Toughening Poly(lactide) with Bio-Based Poly(farnesene) Elastomers
Matthew W. Halloran, Jim A. Nicell, Richard L. Leask, Milan Marić
Abstract
The development and application of bio-sourced elastomers which can be blended with poly(lactide) (PLA) to enhance its poor material properties are of great interest as we move toward replacing petroleum-derived plastics with viable alternatives. As such, this work focused on the valorization of the terpene-based monomer, trans-β-farnesene (farnesene), as a building block to design rubber toughening agents to improve the impact strength of PLA blends. Ternary blends consisting of copolymers of farnesene–glycidyl methacrylate (PFGMA), farnesene–methacrylic acid (PFMAA) (20–30 wt % farnesene copolymers), and PLA exhibited significant improvements in impact strength and elongation at break (i.e., approximately 16-fold and 10-fold, respectively) over neat PLA. Torque mixer measurements and FTIR spectroscopy confirmed the occurrence of epoxy–acid/epoxy–hydroxyl interfacial compatibilization reactions catalyzed through hydrogen-bonding interactions. Phase morphologies of the ternary blends were evaluated with scanning electron microscopy (SEM) and showed an approximate 4-fold reduction in particle diameter relative to the binary systems (i.e., from 4.3 to 1.1 μm) with the compatibilized blend morphology deemed stable upon annealing. The toughening mechanism responsible for the improved mechanical properties observed with the ternary blends was also investigated by examining the impact fractured surface morphologies with SEM. A combination of enhanced interfacial adhesion coupled with shear yielding of the matrix was proposed as the main contributing factor to the improvement in mechanical properties observed in the ternary blends.