• Elastomers and Composites
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• 제38권4호
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• pp.295-302
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• 2003

사출성형에서 성형품의 수축현상은 사출온도, 사출압력, 금형온도와 같은 성형공정에 따라 다르게 나타나며 게이트의 크기 등과 같은 금형설계에 따라서도 다르게 나타난다. 또한 수지의 결정화 유무에 따라 다르게 나타나고 있다. 본 연구에서는 여러가지 공정변수와 수지 특성에 따른 성형 수축률을 결정성수지인 poly(butylene terephthalate) (PBT)와 비결정성 수지인 polycarbonate (PC), poly(methyl methacrylate) (PMMA)를 사용하여 연구하였다. 결정성 수지가 비결정성 수지에 비해 약 3배 정도의 큰 수축률을 보였다. 사출 성형품의 성형 수축은 사출온도와 금형온도가 높을수록 그리고 사출압력이 작을수록 수축률은 커지는 경향을 보였다. 게이트의 크기가 커질수록 캐비티내의 압력전달이 원활하여 성형수축률은 작아 졌다. 또한 수지의 흐름방향과 흐름직각방향의 수축률 실험에서는 흐름방향의 수축이 더 작은 경향을 보였다. 게이트와의 거리에 따른 성형수축률은 게이트에서 가까운쪽의 수축이 먼쪽보다 더 큰 수축을 보였는데 이 현상은 잔류응력의 차이로 인하여 나타난 현상으로 해석된다.

• 접착 및 계면
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• 제9권4호
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• pp.30-33
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• 2008

블락 고분자 박막과 기판 사이의 계면에 1 nm 두께의 얇은 단일 성분 고분자 나노 계면을 도입함으로써 블락 고분자 나노 구조의 배향을 조절하는 연구가 수행되었다. Polystyrene-block-poly (methyl methacrylate) (PS-b-PMMA) 블락 고분자 박막의 나노 구조를 조절하기 위하여 블락 고분자의 각각의 고분자들의 평균 조성을 가지며 한쪽 끝에 히드록시 기를 가지는 단일 성분 고분자인 폴리(4-아세톡시스티렌) (OH-PAS)과 폴리(4-메톡시스티렌) (OH-PMS)를 나이트록사이드를 이용한 라디칼 중합법(nitroxide-mediated radical polymerization, NMP)을 사용하여 성공적으로 합성하였다. 실리콘 웨이퍼 표면과 저압 탈수 반응을 통하여 OH-PAS와 OH-PMS 두 개의 고분자를 성공적으로 표면에 공유결합 하였으며 생성된 두 고분자가 결합된 1 nm 두께의 계면 위에 PS-b-PMMA 블락 고분자 박막을 도포하여 그 나노 구조의 배향을 분석하였다. OH-PMS를 사용하여 제작된 계면의 경우 블락 고분자에 대하여 약 30%의 수직 배향을 보여주었고 OH-PAS를 사용하여 제작된 계면의 경우 수직 배향을 전혀 보여주지 않았고 오직 수평 배향만을 보여주었다. 결과적으로 계면의 화학적 조성을 정밀하게 조절하는 것이 블락 고분자 박막의 나노 구조 배향을 조절하는 데 가장 중요한 요소라고 고려된다.

• 멤브레인
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• 제28권2호
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• pp.121-128
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• 2018

세 가지의 다른 화학 성분으로 구성된 터폴리머는 기체분리막에 거의 활용되지 못하였다. 본 연구에서는 poly(2-[3-(2H-Benzotriazol-2-yl)-4-hydroxyphenyl] ethylmethacrylate)(PBEM), poly(oxyethylene methacrylate)(POEM), methyl methacrylate (MMA)로 구성된 터폴리머를 자유라디칼 중합법으로 합성하였고, 이를 기반으로 하여 이산화탄소/질소 분리를 위한 복합막 제조 공정을 개발하였다. 합성된 PBEM-PMMA-POEM 용액을 다공성 폴리설폰 지지체위에 코팅하여 복합막을 제조하였다. 성공적인 중합, 특성 및 구조분석을 위하여 푸리에 변환 적외선 분광학, X-ray 회절분석법, 열중량 분석 및 전계방사 주사전자 현미경을 사용하였다. PBEM-PMMA-POEM 터폴리머 분리막의 기체 투과도 및 이산화탄소/질소 선택도를 $25^{\circ}C$에서 측정하였다. 최고의 이산화탄소/질소 선택도는 30.2에 도달하였으며, 이산화탄소 투과도는 57.4 GPU ($1GPU=10^{-6}cm^3$(STP)/($s\;cm^2\;cmHg$))이었다.

