• Macromolecular Research
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• 제17권11호
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• pp.856-862
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• 2009

This study examined the effects of liquid and solid additives on the morphological, mechanical and thermal insulating properties of rigid polyurethane foams (PUFs). The PUFs synthesized with tetramethylsilane (TEMS) as a liquid-type additive showed a smaller average cell size and lower thermal conductivity than those with the aerosil 200 and clay 30B as solid-type additives. When TEMS was added, the average cell size of the PUF became more uniform and finer due to the reduced surface tension of the polymer solution, which increased the nucleation rate and number of bubbles produced and reduced cell size. The PUFs with TEMS showed the highest closed cell contents among the PUFs prepared using TEMS, aerosil 200 and clay 30B. This suggests that the insulation properties of PUF can be determined by both the size of the cell structure and the amount of closed cell contents in the system. The compression and flexural strengths of the PUF increased slightly when the aerosil 200, clay 30B and TEMS were added compared those of the neat PUF. The reaction profiles of the PUFs showed a similar gel and tack tree time with the reaction time among the PUFs synthesized with three different additives and neat PUF. This suggests that the nucleating additives used in this study do not affect the bubble growth of the chemical reaction, and the additives may act as nucleating agents during the formation of PUF. From the above results of the cell size, thermal conductivity, closed cell contents and reaction profile of the PUFs, liquid-type nucleating agent, such as TEMS, is more effective in decreasing the thermal conductivity of the PUF than solid-type nucleating agent, such as aerosil 200 and clay 30B.

• 한국결정성장학회지
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• 제30권4호
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• pp.136-142
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• 2020

아연결정유약은 결정생성의 요건을 맞추기 위해서는 조핵제의 생성 - 조핵제의 양 조절 - 결정의 성장 등의 까다로운 소성과정을 거쳐야 한다. 소성온도 폭이 좁고 아연의 상태에 따라 결정에 영향을 미치는 등 사용이 용이하지 않다. 아연결정생성을 촉진시켜 이를 Frit화하여 폭넓은 소성조건에서 안정적으로 재결정화도록 하여 상용유약으로 유약을 개발할 수 있다.

• 한국세라믹학회지
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• 제29권3호
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• pp.223-231
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• 1992

CaO and ZnO were added to Al2O3-SiO2 binary system respectively as flux, then ZrO2 and TiO2 were applied as nucleating agent to these CaO-Al2O3-SiO2 and ZnO-Al2O3-SiO2 ternary system glass. The transparency could not be kept in CaO-Al2O3-SiO2 system glass, whereas the transparent glass-ceramics were prepared in ZnO-Al2O3-SiO2 system glass containing ZrO2 as the nucleating agent. At this time the optimum heating temperatures for the nucleation and the crystal growth were 78$0^{\circ}C$ and 97$0^{\circ}C$. The sizes of the precipitated crystals in the transparent glass-ceramics were below 0.1 ${\mu}{\textrm}{m}$, and their light transmissibilities were more than 80%.

• 한국세라믹학회지
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• 제30권12호
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• pp.1054-1058
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• 1993

The effects of TiO2 addition as a nucleating agent on the cordierite glass-ceramics were investigated. The glass compositiion was stoichiometric cordierite composition of 13.7MgO-34.9Al2O3-51.4SiO2(wt%), and TiO2 as a nucleating agent was added by 5, 10 and 15wt% in addition. The optimum amount of TiO2 addition and appropriate heat treatment schedule were determined by using dilatometer, DTA, XRDA and SEM. The composition containing 10wt% TiO2 was proved to be the best among the investigated compositions. And the optimum heat treatment schedule was 840℃-2h for the nucleation and 1140℃-2h for the crystallization. The properties were as follows. The crystallinity was ∼75%, thermal expansion coefficient 33×10-7/℃(25∼700℃), dielectric constant 7.6(1KHz) and Vicker's hardness 5.1GPa.

• Advances in materials Research
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• 제4권4호
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• pp.207-214
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• 2015

It has been reported in the technical literature that orotic acid can be used in order to induce improved crystallization of biodegradable and biocompatible polymers like poly(L-lactic acid), polyhydroxybutyrate and poly(hydroxybutyrate-co-hydroxyhexaonat). The expected advantage of the changed crystalline structure is a reinforcing effect of the polymers. A lot of papers reported about the application of inorganic and organic agents for acceleration of heterogeneous nucleation. This study reports on an attempt to use orotic acid as appropriate non-toxic nucleating agent for improving mechanical properties of isotactic polypropylene. Special attention is given to demonstrate the effect of nucleation in a typical melt spinning process in order to improve the mechanical properties. The effects were demonstrated using rheology, thermal analysis and tensile testing.

