Experimental evaluations and modeling of the tensile behavior of polypropylene/single-walled carbon nanotubes fibers

Polypropylene fibers containing up to 0.2 vol% of single-wall carbon nanotubes, prepared by melt-spinning, are analyzed in terms of both experimental mechanical properties and numerical nonlocal models. In particular, fibers of a commercial polypropylene (PP) resin are compared with composite fibers, based on the same matrix, reinforced with 0.1 and 0.2 vol% of carbon nanotubes (CNT). Experimental findings shows that, although the applied processing conditions are such that the inclusion of carbon nanotubes does not alter the crystalline structure and the degree of crystallinity of the hosting matrix, tensile properties of nanocomposite fibers vary significantly with the filler content. Specifically, Young modulus, yield strength and ductility show a linear dependence upon the nanotube content over the range of compositions explored; in particular with respect to neat PP fibers filaments containing 0.2 vol% of single wall carbon nanotubes show increases of approximately 16% and 6% in the modulus and the yield strength, respectively, while the ductility decreases of about 65%. Moreover, the analysis of the elastic behavior performed by means of a nonlocal modeling approach based on the two-phase constitutive mixture allows us to identify the values of the small-scale parameter for the considered PP-CNT microrods.