Micromechanical analysis and fracture mechanics of Poly(lactic acid) (PLA)/Polycaprolactone (PCL) binary blends

Even Poly(lactic acid)/polycaprolactone (PLA/PCL) blends have been studied in literature, the deformation mechanism that is related to the toughness increment with respect to pure PLA has not been investigated in detail. The novelty of this work is to understand in depth the correlation between the micromechanical deformation processes occurring in PLA/PCL blends to the macromechanical properties, their morphology and their fracture mechanism. PLA/PCL blends containing increasing amount of PCL (from 10 up to 40 wt%) were produced. A novel characterization approach, not yet investigated for these blends, was carried out by dilatometric uniaxial tests using a videoextensometer. The shape of the dilatometric curves coupled with SEM analysis revealed how changing the PCL amount different concurrent micromechanical deformation processes occurred. When 10 wt% of PCL was added only particles debonding occurred leading to lower enhancement of elongation at break; at 20 wt% both debonding and voids growth along the tensile direction occurred, while at 40 wt% of PCL shear yielding was predominant that lead to a great enhancement of the elongation at break. The PLA/PCL blends capability to absorb energy at slow rate, was evaluated by the elasto-plastic fracture approach based on the ESIS load separation criterion. The results obtained was then correlated with the final blend morphology.