Super-toughening polyamide-612 by controlling dispersed phase domain size: Essential work of fracture assessment

• Super-toughening of PA-612 at a critical domain-size of ∼0.30 μm of POE-g-MA.
• ∼11-Fold toughness-enhancement in PA-612 by addition of 10 wt% of POE-g-MA.
• Maxima in essential work of fracture correspond to the critical domain size.

A new pathway to super-toughen polyamide-612 (PA-612) by incorporating domains of soft poly(octene-co-ethylene)-g-maleic anhydride (POE-g-MA) via melt blending leading to more than ∼1100% increase in notched Izod impact strength vis-à-vis fracture toughness enhancement is demonstrated. Fourier transform infra red (FTIR) studies showed effective phase interactions between PA-612 and POE-g-MA whereas dynamic mechanical analysis (DMA) revealed a reduction in loss-peak intensity at ∼45 °C with increase in the soft phase fraction. The optimal dependence of fracture-toughness (in plane-stress) on domain-size (Dn) of dispersed-phase in the form of a reduction in resistance to crack initiation indicated by essential work of fracture (we) and linear increase in resistance to crack propagation indicated by non-essential work of fracture (βwp) of the blends ⩾10 wt% of POE-g-MA content is correlated to an increase in domain-size ⩾∼0.3 μm. Fracture surface morphology indicated crazing to be responsible for the transition in fracture behavior, i.e. remarkable toughening of PA-612 at the critical rubber phase domain size range of ∼0.2–0.3 μm.

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