• Composites Research
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• 제36권2호
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• pp.126-131
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• 2023

기존의 상용 플라스틱으로 인한 환경 오염에 대한 우려가 높아지면서 대체 재료로서 생분해성 고분자에 대한 연구가 주목을 받고 있다. 본 연구는 생분해성 열가소성 수지인 폴리 젖산에 유기 핵제의 도입으로 물성 강화 및 100% 생분해 가능한 나노복합재 개발을 목표로 한다. 그에 따라 무기 핵제의 대체재로 친환경 소재인 셀룰로오스 나노섬유를 채택하였다. 폴리 젖산 내 셀룰로오스 나노섬유의 균일한 분산을 위해 동결 건조 방식으로 나노화된 섬유 형상을 유지시켰으며, 이축압출기로 1차 교반을 진행하고, 사출 성형을 통해 이중 교반된 물성 시험용 시편을 제작하였다. 보강된 결정성을 확인하기 위해 시차주사 열량분석법을 사용하였고 1 wt%의 셀룰로오스 나노섬유가 보강재 및 핵제로서 작용하여 냉결정화온도가 약 14℃ 가량 감소하며, 결정화되는 정도 또한 증가한 것을 확인하였다. 본 연구는 기존 생분해성 고분자의 무기 핵제를 유기 나노소재로 대체함으로써 100% 생분해 가능한 친환경 나노복합재 개발하여 강화된 물성의 플라스틱 소재 개발을 위한 친환경적 대안을 제시한다.

• 한국산학기술학회논문지
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• 제16권1호
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• pp.914-920
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• 2015

본 논문에서는 PLA(PolyLactic Acid)의 결정화도 및 결정구조에 대해 연구하였다. PLA는 옥수수 전분으로부터 추출한 Lactic acid로부터 얻어지는 친환경적인 열가소성 플라스틱으로 매립시 미생물에 의해 완전히 분해되는 소재로 각광받고 있지만 열 안정성이 낮고 낮은 결정화도로 인해 높은 기계적 물성이 요구되는 용도에는 부적합한 단점을 가지고 있다. 이 중에서도 낮은 결정화도와 느린 결정화 속도는 사출 성형 공정에서 Cycle time을 증가시키는 요인으로 다른 소재와의 경쟁에 매우 큰 단점으로 나타난다. 본 논문에서는 핵제 및 가소제의 종류와 함량에 따른 결정화도 및 결정화 속도의 변화를 연구함으로써 궁극적으로 사출 성형 공정에서 Cycle time을 개선하고자 하였다.

• 폴리머
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• 제24권4호
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• pp.477-487
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• 2000

Poly(L-lactic acid) (PLLA)/poly($\beta$-hydroxynonanoate) (PHN) 블렌드의 흔화도와 결정화거동을 연구하기 위해 여러 중량 흔합비의 시료를 제조하였다. DSC, XRD 및 편광현미경을 이용하여 PLLA/PHN 블렌드의 열적 성질 및 특성을 연구하였다. PLLA와 PHN은 무정형 영역에서 부분적인 상용성을 가졌으며 PLLA의 결정화도는 PHN이 첨가됨으로 인하여 증가되었다. 그리고 PHN이 첨가됨으로써 PLLA의 T$_{g}$, T$_{c}$, T$_{m}$ 의 이동이 있었다. 편광현미경 분석을 통하여 PLLA 구정의 수는 PHN이 증가할수록 증가하는 것을 알 수 있었다. 이로부터 PHN은 PLLA에 대하여 기핵제의 역할이 있음이 관찰되었다.

• Elastomers and Composites
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• 제51권1호
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• pp.56-62
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• 2016

The isothermal crystallization behaviors of blends of poly(ethylene naphthalate) (PEN) and a thermotropic liquid crystalline polymer (TLCP) were investigated by differential scanning calorimetry (DSC) as functions of crystallization temperature and blend composition. Avrami analyses were applied to obtain information on the crystal growth geometry and the factors controlling the rate of crystallization. The crystallization kinetics of the PEN/TLCP blends followed the Avrami equation up to a high degree of crystallization, regardless of crystallization temperature. The calculated Avrami exponents for PEN/TLCP revealed three-dimensional growth of the crystalline region in each blend. The crystallization rate of each blend increased as the crystallization temperature decreased, and decreased as the TLCP content increased. The crystallization of PEN in the blend was affected by the addition of TLCP, which acts as a nucleating agent.

• Macromolecular Research
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• 제17권8호
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• pp.580-584
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• 2009

The effects of crystallinity and radiation crosslinking on the physical properties of a microporous high density polyethylene (HDPE) film with Millad3988 as a nucleating agent were investigated. The pores of the HDPE film were affected by the crystallinity. The crystallinity of the HDPE films increased with increasing Millad3988 amount up to 0.1 wt% but decreased with further addition. The mechanical characteristics of the HDPE containing Millad3988 films improved with increasing irradiation dose up to 50 kGy, but decreased at 75 kGy due to severe degradation. The thermal shrinkage behavior of the HDPE films decreased with increasing radiation dose up to 50 kGy. The porosity of the stretched HDPEIMillad3988 films after ${\gamma}$-ray radiation increased with increasing y-ray radiation dose up to 50 kGy. The pores of the irradiated films were formed more easily by a stretching due to the formation of a crosslinked structure.