Jun Mo Koo

High thermal stability and high tensile strength terpolyester nanofibers containing biobased monomer: fabrication and characterization

This research fabricated novel nanofibers with a terpolyester of isosorbide, ethylene glycol, 1,4-cyclohexane dimethanol, and terephthalic acid (PEICT) using electrospinning and characterized their properties. The nanofibers have higher glass transition temperature (Tg) than other polyester-type polymers, and a smaller diameter nanofiber has higher Tg than a larger diameter nanofiber. This is due to the orientation of polymer chains inside nanofibers, which was verified by DSC and polarized ATR-FTIR. The morphology and diameter of the nanofibers affected by concentration of PEICT solution were studied by SEM. It demonstrated smooth and well-formed nanofibers, and showed an increase of the diameter with increasing concentration. In addition, the tensile property, which was confirmed by UTM, was enhanced with increasing diameter because molecular orientation existed in finer nanofibers. They show a better tensile property than general biobased nanofibers such as silk, chitosan, and gelatin. Finally, fabrication of PEICT nanofibers was optimized and characterized. They can be utilized in various industrial applications such as tissue engineering, wound dressings, and health care devices.

Structural and thermal properties of poly(1,4-cyclohexane dimethylene terephthalate) containing isosorbide

Poly(1,4-cyclohexanedimethylene isosorbide terephthalate) (PICT) copolymers were synthesized by melt condensation with various contents of the corn derived monomer isosorbide (ISB). Since poly(1,4-cyclohexanedimethylene terephthalate) (PCT) has disadvantageous thermal processing properties as well as a high melting temperature, ISB could be used to control Tg and Tm simultaneously. An increased content of ISB can increase the Tg and lower the Tm by affecting the crystallization behavior and structural properties of PCT. The composition of PICT was confirmed using 1H-NMR spectroscopy, and the detailed structure was analyzed with correlation spectroscopy (COSY) and heteronuclear single-quantum correlation spectroscopy (HSQC). 13C-NMR spectroscopy was used for investigating the sequence distribution and from these results, the effect of the ISB-TPA dyad on the thermal properties was revealed. Solid state cross polarization/magic angle spinning (CPMAS) 13C-NMR spectroscopy was used to investigate the free space of an atom due to environment dependent relaxation behavior, which determines whether ISB is excluded from the crystal structure. Then, WAXD was used to analyze the crystal structure, representing the effect of ISB on the crystallization. Finally, polarized optical microscopy and atomic force microscopy were used to visualize the morphological change of the crystallite resulting from ISB.

Self-cleaning effect of electrospun poly (1,4-cyclohexanedimethylene isosorbide terephthalate) nanofibers embedded with zinc oxide nanoparticles:

This study examined the photocatalytic self-cleaning of novel nanofibers of co-polyester poly(1,4-cyclohexanedimethylene isosorbide terephthalate) (PICT). To obtain the self-cleaning property, zinc oxide (ZnO) nanoparticles were blended into the solution of PICT at five different concentrations. The morphology of the nanofibers was analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the degradation spectrum of the target dyes was confirmed by Fourier Transform Infrared (FT-IR) spectroscopy. Especially in the TEM images, there was clear evidence of a uniform dispersion of the ZnO nanoparticles embedded in the nanofibers. As the concentration of ZnO increased to 9 wt%, there was a greater dispersion of the ZnO nanoparticles on the nanofibers. The photocatalytic activity indicated that more efficient self-cleaning occurred at an irradiation time of 3 hours and a 9% concentration of ZnO nanoparticles in the nanofibers. We achieved around 99% self-cleaning efficiency from these nanofibers.

Synthesis and characteristics of biobased copolyester for thermal shrinkage film

A series of poly(1,4-cyclohexanedimethyl-trimethylene glycol terephthalate), (PCTG), co-polyesters were synthesized using 1,3-propanediol (PDO) and 1,4-cyclohexanedimethanol (CHDM) via melt polymerization. The characteristic of having a high thermal shrinkage ratio at low processing temperature conditions and a suitable molecular weight for film manufacture, with Mn ranging from 20 000 to 25 000 g mol−1 and a polydispersity of 1.8–2.0, suggests the use of the biobased monomer, PDO, in the film industry. The composition of the PCTG samples was confirmed using 1H-NMR spectroscopy. 2D NMR analyses (correlation spectroscopy (COSY) and heteronuclear single quantum correlation spectroscopy (HSQC)) were performed to analyze detailed structural information for PCTG. Sequence distribution was used to reveal the effect of PDO dyads in the polyester chain and identify the structural effect. In the case of the transesterification time, under fixed esterification conditions, it decreased as the CHDM content increased due to the high reactivity of CHDM which has a higher boiling point. A thermal shrinkage ratio test was done with the temperature ranging from 70 °C to 100 °C. As the PDO content increased, the low temperature conditions showed a relatively higher thermal shrinkage ratio owing to the structural characteristics of CHDM and PDO. This result could induce advantageous energy savings in heat shrink processes at low temperatures.

Structural deformation phenomenon of synthesized poly(isosorbide-1,4-cyclohexanedicarboxylate) in hot water

Previously syntheses of poly(isosorbide 1,4-cyclohexanedicarboxylate) (PICD) have overcome synthetic problems associated with the low-reactivity of isosorbide, using acetic anhydride to achieve in situ acetylation. However, this amorphous polymer exhibits unusual behavior when submerged in water at 100 °C. Severe deformation occurs, with cylindrical pellets changing into a disc-like morphology, similar to solvent-induced crystallization. The influence of water on the thermal behavior of PICD was analyzed, resulting in a mechanism analogous to solvent-induced crystallization, where the solvent functions as a plasticizer. Furthermore, the effects of acetic anhydride and open-ring isosorbide on structural deformation were investigated, revealing the occurrence of ester hydrolysis. Finally, solid state CP-MAS 13C-NMR was used to elicit the rearrangement or packing of carbons within the PICD structure.