Pentaerythritol and Glycerol Esters Derived from Gum Rosin as Bio-Based Additives for the Improvement of Processability and Thermal Stability of Polylactic Acid

Gum rosin esters are some of the most common gum rosin derivatives used in different applications, such as coatings, paper, varnishes, chewing gum, and food industries. In this study, gum rosin esters are used as additives for polylactic acid (PLA) to improve its processability and thermal stability. Blends of an amorphous PLA with two different gum rosin esters, pentaerythritol ester and glycerol ester, were prepared by melt extrusion process in concentrations from 1, 3, and 5 phr. Besides the comparison of thermal degradation, microstructure assessment, and melt flow index (MFI) analysis, the processability performance during testing samples production by injection molding process was evaluated. Experimental results showed that MFI values of PLA-gum rosin ester blends increased by 100%, 147%, and 164%, along with increasing content of gum rosin esters addition, in both cases. Also, both derivatives slightly improved PLA thermal stability (around 3 degrees C higher). Injection molding temperature decreased by at least 20 degrees C for PLA-gum rosin ester blends compared with neat PLA. Furthermore, the maximum tensile strength of PLA-gum rosin esters was negligibly affected in formulations with low content of gum rosin esters, and the FESEM images revealed a good dispersion and compatibility of gum rosin ester particles into PLA matrix in both concentrations.