Jin Hyun Choi

Effect of stereoregularity on the properties of syndiotactic‐rich ultrahigh molecular weight poly(vinyl alcohol)/dimethyl sulfoxide/water gel

Syndiotactic-rich ultrahigh molecular weight poly(vinyl alcohol) (UHMW S-PVA) gels having syndiotactic diad (S-diad) contents of 61.5, 58.2, and 55.7% and similar molecular weights were prepared in dimethyl sulfoxide (DMSO)/water solution. The gelation temperature of UHMW S-PVA/DMSO/water solution decreases with an increase in syndiotacticity. A great difference in the gel melting temperature (T gm ) was not found between the gels having an S-diad content over 58.2%. However, a significant decrease of T gm was revealed in the gel having an S-diad content of 55.7%. The enthalpy of junction fusion and the number of segments participating in the junction of the UHMW S-PVA gel increases with syndiotacticity, and they are remarkably higher than the values of atactic PVAs reported in previous papers. The higher the syndiotacticity of the UHMW S-PVA gel, the higher is the dynamic storage modulus. The elasticity of the PVA gel with an S-diad content over 58.2% was recovered under cooling after heating, whereas almost no recovery was found in the gel having an S-diad content of 55.7%. The PVA gel having an S-diad content over 58.2% is opaque and exhibits a phase separated appearance in optical morphology, while the PVA gel with an S-diad content of 55.7% is almost transparent and phase separation does not occur. A highly microporous and close structure was observed for the surface of the UHMW S-PVA gels.

Syndiotacticity-rich ultrahigh molecular-weight poly(vinyl alcohol) film. I. Determination of optimum polymer concentration by zone-drawing method in film preparation

A new method using a simple zone-drawing technique has been suggested for determining the optimum initial concentration of a polymer solution that has suitable macromolecular entanglements. This method was developed to replace the incorrect inherent viscosity-measuring method for syndiotacticity-rich (syndiotactic diad content of 63.4%) ultrahigh molecular-weight (number-average degree of polymerization of 12,300) (UHMW) poly(vinyl alcohol) (PVA) solution. Syndiotacticity-rich UHMW PVA films were prepared from dimethyl sulfoxide (DMSO) solutions with different initial concentrations: of 0.1, 0.2, 0.3, 0.4, and 0.5 g/dL. In order to investigate the drawing behavior of the syndiotacticity-rich UHMW PVA films with different solution concentrations, the films were drawn under various zone-drawing conditions. Through a series of experiments, it was discovered that the initial concentration of PVA solution in DMSO caused significant changes in the draw ratio of the syndiotacticity-rich UHMW PVA film. That is, the one-step and maximum zone draw ratios of the film at an initial concentration of 0.3 g/dL exhibited its maximum values and gradually decreased at higher or lower concentrations. Thus, it was disclosed that the initial concentration of 0.3 g/dL is the optimum polymer concentration to produce a maximum draw ratio in this work. Based on the above results, it may be concluded that the optimum concentration of the initial PVA solution can be determined directly by measuring the zone draw ratio. The draw ratio, birefringence, crystallinity, degree of crystal orientation, tensile strength, and tensile modulus of the maximum drawn PVA film were 32.9, 0.0449, 0.61, 0.991, 1.91, and 46.2 GPa, respectively.

Preparation and characterization of syndiotacticity-rich ultra-high molecular weight poly(vinyl alcohol)/imogolite blend film

To enhance the physical properties of syndiotacticity-rich (syndiotactic diad content 63·4%) ultra-high molecular weight (UHMW) (number-average degree of polymerization 12300) poly(vinyl alcohol) (PVA) film, it was solution blended with rigid-rod imogolite in dimethyl sulphoxide. In addition, the blend film prepared was stretched using a high-temperature zone drawing technique for effective orientation of the film. Through a series of experiments, it was found that imogolite caused significant changes in the structure and properties of syndiotacticity-rich UHMW PVA film, i.e. imogolite acted as an important agent which increased crystal orientation of syndiotacticity-rich UHMW PVA, resulting in enhanced tensile strength of the film. However, imogolite played a hindering role in raising the amorphous orientation of syndiotacticity-rich UHMW PVA. The maximum tensile modulus of 19·8GPa and maximum tensile strength of 1·8GPa could be obtained at the maximum draw ratio of 7·45 for PVA/imogolite blend film. In the case of PVA homo film, the highest tensile modulus and strength were 25·2GPa and 1·4GPa, respectively.

