Mechanical Properties, Morphological Characteristics and Microstructural Changes of Poly(glycolide-co-ε-caprolactone-co-l-lactide) Suture during In Vitro Degradation

지민호,최송연,강찬솔,백두현 한국섬유공학회 2023 Fibers and polymers Vol.24 No.9

In this study, as a first step toward the development of novel candidate for absorbable suture materials based on poly(glycolide-co-ɛ-caprolactone), we synthesized a poly(glycolide-co-ɛ-caprolactone-co-L-lactide) block copolymer with ABA block structure via a two-step polymerization process and prepared the final PGCLA suture using a pilot-scale melt spinning machine. Then, to understand the mechanism on the early degradation stage of the PGCLA suture, we systematically investigated the mechanical, morphological properties and microstructural changes of the PGCLA suture through in vitro degradation. As a result, it was observed that, during the in vitro degradation process, the mechanical properties of PGCLA sutures exhibited an overall linear decrease and retained only 32% of its initial strength at 2 weeks of degradation. In addition, it was confirmed that, from FE-SEM analysis, internal degradation and structural changes, including longitudinal cracks on the suture surface, were noticeably appeared at 2 weeks of degradation. Interestingly, the results obtained from 1H-NMR and WAXS analyses exhibited clearly that PGCLA sutures undergo simultaneous degradation of glycolide units and L-lactide units present in the amorphous region during in vitro degradation. Therefore, based on these findings, we concluded that in the early stage of in vitro degradation of PGCLA suture, simultaneous degradation of glycolide units and L-lactide units in the amorphous region occurs, leading to chemical and structural changes such as erosion and cracking of the suture, as well as a decrease in its mechanical properties.

Influences of Tensile Drawing on Structures, Mechanical, and Electrical Properties of Wet-Spun Multi-Walled Carbon Nanotube Composite Fiber

지민호,백두현,최진욱,박성호,정영규 한국고분자학회 2012 Macromolecular Research Vol.20 No.6

A composite fiber based on multi-walled carbon nanotube (MWCNT) and poly(vinyl alcohol) (PVA) is prepared by wet-spinning and then stretched uniaxially with various draw ratios. Structural features and the mechanical and electrical performances of the MWCNT/PVA composite fiber are investigated as a function of draw ratio. It is identified from polarized Raman spectroscopy that the composite fiber exhibits an enhanced alignment of MWCNTs along the fiber axis with increasing the draw ratio. Accordingly, initial moduli and tensile strengths of the drawn composite fibers are much higher than those of undrawn composite fiber because of the efficient stress-transfer between MWCNTs. In addition, electrical conductivity of the composite fiber is significantly increased with the increase of the draw ratio, which is explained by the fact that the alignment of MWCNTs in drawn composite fibers enhances the interaction between MWCNTs, eventually leading to the generation of more efficient paths for electrical conduction.

방향족 폴리히드록시아미드의 합성과 열적 고리화 거동(I) -벤젠고리 치환구조의 영향-

지민호,이주용,백두현,Jee, Min Ho,Lee, Ju Yong,Baik, Doo Hyun 한국섬유공학회 2012 한국섬유공학회지 Vol.49 No.5

We have synthesized polyhydroxyamides (PHAs), a possible precursor which could be converted to polybenzoxazole (PBO) through a thermal cyclization reaction, by low temperature solution polymerization of 3,3'${\AE}$-dihydroxybenzidine with terephthaloyl chloride or isophthaloyl acid. Structural characteristics, solubility, thermal cyclization, and thermal decomposition of the PHAs were investigated by the FT-IR, DSC and TGA in order to understand the effect of chemical structure of acyl chlorides on the thermal properties of PHAs. The FT-IR study reveals that two types of PHAs can cyclize on heating and be transformed into PBOs. The meta-type PHA (m-PHA) shows better solubility in N,N-dimethylformamide and dimethyl sulfoxide than the para-type PHA (m-PHA). DSC and TGA results demonstrate that the m-PHA can cyclize at lower temperature than p-PHA, which is due to the difference in activation energy of thermal cyclization between m-PHA and p-PHA. TGA results reveal that the p-PHA has better thermal stability than m-PHA while in flame.

