• Resources Recycling
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• v.17 no.6
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• pp.34-42
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• 2008

The properties of sodium silicate solution were surveyed by using the yellow silicomolybdic method, and the formation of silica sol from sodium silicate solution and the growth of silica sol were investigated in this study. The $SiO_2$ content of 2 wt% in sodium silicate solution was proper to oxidize sodium silicate with sulfuric acid. After the removal of sodium ions in sodium silicate solution, the pH of silicate solution had to be controlled above 9 for the stabilization of silicate solution. The condensation between silicic acid species and silica nuclei surfaces has been studied at $20{\sim}80^{\circ}C$ and pH 10 in silicate solutions with silica nuclei. The reaction falls into two kinetics regimes, limited at high silicic acid species concentration by polymerization, but at lower concentration by a process whereby deposited silicic acid species condenses further to silica. The overall condensation is first-order in silicic acid species concentration, proceeded toward to pseudo equilibrium concentration, $C_x$, rather than the solubility of amorphous silica. The heat of solution of amorphous silica was 3.34 kcal/mol and exhibits an Arrhenius temperature dependence with an apparent activation energy of 3.16 kcal/mol in the range of $20{\sim}80^{\circ}C$.

• Applied Chemistry for Engineering
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• v.31 no.4
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• pp.383-389
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• 2020

Mesoporous silica solid catalysts modified with sulfonic acid were prepared for cationic ring-opening polymerization of octamethylcyclotetrasiloxane (D₄). Two sets of MCM-41 (1.7 and 2.8 nm) and SBA-15 (8.1 and 15.9 nm) with different pore sizes were used as catalyst supports. The surface of silica materials was modified with (3-mercaptopropyl)trimethoxysilane by silylation reaction and oxidized to sulfonic acid. The structures of the prepared catalysts were examined by X-ray diffraction and nitrogen adsorption-desorption. The pore size, specific surface area, and pore volume of the modified solid catalysts decreased slightly. In addition, the modification of the sulfonic acid on the silica surface was confirmed by using infrared spectroscopy and nuclear magnetic resonance spectroscopy. To observe the effect of the particle size on the catalytic activity, it was observed with a scanning electron microscope. The catalysts were used to synthesize PDMS through a ring-opening polymerization of D₄, and the conversion and polymerization rate of the polymerization reaction depended on the pore size, specific surface area, particle size, and particle agglomeration of the catalysts. In order for the polymerization rate, the catalyst prepared with SBA-15 of 8.1 nm pore size had the fastest reaction rate and showed the best catalytic activity.

• Polymer(Korea)
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• v.24 no.5
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• pp.621-628
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• 2000

Microporous polypropylene (PP) membranes have the high chemical and corrosion resistance, the good mechanical properties and the thermal stability under high temperatures, but its application is restricted within narrow limits due to hydrophobicity of membranes. In order to impart permanent hydrophilicity to the PP microfiltration membrane, the radiation-induced graft of 2-hydroxyethyl methacrylate (HEMA) and acrylic acid (AAc) containing hydrophilic functional group onto the membrane has been studied. The effect of graft conditions such as reaction time, total radiation dose, reaction temperatures, acid compositions on graft yield was investigated. Modified PP membranes were shown to cause an increase in the gas flux. Oil emulsion permeation flux of both original PP membrane and modified PP membrane was examined.

• Polymer(Korea)
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• v.29 no.1
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• pp.14-18
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• 2005

Nylons were synthesized by anionic polymerization of ${\varepsilon}$--caprolactam while varying the content of catalyst. Polymerization rates, molecular weights, mechanical properities and frictional properties of the nylons were investigated. As the ratio of catalyst to initiator was increased up to 1.0%, the polymerization rate, conversion and molecular weight were found to increase, and mechanical properties except impact strength were improved. Frictional properties were affected mainly by tensile strength and hardness. According to the study on the friction coefficient, product of stress (P) and velocity (V), PV limit, and abrasive wear rate, nylon synthesized at 1.0% of the ratio of catalyst to initiator showed the best performance for sliding machine elements.

• Proceedings of the KAIS Fall Conference
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• 2010.11a
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• pp.474-477
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• 2010

최근 디지털 장비의 발전에 발맞추어 고속, 고화질의 컬러 문서가 요구됨에 따라 레이저 프린터의 보급 또한 급속도로 성장하고 있는 실정이다. 토너는 고속, 고화질의 컬러 문서 인쇄에 가장 중요한 역할을 하는 것으로, 크게 분쇄법과 중합법에 의해 제조 되고 있다. 그러나 그 중 분쇄법 토너는 근본적으로 해결되지 않는 문제점들이 있다. 즉, 중합된 수지를 사용함으로 인한 단가상승과 수지와 내첨제를 용융혼합하는 과정에서의 분산의 한계성, 그리고 인쇄 품질의 좋지 않은 것이 그 대표적인 예이다. 이에 본 실험에서는 고속, 고화질의 컬러 프린터에 적합한 중합법에 의한 토너 제조시 하이드록시아파타이트가 토너 제조에 미치는 영향에 대해서 연구하였다. Ca/P의 몰비에 따라 제조된 하이드록시아파타이트가 토너의 입자형성에 크게 영향을 주었으며, 이에 따라 토너의 물성에도 영향을 주는 것으로 나타났다. 또한 pH에 따라서도 토너중합에 많은 영향을 주는 것으로 나타났다. 토너 입자 형성에 적절한 Ca/P의 몰비 및 pH가 존재 하며, 이를 최적으로 조절하면 양질의 토너를 제조 할 수 있을 것으로 판단된다.

