The effects of thermal treatment on the antioxidant activity of polyaniline

• Published in: Polymer degradation and stability Vol. 96; no. 12; pp. 2159 - 2166
• Main Authors: Nand, Ashveen V., Ray, Sudip, Gizdavic-Nikolaidis, Marija, Travas-Sejdic, Jadranka, Kilmartin, Paul A.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.12.2011; Elsevier
• Subjects: 2,2-diphenyl-1-picrylhydrazyl; air; antioxidant activity; Antioxidants; Applied sciences; assays; Benzenoids; Chemical reactions and properties; crosslinking; Degradation; Exact sciences and technology; Fourier transform infrared spectroscopy; free radical scavengers; Free radicals; heat treatment; hydrochloric acid; Nanorods; Nanostructure; Organic polymers; Oxidation; Physicochemistry of polymers; Polyaniline; Polyanilines; polymers; powders; Radical scavenging; scanning electron microscopy; Scavenging; temperature; thermal stability; Thermal treatment; thermogravimetry; Oxidation; Polyaniline; Nanorods; Radical scavenging; Thermal treatment; Heat treatment; Aromatic polymer; Temperature effect; Crosslinking; Antioxidant; Experimental study; Radical scavenger; Thermal stability; Conducting polymers; Thermal properties; Additive; Stabilizer agent; Organic free radical; Morphology; Preparation; Reaction mechanism; Nanorod; Aniline polymer
• ISSN: 0141-3910; 1873-2321
• DOI: 10.1016/j.polymdegradstab.2011.09.013

The thermal stability of chemically synthesized polyaniline (PANI) was examined, including granular (G) polyaniline powders formed conventionally in an HCl medium, and nanorod (NR) samples prepared using a falling-pH synthesis. The samples were examined before and after dedoping (dd) using thermogravimetric analysis (TGA), which showed small mass losses in the 200–300 °C temperature range, and greater mass losses due to oxidative degradation at higher temperatures. Furthermore, samples were treated thermally at 100, 125, 150, 175, 200, 250 and 300 °C for 30 min in air. SEM images did not show any pronounced effect on the morphologies of the samples from thermal treatment up to 300 °C. The ratios of the intensities ( Q/ B) of the predominantly quinonoid ( Q) and benzenoid peaks ( B) from FTIR spectroscopic analysis revealed that NR-PANI and NR-PANIdd underwent cross-linking upon thermal treatment up to 175 °C and were oxidized after treatment above 175 °C. G-PANI and G-PANIdd also underwent the same chemical changes with oxidation occurring above 200 °C. The free radical scavenging capacity of the samples was evaluated using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay, and was found to be independent of the spin concentrations of the samples. All samples exhibited a rapid decline in free radical scavenging capacity when exposed to temperatures above 200 °C, indicating that any polymer processing should be undertaken at temperatures less than this value to achieve high antioxidant activity.