• Bulletin of the Korean Chemical Society
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• 제12권5호
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• pp.569-574
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• 1991

Methyl red diffusion in polymer solutions was studied by a transient holographic method, forced Rayleigh scattering. In semi-dilute solutions of a polystyrene, where no specific interaction with the probe exists, we found within experimental uncertainty that the retardation of diffusion rate of methyl red is independent of the solvents used. This indicates that the hydrodynamic interaction in polymer coils is not affected by the nature of solvents enough to exhibit a detectable change in the diffusion rate of the probe. On the other hand, a substantial reduction of diffusion rate was observed in poly(methyl methacrylate) solutions in toluene. Together with the similar observation reported with poly(vinyl acetate), it is confirmed that hydrogen bond between the probe and the polymer is responsible for the retarded diffusion. The decay-growth-decay profile found in this system reveals a finite difference in diffusion coefficients of cis and trans isomer of methyl red. We estimate the difference and suggest that the cis isomer interacts with the polymer more strongly than the trans isomer.

• 대한치과보철학회지
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• 제39권6호
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• pp.709-734
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• 2001

The aims of this experiment were to investigate the strain and temperature changes simultaneously within autopolymerzing acrylic resin specimens. A computerized data acquisition system with an electrical resistance strain gauge and a thermocouple was used over time periods up to 180 minutes. The overall strain kinetics, the effects of stress relaxation and additional heat supply during the polymerization were evaluated. Stone mold replicas with an inner butt-joint rectangular cavity ($40.0{\times}25.0mm$, 5.0mm in depth) were duplicated from a brass master mold. A strain gauge (AE-11-S50N-120-EC, CAS Inc., Korea) and a thermocouple were installed within the cavity, which had been connected to a personal computer and a precision signal conditioning amplifier (DA1600 Dynamic Strain Amplifier, CAS Inc., Korea) so that real-time recordings of both polymerization-induced strain and temperature changes were performed. After each of fresh resin mixture was poured into the mold replica, data recording was done up to 180 minutes with three-second interval. Each of two poly(methyl methacrylate) products (Duralay, Vertex) and a vinyl ethyl methacrylate product (Snap) was examined repeatedly ten times. Additionally, removal procedures were done after 15, 30 and 60 minutes from the start of mixing to evaluate the effect of stress relaxation after deflasking. Six specimens for each of nine conditions were examined. After removal from the mold, the specimen continued bench-curing up to 180 minutes. Using a waterbath (Hanau Junior Curing Unit, Model No.76-0, Teledyne Hanau, New York, U.S.A.) with its temperature control maintained at $50^{\circ}C$, heat-soaking procedures with two different durations (15 and 45 minutes) were done to evaluate the effect of additional heat supply on the strain and temperature changes within the specimen during the polymerization. Five specimens for each of six conditions were examined. Within the parameters of this study the following results were drawn: 1. The mean shrinkage strains reached $-3095{\mu}{\epsilon},\;-1796{\mu}{\epsilon}$ and $-2959{\mu}{\epsilon}$ for Duralay, Snap and Vertex, respectively. The mean maximum temperature rise reached $56.7^{\circ}C,\;41.3^{\circ}C$ and $56.1^{\circ}C$ for Duralay, Snap, and Vertex, respectively. A vinyl ethyl methacrylate product (Snap) showed significantly less polymerization shrinkage strain (p<0.01) and significantly lower maximum temperature rise (p<0.01) than the other two poly(methyl methacrylate) products (Duralay, Vertex). 2. Mean maximum shrinkage rate for each resin was calculated to $-31.8{\mu}{\epsilon}/sec,\;-15.9{\mu}{\epsilon}/sec$ and $-31.8{\mu}{\epsilon}/sec$ for Duralay, Snap and Vertex, respectively. Snap showed significantly lower maximum shrinkage rate than Duralay and Vertex (p<0.01). 3. From the second experiment, some expansion was observed immediately after removal of specimen from the mold, and the amount of expansion increased as the removal time was delayed. For each removal time, Snap showed significantly less strain changes than the other two poly(methyl methacrylate) products (p<0.05). 4. During the external heat supply for the resins, higher maximum temperature rises were found. Meanwhile, the maximum shrinkage rates were not different from those of room temperature polymerizations. 5. From the third experiment, the external heat supply for the resins during polymerization could temporarily decrease or even reverse shrinkage strains of each material. But, shrinkage re-occurred in the linear nature after completion of heat supply. 6. Linear thermal expansion coefficients obtained from the end of heat supply continuing for an additional 5 minutes, showed that Snap exhibited significantly lower values than the other two poly(methyl methacrylate) products (p<0.01). Moreover, little difference was found between the mean linear thermal expansion coefficients obtained from two different heating durations (p>0.05).

