Antioxidant effect of lignite humic acids and its salts on the thermo-oxidative stability/degradation of polyvinyl alcohol blends

We demonstrate the antioxidant potential of humic acids in (green) polymer chemistry. Lignite humic acids and its sodium and ammonium salts were mixed at different concentrations with polyvinyl alcohol and thermogravimetry was used to assess the influence on the thermo-oxidative stability of resulted blends. Both protonized form and ammonium salt of humic acids caused increased stability of investigated polymers in the studied concentration range (0.5–10% of humic acids in polymer). In contrast to protonized form, the ammonium salt also showed moderating effect on polymer degradation kinetics. Sodium salts caused substantially lower stabilizing effect and presence of 10% of humic matter caused even destabilization. In all cases, however, when the degradation has already started, the presence of humic acids and its salts caused more intensive polymer decomposition, which resulted in lower weight of char.