Oxo-biodegradable polypropylene transition metal-free: evaluation of abiotic degradation by natural weathering and biotic degradation by respirometry

Abstract

Pro-oxidant additives promote thermal oxidation and photooxidation of polymers, producing oxygenated molecular fragments that can be assimilated by microorganisms. In this work, two different concentrations of benzoin were used to obtain oxo-biodegradable PP. The samples, in the form of flat films, were exposed to natural weathering for 20 days in the city of Porto Alegre, during the Brazilian summer. Subsequently, biodegradation was assessed using soil respirometry. The abiotic degradation process was assessed using different PP characterization techniques: dilute solution viscometry, FTIR, contact angle, TGA, DSC and SEM. After exposure to natural aging, the samples processed with the additive showed a greater reduction in molar mass, accompanied by a considerable increase in carbonyl-containing functional groups, which led to a reduction in contact angle values when compared to pure PP. In addition, oxo-biodegradable PP containing 0.5 and 1.5% (w/w) of the additive showed a significant loss of thermal stability, as well as a reduction in melting point, indicating greater degradation of these samples. These changes caused the films to weaken, as evidenced by the appearance of flaking and erosion in the micrographs. The process of biotic degradation was assessed by quantifying the _CO2 produced by aerobic respiration in the respirometers. The biodegradation process of oxo-biodegradable PP began more slowly than that of cellulose. However, after 120 days of cultivation, it was possible to observe that PP containing 1.5% (w/w) benzoin showed mineralization of approximately 16%. Benzoin proved to be an effective pro-oxidant additive, favoring the abiotic and biotic degradation of PP.