Effects of Introduction of L-Lactide on Microstructures, Thermal Properties and In vitro Degradation of Poly(glycolide-co-ε-caprolactone) Block Copolymer

지민호,박지희,최송연,백두현 한국섬유공학회 2022 Fibers and polymers Vol.23 No.10

In this study, poly(glycolide-co-ε-caprolactone) (PGCL) block copolymers, which have an ABA block structure, were prepared by a two-step polymerization process, and their microstructures, thermal properties and in vitro degradation properties according to introducing a small amount of L-lactide as a comonomer in the first step of the polymerization process were systematically investigated. Through our study, it was confirmed that the introduction of L-lactide in the first step of the polymerization process had a great effect on the microstructure of the random PGCL prepolymer (B block) as well as the final PGCL block copolymer (ABA block). Specifically, with the introduction of L-lactide, the average sequence length of glycolide segments on the PGCL prepolymer decreased from 3.32 to 2.40. In addition, it was observed that there is a relatively large difference in the average sequence length of glycolide segments in the final PGCL block copolymers. As a result, these microstructural changes of the PGCL prepolymer originated from the L-lactide comonomer affected significantly the thermal properties and in vitro degradation properties on the final PGCL block copolymers. Compared with the PGCL block copolymer without L-lactide, melting temperature and crystallization temperature of the PGCL block copolymer with L-lactide decreased, as well as their thermal degradation temperature. In addition, the introduction of a small amount of L-lactide comonomer accelerated the hydrolytic degradation of the PGCL block copolymer. Overall, by introducing L-lactide copolymer in the first step of the two-step manufacturing process for the PGCL block copolymer, changes of various properties on the PGCL block copolymer originated from the changes in the microstructure of random PGCL prepolymer were confirmed.

음이온성 공중합 폴리에스터/Dodecylbenzenesulfonate 블렌드 필름의 열적 특성 및 알칼리 감량

지민호,이종환,홍충희,엄대길,김선홍,최진욱,백두현,Jee, Min Ho,Lee, Jong Hwan,Hong, Choong Hee,Eom, Dae Gil,Kim, Sun Hong,Choi, Jin Uk,Baik, Doo Hyun 한국섬유공학회 2014 한국섬유공학회지 Vol.51 No.1

A series of anionic copolyester/dodecylbenzenesulfonate (DBS) blend films were prepared by a melt-compounding method and then annealed under a range of conditions. To eliminate possible experimental errors in measuring the alkaline reduction rate of the samples, the crystallinity should be uniform. We used Fourier transform infrared (FT-IR) spectroscopy to measure and control the relative crystallinity of the annealed samples. The relationship between the crystallinity and reduction rate, as well as the annealing conditions of the annealed blend samples, was derived. FT-IR analysis showed that the crystallization rate of copolyester/DBS blend films is lower than that of pure copolyester. However, the alkaline weight reduction rate of the blend films, which have similar crystallinities, increases dramatically with increasing DBS content, even at a low DBS content of 1 to 3 wt%, although the effect of the DBS becomes negligible above 5 wt%. However, unlike the result for annealed films, the alkaline weight reduction rate for amorphous films exhibited a linear relationship between the alkaline reduction rate and the DBS content for all of the examined DBS content, demonstrating that the effects of the DBS on the alkaline weight reduction of the copolysester could be affected by processing conditions such as post-drawing and annealing.

Effects of Chemical Functionalization of MWCNTs on the Structural and Physical Properties of Elastomeric Copolyetherester-based Composite Fibers

지민호,백두현 한국섬유공학회 2018 Fibers and polymers Vol.19 No.3

Elastomeric copolyetherester (CPEE)-based composite fibers incorporating various neat and functionalized multiwalled carbon nanotubes (MWCNTs) were prepared through a conventional wet-spinning and coagulation process. The influence of functionalized MWCNTs on the morphological features, and the thermal, mechanical properties and electrical conductivity of CPEE/MWCNT (80/20, w/w) composite fibers were investigated. FE-SEM images show that a composite fiber containing poly(ethylene glycol)-functionalized MWCNTs (MWCNT-PEG) has a relatively smooth surface owing to the good dispersion of MWCNT-PEGs within the fiber, whereas composite fibers including pristine MWCNTs (p-MWCNT), acid-functionalized MWCNTs (a-MWCNT), and ethylene glycol-modified MWCNTs (MWCNT-EG) have quite a rough surface morphology owing to the presence of MWCNT aggregates. As a result, the CPEE/MWCNT-PEG composite fiber exhibits noticeably increased thermal and tensile mechanical properties as well as a faster crystallization behavior, which stems from an enhanced interfacial interaction between the CPEE matrix and MWCNT-PEGs.

Graphite와 MWNT를 함유한 폴리우레탄 하이브리드 나노복합체 필름의 전기적 특성 및 발열 성능 평가

지민호,이종환,이인성,백두현,Jee, Min Ho,Lee, Jong Hwan,Lee, In Sung,Baik, Doo Hyun 한국섬유공학회 2013 한국섬유공학회지 Vol.50 No.2

