Joon Pyo Jeun

The Characterization of Polyacrylonitrile Fibers Stabilized by Electron Beam Irradiation

This study investigates polyacrylonitile(PAN) fibers stabilized with various doses of electron beam irradiation (EBI) ability to produce carbon fibers. Feasibility was verified by FT-IR, the percent of gel fraction, density, DSC, XRD, and mechanical measurements. FT-IR spectra showed that the intensities of the stretching C≡N bonds decreased at 2,244 cm−1 with increasing EBI dose. This de crease was related to cyclization of nitrile groups during EBI-stabilization. The degree of cyclization was determined from the gel fraction and density tests. The gel content and density of PAN fibers stabilized by EBI increased with an increase in the EBI dose. Thermal properties were characterized by differential scanning calorimetry (DSC) and thermally activated reactions. DSC curves showed that EBI treatment influenced the quantity of released heat and the exothermic position at low temperature over a wide temperature range. The strongest diffraction peak from the PAN precursor fiber arose from the (100) plane; its stabilization index (SI) was evaluated by X-ray diffraction. The X-ray results showed that the peak intensity decreases gradually with increasing EBI dose. In addition, tensile strength decreased the EBI stabilization level.

Preparation of Cellulose-based Nanofibers Using Electrospinning

Eelctrospinning is a straightforward method to prepare fibers with diameters as small as several tens of nanometers (Doshi & Reneker, 1995). In eclectrospinning, a high electrostatic voltage is imposed on a drop of polymer solution held by its surface tension at the end of a capillary. The surface of the liquid is distorted into a conical shape known as the Taylor cone. Once the voltage exceeds a critical value, the electrostatic force overcomes the solution surface tension and a stable liquid jet is ejected from the cone tip. Solvent evaporates as the jet travels through the air, leaving behind ultrafine polymeric fibers collected on an electrically grounded target (Fong et al., 1999, 2002; Shin et al., 2001). Electrospun mats have a larger specific surface area and small pore size compared to commercial non-woven fabrics. They are of interest in a wide variety of applications including semi-permeable membranes, tissue engineering scaffolds and drug delivery systems (Tsai et al., 2002; Gibson et al., 2001; Kenawy et al., 2002; Luu et al., 2003). Recently, electrospun nanofibers (NFs) based on cellulose and its derivatives have been studied as potential candidates for applications within the field of pharmaceuticals. For instance, several reports deal with the investigation of electrospun fiber mats as delivery vehicles, showing dosage forms with useful and controllable dissolution properties. This interest in cellulose-based NFs is primarily driven by its environmental value as a biomaterial. The cellulose is an abundant and renewable resource found in most parts of the world, which makes it a cheap raw material for various applications (Zeng et al., 2003; Jiang et al., 2004; Verreck et al., 2003; Liu & Hsieh, 2002). However, little research has been done on the use of cellulose and cellulose derivatives as a raw material within electrospinning. The complications involved in electrospinning of cellulose are mainly due to the many difficulties ascribed to the material, one being its reluctance to interact with conventional solvents. Therefore, the choice of solvent systems is very important. Ethyl-cellulose (EC) is a kind of cellulose ether, and it shows a non-biodegradable and biocompatible polymer. EC is one of the extensively studied encapsulating materials for the controlled release of pharmaceuticals (Prasertmanakit et al., 2009). The film made from EC has quite good permeability, it has been widely used industrial air filter (Park et al., 2007). Hydroxypropyl methylcellulose (HPMC) is frequently used as the basis for sustained release hydrophilic matrix tablets (Ford, 1999). HPMC backbone is composed of glucose

Preparation of Ethyl-Cellulose Nanofibers via An Electrospinning

Ethyl-cellulose (EC) nanofibers were fabricated by an electrospinning of an EC solution with a 6-12 wt% concentration. Fiber morphology was observed under a scanning electron microscope and the effects of instrument parameters including the solution concentration, flow rate and electric voltage were investigated.