• Carbon letters
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• 제23권
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• pp.55-62
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• 2017

We report on the dispersion state of partially reduced graphene oxide (PRGO) in organic solvents, namely methyl ethyl ketone, ethyl acetate, methylene chloride, toluene, and xylene, by controlling the carbon to oxygen (C/O) atomic ratio of the PRGOs. A two-phase solvent exchange method is also proposed to transfer PRGO from water to an aprotic solvent, such as methyl ethyl ketone. We achieve relatively good dispersion in aprotic and non-polar solvents by controlling the C/O atomic ratio of the PRGOs and applying the two-phase solvent exchange method. There is an increase in the glass transition temperatures with the dispersion of PRGOs into amorphous polymers, in particular a $4.4^{\circ}C$ increase for poly(methyl methacrylate) and $3.0^{\circ}C$ increase for polycarbonate. Good dispersion of PRGO in a nonpolar polymer, such as linear low density polyethylene, is also obtained.

• Macromolecular Research
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• 제11권6호
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• pp.410-417
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• 2003

Poly(methyl methacrylate-co-acrylonitrile) [P(MMA-co-AN)]/Na-MMT nanocomposites were synthesized through emulsion polymerization with pristine Na-MMT. The nanocomposites were exfoliated up to 20 wt% content of pristine Na-MMT relative to the amount of MMA and AN, and exhibited enhanced storage moduli, E', relative to the neat copolymer. The exfoliated morphology of the nanocomposite was confirmed by XRD and TEM. 2-Acryla-mido-2-methyl-1-propane sulfonic acid (AMPS) widened the galleries between the clay layers before polymerization and facilitated the comonomers, penetration into the clay to create the exfoliated nanocomposites. The onset of the thermal decomposition of the nanocomposites shifted to a higher temperature as the clay content increased. By calculating areas of tan$\delta$ of the nanocomposites, we observed that the nanocomposites show more solid-like behavior as the clay content increases. The dynamic storage modulus and complex viscosity increased with clay content. The complex viscosity showed shear-thinning behavior as the clay content increased. The Young's moduli of the nano-composites are higher than that of the neat copolymer and they increase steadily as the silicate content increases, as a result of the exfoliated structure at high clay content.

• Elastomers and Composites
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• 제56권3호
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• pp.179-186
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• 2021

Carbon-based nanofillers, including nanodiamond (ND) and carbon nanotubes (CNTs), have been employed in epoxy matrixes for improving the toughness, using the tow prepreg method, of epoxy compounds for high pressure tanks. The reinforcing performance was compared with those of commercially available toughening fillers, including carboxyl-terminated butadiene acrylonitrile (CTBN) and block copolymers, such as poly(methyl methacrylate)-b-poly(butyl acrylate)-b-poly(methyl methacrylate) (BA-b-MMA). CTNB improved the mechanical performance at a relatively high filler loading of ~5 phr. Nanosized BA-b-MMA showed improved performance at a lower filler loading of ~2 phr. However, the mechanical properties deteriorated at a higher loading of ~5 phr because of the formation of larger aggregates. ND showed no significant improvement in mechanical properties because of aggregate formation. In contrast, surface-treated ND with epoxidized hydroxyl-terminated polybutadiene considerably improved the mechanical properties, notably the impact strength, because of more uniform dispersion of particles in the epoxy matrix. CNTs noticeably improved the flexural strength and impact strength at a filler loading of 0.5 phr. However, the improvements were lost with further addition of fillers because of CNT aggregation.