• Journal of the Korean Chemical Society
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• v.21 no.2
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• pp.132-138
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• 1977

Anionic polymerization of ${\varepsilon}$-caprolactam via $SO_2$/KOH catalysis was attempted in order to find an optimal reaction condition and physical properties of the polymers. The yield of conversion was relatively low at low temperature and high at high temperature between $150^{\circ}C\;to\;180^{\circ}C$ regardless of $SO_2$/KOH mole ratio in polymerization of ${\varepsilon}$-caprolactam.The inherent viscosity of nylon 6 obtained via $SO_2$/KOH catalysis was 1.2∼2.7. The kinetic equation for the $SO_2$/KOH catalyzed polymerization has been derived and experimentally verified.

• Restorative Dentistry and Endodontics
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• v.33 no.5
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• pp.428-434
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• 2008

The purpose of this study was to compare the microtensile bond strength in Class I cavities associated with different light curing modes of same light energy density. Occlusal enamel was removed to expose a flat dentin surface and twenty box-shaped Class I cavities were prepared in dentin. Single Bond (3M Dental product) was applied and Z 250 was inserted using bulk technique. The composite was light-cured using one of four techniques, pulse delay (PD group), soft-start (SS group), pulse cure (PC group) and standard continuous cure (CC group). The light-curing unit capable of adjusting time and intensity (VIP, Bisco Dental product) was selected and the light energy density for all curing modes was fixed at $16J/cm^2$. After storage for 24 hours, specimens were sectioned into beams with a rectangular cross-sectional area of approximately $1mm^2$ Microtensile bond strength $({\mu}TBS)$ test was per- formed using a univel·sal testing machine (EZ Test, Shimadzu Co.). The results were analyzed using oneway ANOVA and Tukey's test at significance level 0.05. The ${\mu}TBS$ of PD group and SS group was higher than that of PC group and CC group. Within the limitations of this in vitro study, modification of curing modes such as pulse delay and soft start polymerization can improve resin/dentin bond strength in Class I cavities by controlling polymerization velocity of composite resin.

• Polymer(Korea)
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• v.24 no.5
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• pp.610-620
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• 2000

Vinyl acetate (VAc) was polymerized at 30, 40, and 5$0^{\circ}C$ using 2,2'-azobis (2,4-dimethylvaleronitrile) (ADMVN) and tertiary butyl alcohol (TBA) as the initiator and the solvent, respectively. High molecular weight (HMW) atactic poly(vinyl alcohol) (PVA) was prepared by saponifying the poly(vinyl acetate) (PVAc) synthesized. The effect of polymerization conditions were investigated in terms of conversion, degree of branching for acetyl group of PVAc, and molecular weight of both PVAc and PVA. The polymerization rate of VAc in TBA was proportional to the 0.49th power of ADMVN concentration in good accordance with the theoretical value of 0.5. HMW-PVA with high yield could be obtained successfully, probably due to lower polymerization temperature and decreased chain transfer reaction rate which was achieved by adopting ADMVN and TBA. PYAc having average degree of polymerization (P$_{n}$) of 10000~13000 was obtained at the conversion of 35~70%. Saponification of so prepared PVAc yielded PVA having P$_{n}$ of 2400~6100. The syndiotactic diad content increased with decreasing polymerization temperature and increasing VAc concentration due to a steric hindrance effect of TBA during polymerization.

• Proceedings of the Korean Society of Dyers and Finishers Conference
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• 2003.04a
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• pp.93-96
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• 2003

일반적으로 폴리우레탄계 마이크로캡슐은 양말단에 과량의 NCO기를 가지는 폴리우레탄 프리폴리머의 중합에 의한 것으로서, 이어서 수용액상에서 쇄연장제의 첨가에 의해 계면에서 완전한 폴리우레탄막을 중합하는 방법을 취하고 있다. 그러나 이러한 프리폴리머법에 의한 마이크로캡슐의 형성은 여러 가지 제조상의 문제점을 지니고 있다. Vanzo 등이 10$\mu\textrm{m}$이하의 작은 입자를 얻기 위해서는 비교적 고농도의 분산제와 높은 교반속도를 사용할 필요가 있었으며, 또한 그 입자크기분포의 제어가 어려웠다. (중략)

• Polymer Science and Technology
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• v.15 no.2
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• pp.198-208
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• 2004

입자의 크기 및 분산도에 관한 지식은 에멀젼 뿐만 아니라 aerosol, dispersion, suspension을 포함하는 미립자 계에서 중요한 정보이다. 특히 유화 중합에 있어서 입자의 크기 및 분산도의 정확한 측정은 중합 속도론 (입자의 생성, 성장 및 응집)을 다루는데 필수적이며, 입자의 크기 및 분산도는 hiding power, tinting strength 등 최종 물질의 물리$.$화학$.$기계적 성질 결정에 있어서 중요한 변수로 작용한다. 합성 공정에서도 입자의 크기 및 분산도는 콜로이드의 점도에 많은 영향을 미쳐서 공정의 안정성을 좌우하기도 한다.(중략)