Since the discovery of carbon nanotubes by Japanese physicist Sumio Iijima in 1991, the atomic structure and properties of carbon nanotubes have attracted great interest from scientists. Carbon nanotubes have extremely high specific surface area, excellent mechanical properties (the theoretical axial elastic modulus and tensile strength of carbon nanotubes are 1~2TPa and 200Gpa, respectively), and thermal properties (heat-resistance temperature of carbon nanotubes under vacuum is up to 2800 °C) and the electrical properties (the electron carrying capacity of carbon nanotubes is 1000 times that of copper wires). These properties of carbon nanotubes make them an ideal filler in the field of composites. The carbon nanotube composite material can be easily processed and fabricated into a structurally complicated member, and does not damage the structure of the carbon nanotube during processing, thereby reducing production costs. Therefore, carbon nanotube composite materials have been extensively studied.
There are three main preparation methods for carbon nanotube composite materials: liquid phase blending, melt blending and in-situ polymerization. Among them, the liquid phase blending method is the most commonly used preparation method.
Liquid phase blending
The solution method refers to the use of mechanical or magnetic stirring, or high-energy ultrasonic to separate the agglomerated carbon nanotubes and uniformly disperse in the polymer solution, and remove the excess solvent to obtain the carbon nanotube composite material. The advantage of this method is that it is simple to operate, and it is mainly used to prepare membrane materials. Xu et al and Lau et al. used this method to prepare CNT/epoxy composites and reported the properties of the composites. In addition to epoxy resins, other polymers such as polystyrene, polyvinyl alcohol, polyvinyl chloride, etc. can also be used to prepare composite materials by this method.
The melt blending method is to disperse carbon nanotubes in a polymer melt by shear force applied by a rotor. This method is especially useful for preparing thermoplastic polymer/carbon nanotube composites. The advantage of this method is mainly to avoid contamination of the composite by solvent or surfactant, but this method is only suitable for polymers that are resistant to high temperatures and are not easily decomposed. Jin et al. used this method to prepare PMMA/MWNT composites and studied their properties. The results have shown that the carbon nanotubes are uniformly dispersed in the polymer matrix without significant damage and the storage modulus of the composite material is improved.
The in-situ composite method refers to dispersing carbon nanotubes in a polymer monomer, adding an initiator, and initiating in-situ polymerization of the monomers to form polymer/carbon nanotube composites. This method is considered to be an effective method for increasing the dispersion of carbon nanotubes and enhancing their interaction with the polymer matrix. Jia et al. prepared PMMA/SWNT composites by in-situ polymerization. The results have shown that the main reason for the strong bonding between the carbon nanotubes and the polymer matrix is that AIBN opens the π bond of the carbon nanotubes during the initiation process, thereby allowing the carbon nanotubes to participate in the polymerization of PMMA. The use of surface-modified carbon nanotubes to prepare PMMA/carbon nanotube composites not only increases the dispersion ratio of carbon nanotubes in the polymer matrix, but also greatly enhances the mechanical properties of the composite.