충격강도 및 결정화 속도가 개선된 Fused Deposition Modeling 방식 3D 프린터용 Poly-L-lactic acid 기반 필라멘트

이종인(Jong In Lee),오승주(Seung-Ju Oh),정지수(Ji Su Jeong),황영재(Young Jae Hwang),배진우(Jin Woo Bae),남병욱(Byeong Uk Nam) 한국산학기술학회 2021 한국산학기술학회논문지 Vol.22 No.7

열가소성 플라스틱의 필라멘트를 사용하는 Fused deposition modeling (FDM) 방식의 3D 프린터는 다른 종류의 3D 프린터에 비해 저렴한 비용과 편의성 때문에 다양한 산업분야에서 사용되고 있다. Poly-L-lactic acid (PLLA)는 생분해성이 있는 친환경 바이오 플라스틱으로 변형이 거의 없으며, 높은 탄성률을 가졌기 때문에 FDM 방식 3D 프린터용 필라멘트로써 많은 관심을 받고 있다. 하지만, PLLA는 FDM 방식 3D 프린터용 필라멘트로 사용되기에는 낮은 충격 강도와 느린 결정화 속도를 보인다. 본 연구에서는, PLLA의 낮은 충격강도와 느린 결정화 속도를 개선하기 위하여 PLLA에 생분해성 플라스틱이면서 충격보강제인 Poly(butylene adipate-co-terephthalate) (PBAT)와 핵제인 Talc를 함께 첨가하여 이축 압출기를 통해 용융 블렌드하였다. PBAT의 첨가는 PLLA의 충격강도를 33 J/m에서 54 J/m 까지 증가시켰다. 반면, PLLA/PBAT 블렌드 조성에서 Talc의 첨가는 PLLA의 충격강도를 46 J/m까지 감소시켰지만, 결정화 온도를 96.1 ℃까지 증가시켰다. 특히, Talc가 3 phr 첨가된 PLLA/PBAT (80/20 wt%) 블렌드 조성은 최적의 충격강도(48 J/m)와 결정화 온도 (94.4 ℃)를 달성하였고, neat PLLA보다 우수한 충격강도 및 빠른 결정화 속도를 보였다. Fused deposition modeling (FDM) type 3D printers, which use thermoplastic filaments, find application in a greater number of industries compared to other types of 3D printers because of their low cost and convenience. Poly-L-lactic acid (PLLA) has received considerable attention as a filament material for the FDM type 3D printer as it is an eco-friendly bioplastic that is biodegradable. Besides, it has lower shrinkage and a high modulus. However, PLLA has a low impact strength and a slow crystallization rate which makes it unsuitable for use as a filament in an FDM type 3D printer. To improve these properties, in this study, PLLA was melt-blended using a twin-screw extruder into poly(butylene adipate-co-terephthalate) (PBAT) and Talc as an impact modifier and nucleating agent, respectively. The addition of PBAT increased the impact strength of the PLLA from 33 J/m to 54 J/m. However, the addition of Talc in the PLLA/PBAT blend decreased the impact strength of the PLLA from 54 J/m to 46 J/m while the crystallization temperature increased to 96.1 ℃. In particular, the Talc addition of 3 phr in the PLLA/PBAT (80/20 wt%) blend achieved optimum impact strength (48 J/m) and crystallization temperature (94.4 ℃), resulting in the superior impact strength and faster crystallization rate compare to neat PLLA.

