Eui Sang Yoo

Compatibility and physical properties of poly(lactic acid)/poly(ethylene terephthalate glycol) blends

AbstractBlends of poly(lactic acid) (PLA) and poly(ethylene terephthalate glycol) (PETG) of various compositions were prepared by melt compounding and their compatibilities, physical properties, and isothermal crystallization behaviors were investigated. The calculated solubility parameters of PETG are similar to those of PLA. The interaction parameter between PLA and PETG was derived from the Flory-Huggins theory and predicted that PLA and PETG are miscible when PETG contents are below 22 wt%. In accordance with this result, the tan δ peak and glass transition temperatures of blends determined from dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) showed a single peak at PETG contents lower than 22 wt%. Tensile test results showed that the elongation at the break of blends increased with an increase in PETG content. DSC and isothermal crystallization results showed that PETG accelerates the crystallization rate of PLA at PETG contents lower than 22 wt%, indicating that PETG acts as a nucleation agent in the crystallization of PLA. Wide angle X-ray diffraction results (WAXD) showed that the crystalline structure of PLA is not affected by the incorporation of PETG.

Fabrication of superabsorbent ultrathin nanofibers using mesoporous materials for antimicrobial drug-delivery applications

AbstractThe goal of this study was to prepare functionalized, ultrathin nanofibers using mesoporous materials (TS-1 zeolite) with maximum capability to both absorb drug and control drug release (these fibers are herein referred to as PZ-01); a second goal was to prepare nanofibers that exhibit biodegradability after drug release. Under optimal conditions, the characteristic of TS-1 zeolite enabled the preparation of ultrathin nanofibers with diameters below 100 nm, or one-twentieth the size of homo-poly(butylene succinate) (PBS) fibers. In addition, PZ-01 nanofibers exhibited high drug loading capacity compared to homo-PBS fibers. This result was attributable to the large surface area of ultrathin nanofibers and to the strong ionic interaction between hydrophilic drugs and the metal ions of TS-1 zeolite. In vitro cytostatic assay indicated that prepared PZ-01 has cytostatic action toward both Gram-positive and Gram-negative bacteria. The excellent drug wetting behavior of PZ-01 led to longer drug-release times. After drugrelease tests, antibacterial tests confirmed that homo-PBS fibers had diminished antibiotic activity regardless of the type of bacteria, whereas the antibacterial activity of tested PZ-01 was highly efficient against both Gram-positive and Gram-negative bacteria. In the cell viability test, PZ-01 exhibited a greater decrease in cytotoxicity and an increase in cell viability compared with the homo-PBS nanofiber. Based on this research, we anticipate that these materials will be promising candidates for biomedical applications such as biofilters for microbes, wound dressings, and drug-delivery products.

Effect of the mesoporous structure of titanium silicate (TS-1) zeolite on the melting behavior and isothermal crystallization behavior of poly(butylene succinate)/TS-1 zeolite hybrid composites

AbstractIn this study, we investigated the effects of mesoporous titanium silicate (TS-1) zeolite on the melting behavior and isothermal crystallization in poly(butylene succinate) (PBS)/TS-1 zeolite hybrid composites (PTHC). Isothermal crystallization results revealed that TS-1 zeolite acted as a nucleation agent in PTHC, thus the t1/2 of PTHC was faster than that of homo-PBS. However, the nucleation effect of TS-1zeolite did not depend on the TS-1 zeolite content. The large surface area of the mesoporous structure readily formed molecular chains inside and outside of the pore mouths of TS-1 zeolite, covering the nucleation site, as a result of the byproduct deposition during polymerization. At isothermal crystallization, temperatures ranging from 88 to 92 °C, nucleation of TS-1 zeolite occurred because of the presence of free byproducts and the formation of a molecular chain in the pore mouths. In contrast, isothermal temperatures ranging from 80 to 84 °C resulted in ineffective nucleus activation because of the steric hindrance in the porous structure. Synchrotron small-angle X-ray scattering (SAXS) analysis revealed that TS-1 zeolite can accelerate lamellar recrystallization during heating.