Carbon nanotube size effect on the mechanical properties and toughness of nanocomposites

To evaluate the nanotube size effect on the material properties of nanotube‐modified nanocomposites, two types of multi‐walled carbon nanotubes with various dimensions were used to form nanocomposites, and then the mechanical properties and the toughness were measured. The well‐known issue of nanotube dispersion was examined using various microscopic observations, and an ideal dispersion process was identified. The results revealed that adding nanotubes led to increases in the Young's modulus and toughness of the nanocomposites. A maximum measured value of the fracture energy was recorded at 237 J m⁻² for the nanocomposite toughened with 0.5 wt% of the longer nanotubes. This is ∼90% higher than the unmodified epoxy, and a 40% increase in the fracture energy compared with the sample containing the shorter nanotubes under identical nanotube loading. This indicated that the length of the nanotubes severely affected the toughness of the nanotube‐modified polymers. However, the increased moduli, triggered by the addition of the various types of carbon nanotubes, were similar. The toughening mechanisms were identified via studying the fracture surfaces of the nanocomposites. POLYM. COMPOS., 39:E1072–E1086, 2018. © 2017 Society of Plastics Engineers