Clay 또는 TS-1 Zeolite를 함유한 생분해성 폴리에스터 나노복합체의 미세구조와 물리적 특성

Abstract

Poly (butylene succinate)(PBS)/ organo-modified clay nanocomposites (PONC) and PBS/TS-1zeolite hybrid composites (PTHC) were prepared by in situ polymerization. This thesis focused on the physical properties such as crystallization behavior, resultant morphology and enzymatic hydrolysis of the nanocomposites. In addition, to expand the potential application fields of the biodegradable nanocomposites, nanofibers of the composites were obtained by electrospinning. The morphology and drug release behavior of nanofiber were investigated as well. In the first chapter, we successfully modified organic clays containing the urethane group by introducing a covalent bond between silanol group on the clay and hydroxyl group of organic modifier in the silicate layer using 1,6-diisocyanatohexane (HDI), namely surface treated montmorillonite (30BM), to increase basal spacing and affinity between clay and polymer. The effect of the surface urethane modification of clay on the physical properties of PBS/30BM nanocomposites was examined. The results of transmission electron microscopy and X-ray diffraction measurements revealed the effect of surface urethane modification of clay on the exfoliation and dispersion of the clay in the PBS matrix. As results of high exfoliation, PBS/30BM nanocomposites not only exhibited good thermal properties, but also a remarkable increase in physical properties (e.g., tensile strength, Young’s modulus, elongation at break). It also led to wide gallery spacing and predominant affinity between PBS and clay. The crystallization behavior and resultant structure of intercalated (30B20) and exfoliated PBS (30BM20) nanocomposites were investigated via isothermal crystallization and synchrotron small-angle X-ray scattering (SAXS). The dynamic viscosity of 30BM20 was markedly increased due to favorable interactions between the PBS matrix and the urethane group on the clay surface. However, 30BM20 showed similar crystallization rates to that of homo PBS because the surface urethane modification for 30BM precluded PBS matrix from the metallic group into clay to difficult in contact with each other, resulting in a reduced nucleation activity for the metallic group. SAXS profiles revealed that the long period and amorphous region size for 30B20 drastically decreased during isothermal crystallization. Meanwhile, 30BM20 gave similar values to homo PBS. In consequence, the introduction of a urethane modification considerably enhanced the physical properties of PBS but caused retarded crystallization. The second Chapter investigated how the water uptake features and carrier characteristics of the TS-1 zeolite affected the physical properties and enzymatic hydrolysis of biodegradable polymer. The TS-1 zeolite was adopted to prepare PTHC without heavy metal toxic substance, which can act as a catalyst as well as a reinforcement filler in PTHC. The rheological properties of PTHC with high zeolite contents showed low complex viscosity, as compared with PTHC with low TS-1 zeolite contents. The introduction of the TS-1 zeolite in the PBS matrix did not significantly affect the changes in the size of the long period, lamella thickness, or the amorphous region, indicating that PBS chains do not penetrate into zeolite pores, as confirmed by SAXS profiles. In enzymatic hydrolysis for 90 days, TS-1 zeolite more accelerated the hydrolysis of PTHC than that of homo PBS, indicating that TS-1 zeolite can act as a carrier for enzyme activation. In isothermal crystallization, TS-1 zeolite played a role of a nucleation agent of PTHC, resulting in a decrease in the half-time of crystallization compared with homo PBS. However, nucleation effect of TS-1 zeolite does not depend on TS-1 zeolite content. The large surface area of the mesoporous structure make chain movement into and out of mesoporous mouths of TS-1 zeolite facile, leading to cover the nucleation site due to byproduct deposition during the polymerization process. In the case of isothermal crystallization temperature ranged from 88°C to 92°C, nucleation of TS-1 zeolite occurred with TS-1 zeolite contents due to the presence of free byproducts and formation of a molecular chain into the mesoporous mouths. On the other hand, isothermal crystallization temperature ranged from 80°C to 84°C, resulted in little nucleation effect due to steric hindrance in the mesoporous structure. Synchrotron SAXS analysis suggested that TS-1 zeolite might accelerate lamellar re-crystallization during the heating process. In the third chapter, the possibility of application of eletrospun fiber to biomedical fields was checked. To use electrospun fibers as drug carrier and wound dressing materials, there have to meet essential factors such as evenness, thin diameter and lower air porosity. Ultra-thin PTHC nanofibers of less than 100 nm were prepared for biomedical applications. This is a tenth part compare to that of homo PBS, attributed to magnetization effect of TS-1 zeolite. Homo PBS has no cytostatic ability, whereas decreasing extent of cytostatic (%) for PTHC nanofiber has 99.8% to klebsiella pneumonia bacterica. The release of the triclosan drug was followed by UV-vis spectroscopy in phosphate buffer of Ph 7.4 at 37.5°C. The absorbed drug contents onto nanofiber based on PTHC materials was higher than that of homo PBS. This is attributed to large surface area and absorption characteristics of TS-1 zeolite. After drug release test for 10 days, we performed antibacterial activity assessment of homo PBS and PTHC nanofibers to investigate the durability of antibacterial activity toward grampositive and gramnegative bacteria. As time passed, the antibacterial activity of two nanofibers was gradually decreased. Although drug released was completed after 5 days, PTHC nanofiber exhibited higher antibiosis capacity than homo PBS. This is attributed to the fact that TS-1 zeolite has a cytostatic action and it also made the electrospun fibers thinner, producing larger surface. After 10 days, enzymatic hydrolysis of PZ15-02 was significantly higher than that of homo PBS.