Optimization of PLA compounds using novel nucleating agents and plasticizers

Biopolymers such as Polylacticacid (PLA) by politicians and the press are often referred as the materials of the future. However, this overlooks the fact that the material properties of many biopolymers are not yet equal to those of conventional industrial polymers. For this reason, their use is currently limited to the packaging and medical sectors. Unmodified PLA has relatively low heat and impact resistance, which is insufficient for most technical applications. The aim of this work is to improve the characteristics of PLA by optimizing the crystallization properties through the addition of novel nucleating agents (twin-screw compounding). The assessment is carried out using DSC analysis and the resulting calculated thermodynamic parameters. Subsequently chosen compounds are selected for measuring mechanical properties. The methods used for measuring these properties are tensile tests, the Charpy impact test, and the measurement of the heat deflection temperature (HDT). The results show that sorbitol is the most effective nucleating agent for the nucleation of PLA 4032D, with regard to the optimization of the heat resistance and toughness of the material. However the best crystallization rates from the melt can only be achieved by the further addition of polyethylene glycol (PEG) as a plasticizer. The combined influence of sorbitol and PEG in PLA 4032D, can improve the impact properties by more than 500 % to a value of 131.3 kJ/m2 (reference sample 21.8 kJ/m2) and the heat resistance by about 20 % to 65.9 °C (reference sample 54.0 °C).