Synthesis and Characterization of Cation-Exchange Fibers with Radiation-Induced Grafting of Glycidyl Methacrylate onto Cotton Cellulose

Conventional ion exchange beads are used for purification and demineralization of water and for various other applications in the chemical synthesis, hydrometallurgy, and agricultural industries. However, there are some disadvantages associated with ion exchange beads, such as distillation causing porosity during solvent removal, pre-swelling of beads to allow for core functionalization, and pre-swelling of beads overnight prior to end use. Fibrous ion exchange materials have advantages over the conventional ion exchange beads, including simplification of the overall preparation. In this study, a cation-exchange fiber was prepared by a radiation-induced grafting method. Glycidyl methacrylate (GMA) was grafted onto cotton cellulose using a pre-irradiation method by electronbeam irradiation. Sequential treatment with sulfonic acid was performed to react with the cation pollutants. The degree of grafting increased up to 812% with the increase of absorbed dose, reaction time and monomer concentration. It was found that the sulfonation reaction occurred smoothly with 10% sodium sulfite solution, and a high 2.0 meq/g ion exchange capacity was obtained from 140% GMA-grafted non-woven cotton fabric.

Radiolytic Preparation and Characterization of Poly(styrene sulfonic acic)-grafted ETFE Membranes

In this study, ETFE-g-PSSA membranes with various degrees of grafting (DOG) and thicknesses were prepared by a simultaneous irradiation method. SEM-EDX instrument was applied to measure the relative distribution of sulfur which is corresponding to that of a grafted polymer over the Cross-section of the ETFE-g-PSSA membranes prepared at various irradiation conditions. The results indicate that to obtain the evenly-grafted membranes, a styrene/dichloromethane ratio is needed to be under 60 (v/v%), and a higher DOG is required as the film thickness increases. The effects of DOG and thickness on the ion exchanging capacity (IEC) and water uptake (WU) were investigated by measuring the IEC and WU values of the membranes with various DOG and thicknesses.

Preparation and Characterization of Polypyrrole-Coated Silicon Nanoparticles

Silicon (Si) nanoparticles were stabilized by sodium dodecyl sulfate and poly(Nvinylpyrrolidone) in water, and coated with polypyrrole (PPy) via an in-situ polymerization of pyrrole with FeCl3. TEM images revealed that the Si nanoparticles were successfully coated with PPy (average thickness, ~2 nm). The Li/PPy-coated Si electrode exhibited improved discharge capacities, when compared to that of a reported Li/pure Si electrode. PPy-coatings on the Si nanoparticles acted as efficient conducting agents and prevented an extraction of the cracked Si fragments into the electrolyte to some extent.

Graft Polymerization of Styrene onto Alumina Nanoparticles by a Radiation

Polystyrene-grafted γ-Al2O3 nanoparticles were successfully synthesized by a high energy irradiation technique. Surface modification of the nanoparticles with silane coupling agents was performed to introduce active sites on the γ-Al2O3 nanoparticles for a radiation-induced graft polymerization. The polymer graft yield increased with the absorbed dose. The graft yield was higher at a 50 vol% monomer solution than at 70 vol%.

Radiation Effect on Poly(ε-Caprolactone) Nanofibrous Scaffold

Nano- to micro-structured biodegradable poly(ε-caprolactone) nanofibrous scaffolds (PCL NFSs) were prepared by an electrospinning. Electrospinning has recently emerged as a leading technique for generating the biomimetic scaffolds for tissue engineering applications. The average diameter of the electrospun PCL NFSs ranged from 0.5 to 2 ㎛ depending on the solvent/nonsolvent mixture. PCL NFSs were irradiated using γ-ray and their mechanical properties and biodegradability were measured. In vitro/vivo degradation studies of the scaffolds as a function of the radiation dose were performed. The scaffolds were degraded more slowly in vitro than in vivo.