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 degrees 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 nano-mechanical 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 embrit-tlement 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.
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