Sung Yeon Hwang

Superior Toughness and Fast Self‐Healing at Room Temperature Engineered by Transparent Elastomers

The most important properties of self-healing polymers are efficient recovery at room temperature and prolonged durability. However, these two characteristics are contradictory, making it difficult to optimize them simultaneously. Herein, a transparent and easily processable thermoplastic polyurethane (TPU) with the highest reported tensile strength and toughness (6.8 MPa and 26.9 MJ m-3 , respectively) is prepared. This TPU is superior to reported contemporary room-temperature self-healable materials and conveniently heals within 2 h through facile aromatic disulfide metathesis engineered by hard segment embedded aromatic disulfides. After the TPU film is cut in half and respliced, the mechanical properties recover to more than 75% of those of the virgin sample within 2 h. Hard segments with an asymmetric alicyclic structure are more effective than those with symmetric alicyclic, linear aliphatic, and aromatic structures. An asymmetric structure provides the optimal metathesis efficiency for the embedded aromatic disulfide while preserving the remarkable mechanical properties of TPU, as indicated by rheological and surface investigations. The demonstration of a scratch-detecting electrical sensor coated on a tough TPU film capable of auto-repair at room temperature suggests that this film has potential applications in the wearable electronics industry.

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.

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.

Heterogeneous zirconia-supported ruthenium catalyst for highly selective hydrogenation of 5-hydroxymethyl-2-furaldehyde to 2,5-bis(hydroxymethyl)furans in various n-alcohol solvents

5-Hydroxymethyl-2-furaldehyde (HMF) was hydrogenated to 2,5-bis(hydroxymethyl)furan (BHMF) (>99% yield) in various n-alcohol solvents using a Ru(OH)x/ZrO2 catalyst. The TON and TOF for the hydrogenation were calculated to be 912 and 304 h−1, respectively.

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.

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.

Butanol-mediated oven-drying of nanocellulose with enhanced dehydration rate and aqueous re-dispersion

AbstractThe application potential of nanocellulose has been previously hindered by the costly and slow drying methods that this material requires, including freeze/supercritical drying process. The main issue for nanocellulose commercialization is how effectively and rapidly its high water contents (90–99%) can be removed, all of which raise its transportation and processing costs. Oven-drying is the fastest, most economical, and most scalable method for dehydrating nanocellulose, but causes strong interfibrillar aggregation and leads to poor aqueous re-dispersion. Here, we report that the problems of nanocellulose oven-drying are comprehensively overcome by adding tert-butanol (t-BuOH) to the nanocellulose solution at >90%. In a lab-scale comparison, the t-BuOH-mediated oven-drying of aqueous nanocellulose showed lower drying times by a factor of 2–12 compared to water only oven-drying and freeze drying of the same material. The dispersibility of this dried nanocellulose is as high as the never-dried material in terms of particle size, light transmittance, and sedimentation. t-BuOH reduces interfibrillar shrinkage due to the lower surface tension of t-BuOH compared to water, and a remaining t-BuOH/water mixture decreases interfibrillar adhesion and contact. Graphical abstractThis paper suggests a strategy to improve the aqueous re-dispersibility of oven-dried nanocellulose, and to accelerate oven-drying rate.

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.

Trans crystallization behavior and strong reinforcement effect of cellulose nanocrystals on reinforced poly(butylene succinate) nanocomposites

Correction for ‘Trans crystallization behavior and strong reinforcement effect of cellulose nanocrystals on reinforced poly(butylene succinate) nanocomposites’ by Taeho Kim et al., RSC Adv., 2018, 8, 15389–15398.

Effect of Zeolite as a Green Catalyst and Nucleation Agent on the Physical Properties of Poly(Ethylene 2,5-Furan-Dicarboxylate)

In this study, poly(ethylene 2,5-furan dicarboxylate) (PEF) was synthesized from biomass-based dimethyl furan-2,5-dicarboxylate using different-sized zeolites, with substituted ions such as Li and K, as efficient green catalysts for in situ polymerization. The Z5Ali catalyst yielded the PEF biopolyester with the highest weight-average molecular weight among all the samples: 53,800 g/mol. From their TGA curves, it was confirmed that the PEF sample with ZA5Li as the catalyst showed an increased thermal stability compared to homo-PEF. Generally, homo-PEF exhibited a very low melt-crystallization rate with low enthalpy. However, all the PEF samples using zeolite as the catalyst formed endotherms I and II. This result was attributed to the fact that zeolite affects the melt and recrystallization of imperfect crystals due to physical hindrance.