Physical aging-induced embrittlement of PLA/PBAT blends probed by tensile test and AFM nanomechanical mapping

Poly(lactic acid) (PLA) is a well-known biodegradable sustainable polyester but with intrinsic brittleness. PLA can be toughened through blending with immiscible rubbery polymers like biodegradable poly(butylene adipate-co-terephthalate) (PBAT). However, little was done to examine the effectiveness of the additives after long-term physical aging. Herein, the mechanical properties of PLA/PBAT (80/20) blends were measured by combining tensile tests and atomic force microscopy (AFM) based nanomechanical mapping after ageing at 40 °C for different periods. It is found that the elongation at break of the blends decreases dramatically from 257 % after compression molding to 14 % after aging for 7 days, and an equilibrium value is not yet reached. AFM nanomechanical mapping reveals that the microscopic Young’s modulus distribution of PLA matrix broadens significantly with increasing aging time, reflecting the increase of heterogeneity and resulting in the embrittlement of the blends. This work raises the severe impact of physical aging on the mechanical properties of PLA based blends, which is usually overlooked but may limit their applications.