Kinetic and structural interpretations of post-yield crack resistance behavior of polyamide-6/polyolefin-g-maleic anhydride blends

Binary blends of polyamide-6 (PA-6)/polypropylene-grafted-maleic anhydride (PP-g-MA) and PA-6/low density polyethylene-grafted-maleic anhydride (LDPE-g-MA) were prepared with varied concentration (0–30 wt%) of maleic anhydride-grafted polyolefinic (PP) moiety as the impact modifier. The microstructural attributes and thermal properties of the blends were characterized by WAXD, FTIR, SEM, DSC, and TGA. The WAXD/DSC studies have revealed that the crystallinity of the blends decreased with the increase in the PP modifier whereas the onset of degradation temperature remained nearly unaffected. Comparative assessment of the crack toughness behavior of the blends has been carried out following the essential work of fracture (EWF) approach based on post-yield fracture mechanics (PYFM) concept. The kinetics of crack propagation of the blends has been discussed in the realms of structural and compositional parameters. An enhancement in the toughness (resistance to stable crack propagation) as indicated by a maximum in the non-EWF (βw p) values have been observed at 10 and 20 wt% followed by a sharp and consistent drop in the composition regime of 10–20 and 20–30 wt% of PP-g-MA and LDPE-g-MA, respectively; conceptually implying possible ductile-to-semiductile transitions in the blend systems. The equivalence of PYFM–EPFM fracture parameters have been discussed following inequality criterion. Fractured surface morphology investigations revealed that the failure mode of the blends undergo a systematic transition from matrix-controlled homogeneous flow/deformation in the PP/polyamide phase to blend composition-dependent changes in the modes and extent of fibrillation via cavitation and shear-banding mechanisms.