Jin-Bum Moon

Physico-chemical characteristics of high performance polymer modified by low and atmospheric pressure plasma

In this work, the effect of low pressure plasma and atmospheric-pressure plasma treatment on surface properties and adhesion characteristics of high performance polymer, Polyether Ether Ketone (PEEK) are investigated in terms of Fourier Transform Infrared Spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and Atomic Force Microscopy (AFM). The experimental results show that the PEEK surface treated by atmospheric pressure plasma lead to an increase in the polar component of the surface energy, resulting in improving the adhesion characteristics of the PEEK/Epoxy adhesive system. Also, the roughness of the treated surfaces is largely increased as confirmed by AFM observation. These results can be explained by the fact that the atmospheric pressure plasma treatment of PEEK surface yields several oxygen functionalities on hydrophobic surface, which play an important role in increasing the surface polarity, wettability, and the adhesion characteristics of the PEEK/Epoxy adhesive system.

Processing and Characterization of Space-Durable High-Performance Polymeric Nanocomposite

In this investigation, efforts were given to develop carbon-nanofiber-reinforced polybenzimidazol nanocomposite for space application. Processing of polybenzimidazol was carried out by using polybenzimidazol in powder and solution forms. Thermomechanical properties of compression-molded polybenzimidazol, unfilled polybenzimidazol films, and nanofiber-reinforced polybenzimidazol films were investigated using thermogravimetric analysis, dynamic mechanical analysis, and tensile testing. Thermogravimetric analysis revealed that both compression-molded polybenzimidazol and polybenzimidazol films show high thermal stability. Dynamic mechanical analysis studies depicted that both compression-molded polybenzimidazol and polybenzimidazol neat films exhibited a high storage modulus, even at a temperature of 250°C. Polybenzimidazol nanocomposite films were cast with different loadings of carbon nanofibers from 0.5 to 2 wt % in polymer solution. Addition of carbon nanofibers improved the thermal stability and storage modulus of polybenzimidazol film. Mechanical testing showed that both compression-molded polybenzimidazol and polybenzimidazol films resulted in the highest ultimate tensile strength in comparison to any unfilled polymer. Investigation under scanning electron microscopy confirmed uniform dispersion of carbon nanofibers in polymer solution. Analysis of fractured surfaces revealed that neat polybenzimidazol film exhibited ductile failure and dispersion of carbon nanofibers into the polybenzimidazol, resulting in transformation from ductile to brittle failure.

High velocity impact characteristics of MWNT added CFRP at LEO space environment

In this paper, multi-wall carbon nanotube (MWNT) added carbon fiber reinforced plastics (CFRP) composites are suggested as solutions to improve the impact energy absorbing capability of CFRP for spacecraft application because it was proven that the resistance against LEO environment and the quasi-static material properties of CFRP can be improved by adding MWNT in previous papers. To verify the effect of MWNT on the impact energy absorbing capability of composite materials, normal CFRP and MWNT-reinforced CFRP were prepared and tested by using a two-stage light gas gun that can accelerate an aluminum ball of a diameter of 5.56 mm to 1 km/s. And the applicability of MWNT against hypervelocity impact of space debris was studied. In addition, accelerated ground simulation experiments were performed for each material model to simulate the aging of composite materials to verify the effect of LEO environmental aging on impact absorbing capability of composites. For the aging experiment, the impact specimens were simultaneously exposed to high vacuum, atomic oxygen, ultra violet light, and thermal cycling. After being exposed to simulated LEO environment, high velocity impact tests were performed for each material. As a result, MWNT did not have a significant improvement on the impact energy absorbing capability of CFRP under high velocity impact, even though the quasi static material properties are improved by adding MWNT. This is caused by the early generation of fiber breakages on the impact surface before enough generation of progressive failure which is one of the impact energy absorbing mechanism. Similarly, MWNT has less effect on the impact energy absorbing capability of CFRP under LEO environment.