5TH International Congress on Technology - Engineering & Science - Kuala Lumpur - Malaysia (2018-02-01)

Radical Scavenging Abilities Of Carbon Nanotubes And Their Applications

Radical scavenging efficiencies of various modified multiwalled carbon nanotubes (CNT) including ball-milled CNT (bmCNT), benzoyl peroxide-treated CNT, acid-treated CNT (CNT-COOH), and microwave-treated CNT were investigated in this study. Raman spectrometry, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy dispersive spectrometry were used to characterize these modified CNT. Electron paramagnetic resonance (EPR) and ultraviolet/visible spectrophotometer (UV/Vis) were used to measure radical scavenging efficiencies of the modified CNT for hydroxyl (OH.) radical and 2, 2-diphenyl-1-picrylhydrazyl (DPPH) radical, respectively. EPR, UV/Vis, and Raman spectra revealed that the radical scavenging efficiencies for both radicals increased with increasing contents of defect sites on the modified CNT. The DPPH radical scavenging efficiencies of the modified CNT were found to be relatively low as compared to the OH· radical scavenging efficiencies; the rankings in the scavenging efficiencies, however, were similar for both radicals. The findings in this study that the modified CNT were effective radical scavengers suggested that these CNT have potential applications as antioxidants or stabilizers. We also investigated the radical scavenging efficiencies of silane-grafted CNTs for OH and DPPH radicals, using EPR and UV–Vis, respectively. We used thermogravimetric analysis, Raman spectrometry, XPS, and SEM to characterize the silane-grafted CNTs. The EPR, UV–Vis, and Raman spectroscopic data revealed that the radical scavenging efficiencies of the silane-grafted CNTs increased upon increasing the degree of damage to the CNT structures following the grafting reactions, but decreased upon increasing the degree of the silane grafting, due to the steric bulk of the silane grafts on the surfaces of the CNTs. We used differential scanning calorimetry to examine the effects of the silane-grafted CNTs on the exothermic peaks of the free radical–initiated crosslinking reactions of vinyl ester/styrene resins. The silane-grafted CNTs retarded the crosslinking reactions to various extents: a higher degree of grafting resulted in a lower radical scavenging efficiency, leading to a lower degree of crosslinking retardation of the vinyl ester/styrene resins. CNT, bmCNT, and CNT-COOH were also assessed as thermal stabilizers in poly(vinyl chloride) (PVC). Films of pure PVC, CNT/PVC, bmCNT/PVC, and CNT-COOH/PVC cast from tetrahydrofuran were subjected to thermal aging in N2 in a test tube submerged in an oil bath maintained at 180 °C for a certain time. FTIR and UV-Vis spectra and discoloration of aged PVC composites were investigated on the formation of conjugated polyene structure in PVC. The results found that all three types of CNT of small amounts (0.1 or 0.3 phr) could stabilize PVC against thermal degradation by retarding the rate of formation of a conjugated polyene structure, with the stabilizing efficacy in the order of bmCNT > CNT > CNT-COOH. Moreover, Congo red and dehydrochlorination (pH measurement) tests were investigated on the degradation of PVC to HCl during the thermal aging as a function of time, CNT type and content. Thermal degradations of PVC to HCl were promoted by all three types of CNT in the initial 30 min of aging but were clearly stabilized against degradation over prolonged aging (for instance, 120 min) by bmCNT followed by CNT-COOH, both exhibiting the optimal stabilizing efficacy at 1 phr. The bmCNT was the most effective thermal stabilizer among the three types of nanotubes studied in PVC to resist both its discoloration and degradation of HCl. This newly-developed PVC composite with CNT as an additive provides an efficient route towards the development of highly thermal-stabilized PVC.
Yeong-Tarng Shieh, Wan-Wen Wang, Kai-Chu Hsieh