Radical scavenging capacity of lignin and its effect on processing stabilization of virgin and recycled polypropylene

Abstract

AbstractThe radical scavenging capacity of lignin was determined using spectrophotometric method by means of scavenging of the free radical 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH•) and compared with that of synthetic antioxidant Irganox 1010. Lignin reacted progressively with the DPPH• reaching a steady state in 6 h, showing high antiradical activity with a stochiometry of 5.5 reduced DPPH• molecules. Irganox 1010 showed lower antiradical activity reaching a steady state with DPPH• after 13 h. Moreover, stabilization efficiency of lignin has been investigated in virgin and recycled polypropylene. The stabilization effect of lignin was evaluated by melt volume rate (MVR). The efficiency of lignin as processing stabilizer in both series polypropylene samples was compared with that of synthetic antioxidant Irganox 1010. The presence and behavior of free radicals in the lignin/polypropylene composites formed during processing was determined by electron paramagnetic resonance (EPR). It was observed that used lignin sample could stabilise both virgin and recycled polypropylene. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007