Poly(D-lactic acid-b-L-lactic acid)의 결정화거동 및 열적 특성

이경우,박흥수,김영호,Lee, Kyoung-Woo,Park, Heung-Su,Kim, Young-Ho 한국섬유공학회 2010 한국섬유공학회지 Vol.47 No.6

A stereocomplex of poly(lactic acid) (PLA) from the opposite enantiomeric configurations of the L and D forms has higher thermal resistance and mechanical properties than poly(L-lactic acid) (PLLA), which may overcome the problems with the low melting temperature of PLLA when used as a commercial fiber. In this study, the crystallization behavior and thermal properties of poly(D-lactic acid-b-L-lactic acid) (PDLLA) block copolymer (50:50, w/w) were characterized by differential scanning calorimetry (DSC), dynamic mechanical analysis, and wide angle X-ray diffraction (WAXD) analysis. DSC showed that the melting temperature of the stereocomplex crystal was approximately $215^{\circ}C$, which was much higher than that of homo PLLA (${\sim}168^{\circ}C$). The equilibrium melting temperature and stability parameter of PDLLA obtained from the Hoffman-Weeks plot was $230^{\circ}C$ and 0.44, respectively. Compared to the WAXD peaks of the ${\alpha}$-form crystal of PLLA, additional peaks were observed for PDLLA at $11.9^{\circ}$, $20.8^{\circ}$, and $23.6^{\circ}$ $2{\theta}$ arising from the D,L-stereocomplex crystal of PLA. The crystallization behaviors of PDLLA and PLLA during the heating and cooling processes from the melt-quenched state and from the molten state, respectively, were compared using the WAXD curves obtained from a synchrotron X-ray source. The effects of annealing of both PLLA and PDLLA films at different temperatures on the crystal formation were also examined.

Effects of L-lysine and D-lysine on ε-Poly-L-lysine Biosynthesis and Their Metabolites by Streptomyces ahygroscopicus GIM8

Liu Shengrong,Wu Qingping,Zhang Jumei,Mo Shuping 한국생물공학회 2012 Biotechnology and Bioprocess Engineering Vol.17 No.6

ε-Poly-L-lysine (ε-PL), produced by Streptomyces or Kitasatospora strains, is a homo-poly-amino acid of Llysine,which is used as a safe food preservative. In this study, the effects of L-lysine and its isomer, D-lysine, on ε-PL biosynthesis and their metabolites by the ε-PLproducing strain Streptomyces ahygroscopicus GIM8 were determined. The results indicated that L-lysine added into the fermentation medium in the production phase mainly served as a precursor for ε-PL biosynthesis during the flask culture phase, leading to greater ε-PL production. At an optimum level of 3 mM L-lysine, a ε-PL yield of 1.16 g/L was attained, with a 41.4% increment relative to the control of 0.78 g/L. Regarding D-lysine, the production of ε-PL increased by increasing its concentrations up to 6 mM in the initial fermentation medium. Interestingly, ε-PL production (1.20 g/L) with the addition of 3 mM D-lysine into the initial fermentation medium in flasks was higher than that of the initial addition of 3 mM L-lysine (1.06 g/L). The mechanism by which D-lysine improves ε-PL biosynthesis involves its utilization that leads to greater biomass. After S. ahygroscopicus GIM8 was cultivated in the defined medium with L-lysine, several key metabolites, including 5-aminovalerate, pipecolate, and L-2-aminoadipate formed in the cells, whereas only L-2-aminoadipate was observed after D-lysine metabolism. This result indicates that Llysine and D-lysine undergo different metabolic pathways in the cells. Undoubtedly, the results of this study are expected to aid the understanding of ε-PL biosynthesis and serve as reference for the formulation of an alternative approach to improve ε-PL productivity using L-lysine as an additional substrate in the fermentation medium.

Investigation of transient current characteristics with scaling-down poly-Si body thickness and grain size of 3D NAND flash memory

Lee, Sang-Ho,Kwon, Dae Woong,Kim, Seunghyun,Baek, Myung-Hyun,Lee, Sungbok,Kang, Jinkyu,Jang, Woojae,Park, Byung-Gook Pergamon Press 2019 Solid-State Electronics Vol. No.

