Assembly and Fracture of Supramolecular Crystals in PLA─Demonstration of a Novel Strategy for Imparting Ductility

The deployment of novel sustainable plastics often encounters the problem of mechanical brittleness. This work demonstrates a supramolecular-additive strategy of imparting ductility to an otherwise brittle glassy polymer using poly(lactic acid) (PLA) as an example. In the presence of 5 wt % of a β-alanine derivative, PLA displays ductile deformation with the uniaxial strain at break reaching ∼50% and the modulus unaffected. The overall toughness is improved ∼5.8 times, and embrittlement is absent over 50 days. The hierarchically self-assembled structure of the additive in the PLA phase is elucidated by a combination of X-ray scattering, spectroscopic, and microscopic methods. The mechanism of the ductile deformation is proposed to involve crazing initiated by the fracture of the supramolecular assemblies uniformly distributed in the PLA phase. The molecular structure of the additive is simple and thus practical, and the modular synthesis permits easy alterations for toughening different brittle plastics.