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Antioxidative Activity of Carbon Nanotube and Nanofiber
Carbon nanotubes (CNTs) and carbon nanofibers (CNFs) have electron affinities similar to those of fullerenes C60 and C70 and they aretherefore capable of acting as radical scavengers in free radical chain reactions, including polymerisation and the thermo-oxidative degradation of polymers. It is assumed that the CNTs and CNFs used asintegral part of polymer composites are able to exhibit an antioxidant effect in these materials because of their radical accepting capacity. To examine this presumption the antioxidative activity oforiginal and purified commercial multiwall carbon nanotube MWCNT and carbon nanofibre of platelet structure CNF-PL has been studied by means of a model oxidation reaction of cumene initiated(2,2'-azobisisobutyronitrile, AIBN) in liquid phase. This model reaction was designed to simulate the thermo-oxidative processes in carbon-chain polymers and allows comparison and transfer of obtained results to apolymer system. Kinetic measurements of oxidation rates showed that the effect of inhibition for the model oxidative reaction in the presence of the original and purified MWCNT and CNF-PL stronglydepends on the presence of metals (Co, Fe) in the nanoparticles. Rates of oxidation Wo2 (CNT;CNF) observed for the unrefined samples are result of the two competing rates - rate of inhibition Winh.(CNT;CNF) caused by structures of the CNT or CNF and the rates of initiation Wi(M) due to the following interaction: ROOH + M (Co;Fe) i.e, Wo2 ~ W inh (CNT;CNF) + Wi(M). The effective rate constants forthe addition of cumyl radicals (R??) to MWCNT and CNF-PL have been determined. These constants reduced to the same concentration (0.5wt.%) and temperature (60oC) units have magnitudes: k1(MWCNT) [MWCNT]= (2.8 ± 0.3) ??104 s-1and k1(CNF) [CNF] = (6.0 ± 1.0) ??103 s-1. Thus, the effective rate constant, reflecting the antioxidative activity for the CNT, is five times higher than that for the CNF,...