Tensile modulus of carbon nanotube/polypropylene composites - A computational study based on experimental characterization

Micromechanical and computational models significantly over-predict the tensile modulus of composites, as they ignore many experimentally observed factors. Computational models that capture the effect of polymer-filler contact, the presence of carbon nanotube (CNT) agglomerates and the alignment of CNTs with respect to the applied load on the tensile modulus of CNT-reinforced polypropylene (PP) are proposed and discussed in detail in this study. The CNT/PP composites are made by melt mixing and injection molding. The CNT/PP contact area is characterized in terms of width and modulus using Atomic Force Microscope (AFM). The presence, including the size and distribution of CNT agglomerates, is characterized using Scanning Electron Microscope (SEM). The tensile modulus of CNT/PP composites, measured as a function of CNT content according to ASTM D638, is compared to predictions made using numerical methods based on Finite Element Analysis (FEA) within the composite's elastic regime. The model over-predicts the modulus of the CNT/PP composites by 85% for 5 wt.% CNT/PP composites assuming perfect filler-polymer interfacial contact. When imperfect CNT/PP contact, CNT agglomerates and alignment are accounted for in the model the effective composite modulus predicted is in good agreement with the experimental data. The computational design tools proposed in this study by systematically incorporating experimentally observed characteristics, in combination with the manufacturing method used to make the CNT/PP composites, can lead to composites with engineered properties made by a scalable and cost effective method. (C) 2011 Elsevier B.V. All rights reserved.