Toughening of polylactide by two core-shell rubbers

Two different approaches were employed for toughening polylactide (PLA). In one method, hybrid impact modifier (EGMA) and nanoclay (Cloisite 93A) were simultaneously melt blended with PLA. In the second method, ultra-fine and fully-vulcanized acrylonitrile butadiene rubber particles functionalized with carboxyl groups (Narpow) were used to toughen PLA. These two types of PLA-based composites were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), tensile tests and J-integral measurements. It was found that PLA/Narpow composites showed increases in elongation-at-break and toughness compared to neat PLA. But these improvements were lower than those obtained in PLA/EGMA/Cloisite 93A composite and could be attributed to their different morphology. TEM images revealed that nanoclay was embedded within the EGMA particles, yielding a "core-shell" structure which was well-dispersed in the PLA matrix. By contrast, SEM images of the fracture surfaces exhibited vast agglomeration of the core-shell Narpow particles in PLA, which explained its low toughness. The PLA/EGMA/Cloisite 93A composite displayed evident matrix plastic shear deformation, leading to much enhanced toughness (JC). Thus, the JC values were increased from 0.32 kJ/m2 in neat PLA to 0.50 and 2.2 kJ/m2 for PLA/Narpow (86/14 w/w) and PLA/EGMA/Cloisite 93A (86/10/4 w/w) composites, respectively.