Tunable radical scavenging activity of carbonaceous structures and their anti-oxidant behaviour in polymer based nanocomposites

Abstract

Introduction: Carbon nanotubes (CNTs), due to their electronic properties, show radical scavenging activity toward the radical formed during the degradation processes of polymeric materials. In this work, we propose a novel strategy to control the CNTs anti-oxidant features through the application of an ultrasound treatment (us). Materials and Methods: Ultra high molecular weight polyethylene (UHMWPE); multi-walled carbon nanotubes (CNTs); CNTs have been sonicated at room temperature for different time intervals. Nanocomposites have been prepared though hot compaction and fully characterized. Results: The content of CNTs structural defects, evaluated through Raman-spectroscopy, increases with increasing the us-time and the last can be invoked as responsible for the amplified radical scavenging efficiency of us-CNTs, estimated through DPPH assay. The us-CNTs containing nanocomposites have been subjected to thermo- and photo- oxidative treatment and the progress of the degradation processes has been followed by analyzing the evolution in time of the FTIR spectra collected on nanocomposite thin films at regular time intervals. The nanocomposites show progressively improved thermo- and photo- oxidative stability with increasing the us-time, indicating that the oxidative resistance of the nanocomposites is strictly dependent on the CNTs defect amount. Discussion: CNTs have been subjected to us treatment with the aim to capitalize the structural defects induced by sonication, to obtain nanofillers with controlled radical scavenging activity. Nanocomposites containing us-CNTs show a photo- and thermo- oxidative resistance significantly improved with respect to that of UHMWPE/untreated CNTs, indicating that us treatment is effective in enhance the reactivity of CNTs toward macroradicals coming from the polymer degradation reactions. In all, polymer-based nanocomposites with modulated photo- and thermo-oxidative resistance can be achieved, tuning the CNT radical scavenging properties, which can be rationally controlled by the ultra-sound assisted defects formation.