Structural orientation and tensile behavior in the extrusion-stretched sheets of polypropylene/multi-walled carbon nanotubesʹ composite

In this paper, the structural orientation and tensile properties were investigated on the extrusion-elongated sheets of polypropylene (PP)/multi-walled carbon nanotubesʹ (MWCNTs) composites. The MWCNTs were modified via reactive grafting with octadecylamine to enhance the capability of dispersion in PP matrix. The orientation level of composite sheets was adjusted through adopting various drawn speeds after extrusion, and the structure–property relation was inspected systematically through the combination of two-dimensional wide-angle X-ray scattering, polarized light microscopy and tensile mechanical testing. The tensile behavior of the extrusion-drawn sheet was significantly impacted by both adding MWCNTs and increase of drawn speed. An optimization for simultaneously strengthening and toughening was achieved in the sample with relatively high content MWCNTs prepared upon fast drawn speed. Incorporation of nanotubes didnʹt alter the orientation degree of crystalline lamellae obviously, but the oriented nanotubes could act as the nucleating templates for the growth of oriented crystalline superstructure. Combined with the present morphological characterizations and the results in other published papers, it was postulated that the oriented superstructure of cylindrulites composed of rigid CNTs as nucleus and PP lamellae as kebabs might be generated in the extrusion-elongated sheets of PP/MWCNTs, which was regarded as the morphological reason for a reinforcing effect on tensile performances.