Polyurethane(PU) hybrid nanocomposite films containing graphite and multiwalled carbon nanotubes (MWNTs) were prepared by a solution-casting method, and their electrical properties and heating performance were investigated as a function of conducting hybrid filler content. The electrical resistivity of the PU/hybrid nanocomposite films decreased slightly from $2.40{\times}10^2{\Omega}cm$ to $2.79{\times}10^1{\Omega}cm$ with increasing the hybrid filler content (5.0~9.0 wt%). The current-voltage (I-V) characteristics of these nanocomposite films indicate a significant increase in current level with 9.0 wt% hybrid filler content, which reflects the fact that above the percolation threshold, the conduction mechanism in the nanocomposite films changes from tunneling conduction (nonlinear) to ohmic conduction due to the direct contact between the graphite and the MWNTs (linear). As a result, the PU/hybrid nanocomposite films containing 9.0 wt% hybrid filler with 4.5 wt% graphite and 4.5 wt% MWNTs can be quickly heated from room temperature to $48.8^{\circ}C$ within 80 s by applying a DC voltage of 30 V, whereas the PU nanocomposite films containing 30.0 wt% graphite or 5.0 wt% MWNTs could only be heated to $39.2^{\circ}C$ and $30.6^{\circ}C$, respectively.

방향족 폴리히드록시아미드의 합성과 열적 고리화 거동(II) -플루오르 치환체의 영향-

지민호,백민정,강찬솔,백두현,Jee, Min Ho,Paik, Min Jung,Kang, Chan Sol,Baik, Doo Hyun 한국섬유공학회 2013 한국섬유공학회지 Vol.50 No.5

Polyhydroxyamide (PHA) was synthesized via low-temperature solution polymerization of 3,3'-dihydroxybenzidine with isophthaloyl chloride, and the derivatives of PHA containing fluoro-substituents were investigated for exploring their potential application as new thermally stable polymer material. The structural properties, solubility, and thermal cyclization of the PHA and its derivatives were characterized using FT-IR, DSC, and TGA to derive the relationship between the structure of the PHA derivatives and the thermal properties and cyclization behavior of the polymer. The PHA derivatives containing fluoro-substituents were readily soluble in a variety of solvents without LiCl, whereas the pristine PHA was soluble only in the presence of LiCl. The DSC analyses under isothermal conditions showed that the PHA derivatives exhibited a faster cyclization rate than the pristine PHA at $220^{\circ}C$ and $250^{\circ}C$. In addition, the DSC and TGA results revealed that the PHA derivatives could be cyclized into the corresponding polybenzoxazoles at lower temperatures than the pristine PHA; this could be attributed to the lower thermal activation energy of the derivatives owing to the introduction of the fluoro-substituents.

동시 중합법으로 제조된 폴리에틸렌나프탈레이트/MWNT 나노복합체의 제조와 물성(I) -합성과 특성 분석-

지민호,이민호,윤여훈,백두현,Jee, Min-Ho,Lee, Min-Ho,Yoon, Yeo-Hoon,Baik, Doo-Hyun 한국섬유공학회 2008 한국섬유공학회지 Vol.45 No.1

Multi-walled carbon nanotubes (MWNT) reinforced poly(ethylene 2,6-naphthalate) (PEN) nanocomposites were prepared by in situ polymerization. To improve the dispersibility of nanotubes, MWNT was treated with acid and consequently carboxylic acid groups were introduced on the surface of MWNT. The carboxylic acid groups formed on the surface of MWNT were confirmed by XPS analysis. Acid-modified MWNT showed a good dispersiblity in ethylene glycol. MWNT dispersion in ethylene glycol was introduced into the bis-hydroxyethylnaphthalate (BHEN) melt at the end of the ester-interchange reaction stage of poly(ethylene 2,6-naphthalate) synthesis. Crystallinity and crystallization temperatures were increased with MWNT content, which implied that MWNT could aid PEN to crystallize more fast and much more.

Stretching-induced Alignment of Carbon Nanotubes and Associated Mechanical and Electrical Properties of Elastomeric Polyester-based Composite Fibers

지민호,백두현 한국섬유공학회 2019 Fibers and polymers Vol.20 No.8

Composite fibers composed of elastomeric segmented copolyetherester (CPEE) and poly(ethylene glycol)-functionalized multi-walled carbon nanotubes (MWCNT-PEG) (80/20 by wt%) were manufactured using wet-spinning andstretched up to 200 % at room temperature. It was confirmed that the introduction of PEG chains on the surfaces of theMWCNTs provides a specific interfacial interaction between the MWCNTs and CPEE matrix, which results in an enhancedalignment of the MWCNTs in the CPEE/MWCNT-PEG composite fibers through a simple stretching at room temperaturewithout any high-temperature conditions required for the general drawing or stretching processes. As a result, the initialmodulus and tensile strength of the composite fibers stretched up to 200 % were increased by 320 % and 350 %, respectively,as compared to the as-spun composite fibers. In addition, the electrical conductivity of the composite fibers was alsonoticeably increased with an increase in the stretching ratio. Interestingly, the correlation coefficient among the MWCNTalignment, modulus, and conductivity is 0.97, which means that the alignment of the MWCNTs is closely related to thechange in the physical properties of the composite fibers.