The role of agglomeration in the physical properties of CNTs/polymer nanocomposites: A literature review

Abstract

The physical properties of nanocomposites may be improved by addition of low content of carbon nanotubes (CNTs). In contrast, for higher concentrations of CNTs, the physical properties of nanocomposites may be degraded owing to agglomeration. In recent years, due to the increasing applications of CNTs, many efforts have been performed to overcome the agglomerates, achieving the real potential of CNTs in improving the performance of nanocomposites. To this end, in this review paper, the impact of agglomeration on various physical properties of CNTs/polymer nanocomposites was investigated. Besides, the present work provides a review of the effective factors that lead to the CNTs agglomeration. The conventional and novel strategies adopted to control this phenomenon are also presented. The findings revealed that dense agglomerates negatively affect all physical properties of nanocomposites. It was observed that the elastic modulus and tensile strength of epoxy-based nanocomposites can be degraded around 25 and 35% when the weight fraction of CNTs is increased from 0.5 to 1.0 wt.%. Besides, in the case of fracture toughness, it was reported that by adding 0.1, 0.2, 0.3 and 0.4 wt.% of CNTs to an epoxy-based nanocomposites, the fracture toughness enhances around 17, 24, 30, and 4%, respectively. In addition, a 50% reduction in the thermal conductivity of the nanocomposite may be happened due to the formation of CNTs agglomeration. It was also concluded that in the presence of agglomerates, the coefficient of friction of a polymer-based nanocomposites can increases from 0.027 to 0.034. In contrast, slight agglomerates may improve electrical properties to a certain extent. It was also concluded some of the expensive strategies proposed to overcome the agglomeration may adversely affect the CNTs structure, may not be so effective to prevent the occurrence of agglomeration, or may not be applicable in high-volume production of nanocomposites. However, the implementation of novel strategies such as 3D porous structures could overcome this challenge significantly.