Effect of zone drawing accompanied with crosslinking on the structure and properties of ultrahigh molecular weight polyethylene gel film

To enhance the thermal properties of ultrahigh molecular weight ( UHMW ) (viscosity-average molecular weight of 6 x 10 6 ) polyethylene (PE) gel film, this was crosslinked by dicumyl peroxide ( DCP ) during a high-temperature zone drawing, which is effective to orient film. Through a series of experiments, it turned out that crosslinking actualized by an optimum amount of DCP and high-temperature zone drawing technique caused significant changes in the structure and properties of UHMW PE gel film. That is, crosslinking increased storage modulus of UHMW PE gel film at 25°C, resulting in improving thermal properties of the film. On the contrary, the crosslinking effect played a hindering role in raising the draw ratio of UHMW PE gel film. Maximum storage modulus of 165 GPa at 25°C could be obtained at the draw ratio of 324 of uncrosslinked homo-PE gel film. In the case of crosslinked PE gel film, the highest storage modulus at 25°C reached 65 GPa at maximum draw ratio of 150. Crosslinked film exhibited high modulus, even at 190°C, to some extent, while uncrosslinked homo-PE gel film was molten completely at 150°C.

Biologic filler using human fibroblasts and placenta extracts.

Soft tissue augmentation with injectable materials has been a challenging problem for plastic and reconstructive surgeons. Although filler materials have been used for soft tissue augmentation, adverse effects such as inflammation, distortion, and repeated procedures due to absorption still exist. In this study, biologic filler containing human fibroblasts and placenta extracts was developed to overcome these problems as a concept of cell therapy. In an in vivo assay, 40 nude mice were divided into 4 groups: 1 control group and 3 experimental groups. Biologic fillers containing human fibroblasts untreated (control), cultured with 0.1% placenta extract (group 1), cultured with 10% fetal bovine serum (group 2), and cultured with both 0.1% placenta extract and 10% fetal bovine serum (group 3) were used in each groups. Cultured human fibroblasts were injected into the back of each mouse with fibrin glue to maintain the shape and volume. These groups were compared during an 8-week period. The gross, histologic, and biomolecular studies were proceeded to evaluate the effect of biologic filler. In geometric maintenance, volumes in experimental groups were 1.6 (group 1), 1.2 (group 2), and 1.9 times (group 3) more reserved than that in the untreated control group (control) at 8 weeks. In histology, abundant proliferation of fibroblasts as well as extracellular matrices including collagen and glycosaminoglycan was visualized in experimental groups. Enzyme-linked immunosorbent assay was used to analyze collagen and glycosaminoglycan, and reverse transcription-polymerase chain reaction was used to analyze the messenger RNA expression of COL1A1, a gene for collagen type 1, which shows a significant difference between control and experimental groups. There is no statistically significant difference between groups 1 and 2; on the other hand, group 3 statistically has the best outcome among the experimental groups.

Electrospinning Fabrication of Poly(vinyl alcohol)/Pullulan/TiO 2 Nanofibers

Poly(vinyl alcohol)(PVA)/pullulan/titanium dioxide(TiO2) composite nanofibers were produced at different TiO2 concentrations(1 and 3 wt.%) using the electrospinning method. The parameters of electrospinning including polymer contents, voltage and tip-to-collector distance(TCD) were optimized for fabrication process. The study showed that the best condition to make PVA/pullulan nanofiber and effect of TiO2 nanoparticles. The PVA/pullulan/TiO2 nanofibers were characterized by scanning electron microscope(SEM), transmission electron microscope(TEM), Thermogravimetric analysis (TGA) and X-ray diffraction(XRD).

Effect of Ethanol/water Solvent Ratios on the Morphology of Zein Nanofiber Mats and their Wettability

Zein is a hydrophobic protein produced from maize and has great potential in a number of industrial applications, such as food, food coating and food packaging. To obtain suitable electrospinning conditions for thinner and uniform zein nanofiber mats, a series of experiments was conducted on various volume ratios (v/v) of ethanol/water solutions with different zein concentrations. The prepared zein nanofiber mats were characterized by field emission scanning electron microscopy and contact angle measurements. Uniform zein fibers with a average diameter in the nanometer scale (300~500 nm) could be prepared from 30 wt.% zein in 7/3 (v/v) ethanol/water solutions.

Characterization of Nitro-Substituted Polybenzimidazole Synthesized by the Reaction with Nitric Acid

Abstract Nitro-substituted poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole]s (PBIs) were synthesized by the reaction of PBI with nitric acid in sulfuric acid under various conditions. The number of nitro groups substituted on the aromatic ring of PBI per polymeric unit varied from 1.44 to 3.55 according to the reaction conditions. An increase in reaction temperature and concentration of the nitric acid increased the degree of substitution. The inherent viscosity of the substituted polymer increased as the reaction temperature decreased. When the reaction temperature was 30°C, the inherent viscosity of the polymer increased as the concentration of nitric acid increased. The nitro-substituted PBI exhibited polyelectrolyte behavior in formic acid. The nitro groups substituted on PBI were dissociated when the polymer was heated to 450°C, displaying exothermic behavior, and the decomposition of polymer was proportional to its nitro group content. All nitro-substituted PBIs showed better solubilities in polar apro...