.% NaF were fabricated using Bis-GMA or rosin as the resin base. The components were mixed with over-head stirrer under warming up in a double boiler for 30 minutes. Four commercial fluoride varnishes (V-varnish, Flor-opal, Cavity shield, Fluor protector) were compared with the experimental fluoride varnishes. Vickers hardness was measured on the labial surface of bovine anterior teeth after applying fluoride varnish on 5th and 30th day. The surface of bovine teeth was observed with a scanning electron microscope before and after applying fluoride varnish and the change of the components on the bovine teeth surface was measured with EDX. In terms of hardness, the experimental rosin-based fluoride varnish showed significantly higher hardness on the 5th and 30th day than the control (bovine teeth without fluoride treatment)(p<0.05). EDX results showed that the fluoride content on the surface of bovine teeth treated with the experimental rosin-based fluoride varnish was highest on the 1st and 10th day. The higher hardness and fluoride content of experimental rosin-based fluoride varnish can be considered to be used as an effective fluoride varnish to prevent dental caries.

• Composites Research
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• 제34권5호
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• pp.277-282
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• 2021

초임계유체 조건은 별도의 환원제와 높은 열처리 공정조건 없이 산화그래핀으로부터 그래핀을 제조할 수 있다. 본 연구에서는 메탄올과 에탄올 용매의 초임계유체 조건에서 산화그래핀을 그래핀으로 변환시키는 공정을 연구하였다. 제조된 그래핀의 구조를 FE-SEM과 XRD를 사용하여 분석하였을 때, 초임계 조건에서 산화그래핀의 환원반응은 다른 변수(농도, 반응시간)보다는 용매의 변화에 더 크게 영향을 받았다. 에탄올 용매의 사용이 메탄올을 사용했을 때보다 환원반응에 더욱 좋은 결과를 보여주었다. 본 연구에서 준비된 그래핀을 20 wt%까지 에폭시수지와 혼합하여 복합수지 조성물을 제조하여, 이 조성물의 열전도특성을 분석하였다. 복합수지조성물의 열전도도는 그래핀의 함량에 비례하여 상승하였고, 에탄올 초임계 용액조건에서 제조된 그래핀이 복합수지조성물의 열전도도에 더 효과적이었다.

• Nuclear Engineering and Technology
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• 제53권12호
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• pp.4158-4165
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• 2021

In this study, tissue equivalency (TE) of a newly developed epoxy-based phantom to 3-5 years child's tissue was investigated in paediatric energy range. Epoxy-based TE-phantoms were produced at different glandular/adipose (G/A) ratios of 17/83%, 31/69%, 36/64% and 10/90%. A procedure was developed in which specific amounts of boron, calcium, magnesium, sulphur compounds are mixed with epoxy resin, together with other minor substitutes. In paediatric energy range of 40-60 kV_p half-value layer (HVL) values were measured and then Hounsfield Units (HU) were determined from Computed Tomography(CT) scans taken in the X-ray energy range of 80-120kV_p. It is found that radiation absorption properties of these phantoms in terms of the measured HVL values related to linear attenuation coefficients (µ) are very well mimicking a 3 years child's soft tissue in case a ratio of 10/90%G/A. Additionally, the HU values of phantoms were determined from the CT scans. The HU = 47.8 ± 4.8 value was found for the epoxy-based phantom produced at a ratio of 10/90%G/A. The obtained HVL and HU values also support the suitability of the new epoxy based-phantom produced at a ratio of 10/90%G/A for a satisfactory mimicking a 3 years child's soft tissue by 5%. Thus they can have a potential use to perform the quality controls of medical X-ray systems and dose optimization studies.

• Journal of Korean Academy of Oral Health
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• 제41권4호
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• pp.231-236
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• 2017

Objectives: The objectives of this study were to investigate the changes in bisphenol A (BPA) concentrations in urine from before to after sealant filling and the relationship between BPA and the number of teeth with sealed surfaces. Methods: Thirty-one children aged 6 and 7 years from three elementary schools in Daegu city who did not have any sealant and resin filling were selected as subjects. Urine samples were collected before and after sealant filling until 24 hours, with informed consent from their caregivers. The BPA concentration in all the collected urine samples was analyzed at Seegene Medical. Statistical analysis was performed using the Friedman test, Scheirer-Ray-Hope test, and the repeated-measures generalized linear mixed model of SPSS version 22.0. Results: The BPA concentrations increased from $3.49-{\mu}g/g$ creatinine before to $4.91-{\mu}g/g$ creatinine 2-3 hours later and to $4.15-{\mu}g/g$ creatinine after 24 hours. The more teeth with sealed surfaces, the higher the BPA concentration in children, but the difference was not statistically significant (P>0.05). Conclusions: The BPA concentrations were highest at 2-3 hours after sealant filling and decreased at 24 hours. Exposure to the sealant appears to have a meaningful correlation with the concentration of BPA in the urine of children.

• 보존과학회지
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• 제34권6호
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• pp.569-580
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• 2018

The possibility of applying poulticing was studied for removing Paraloid B72, a resin used for fixing an earthen mural painting. Five types of poultices were selected from clay and gel types, and acetone, ethanol, and methyl ethyl ketone(MEK) were used as mixed solvents. The possibility of mixing between the poultice and solvent was investigated, and then the spreadability, fluidity, acidity, drying properties, and solubility of the poultices were examined to confirm the characteristics. A poultice agent, which is suitable for applying to a mural painting, was selected and applied to a painting layer sample coated with Paraloid B72. As a result, all painting layers were good condition at under 50% of the solvent. The removal efficiency of Paraloid B72 was more effective when most of the solvents were used at 50%, rather than at 25%. However, it is difficult to mix 50% of MEK and ethanol with the gel-type poultices. When used at 25%, the removal performance was poorer than that at 50%, but the mixing with all the poultices was successful. In addition, the adsorption and removal power of the gel-type poultice were better than those of the clay-type, but the latter was expected to be more suitable in short-time cases due to its high drying speed. The results of this study show that the dissolution performance varies depending on the poultices and solvents. Hence, the poultice and solvent should be selectively applied, considering the fixative of the mural to be removed.