On the design and fabrication of biomedical devices, the mechanical integrity and the thermal stability of the materials used are of paramount consideration. In this study, the effects of 13.56 MHz radio frequency plasma modification using argon (Ar) and oxygen (O2) discharges on the morphology, thermal properties, and tensile properties of the nonwoven electrospun chitosan/poly(vinyl alcohol) nanofiber mats were investigated. The scanning electron microscope images showed a significant change in the morphology of the nanofiber mats due to the Ar and O2 plasma treatment. The thermogravimetric-differential thermogravimetry data revealed two major degradation steps for both the pristine samples and the Ar plasma-treated samples due to the molecular backbone degradation and decomposition of polyene and carbonyl residues. However, a third peak was observed for O2 plasma-treated samples which may be due to the oxygen functionalities imparted by the discharge as seen from the Fourier-transform infrared spectroscopy data. Differential scanning calorimetry (DSC) results have shown the glass transition temperature at 65–68 °C and a melting temperature at around 200–220 °C. Also, a decrease in the crystallinity of the plasma-treated samples were noted from the DSC thermograms. A significant (p < 0.05) decrease in the tensile strength, yield strength, Young's modulus, and elongation at break were noted for the plasma-treated samples due to the etching and ablation effects induced by energetic particle interactions. However, the mechanical properties are still comparable with the tensile properties of human tissues such as the skin. These nonwoven mats with tunable properties have potential use in biomedical engineering, particularly as tissue scaffolds, wound dressings, sutures, and antibacterial gauzes.
Natural zeolites such as mordenite are excellent adsorbents for heavy metals. To enhance the adsorption capacity of zeolite, sodium-exchanged samples were irradiated with 13.56 MHz capacitively coupled radio frequency (RF) argon gas discharge. Hexavalent chromium [Cr(VI)] was used as the test heavy metal. Pristine and plasma-treated zeolite samples were soaked in 50 mg/L Cr solution and the amount of adsorbed Cr(VI) on the zeolites was calculated at predetermined time intervals. Compared with untreated zeolite samples, initial Cr(VI) uptake was 70% higher for plasma-treated zeolite granules (50 W 30 min) after 1 h of soaking. After 24 h, all plasma-treated zeolites showed increased Cr(VI) uptake. For a 2- to 4-month period, Cr(VI) uptake increased about 130% compared with untreated zeolite granules. X-ray diffraction analyses between untreated and treated zeolite samples revealed no major difference in terms of its crystal structure. However, for plasma-treated samples, an increase in the number of surface defects was observed from scanning electron microscopy images. This increase in the number of surface defects induced by plasma exposure played a crucial role in increasing the number of active sorption sites on the zeolite surface.
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