Document Type: Original research
Instituto de Macromoléculas (IMA) - Universidade Federal do Rio de Janeiro - UFRJ, CP 68525, CEP 21941- 590, Rio de Janeiro-RJ, Brazil
A fourth-generation Ziegler-Natta catalyst was prepared to synthesize polypropylene (PP), which was stabilized by in situpolymerization employing lignin as antioxidant. The antioxidant properties of lignin were compared with those of the commercial antioxidant Irganox 1010. The presence of lignin in the reaction medium slightly decreased the catalytic activity of the reaction. The isotacticity index (I.I.) of PP synthesized with lignin (PP-lig) was not affected by the presence of the additive in the reaction medium. The thermal properties, characterized by differential scanning calorimetry, showed slightly decreased degree of crystallinity (Xc), but the melting temperature (Tm) and crystallization temperature (Tc) were not affected when compared with the neat polymer. Lignin showed good activity as a stabilizer by thermogravimetry. The initial temperature of degradation (Tonset) increased when compared to the pure PP and PP stabilized with the commercial antioxidant. The lower carbonyl index of the PP, evaluated by infrared spectroscopy (FTIR) after thermo-oxidative treatment, also revealed the stabilizing action of lignin.