Poly (lactic acid) (PLA) was submitted up to five cycles of extrusion in order to evaluate the effect of mechanical recycling. The material was evaluated under two conditions, thoroughly dried before processing and without drying. The changes in the molecular weight, acidity, thermal properties and coloring were assessed after each extrusion, and with this information, mechanisms of degradation were purposed. Molecular weight was reduced at a maximum of 30% after the most aggressive condition; five cycles without drying, which caused also an increase in acidity due to hydrolysis. Thermal properties were not significantly altered, which in combination to the molecular weight decrease allow to infer the recyclability of PLA. However, the most degraded samples had developed strong yellowing, particularly for samples without drying, which could be a problem for final products.

Resumo Sistemas pró-degradantes fundamentados em estearatos de ferro e de manganês e o aditivo comercial d2w, fundamentado em sal orgânico de manganês, foram avaliados em filmes de polietileno de alta densidade (PEAD) em ambiente termooxidativo (estufa a 80 °C e ausência de luz). A degradação termooxidativa foi monitorada por propriedades mecânicas, espectroscopia de infravermelho e cromatografia por exclusão de tamanho. Os resultados mostram que ambos os metais aceleram a degradação termooxidativa do PEAD. Entretanto, o desempenho pró-degradante do estearato de manganês é significativamente superior ao do estearato de ferro. Para o ferro, a degradação aumenta com o aumento da concentração do metal, enquanto que o manganês apresenta valor máximo de degradação em função da concentração. O estado de oxidação do ferro não interfere no desempenho pró-degradante. O aditivo comercial d2wTM acelera, significativamente, a termooxidação do PEAD, mas seu desempenho é inferior ao estearato de manganês provavelmente em função do conjunto de estabilizantes adicionados ao produto comercial.

Abstract The evaluation of pro-degradant systems based on iron and manganese in the form of metallic stearate, and d2wTM commercial additive, based on organic salt of manganese, was carried out on films of high density polyethylene (HDPE) in thermal oxidative conditions (80 °C oven and absence of light). The thermo oxidative degradation was monitored by mechanical properties, by infrared spectroscopy and by size exclusion cromatography. The results show that both metals accelerate thermal oxidative degradation of HDPE. However, the pro-degrading performance of manganese is significantly higher than iron. Considering iron, the degradation increases with increasing concentration of the metal, while manganese presents the maximum value of degradation depending on the concentration. The oxidation state of iron does not interfere with pro-degrading performance. The commercial additive d2wTM significantly accelerates HDPE thermo-oxidation, but its performance is lower than manganese stearate as a function of the set of stabilizing additives to be added to the commercial product.