Bio-based poly(L-lactide)/poly(amide-11) blends (PLA/PA11, 80/20 w/w) and poly(L-lactide)/poly(amide-6) blends (PLA/PA6, 80/20 w/w) are processed by twin-screw extrusion followed by injection-moulding and key rheological parameters controlling their morphologie are investigated. The same work is done using the same PLA modified by a multi-step reactive extrusion route with an epoxy-based chain extender to obtain modified poly(lactide)/poly(amide-11) (PLA-j/PA11 80/20 w/w) blends. The morphologies of the extruded materials and of the injection moulded parts are characterized by SEM and their formation is deeply discussed via rheological investigation to highlight the contribution of viscosity, elasticity and interfacial tension. The existence of a critical shear rate related to the transition from nodular to fibrillar morphology is highlighted and the results are in good agreement with the condition of fibrillation Ca/Ca (crit) $ 4. Interestingly, with the exception of PLA/PA6 specimens, all blends obviously display uniform thin-thread fibrillar morphologies after injection-moulding. Compared with pure PLA, a drastic increase of the ductility was observed in the blends exhibiting a fiberlike structure without meanwhile sacrificing the stiffness. This study confirms that, through the appropriate choice of blend components (viscosity and elasticity ratio, flow conditions, interfacial tensions) the in situ fibrillation concept provides access, at a reasonable cost, to new materials with improved thermomechanical performances, without sacrificing weight and ability to be recycled.
In situ fibrillation of PP/PA6 blends (85/15 wt %) is investigated in presence of two kinds of organically modified montmorillonite, differing by the polarity of their surfactant. The organoclay is primary dispersed either in the PP (for the low-polarity Cloisite V R 15A) or in the PA6 (for the high-polarity Cloisite V R 30B), according to its assumed affinity. In absence of organoclay, a fibrillar morphology is achieved after the melt-blending and hot-stretching step, as evidenced by SEM analysis. Upon clay addition, different morphological trends are evidenced. The C15A leads to a refinement of the fibrils whether the C30B induces a transition from fibrillar to nodular structure. These trends are ascribed to drastic changes in viscosity and elasticity ratios, due to the filler initial localization. Several techniques (DSC, STEM) point out a C15A migration from the PP to the PP/PA6 interface. Rheological measurements highlight the possibility of a double-percolation phenomenon, linked to the fibrillar microstructure of the PP/PA6/C15A blend.
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