• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2009년도 추계 학술논문 발표대회
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• pp.55-59
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• 2009

The epoxy resin without hardener can harden by a ring-opening reaction in the presence of the alkalies produced by the hydration of cement in epoxy-modified mortars and concretes. This paper investigates the effect of curing conditions on the strength improvement of polymer-modified mortars using bisphenol A-type epoxy resin without hardener. The polymer-modified mortars using epoxy resin are prepared with various polymer-cement ratios, and subjected to ideal, water, dry and heat cures. In the heat cure, the epoxy-modified mortars are sealed or unsealed with a PVDC (polyvinylidene chloride) film. The epoxy-modified mortars are tested for flexural and compressive strengths at desired curing methods. The microstructures of the epoxy-modified mortars are also observed by scanning electron microscope. The effects of curing conditions on the strength development of the epoxy-modified mortars are examined. From the test results, the marked effectiveness of the heat cure under the PVDC film sealing against the development of the strength of the epoxy-modified mortar without the hardener is recognized. The flexural and compressive strengths of 7-day-90℃ heat-cured, PVDC film-sealed epoxy-modified mortars without hardener reach 7 to 17MPa and 24 to 44MPa respectively, and are two to three times of Unmodified mortar. Such high strength development of the epoxy-modified mortars may be achieved by the dense microstructure formation by cement hydrates and the hardening of the epoxy resin in the mortars.

• Design & Manufacturing
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• 제17권1호
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• pp.1-5
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• 2023

In multi-material injection molding, since two or more materials with different process conditions are used, it is essential to maximize process efficiency by operating the cooling or heating system to a minimum. In this study, Liquid silicone rubber (LSR) that can be cured at a low temperature suitable for the multi-material injection molding was selected and the cure behavior according to the process conditions was analyzed through differential scanning calorimetry (DSC). Dynamic measurement results of DSC with different heating rate were obtained, and through this, the total heat of reaction when the LSR was completely cured was calculated. Isothermal measurement results of DSC were derived for 60 minutes at each temperature from 80 ℃ to 110 ℃ at 10 ℃ intervals, and the final degree of cure at each temperature was calculated based on the total heat of reaction identified from the Dynamic DSC measurement results. As the result, it was found that when the temperature is lowered, the curing start time and the time required for the curing reaction increase, but at a temperature of 90 ℃ or higher, LSR can secure a degree of cure of 80% or more. However, at 80 ℃., it was found that not only had a relatively low degree of curing of about 60%, but also significantly increased the curing start time. In addition, in the case of 110 ℃, the parameters were derived from experimental result using the Kamal kinetic model.

• Design & Manufacturing
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• 제8권2호
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• pp.46-49
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• 2014

Silicone is recently used for LED chip lense due to its good thermal stability and optical transmittance. In order to predict residual stress which causes optical briefringence and mechanical warpage of silicone, finite element analysis was conducted for curing process during silicone molding. For analysis of curing process, a dynamic cure kinetics model was derived based on the differential scanning calorimetry(DSC) test and applied to the material properties for finite element analysis. Finite element simulation result showed that the slow cure reduced abrupt reaction heat and it was predicted decrease of the residual stress.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2012년도 추계 학술논문 발표대회
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• pp.255-257
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• 2012

Epoxy resin without any hardener can harden in the presence of hydroxide ions in cement mortars and concretes at ambient temperature. The purpose of present study is to examine the hardening properties of hardener-free epoxy-modified mortars by curing conditions. The hardener-free epoxy-modified mortars using diglycidyl ether of A epoxy resin are prepared with various polymer-cement ratios, and subjected to initial moist/dry curing, initial steam(90℃) curing, initial steam/heat(80℃, 100℃) curing.As a result, degree of hardening of epoxy resin in initial moist/dry cured, initial steam cured and initial steam/heat(80℃) cured hardener-free epoxy-modified mortars is decreased with increasing polymer-cement ratio. However, it is markedly improved with additional dry-curing periods. On the other hand, regardless of the polymer-cement ratio and dry curing periods, degree of hardening of hardener-free epoxy-modified mortars with initial steam/heat(100℃) cure is over 95%.

• Composites Research
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• 제27권3호
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• pp.90-95
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• 2014

복합재료의 경화 시 발생하는 수축 변형률은 복합재료 구조물 내에 잔류응력을 발생시키며 이러한 잔류응력은 spring-in, spring-out, warpage와 같은 구조물 변형의 원인이 된다. 본 연구에서는 Hexcel사의 "Hexply M21EV/34%/UD268NFS/IMA-12K" prepreg를 사용하였다. 시험편의 경화에 따른 cure shrinkage 변화를 DSC(differential scanning calorimetry)와 TMA(thermomechanical analyzer)를 이용하여 측정하였다. 수지의 수축률은 $140{\sim}240^{\circ}C$ 구간에서 $20^{\circ}C$ 간격으로 질소 분위기에서 측정하였다. 경화도는 dynamic과 isothermal DSC scanning을 통하여 측정된 반응열을 이용하여 산출하였으며, DSC 시험은 Argon 분위기에서 수행하였다. 시험결과, 열경화성 수지는 27~80% 경화도에서 급격한 수축이 일어났으며, 경화온도가 높을수록 더 낮은 경화도에서 수축이 시작되는 것을 알 수 있었다.

