Finite element modeling of carbon nanotube agglomerates in polymers

While the negative effect of carbon nanotube (CNT) agglomerates on the effective mechanical properties of CNT-reinforced polymers and composites has been well recognized through mechanical tests and microscope observations, little has been done on the modeling of CNT agglomerates and the understanding of the role of their specific characteristics. In the present work, a detailed finite element (FE) model of CNT agglomerates is proposed. The geometry modeled represents a cubic representative unit cell comprising the agglomerated CNTs and the surrounding matrix. The FE model of the unit cell was used to perform a parametric study on the effect of agglomerates' geometrical characteristics on the homogenized elastic properties of the CNT/polymer material. The study shows that the waviness, the multitude and the topology of the agglomerated CNTs has a considerable effect which varies for the different material properties. Using the unit cells of the agglomerates, the Young's modulus of the CNT/polypropylene material was predicted by employing a multiscale analysis. The characteristics of the unit cells used for the modeling of the CNT/polypropylene material were determined from processing and analysis of scanning electron microscopy images of the nanocomposites. The comparison between numerical and experimental results indicates that the model is capable of accurately predicting the Young's modulus of materials at which the agglomeration effect is prominent, however, it tends to underestimate the Young's modulus of materials at which agglomeration is minor. (C) 2015 Elsevier Ltd. All rights reserved.