The microstructural, thermomechanical, and quasistatic mechanical properties of biobased polyamide 410 (PA410)/ poly(octane-co-ethylene)-g-maleic anhydride (POE-g-MA) blends with the impact toughener in the composition range of 0−20 wt % have been investigated, with an aim to overcome the poor notch and strain sensitivity of PA410. The crystallinity of the blends obtained from enthalpic measurements and initial degradation temperature indicating thermal stability remained mostly unaffected. A remarkably substantial increase, i.e., ∼15-fold enhancement, in the impact strength of the PA410/POE-g-MA blends leading to ultratoughening of PA410 accompanied by a significant increase in tensile strain at breaking is achieved though the elastic modulus (E) and yield strength (σ) decreased with impact modifier content. Thermomechanical analysis revealed a broadening in the loss tangent peak in the temperature range of ∼−50 to −30 °C corresponding to the POE phase, whereas the loss tangent peak corresponding to the PA410 phase stayed unaffected. Conventional theoretical models such as the rule of mixture and foam model were used to analyze the micromechanics of low-strain (<1%) mechanical response (E), and Nikolais−Narkis model and Isahi−Cohen models, for high-strain (>2%) mechanical response (σ). The interdependence of impact toughness, ductility ratio, and domain size of the dispersed rubber phase in the PA410/POE-g-MA blends could successfully be established vis-a-vis the mechanistic role of interparticle distance. Scanning electron microscopy showing domain coalescence of the soft elastomeric POE phase thus reiterated the pivotal role of interdomain distance and domain size in influencing the toughening mechanism of PA410/POE-g-MA blends. The qualitative phase distribution attributes based on atomic force microscopy remained in sync with quantitative parameters, such as domain size, hence reaffirming the mechanism behind ultratoughening of PA410 by POE.

The sol–gel or viscous‐elastic transitions of the bio‐based polyamide 410/POE‐g‐MA (polyethylene‐co‐octene copolymer grafted with maleic anhydride) blends have been systematically discussed in the framework of melt rheology as assessed on a parallel plate rheometer set‐up in small amplitude oscillatory shear mode and solid state dynamic mechanical relaxation measurements. The viscous response dominated enhancement in elastic moduli of the blends that was characterized by the phase transitions across the composition range of 10–15 wt% of POE‐g‐MA. A direct correlation between the gel point (estimated from the cross‐over of frequency‐independent loss tangent curves) and the ultra‐toughness (maximized to an extent of ~15‐fold increase in notched Izod impact strength) could be established vis‐a‐vis its corroboration from the morphology of the impact‐failed surfaces. The extent of maleic anhydride (−MA) content induced phase interaction with polyamide 410 via the formation of a polyamide‐co‐(polyoctene‐co‐ethylene) type copolymer linkage in solid‐state and its subsequent impact on solid‐state damping was analyzed. The study establishes qualitative correlation between ultra‐toughening of polyamide 410 to that parameters based on relaxation dynamics measurements using melt rheology and solid‐state dynamic responses conforming to the principles of gelation rheology.

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The influence of elastomeric poly (octene-co-ethylene) on the crystallization of polyamide 410 in PA-410/POE-g-MA blends was systematically analyzed using a non-isothermal crystallization kinetics approach. A novel power-law criterion was employed to characterize the crystallization regimes (primary and secondary) as a function of cooling rate to understand the nature of crystal arrangement vis-a-vis various kinetic models proposed by Avrami, Jeziorny (modified Avrami method), Ozawa and Liu-Mo. The activation energy pattern with fractional crystallinity from onset to fully developed crystals is discussed as per Friedman's theory. The POE phase acted as a weak nucleating agent for PA 410. The effect of elastomer on crystallization rate constant remained almost unchanged regardless of the blend composition. This insensitivity is attributed to (1) nucleating effect of POE-g-MA (because of resemblance in the molecular scheme) and (2) hindrance effect through the formation of an interfacial network; these two effects nearly offset one another. Our study illustrates the crucial dependence of acceleration of cooling that is, acceleration required for attaining a certain fraction of crystallinity with composition (threshold elastomer concentration), on an interfacial network in binary blends.

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