• Bulletin of the Korean Chemical Society
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• 제32권9호
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• pp.3295-3305
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• 2011

Thermal behavior of poly (methyl methacrylate) was analyzed in the presence of tin (IV) chloride. Five different proportions - polymer to additive - were selected for casting films from common solvent. TG, DTG and DTA were employed to monitor thermal degradation of the systems. IR and py-GC-MS helped identify the decomposition products. The blends start degrading at a temperature lower than that of the neat polymer and higher than that of the pure additive. Complex formation between tin of additive and carbonyl oxygen (pendent groups of MMA units) was noticed in the films soon after the mixing of the components in the blends. The samples were also heated at three different temperatures to determine the composition of residues left after the expulsion of volatiles. The polymer, blends and additive exhibited a one step, two-step and three-step degradation, respectively. $T_0$ is highest for the polymer, lowest for the additive and is either $60^{\circ}C$ or $70^{\circ}C$ for the blends. The amount of residue increases down the series [moving from blend-1 (minimum additive concentration) to blend-5 (maximum additive concentration)]. For blend-1, it is 7% of the original mass whereas it is 16% for blend-5. $T_{max}$ also goes up as the concentration of additive in the blends is elevated. The complexation appears to be the cause of observed stabilization. Some new products of degradation were noted apart from those reported earlier. These included methanol, isobutyric acid, acid chloride, etc. Molecular-level mixing of the constituents and "positioning effect" of the additive may have brought about the formation of new compounds. Routes are proposed for the appearance of these substances. Horizontal burning tests were also conducted on polymer and blends and the results are discussed. Activation energies and reaction orders were calculated. Activation energy is highest for the polymer, i.e., 138.9 Kcal/mol while the range for blends is from 51 to 39 Kcal/mol. Stability zones are highlighted for the blends. The interaction between the blended parts seems to be chemical in nature.

• The Journal of Advanced Prosthodontics
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• 제10권2호
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• pp.113-121
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• 2018

PURPOSE. The aim of this preliminary study was to investigate, for the first time, the effects of addition of titania nanotubes ($n-TiO_2$) to poly methyl methacrylate (PMMA) on mechanical properties of PMMA denture base. MATERIALS AND METHODS. $TiO_2$ nanotubes were prepared using alkaline hydrothermal process. Obtained nanotubes were assessed using FESEM-EDX, XRD, and FT-IR. For 3 experiments of this study (fracture toughness, three-point bending flexural strength, and Vickers microhardness), 135 specimens were prepared according to ISO 20795-1:2013 (n of each experiment=45). For each experiment, PMMA was mixed with 0% (control), 2.5 wt%, and 5 wt% nanotubes. From each $TiO_2$:PMMA ratio, 15 specimens were fabricated for each experiment. Effects of $n-TiO_2$ addition on 3 mechanical properties were assessed using Pearson, ANOVA, and Tukey tests. RESULTS. SEM images of $n-TiO_2$ exhibited the presence of elongated tubular structures. The XRD pattern of synthesized $n-TiO_2$ represented the anatase crystal phase of $TiO_2$. Moderate to very strong significant positive correlations were observed between the concentration of $n-TiO_2$ and each of the 3 physicomechanical properties of PMMA (Pearson's P value ${\leq}.001$, correlation coefficient ranging between 0.5 and 0.9). Flexural strength and hardness values of specimens modified with both 2.5 and 5 wt% $n-TiO_2$ were significantly higher than those of control ($P{\leq}.001$). Fracture toughness of samples reinforced with 5 wt% $n-TiO_2$ (but not those of 2.5% $n-TiO_2$) was higher than control (P=.002). CONCLUSION. Titania nanotubes were successfully introduced for the first time as a means of enhancing the hardness, flexural strength, and fracture toughness of denture base PMMA.