<P><B>Abstract</B></P> <P>In order to verify the effects of polycrystalline Si (poly-Si) body thickness scale-down on read operation in 3D NAND flash memory which has tube type thin body, TCAD simulations and the measurements of fabricated devices are performed. <I>I<SUB>D</SUB> </I>-<I>V<SUB>G</SUB> </I> characteristics and transient drain current behaviors are investigated in 3D NAND devices with various body thicknesses and grain sizes. It has been known that drain current undershoot/overshoot is observed in poly-Si channel devices by falling/rising step gate bias. These phenomena are strongly related with transient of potential barrier height due to slow capture/emission rate of poly-Si grain boundary traps. As the body thickness decreases with the same grain size, the transient current instability, on-state current, and subthreshold-swing are improved. When the grain size is increased with the same body thickness, the transient current instability, on-state current, and subthreshold-swing are improved.</P> <P><B>Highlights</B></P> <P> <UL> <LI> I<SUB>D</SUB>-V<SUB>G</SUB> characteristics and transient drain current behaviors are investigated in 3D NAND flash devices with various body thicknesses and grain sizes. </LI> <LI> As the body thickness decreases with the same grain size, the transient current instability and on-state current are improved. </LI> <LI> When the grain size is increased with the same body thickness, the transient current instability and on-state current are improved. </LI> </UL> </P>

폴리(DL-락틱 엑시드) 첨가에 의한 폴리(L-락틱 엑시드)와 폴리(D-락틱 엑시드)의 스테레오 복합화 향상

김성혜,이상철,Kim, Sung Hea,Lee, Sang Cheol 한국섬유공학회 2015 한국섬유공학회지 Vol.52 No.2

Ternary blends of poly(L-lactic acid)(PLLA)/poly(D-lactic acid)(PDLA)/poly(DL-lactic acid)(PDLLA), with the PLLA/PDLA blend ratio fixed at 50:50 (w/w), were prepared by the solution blending method, and their thermal properties were investigated by differential scanning calorimetry. Ternary blends containing less than 30% PDLLA exhibit double melting peaks at around $170^{\circ}C(T_{m1})$ and $220^{\circ}C (T_{m2})$, where $T_{m1}$ and $T_{m2}$ are the melting peaks of the homopolymer (PLLA and PDLA) and stereocomplex crystals, respectively. On the other hand, blends containing more than 50% PDLLA exhibit only one melting peak at about $220^{\circ}C$, which corresponds to the melting peak of the stereocomplex crystal. Further, the heat of fusion of the homopolymer crystals decreases with increasing PDLLA content in the blend, whereas that of the stereocomplex crystal increases with increasing PDLLA content. Therefore, it may be concluded that while the addition of PDLLA to the PLLA/PDLA (50:50) binary blend enhances the stereocomplexation of PLLA and PDLA, it also disturbs the crystallization of the homopolymers.

한국 폐경여성에서 비타민 D 수용체 유전자내 Poly (A) 다형성과 골밀도의 연관성

김정구 ( Jung Gu Kim ),권재희 ( Jae Hee Kwon ),김석현 ( Seok Hyun Kim ),최영민 ( Young Min Choi ),문신용 ( Shin Yong Moon ),이진용 ( Jin Yong Lee ) 대한산부인과학회 2003 Obstetrics & Gynecology Science Vol.46 No.4

목적 : 한국 폐경여성에서 VDR 유전자내 poly (A) 다형성양상을 알아보고 이런 양상과 골밀도 사이에 연관성이 있는가를 규명하고자 하였다. 연구 방법 : 자연 폐경여성 417명에서 VDR 유전자내 poly (A) 다형성양상을 urea-polyacrylamide 겔 전기영동, GeneScan, 염기서열분석으로 분석하고 혈청 CTX, osteocalcin, BAP, 1,25 (OH)2 비타민 D3 농도를 효소면역법과 면역측정법으로, 요추 및 대퇴 근위 Objective : To investigate a poly (A) microsatellite in vitamin D receptor (VDR) gene and to evaluate its relationship with bone mineral density (BMD) in postmenopausal Korean women. Methods : The poly (A) polymorphism was analyzed in 417 postmenopausal K

