On the Production of Poly(Lactic Acid) (PLA) Compounds with Metallic Stearates Based on Zinc, Magnesium and Cobalt. Investigation of Torque Rheometry and Thermal Properties

The addition effects of zinc (Zn), cobalt (Co), and magnesium (Mg) based metallic stearates into poly (lactic acid) (PLA) matrix were investigated through torque rheometry, thermogravimetry (TG) and in the Differential Scanning Calorimetry (DSC). PLA compounds/metallic stearates were processed using an internal laboratory mixer with 0.25 wt% Zn, Co, and Mg. Torque rheometry results indicated that PLA/stearate compounds showed higher thermomechanical degradation during processing related to PLA. PLA viscosity is reduced upon stearates addition, especially in the compound with Zn. This behavior suggested PLA chain scission in the presence of metallic stearates during processing, corroborating the decrease in the torque plots. PLA/Zn started to lose weight at lower temperatures than the other compounds, indicating higher pro-oxidant potential. It was observed that Co and Zn significantly reduced the glass transition temperature (Tg), as well as PLA's crystalline parameters, which suggests PLA's molecular scission during processing, heading to greater flexibility and reducing Tg. Zn stearate was the most aggressive to PLA's thermomechanical degradation, suggesting a stronger pro-degradant effect.