Flexural properties of multi-wall carbon nanotube/polypropylene composites: Experimental investigation and nonlocal modeling

Melt compounded polymer nanocomposites containing up to 2.5% in volume of multiwalled carbon nanotubes are investigated in terms of flexural behavior and morphological aspects. Effects related to inclusion of non-functionalized and amino-functionalized carbon nanotubes, having the same aspect ratio, on the properties of polypropylene based systems have been analyzed. Flexural results, obtained by typical experimental tests, show that elastic modulus and strength reach a maximum in presence of 0.5 vol% of carbon nanotubes. This behavior is enhanced in systems containing functionalized fillers whereas it is reversed for further increases of the filler content, mainly due to the occurrence of filler agglomeration phenomena, confirmed by SEM observations. SEM morphological observations show a satisfying dispersion of carbon nanotubes with presence of agglomerates of increasing sizes with the filler content. The elastic behavior is interpreted by means of a nonlocal modeling approach. The analysis of the elastic behavior performed through this numerical approach reveals that the microstructural changes due to the nanotubes affect the theoretical prediction of the flexural elastic modulus, showing significant differences with classical beam theory. (C) 2015 Elsevier Ltd. All rights reserved.