Surface Structure and Stereocomplex Formation of Enantiomeric Polylactide Blends Using Poly(dimethyl siloxane) as a Probe Polymer

Lee, Jin-Kook,Kim, Mi-Ra,Lee, Hyun-Jeong,Chung, Ildoo,Lim, Kwon Taek,Jeon, Sangik,Lee, Won-Ki WILEY-VCH Verlag 2006 Macromolecular symposia Vol.239 No.1

<P>In the stereocomplex between enantiomeric poly(l-lactide) (l-PLA) and poly(d-lactide), crystallites formed as a result of stereocomplexation, equimolar l- and d-lactide unit sequences are packed side by side. The stereocomplex exhibits a melting temperature higher by about 50 °C than that of each homopolymer. In this study, we attempt to obtain further insight into the stereocomplex-induced surface structure of enantiomeric PLA blend films. The design of the blend systems is based on principles of surface segregation of multicomponent polymeric systems with a low surface energy, triblock copolymer (l-PLA-b-PDMS-b-l-PLA) of l-PLA and poly-(dimethyl siloxane). (l-PLA-b-PDMS-b-l-PLA/l-PLA) blend films showed the surface segregation of PDMS, regardless of blend composition while the surface composition of PDMS in the (l-PLA-b-PDMS-b-l-PLA/d-PLA) blend films was strongly depended on blend composition or a degree of complexation. These results are likely due to strong interaction between d- and l-lactide unit sequences, which prevents the surface segregation of PDMS.</P>

Simulation of Residual Stress and Its Impact on a Poly-Silicon Channel for Three-Dimensional, Stacked, Vertical-NAND Flash Memories

김규범,오영택,송윤흡 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.70 No.12

In this work, we present the results of an investigation of the impact of the stress on a poly-silicon channel induced by the neighboring layers in three-dimensional vertical NAND (3D V-NAND) flash memories. Using 3D process simulations, we confirmed the distributions of the residual stress after each process step in the cross-section of a NAND flash unit cell. To investigate the impact of the stress on the poly-silicon channel, we also studied the residual stress after changing the intrinsic stresses of the oxide-nitride-oxide (ONO) layer and the tungsten layer used as a gate. We found that the amplitude of the residual stress in the applied layer became larger as the intrinsic stress increased. In addition, the intrinsic tensile/compressive stresses in the outer layers affected the residual stresses of the previously deposited layers in an opposite nature of the stresses. The cylindrical poly-silicon channel was influenced by the intrinsic stresses of the oxide layers adjacent to the nitride and the tungsten films, with the intrinsic stress of the tunnel oxide having the greater effect on the residual stress in the channel. Because such stresses affect the electrical properties of the devices, optimized deposition conditions are required to control them. Such conditions would aid in improving the performances of 3D NAND flash memories.

Alprazolam함유 poly(D,L-lactic acid) microsphere의 제조 및 평가

용철순,오두만,권미라,박새해 영남대학교 약품개발연구소 1996 영남대학교 약품개발연구소 연구업적집 Vol.6 No.-

Poly(D.L-lactic acid)(PLA) microspheres containing alprazolam(APZ) were prepared by a solvent-emulsion evaporation method and their release patterns were invostigated in vitro. Various batches of microspherss with different size and drug content were obtained by changing the ration of APZ to PLA, PLA concentration in the dispersed phase and stirring rate. Rod-like APZ crystals on microsphere surface, which were released rapidly and could act as a loading dose, were observed with increasing drug content. The release rate was increased with increase in drug contents and decresase in the molecular weight of PLA. The release rate of APZ for long-acting injectable delivery system in vitro, which would aid in predicting in vivo release profile, could be controlled by properly optimizing various factors affecting characteristics of microspheres.

프랑스 라디오 토론에서 의견불일치 행위

김진무,임종보 한국프랑스학회 2007 한국프랑스학논집 Vol.57 No.-