• Composites Research
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• 제33권2호
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• pp.44-49
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• 2020

본 연구에서는 시차주사 열량계(differential scanning calorimetry, DSC)를 이용하여 진공백 성형 공정에 사용되는 탄소 섬유 프리프레그의 경화 거동을 연구하였다. 프리프레그를 이용한 동적주사 시험을 통해 전체 발열량(ΔH_total = 537.1 J/g)을 측정하였고, 130℃~180℃에서 등온주사 시험을 실시하였다. 등온주사 시험의 결과는 온도가 올라감에 따라 발열 반응이 증가되는 것을 확인하였다. 시험 결과를 토대로 수지의 경화 거동을 분석하기 위하여 Kratz 모델을 적용하였다. 서로 다른 경화 사이클로 제작된 평판의 경화도를 경화 예측 모델과 실험값을 비교하였다. 경화 예측 모델은 실험값 대비 3.4% 이하의 오차율을 보여 결과가 잘 부합하는 것을 확인하였다.

• Composites Research
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• 제36권5호
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• pp.315-320
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• 2023

오토클레이브를 사용하는 열경화성 탄소 섬유 복합재 성형 공정에서는 설정한 온도 사이클에 따라 내부 온도가 변화한다. 이 온도 변화에 따라 복합재 수지가 경화되며 성형이 진행된다. 이러한 과정에서 수지의 화학 반응으로 열이 발생하며, 이로 인해 오토클레이브 내부 온도와 복합재의 온도가 다를 수 있는 상황이 나타난다. 이전 연구에서는 복합재와 오토클레이브의 온도를 동일하게 가정하고, 성형 후에 발생하는 잔류 응력과 열 변형을 예측하였다. 그러나 잔류 응력과 열 변형은 복합재 온도와 경화도에 따라 영향을 받는 요소이기 때문에, 본 연구는 수지의 화학 반응열을 고려하여 정확한 온도와 경화도 변화를 계산하는 열화학 모델 해석 기법을 검증하였다. 또한, 이 모델이 다른 두께에서도 이와 같은 경향성을 나타내는지 확인하기 위해 두께별 케이스 연구를 하였다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1992년도 춘계학술대회 논문집 92
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• pp.177-200
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• 1992

A thermo-viscoplastic finite element program was developed to analyze the compression molding of SMC process. Deformation of the material was modelled by using the flow-rule. Heat balance during the process was coupled to the deformation. In the cure study, a kinetic model was adopted to describe the cure behavior. The numerical kinetic model was integrated with the thermo-viscoplastic numerical analysis by adding heat generation due to the chemical reaction of the workpiece in the heat transfer analysis. The integrated finite element program can simulate a whole sequential molding process including deformation, heat transfer, and chemical reaction. A practical SMC molding process with T-shaped substructure was simulated. The simulated results showed good agreements with experiments.

• 공업화학
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• 제16권6호
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• pp.842-847
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• 2005

니트릴고무(NBR) 신재와 작업현장에서 나온 스크랩을 고온 전단분쇄기술로 분말화한 재료(재생 NBR)를 다양한 혼합비로 블렌드물을 제조하고, 재생재료의 함량에 따른 블렌드물의 가황 거동, 물리적 특성의 변화를 조사하였다. 또한, 열 및 각종 유체에 대한 각 블렌드물의 저항성을 물리적 방법으로 조사하였다. 신재 NBR에 고온 전단 분쇄기술로 제조한 재생NBR을 0~50 phr의 함량으로 블렌드하여 가황거동 및 물리적 특성을 측정한 결과, 가황 거동은 점도가 증가하고 스코치 시간은 감소하였으며, 내열 및 유체특성은 향상되었다.

• 한국환경과학회지
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• 제10권1호
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• pp.73-77
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• 2001

This study examined blends of styrene butadiene rubber(SBR) and chloroprene rubber(CR) prepared from an open 2-roll mill following the conventional polymer blend method for a wide range of the blend composition. Rubber vulcanizates were manufactured by hot press and then mechanical properties, heat and ozone resistance of the specimens were examined. Due to the post cure during the aging test, hardness of vulcanizates was increased. It was found that the undesirable characteristics of heat and ozone resistance of pure SBR was significantly improved through the blending of SBR with CR.