Polylactic acid (PLA) is an emerging bio-based polymer, capable of replacing polyolefins. Although its production is increasing, high molecular weight PLA is difficult to achieve. As a result, it has low melt strength – limiting its ability to undergo different processing methods. Chain extension is a basic resolution, but common extenders are small molecules, reduces PLA biodegradability, and are hazardous to the environment after degradation. In this study, tannic acid – an organic macromolecule – was epoxidized and used as a PLA chain extender. The reaction occurs during melt processing using a twin-screw extruder, where the epoxy groups of tannic acid react with the end groups of PLA to achieve extension or branching. Initial observations indicated that low epoxidized tannic acid (ETA) loading, at constant extrusion parameters, reduces the complex viscosity and number-average molecular weight. However, the weight-average molecular weight was only slightly reduced compared to the pure polymer and the polydispersity index (PDI) increased, suggesting different chain lengths were formed. As ETA loading increased, a decreasing trend was perceived for both weight-average molecular weight and PDI – implying that chain extension is dominating. Hence, we hypothesize that the optimum extrusion parameters play a critical role in overcoming thermo-oxidative degradation and maximize the chain extension capabilities of ETA. To further investigate, we vary the rotation speed and temperature profile of the extruder, which allows us to determine the optimal parameters for chain extension. In addition, we analyze different degrees of chain extension and/or branching obtained from varying extrusion parameters by correlating the reaction efficiency with the specific mechanical energy, residence time, and rheological properties of the extended PLA. Furthermore, recycling performance, 3D printing capability, and biodegradability will also be explored. Therefore, a bio-based macromolecule can be used as a chain extender for PLA to increase its molecular weight and maintain its nature-friendly characteristic.
